Construction and Building Materials 33 (2012) 164–180

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Construction and Building Materials

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Synergic effect of Friedel’s salt from pozzolan and from OPC co-precipitatingin a chloride solution

Rafael Talero‘‘Eduardo Torroja’’ Institute for Construction Sciences – CSIC, Serrano Galvache n� 4, 28033 Madrid, Spain

a r t i c l e i n f o

Article history:Received 28 February 2011Received in revised form 16 November 2011Accepted 4 December 2011Available online 9 March 2012

Keywords:Chlorides attackPozzolansPortland cements‘‘Rapid’’ and ‘‘slow’’ forming Friedel’s saltSynergy of chemical reactions

0950-0618/$ - see front matter � 2012 Elsevier Ltd. Adoi:10.1016/j.conbuildmat.2011.12.040

E-mail address: rtalero@ietcc.csic.es

a b s t r a c t

Two prior papers on this subject have shown, with XRD and SEM techniques, that almost all pozzolanicadditions can induce the rapid formation of Friedel’s salt in quantities in keeping with the reactive alu-mina, Al2Or�

3 (tetra- or penta-coordinated alumina) content of the pozzolan. The formation rate of Fri-edel’s salt of pozzolan origin has also been shown to be higher than the rate in the slower formingcompound, whose origin is the C3A in OPC. Consequently, the plate-like hexagonal crystals are smallerand less perfectly shaped in fast- than in slow-forming Friedel’s salt.

To describe the inter-relationships between these two non-expansive processes, a terminological anal-ogy is drawn between the rapid and slow formation of Friedel’s salt and drug interaction. A commondevelopment in the treatment of certain diseases, drug interaction may be quantitative or qualitativeand, depending on the end result, is typed under one of the following headings: additive synergy, partialantagonism, competitive antagonism, potentiating synergy, non-competitive antagonism or physiological andfunctional antagonism. Borrowing from this classification, the present study sought to determine whetherthe joint formation of Friedel’s salt from pozzolan and from OPC in a common chloride solution is syner-gic, additive, antagonistic or able to invert the expected outcome.

To this end, 14 binders, 2 PC (1 OPC and 1 SRPC) and 12 blended cements containing 20% or 30% of oneof six pozzolans, were analysed with XRD technique. Water resistance, capillary absorption and totalporosity were also determined, along with the chemical composition and physical properties of somecement tested.

The experimental results showed that fast- and slow-forming Friedel’s salt precipitated in a commonchloride solution not separately but inter-dependently and the closer the pozzolan particles were tothe cement particles, the greater was that inter-dependence. Moreover, the joint precipitation – co-pre-cipitation – of the Friedel’s salt from the Al2Or�

3 present in pozzolans and the Friedel’s salt from the C3Apresent in OPC was, to use drug interaction terminology, consistently more synergic than additive. Fur-thermore, depending on the parameter considered and from a purely technological point of view, thepractical implications of the Synergic Effect (SE) between the two types of Friedel’s salt were always ben-eficial. The experimental results showed, in addition, that the pozzolanic activity of three of the pozzolanstested, C, M1 and M0 specially, once again proved to be more specific than generic in chloride and waterenvironments. This would induce speedier chloride hydration of all or part of the C3A in the OPC fractionthan when the OPC was hydrated without the pozzolan. Moreover, the Friedel’s salt from the Al2Or�

3 inthese pozzolans was the chief direct and indirect cause of the SE, in conjunction with the Friedel’s saltfrom the C3A in PC, due to their very specific pozzolanic activity in such chloride media. In contrast, whenthe pozzolan used was silica fume (SF), its pozzolanic activity is not also more specific than generic for thesame result but for the contrary result, that is, SF is unspecific for the same result.

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1. Introduction

Two prior papers devoted to Friedel’s salt showed, with XRD[1] and SEM [2] techniques (Fig. 1a–d), that almost all pozzolanicadditions can induce the rapid formation of Friedel’s salt, Fs-rf,[1] in quantities in keeping with their reactive alumina, Al2Or�

3

ll rights reserved.

(or tetra- or penta-coordinated alumina [3]) content. Friedel’ssalt has also been found to form at a faster rate from the reac-tive alumina in pozzolans than from the C3A in Portland cement[2]. Consequently, the crystals in the former, known as Fs-rf, aresmaller and exhibit numerous lattice flaws (Fig. 1b and d). Sim-ilar observations were made with respect to ettringite formationfrom the same two origins in a common plaster-bearing solution[4–7].

Fig. 1. SEM morphology of the (a) slow-forming Friedel’s salt from C3A of OPC P1, Fs-lf, and (b) rapid-forming Friedel’s salt from Al2Or�3 of PC PY6/M0 60/40 blend (Fs-rf) as

well as its respective (c and d) EDX analysis. Saline hydration at 180 days-age.

R. Talero / Construction and Building Materials 33 (2012) 164–180 165

While researchers have yet to reach a consensus about the ef-fect of pozzolans on Friedel’s salt (Fs) formation kinetics [1,2],the additional reasons and proofs set out below contribute to theestablishment of a definitive behavioural hypothesis. In this as inthe prior studies [1,2]. XRD analysis was used, although a differentapproach was adopted to indisputably show that the formationrate (Vf) of Fs from the Al2Or�

3 present in pozzolans (Fs-rf1) is great-er than the Vf of Fs from the C3A present in OPC (Fs-lf2). Further-more, the inter-relationship between the two formation processesis also addressed.

The aforementioned two prior studies [1,2] showed that Fri-edel’s salt can form from different origins, the Al2Or�

3 in pozzolansand the C3A in OPC, at different formation rates, giving rise to dif-ferent crystal sizes and quantities. Moreover, the two precipitationprocesses are competitive, inasmuch as both involve reactions withportlandite, chlorides and water.

Four of the aforementioned articles [4–7] showed that expan-sion in blended Portland cement concretes, mortars and pastescontaining pozzolanic additions that are more aluminic than silicic[8] in chemical character, when attacked by sulphates, is caused bythe co-precipitation of ettringite of rapid formation, ett-rf, from theAl2Or�

3 present in pozzolans and the ettringite of slow formation,ett-lf, from the C3A present in OPC. They further showed that suchjoint precipitation – co-precipitation – is more synergic than addi-tive [4,5] and explained and justified that premise [6,7]. It wasagainst that backdrop that the present study was also designedto ascertain whether the co-precipitation of Fs-rf and Fs-lf in acommon chloride solution is also more synergic than additive, asin ettringites [4–6]. That the answer to this question is implicit

1 Friedel’s salt that forms rapidly from Al2Or�3 origin present in pozzolans.

2 Friedel’s salt that forms much more slowly from C3A origin present in PC, after itsinitial hydration; the term Fs-lf is not intended to mean that this type of Friedel’s salis always necessarily the product of slow formation when co-precipitating with Fs-r[1,2], but merely that in the latter circumstances, it is formed from the C3A (%) contenpresent in OPC.

tft

in the title of this paper is irrelevant, for the primary concernshould be to actually prove these assertions with respect to Fs-rfand Fs-lf. The possible practical implications of these results areformulated below:

– Co-precipitation of the two types of Friedel’s salt might affectcement durability, whether or not it is attacked by de-icing salts(chlorides [9–13]), sea spray (chlorides, sulphates, magnesium,etc.) or atmospheric CO2 (carbonation), or subject to the alkali-sil-ica reaction or drying shrinkage (owing to excess heat of hydration[14–23]).– The practical implications of that effect may be beneficial or

adverse, or some beneficial and others adverse. In the latter case,one and the other should be identified.

The aforementioned issues lie outside the limits of this paperand must necessarily be tackled in other studies. Some have al-ready been published [1,2,4–6,8–23], other is presently under re-view [7] and yet others are still underway. That notwithstanding,some are briefly addressed in the Section 5 below.

2. Objectives

The objectives of the research reported here were as follows:

1. To determine the existence or otherwise of a relationshipbetween Fs-rf and Fs-lf during their formation in a commonchloride medium – co-precipitation –.

2. To quantify the co-precipitation of Fs-rf and Fs-lf in a chloridesolution, using chemical and physical parameters.

3. To determine, on the grounds of the quantitative findings,whether the co-precipitation of Fs-rf and Fs-lf in a chloridesolution can be regarded to constitute addition, synergism,antagonism or to invert the expected action, with a view toappropriately denominating the result of such co-precipitation.

Table 1Physicochemical characteristics of cementitious materials.

Chemical parameters (%) Portland cements Pozzolanic additions (=Z pozzolan)

P1 PY6 SF D A C M1 M0

LOI 1.60 1.11 6.28 0.23 3.92 6.92 0.60 0.40IR 0.70 0.15 – 0.42 – 0.43 0.22 –SiO2 19.18 21.70 92.02 91.81 41.38 54.18 73.55 57.48Al2O3 6.44 1.52 0.70 1.91 19.36 20.10 23.11 41.55Fe2O3 1.75 4.11 0.39 2.39 12.05 3.12 1.19 0.50CaO 63.94 67.97 0.00 1.23 11.11 2.38 0.63 0.01MgO 1.48 0.42 0.00 0.38 10.58 2.04 0.03 0.00Na2O 0.90 0.43 0.00 1.50 1.24 5.64 0.07 –K2O 0.52 0.20 0.00 0.12 0.44 5.17 0.17 –SO3 3.50 2.34 0.06 0.00 0.00 0.00 0.00 0.00Total 100.01 99.95 99.45 99.99 100.08 99.98 99.57 99.94SiOr�

2 – – 88.5 89.0 37.5 39.0 38.5 48.5

Al2Or�3 – – 0.0 0.0 8.0 11.5 15.0 29.0

Physical parameter P1 PY6 SF D A C M1 M0Real density (g/cm3) 3.08 3.21 2.10 2.59 2.41 2.68 2.55 2.52SEB (m2/kg) 319 329 34,590 – 403 402 398 333BET (m2/kg) – – 22,100 720 – – 7260 9000

166 R. Talero / Construction and Building Materials 33 (2012) 164–180

4. To attempt to prove that the effect of the co-precipitation ofFs-rf and Fs-lf is more synergic than additive, quantitativelyspeaking.

5. To determine whether the consequences of objectives 3 and 4can be deemed to be beneficial.

3. Experimental

3.1. Materials

The materials listed in Table 1 were chosen for this study [1,2] on the grounds ofthe CaO–Al2O3–CaCl2 stable ternary system [24–27].

Two Portland cements with opposite potential mineralogical compositions, P1(14% C3A) and PY6 (<1% C3A), were used to prepare cement blends or POZCs withthe following six siliceous or siliceous and aluminous (pursuant to the ASTM stan-dard 618 classification [28]) pozzolanic additions (=‘‘Z’’ or Z pozzolans): artificialand vitreous, silica fume (SF); natural and vitreous, diatomite (D, from organic ori-gin); two natural Spanish pozzolans, A (Ciudad Real) and C (Islas Canarias); and anactivated clay (metakaolin) with and without 50% quartz filler, M1 and M0. Bothmetakaolins were prepared by firing kaolin at 750 �C and grading the ground prod-uct to ASTM standard C 595M [29] requirements (maximum 20% retained whenwet-sieved through sieve No. 325 (45 lm)). Merck-type NaCl salt was used, alongwith distilled water for mixing the pure and blended cement pastes. In this study,the cement pastes were hydrated with a 3.75% NaCl solution (=saline solution oraqueous chloride medium).

3.2. Operating procedure

Twelve POZCs or blended cements with a 70/30 (wt%) PC/Z pozzolan ratio, wereprepared with two PCs, P1 and PY6, and the six pozzolanic additions: M0, M1, C, A,D and SF. Exceptionally, the PC/Z ratio used for SF was 80/20, while a ratio of 100/00denotes pure PC.

Table 2Times of setting, w/b ratios and Al2Or�

3 (%) and SiOr�2 (%) contents of P P1 and PY6 with SF

Cements Times of setting (h:min) Water for normal consistency

Initial Final Time

P1 100/00 3:20 5:10 1:50 155.00P1/SF 80/20 0:35 3:55 3:20 225.00P1/D 70/30 4:05 >12:00 – 360.00P1/A 70/30 2:35 4:45 2:10 173.75P1/C 70/30 2:55 4:05 1:20 177.00P1/M1 70/30 3:00 4:55 1:55 198.70P1/M0 70/30 2:50 4:60 2:10 200.00PY6 100/00 4:30 6:15 1:45 140.00PY6/SF 80/20 3:30 9:20 5:50 220.00PY6/D 70/30 7:10 9:35 2:25 350.00PY6/A 70/30 3:15 5:45 2:30 147:5PY6/C 70/30 4:45 6:45 2:00 171.25PY6/M1 70/30 5:20 8:15 2:55 192.5PY6/M0 70/30 5:40 6:50 1:10 200.0

The values of the physical–chemical parameters for the Portland cements andthe pozzolans given in Table 1 were determined as per EN 196-2 [30] and ASTMC311 [31], respectively. Based on these results, the potential Portland cementcomposition calculated with the Bogue formulas [32] for P1 (OPC) was: 51%C3S, 16% C2S, 5% C4AF and 14% C3A; and for PY6, 79% C3S, 2% C2S, 10% C4AF and0% C3A (estimated to be <1% [33]). The reactive silica ðSiOr�

2 Þ, and reactive aluminaðAl2Or

3Þ contents of the pozzolans, in turn, were determined as laid down in Span-ish standard UNE 80-225-93 [34] and the Florentin method [35], respectively, andare also listed in Table 1. The physical parameters such as real density and Blainespecific surface (BSS) were found as recommended in Spanish standardsUNE 80103 [36] and UNE 80122 [37], respectively. The normal consistency andsetting times of the cements given in Table 2 were established pursuant to Euro-pean standard EN 196-3 [38].

The 1-, 2-, 7- and 28-day pozzolanic activity for the six pozzolanic additions wasdetermined chemically as described in EN 196-5 (=Frattini test) [39]. Pozzolanicactivity was regarded to be present (=positive result) when the calcium hydroxideconcentration in the sample solution fell bellow the Ca(OH)2 solubility isotherm inan alkaline solution at 40 �C. The findings are given in Table 3.

The pozzolanic activity index (PI) values for the 28-day pastes listed in Table 4were found as specified in ASTM C 311 [31].

All the POZCs prepared were exposed to a chloride ion solution (3.75% NaCl) for1, 7, 14, 21, 28, 60, 90, 270 or 730 days. At each trial age, the sample was dried,ground and pressed into pellets for X-ray diffraction analysis (XRD). The XRD traceswere interpreted by estimating the integrated intensities of the most characteristicreflection attributed to Friedel’s salt, which was located in 2h range =11.16� � 11.34�. The findings were classified by family (P1/Z or PY6/Z) and listedin Tables 5–9 and illustrated in Figs. 2 and 3.

PCs P1 and PY6 and their respective POZCs were studied for porosity andwater absorption. The water absorption test was conducted as described by Fag-erlund [40], which involved preconditioning the pastes at 105 �C. Water resis-tance, m, is compared to the SiOr�

2 (%) and Al2Or�3 (%) contents of the Z

pozzolans in Table 10.

, D, A, C, M1 and M0 pozzolans.

(ml) SiOr�2 (%) content of Z pozzolan Al2Or�

3 (%) content of Z pozzolan

– –88.5 0.089.0 0.037.5 8.039.0 11.538.5 15.048.5 29.0– –88.5 0.089.0 0.037.5 8.039.0 11.538.5 15.048.5 29.0

Table 3Pozzolanicity (Frattini test). Results: at 1, 2, 7 and 28 days.

Cements 1 day 2 days 7 days 28 days

[OH�] (mM/l) [CaO] (mM/l) [OH�] (mM/l) [CaO] (mM/l) [OH�] (mM/l) [CaO] (mM/l) [OH�] (mM/l) [CaO] (mM/l)

P1 100/00 66.50 8.73 72.50 7.60 71.25 6.80 78.00 6.45P1/SF 80/20 57.50 6.13 55.50 5.50 40.00 4.90 45.00 2.35P1/D 70/30 62.75 10.00 61.00 9.75 62.25 6.05 74.50 3.30P1/A 70/30 54.50 10.36 62.50 10.10 67.40 3.75 83.50 4.35P1/C 70/30 73.00 4.93 83.40 3.30 84.10 3.00 116.50 2.00P1/M1 70/30 58.00 10.23 48.50 5.50 48.50 2.20 58.00 5.00P1/M0 70/30 58.00 8.40 41.00 1.55 45.75 1.50 46.00 0.75PY6 100/00 42.75 28.33 42.50 21.50 39.45 16.55 42.00 16.10PY6/SF 80/20 33.25 18.33 32.00 15.25 27.00 11.75 21.50 7.50PY6/D 70/30 43.00 24.29 42.50 20.50 45.50 14.60 47.50 7.00PY6/A 70/30 30.00 25.19 47.00 20.20 47.00 14.15 55.00 7.30PY6/C 70/30 52.00 10.73 57.50 7.05 69.25 3.80 96.50 2.50PY6/M1 70/30 36.00 17.00 34.50 13.50 27.90 9.00 24.50 5.80PY6/M0 70/30 28.50 7.50 26.50 10.50 22.00 4.60 17.50 2.95

Table 4Pozzolanic acitivity index, PI [31].

Pozzolans PI (%) Water (%) SiOr�2 (%) content

of Z pozzolanAl2Or�

3 (%) contentof Z pozzolan

D 45.2 132.5 88.5 0.0SF 90.6 108.0 89.0 0.0A 71.0 99.6 37.5 8.0C 59.2 106.0 39.0 11.5M1 75.1 108.0 38.5 15.0M0 77.2 110.0 48.5 29.0

‘‘Control’’ mortar: w/c ratio = 0.58Compressive strength at 28 days and 40 �C = 38.6 MPa.

R. Talero / Construction and Building Materials 33 (2012) 164–180 167

Finally and according to chemical fundamentals, the Friedel’s salt forming dur-ing the saline hydration of OPC, with or without pozzolanic or of blast furnace slagadditions, is not expansive. Inasmuch as this fact has been consistently confirmedby real-life conditions, volume stability over time was not determined for the pastesexposed to this saline medium (3.75% NaCl solution).

4. Results and discussion

4.1. Times of setting

POZCs rheology was also analysed in this study, determiningnormal consistency and setting times (Table 2). The findingsshowed that the addition of a Z pozzolan to PCs P1 and PY6 af-

Table 5Interdependence between the Fs-rf formation of Al2Or�

3 from Z pozzolan origin, and Fsprecipitation – in the PC/Z pozzolan saline hydration (with 3.75% NaCl solution), based on

Cements Zpozzolan

Integral Area (IA) correspondent to% pozzolan (a.u.)a

1 7 14 21 28 60

P1 P1 100/00 – 20.97 75.76 84.72 122.30 123.60 2030% of Zpozzolan

M0 113.92 167.37 216.50 408.69 501.88 62M1 47.98 101.37 91.90 147.49 300.88 48C �14.68 46.92 71.60 67.19 80.38 9A �14.68 �1.58 �1.04 �20.98 78.78 �D �14.68 1.72 �21.33 �12.66 �22.92 �7

20% of SF SF �16.79 �60.61 �12.63 �12.09 �7.63 �6

PY6 PY6 100/00

– 0.00 7.70 34.34 19.52 22.00 4

30% of Zpozzolan

M0 89.80 137.61 120.26 230.44 302.30 33M1 0 �5.39 53.61 113.74 141.90 23C 0 22.39 47.79 52.82 52.73 5A 0 �5.39 1.82 23.18 38.88 2D 0 �5.39 �24.04 �13.66 �15.40 �3

20% of SF SF 0 �6.16 �27.47 �15.62 �2.87 �3

a Calculus: IA (a.u.) 30% Z = IA (a.u.) PC/‘‘Z’’ 70/30 � 70% � IA (a.u.) PC IA (a.u.) 20% SF

fected the original setting properties of their pastes. This effectwas more intense when SF was the pozzolan added, for thesepastes took at twice as long to set as the others. That notwithstand-ing, both the initial (especially) (IST) and the final (FST) settingtimes were substantially shorter than in the plain PC. In POZC/SF,the IST was affected by both direct and non-direct stimulation ofearly age PC P1 or PY6 hydration [14–16], while the change in itsFST was the result of the unspecificity or anti-specificity in SF forthe indirect stimulation of C3A hydration [6,14,17–19]. The latterwas due more to physical than chemical reasons, however. Thesmall, spherical silica fume particles contrast sharply with the lar-ger and more peculiarly shaped pozzolan D particles, whose,empty, perforated sheaths induce high capillary suction and theabsorption of mixing water into their interior. The reactive silicacontent, SiOr�

3 , of these two pozzolans, is very similar, however:88.5% and 89.0%, respectively. When pozzolan D, likewise siliceousin nature, according to ASTM 618 standard [28], and chemically si-licic [8] like SF, more water was needed to reach normal consis-tency than with SF. That notwithstanding, its IST, FST and STwere longer than for SF, because the portlandite was over-diluted.

The IST, FST and ST of the pastes containing artificial pozzolansM0, M1 and SF were all shorter than the plain PCs, with the excep-tion of SF whose FST was logically longer. This clearly variantbehaviour was the result of the differences in their chemical char-acter [8], aluminic for M0 and M1, and silicic for SF. In other words,the Al2Or�

3 (%) in M0 and M1 stimulated PC hydration both directly

-lf formation of C3A from PC (P1 or PY6) origin, during their joint formation – co-the XRD patterns semi-quantitative analysis.

SiOr�2 (%) content of

Z pozzolanAl2Or�

3 (%) contentof Z pozozlan90 270 730

0.60 257.90 369.30 648.80 – –9.28 728.17 1133.80 1105.34 48.5 29.06.98 536.17 910.10 943.54 38.5 15.07.78 383.67 555.90 709.54 39.0 11.53.62 �15.83 �83.01 �173.46 37.5 8.06.62 �46.13 �42.01 �206.66 89.0 0.06.15 �84.52 �86.14 �288.74 88.5 0.0

9.36 88.20 75.03 73.82 – –

1.15 338.26 744.68 1528.63 48.5 29.04.25 246.06 268.38 579.43 38.5 15.05.77 38.36 73.08 60.63 39.0 11.57.00 9.30 51.28 31.12 37.5 8.04.55 �26.29 �1.86 �1.28 89.0 0.09.49 �35.25 �22.60 �8.82 88.5 0.0

= IA (a.u.) PC/SF 80/20 � 80% � IA (a.u.) PC.

Table 6Demonstration of the Synergic Effect of Friedel’s salt from pozzolan and OPC: real value/theoretical value ratio for each POZC-Z pozzolan at each age.

Multiplicator factor of real reading over theoretically estimated value (based on the appropriate (5) or (6)) at each age SiOr�2 (%) content

of Z pozzolanAl2O3r� (%) contentof Z pozzolan

Z pozzolan 1 day 7 days 14 days 21 days 28 days 60 days 90 days 270 days 730 days

M0 (70/30) 1.23 1.16 1.54 1.56 1.51 1.63 1.75 1.39 0.79 48.5 29.0M1 (70/30) 4.27 3.24 1.34 1.17 1.70 1.68 1.68 2.22 1.35 38.5 15.0C (70/30) 0.00 1.33 1.22 1.10 1.20 1.21 2.58 2.46 2.26 39.0 11.5A (70/30) 0.00 1.08 0.95 0.59 1.32 0.82 0.87 0.57 0.58 37.5 8.0D (70/30) 0.00 1.15 1.08 1.01 0.89 0.60 0.87 0.84 0.55 89.0 0.0SF (80/20) 0.00 0.00 1.37 1.04 0.95 0.77 0.71 0.77 0.45 88.5 0.0

Table 7Integral area (a.u.)/g PC P1.

Cements Integral Area (a.u.)/g PC P1 SiOr�2 (%) content

of Z pozzolanAl2Or�

3 (%) contentof Z pozzolan1 day 7 days 14 days 21 days 28 days 60 days 90 days 270 days 730 days

P1 1.05 3.79 4.24 6.12 6.18 10.03 12.90 18.47 32.44 – –P1/Inert 70/30 0.73 2.65 2.97 4.28 4.33 7.02 9.03 12.93 22.71 – –M0 9.19 15.74 19.70 35.31 42.03 54.98 64.91 99.45 111.39 48.5 29.0M1 4.48 11.03 10.80 16.65 27.67 44.81 51.19 83.47 99.84 38.5 15.0C 0.00 7.14 9.35 10.91 11.92 17.01 40.30 58.17 83.12 39.0 11.5A 0.00 3.68 4.16 4.62 11.81 9.77 11.76 12.54 20.05 37.5 8.0D 0.00 3.91 2.71 5.21 4.54 4.56 9.60 15.46 17.68 89.0 0.0P1/Inert 80/20 0.84 3.03 3.39 4.89 4.94 8.02 10.32 14.77 25.95 – –SF 0.00 0.00 3.45 5.36 5.70 5.90 7.61 13.08 14.39 88.5 0.0

Table 8Integral Area (a.u.)/g PC PY6.

Cements Integral Area (a.u.)/g PC PY6 SiOr�2 (%) content

of Z pozzolanAl2Or�

3 (%) contentof Z pozzolan1 day 7 days 14 days 21 days 28 days 60 days 90 days 270 days 730 days

PY6 0.00 0.39 1.72 0.98 1.10 2.47 4.41 3.75 3.69 – –PY6/Inert 70/30 0.00 0.27 1.20 0.68 0.77 1.73 3.09 2.63 2.58 – –M0 6.43 10.21 10.31 17.44 22.69 26.12 28.57 56.94 112.88 48.5 29.0M1 0.00 0.00 5.55 9.10 11.24 19.20 21.99 22.92 45.08 38.5 15.0C 0.00 1.98 5.13 4.75 4.87 6.45 7.15 8.97 8.02 39.0 11.5A 0.00 0.00 1.85 2.63 3.88 4.40 5.07 7.41 5.91 37.5 8.0D 0.00 0.00 0.00 0.00 0.00 0.00 2.53 3.62 3.60 89.0 0.0PY6/Inert 80/20 0.00 0.31 1.37 0.78 0.88 1.97 3.53 3.00 2.95 – –SF 0.00 0.00 0.00 0.00 0.92 0.00 2.21 2.34 3.14 88.5 0.0

168 R. Talero / Construction and Building Materials 33 (2012) 164–180

and non-directly [14–16], but primarily indirectly [6,14,17–19],which means that it induced more intense C3A hydration in thePC fraction of the blend than was observed in the unblended PC(in both materials, with respect to C3S hydration). Finally, theSiOr�

2 present in SF, by contrast, was unable to stimulate C3A hydra-tion indirectly [19,21].

The performance of the POZCs containing pozzolan C in this testprovided further support for the latter hypothesis. Qualitativelyspeaking, it behaved more like M0- and M1- than pozzolan A-blended POZC, an indication that the reactive alumina, Al2Or�

3 , inpozzolan C must have been closer in amount and physical nature(amorphous) to the compound in metakaolin than to the Al2Or�

3

in fly ash (vitreous). No such resemblance can be attributed to poz-zolan A, however.

As a result of the foregoing, water demand3 rose with the addi-tion of the more or less aluminic pozzolans (pozzolans M0, M1, C and

3 This finding signifies that this simple, easy, fast, reliable, reproducible andinexpensive method can be used to rapidly determine the chemical character of agiven natural and/or artificial pozzolan, and, as a consequence, be then used to deduceits likely behaviour in an aggressive medium (sulfates, chlorides, sea water,carbonation, ASR, etc.) and heat hydration released at early ages, and logically, forthis very interesting purpose, at least, its previous physics-chemical analysis [30–32][34–38], Frattini test [39] at 1, 2, 7 and 28 days-aged and/or mechanical strengths[28,29,31,32,49–51] will be needed as well, to verify before its pozzolanicity.

A), a development directly related to their reactive chemical compo-sition, in particular to their intense early pozzolanic activity result-ing from their Al2Or�

3 content [1,2,22,23] mainly, their very smallparticle size (SF) or their specific morphology (D). The tiny sphericalparticles (with a very high BET-SS, Table 1) comprising SF tended totend to absorb water molecules during hydration; first physicallyand then chemically on the surface, whereas D, with larger, emptysheath-like particles, took the mixing water up into its structure.The cement pastes containing these two pozzolanic additions there-fore called for more water than the respective plain PC paste or thepastes containing pozzolans M0, M1, C or A. Thus, the amount ofwater needed to reach normal consistency with pozzolan D was evengreater because its particles physically took up the water moleculesas described above, leading to an initially dry paste.

The strength activity index (SAI) or pozzolanic activity index(PI) results are given in Table 4. As the Table 4 shows, the PI valuesfor pozzolans D and C were significantly below the 75% lower limitlaid down in ASTM C 618 for such pozzolanic additions [28]. Poz-zolan A, while also below that limit, exhibited certain differences.The best results were observed for silica fume (SF) and the metaka-olins (M0, M1), which were slightly over the threshold stipulated.The less than impressive pozzolan C behaviour in terms of thismechanical parameter was due to its fairly high NaO2eq. (%) con-tent (=9.04% > 0.60% is the maximum allowed quantity for low al-kali-cements [41]).

Table 9Classifications of the Z pozzolans in function of Friedel’s salt amount precipitated in the blends (starting with minimum value).

Age (days) PC P1/Z pozzolan and PC PY6/Z pozzolan blend series

1 PY6/SF = PY6/D = P1/SF = P1/D = P1/A < PY6/A < PY6/C < PI < PY6/M1 < P1/C < PY6 < P1/M1 < PY6/M0 < P1/M07 PY6/SF = PY6/D = P1/SF < PY6/M1 < PY6/A < PY6/C < PY6 < P1/D < P1 < P1/A < P1/C < PY6/M0 < P1/M1 < P1/M014 PY6/SF = PY6/D < PY6/A < PY6 < P1/D < PY6/C < P1/SF < P1/A < PY6/M1 < P1 < PY6/M0 < P1/C < P1/M1 < P1/M021 PY6/SF < PY6/D < PY6 < PY6/A < P1/A < PY6/C < P1/SF < P1/D < P1 < P1/C < PY6/M1 < P1/M1 < PY6/M0 < P1/M028 PY6/SF < PY6/D < PY6 < PY6/A < P1/D < PY6/C < P1/SF < P1/A < P1 < P1/C < PY6/M1 < PY6/M0 < P1/M1 < P1/M060 PY6/SF < PY6/D < PY6 < PY6/A < P1/D < PY6/C < P1/SF < P1/A < P1 < PY6/M1 < P1/C < PY6/M0 < P1/M1 < P1/M090 PY6/SF < PY6/D < PY6 < PY6/A < PY6/C < P1/SF < P1/D < P1/A < P1 < PY6/M1 < PY6/M0 < P1/C < P1/M1 < P1/M0270 PY6/D < PY6/SF < PY6/A < PY6/C < PY6 < P1/A < P1/SF < P1/D < PY6/M1 < P1 < PY6/M0 < P1/C < P1/M1 < P1/M0730 PY6/SF < PY6/D < PY6/A < PY6 < PY6/C < P1/SF < P1/D < P1/A < P1 < PY6/M1 < P1/C < PY6/M0 < P1/M1 < P1/M0Classification of the pozzolans

in function of its Al2Or�3 (%) content

SF0%¼ D

0%< A

8:0%< C

11:5%< M1

15:0%< M0

29:0%

R. Talero / Construction and Building Materials 33 (2012) 164–180 169

Finally, the water demand in the respective mortars [31](Table 4) was apparently the same for all the pozzolans except silicafume (SF), due to the percentage used (20%), and in particular diat-omite (D), whose morphology generated much greater demand.While in fact, the water demand3 in the respective mortars [31] alsorose really (Table 4) when the more or less aluminic pozzolans(pozzolans M0, M1, C and A, respectively) were added. This wasonce again directly related to their intense early pozzolanic activityinduced by their respective Al2Or�

3 content [1,2,22,23] mainly.

4.2. XRD results (Tables 5–9 and Figs. 2 and 3)

The semi-quantitative analysis of the blends at different ages (1,7, 14, 21, 28, 60, 90, 270, 730 days) by XRD technique is shown inTables 2 and 3. In order to quantify the Fs formed, the integral area,IA (a.u.) of its most characteristic peak of the XRD spectrum hasbeen determined. Therefore, possible Fs crystalline system transi-tion (monoclinic/rhombohedral) at 35 �C [42,43] and preferentialorientation problems so frequent to Layered Double Hydroxides(LDH) such as Fs, have been taken into the appropriateconsideration.

4.2.1. Proof of the inter-dependence between Fs-rf and Fs-lf duringjoint formation or co-precipitation in a chloride solution (3.75% NaCl)4.2.1.1. First proof of inter-dependence or co-precipitation. Calcula-tions. The present proof entailed calculating and comparing theIA values attributable to the 30% Z pozzolan (20% for SF) in POZCfamilies P1/‘‘Z’’ and PY6/‘‘Z’’, respectively, analysed by XRDtechnique (Table 5 and Fig. 2a and b).

Fig. 2b shows that the absolute and relative IA values for the 70/30 POZCs in which nearly all the Al2Or�

3 was present in the pozzo-lan only, i.e., the PY6/‘‘Z’’ POZC family (PY6 containing 0% C3A andthe Z pozzolan being M0, M1, C or A), were consistently lower(Table 5) than for the blends containing an OPC with a highC3A (%) content, i.e., the P1/‘‘Z’’ family (Table 5 and Fig. 2a). Thissupports the inter-dependent, as opposed to separate, formationof Fs-rf and Fs-lf in their respective pastes. In other words, thetwo types of Friedel’s salts co-precipitated. Moreover, the closerthe Z pozzolan (its Al2Or�

3 ) and the OPC P1 (its C3A) particles wereto one other, the more inter-dependent was the formation of thesalt. The Fs from both sources was therefore concluded to be gen-erated when the original reactive materials, Z pozzolan and OPC,were present in the same aqueous chloride medium. By contrast,Fs-rf and Friedel’s salt of very slow formation (Fs-vlf), from C4AForigin present in the same PC would most probably not be joint,but separate events.

Moreover, according to prior semi-quantitative XRD studiesconducted on Friedel’s salt formation [1,2], the formation rate, Vf,of Fs-rf (from the Al2Or�

3 present in the Z pozzolan) was necessarily

higher than the Vf of the Fs-lf (from the C3A present in the PC). Thatfinding is the first axiom of the present paper:

VfFs-rf is > VfFs-If ð1Þ

Consequently, Fs-rf logically comprises smaller and less perfectcrystals than Fs-lf (see Fig. 1).

Of the total IA (=relative content of Friedel’s salt derived fromthe respective XRD pattern, in a.u.) generated by the blends at eachexperimental age, 30% would be attributable to the Z pozzolan con-stituent (M0, M1 or C, which are more aluminic in chemical charac-ter than A [1,2]), i.e.:

for PC P1 and its 70/30 POZCs P1/‘‘Z’’ (80/20 for P1/SF), the fol-lowing expression was applied:

IA of 30%\Z" ¼ IAxdays 70=30 POZC P1=\Z"

� 70% IAxdaysPC P1 ð2Þ

and

for PC PY6 and its 70/30 POZCs PY6/‘‘Z’’ (80/20 for PY6/SF), the fol-lowing equation was formulated:IA of 30%\Z" ¼ IAxdays 70=30 POZC PY6=\Z"

� 70% IAxdays PC PY6 ð3Þ

An initial analysis of the respective IA values given in Table 5showed that when 30% of the Z pozzolan (20% for SF) was blendedwith PC P1, its IA was from 1.22 to 11.70-fold greater than whenthe addition was blended with PC PY6.

What is the main reason for such disparity?According to the first axiom, the real amount of Friedel’s salt

generated by each Z pozzolan at a given experimental age asdetermined by the XRD analysis of the respective paste must bevery close to the real value when the pozzolan was blended withPC PY6, since this PC had a nil C3A (%) content. PC P1, by contrast,contained a substantial amount of C3A (14%), which has also beenshown to be a source of Friedel’s salt [1,2] when its POZC-P1 wereexposed to chlorides. Hence, pursuant to the ‘‘principle of theconservation of matter’’ (second axiom of this study), the excessFriedel’s salt generated by each Z pozzolan when blended withPC P1 could not have been formed by the Z pozzolan only. Indeed,further to the two axioms, the amount of Friedel’s salt formed bythe Z pozzolan would necessarily have to be the same for bothPOZC families, and in the PC P1 blends, it should form beforethe salt generated from the C3A present in each POZC-P1, dueto the visibly higher formation rate observed in the former thanin the latter. Therefore, the origin of the excess Friedel’s salt form-ing in 70/30 POZC P1/‘‘Z’’, would have necessarily had to be the9.8% (=14% � 70%) of C3A present in the PC P1 with which the Zpozzolan was blended. The aforementioned findings proved that

21,075,8 84,7

122,3 123,6

200,6

257,9

369,3

648,8

128,6

220,4275,8

494,3

588,4

769,7

908,7

1392,3

1559,5

62,7

154,4 151,2

233,1

387,4

627,4

716,7

1168,6

1397,7

0,0

100,0130,9 152,8 166,9

238,2

564,2

814,4

1163,7

0,054,8 38,0

73,0 63,6 63,8

134,4

216,5247,5

0

200

400

600

800

1000

1200

1400

1600

1800

1 7 14 21 28 60 90 270 730

Inte

gral

are

a[a

.u.2 ]

Age [days]

P1

P1/M0

P1/M1

P1/C

P1/A

P1/D

P1/SF

90,0143,0 144,3

244,1

317,7365,7

400,0

797,2

1580,3

0,0 0,0

77,7127,4

157,3

268,8307,8 320,9

631,1

0,027,8

71,8 66,5 68,1 90,3 100,1125,6 112,3

21,075,8 84,7

122,3 123,6

200,6

257,9

369,3

648,8

0

200

400

600

800

1000

1200

1400

1600

1800

1 7 14 21 28 60 90 270 730

Inte

gral

are

a[a

.u.2 ]

Age [days]

PY6

PY6/M0

PY6/M1

PY6/C

PY6/A

PY6/D

PY6/SF

P1

(a)

(b)

Fig. 2. XRD semi-quantitative analysis of Friedel’s salt formation from the (a) OPC P1 and (b) SRPC PY6 and their POZC with ‘‘Z’’ pozzolan hydrated with 3.75% NaCl solution.

170 R. Talero / Construction and Building Materials 33 (2012) 164–180

saline hydration (with 3.75% NaCl solution) in the P1/‘‘Z’’ blendswas stimulated more indirectly than directly and non-directly(see the fundamentals in item 4.4 below) as a result of the high,fast and early pozzolanic activity developed by the Z pozzolan,even in the 1-day pastes (Table 2). That in turn supports the pre-mise that joint Friedel’s salt formation in the common salinemedium (3.75% of NaCl solution in this study) was due to coordi-nated co-precipitation. In other words, the Fs-rf from the Al2Or�

3

in the Z pozzolan did not form separately from the Fs-lf fromthe C3A in the PC. Hence, like sulphates [6,17–19,23], in salinemedia the pozzolanic activity attributed to the Al2Or�

3 in the Zpozzolan was once again [6,17–19,23] more specific than generic.That induced greater, faster and earlier saline hydration of the

C3A, but not of the C3S, present in its PC P1 fraction, than whenthe PC P1 was hydrated under the same conditions but withoutthe pozzolan. The pozzolanic activity of SiOr�

2 was similarly[6,19–21] non-specific or anti-specific or contra-specific, however.Furthermore, the paradoxical observation that POZC P1/SF (80/20) generated small quantities of Friedel’s salt, 0.14 and4.73 a.u. after 21 and 28 days, respectively, would corroboratethe foregoing, since precipitation would have had to be a resultof the direct [15] and non-direct [16] stimulation of saline hydra-tion induced by the action of the SF particles (present in 20% frac-tion) on the 11.2% C3A (=14% � 80%) content of the PC P1 fraction(80%) with which they were blended. Nonetheless, in keepingwith these purely physical considerations, a new proposal might

P1/SFP1/DP1/AP1P1/CP1/M1P1/M0

0

1000

2000

3000

4000

5000

6000

7000

8000

10,6 10,8 11,1 11,3 11,6 11,8

Inte

nsity

[a.u

.]

Angle [2theta]

PY6/SFPY6/DPY6/APY6PY6/CPY6/M1PY6/M0

0

1000

2000

3000

4000

5000

6000

7000

8000

10,6 10,8 11,1 11,3 11,6 11,8

Inte

nsity

[a.u

.]

Angle [2theta]

P1/SFP1/DP1/AP1P1/CP1/M1P1/M0

0

1000

2000

3000

4000

5000

6000

7000

8000

10,6 10,8 11,1 11,3 11,6 11,8

Inte

nsity

[a.u

.]

Angle [2theta]

PY6/SFPY6/DPY6/APY6PY6/CPY6/M1PY6/M0

0

1000

2000

3000

4000

5000

6000

7000

8000

10,6 10,8 11,1 11,3 11,6 11,8

Inte

nsity

[a.u

.]

Angle [2theta]

(a) (b)

(c) (d)

Fig. 3. XRD patterns of the most significant peak for Friedel’s salt originated by 70/30 POZC P1/‘‘Z’’ pozzolan, (a and c), and 70/30 POZC PY6/‘‘Z’’ pozzolan (b and d), at 270 (aand b) and 730 (c and d) days of their saline hydration with 3.75% NaCl solution.

R. Talero / Construction and Building Materials 33 (2012) 164–180 171

be put forward, namely that the effect of SF stimulation was morechemical than physical. This would be more likely if the salinehydration had been stimulated indirectly [6,19–21], due to thelikewise high, fast and early pozzolanic activity (Table 3) devel-oped by the SF fraction in POZC P1/SF under the same salinehydration conditions. Unfortunately, this premise cannot be ac-cepted, for when diatomite, pozzolan D, was used, its 70/30POZCs P1/D and PY6/D pastes generated no significant amountsof Friedel’s salt at any age of the analysis (Fig. 2a, b and 3b andd), despite the fact that both the pozzolan D in POZCs PY6/Dand P1/D (30%) and its SiOr�

2 content (89.0%) were higher thanthe POZC PY6/SF and P1/SF values: 20% SF and 88.5% SiOr�

2 con-tent, respectively.

4.2.1.2. Second proof of inter-dependence or co-precipitation (Table 5)(Figs. 2 and 3). The 270 and 730-day IA (a.u.) values for the Fs form-ing with each POZC (Table 5) are discussed in this item. The find-ings clearly confirmed that the higher the Al2Or�

3 (%) content inthe Z pozzolans blended with PC P1 (14% C3A content), the greaterwas the difference in the 270- and 730-day IAs compared to therespective POZC-PY6 (0% C3A content). To put it another way, insaline media, the higher the reactive alumina, Al2Or�

3 (%), contentin the pozzolan, the greater was the inter-dependence in jointFs-rf and Fs-lf formation – co-precipitation –.

Moreover, while all the P1/‘‘Z’’ POZCs had the same C3A content(9.8% = 14% � 70%), the IA values indicative of the amount of Fri-edel’s salt formed varied. They were proportional, however, tothe Al2Or�

3 (%) content in the respective Z pozzolan and completelyindependent of the SiOr�

2 (%) content. Therefore, the main reasonfor such variations in the IA findings was the Al2Or�

3 contributedby each Z pozzolan to its POZC. At the same time, this definedthe degree of pozzolanic activity and constituted the cause of theproportional indirect stimulation of saline hydration throughoutthe trial (see the fundamentals in Section 4.4 below), targetingthe 9.8% C3A (not the 35.7% C3S) in the POZC. Furthermore, pozzo-lans with Al2Or�

3 , M1, C and A, were potentially the most effective Zpozzolans because of their greater power to indirectly stimulate the9.8% C3A than exhibited by pozzolan M0 and its POZC. The reasonfor that paradox may lie in the smaller crystalline fraction formingpart of pozzolans M1, C and A (quartz, diopside, artinite, magne-sium hedenbergite, forsterite and stishovite), whose physical dilu-tion may have improved their pozzolanic activity in the chloridesolution, facilitating and expediting the process. As a result, thiswould have stimulated the indirect saline hydration of the C3A,but not of the C3S, present in the PC P1 fraction, and also by directand non-direct way properly, but less or much less according to itsAl2Or�

3 (%) content is low, A pozzolan, or high, M1 and C pozzolans,respectively. This was further justified by the multiplying factors for

Table 10Technical consequence of the SE: Absorption test [40]. Results for the PC P1 and their POZC which each Z pozzolan.

Cements m (R)(107 s/m2)

m (T)(107 s/m2)

k (R) (kg/m2 s½)

k (T) (kg/m2 s½)

a3 (R) (g/m2 s½)

a3 (T) (g/m2 s½)

a24 (R) (g/m2 s½)

a24 (T) (g/m2 s½)

Total Porosity(R) (%)

Total Porosity(T) (%)

SiOr�2 content of Z

pozozlan (%)Al2Or�

3 content of Zpozzolan (%)

P1 100/00 1.81� – 0.0427� – 43� – 24� – 19.0� – – –P1/SF 80/

204.31 >2.146 0.0443 <0.06114 45 63.4 38 37.4 24.0 <29.44 88.5 0.0

P1/D 70/30

1.67 �� 0.0603 �� 61 �� 32 �� 25.8 �� 89.0 0.0

P1/A 70/30

2.28 �� 0.0464 �� 43 �� 28 �� 22.7 �� 37.5 8.0

P1/C 70/30

2.87 >2.519 0.0398 <0.04411 40 44.1 27 28.6 21.5 >21.41 39.0 11.5

P1/M1 70/30

4.69 >2.809 0.0190 <0.03631 18 37.1 12 23.6 19.6 <20.11 38.5 15.0

P1/M0 70/30

7.20 >5.389 0.0234 <0.02911 22 30.1 20 23.6 16.2 <20.21 48.5 29.0

PY6 100/00

2.14� – 0.0434� – 40� – 26� – 18.7� – – –

PY6/SF 80/20

2.41� – 0.0617� – 61� – 39� – 29.2� – 88.5 0.0

PY6/C 70/30

2.75� – 0.0446� – 42� – 30� – 21.2� – 39.0 11.5

PY6/M170/30

3.04� – 0.0368� – 35� – 25� – 19.9� – 38.5 15.0

PY6/M070/30

5.62� – 0.0296� – 28� – 25� – 20.0� – 48.5 29.0

m = Water penetration resistance; k = capillary absorption coefficient; a3 = capillary absorption coefficient at 3 h; a24 = capillary absorption coefficient at 24 h; (R) = Real; (T) = Theoretical; porosity = effective porosity. ⁄ Valuesneeded for calculations. ⁄⁄ These values are not the more significant neither for comparison nor calculations of this Synergic Effect’s consequence: the physical parameter of absorption, neither qualitative nor quantitatively. m isconsidered to be a function of the porous structure but not of the total porosity; hence, when the porous system is smaller, the water is absorbed into its interior much more slowly and, in consequence, the m parameter takes amajor value.

172R

.Talero/Construction

andBuilding

Materials

33(2012)

164–180

R. Talero / Construction and Building Materials 33 (2012) 164–180 173

the Synergic Effect originated by joint Fs-rf and Fs-lf formation at7, 28 and especially 730 days (Table 6).

Finally, here also the combined formation of the Fs-rf and Fs-lfin a common chloride solution has been shown not to take placeindependently, but rather inter-dependently, jointly, in combina-tion or interactively – co-precipitation –, and the reaction productswere found to be closer to Fs-rf than Fs-lf when more Al2Or�

3 fromthe Z pozzolan was present. In any event, TPQ (topochemical)mechanism preceded by dissolution would have had to prevailover any TS (through-solution) mechanism.

4.3. Co-precipitation of Friedel’s salt from Al2Or�3 and C3A origins:

proof of the Synergic Effect, SE (Tables 6–8)

The proven co-precipitation of Friedel’s salt in an aqueous chlo-ride medium from both the Al2Or�

3 in pozzolans and the C3A in PC,like the co-precipitation of ettringite with the same origins in agypsum solution [4–6], has led to the identification of a new Syn-ergic Effect, SE. The two methods deployed to prove the existenceof this new SE, both requiring the XRD analysis of the PC and POZC-Z pozzolan pastes used in the foregoing experiments (Tables 6–8),are described below.

4.3.1. Proof of the Synergic Effect: Method 1 (Table 6)The first method consisted of estimating the ‘‘theoretical

amount of Fs (a.u.)’’ generated by each POZC when attacked bythe saline solution (3.75% NaCl) and comparing that value to thereal amount obtained from the XRD analysis, ‘‘real Fs (a.u.)’’. The‘‘real Fs’’/‘‘theoretical Fs’’ ratio was then determined for each age.Assuming the C3A content of PC PY6 to be nil practically, the equa-tions formulated were as follows:

IT;P1=Z pozzolan ¼ 70% � IR;P1 þ IR;PY6=Z pozzolan � 70% � IR;PY6 ð4Þ

Multiplying factorZ pozzolan ¼IR;P1=Z pozzolan

IT;P1=Z pozzolan

¼ IR;P1=Z pozzolan

70% � IR;P1 þ IR;PY6=Z pozzolan � 70% � IR;PY6

ð5Þ

Multiplying factorSF ¼IR;P1=SF

IT;P1=SF

¼ IR;P1=SF

80% � IR;P1 þ IR;PY6=SF � 80% � IR;PY6ð6Þ

where IT,P1Z pozzolan (a.u.) is the theoretical value estimated for theIntegral Area (IA) on the XRD pattern for the P1/Z pozzolan blend;IR,PY6/Z pozzolan (a.u.) is the real IA of the respective Fs line on thePY6/Z pozzolan blend diffractogram; IR,P1 (a.u.) is the real IA of theFs line on the ‘‘X-day’’ plain PC P1 XRD trace; and IR,PY6 (a.u.) isthe real IA of the Fs reflection on the same ‘‘X-day’’ plain PC PY6 dif-fractogram. The findings stemming from this mathematical proce-dure are given in Table 6.

In the P1/M1 blend, the greatest Synergic Effect, SE, was ob-served at early ages, when its multiplying factor was from 2 to3-fold greater than the equivalent value for M0 pozzolan, eventhough the Al2Or�

3 (%) content was double in the latter. The reasonfor this discrepancy must have been [1] the physical dilution re-ferred to earlier. The �50% of quartz (non-pozzolanic mineral addi-tion) content would favour chloride penetration deep into the M1POZC paste mass, especially at early ages when ion mobility de-pends on permeability, diffusion (limited by the chloride concen-tration gradient from the surface to the interior of the POZCpaste) and capillary suction. The SE multiplying factors for all theexperimental ages are listed in Table 6.

4.3.2. Proof of the Synergic Effect: Method 2 (Tables 7 and 8)The fundamentals of this second method borrow from the 1st

proof of the inter-dependence between Fs-rf and Fs-lf during theirjoint formation or co-precipitation in a chloride solution (see thefirst and second axioms). Taking the 1-day results, when pozzolanM0 (30%) was mixed with SRPC PY6 (70%; 0% C3A content), the Fs/g PY6 IA came to 6.430 a.u. (which must have been primarily gen-erated by the M0 pozzolan). When pozzolan M0 was blended withOPC P1 (70%; 14% C3A content), in turn, the Fs/g PC P1 formed hadan IA of 9.190 a.u. The difference in IA came to: 9.190 a.u. Fs/g PCP1– 6.430 a.u. for Fs/g PC PY6 = 2.760 a.u. Fs/g PC P1, although theOPC P1 alone accounted for 0.735 a.u. (=70% � 1.05 a.u./g PC P1)(Table 7). Therefore, the question posed here is: why is the behav-iour of OPC P1 not the same in the absence of pozzolan M0? Thereason is the lack in the pure OPC P1 of the prior pozzolanic activity(Table 3) afforded by the Z pozzolan, since when the PC P1 wasblended with M0, its 9.8% C3A content (70% � 14%) generated Fs-rf, just as the 8.7% Al2Or�

3 (29% � 30%) in pozzolan M0 did. As salinehydration progressed, the entire C3A content might have also beentransformed into Fs-rf.

Taking the 1-day findings for the OPC P1, where the Fs/g PC P1came to only 0.735 a.u. (70% � 1.05 a.u., Table 7), the difference9.190 � 0.735 = 8.455 a.u. must necessarily have been generatedby the OPC P1 itself. Here, however, the salt was generated not di-rectly, such as when plain PC P1 was hydrated in a saline solution,but indirectly, i.e., after pozzolan M0 stimulated faster and earliersaline hydration thanks to its 8.7% Al2Or�

3 content which developedits prior pozzolanic activity: high, fast and very early (Table 3). Forthis reason, the pozzolanic activity involved was more specific thangeneric, prompting more intense C3A than C3S saline hydration ofthe PC P1. Furthermore, pursuant to the second axiom, pozzolanM0 alone would have never been able to generate 9.190 or even2.760 a.u. Finally, these findings were corroborated as salinehydration progressed, as might be logically expected, for even inthe 730-day pastes, in the near absence of C3A, the C4AF contentin the PCs [3.5% (=5% � 70%) and 7.0% (=10% � 70%), in P1 andPY6, respectively], can acquire its role as well and generate greatervalues with PC PY6 than with PC P1, as logical.

4.4. Co-precipitation of Friedel’s salt from Al2Or�3 and C3A origins.

Consequence: Synergic Effect, SE. Fundamentals and justification(Tables 6–8)

But while the SE has been ‘‘proven’’ by two different methods, noconvincing explanation or justification has yet been forthcoming ofwhy the two types of Friedel’s salt behave as they do in a commonchlorides and water environment, giving rise to this new SE (in agreater or a lesser degree). Another question that must be posedis: why do these two types of Friedel’s salt generate more or lessappreciable SE once they co-precipitate in a common chloridesand/or water environment? Assumption or explanation:

Intuitively, the first assumption or explanation that comes tomind is that since Vf Fs-rf is >Vf Fs-lf (1) [1,2],

– the Fs-rf from the Al2Or�3 in the Z pozzolan (C, M1 and M0 espe-

cially) would form first, and– the Fs-lf from the C3A present in the OPC would form thereafter,

but its chlorides-mediated hydration should not being favouredby the chloride ions penetration into their respective POZCpaste mass, at early ages especially, because it would dependmore on their permeability, diffusion (limited by a concentra-tion gradient of the chlorides between the outside and insideof the its POZC paste) and capillarity suction phenomenon.

But this assumption is incorrect for several reasons. The first isthat if it were true, it would be tantamount to acknowledging

4 Ref. [6]: (Section 4.3. Existence of ESE: Fundamentals, explanation and justification,paragraph 9, line 10, page 1150). In Eqs. (9)–(11) might have been more suitablyexpressed with ‘‘greater than’’ (>) than with the ‘‘less than’’ (<) symbol and introducedas being shown in descending rather than ascending order. This correction would not,of course, have affected the fundamentals, explanations, justifications and/orconclusions set out in that paper in any way whatsoever. In addition, in the Fig. 3of this Ref. [6], P-1/M should be read P-1/MK.

174 R. Talero / Construction and Building Materials 33 (2012) 164–180

that C3A content from OPC fraction of the POZC would not beginto hydrate itself in the saline solution until the respective Z poz-zolan fraction with which it was blended had exhausted all its poz-zolanic activity, which takes at least 28 days [5–9,12–14,17–23](Table 3). But this is obviously, inaccurate, since the saline hydra-tion reactions in both Z pozzolan and OPC fractions of each POZC– whose Friedel’s salt forming mechanisms, formation rates, per-fection and sizes of the crystals are wholly different –, must beginfrom the very moment that the mixing and/or curing water withchlorides comes into contact with their respective particles,regardless of the number, shape and size of such particles per-taining to each fraction, and if there is chlorides excess guaran-teed or not.

In addition, from the outset the Al2Or�3 and C3A contents in the

respective fractions must compete for the chlorides in the curingwater – 3.75% NaCl solution – to form Friedel’s salt from differentorigins and at different rates as per Eq. (1)? In other words, despitethe fact that Vf is higher in Fs-rf than in Fs-lf (Eq. (1)), as has beenshown in prior studies [1,2], the competition between the originalreagents, Al2Or�

3 and C3A, to fix the 3.75% NaCl solution, actuallyexists throughout the trial, and may even be particularly intenseat the beginning of the process (Tables 3 and 5–7). The former,Al2Or�

3 , cannot in any case prevent the latter, C3A, from formingalso Friedel’s salt, despite or rather precisely because of the greaterphysical–chemical suitability of the Al2Or�

3 [1,2]. Therefore, pursu-ant to the foregoing but especially to the experimental results ob-tained for all the POZC families, the TOTAL Friedel’s salt at the ageof 7 days, Fs-T7d, i.e., the sum of Fs-rf7d and Fs-lf7d, has to be nec-essarily greater in the POZC-M0 pozzolan than in the POZC-M1pozzolan, than in the POZC-C pozzolan and than in the POZC-Apozzolan (Table 5). This fact converges with the respective Frattinitest values for [OH�] and [CaO] (Table 3) already from 1 day-age.

Now and similarly to when the sulphate attack and the ESE [6]originated, competition between the total amounts of Al2Or�

3 andC3A in any POZC-Z pozzolan to be totally or partially converted intoFriedel’s salt, exists, as well as its greater or lesser non-expansiveconsequences do, because the molar volume of Friedel’s salt,296.69 cm3, is of the same magnitude order like its equivalent forthe different calcium aluminates hydrated of PC origin (OPC and/or SRPC) – unlike the ettringite from any origin, 715.09 cm3, PCor Al2Or�

3 [4–8] –, and therefore, the great tendency of Friedel’s saltto fill its macroporous, porous, microporous and capillary systemin cement pastes, mortars and/or concretes. And such competitiondepends directly, among others, on:

– whether the physical–chemical properties of Al2Or�3 make it a

more active reagent than C3A [1,2], and according to the resultsobtained to date [1,2] they do,

– the amount of Al2Or�3 and C3A present in each POZC paste,

– the B-SS of Z pozzolan and the type of PC mixed in each POZCblend, and

– the paste age.

Therefore, further to the foregoing, it may be asserted that oncea certain amount of time has lapsed, the TOTAL amount of Friedel’ssalt, Fs-T, in each POZC paste is impacted to a lesser or greater ex-tent by the following:

– the Friedel’s salt from C3A origin, present in equal quantity in allthe 70/30 POZC pastes (80/20 for the POZC-SF paste), and/or

– the Friedel’s salt from Al2Or�3 origin, likewise present in the

above POZC pastes but in different quantities because theAl2Or�

3 (%) content of each Z pozzolan is different.

Consequently, since several different types of POZC pastes werehydrated with 3.75% NaCl solution, and analysed at different ages,

the kind and the final amount of Friedel’s salt formed by eachPOZC, would be expected to have varied depending on the testage considered. And the findings of this study concurred with suchexpectations. See Figs. 2 and 3.

But all the reasoning set out above would lead to the conclusionthat the Friedel’s salt formation by each POZC is the mere sum ofthe various types of Friedel’s salt formed by its respective blendedcement at a given age, and, as mentioned earlier, the matter isactually not quite so simple. Thus, prior papers on Friedel’s salt for-mation [1,2] and the SE generated thereby when forming in oneand the same chlorides and water co-environment, have shownthat: first of all, from the outset, the two types of Friedel’s salt fromdifferent origins do not form separately, but rather more or less in-ter-dependently in the shared chloride medium – co-precipitation– (this fact is the second reason for challenging the above sequen-tial formation assumption), and secondly, the effect resulting fromthe co-precipitation of the Friedel’s salt from both origins in theshared chloride medium is more synergic than additive (thiswould be a third reason for refuting the above assumption), be-cause, as it has been demonstrated above in Section 4.3, the realTotal Friedel’s salt amount originated at any age of the trial andby any aluminic Z pozzolan with the PC P1, is No.-fold greater thanthe theoretical.

For these three reasons, the initial assumption or explanationis incorrect. This calls, then, for another – the second one and defin-itive explanation or interpretation – of the actual cause underly-ing the SE generated by the two types of Friedel’s salt in each POZCpaste, which would, moreover, justify each specific case as cor-rectly as possible. Providing such an explanation entails analysingthe results of the Frattini test for the four 70/30 POZC-Z pozzolanwith more or less Al2Or�

3 (%) content, i.e., ranking the [CaO] con-tents in their 7-day liquid phases (Table 3) in descending4 order(as per Eq. (7)). For the four POZCs studied, the order was foundto be as follows:

> ½CaO�7days >; 70=30 P1=Z pozzolan; 100=00 > A > C

> M1 > M0 ð7Þ

< IAða:u:2Þvaluesxdays < 70=30 P1 or PY6=Z pozzolan;

A < C < M1 < M0 ð8Þ

< Al2Or�3 ð%Þ content < A < C < M1 < M0 ð9Þ

< SiOr�2 ð%Þ content < A < C < M1 < M0 < SF < D ð10Þ

Note that Eq. (7) (1st Group) does not converge with Eqs. (8)–(10)(2nd Group), in as much as that Eq. (7) was obtained on basis ofthe chemical parameter, [CaO]7d, mainly, for these Z pozzolans,whereas Eq. (8) was obtained from different Friedel’s salt contents[=IA (a.u.)] at each age by the XRD semi-quantitative analysis oftheir respective POZC pastes, and Eq. (9) by the Florentin method[35]. In other words, in this study of the chloride attack (with3.75% NaCl solution), by contrast to the study substantiating ESEon the grounds of the sulphate attack (from gypsum origin) [6],no convergence with other [CaO]xdays values was found, due tothe very significant role played by the high Na2Oeq. (%) content inpozzolan C (9.04%) in the Frattini test [44].

R. Talero / Construction and Building Materials 33 (2012) 164–180 175

The questions posed here are:

– Why should the 1st and 2nd Groups of equations not converge?– Why are all these Friedel’s salt contents the result of the chem-

ical parameter [CaO] content? and finally,– Why are all these chemical parameters indicative of the gener-

ation of greater or lesser SE by Friedel’s salt from Z pozzolan andFriedel’s salt from OPC origin when they co-precipitate in acommon chlorides and water environment?

The reasoning or explanation would be as follows: from the out-set, the pozzolanic activity of any Z pozzolan causes the [OH�] and[CaO] to decline as the reaction progresses until portlandite solu-bility falls below saturation in the liquid phase: be this in theFrattini test or any other test, as well as in real life situations. Inthe present study, that pozzolanic activity was so ostensible, earlyand speedy in all the Z pozzolan (C, M1 and M0 specially) POZC,that most of them have met the Frattini test requirement at1 day-age (Table 3).

Therefore, from the very beginning of saline hydration, [OH�]and [CaO] in the liquid phase, surrounding the respective OPC par-ticles in each paste, were below saturation level. Such circum-stances favour more or less rapid chlorides-mediated hydrationof certain amount of still anhydrous C3A in the OPC P1 fraction ineach POZC paste, the outcome being Friedel’s salt formation. It oc-curs because, among others, C3A hydrates more rapidly than theother main components of Portland clinker (C3S, C2S and C4AF).In a word, based on the experimental results, this other Friedel’ssalt from C3A origin must have been formed more and faster thanwhen happens for the plain OPC, the higher pozzolanic activitypreviously developed by Z pozzolan, e.g. the more Al2Or�

3 addedto the OPC, and vice versa (i.e., its Vf may be even as fast as theVf Fs-rf originated from the Z pozzolan). For this reason, largerquantities of chlorides would be expected to be fixed already atearly ages in these blends than in its respective plain OPC. In thiscase, moreover, there is reason to believe that if the Friedel’s saltformation mechanism is topochemical (TQ), as it is in all likelihoodto be expected to appear, however it would logically entail priordissolution.

Conclusively, in the first place, due to the early and speedypozzolanic activity of the Al2Or�

3 (present in each Z pozzolan)in a chlorides and water environment, Fs-rf is formed as a resultof its higher Vf. And this Fs-rf formed in turn must generate aconcomitant decline in the [OH�] and [CaO] in the curing waterwith chlorides, along with a decrease in porosity because theFriedel’s salt is not expansive like ettringite, and for this reason,Friedel’s salt gives rise to fill full its macroporous, porous, micro-porous and capillary system [1,2]; with both [OH�] and [CaO]below their respective saturation values, i.e., below the Frattinicurve, chlorides-mediated hydration of the C3A present in thestill anhydrous OPC in the various POZC would be expected totake place more abundantly, readily and speedily. For all theforegoing – initial [OH�] and [CaO] < saturation in the curingwater with 3.75% NaCl and decline in {NaCl}cw as well – theresidual C3A in the still anhydrous fraction of the OPC P1 (theoriginal amount less the amount generating calcium aluminateshydrated with the water used to mix the POZC paste) wouldform its respective Friedel’s salt as part of a chain reaction trig-gered by the primary Fs-rf or Fs-rf formed previously by the Zpozzolan with which the OPC P1 was mixed, either at the sametime and as subsequent thereto. In short, if the Z pozzolan hadpreviously generated sufficient pozzolanic activity from Al2Or�

3

origin, all the Friedel’s salt from the C3A origin in the OPC P1,for instance, would not be Fs-lf but Fs-rf as well. But otherwise,only part of that possible total amount of Friedel’s salt would beFs-rf, and such part would be proportional to the amount of

pozzolanic activity previously exhibited by the respective Z poz-zolan fraction in the POZC OPC P1-containing.

This process would continue until the pozzolanic activity of therespective Z pozzolan fraction was depleted. By that time, all theC3A may have been converted into Fs-rf; if not, any remainingC3A will have been transformed into Fs-lf. In other words, the for-mation of Friedel’s salt from different origins would initially takeplace like the elements in a chain reaction, to ultimately behavelike steel shavings (the C3A content in the anhydrous OPC P1 par-ticles) attracted to a magnet (Fs-rf) which, once attached by thechlorides, also become magnetised, i.e.: become Fs-rf. None ofthe foregoing can occur, however, unless the Z pozzolan exhibitssufficient pozzolanic activity from Al2Or�

3 origin. If it does not, partof the initial amount of C3A will form Fs-rf, along with all of theAl2Or�

3 from the Z pozzolan fraction, while the rest will form Fs-lfas it does when Friedel’s salt is formed in plain OPC. Indeed,depending on degree of the previous Z pozzolanic activity devel-oped from Al2Or�

3 origin, the rates will be, or not, the same. In otherwords, why is the behaviour of C3A not the same in the absence ofZ pozzolan (C, M1 and M0 especially)? Because there is no priorpozzolanic activity of Z pozzolan, since if there had been any, theC3A content might have generated Fs-rf, just as Al2Or�

3 does. Andif the Al2Or�

3 content of Z pozzolan fraction is high in relation tothe C3A content of the PC fraction with which was mixed, the en-tire C3A content could be transformed into Fs-rf as well: otherwise,this transformation may affect only a part of the entire content.The rest, like the plain OPC which it derives from, generates Fs-lf.

In consequence and based on the outlined explanation, thehigher and earlier the pozzolanic activity originated by these Zpozzolans due to its higher Al2Or�

3 contribution, the total C3A con-tent in the respective OPC P1 fraction should form its Friedel’s saltas Fs-rf; and if not, it should form Fs-lf, e.g., only a part as Fs-rf, andthe rest, as Fs-lf properly. This would have been the reason that ablend of 70% of OPC P1 and 30% of Z pozzolan, have given rise to ahigher 7 days-age IA (a.u.)7d value than the plain OPC P1. In otherwords, the Z pozzolan (30%) forming Fs-rf [1,2], or more precisely,the Al2Or�

3 present in Z pozzolan (including the A pozzolan) whenconverted into Fs-rf was the chief direct and indirect cause due tothe specificity of its pozzolanic activity for the C3A (%) of the OPCP1 in a common chlorides and water environment, but not for itscorresponding C3S (%) content.

The behaviour of these Z pozzolans proves once again that, notonly at very early ages but from beginning to the end of the chlo-rides attack, the pozzolanic activity of its reactive alumina, Al2Or�

3

(%), content, mainly, is more specific than generic for a greater andfaster hydration reaction of the C3A than of the C3S, both present inthe fraction of OPC P1 or PY6 (i.e. case of significant or very signif-icant Al2Or�

3 (%) contents: C, M1 and M0 mainly). Furthermore, thisvery particular stimulation of the hydration reactions of C3A espe-cially, has already been named as ‘‘indirect way’’ [6,17–19,23], sinceit is totally different from the induced stimulation by ‘‘direct way’’[15] and ‘‘non-direct way’’ [16] which are mediated by the mixingwater wetting the Z pozzolan particles originally, and by their ini-tial behaviour as ‘‘nucleation or precipitation centres’’ of smallportlandite crystals (or ‘‘seed crystal’’ in the case of mineral addi-tions, crystalline or non-pozzolanic, calcareous in nature), due tothe zeta potential developed when the hydration reactions movesforward, respectively. Nevertheless and for the Z pozzolan particles,this ‘‘direct way’’ and ‘‘non-direct way’’ of stimulation are always over-lapped with the ‘‘indirect way’’ stimulation [6,17–19,23], as logical, tosuch an extent that comparatively, their significances for thehydration advance are nil practically.

In any event, proof of the validity of the above second and defin-itive assumption or explanation would be of greater value and sig-nificance. And that calls for results such as the following: Table 3shows that for samples with the same POZC and PC matrix, the

176 R. Talero / Construction and Building Materials 33 (2012) 164–180

2- and 7-days Frattini test values for the pozzolans SF and M1 wereof the same or with a very similar order of magnitude. That not-withstanding, the [CaO] but especially the [OH�] values were con-sistently found to be somewhat lower in SF POZC, as wouldlogically be expected, for the SiOr�

2 [34] content in SF – 88.46% –is substantially higher than in M1 – 38.30%–. Moreover, SiOr�

2 poz-zolanic activity is known to be materialised by forming CSH gels(subsequently transformed into tobermorites) and silanol groups,Si–OH (later converted into hydrated silicic acid) with Ca2+ andOH� ions, respectively, both present in the Frattini test liquidphase. The Al2Or�

3 from the M1 (=4.5% = 15% � 30%), in turn, formsseveral hydrated calcium aluminates, particularly Stratling’s com-pound [45], and whether chlorides are present in the medium: Fri-edel’s salt [1,2].

In a nutshell, in the Frattini test, primarily as far as the chemicalparameter [CaO] is concerned (more important of both [CaO] and[OH�], from the mechanical strengths standpoint), all other thingsbeing equal, the SF and M1 POZC exhibited equivalent or very sim-ilar behaviour at the ages of 2 and 7 days (Table 3). By contrast,when the POZC elaborated with these two pozzolans were sub-jected to chlorides presence or to water reaction only, their behav-iour was diametrically opposed, see Tables 3–8 (due to that fromthe chloride resistance standpoint, the CSH gel and the silanolgroups are also important, and for this reason, both SF and M1POZC exhibited in general, very different behaviour in the Frattinitest for the chemical parameter of [OH�] at 1, 2, 7 and 28 days pre-cisely, see Table 3).

The foregoing indicates that the pozzolanic activity of Al2Or�3 in

a common chlorides and water environment causes more of theC3A present to hydrate more rapidly – in this common chloridesmedium and by indirect way stimulation [6,17–19,23], mainly –than when the C3A is alone in a plain OPC. The pozzolanic activityof SiOr�

2 , on the contrary, induces the opposite effect [1,2], i.e., hin-dering or even preventing chloride hydration altogether, due to itsgreater SiOr�

2 content than M1 (Al2Or�3 content of SF must be very

scarce or practically nil because its Al2O3 total content is verysmall, 0.70% only) and despite the fact that its pozzolanic activityis also very high, fast and early (Table 3).

Briefly, this second and definitive assumption or explanation,duly verified, is the chief indirect cause of the SE generated.

Consequently, the pozzolanic activity of Al2Or�3 present in M1

once again [6,17–19,23] can be defined as being more specific thangeneric to generating greater, speedier and more proportionalchlorides-mediated hydration of the C3A (than of the C3S) in thefraction of OPC with which M1 is mixed than in its plain OPC: inother words, to facilitating the chemical reaction by the chloridesexcess in its POZC. On the contrary, the pozzolanic activity ofSiOr�

2 , cannot be so defined, since, conversely and after the veryearly ages of hydration (616 h [19–21]), causes the C3A in the POZCto hydrate less, even in the same chlorides medium, than it does inplain OPC. Therefore, the pozzolanic activity of SiOr�

2 is also spe-cific, but to the opposite action, namely hindering and even imped-ing chlorides chemical reaction with its POZC – physically beforethe 16 first hours of hydration [19–21], and physic-chemically atleast after the 16 first hours of hydration [19–21] – on the respec-tive POZC containing P1 and SF, and by extension, protecting anOPC from chlorides chemical reaction with its C3A (%) content,and to the steel reinforcements of its concrete as well, due to thevery small size and peculiar morphology and chemical composi-tion of its particles (with very high SiOr�

2 content, 88.5%) in vitreousstate, and as a consequence, due to its very high, fast and early poz-zolanic activity, but in any case, depending also on the C3A (%) con-tent and the amount of SF added (like when sulphate attack [6]).Nevertheless, the reason for the protection afforded C3A by SiOr�

2

in a chlorides and water co-environment must also be finally ofmore chemical than physical nature, but the protective physical

aspect holding priority for the 80/20 P1/SF paste, despite the factthat these two pozzolans, M1 and SF, have substantially differentBET-SS.

Although for this last one reason indeed, it could also be permis-sible to think nonetheless, that the protective effect of SF is alwaysmore physical than chemical. But this possibility is not acceptablebecause when diatomite, D, was used, whose total SiO2 (%) contentand SiOr�

2 (%) content are very similar to those for SF (Table 1), buthowever, their morphology and BET-SS (Table 1) are clearly differ-ent, until the point that these siliceous pozzolans, SF and D, showalso a different degree of water absorption amount produced bycapillary suction (Table 10) (see Section 4.5.2), and in addition,more unfavourable, but not for that reason and to equality of allthe others, D pozzolan lets protect of the C3A hydration as well:in a presence of both sulphates [16,19] or chlorides [1,2], eventhough for this latest case its protective effect may be broughtout a bit late. It occurs perhaps because the solubility of NaCl isat least 185-fold greater than the solubility of gypsum. Finallyand for this reason precisely, its contribution to chlorides diffusion(chloride ions can be transported by diffusion or conduction ormigration) and corrosion resistance of steel reinforcement (bythe half cell potentials and using the linear polarisation resistancetechnique) must be necessarily very different as well. And althoughthese issues have not been object of the present study, it is found tobe a questions worth exploring in greater depth and in fact will beaddressed in future publications.

In a nutshell, the mentioned SE is caused, therefore, by thefollowing:

– firstly, because of the Al2Or�3 (%) content of the M0 pozzolan in

the P1/M0 70/30 blend, as well as due to the other pozzolanspresence in the rest of the PC blends, i.e. PC/M1 and PC/C, whichpossess also considerable amount of Al2Or�

3 , however they orig-inate weaker SE than the M0 pozzolan, as a direct consequenceof lower than M0, Al2Or�

3 content, 15.00% and 11.50%, respec-tively; the other reason for such statement is that the men-tioned SE has not been formed in the PC/SF blends at all,despite of its high pozzolanic activity at 1 and 2 days age (thesame for the PC/M0, M1 and C pozzolan blends), since itsAl2Or�

3 content is 0.00% and its high reactivity is due to its veryhigh SiOr�

2 content, 88.50%, only, and– secondly, the mentioned SE is caused by indirect stimulation of

the C3A from OPC fraction saline hydration (with 3.75% NaClsolution) with which the pozzolans have been mixed. The men-tioned indirect stimulation has taken place for the C, M1 and M0blends especially, due to high, rapid and early pozzolanic activ-ity of their respective Al2Or�

3 (%) contents that these pozzolansparticularly develop. Therefore, the following deduction couldbe made once again: the mentioned pozzolanic activity ofAl2Or�

3 component of pozzolans is once again [6,17–19,23] morespecific than generic, on the contrary, the SiOr�

2 component ismore unspecific for the same purpose [16,19].

In short, the Frattini test results confirm an outstanding, high,early and rapid pozzolanic activity of the M0 pozzolan, by virtueof which, the P1/M0 blend shows pozzolanic activity already at24 h, which is related to its very significant Al2Or�

3 (%) contentmainly, and causes the mentioned SE in the Fs formation like theM1 and C pozzolans blends, especially, since the P1/SF blend showsalso pozzolanic activity already at 24 h, but no SE in the Fs forma-tion is observed (Tables 6 and 7) due to its null Al2Or�

3 (%) content.In case of the PC PY6 sample with SF pozzolan, which demonstratesa significant pozzolanic activity as well even at early ages, the sim-ilar indirect stimulation phenomenon already mentioned in thisstudy is not observed at all as it happens to C, M1 and M0 pozzo-lans especially (in contrast with their action in the PC phases saline

R. Talero / Construction and Building Materials 33 (2012) 164–180 177

hydration stimulation). Moreover, their presence in blend seems tohinder the C3A and C4AF saline hydration process, since the P1/SFand PY6/SF blends have originated low amount of Fs (it is still asignificant low content observed even if SF would acted as an ‘‘in-ert’’ from the physical and chemical point of view [14]). The samephenomenon is being observed for the D pozzolan, but in differentdimension and with other velocity, since both of the pozzolans areof unlike origin and morphology, even though their physical state(vitreous) and reactive chemical compositions are equalpractically.

The Synergic Effect, SE, therefore, will result beneficial for thematrix cement in the chemical attack by chlorides (see Section4.5 later on), since the molar volume of originated Fs is similar tothe calcium aluminates hydrates one (hydration process productsof the C3A and Al2Or�

3 origin in this study and in previous studies[1,2]). That is to say, the Fs compound is not expansive [1] as itssulphate equivalent, ettringite, and its notable rapidity of forma-tion may contribute to soothing effect on the macroporous, porous,micropous and capillary network of concrete, especially if the sub-strates C3A and/or Al2Or�

3 do not originate it separately. This phe-nomenon is possible because the Fs formation rate from theAl2Or�

3 origin is higher than from the C3A one [1,2], therefore theco-precipitation in this case would provoke greater and speedierhydration of the C3A phase than it is even observed in the plain PC.

Recapitulating, it can be seen that the explanation and justifica-tion given for the ESE [6], a phenomenon originated by bothexpansive ett-rf from Al2Or�

3 origin of pozzolans and ett-lf fromC3A origin of PC, when co-precipitating in a common plaster-bear-ing solution, is homological and equivalent to this already exposedfor the SE, merely replacing sulphates by chlorides and, as a conse-quence, the ett-rf and the ett-lf by the Fs-rf and the Fs-lf,respectively. However and it has to be emphasised that their corre-spondent technical consequences are opposite, since whereas theESE, of greater or lesser degree, gives rise to a respective increasein diameter [8]/length [4–6,8]/volume of the specimens, the SEdoes not, because its originating Friedel’s salt types are not expan-sive, only replenishing for the macroporous, porous, microporousand capillary network of cement concretes, mortars and pastesmanufactured with PC and Z pozzolan with sufficient aluminicchemical character [8]: C, M1 and M0 pozzolans especially in thisstudy.

Logically, referred explanation and justification is applied alsofor all the POZCs hydrated with water solely, i.e., when exposedto neither sulphate nor chloride solutions. The results for this lastcase, hydrated with water solely, including their water amount fornormal consistency, times of setting, volume stability and mechan-ical strengths can be consult in the Refs. [1,6,8,9,11–19,22,23].

4.5. Consequences of SE

4.5.1. In chloride solution: consequences of the SE for XRD results4.5.1.1. Comparative study of POZCs P1/M0, P1/M1, P1/C and P1/A(Table 9). Prior semi-quantitative XRD findings [1,2] showed that:

1. The amount of Fs formed by each pozzolan at a given age wasproportional to its Al2Or�

3 (%) content, and2. The Fs from Al2Or�

3 origin, present in pozzolans, formed at ahigher rate than the Fs from the C3A origin, present in OPC.

In light of those results, the two families of blends (POZCs P1and PY6) and the plain PC (P1 and PY6), were ranked within eachexperimental age by the Integral Area (=integrated intensity) ofthe most characteristic Fs reflection on their respective diffracto-grams. The rankings are listed in Table 9, along with a classificationof the pozzolans used in ascending order of their Al2Or�

3 (%)

content. The following observations are based on the informationcontained in this Table 9.

The P1/M0 blend was logically positioned at the extreme right(14th position) in all the classifications, since its C3A + C3Aeq. (i.e.,14% of the C3A released by the 70% PC P1, plus the C3A equivalentfrom the Al2Or�

3 supplied by the 30% M0, for a total of 18.50 wt%)constituted the largest source of alumina in all the POZCs. Theother metakaolin blend, PC P1/M1, was not positioned immedi-ately adjacent to the PC P1/M0 (13th position) in all the series, de-spite its only slightly lower C3A + C3Aeq. content (14.30 wt%). Infact, while it stood in the 13th position in the 7-, 14-, 28-, . . . ,730-day series, in the 1- and 21-day series it was in the 12thposition, while the POZC PY6/M0 blend was in the 13th. A possibleexplanation for the 1- and 21-day values may be that Fs must havebeen generated twice as readily by POZC P1/M0 as by POZC P1/M1,since the Al2Or�

3 content in M1 (15 wt%) was approximately one-half the M0 value (29 wt%). For that reason, no more than Fs musthave formed before the paste set (ITs: 2:50 and 3:00, respectively)but after (FTs: 4:60 and 4:55, respectively), and then, subsequentpenetration of the chlorides into its pores and capillary systemswould have been governed predominantly by the diffusion coeffi-cient especially. This was not the case in POZC P1/M0, as logical(STs: 2:10 and 1:55, respectively). Moreover, Fs formation in hard-ened paste was not stimulated by Fs itself, as observed for ettring-ite, whose tendency to expand (molar volume: 715.09 cm3) widenspores and facilitates SO2�

4 ion ingress. Fs, by contrast, has a molarvolume (296.69 cm3) of the same order of magnitude as the cal-cium aluminate hydrates present in the OPC and tends to clog poreand capillary systems [1], hindering the uptake of further chlorideions. Chloride penetration, then, depends on physical parameterssuch as permeability, diffusion (conditioned as well by the Cl� con-centration gradient between the surface of the paste and inside itspores) and capillary suction. All these parameters are also condi-tioned by each POZC’s post-setting hardening rate in the salinesolution (3.75% NaCl). And whether any Synergic Effect is alsopresent (possible with POZC P1/M1, because its C3A content is9.8%, but less or nothing possible with PY6/M1, because its C3Acontent is <0.7%), with more reason yet.

Consequently, the lower the total C3A + C3Aeq. content in aPOZC, the lower would its rank number be in all the series. Thatis exactly what was observed for POZCs P1/M1, P1/C and P1/A, withC3A + C3Aeq. contents lower than in POZC P1/M0, as well as forPOZCs PY6/M0, PY6/M1, PY6/C and PY6/A, whose C3A content inits PC fraction, PY6, was practically nil (<1%). POZCs P1/SF andP1/D, while appearing in the Table 9 at the low end of the series,were not actually taken into consideration in the comparison,due to the siliceous nature (ASTM standard C 618-95a [28]) and si-licic chemical character (Talero [8]) of their pozzolans. The behav-iour of these pozzolans will be analysed and discussed insubsequent research.

Finally, POZCs P1/M0 and P1/M1 ranked higher than plain PC P1in all the series, for they had a higher C3A + C3Aeq. content (18.5 and14.30 wt%) than PC P1 (14.00 wt%). These two POZCs also obvi-ously raked higher than the PY6 PC blends (C3A content <1%). Fur-thermore, a Synergic Effect (SE) must have been in place thatcontributed to the results for the two metakaolin POZCs. The phys-ical–chemical mechanism involved in that effect has been de-scribed in Sections 4.3 and 4.4 above. The behaviour observed inPOCZ P1/C must have also been the result of the SE, since whileat 13.25% its C3A + C3Aeq. content was lower than the 14% foundfor PC P1, it ranked higher than its plain PC P1 in all the series.

In short, the only POZCs that ranked higher than PC P1 in almostall the series were the chemically aluminic blends [8], i.e., theblends containing M0, M1 or C pozzolan. However, in POZC P1/M1 the Fs output was much higher than expected. Pursuant tothe law of mass action, its position should have concurred with

178 R. Talero / Construction and Building Materials 33 (2012) 164–180

plain PC P1 in all the series because their respective C3A + C3Aeq.

contents, at 14.30% and 14%, were practically the same.These observations obviously infer that the 70% PC P1 (i.e., 14%

C3A � 70% = 9.80%) in the blend had a consistently higher inte-grated intensity than plain PC P1 (14% C3A) thanks to the contribu-tion made by the 30% pozzolan M1, or more precisely, the 4.50% ofAl2Or�

3 present in that pozzolanic addition (=15%Al2Or�3 � 30%). In

other words, the unexpected behaviour observed in POZC P1/M1was due primarily to the presence of 30% pozzolan M1 in the blend.Had more PC P1 been replaced by pozzolan M1 in the P1/M1 blendor if the Al2Or�

3 (%) content of M1 pozzolan had been greater, forinstance, 29%, the total reactive alumina content of POZC P1/M1would have been as in POZC P1/M0, i.e., greater as well, and the dif-ference with the unblended paste would have been wider. That isexactly what was observed in the present study for POZC P1/M0,which ranked higher than plain PC P1 in all the series.

4.5.1.2. Comparative study of POZCs P1/M0, P1/M1, PY6/M0 and PY6/M1. Just as the findings for POZC P1/M1 were similar to the P1/M0results from 28 days onward (i.e. during nearly the entire 24-month experiment, excluding the first few days), POZC PY6/M1and PY6/M0 however exhibited similar behaviour from beginningto end. Since the sole compositional difference between the twofamilies was the presence/practical absence of C3A (9.8% in POZCsP1/M1 and P1/M0 and <0.7% in POZCs PY6/M1 and PY6/M0, respec-tively), the consistently higher IA (a.u.) values in the PC P1 blends(comparing P1/M0 to PY6/M0 and P1/M1 to PY6/M1) must beattributed to that difference. Consequently, the aforementionedSE that appeared either during early or later stages of saline hydra-tion (in POZC P1/M0 from the first few days of the experiment, dueto presence of the chemically aluminic M0; in POZC P1/M1 from the28th day, due to the presence of the less chemically aluminic M1,respectively) was induced in the P1 but not the PY6 blends. TheC3A (9.8%) content in PC P1 and the Al2Or�

3 (8.7% and 4.5%, respec-tively) content in the pozzolans, explained the appearance of SE inthe former, while the practical absence of C3A in PC PY6 precludedthe existence of SE in the latter blends.

4.5.2. Consequences of SE for paste water resistance, capillaryabsorption and total porosity (Fagerlund method) [40] (Table 10)

The technical consequences of SE are listed below:

– The real resistance to water penetration, m, for pozzolans M0,M1 and C was 1.34-, 1.67- and 1.14-fold higher than the respec-tive theoretical values.

– The real capillary absorption coefficients, k, for pozzolans M0,M1 and C were 1.11-, 1.91-and 1.24-fold lower than the respec-tive theoretical values.

– The real total porosity for pozzolans M0 and M1 was 1.25- and1.03-fold lower than the respective theoretical values.

In a nutshell, SE had beneficial implications in terms of totalporosity and consequently for durability of reinforced concrete ex-posed to chloride attack.

All the aforementioned physical parameters are listed in Table10, which also gives the SiOr�

2 (%) and Al2Or�3 (%) contents in each

Z pozzolan (Table 10). As the Table 10 shows, the determining fac-tor of the existence or otherwise of SE was the Al2Or�

3 (%) content inthe Z pozzolans. The amount of Al2Or�

3 present in the POZC-P1blend and its more specific than generic pozzolanic activity wasresponsible for its indirect stimulation of C3A saline or otherwisehydration, rendering it faster, earlier and more intense than theC3S hydration observed in the PC P1 with which it was mixed.

Finally, regardless of the physical parameter considered, thevalues obtained for pozzolans SF and D differed widely due to theirvery different BET-SS (Table 1) and especially the differences in

their morphology described in Section 4.1. Both are nonethelesssiliceous in nature, according to ASTM standard C 618-95a [28],and silicic in chemical character (Talero [8]) and consequently havesimilar physical–chemical characteristics (vitreous) and reactivechemical compositions.

4.6. Summary

This new study of chloride attack on 70/30 POZC P1/Z pozzo-lan (C, M1 and M0 especially) substantiates the following pre-mise: a Synergic Effect, SE, contributes to Friedel’s saltformation from the Al2Or�

3 present in pozzolans and the C3A pres-ent in OPC when they co-precipitate in a common chloride-watersolution. This development follows the same pattern as theExpansive Synergic Effect, ESE, defined by Talero [6], which is in-duced not by chlorides but by chemically aluminic pozzolans,OPC, water and gypsum (sulphates), in which ett-rf co-precipi-tates in a gypsum solution from both the Al2Or�

3 in the pozzolansand the C3A in OPC. Deduction No. 1 from that study [6] can besummarised as follows:

‘‘As the Friedel’s salt from pozzolan and/or OPC origin is non-expansive due to its molar volume, Vm, has similar magnitudeorder than the different calcium aluminate hydrates from C3Apresent in OPC one, unlike ettringite expansive action fromany origin. And if Friedel’s salt is not expansive, it has to havenecessarily ‘‘filling-in’’ effect of the pore and capillary systemsin the POZC mass, which with the SE generated is the subsidiarycause of its mentioned protective behaviour: hindering or evenpreventing chlorides attack on the steel in reinforced concrete,first, chemically, and then, physically. Because its main causeand origin is really the precipitation of the chlorides as rapidforming Friedel’s salt from any origin, Al2Or�

3 of pozzolans andC3A of OPC in this study, at very early ages, due to the SE whichboth of them originate’’.

5. Conclusions

Based on the semi-quantitative XRD analysis and test results re-ported herein, their discussion and interpretation, the followingconclusions can be drawn:

1. The joint formation of Fs-rf and Fs-lf in a common chloridesolution takes place not separately, but inter-dependently, incombination or interactively – co-precipitation –, and the closerthe Z pozzolan particles (its Al2Or�

3 content) are to the OPC P1particles (its C3A content), the greater is the inter-dependencein such co-precipitation. While both Friedel’s salts are formed,the end reaction product is closer to Fs-rf than Fs-lf, especiallywhen the Al2Or�

3 (%) content in the Z pozzolan is very high. Fri-edel’s salt of very slow formation, Fs-vlf, from C4AF origin pres-ent in the same OPC as well, must logically be, by contrast, moreindependent than inter-dependent.

2. Borrowing from the pharmacological terminology used todescribe drugs interaction, the co-precipitation of Friedel’s saltin a chloride solution from both, the Al2Or�

3 present in pozzolansand the C3A present in OPC, has been shown to be always quan-titatively speaking, more synergic than additive, regardless ofthe analytical technique, test method or physical and chemicalparameters considered. For this reason, the result of this inter-dependence and co-precipitation has been termed the SynergicEffect, SE.

3. The main explanation for the SE is that aluminic pozzolans tendto stimulate C3A hydration of OPC, saline or otherwise, indi-rectly, whereas silicic pozzolans exhibit no such behaviour.

R. Talero / Construction and Building Materials 33 (2012) 164–180 179

4. Depending on the physical or chemical parameter consideredand from the technological standpoint only, the consequencesof the Synergic Effect, SE, between these two types of Friedel’ssalts can be deemed to always be beneficial in terms of theestablishment of the pore and capillary systems during hydra-tion, saline or otherwise. The consequences of this are discussedin the Final question in Section 6 below.

5. The pozzolanic activity of the clearly aluminic Z pozzolans usedin this study (C, M1 and M0 in particular) proved to be more spe-cific than generic in chloride and aqueous environments, andtheir specificity was found to rise with their Al2Or�

3 (%) content(in C, M1 and M0 especially). In fact, in the saline medium used(3.75% NaCl solution), the Al2Or�

3 content expedited the salinehydration of all or part only of the C3A released by OPC P1 frac-tion than when the plain OPC in question was hydrated in thesame manner but without any Z pozzolan. Such a greater or les-ser but speedier hydration in a chloride medium affected the C3Abut not the C3S in OPC P1, due to the very specific pozzolanicactivity of Al2Or�

3 . The hydration rates reached may even be com-parable to the rates observed for Al2Or�

3 (with C, M1 and M0especially) when the POZC contains a suitable proportions of Zpozzolan and PC, with which to generate greater or lesser quan-tities of both, Al2Or�

3 and C3A, and these, in turn, their respectiveFs-rf, and as a result, a stronger or weaker SE. For more detail, seeconclusion 6. When OPC P1 was hydrated with 20% SF (silicicpozzolan in chemical character) chloride hydration of C3A wasobstructed. For this reason, its pozzolanic activity was not morespecific than generic, but on the contrary, pozzolan SF wasunspecific for this chemical reaction. Consequently, its earlyage protection would have had to be more physical than chemi-cal. As saline hydration progressed and the SF developed its fullpozzolanic activity, its action must have been chemical as well,or perhaps physical–chemical, because the physical contributioncontinued to prevail. By contrast, the protective effect affordedby pozzolans M0, M1 and C was more chemical than physicalor chemical-physical, i.e., completely contrary, as logical,because their common chemical character is completely con-trary as well: aluminic, more or less, respectively.

6. The Fs-rf from the Al2Or�3 origin present in Z pozzolans (C, M1

and M0 especially) is, therefore, the chief direct and indirect causeof the greater or lesser SE appearing in conjunction with the for-mation of Friedel’s salt from the C3A origin present in PC, due toits very specific pozzolanic activity in chloride media. Proof ofthis specific pozzolanic activity is found essentially in the factthat at 1 and/or 2 and 7 days, the [OH�] and [CaO] were clearlyin the sub-saturation or positive result region in almost all theliquid phases of the Frattini test: this is the chief direct causeof the SE. As a result, more of the C3A present in the respectiveOPC fraction (which also formed Fs-rf in proportion to theamount of the prior pozzolanic activity generated by theAl2Or�

3 in the Z pozzolan with which it was mixed) was hydratedmore readily and rapidly in the chloride medium: this is the chiefindirect cause of the SE. This very specific pozzolanic behaviourin response to chlorides [1,2] (and sulphates [4–12], separately),is the main criterion on which to base the classification of the Zpozzolans as chemically aluminic, less or more, respectively.

7. Pursuant to the fundamentals of the SE attendant upon Friedel’ssalt formation from A, C, M1 and M0 pozzolan and OPC, the Fs-rf identified in this study may have had at least two origins: theAl2Or�

3 in pozzolans and the C3A in OPC, if blended with suitablequantities of appropriate aluminic pozzolans, due to the veryspecific pozzolanic activity of their Al2Or�

3 . On the contrary, onlyone origin was identified for Fs-lf: the C3A present in OPC P1.

8. In Fs-rf, Fs-lf and Fs-Total formation, the TQ (topochemical)mechanism preceded by dissolution must prevail over the TS(through-solution) pathway.

9. The technical consequences deriving from the SE associatedwith Friedel’s salt co-precipitation from such Z pozzolans, A,C, M1 and M0, and OPC in a chloride solution can only be ben-eficial. Unlike ettringites, whose molar volume expands, in Fri-edel’s salt it is similar to the Vm of the calcium aluminatehydrates forming from the C3A present in OPC. For this reason,Friedel’s salt fills the pore and capillary systems in cement con-cretes, mortars and pastes. Likewise for this reason, Z pozzolanbehaviour in the Fagerlund test was proportional to theirAl2Or�

3 (%) content but not to their SiOr�2 (%) content.

6. Final questions and consideration

Both saline (3.75% NaCl solution) and water hydration havebeen used to prove that the SE was attendant upon Fs-rf and Fs-lf co-precipitating in a chloride solution. Irrespective of the resultsobtained for each type of hydration, however, and given that all ce-ments release heat at early ages (heat of hydration by unit of massunit or specific heat), the following final questions are posed:

What will happen when the OPC-pozzolan blends are hydratedwith water only? Will a Calorific Synergic Effect appear as well?How will each Z pozzolan behave, depending on whether it is morechemically aluminic or silicic? How will the PC contribute to theprocess and will the contribution be the same in OPC and SRPC?

And if the water contains chlorides. . ., how will each Z pozzolan,OPC or SRPC behave in terms of the chloride diffusion coefficientand the parameters that measure electrochemical corrosion inreinforcing steel? Will their behaviour be beneficial, adverse orindifferent, such as with the ESE associated with sulphate attackunder the same circumstances [4–6]?

One final consideration is in order. In reinforced concretepathology, while a diagnosis of the condition of a structure at a gi-ven age is important, the timely adoption of suitable strengtheningor repair measures is even more so, for preventive measures are al-ways much less costly and less inconvenient for all concerned thanthe full-blown repair of structural damage due to chloride corro-sion, for instance.

A suitable diagnosis is useless if it is not followed up by appro-priate action. New analytical methods and standards for pozzolansare needed for this purpose, because none of the existing ASTM (C618-08 [28], C 595M [29], C 311-07 [31], C 593-95 [46], C 563 [47])or EN (197-1 [48], 450 [49]) standards is apt for determining thechemical character of any Z pozzolan in a reasonably short time.This information is essential to predicting their reaction when ex-posed to sulphates, chlorides, sea water or carbonation; their resis-tance to the ASR; their rheological behaviour and early age heat ofhydration; as well as to determining the optimum dosage of theirsetting regulator (natural stone gypsum or soluble anhydrite) [8].In short, the natural and artificial pozzolanic additions commonlyused to manufacture cements, concretes and mortars cannot con-tinue to be classified only by origin and accepted or rejected bymechanical strengths [28,29,31,32,49–51] and other chemical-physical parameters [28–32,34–39,46–51]. Rather, they must beclassified on the grounds of specific utility and durability criteriasuch as applied to PC.

Future research will naturally address these interestingquestions.

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[47] ASTM 563 Standard. Standard test method for optimum SO3 in hydrauliccement using 24-h compressive strength. Annual book of ASTM standards,section 4 construction, vol. 04.01, cement; lime; gypsum; 1995. p. 279–81.

[48] EN 197-1 Standard: Cement. Composition, specifications and conformitycriteria. Common cements [AENOR].

[49] EN 450 Standard: fly ash for concrete. Definitions, requirements and qualitycontrol [AENOR].

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