Construction and Building Materials 26 (2012) 619–627

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Construction and Building Materials

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Beneficial use of limestone filler with calcium sulphoaluminate cement

Laure Pelletier-Chaignat a, Frank Winnefeld a,⇑, Barbara Lothenbach a, Christian Jörg Müller b

a Empa, Swiss Federal Laboratories for Materials Science and Technology, Laboratory for Concrete/Construction Chemistry, Überlandstrasse 129, 8600 Dübendorf, Switzerlandb Saint-Gobain Weber AG, Technoramastrasse 9, 8404 Winterthur, Switzerland

a r t i c l e i n f o

Article history:Received 15 February 2011Received in revised form 23 May 2011Accepted 18 June 2011Available online 12 July 2011

Keywords:Calcium sulphoaluminate cementLimestoneFillerCalorimetryThermogravimetryX-ray diffractionThermodynamic modellingStrengthMortar

0950-0618/$ - see front matter � 2011 Elsevier Ltd. Adoi:10.1016/j.conbuildmat.2011.06.065

⇑ Corresponding author. Tel.: +41 58 765 45 35.E-mail address: frank.winnefeld@empa.ch (F. Win

1 Cement notation will be used in the text: A = Al2OS = SiO2, S ¼ SO3, T = TiO2.

a b s t r a c t

The present study compares the cement hydration process and the mortar properties of samples contain-ing calcium sulphoaluminate clinker and gypsum combined with quartz filler or limestone filler. Two dif-ferent calcium sulphoaluminate clinker to gypsum mass ratios are tested, 5.26 and 2.50, at 20 �C and at5 �C. Cement hydration is studied by isothermal calorimetry, X-ray diffraction and thermogravimetry oncement pastes containing filler. Setting time, strength development and volume stability are measured onmortar samples containing additional sand. The results show that the use of limestone filler instead ofquartz filler modifies the cement hydration process and is beneficial for the mortar properties at 20 �Cand at 5 �C. It accelerates the early hydration of the cement, thus shortening the initial setting time. Aftersome days, the calcite from the limestone filler leads to the formation of hemicarbonate, which tends tostabilize ettringite and to minimize the formation of monosulphoaluminate. This efficiently increases thestrength of the mortars containing limestone filler rather than quartz filler.

� 2011 Elsevier Ltd. All rights reserved.

1. Introduction

While calcium sulphoaluminate cements have been used in Chi-na for about 40 years and standardized [1–3], their developmentand use in other countries is currently not widespread. The interestin these cements is growing because they represent a low CO2-alternative to Portland cement, mainly because they generate low-er CO2 emissions during the clinkering process [4,5] and duringgrinding. Moreover, they can be manufactured using many differ-ent industrial by-products such as fly ash, blast furnace slag, phos-phogypsum or scrubber sludge [6].

The main component of the calcium sulphoaluminate clinker isthe ye’elimite (C4A3S in cement notation1). The accessory phasescan include C2S, C4AF, C3FT, anhydrite, C2AS, C12A7 or CA. Calciumsulphoaluminate cements are produced by blending calciumsulphoaluminate clinker with gypsum or anhydrite. The addition ofcalcium sulphate has to be dosed to reach the optimum setting time,strength development and volume stability.

The main hydration products are ettringite, monosulphoalumi-nate and aluminium hydroxide [7,8]. In cements containing acces-sory phases, C–S–H, C2ASH8 or calcium aluminate hydrates, mainlyCAH10 or C4AH13, can be formed during hydration [9–12]. The reac-

ll rights reserved.

nefeld).

3, C = CaO, F = Fe2O3, H = H2O,

tivity of the calcium sulphate influences the early hydration kinet-ics [13]. In the presence of a fast-reacting calcium sulphate,ettringite will be formed in association with aluminium hydroxideaccording to reaction (a). In the absence of calcium sulphate orwith a slowly soluble calcium sulphate (e.g. natural anhydrite),monosulphoaluminate and aluminium hydroxide will be formedaccording to reaction (b) [10,12,14,15].

C4A3Sþ 2CSH2 þ 34H! C3A � 3CS �H32 þ 2AH3 ðettringite formationÞðaÞ

C4A3Sþ 18H! C3A � CS �H12 þ 2AH3 ðmonosulphoaluminate formationÞðbÞ

The calcium sulphoaluminate clinker to calcium sulphate ratiodetermines the ettringite to monosulphoaluminate ratio in the finalproduct [7,8,13], which increases with increasing calcium sulphateaddition. The maximum reachable ettringite content correspondsto an addition of calcium sulphate of about 30%, which also corre-sponds to the maximum water demand for the complete hydrationof the cement [16].

The addition of calcium sulphate to the clinker is linked to thecement properties. By optimizing this addition, targeted propertiescan be reached. With increasing calcium sulphate addition, rapidhardening/high strength or expansive mortars can be produced[3,13,17]. Therefore, the calcium sulphoaluminate cements canbe used in many different products, such as expansive compounds

620 L. Pelletier-Chaignat et al. / Construction and Building Materials 26 (2012) 619–627

in shrinkage-compensated cements, in rapid-hardening mortars orconcretes, in glass–fibre reinforced cements or in self-levellingfloor screeds [18–22]. They can additionally be used to encapsulatewaste due to their low porosity, low pH, and to the presence ofettringite and/or monosulphoaluminate, which can potentiallybind a significant amount of heavy metals [23].

In certain industrial products, such as ready-mix mortars, fillersare added to the cement reducing its cost. The addition of non-hydraulic filler to Portland cement accelerates its early hydrationand improves its strength at early age [24–30], mainly because itprovides additional nucleation sites. It also allows a reduction ofshrinkage, because the amount of cement is decreased. Publica-tions showed that limestone filler can take part in the hydrationprocess when mixed with Portland cement [24,31,32] or with highalumina cement [33]. When a sufficient amount of calcite is used,which is the main component of limestone filler, ettringite is stabi-lized during hydration because monocarbonate tends to be stableinstead of monosulphoaluminate.

While the addition of limestone filler to Portland cement is wellknown, its addition to calcium sulphoaluminate cement has notbeen investigated yet in detail. Our paper discusses the impact ofthe addition of limestone filler to calcium sulphoaluminate clinker– gypsum mixes at 20 �C and 5 �C. Similar mixes containing quartzfiller are used as a reference. The hydration process is investigatedby isothermal calorimetry, X-ray diffraction and thermogravimetryon mixes containing cement and filler. Thermodynamic calcula-tions are used and compared to the experimental results. The re-lated mortar properties such as setting time, strengthdevelopment and volume stability are measured on mixes contain-ing cement, filler and sand.

2. Materials

The mineralogical and chemical compositions of the commercial calciumsulphoaluminate clinker and gypsum used can be found in Table 1. The mineralog-ical composition was determined from the X-ray diffraction (XRD) patterns usingRietveld refinement. The calcium sulphoaluminate clinker used contains 62.8%ye’elimite ðC4A3SÞ and is characterized by CA and CA2 present as minor hydrauliccomponents, 8.1% and 3.1% respectively. It also contains 18.3% of C2AS, which isconsidered as partially inert. It has a Blaine fineness of 4180 cm2/g. The gypsumused is a gently dried natural product, which contains some anhydrite (3.3%). Thechemical composition was measured by X-ray fluorescence (XRF), except for sul-phur which was determined with a Leco� carbon/sulphur analyser and the freelime, which was assessed by the Franke method [34].

Two types of filler were selected for the study, a limestone filler with about 99%of CaCO3 (calcite) and a quartz filler with about 99% of SiO2 (a-quartz). The lime-stone filler has D10%, D50% and D90% values of 1.0 lm, 4.8 lm and 30.1 lm, while

Table 1Mineralogical and chemical compositions of calcium sulphoaluminate clinker (CSA) and g

CSA (wt.%) Gypsum (wt.%) CSA (wt.%) Gypsum

C4A3S 62.8 SiO2 4.5CT 5.7 A12O3 45.0C2AS 18.3 Fe2O3 1.5CA 8.1 CaO 36.1 33.3CA2 3.1 Na2O 0.07MA 1.8 K2O 0.35CS 3.3 MgO 0.91 0.3

CSH2 96.7 SO3 8.6 46.7MgO 0.2 TiO2 2.23CaOf 0.01 p2o5 0.08K2SO4 0.056 Mn2O3 0.02Na2SO4 0.005 SrO 0.09

L.O.I. 0.7 21.5Total 100.2 101.7

Mineralogical composition determined by Rietveld refinement from XRD curves. CaOf deta LECO apparatus. L.O.I measured until 950 �C. K2SO4 and Na2SO4 in CSA clinker measured5 min).

the quartz filler has values of 3.0 lm, 29.7 lm and 89.0 lm. The sand used forthe production of the mortar prisms for setting, strength and volume stability mea-surements, exhibits a maximum diameter of 0.25 mm.

Two formulations were selected and tested with limestone filler and quartz fil-ler (Table 1). They were chosen to work at constant cement to filler ratio and at con-stant water to cement ratio. The first one has a calcium sulphoaluminate clinker togypsum mass ratio of 5.26 (BL-h and BQ-h), while the second one has a ratio of 2.50(BL-l and BQ-l). The cement to filler ratio was set to 1.13, which is 46.9% filler of to-tal cement plus filler (= fines). In the mortar formulations the ratio between finesand sand is approximately 1.0. The values of both ratios resemble those generallyused in ready mixed mortars like tile adhesives.

3. Methods

3.1. Measurements on pastes

All the experiments were performed at 20 �C and 5 �C at a waterto cement ratio of 0.80, corresponding to a water to solid ratio of0.42. Heat flow curves were obtained by isothermal calorimetrywith a Thermometric TAM Air instrument calibrated at 600 mW,in order to obtain an overview of the hydration kinetics of thebinders with filler. For the analysis, about 3 g of paste containingfiller were mixed inside the apparatus using the admix ampoules[35]. X-ray diffraction (XRD) and thermogravimetry (TGA) wereused to determine the mineralogical composition of the solidphase. Prior to the analyses, hydration was stopped by plungingthe samples 30 min in isopropanol and rinsing twice withdiethyl-ether. Samples were subsequently dried in a desiccatorovernight at room temperature. Prior to XRD and TGA, cementwas ground to a grain size 663 lm for the analysis. XRD data werecollected using a PANalytical X’Pert Pro MPD diffractometer in ah � 2h configuration using incident beam monochromator employ-ing the Cu Ka radiation (k = 1.54 Å) with a fixed divergence slit of1� and a rotating sample stage. The samples were scanned between5� and 80� with the X’celerator detector. The thermogravimetricanalyses were done with a Mettler Toledo TGA/SDTA851e, where8–12 mg of sample were placed in an open vessel under N2 atmo-sphere, heating up 20 �C/min up to 980 �C. The amount of ettringitein the hydrated pastes was determined as described in [36],assuming that the weight loss between 50 �C and 120 �C corre-sponds to 20 molecules of crystal water per molecule of ettringite.Calcite content was calculated from the TGA weight loss between670 �C and 800 �C. Some of the TGA, XRD and calorimetric mea-surements were duplicated to check accuracy.

To carry out the thermodynamic calculations, the geochemicalGEMS-PSI software was used linked to the cement-specific

ypsum and used formulations.

(wt.%) BL-h (g) BQ-h (g) BL-1 (g) BQ-1 (g)

CSA 22.06 22.06 18.75 18.75Gypsum 4.19 4.19 7.50 7.50Limestone filler 23.17 23.17Quartz filler 23.17 23.17Sand 50.34 50.34 50.34 50.34

w/c 0.80 0.80 0.80 0.80

CSA/gypsum 5.26 5.26 2.50 2.50Gypsum/CSA 0.19 0.19 0.40 0.40

ermined according to [34]. Chemical analyses by XRF, except for SO3 measured withby ion chromatography in solution (5 g cement in 50 ml deionized water stirred for

L. Pelletier-Chaignat et al. / Construction and Building Materials 26 (2012) 619–627 621

CEMDATA database [37–41]. GEMS is a broad-purpose geochemi-cal modelling code which computes equilibrium phase assemblageand speciation in a complex chemical system from its total bulkelemental composition. Chemical interactions involving solids, so-lid solutions, and aqueous electrolytes are simultaneously consid-ered. The speciation of the dissolved species as well as the kind andamount of solids precipitated are calculated.

The modelling was used to study the chemical and mineralogicalchanges associated with increasing limestone filler content in thecalcium sulphoaluminate cement (clinker + gypsum) at 20 �C and5 �C. The water to cement ratio was fixed at 0.80. The bulk chemicalcomposition of the calcium sulphoaluminate clinker and gypsumwere used as input. The CT and C2AS phases from the calcium sulp-hoaluminate clinker were considered to be inert. Limestone fillerwas progressively added to the cement as calcite, replacing the inertquartz filler. To simplify the calculation, the limestone filler wasconsidered to be composed of 100% of calcite (instead of 99%).Two calculations were performed, one with a calcium sulphoalumi-nate clinker to gypsum ratio of 5.26 and one with a ratio of 2.50. Inthe graphs presenting modelling results, ettringite is subdividedinto SO4-ettringite and CO3-ettringite to emphasize that ettringiteis formed as a solid solution which can bind some CO3 in itsstructure.

3.2. Measurements on mortars

Setting time was determined using a Vicat apparatus. The sam-ples were measured according to EN 196-3, but using mortars in-stead of pastes. In order to be able to measure volume changesand strength of the samples at 5 �C, part of the material (mortar,water, bowls, moulds, etc.) was pre-stored for 16 h in a refrigeratorat 5 �C prior to mixing. On the next day mortars were prepared,poured into 4 � 4 � 16 cm3 moulds and covered with a glass plate.They were subsequently stored at 20 �C/100%RH, or at 5 �C/70%RHin a refrigerator until demoulding.

For strength measurements, the samples were stored in air at70%RH at 20 �C or at 5 �C. For the measurements at 20 �C, mortarprisms were demoulded after 6 h, while they were demouldedafter 24 h for the measurements at 5 �C. Strength data were ob-tained after 6 h (only at 20 �C), 1 day, 7 days and 28 days (twoprisms per hydration time). For expansion/shrinkage and massmeasurements, mortars were demoulded after 24 h and separated

Table 2Results of strength and setting time measurements.

Compressive strength Flexural strength

(days) 20 �C (MPa) ± 5 �C (MPa) ± 20 �C (MPa) ±

BL-h 0.25 5.0 0.2 n.m. 1.6 0.11 24.1 0.4 <1 3.9 0.77 33.1 0.3 28.3 0.5 4.6 0.128 34.4 0.7 27.6 0.8 4.2 0.0

BQ-h 0.25 6.8 0.2 n.m. 1.81 22.8 0.5 <1 3.1 0.17 30.5 0.4 20.7 1.3 4.1 0.628 30.8 0.5 22.4 1.4 3.3 0.1

BL-1 0.25 5.9 0.2 n.m. 1.7 0.11 23.4 0.4 <1 3.9 0.17 32.9 0.4 28.0 0.7 4.2 0.128 33.7 0.9 30.2 0.9 3.0 0.0

BQ-1 0.25 10.0 0.2 n.m. 2.3 0.21 22.5 0.4 <1 3.9 0.47 28.9 0.7 24.8 1.0 4.5 0.028 29.5 0.1 22.2 2.1 3.8 0.0

The standard deviation of compressive and flexural strength refers to two prisms (twoproduced from one mortar batch. Setting times are single determinations. The error is gn.m.: not measurable.

according to their future use at 20 �C or at 5 �C. Three prisms pertemperature were stored in water (one plastic box per sample)and three prisms in air at 70%RH.

4. Results

4.1. Setting time and strength development

At 5 �C, the presence of limestone filler decreases the time of theinitial set (Table 2). This time is reduced of more than 1 h betweenBQ-h and BL-h and of about 2 h between BQ-l and BL-l. At 20 �C,the decrease of the initial setting time is also observed betweenthe samples BQ-h and BL-h with a difference of more than 1 h,while between BQ-l and BL-l an increase of about 1 h is observedin the presence of limestone filler.

At 20 �C after 6 h of hydration, the compressive strength of themortars ranges between 5.0 MPa and 10.0 MPa and the flexuralstrength between 1.6 MPa and 2.3 MPa (Table 2). After 6 h, the for-mulations containing quartz filler have higher compressive strengththan those containing limestone filler. On the contrary, beyond 6 hthe limestone-bearing formulations BL-h and BL-l systematicallyshow after 1 day similar and after 7 and 28 days higher compressivestrength than the mortars with quartz fillers (Fig. 1). All samplesshow a decrease of flexural strength between 7 and 28 days. Forthe mortars with a calcium sulphoaluminate clinker to gypsum massratio of 5.26, this loss of strength is minimized when limestone filleris used. Low CSA/gypsum ratios yield higher flexural and compres-sive strengths than high CSA/gypsum ratios after 8 h, whereas sim-ilar strengths are reached after 1, 2 and 28 days.

At 5 �C, all the samples have very low compressive and flexuralstrengths after 1 day of hydration, <1 MPa and <0.4 MPa respec-tively (Table 2). The strength increases very fast between 1 dayand 7 days. Values above 20 MPa are reached for the compressivestrength and above 3 MPa for the flexural strength. The mortarscontaining limestone filler tend to have higher strength than thosecontaining quartz filler. There is no significant impact of the CSA/gypsum ratio on flexural and compressive strength.

4.2. Volume stability

The volume stability of the mortars cured in water is different at20 �C or at 5 �C (Fig. 2). However, the maximum amount of expan-

Initial set Final set Initial set Final set

5 �C (MPa) ± 23 �C (min) 23 �C (min) 5 �C (min) 5 �C (min)

n.m. 60 185 150 2400.3 0.04.2 0.14.7 0.1

n.m. 155 200 225 3450.1 0.03.2 0.13.2 0.4

n.m. 145 190 165 3000.2 0.03.4 0.23.9 0.0

n.m. 90 200 285 3750.1 0.03.6 0.33.9 0.1

determinations of flexural strength, four determinations of compressive strength)enerally in the order of ±5%.

Fig. 1. Compressive and flexural strengths at 20 �C (up) and at 5 �C (down) ofmortars stored under water after 24 h of hydration.

622 L. Pelletier-Chaignat et al. / Construction and Building Materials 26 (2012) 619–627

sion reached is not problematic for many practical applications. At20 �C, all samples have similar curves with a maximum expansionbetween 0.05 mm/m and 0.2 mm/m reached after a few days. At5 �C, BL-h and BQ-l show a limited amount of expansion with a max-imum of 0.1 mm/m. BQ-h and BL-l show a continuous expansion un-til about 16 days, where they reach a maximum length change of0.8 mm/m and 0.65 mm/m respectively. The strongest expansion

Fig. 2. Volume stability of mortars stored under water after 24 h of hydration at 20 �Cexpansion which is usually acceptable for many industrial applications.

rate about 0.1 mm/m per day occurs within the first 7 days in BQ-h and BL-l, when the ettringite is formed in the solidified mortars(see Section 4.4). Why such an expansion is not observed in BL-hand BQ-l at 5 �C, where ettringite is also formed during this period,is difficult to explain. This could be related to a difference in porositycoupled to the amount of hydrates crystallized.

4.3. Isothermal calorimetry

Compared to quartz filler, the samples with limestone fillershow a higher and earlier heat flow maximum related to earlyhydration at 20 �C or at 5 �C. This observation is valid for both stud-ied calcium sulphoaluminate clinker to gypsum ratios (Fig. 3). At20 �C the increase of heat flow after around 4 h at the end of thedormant period, which is related to the massive formation of hy-drates in the cement pastes, occurs simultaneously in the fourstudied samples. However, the mixes containing limestone fillerhave a higher heat flow maximum than the corresponding onescontaining quartz filler, e.g. maximum peak at 21 J/(g h) for BL-hand at 17 J/(g h) for BQ-h. At 5 �C, the onset of hydration is delayedby more than 20 h compared to the curves at 20 �C and the lengthof the dormant period is different for each of the studied mixes.The onset of hydration is strongly accelerated in the presence oflimestone filler instead of quartz filler, of about 15 h for BL-hcompared to BQ-h and about 20 h for BL-l compared to BQ-l. Thisis probably partially related to a nucleation site effect due to thehigher fineness of the limestone filler (D50% = 4.8 lm) comparedto the quartz filler (D50% = 29.7 lm) [24–30,33].

The CSA/gypsum ratio influences the shape of the calorimetriccurve. The samples with a high ratio (BL-h, BQ-h) exhibit two max-ima after the dormant period. The first maximum can be explainedby ettringite formation, whereas the second maximum indicatesthe depletion of gypsum [13,15]. When comparing calorimetryand setting times, no direct correlation can be observed. However,it has to be taken into account that hydration heat flow is related tothe dissolution of clinker phases and precipitation of hydrates,whereas setting is mainly influenced by the morphology and theinterlocking of early hydrates.

4.4. X-ray diffraction and thermogravimetry

The hydration process is similar at 20 �C and at 5 �C, the maindifference being the slower hydration kinetics at lower tempera-ture. The dissolution of the ye’elimite and gypsum leads to the

(left) and at 5 �C (right). The dashed line at 1 mm/m represents the maximum of

Fig. 3. Heat flow curves measured by isothermal calorimetry at 20 �C and at 5 �Cwith a water to cement ratio of 0.80 and a water to solid ratio of 0.42. The grams (g)given in the heat flow unit correspond to the mass of cement (clinker + gypsum)plus filler.

L. Pelletier-Chaignat et al. / Construction and Building Materials 26 (2012) 619–627 623

formation of ettringite and aluminium hydroxide (Figs. 4 and 5). Insamples with a calcium sulphoaluminate clinker to gypsum massratio of 5.26, gypsum is fully consumed after 7 days of hydration,while it is still present after 28 days in the samples with a ratioof 2.50 where a lower clinker to gypsum ratio was used. This re-flects the ye’elimite to gypsum molar ratio used in the two formu-

Fig. 4. XRD diffractograms of BL-h, BQ-h, BL-l and BQ-l at 28 days illustrating thehydrates formed and the presence or absence of hemicarbonate at 20 �C (up) and5 �C (down).

Fig. 5. Derivative curves from the thermogravimetric analyses at 28 days for BL-h,BQ-h, BL-l and BQ-l at 20 �C (up) and 5 �C (down) illustrating the formation ofettringite, monosulphoaluminate and aluminium hydroxide.

lations. In the samples BL-h and BQ-h, the ye’elimite to gypsummolar ratio is close to 1, while a ratio of 0.5 is needed to satisfythe ettringite forming reaction and therefore to completely con-sume the gypsum. In samples BL-l and BQ-l, the ye’elimite to gyp-sum molar ratio is close to 0.44. In that case, the higher gypsumcontent used in the formulation is not consumed after 28 days ofhydration.

In all the studied samples, the X-ray patterns confirmed that themonocalcium aluminate (CA) from the clinker is fully consumedafter 1 day of hydration at 20 �C and after 7 days at 5 �C. The dical-cium aluminate (CA2) dissolves slower than the monocalcium alu-minate and is fully consumed in all the samples after 28 days.However, its consumption is fast in sample BL-h where it is absentfrom the X-ray curves after 1 day at 20 �C and at 5 �C.

Minor amounts of monosulphoaluminate are additionally ob-served in all the studied samples (Figs. 4 and 5). In the samples witha calcium sulphoaluminate clinker to gypsum mass ratio of 5.26, thepresence of limestone filler in BL-h reduces the amount of mono-sulphoaluminate formed compared to BQ-h and leads to the forma-tion of hemicarbonate (Fig. 4). Monosulphate and hemicarbonateare both stable as individual phases, as no extensive solid solutionformation between sulphate- and carbonate-AFm occurs [42]. Thepartial dissolution from the calcite is confirmed by the calculationof the calcite content deduced from the CO2 loss measured by ther-mogravimetry between 670 �C and 800 �C (Table 3). It shows thatcalcite is progressively consumed over time. While the calcite con-sumption is slower within the first 24 h at 5 �C than at 20 �C, theamount of calcite consumed is more pronounced at 5 �C after28 days of hydration. The onset of reaction of calcite within the firstday of hydration is fast compared to its reaction in association withOPC, which mainly occurs between 1 day and 7 days [32]. This iscertainly related to the higher Al2O3 and SO3 contents availableduring the early hydration of CSA cements compared to OPC, leading

Table 3Calcite and ettringite contents calculated from the TGA.

Time Calcite Calcite Ettringite Ettringite

(days) 20 �C (g/100 g dry binder) 5 �C (g/100 g dry binder) 20 �C (g/100 g dry binder) 5 �C (g/100 g dry binder)

BL-h 0 46.3 46.3 0.0 0.01 44.4 44.7 33.7 23.97 44.1 44.1 37.3 41.2

28 44.0 42.9 37.1 46.1

BQ-h 0 0.0 0.01 34.8 7.67 32.1 37.1

28 31.7 41.4

BL-1 0 46.4 46.4 0.0 0.01 44.2 45.4 41.8 17.37 44.3 43.8 44.4 46.5

28 43.8 43.2 44.7 50.2

BQ-1 0 0.0 0.01 33.8 8.57 40.3 43.4

28 40.2 45.0

The accuracy of calcite and ettringite contents are ±0.5 and ±1.0 g/100 g, respectively.

624 L. Pelletier-Chaignat et al. / Construction and Building Materials 26 (2012) 619–627

to the formation of significant amounts of ettringite and monosulp-hoaluminate within the first day of hydration.

From the calculation of the ettringite content from the TGA re-sults, it is clear that at 20 �C the presence of calcite from the lime-stone filler stabilizes the ettringite (Table 3). While in BL-h theettringite content increases until 7 days and then stays approxi-mately constant, in BQ-h it increases until 1 day and then slowlydecreases over time. This is in agreement with previous observa-tions made on the addition of limestone filler to Portland cement[24–30]. This stabilization of ettringite by calcite cannot be ob-served at 5 �C. However, the amount of ettringite present after28 days in the samples containing limestone filler at 20 �C or at5 �C is systematically higher than in the corresponding samplescontaining quartz filler (Table 3).

In the samples with a calcium sulphoaluminate clinker to gyp-sum mass ratio of 2.50, no hemicarbonate is observed in the XRDpatterns (Fig. 4). However, the derivative thermogravimetriccurves of BL-l confirm that part of the calcite is dissolved until28 days (Table 3). The absence of a signal for hemicarbonate inthe diffraction patterns could be related to its low concentrationin the cement paste. In this sample series, the stabilization ofettringite by the presence of limestone filler is not observed withinthe first 28 days (Table 3), as the ettringite content is increasingover time in any case.

4.5. Thermodynamic modelling

The results obtained by thermodynamic modelling confirm thatthe main hydration products are ettringite, monosulphoaluminateand aluminium hydroxide in the samples containing quartz filler(Figs. 6 and 7a). It also shows that monocarbonate and carbon-ate-bearing ettringite can form when limestone filler is added(Figs. 6 and 7b). The prediction of monocarbonate is partially inagreement with the experimental results where hemicarbonate isobserved by XRD (Fig. 4). The prediction of monocarbonate insteadof hemicarbonate can be related to the slow kinetics of monocar-bonate formation, as the dissolution of calcite is a slow processand thus not enough carbonate is provided to make monocarbon-ate. Alternatively, a decrease of the solubility product of hemicar-bonate by 0.2 log units, which is within the inaccuracy of thesolubility products used, would lead to the prediction of hemicar-bonate. In OPC blended with limestone (4 wt.%), hemicarbonatehas been observed as intermediate phase which was later trans-formed to monocarbonate [32]. Hydrotalcite occurs as minor

hydrate phase. It forms as stable phase when the periclase andthe MgO incorporated in the clinker phases dissolve and enoughaluminium is present to form hydrotalcite.

According to the model, the amount of calcite which can be dis-solved depends on the calcium sulphoaluminate clinker to gypsummass ratio (Figs. 6 and 7a). With a ratio of 5.26, the calcite is fullyconsumed if the calcite addition to the mix is 68%. With a ratio of2.50, the calcite is fully consumed if its addition is 63%. This is pos-itively correlated to the amount of monosulphoaluminate whichcan form in the cement paste, the higher the monosulphoalumi-nate content in the sample containing quartz filler (Fig. 7a) thehigher the amount of calcite which can be consumed in the corre-sponding sample containing limestone filler (Fig. 7b). The amountof calcite consumed calculated by GEMS for BL-h is close to theexperimental TGA result after 28 days at 20 �C (Table 3), where43.7 g of calcite for 100 g of dry cement are calculated by GEMSand 44.0 g are deduced from the TGA. For BL-l, the model underes-timates the amount of calcite which can be dissolved; the differ-ence is about 2%.

The model predicts that the ettringite to monosulphoaluminatemass ratio in BQ-h is lower than in BQ-l (Fig. 7a and b). This is inagreement with the XRD results, where a bigger ettringite reflec-tion is observed for BQ-l in comparison to BQ-h, indicating a higheramount of ettringite. The TGA results also show that the amount ofettringite present in the samples containing limestone filler is sys-tematically higher at 28 days than in the corresponding samplescontaining quartz filler (Table 3), which is in agreement with theresults given by GEMS (Fig. 7). The model also shows that the pres-ence of calcite tends to stabilize the ettringite and generates theformation of monocarbonate instead of monosulphoaluminate(Fig. 7a and b), which is evidenced by the decreasing contributionof the monosulphoaluminate to the overall phase assemblage withincreasing limestone content. At the maximum limestone content,which can chemically react, no monosulphoaluminate is present inthe phase assemblage (Fig. 6). This stabilization of ettringite by cal-cite is also observed by TGA at 20 �C (Table 3). While a decrease ofthe ettringite content is observed between 1 and 28 days in BQ-h, itis not observed in BL-h. The calculated phase assemblage in thesamples with limestone filler are slightly changed at 5 �C (Fig. 7c)compared to 20 �C (Fig. 7b). At 5 �C, the formation of carbonate-bearing ettringite is favoured against the formation of monocarbonate at low gypsum/CSA ratios. The presence of carbonate-bear-ing ettringite is not evident from the XRD data, as the resultingpeak shifts as described in [43] are quite small until a carbonate

Fig. 6. GEMS modelled changes for a complete hydration of the binders at 20 �C andwater to cement ratio of 0.80, for a sample series with (a) a calcium sulphoalu-minate clinker (CSA) to gypsum ratio of 5.26 and (b) for a sample series with a CSAto gypsum ratio of 2.50. Volume expressed as cm3/100 g dry cement. The x-axisrepresents the limestone filler content in the cement. AH3 refers to aluminiumhydroxide and inert CSA includes CT and C2AS. Ettringite is formed as a single phase(solid solution) and is subdivided into SO4-ettringite and CO3-ettringite in the graphto emphasize that in the presence of calcite, some CO3 can be incorporated in thesolid solution.

Fig. 7. GEMS modelled changes for a complete hydration of the binders at 20 �C andwater to cement ratio of 0.80, depending on the gypsum to CSA ratio, (a) for the BQsample series with quartz filler (including BQ-h and BQ-l) at 20 �C, (b) for the BLsample series with limestone filler (including BL-h and BL-l) at 20 �C and (c) for theBL sample series with limestone filler (including BL-h and BL-l) at 5 �C. AH3 refers toaluminium hydroxide and inert CSA includes CT and C2AS. Ettringite is formed as asingle phase (solid solution) and is subdivided into SO4-ettringite and CO3-

L. Pelletier-Chaignat et al. / Construction and Building Materials 26 (2012) 619–627 625

replacement of 70%. For the samples with quartz filler, the phasecomposition at 5 �C (graph not shown) does not differ from theone at 20 �C (Fig. 7a).

The water to binder ratios needed for complete hydration can bederived from Figs. 6 and 7. For BQ-l and BQ-h, 0.458 and 0.515 arecalculated for both temperatures, respectively. At 20 �C, 0.546 isdetermined for BL-l and 0.557 for BL-h. The values for 5 �C are0.547 (BL-l) and 0.629 (BL-h). Thus, the binders containing lime-stone are able to bind more water in the hydrate phases than thosewith quartz filler, as the carbonate takes part in the hydration reac-tions, thus stabilizing ettringite. The differences in water to binderratio of the calcite-bearing systems is explained by a higher bindingof carbonate into carbonate–ettringite at 5 �C compared to 20 �C.The results show as well that the water/binder ratio of 0.80 usedin the experiments is well above the theoretical water demand.

ettringite in the graph to emphasize that in the presence of calcite, some CO3 canbe incorporated in the solid solution.

5. Conclusion

The hydration and strength development of CSA cements withadded filler has been investigated varying the type of filler (lime-stone, quartz), the CSA clinker to gypsum ratio (5.26 and 2.50)

and the curing temperature (20 �C and 5 �C). In all tested mortars,ettringite is the main hydration product. All mortars exhibit highvolume stability in water at 20 �C, while some mortars show aslight expansion (max. 0.8 mm/m) in water a 5 �C.

626 L. Pelletier-Chaignat et al. / Construction and Building Materials 26 (2012) 619–627

In detail, the following conclusions can be made:

(i) In samples with limestone filler the setting time is in mostcases shorter than in those with quartz filler and calorimet-ric measurements show an earlier and enhanced hydrationheat development. This can be explained by the filler effect,which is more efficient in the case of the fine limestone pow-der used in this study. Limestone powder compared toquartz improves the strength at later times (7 and 28 days),which is an effect of its chemical contribution to the hydra-tion reactions. With limestone, less monosulphate is formed,whereas the formation of hemicarbonate and monocarbon-ate is enhanced thus stabilizing ettringite. This leads, as cal-culated by thermodynamic modelling, to a higher totalvolume of solids in limestone blended CSA cements than inblends with quartz. It also generates lower porosity results,explaining the higher strengths observed at later ages.

(ii) The CSA/gypsum ratio does not significantly influence set-ting times or strength (with the exception of the 8 h strengthat 20 �C which is higher at a lower CSA/gypsum ratio). Themain impact of the amount of gypsum addition is the changein the hydrate assemblage. At high CSA/gypsum ratio thegypsum is consumed after 7 days, whereas at lower ratiogypsum is still present after 28 days. The gypsum depletioncan be recognized in the calorimetric curves as the secondmaximum after the main hydration peak.

(iii) The temperature influences on one hand the hydrationkinetics, setting times and early strength development. At5 �C a significantly later initial and final setting, a longer dor-mant period in the calorimetric curves and much lowerstrength up to 1 day are observed compared to 20 �C. Onthe other hand the calculated phase assemblage differsbetween the two temperatures in the case of limestone pow-der. At 5 �C the formation of carbonate ettringite is more sig-nificant, whereas the monocarbonate forms to a lesserextent. In the case of the quartz filler the same hydrateassemblages are present at both temperatures.

Thus, the use of limestone instead of quartz filler in combina-tion with calcium sulphoaluminate cement is advantageous, whichis evidenced both at 20 �C and 5 �C. It accelerates the early hydra-tion especially at low temperatures. On the long-term, the lime-stone addition significantly increases the strength of the mortarsafter 7 days of hydration and beyond compared to mortars con-taining quartz filler. This is due to the chemical contribution ofthe calcite to the hydration reactions.

Acknowledgements

The authors would like to thank the innovation promotionagency (CTI) in Switzerland for its financial support (Project No.9623.1; 3 PFIW-IW) and the Saint Gobain Weber research teamincluding C. Famy and R. Blumer. The authors express their thanksto G. Beauvent for the fruitful discussions. Thanks are extended toL. Brunetti and B. Ingold (Empa) for their experimental support inthe laboratory.

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