Introduction - WIT Press · 2014. 5. 16. · hardening; Mechanical Strength Tests (DIN 18555 Sept. 1982) with a Technik-Toni TROL Co, estimating the strength of the mortar during

Compatible restoration mortars for Hagia

Sophia earthquake protection

A.Moropoulou, A.Bakolas, ™ P.Moundoulas, ™ A.S.Cakmak ®™ National Technical University of Athens, Faculty of ChemicalEngineering, Dpt. of Materials Science and Engineering, 9, IroonPolytechniou, Zografou Campus, 15773 Athens, Greece,E-mail: [email protected]^ Princeton University, School of Engineering and Operations Research,Dpt of Civil Engineering and Operations Research, Olden Street, OldenStreet, NJ 08544, USA, E-mail: [email protected]

Abstract

Structural studies to determine the earthquake worthiness of Hagia Sophia inIstanbul have proved that the monument's static and dynamic behavior dependsvery strongly on the mechanical, chemical and microstructural properties of themasonry mortars and bricks. The results show a decrease of 5-10% in the naturalfrequencies, as the amplitude of the accelerations increases and returns to theirinitial values, due to the non-linear nature of the masonry (Cakmak et al*). Theanalysis of the historic mortars has indicated that the amorphous C-S-H gel-formation between the crystalline phases of the calcite and the dispersed ceramicfragments allows for energy absorption by the structure during an earthquake,without affecting the materials properties irreversibly, while the compatibility ofthe mortars to the original building units allows for continuous stresses andstrains. In the present work the synthesis of restoration mortars has beenperformed, following the methodology of reverse engineering, i.e. to evaluateand simulate their physico-chemical and mechanical characteristics to thehistoric ones. During setting and hardening, thermal (DTA-TG), porosimetricanalysis and mechanical tests (compressive, flexural strength) were performedThe results indicate that mortar syntheses with hydraulic lime as binding materialand being admixed with crushed brick, present a better behavior to those madewith aerial lime, or lime-cement, or lime-pozzolanic additives, confronting thecriteria set by the analysis of the historic mortars, which have proved to beearthquake resistant.

Transactions on the Built Environment vol 38 © 1999 WIT Press, www.witpress.com, ISSN 1743-3509

522 Earthquake Resistant Engineering Structures

Introduction

The original mortars, deteriorated by natural weathering, salt decay and bycorrosive action of polluted atmospheres, have to be replaced. The uncontrolledand rather extensive use of cement and polymer-based mortars, employed untilnow for restoration, have rendered unsatisfactory results, due to the high contentof soluble salts and the limited compatibility with the original components of themasonry (Rota Rossî ). The consequently induced anisotropic behavior of thehistoric structures might become even catastrophic, in response to seismic risks.Therefore, restoration mortars with similar characteristics to those of the originalmaterials to be repaired should be searched out.

The research was undertaken at the NTU-A MSCE Dpt. in order to developreliable criteria arising from the evaluation of the physico-chemical andmechanical characteristics of the historic mortars, to screen the acceptability of therestoration ones.The investigations of the crushed brick-lime mortars of HagiaSophia (Moropoulou et al/) have led to the following conclusions.The crushedbrick-lime mortars were prepared with lime as binder material and brick powderwhich acts as a pozzolan and with crushed brick as active aggregate or pureaggregate in various gradations, as well as with aggregates of carbonate or silico-aluminate compositions. These mortars present hydraulic characteristics from thepozzolanic reactions, which take place at the binder/ceramic interface.(Moropoulou et al/, Livingston et al.̂ , Binda & Baroniô ). The mix proportionsbinder/aggregates varies from 1:2 to 1:4 by weight with an average 1:3. Theaverage grain gradation of these mortars is reported in the following histogram(Moropoulou & Bakolaŝ ) : These materials present a CO: content

Earthquake Resistant Engineering Structures 523

Materials, syntheses evaluation, test methods and techniques

The raw materials used for the production process are classified as : (a) Bindingmaterials: lime putty, hydraulic lime and cement; (b) Aggregate materials: sand ofsilicate composition and crushed tile; (c) Admixtures : natural pozzolanic materials(earth of Milos) and artificial pozzolanic materials (brick powder), aluminumpowder. The selection of the raw materials results from a specific market researchand testing in relation to the technical requirements they should fulfill, as arisedfrom research data, experience and literature concerning historic mortars.

The raw material for lime putty production should contain 98-99% of CaCOg.The firing temperature of the limestones for the production of quick lime shouldbe below 900°C in order to obtain micro-crystals of CaO and a high specificsurface area, providing high reactivity for the slaking process appropriate for theproduction of effective lime putty. The lime putty should contain more than 94%of (CaO+MgO) and free water in the paste not more than 60%.

The firing temperature for hydraulic lime production should not exceed the900°C, as above. The presence of adequate C:S and CA is needed (where: C:S:2CaO.SiQ2,CA: CaO.Â Q,) and the Index of hydraulicity should be between 0.31-0.42, i.e., i = &+&+#/ Pc+Pm

The silicate sand should be pure, without extraneous compounds, mineralsalts, clays, silts, etc. It should be of silicate nature because it infers highermechanical strengths and weathering resistance. A wide range of grain sizedistribution is required following the results from the reverse engineeringprocess. "River sand" from Aliartos River was chosen due to the above reasons.

Crushed brick was used for its physical, physico-chemical properties.Concerning its physical function, the tile has small specific weight, therefore themortar produced is lighter than the mortar containing only sand It gains elasticityand better behavior to mechanical loads and earthquake stresses. If the ceramicsare fired at a temperature < 850-900°C (Moropoulou et al."), in relation to theircomposition, amorphous silicates could react at the ceramic interface.

There are used natural and artificial pozzolanic additives. As binding materialsthey should fulfill specific technical characteristics, like compressive strength above5 MPa (GR Law 29/2/80) (pozzolanicity test) and active silica above 10% (EN-196-2).

The earth of Milos is a natural pozzolanic additive. The pozzolanicity testgave compressive strength 8 MPa. Active silica has been estimated at 40%.

The brick powder is an artificial pozzolana. The clays, depending on theircomposition temper materials, and firing temperature present pozzolanic activity * *.The pozzolanicity test showed compressive strength of 6.2 MPa . Active silicahas been estimated at 18%. Crushed bricks, as well, have active silica, which isimportant for interface pozzolanic rections.

The aluminum powder is an air-entraining agent added in order to amelioratethe workability of the mixture, the cohesion of the fresh mortar and to obtain alower apparent density. Through the formation of a system of micro-bubbles, theporosity of hydraulic composites is augmented, and compatibility to originalmortars is assured Tensioactive additives may be admixed to control the stabilityof the microstructure.



Procedures for the preparation of restoration mortars syntheses

Syntheses of restoration mortars, according to the directives deduced from theinvestigation of the original ones *, are mixtures of different ratios of binders /aggregates / additives, with different grain size distributions, prepared undervarious operating conditions (Moropoulou et al.*\ as shown in Table 1.

Evaluation of restoration mortars

In this step the optimization of the mortar pastes on the basis of waterrequirement and proper workability was searched out. The reproducibility of thepreparation process was attempted by air content, bulk density, consistence andretained water tests (DIN 18555, 1982) estimating the technical characteristics ofthe acceptable fresh mortars. The optimum workmanship was decided in thebasis of a good workability of the mixture, an appropriate cohesion of the pasteand an efficient applicability on a pilot masonry structure.

The produced pastes syntheses were molded (DIN 1164 Part 7) in moulds of4x4x16cm and stored under controlled conditions, appropriate for the setting andhardening of the mortars.

In order to evaluate the various syntheses during setting and hardening of themortars, the following measurements were performed : Differential ThermalAnalysis - Thermo Gravimetry (DTA - TG) using a NETZSCH STA 409 EP,thermal analyzer system, in a static air atmosphere with a temperature gradient of10°C/min and a-alumina as reference material, in order to estimate the kineticshardening through the carbonation of the binder and the development of thehydraulic phases; Porosimetry, using a Porosimeter 2000 Series by FisonsInstruments, in order to estimate the change of the microstructure duringhardening; Mechanical Strength Tests (DIN 18555 Sept. 1982) with a Technik-Toni TROL Co, estimating the strength of the mortar during hardening.

Results and Discussion

Thermal analysis results are demonstrated in Figure 1, which shows theevolution of the carbonation for different categories of restoration mortars for 0,7, 15 days, 1, 3 and 6 months. The reported results are expressed as Ca(OH)2 %versus ACaCQs % (related to 0 days), which reports the contribution of thecarbonation of Ca(OH>2 to the total amount of CaCOs, although a part of CaCOsof aggregate continues to contribute to this component.

The syntheses containing sand aggregates have been noted as referencecurves, varying for diverse binders. For the lime putty - sand mortars asignificant increase of the rate of carbonation is observed for the period between1 and 3 months, continuing with a slighter rate from 3 to 6 months, withoutcoming to a full conversion yet. For the hydraulic lime - sand mortars theconversion of Ca(OH>2 to CaCOg is completed by the period of 6 months. Forthe pozzolanic - sand mortars, although they contain pozzolanic admixtures, afull conversion is not achieved by the period of 6 months. The comparison of theresults of the crushed brick mortars with the reference curves shows that theredartation of the carbonation is due to the humidity of the crushed brick.



Figure 1 : Diagram of the Ca(OH)2 % versus ACaCOs for different categories ofrestoration mortars for 0, 7,15 days, 1, 3 and 6 months.

In Figure 2 the ratio of AGO] / structurally bound water which expressesinversely the hydraulicity rate versus the of ACC>2% (Moropoulou, Bakolas,Bisbikoû ) after 6 months of hardening, is shown. The lowest levels of the ratioare attained by the hydraulic lime syntheses. The highest level of the ratio isattained by the lime putty syntheses and the pozzolnanic and / or with cementsyntheses lay in between. It is observed that the crushed brick mortars in all thecategories of binders present the higher levels of hydraulicity. Actually, thehydraulic lime - crushed brick mortars attain the highest levels of ~ 2 of theACO: / structurally bound water ratio, the pozzolanic - crushed brick mortarsattain a level of ~ 4 of the ACQz / structurally bound water ratio, overlaping thecement lime - crushed brick mortars, while the lime - crushed brick mortarsexceed the 10 value of the ACO% / structurally bound water ratio. These resultsare in agreement with the relevant evaluation of historic mortars (Moropoulou et.al̂ ). Relative is the evolution of the carbonation as in Figure 1, the lime mortarsattaining the highest ACQz% (-12%), the hydraulic lime the lowest (-3-5%), thepozzolanic and cement lime mortars, intermediate values (5-10%).

8 ":/242 #10-I

ratio ACO2

/Hy

after 6 m 8 -

6 -42 -n -

+

7 AC02 % 9 11 13 15

Figure 2 : Diagram of the ratio ACO2/Hydraulic water versus ACO2 % after 6months of hardening



Table 2 reports the results of Porosimetry and Mechanical Tests after 1, 3 and6 months of hardening. It is expected that in the evolution of the carbonationprocess the porosity will tend to decrease due to the increase of the largermolecular mass of the CaCOg as compared to the Ca(OH)2. It is observed that inthe mortar categories where the carbonation is in evolution (lime putty-sand,pozzolanic-sand mortars), the total porosity decreases and the mechanicalstrength increases. For hydraulic lime mortars where the carbonation iscompleted, a variation in total porosity is observed Concerning crushed brickaggregate mortars, the total porosity, as well as the total cumulative volume arein close relation with the nature of the aggregate. The high porosity, as well asthe low bulk density of the crushed brick aggregate is the reason why the crushedbrick aggregate mortar categories present higher commulative volume, lowerbulk density and higher total porosity than the sand aggregate ones.

From the obtained results there is no correlation between cumulative volumeand mechanical strength. The specimens with the lowest cumulative volume arethose made with hydraulic lime and sand aggregate, which also present appropriatemechanical strengths (Schafer & Hilsdorf̂ ). On the contrary the specimens with thehighest values of the mechanical strengths show high values of cumulative volume.

From the comparison of the results between 1, 3 and 6 months the followingare deduced. The cumulative volume is lower in the period of 3 and 6 months incomparison to the results of 1 month. The decrease of the cumulative volumeleads, in general, to greater mechanical strengths, but this increase is not in closeproportion to the decrease of the cumulative volume. The bulk density increasesmore or less in all categories. As the bulk density increases, so does themechanical strength, although there is no full accordance to that rule. Theaverage pore radius in almost all categories is lower in the periods of 3 or 6months in comparison to 1 month, due to a development of the hydraulic phases.The specific surface area increases from 1 to 3 or 6 months. This increase almostin all categories is in accordance to the decrease of the average pore radius.

Hydraulic lime mortar category presents the highest strength values regardlessthe nature of the aggregate. The values of the lime putty - pozzolanic - cementcategories vary, but remain much lower than those of hydraulic lime mortars.

Comparing the categories with the same binding material and with differentcomposition and gradation of aggregates, the following remarks are deduced incomparison between 1, 3 and 6 months :

Lime putty category : present higher mechanical strengths from 1, 3 and 6months, but in general low values. The carbonation is still in evolution.

Hydraulic lime category : present the highest mechanical strengths in respectto all other categories. The synthesis with only crushed-brick as aggregate andair entraining agent presents the higher values in respect to the one with onlysand and sand-crushed brick aggregate. The higher values of mechanicalstrengths could be attributed to the nature of the binding material.

Lime admixed with pozzolanic additives category : both specimens with sandand sand-crushed brick aggregates present very low mechanical strengths, exceptfor the synthesis of lime putty - powder of brick - coarse sand - crushed brick.

Lime putty-cement category : specimens with only sand aggregate presenthigher mechanical strengths to those with sand-crushed brick aggregate.



The compressive strengths of masonry with thick bed joints is estimated bylaboratory measurements for 6 months (Figure 3) of mortars' strength, accordingto the equation of the least-squares, which is applied in other monuments as wellfor the prediction of masonry strength (Papayianni, Karavezirogloû ,Karaveziroglou, Papayianni* ') is :

c= 1/100*(62 - 0.8t)(0.557 0.0659 f̂ + 10.061)

compressive strength ofwhere, f̂ : compressive strength of masonry,mortar, andt: thickness of bed joint

By these experimental data evaluations, both the shape of the cross-sectionalarea and the depth of the bricks do not influence considerably the compressivestrength of the masonry specimens.

Hydraulic lime - crushed brick - aluminum powder mortar synthesis infers tothe masonry compressive strength the highest values. All the others hydrauliclime mortars lay in between the above synthesis and lime, lime cement mortarswhich attain the minimum values. The most realistic approach to Hagia Sophiaas baring elements is the 40-mm thickness of bed joint.

The above evaluation is sound in the structural parts of the monumentscompressed likewise the supporting masonry of the dome. However a generalrequirement for repair mortars is to serve both purposes in the masonry structure:

To infer to the masonry strength and to provide elastic bonds compatiblyjoining the building units.

12

10E"5

0 1 2 3 4 5 6com pressive strength of m ortar

Figure 3 : Diagram of compressive strength of masonry versus compressive strengthof mortars after 6 months of hardening (thickness of bed joint 25 mm)

Hence a combined assessment of the tensile strength and the ratio fm,t/fm,c hasto be performed in order to screen the acceptable among the tested syntheses.

Acceptability limits of the above mentioned ratio are determined between 1/4and 1/6 in previous investigation on historic masonries. (Tassios, Chronopoulos,unpublished data). In Table 2 the estimated values of tensile strength (f̂ = 2/3*fm,f) and the fm/fm,c ratios are presented It results that hydraulic lime - crushedbrick - air entraining agent mortar, lime - powder of brick - crushed brickmortar and hydraulic lime - fine sand mortar fulfill that criterion, while



hydraulic lime - crushed brick mortar and hydraulic lime - coarse sand mortarcould fulfill the same criterion by improving die gradation of the aggregates.

Finally, the type of the adhesion bonds developed at the crushed brick / limeinterfaces screens the ability of the prepared composites to absorb energy andprovide earthquake protection to the structure.

Conclusions

Consequently, the development of new materials for cultural, heritageconservation has the indispensable task to rediscover and ameliorate theproduction technologies of the historic ones, especially when compatible anddurable mortars are required The obtained results from the various techniquesand tests employed for the evaluation of restoration mortars during setting andhardening, lead to the following conclusions.

The raw materials used to produce restoration mortars as well as then-proportions and gradation of aggregates are fulfilling the technical characteristicsthat were found from the reverse engineering process. The mechanical strengthsare directly related to the rate of hardening of the binding material. Hence themortars with hydraulic lime admixed with crushed-brick present the highestmechanical strengths to those with aerial binder that present the lowestmechanical strengths. The thermal analysis results, which render the evolutionof the mortars during setting and hardening, showed that hydraulic lime mortarsperform the higher rates of carbonation, while lime putty syntheses perform theslower ones. As far as the structurally bound water is concerned, the highestamounts are observed on the hydraulic mortars with crushed-brick, which alsoexplain why these mortars present the highest mechanical strengths. The study ofthe microstructure shows that cumulative volume is lower in 3 and 6 months incomparison to these of 1 month - which leads to greater mechanical strengths -,the bulk density is increasing - which also leads to greater mechanical strengths-,the average pore radius in almost the total of the syntheses is lower in 3 and 6months in comparison to 1 month.

The results indicate that mortar syntheses with hydraulic lime as bindingmaterial and being admixed with crushed brick and air entraining agent present abetter behavior, confronting the criteria set by the analysis of the historic mortarsand masonry concerning both microstructural and mechanical characteristics.

Finally, the type of the adhesion bonds developed at the crushed brick / limeinterfaces screens the ability of the prepared composites to absorb energy andprovide earthquake protection to the structure.

Acknowledgments

Acknowledgments are attributed to the Research Center of Titan Cement IndustriesS.A. that hosted the pre-semi-industrial preparation and technical testing ofmortars, and particularly to Mr. K. Simeonidis, Mr. K. Niskopoulos, Mr. Em.Chaniotakis and the Technical Stuff for their kind contribution. This research hasbeen performed under the joint research initiative according to the trilateralprotocol agreement, established in Istanbul in March 19, 1994, among Princeton



University, Bogazici University and National Technical University of Athens, forthe earthquake protection of Hagia Sophia and historic monuments in Istanbul andAthens. Acknowledgments are also attributed to Mr. E. Pavlides, Chem. Eng., Ms.S.Anagnostopoulou, Chem. Eng. Stud, and Ms. C. Melanidi, Chem. Eng. Stud.

References

1. Cakmak, A.S., Moropoulou, A., Mullen, C.A. Interdisciplinary Study of DynamicBehaviour and Earthquake Response of Hagia Sophia, Soil dynamics and earthquakeengineering, 14, pp. 125-133,1995.

2. Rota Rossi, P. Mortars for restoration : basic requirements and quality control,Materiaux et Constructions, 19, pp. 445-448,1989.

3. Moropoulou, A., Cakmak, A.S., Biscontin, G. Crushed brick lime mortars of Justinian'sHagia Sophia, Mater. Issues in Art & Archaeology, V, 462, pp. 307-316,1996.

4. Moropoulou, A., Biscontin, G., Bisbikou, K., Bakolas, A., Theoulakis, P., Theodoraki, A.,Tsiourva, Th. Physico-chemical study of adhesion mechanisms among binding materialand brick fragments in'cocciopesto', Scienza eBeni Culturali, Vol. .DC, pp.415-429,1993.

5. Livingston, A.R., Stutzman, E.P., Mark, R., Erdik, M. Preliminary analysis of themasonry of the Hagia Sophia Basilica Istanbul, Mater. Issues in Art and Archaeology,H 267, pp. 721-730,1992.

6. Binda, L., Baronio, G. Indagine sull'aderenza tra legante e laterizio in malte edintonaci di 'cocciopesto', Bolettino d'Arte, 35-36, pp. 109-115,1986.

7. Moropoulou, A., Bakolas, A. Range of acceptability limits of physical, chemical andmechanical characteristics deriving from the evaluation of historic mortars, PACT, 56,pp. 165-178,1998.

8. Tassios, T.P. National Technical Univ. of Athens, Civil Engineering, Dpt, Testreport, as personal communication to A.S. Cakmak, 1 Sept 1993.

9. Moropoulou, A. Reverse engineering to discover traditional technologies: A properapproach for compatible restoration mortar, PACT, 57, pp. 1-16,1998.

10. Delgado Rodrigues, J. In the search for tentative recommendations regardingcompatible restoration mortars, PACT, 56, pp. 141-147,1998.

11. Moropoulou, A., Bakolas, A, Bisbikou, K. Thermal Analysis as method of characterizingancient ceramic technologies, Thermochimica Acta, 2570, pp.743-753, 1995

12. Moropoulou, A., Bakolas, A., Moundoulas, P., Cakmak AS. Compatible restorationmortars, preparation and evaluation for Hagia Sophia earthquake protection, PACT, 56,pp. 79-118,1998.

13. Moropoulou, A., Bakolas, A., Bisbikou, K., Characterization of ancient, byzantineand later historic mortars by thermal analysis and X-ray diffraction techniques,Thermochimica Acta, 269/270, pp. 779-795, 1995.

14. Moropoulou, A., Bakolas, A., Michailidis, P., Chronopoulos, M., Spanos, Ch.Traditional technologies in Crete providing mortars with effective mechanicalproperties, Structural Studies of Historical Buildings IV, Computational MechanicsPubl, Southampton, Boston, pp.151-161,1995.

15. Schafer, J., Hilsdorf, R K. Ancient and new lime mortars - The correlation betweentheir composition, structure and properties, Conservation of Stone and OtherMaterials, RILEM-UNESCO, Chapman & Hall, Paris, Vol.2, pp.605-612,1993.

16. Papayianni, L, Karaveziroglou, M. Aggregate gradation of ancient mortars.Relationship to strength and porosity, Conservation of Stone and OtherA/afena/5,RILEM-UNESCO,Chapman&HaUJParis, Vol.2, pp.493-500, 1993.

17. Karaveziroglou, M., Papayianni, I. Compressive strength of masonry with thickmortar joints, Conservation of Stone and Other Materials, RILEM-UNESCO,Chapman & Hall, Paris, Vol 2, pp. 212-219, 1993.



Table 1: Classification and legend for the categories of the tested restorationmortar syntheses

A Lime Putty Mortars _- Synthesis LS2 (L:30% - S:70%)[10,5%


Table 2 : Microstructural and mechanical properties of the restoration mortarsyntheses during hardening.

Synthesis

LS2

HLS2

LPBS2

LPS2

LCS2

LS2CB

HLS2CB

LPBS2CB

LPS2CB

LCS2CB

LSI

HLS1

HLCBA

months

1m3m6m1m3m6m1m3m6m1m3m6m1m3m6m1m3m6m1m3m6m1m3m6m1m3m6m1m3m6m1m3m6m1m3m6m1m3m6m

As(m%)4,832,711,681,873,844,432,282,402,182,562,922,032,963,086,032,383,013,124,055,595,273,233,803,122,842,966,544,134,444,962,845,562,693,103,983,174,385,626,73

d(S/cnr*:1,992,042,131,921,951,931,891,912,011,961,972,111,821,831,851,741,721,721,631,661,741,741,761,821,711,731,731,581,591,571,841,881,991,721,741,811,551,561,54

Tin(Mm)0,380,310,400,340,290,280,380,320,290,390,350,400,370,350,350,500,540,500,300,290,270,460,360,440,670,620,680,510,560,609,407,597,100,400,370,360,890,830,78

P%

33,529,729,828,128,230,832,231,330,433,833,530,231,130,729,042,741,642,842,540,942,143,541,042,444,042,748,143,143,140,240,539,337,336,335,434,143,343,241,8

Cv(imrrVg)169,3146,0140,0146,4144,5159,7170,4164,2151,3172,6170,2143,1170,9168,3156,9245,7241,1248,9260,7246,9241,8250,0232,7233,1257,3248,2277,8272,8270,6255,8220,1209,5187,5211,3202,9188,3279,4277,2271,5

*m,c(MPa)0,00,51,23,04,04,90,50,81,60,00,70,90,80,91,60,40,51,12,53,53,40,81,62,00,50,50,50,70,40,50,00,81,12,33,02,94,95,45,2

fm,f(MPa)0,30,30,30,70,71,00,20,30,40,10,30,40,20,30,50,20,30,30,40,60,70,30,50,40,20,30,40,20,20,30,30,30,30,50,70,71,71,71,8

4n,t(MPa)

0,20,2

0,50,7

L. 0,20,3

0,20,3

0,20,3

0,20,2

0,40,5

0,30,3

0,20,3

0,10,2

0,20,2

0,50,5

1,11,2

f fiiruAm,c

1 / 2,51/6

1 78,51/7

1/41/5,3

1/3,51/3

1/41/5,3

1/2,51/5,5

1 / 8,751/6,8

1/4,81/6,7

1/2,51/1,7

1/3,11 / 2,5

1/41/5,5

1/6,31/5,8

1/4,81/4,3

where:As : Specific surface area (nf/g) - d : Bulk density (g/cnf) - r^ : Average poreradius (jim) - P %: Total porosity (%) - Cv: Total cumulative volume (mmVg) -fn,c: Compressive strength (MPa) - 4,f - Flexural strength (MPa) - Qt : Tensilestrength (MPa) - f̂ t / fm,c * Ratio tensile strength / compressive strength


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Introduction - WIT Press · 2014. 5. 16. · hardening; Mechanical Strength Tests (DIN 18555 Sept. 1982) with a Technik-Toni TROL Co, estimating the strength of the mortar during