Structural Analysis of Historic Construction – D’Ayala & Fodde (eds)© 2008 Taylor & Francis Group, London, ISBN 978-0-415-46872-5

Experimental techniques for the evaluation of the long-term behaviour ofmasonry strengthening materials

P. Bocca & A. GrazziniDepartment of Structural Engineering and Geotechnics, Turin Polytechnic, Italy

ABSTRACT: The restoration of historical buildings is a delicate, complex process, in that newly developedstrengthening materials, whose long-term effects have not yet been fully tested, may interact adversely with thematerials making up the masonry. In the analysis of the behaviour of masonry structures and their constituentmaterials, increasing importance has been assumed by the study of the long-term evolution of deformation andmechanical characteristics, that may be affected by both loading and environmental conditions, especially inthe case of structural restoration by means of innovative materials, which is compounded by the problem ofthe durability of the support-mortar system. The purpose of this investigation is to develop a methodology tobe used in laboratory tests as a preliminary design stage for structural interventions, in order to pre-qualify thestrengthening mortars and be able to formulate a judgement as to their compatibility and long-term behaviourwhen applied to historical masonry walls.

1 INTRODUCTION

Historical buildings often require drastic interven-tions, performed with techniques that make extensiveuse of the new products. The tests conducted are oftenlimited to determining their ultimate strength, dis-regarding their durability and their interaction withpre-existing materials. Unfortunately, where technical,conceptual and cultural aspects are concerned, there isnot much clarity yet about the use of modern materialsin ancient constructions. In many instances, restora-tion works are performed according to the criteriaof modern technologies, with newly-developed mate-rials, modelling the buildings according to resistingschemes that are not appropriate to structures cre-ated in stages at different times, thereby giving riseto hybrid forms of behaviour that cannot be read-ily foreseen (Binda & Saisi 2002). As a result, itproves virtually impossible to verify their efficacy anddurability.

For years, the Non Destructive Testing Labora-tory of the Structural Engineering Department of thePolitecnico of Turin has been working on a line ofresearch within the framework of an important con-vention stipulated with the Cultural Heritage Divisionof the Piedmont Region, on the theme “Study of thequality of the applications of innovative materials instrengthening interventions on historical artefacts”.The field of application is a site in the proximityof Turin, where the restoration works on the RoyalPalace of Venaria Reale (one of the most important

Figure 1. The Royal Palace of Venaria Reale.

residences of the Savoy family) represent the mostsignificant restoration project under way in Europe(www.lavenaria.it, Fig. 1). The goal of the research isthe experimental study of the long-term behaviour ofthe constituent materials of the masonry, with specialregard to the mechanical interaction between historicalbricks and modern strengthening mortars. Their long-term behaviour remains unknown in several respects,especially when they are applied to deteriorated histor-ical masonry structures, whose mechanical behaviour

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is often difficult to analyse and has to be assessed caseby case.

Through a rather fast laboratory procedure(Bocca & Grazzini 2004), this method supplies usefulindication for selecting, from a range of alternatives,the product that is best in keeping with the mechan-ical characteristics of the historical material, therebyavoiding the errors associated with materials that arenot mechanically compatible (Valluzzi et al. 2002). Byfocusing on the evolution of the deformation param-eters in accordance with recent damage models, it ispossible to compare the characteristics of the materi-als, assess their interaction and fatigue behaviour. Animportant part was devoted to the execution of cyclictests, using new monitoring criteria, leading to a morecomprehensive understanding of the fatigue phenom-ena that jeopardise the brick-mortar system. Specialattention was devoted to thermo-hygrometric aspects,which are often overlooked, but whose effects on themasonry system are often significant enough to com-promise the validity of strengthening interventions.

2 EXPERIMENTAL CAMPAIGN:INSTRUMENTATION AND MATERIALS

The materials used consisted of historical bricks fromthe Royal Palace of Venaria Reale and four differ-ent types of mortar (referred to as “A”, “B”, “C”,“D”) produced by different manufacturers, suitablefor the consolidation of monumental masonry struc-tures through the following types of intervention:application of plaster to historical masonry (A; C),joint closing (A; D), jacketing of masonry walls (D),reinforcement of vaults (D), consolidation by groutinjection (B). The mechanical characteristics of singlematerials have been investigated (table 1) by means oftest pieces 40 × 40 × 160 mm (Fig. 2).

Special attention was devoted to the study ofmixed brick-mortar test pieces, produced for the pre-qualification of a strengthening product. These testpieces were subjected both to static and to cyclic load-ing tests and to freezing-thawing tests, by selectingappropriate measuring systems in order to analyse, inparticular, the variations in the deformation status ofthe materials under the various loads that can affect themasonry structure after the restoration process. Thematerial used to produce the mixed tests pieces wasobtained from historical bricks cutted, using speciallydesigned timber mould measuring 223 × 57 × 83 mm(30 mm thick layer of mortar).

Each mixed piece was labelled with “X” L, where“X” stands for the code of the relative mortar. Cyclicand static compressive tests were performed with theaid of a 250 kN model 810 MTS. The mixed pieceswere instrumented with three pairs of transducers,according to the scheme shown in figure 3: a vertical

Table 1. Elastic modulus and compressive strength ofmaterials.

Eaverage σaverage �%σ

Material (N/mm2) νaverage (N/mm2) (6 months)

Mortar A 6208 0.12 8.27 −7.50Mortar B 7534 0.19 10.91 +111.55Mortar C 12678 0.23 10.34 +146.39Mortar D 12274 0.32 24.95 +57.47Historical 4099 0.08 8.09 –

brick

Figure 2. Single specimens.

Figure 3. Instrumentation for mixed brick-mortar testpieces.

pair was anchored to the plates of the MTS and anothervertical pair was applied directly to the test piece onthe opposite faces of the two materials; finally, a thirdpair arranged horizontally was used for measuring thedisplacements due to bulging. Completing the system,

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Table 2. Mechanical characteristics during maturation:mortar B.

σ �σ % E � E%Test Piece Days (N/mm2) (28-d) (N/mm2) (28-d)

MB 4.1 28 12.38 7262MB 7.3 28 12.54 6960MB 9.3 28 11.32 7944Average 28 12.08 – 7389 –

MB 3.3 90 19.74 10676MB 1.3 90 19.59 10089MB10.2 90 20.37 11290Average 90 19.90 +64.71 10685 +44.62

MB 2.2 150 17.24 8347MB 6.1 150 20.02 7923MB 6.2 150 20.22 9046Average 150 19.16 +58.61 8439 +14.21

MB 2.3 210 17.47 12000MB 8.1 210 17.94 10223MB 3.1 210 19.02 9680Average 210 18.14 +50.16 10634 +43.92

a pair of electrical strain gauges on the opposing verti-cal faces of the test pieces measured transverse strains.In this manner it’s possible to measure all the axialdeformations (in vertical, horizontal and transversedirections), whose algebraic sum yields the volumetricdeformation.

3 RESULTS OF THE EXPERIMENTALCAMPAIGN: SINGLE MATERIAL

3.1 Static and freezing-thawing tests

For mortar B and D, the evolution of mechanical char-acteristics in the time due to the maturation effects hasbeen analysed, verifying that the changes in mechan-ical behaviour are remarkable (tables 2–3). A consid-erable increase in the compressive strength (+64.71%for B, +36.87% for D) is registered between 28 and 90days, in addition to which values are stabilized a slightdecrease (Figs 4–5). The elastic modulus increasessensitive value: mortar B reaches the peak (+44.62%)in 90 days, at 90 days mortar D records a smallerincrease (+16.32%) that remains constant over time.

The test piece of mortar B and D were subjected tofreezing-thawing tests, in order to analysis the behav-ior of materials exposed to adverse environmentalconditions as seasonal temperature ranges (table 4).None of the test piece B remained intact to reach theminimum threshold of 25 cycles. On the contrary mor-tar D after 25 cycles showed a significant increase inresistance (+34.27%), while the elastic modulus val-ues has been discordant showing individual variations

Table 3. Mechanical characteristics during maturation:mortar D.

σ �σ % E � E%Test Piece Days (N/mm2) (28-d) (N/mm2) (28-d)

MD 4.3 28 20.08 9886MD 6.2 28 20.97 10957MD 7.3 28 20.87 11231Average 28 20.64 – 10691 –

MD 9.3 90 28.33 12455MD 5.3 90 28.32 12907MD 9.1 90 28.09 11947Average 90 28.25 +36.87 12436 +16.32

MD 1.1 150 28.99 12849MD10.2 150 28.46 13152MD 6.2 150 28.10 10448Average 150 28.52 +38.18 12150 +13.64

MD10.1 210 28.91 12406MD 6.3 210 29.16 14821MD 2.2 210 29.66 16177Average 210 29.24 +41.70 14468 +35.32

Figure 4. Compression test during maturation: mortar B.

(−1.95% on the average). After 50 cycles there is adecrease in compressive strength against the first setof 25 cycles (Fig. 6), bringing the average values closeto the virgin reference (−3.12%). The elastic modulusdecreses −5.77%.

3.2 Brittleness index

It’s possible to evaluate the mechanical behaviourof mortars in terms of brittleness (Bocca et al.1988, Krajcinovic 1996), extrapolating the brittle-ness indexes bind to the subtended areas under theload-displacement curves, corresponding to the workdeveloped by the material during compressive tests.

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Figure 5. Compression test during maturation: mortar D.

Figure 6. Compression test after freezing-thawingcycles: m. D.

Table 4. Static tests after freezing-thawing cycles: mortar D.

σi σf �σ % Ei Ef �E %Piece Cycles (N/mm2) (0-cycl) (N/mm2) (0-cycl)

MD 1.2 25 20.64 29.66 +43.70 13557 11119 −17.98MD 8.2 25 20.64 25.59 +23.98 13201 10376 −21.40MD 5.2 25 20.64 27.88 +35.08 11066 11257 +1.73MD 3.2 25 20.64 – – 11841 13386 +13.05MD 4.2 25 20.64 – – 8826 12167 +37.85MD 7.1 25 20.64 – – 9003 7869 −12.59Average 25 20.64 27.71 +34.27 11249 11029 −1.95

MD 3.2 50 20.64 24.08 +16.67 11841 12930 +9.20MD 4.2 50 20.64 17.37 −15.84 8826 10453 +18.43MD 7.1 50 20.64 18.53 −10.22 9003 8418 −6.50Average 50 20.64 19.99 − 3.12 11249 10600 −5.77

Two parameters are extrapolated: pre-failure index(Ipf ) and post-failure index (Ipstf ). Ipf gives infor-mations about the brittleness of material and can be

Figure 7. Apf and Apstf compute.

evaluated as the ratio between the subtended area Apfunder the rising branch until ultimate load and the totalarea Atot (Fig. 7):

to increase the value of such index the brittleness willincrease. Such characteristic corresponds to the apti-tude of the material to arrive to failure in a suddenway. Ipstf represents, on the contrary, the tendency tohave a ductile behaviour, and it’s expressed by the ratiobetween the area Apstf subtended under post-failurecurve and the total area Atot (Fig. 4):

to increase Ipstf the ductility will increase, that is thecapacity to distribute the strains, to happened failure,deforming plastically.

However just referring to these ratio it’s not pos-sible to consider the real value of failure load, sincematerials with different strength could have the sameindexes. In order to consider the rapidity by the mate-rial loses the capacity to resist to further strains oncethe collapse, it’s possible considering the slope ofthe unloading branch of load-displacement diagram:to increase the slope the brittleness will increase, ofagainst, a slope less accentuated will be index ofductility. It’s possible to express brittleness index Ib as:

where Ccs is the angular coefficient of the descendingbranch which interpolate the values of the post-failurecurve when there is a precipitous loss of performance.By means of index Ib has been possible evaluatingthe brittle or ductile mortars behaviour during theirmaturation (tables 5–6).

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Table 5. Brittleness index during maturation: mortar B.

Apf Apstf �Ib%Piece d (KNmm) Ipf Ipstf | Ccs | Ib (28-d)

MB 4.3 28 24.64 7.73 0.761 0.239 14.27 0.011MB 6.2 28 21.61 16.03 0.574 0.426 11.86 0.007MB 7.3 28 20.64 14.31 0.591 0.409 14.96 0.009Average 28 0.009 –

MB 3.3 90 15.00 3.39 0.816 0.180 151.89 0.124MB 1.3 90 13.46 4.10 0.767 0.233 151.39 0.116MB10.2 90 17.12 7.42 0.698 0.302 72.41 0.051Average 90 0.097 +995

MB 2.2 150 12.19 2.60 0.824 0.176 177.03 0.146MB 6.1 150 15.20 3.31 0.821 0.179 199.05 0.163MB 6.2 150 18.82 3.22 0.854 0.146 206.54 0.176Average 150 0.162 +1732

MB 2.3 210 10.71 1.81 0.855 0.145 316.93 0.271MB 8.1 210 12.85 3.50 0.786 0.214 213.83 0.168MB 3.1 210 14.12 1.11 0.927 0.073 910.29 0.844Average 210 0.428 +4741

Table 6. Brittleness index during maturation: mortar D.

Apf Apstf �Ib%Piece d (KNmm) Ipf Ipstf | Ccs | Ib (28-d)

MD 4.3 28 16.00 6.65 0.706 0.294 87.84 0.062MD 6.2 28 19.17 5.35 0.782 0.218 116.64 0.091MD 7.3 28 17.72 6.17 0.742 0.258 89.20 0.066Average 28 0.073

MD 9.3 90 29.56 13.27 0.690 0.310 91.30 0.063MD 5.3 90 28.23 5.01 0.849 0.151 198.67 0.169MD 9.1 90 30.88 8.45 0.785 0.215 123.42 0.097Average 90 0.110 +49.8

MD 1.1 150 28.20 6.34 0.816 0.184 188.40 0.154MD10.2 150 32.75 14.33 0.696 0.304 83.68 0.058MD 8.1 150 23.86 7.68 0.757 0.243 106.21 0.080Average 150 0.097 +33.2

MD10.1 210 27.50 5.63 0.830 0.170 155.69 0.129MD 6.3 210 28.70 4.38 0.868 0.132 282.39 0.245MD 2.2 210 27.72 2.67 0.912 0.088 313.81 0.286Average 210 0.220 +201

The pieces of mortar B tested within 28 days show alow brittleness index which initially justifies the duc-tile behaviour. But during the maturation there is aremarkable increase of Ib, about 4700%. Such ten-dency finds on facts in the diagrams which show analways steeper slope unloading branch as it evolvesthe maturation of material (Fig. 4). On the contrary,mortar D shows at 28 days a less ductile behaviour,but during the maturation the increase of brittlenessis modest (50–200%) so it highlights a much moreconstant behaviour in the time.

Table 7. Brittleness index after freez.-thawing cycles:mortar D.

� Ib%Piece Cycles Ipf Ipstf | Ccs | Ib (0-cycles)

Average 28 days 0.073

MB1.2 25 0.811 0.189 135.52 0.110MB5.2 25 0.689 0.311 106.02 0.073Average 25 0.092 +25.08

MB3.2 50 0.894 0.106 279.54 0.250MB4.2 50 0.721 0.279 83.58 0.060MB7.1 50 0.718 0.282 83.71 0.060Average 50 0.123 +68.73

Table 8. Results of preliminary static tests on mixed testpieces.

Pmax σmax σaverage ESeries Test piece (KN) (N/mm2) (N/mm2) (N/mm2)

AL AL02 102.75 19.30 11988AL04 59.76 11.49 15.40 14157

BL BL01 108.51 22.17 16940BL02 52.30 11.60 16.89 4400

CL CL01 40.78 9.71 6597CL02 76.98 15.46 12.58 12478

DL DL01 58.50 12.10 6191DL02 60.45 11.98 12.04 8106

Table 9. Results of static tests after freezing-thawing cycles.

Pmax σmax σaverage ESeries Piece Condition (KN) (N/mm2) %σ var. (N/mm2)

AL AL03 cracked 95.54 19.78 10050AL06 detached 81.00 15.83 8151AL08 detached 59.30 12.03 15.88 +3.15 6701

BL BL07 cracked 76.30 14.23 6250BL10 cracked 66.50 13.52 13.88 −17.81 6582

CL CL06 whole 104.50 9.92 10604CL08 whole 54.62 11.13 14.88 +18.25 7191

DL DL08 whole 107.40 21.52 35358DL07 whole 129.30 24.22 22.87 +89.93 16249

4 RESULTS OF THE EXPERIMENTALCAMPAIGN: MIXED TEST PIECES

4.1 Static tests

Compression tests were performed in order to deter-mine the failure load (table 8). Others mixed testpieces were subjected to 28 freezing-thawing cycles.Of special interest is the medium and great increasein strength observed in CL and DL series after thefreezing-thawing cycles (table 9).

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Figure 8. Monoaxial cyclic compression test σ − ε curve.

4.2 Cyclic loading tests

These tests were the most significant part of the testingcampaign, on account of being of decisive impor-tance in the evaluation of the long-term behaviour ofstrengthening mortars. The high value selected for thecyclic load (70% of the static load) was designed tomake the test severe enough despite the short durationof the test (100000 cycles −1.3 Hz), and to high-light the potential of several indicators monitored overtime. Among these, the evolution of the volumet-ric deformation of mixed pieces was analysed, sinceits propensity to assume negative values (increase involume) can reflect a lesser degree of collaborationbetween the two materials, or even their detachment atthe interface. Together with the vertical and horizontaldeformations, this is an indicator of the validity of thecombination between the historical material and thestrengthening mortar. The test was performed throughfour steps:

– initial 70% loading-unloading test (3 cycles);– 70% cyclic test (100000 cycles);– final 70% loading-unloading test (1 cycle);– post-cyclic compression test to failure.

In a typical σ − ε curve of a cyclic fatigue test(Fig. 8) it is possible to identify three distinct stages:stage I, where deformations are seen to increase rapidly(accounting for ca 10% of the service life of thetest piece); stage II, of stabilisation, where the defor-mations increase gradually at a virtually constantstress (10–80% of test piece life); stage III, with arapid increase till failure (Anzani et al. 2006). Var-ious authors (Minh-tan et al. 1993, Mu et al. 2005)have shown that the fatigue life of a material sub-jected to cyclic loading tests is strictly correlated tothe evolution of the deformations during stage II.

By analogy with the method suggested for concrete(Taliercio & Gobbi 1996), the evolution of verticaldeformations over time is analysed as the primaryparameter for predicting and quantifying the fatiguestrength of the material (Carpinteri et al. 2006). The

Figure 9. AL series cyclic tests: max vertical deformations.

Figure 10. BL series cyclic tests: max vertical deforma-tions.

Figure 11. CL series cyclic tests: max vertical deforma-tions.

goal is to ascertain whether the fatigue life of themixed brick-mortar system also depends on the rateof increase of vertical deformations during stage II(secondary creep rate). In figures 9–12, it can be seenthat the test pieces that reached failure displayed asteeper slant in the stage II section of the curve, fol-lowed, at ca 80–90% of test piece life, by a suddenincrease at stage III (failure). Conversely, the curvesobtained for the pieces that passed the 100000 cyclesmark displayed a lesser slant, which remained virtu-ally the same through the end, reflecting an effectivebehaviour still far from the failure.

From the results of the cyclic tests described above,through linear interpolation between 20% and 80%of secondary creep values, derivatives ∂εv/∂n (i.e., thevariations in the deformation vs. time curve during

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Figure 12. DL series cyclic tests: max vertical deforma-tions.

stage II) were worked out. Through a linear regressionon the logarithmic scale (Grazzini 2004), it is possibleto plot the data in a diagram to obtain an analyticalrelationship (10) between secondary creep variations,∂εv/ ∂n, and the number of cycles (N) to fatigue failure:

In a majority of cases, especially in the case of thetest pieces which failed to complete the cyclic test, theagreement is very good.

The goal is to focus on the deformation responseof the material subjected to fatigue tests consistingof different cyclic load combinations. This requiresconsidering additional factors affecting deformationbehaviour, as a study of these parameters is neededto complete the analysis of all the mechanical prop-erties and be able to predict the fatigue responseof the material. A valid correlation was establishedbetween secondary creep rate (∂εv/∂n) during stage IIand fatigue life (number of cycles to failure, N). Byperforming a certain number of cycles on the materialuntil it reaches the stage where deformations increaseat a constant rate, it is possible to predict fatigue lifewith a good degree of approximation.

Failure occurs when a deformation limit (corre-lated to the loading level) is reached, after which thevolume begins to increase; if the deformation rate istoo slow, the material does not reach the limit valueduring cyclic loading and the values of volumetricdeformation remain positive.

In some samples, the theoretical value Nthe wasfound to be lower than the value obtained from lab-oratory tests. From a case-by-case analysis it can beseen that relationship (10), which is a function of thesecondary creep rate, is able to indicate the onset of thecrisis of the brick-mortar systems immediately preced-ing the final value of the testing cycles. The analysisof the horizontal and volumetric deformations of thesetest pieces, in fact, demonstrated that the theoreticalvalue obtained from expression (10), that was smaller

Figure 13. AL series cyclic tests: volumetric deformation.

Table 10. Analysis of the data.

Test Logpiece n ∂εv/∂n LogN (∂εv/∂n) Nthe

AL01 22380 0.0270 4.350 −1.569 25583AL05 53465 0.0198 4.728 −1.703 32029BL03 100000 0.0047 5.000 −2.323 90605BL05 100000 0.0040 5.000 −2.398 102716BL06 100000 0.0024 5.000 −2.612 147056CL05 461 5.1818 2.664 0.714 555CL09 1223 2.5110 3.087 0.400 941CL10 15835 0.0501 4.200 −1.300 16294DL03 1149 0.4704 3.060 −0.328 3187DL05 100000 0.0015 5.000 −2.813 206028DL06 100000 0.0070 5.000 −2.155 68328BL04 40993 0.0340 4.613 −1.469 21612BL09 360 9.4729 2.556 0.976 358CL04 100000 0.0035 5.000 −2.454 112832CL07 46622 0.0192 4.669 −1.717 32795DL09 100000 0.0025 5.000 −2.594 142671DL10 100000 0.0113 5.000 −1.947 48171

than the actual value, corresponded to the time whena significant variation in trend was recorded, i. e. forpiece AL05 in figure 13 (table 10): horizontal defor-mations growing to a significant extent or volumetricdeformations shifting to a negative sign (test piecepropensity to bulge due to poor vertical collaborationor detachment at the interface between the two mate-rials). The methodology and the numerical analysisproved very sensitive to the initial signs of weakeningof the brick-mortar system, indicating clearly the onsetof a crisis due to fatigue (Grazzini 2004, 2006).

4.3 Brittleness index: comparison between staticcompressive tests, before and afterfreezing-thawing and loading cyclic

The figures 15–18 illustrate the static tests performedon mixed test pieces. As for static strength afterfreezing- thawing cycles, the values obtained for amajority of the series remained within the averageof the two preliminary tests, save for the series DL(Fig. 18), which displayed a considerable increase in

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Figure 14. AL series static tests.

Figure 15. BL series static tests.

Figure 16. CL series static tests.

strength. In most cases, the static curves after freezing-thawing revealed a more brittle behaviour (table 11):for AL and DL series further 340%. BL test pieces(Fig. 16), instead, retained a good degree of ductil-ity. The test pieces of BL and DL series that passed100000 cycles mark were tested on to failure. Theformer revealed a strength value in keeping with theaverage values of preliminary tests and for BL series aslightly less brittle behaviour (−32.3%); the DL seriesdisplayed too a noticeable increase in their mechanicalproperties and brittleness (+138%). Some CL and DLtest pieces were subjected both to the freezing-thawingtest and to cycling loading: piece CL maintained astatic behaviour similar to the weakest preliminary test

Figure 17. DL series static tests.

result (Fig. 17) and a decrease of brittleness (−75.8%).In the DL series, instead, an appreciable increasein strength was mated to a lesser degree of brittle-ness compared to the test pieces subjected to cyclicloading only.

5 CONCLUSIONS

The methodology adopted in the testing campaignmade it possible to identify a number of key parametersfor interpreting the long-term behaviour of strengthen-ing mortars, based on the mechanical interaction withthe historical brick structure to which the mortar isapplied. In particular the evolution in the time of themechanical characteristics, due to maturation, thermo-hygrometric and cyclic loading condition has beenpossible to investigate in order to make a judgmentabout the durability of materials.

In accordance with the theories formulated bydifferent authors, the analytical formula based on sec-ondary creep variations during stage II demonstratedthe same sensitivity and the same degree of accuracy asthe volumetric deformation, by supplying the numberof cycles after which the collaboration between the twomaterials begins to be undermined, without necessarilyresulting in test piece failure. By performing a certainnumber of cycles on the material, until it reaches thestage when the deformations grow at a constant rate, ittherefore becomes possible to predict the fatigue lifeof the brick-mortar combination with a good degree ofapproximation, without having to perform long seriesof fatigue cycles.

Finally, the severity of freezing-thawing tests helpedto achieve a more comprehensive assessment of thelong-term behaviour of the materials, confirmingthe influence of thermo-hygrometric stresses on themasonry system. The investigation highlighted theimportance of the evolution over time of deformability,as affected by loading and environmental conditions,in the study of the fatigue behaviour of masonrystructures and their constituent materials.

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Table 11. Brittleness index.

Apf ApstfPiece (KNmm) Ipf Ipstf | Ccs | Ib �Ib%

AL02 48.61 50.34 0.491 0.509 103.62 0.051AL04 128.06 217.99 0.370 0.630 50.86 0.019Average AL (virgin) 0.035

AL03 46.64 18.27 0.719 0.281 252.31 0.181AL06 46.16 11.58 0.800 0.200 278.34 0.223AL08 33.13 21.20 0.610 0.390 64.68 0.039AL07 38.10 41.96 0.476 0.524 74.53 0.035Average AL after 25 freezing-thawing cycles 0.120 +342

BL01 64.12 31.16 0.673 0.327 230.85 0.155BL02 56.01 24.10 0.699 0.301 54.75 0.038Average BL (virgin) 0.096

BL07 52.16 50.53 0.508 0.492 58.22 0.030BL10 57.73 30.80 0.652 0.348 62.00 0.040Average BL after 25 freezing-thawing cycles 0.035 −63.5

BL03 25.91 26.46 0.495 0.505 103.94 0.051BL05 48.07 26.14 0.648 0.352 175.10 0.113BL06 25.55 28.61 0.472 0.528 68.22 0.032Average BL after 100000 loading cycles 0.065 −32.3

CL01 21.18 25.92 0.450 0.550 23.67 0.011CL02 55.15 17.18 0.762 0.238 215.20 0.164Average CL (virgin) 0.087

CL06 56.30 16.46 0.774 0.226 331.05 0.256CL08 13.32 26.89 0.331 0.669 35.43 0.012Average CL after 25 freezing-thawing cycles 0.134 +154

CL04 12.32 22.62 0.353 0.647 59.14 0.021Average CL after28 freez-t. + 100000 loading cycles −75.8

DL01 25.81 17.71 0.593 0.407 124.19 0.074DL02 30.30 28.11 0.519 0.481 40.49 0.021Average DL (virgin) 0.047

DL07 76.17 23.96 0.761 0.239 309.12 0.235DL08 56.94 25.05 0.695 0.305 194.16 0.135DL04 52.37 12.13 0.812 0.188 203.18 0.165Average DL after 25 freezing-thawing cycles 0.178 +379

DL05 59.80 91.16 0.396 0.604 204.22 0.081DL06 42.80 28.10 0.604 0.396 81.05 0.049Average DL after 100000 loading cycles 0.065 +138

DL09 44.92 45.33 0.498 0.502 88.00 0.044DL10 33.05 42.60 0.437 0.563 89.28 0.039Average DL after 28 freez-t. + 100000 load cycles 0.042 −10.6

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