12TH INTERNATIONAL

BRICK/BLOCK Masonry c O N F E R E N C E

Des

"PERFORMANCE AND DURABllITY TESTS FOR PlASTERING MORTARS"

P. Dessi, A .. Fantuccil, V.GalimbertP, L.Nironi4

IClTE / CNR5

'Architect, CNR Researcher

' Geometer, CNR Technical Specialist for Research Bodies

3Architect, Ph.D.in Building Ergotechnical Engineering, CNR Researcher

'Architect, CNR Researcher

'Central Institute for Building Industrialization and Technology (IClTE)

of The Italian Research Council (CNR)

ABSTRACT

In order to supply methods and tools for the assessment of performance and durabil­ity of plastering mortars, a series of tests have been carried out at IClTE-CNR in 7999. This paper shows some results both from the standard tests and the adapted tests to hydrated lime mortars, plastered units and solid masonry samples. This experimental research led, on the one hand to locate the mortar with best performance in terms of masonry compatibility and ageing resistance and on the other hand to verify the method which resulted to be valid. Several technical information were 0150 obtained from tests to define good practice for real working under local cJimatic conditions.

Key Words: ExternaI rendering, hydrated lime, units and plastered wallettes, perfor­mance and durability tests.

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1. INTRODUCTION

Over the last decades the investments in the restoration field in Italy have re­markably increased. The most part of building works already executed or still un­der way have in fact concerned buildings externai envelope, façade and roofings, very frequently regarding interventions aimed at recovering damaged plasters. Even though the construction products industry has developed and marketed new premixed products for the preparation of plastering mortars, the works car­ried out in th is way not always proved to be durable over the time. The incom­patibility between base material and mortar, the w rong stratif ication of plaster, the poor knowledge of techniques for the application of mortar, are some of the possible causes leading to the rapid pathological degradation of this kind of coat­ings. In an attempt to solve these technical problems, an ad hoc experimental campaign, which consisted of both characterization and durability tests on hy­drated lime plastering mortars, has been carried out.

2. RESEARCH PROGRAMME

The different phases of the research programme were: study of the existing stan­dards and literature; characterization of materiais; preparation of mortar speci­mens; preparation of masonry samples covered with different types of plastering mortar; laboratory tests on mortar specimens; laboratory tests on masonry sam­pies; data processing and drafting of the results. The experimentation has been carried out parallely on two types of plastering mortar, the mixes of wh ich must be kept confidentia l for industrial reasons:

A hydrated lime mixture with weak hydraulic properties, to be used as undercoat; hydrated lime mixture with weak hydraulic properties, to be used as middle coat; hydrated lime mixture with weak hydraulic properties, to be used as final coat;

B hydrated lime mixture w ith weak hydraulic properties, to be used as under­coat; hydrated lime mixture with weak hydraulic properties, to be used as mid­dle coat (different proportions compared with A type); hydrated lime mixture with weak hydraulic properties, to be used as f inal coat (different proportions compared w ith A type) .

Solid bricks bound together wi th hydraulic lime and serena stone blocks were used as base materiais for both types of plastering mortars.

3. TESTS

Tests procedures have mainly been extracted from European standards or drafts not specifically conceived for hydrated or weakly hydraulic lime binders. To eval­uate certain performances not envisaged in the standards, ad hoc testing proce­dures had to be implemented and new experimental equipment had to be set up,

sometimes through the adaptation of procedures specifically addressed to other materiais as well. Hereby the carried out experimental ad hoc procedures will be specially stressed.

3.1. On plastering mortars

Before preparing the specimens, the determination of consistency of mortars us­ing a flow table (2) and determination of service life of fresh mortar (17) tests were carried out. Then, two sets of mortar specimens of suitable size were made. After a 60 days curing period at 20°C temperature and 50% R.H ., the specimens were subjected to the following tests: compressive strength (19), hydraulic shrink­age determination (13), determination of water vapour permeability (5), deter­mination of the evaporation curve (8), determination of water absorption by cap­illarity (7) and determination of linear expansion due to water absorption (11).

3.2. On small masonry samples

Small masonry samples coated with the two analyzed types of plastering mortar were made. After a 60 days curing period at 20°C temperature and 50% R.H., the samples were subjected to the following tests: determination of adhesion of hard­ened plastering mortar (15), determination of freeze/thaw resistance (16) (figure 1), crystallization by total immersion (10), crystallization by partial immersion (9) and determination of the resistance against sulphates (4). Further characterization tests such as watertightness under pressure (14) and air permeability (3), were carried out through the adaptation of procedures specifically addressed to other materiais.

Figure 7. A sample after the freeze/thaw testo

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3.2.1 Watertightness test (14)

One change in the standard equipment concerned the utilization ot circular met­al bands for restraining the masonry sample (bricks bound with cement mortar). Moreover, sample and bands were mutually fastened in order to prevent crack­ing due to high pressure and side water dripping. Siporex and tuff samples were also prepared to allow further comparison. Watertightness is expressed as the wa­ter pressure value (kPa) at which samples do not show dripping and do not allow water to pass through . The test was carried out on each sample by scaling up pressure of 0,5 kPa every 5 mino until widespread water dripping occurred. Time and correspondent water pressure were recorded (figure 2).

3.2.2. Air permeabi/ity test (3)

One change in the standard equipment concerned the preparation of square masonry coated samples (30 x 30 cm 2

), which were particularly suitable for be­ing put into an airtight square box and sealed to it so that they divided the box in two parts: while the lower part could be pressurized through a volu­metric compressor, the upper part, conveniently covered with a lid, was con­nected to a soap bubble flowmeter through a valve. Tested samples were sub­jected to sequential pressure increments and each step was kept for some minutes before noticing the air flow (cm 3/min) passed through the sample. In order to allow further comparison, siporex and tuff samples were tested as well (figure 5).

Figure 2. The apparatus for watertightnesstest.

Figure 5. The apparatus for air permeability testo

3.2.3. Determination of the "open time" of fresh mortar and of the thickness of each fayer

As precise practical rules for applying hydrated lime mortars were lacking, having the latter fallen out of use since a long time, an ad hoc experimetal campaign was carried out with the aim of establishing the "open time" of stratification of mortar layers. The objective was to find the usefulf time whithin which it was gained the best adhesion between mortar layers and to determine the optimal thickness of the layers themselves. Two materiais were chosen as base materiais: serena stone blocks (non porous material) and solid bricks (highly porous material). Hereafter only the experimental campaign on serena stone blocksis described. The experi­mentai parameters which were conveniently varied were mortar thickness and the waiting time before coating, that is to say the time when one further coat is ap­plied on the coat previously laid . 35 serena stone blocks of 15 x 30 x 15 em' (of 15 x 30 cm2 plasterable surface) (figure 3) were simultaneously given the undercoat (of 0,5 em thickness); subsequently, layers of coat of different thickness (1; 1,5; 2; 2,5; 3 em) were applied to each set of 5 blocks at prefixed time intervals, which had been computed starting from the application of the undercoat (after 2 h, 4 h, 8 h, 24 h, 72 h, 168 h e 336 h) (table 1). Immediately after the application of the coat, samples were inspected during the curing phase at prefixed time intervals and ali the possible observations about the surface appearance were gathered. At

Table 7. Scheme of samples to find out "open time" to apply coat on undercoat.

Waiting time belore applying coaI

on undercoat (hours

2 1 1,5

4 1 1,5

8 1 1,5

24 1 1,5

72 1 1,5

168 1 U 336 1 1,5

Thickness 01 the coat applied on the undercoat

lor each set 01 5 blocks (em)

2 2,5 3

2 2,5 3

2 2,5 3

2 2,5 3

2 2,5 3

2 2,5 3

2 2,5 3

Figure 3. A general view of coated blocks.

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the end of the curing phase, during which samples had been exposed to appro­priate conditioning, direct pull tensile force tests were carried out to evaluate ad­hesion between different layers: the envisaged load was appl ied to the pull-head plates previously glued with epoxy resin through a dynamometer (figure 4).

3.3. On walletts

The experimental samples consisted of solid brick wallets of 150 x 150 x 12 cm 3,

plastered on one side with either A or B type mortar and cured for at least 60 days in an unconditioned shed where relative humidity varied between 35 and 50% and temperature varied between 15 and 25°C.

3.3.1. Test of water penetration and leakage through masonry (21)

On both samples, each coated w ith one type of mortar, it was requ ired to mea­sure the size of damp areas at the end of a 4 hours test which was aimed at sim­ulating the resistance to water penetration of a wall exposed to ra in and w ind. Af­ter the seeped water had been allowed to evaporate for a convenient time period, both samples were subjected to adhesion tests to check the adhesion between mortar and base (15), by applying a tensile force with a dynamometer.

3.3.2. Acid rain test (1)

Two masonry samples coated on one side were located close to one another in order to be simultaneously subjected to artificial ageing treatment, unlike it is en­visaged in the TNO test procedure (1). Furthermore, a third of the plastered sur­face was protected against artificial ageing through polycarbonate panels in or­der to allow the operator to draw, at the end ot the test, a precise comparison with the portion subjected to the acid rain treatment (figure 6). In compliance w ith the acid ra in test, fi rst 75 natural rain cycles (pH 5,6) and then 75 acid rain cycles with water to which su lphuric acid had been added (pH = 3,5), were car-

Figure 4. The adhesive strength tes ts on coated blocks.

Figure 6. The apparatus for acid-rain testo

ried out. Each cyele consisted of 1 hour of raining (25 I/min) and three hours of infrared radiation at a levei of approximately 650 W/ m2. It was deemed that the following test could be profitably carried out to check the lowering of the wallets performances after the artificial ageing treatment (in comparison with the per­formances of the portion not subjected to any treatment) :

- test of water absorption under low pressure (6).

- adhesion test, to check the adhesion between plaster coats and base (15).

3.3.2.7. Test of water absorption under low pressure (6)

The water absorption test, which quantifies the water absorbed owing to a col­umn of water applied to a limited area for a certain period of time, was carried out in order to find possible changes in the porosity of the analyzed plaster. On each sample, water permeability was measured in three points before the ageing treatment took place, after 75 cycles of natural rain (pH 5,6) and after the fol­lowing 75 cyeles of acid rains (pH 3,5) (figure 7).

3.3.2.2. Direct pull tensile force tests to check the adhesion between plaster and base (75)

The procedure envisages to cut through the mortar layer circular test areas (0 =

50 mm) to a depth of approximately 5 mm into the masonry substrate. Subse­quently, on each test area a stainless steel pull-head plate (0 = 50 mm; thickness = 17 mm) must be glued with epoxy resin before carryng out the test after 24

Figure 7. Water absorption test on wal/ette sujected to acid rain test.

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hours. The test was carried out on the plastered surfaces subjected to the whole of the acid rain cycles as well as on the so-called "witness mark" surface, once the protective panels had been removed . For each specific case, five individual values of direct pull tensi le force were taken (figures 9-10).

Figure 9. Samples after acid rain test ready for the adhesive streng th tes ts.

4. RESUlTS

Figure 7 O. Apparatus for the adhesive streng th tes to

Data risen from the experimental activity have been processed in order to assess the two type of plastering mortars performances. Some of the most significant re­sults are reported in the following paragraphs. The examinated products have been evaluated by comparing the performaces of both types of mortar since, in the majority of the cases, reference values and acceptance limits are not available in standards.

4.1 . Plastering mortars

The mean compressive strength of the mortar, after a 28 days curing period, lies between 9 and 12 da/N cm 2

, depending on the mortar layer considered (figure 11). Low increments in the the compressive strength values were recorded after 60 days of curing. In general, at the dismantling time, strong shrinkage was ob­served for both types of mortar cured at 50% UR: about 1,8 mm compared to the total specimen length of 160 mm. This phenomenon, for each mortar typology, ended in a very short period between 10 and 16 days maximum. The determi­nation of water vapour permeabil ity (figure 14) showed similar permeabil ity val­ues for both mortar typologies, despite the different binder percentage included

Figure 7 7. Curing curve of one cooting mortor.

10 .c ./ t], 8 c ..,," Ol-~'" 6 t> E ~~ 4 ./ .- z Ul ro

./ "'-o ~- 2 a. io""" E --o o ()

o 7 14 21

time (days )

Figure 73. Curve of woter obsorption by capillority of 3 mortor samples.

Cl e Q)

"' ~ 0,04 (.)

.!: 1:' .,

o o 10 20

time (h)

28

30

Figure 72. Evoporation curve of 3 somples of one cooting mortor.

0,3

'\ f\ i'

~-::,. 1"' .....

o o 500 1000 1500

time (h)

Figure 74. Meon woter vopour permeobility volues of 2 mortors.

4

~ 3,5 .r;

3 - - -N

:2 2,5 - -C> OI 2 I- -o c 1 ,5 I- -lU OI 1 I- -ê OI 0,5 I- -o..

o A Type B Type

in the two mixture. The evaporation curves (figure 12), obtained from the mean values of the tests results on middle coat specimens, show a similar behaviour for each mortar typology. The crystallization tests highligted a weakness of the the specimens against salts. On the whole ali the tests reuslts (water permeability, capillarity, evaporation curve) show a high porosity of the two mortar typologies.

4.2, Small masonry samples

The freeze/ thaw test results, carried out in the climatic box, show the two mor­tar typologies different behaviour considering the loss of mass after the cycles (figure 15). The results derived from the test of the detemination of the resistance against sulphates seemed to be negative for both mortar typologies: a clear-cut

AI A2 8 1

sampJe tesled

82

Figure 75 . Some results from freeze/ thow tests.

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Figure 76. Mean values from air permeability Figure 77. Mean values from watertightness tests. tests.

95-13

c 65-13 .!II

tE ~ 35-13

lo< o

IJ brick o siporex I!I Tufo brick sipa-ex tufo

separation between the undercoat and the coat occured after 24 hours of im­mersion of the specimens in the salty solution. When deal ing with small samples, it should be taken into account that samples have to be prepared following the same technica l laying procedures used for full scale elements. In particu lar best resu lts rose from small samples cut from large plastered surfaces.

4.2.1. Watertightness test

The results related to some samples (brick, siporex, tuff) subjected to the test are visualized (figure 17) stressing the pressure mean value when dripping, through materiais, occurred.

4.2.2. Air permeabiJity test

The experimental data were processed using the standard formula which allows to determine the K coefficient, wh ich espresses the permeabi lity value of each tested material with no links with th ickness and externai cond itions (temperature and moisture). The K va lues of the samples made of siporex are lower than those obtained from samples made of brick. This phenomenon seems to be related to the material peculiarities ("closed cells"); on the contrary the K values of the sam­pies made of tuft, are much higher than those related to the other materiais (fig­ure 16). This could be put down to the strong tuff porosity.

4.2.3. Open time and optimal adhesion between mortar layers

The results risen from the experimental activity consist of visual survey of the samples during the curing period (recorded in photografic images), and of data obtained from adhesion tests carried out after a 60 days curing period at 20°C and 50% UR. Some ind ications came out and they can be synthetized as fol lows:

- samples prepared laying mortar fresh on fresh (the application of t he coat oc­curred within 4 hours starting from the laying of the undercoat) showed a small

cracking between the undercoat and the base material. The bigger was the thikness of the layer, the clearer the cracking . This phenomenon did not occur when the application of the coat took place at least after 8 hours from the un­dercoat application .

samples prepared laying mortar after 4 hours on from the application of the undercoat, showed a clear separaton between the coat and the undercoat 10-cated on the perimeter. The bigger was the thikness of the layer, the clearer the separation.

samples prepared with thin layers thickness (up to 1,5 cm included) in compli­ance with the envisaged waiting time for coating, except for the 4 hours case,

Table 2. Mortar adhesive strengtj values in the coated serena stone blocks.

Sample Waiting time before Mortar location of breaking Mortar location of breaking applying 2"' coat) / adhesion: Une inside the adhesion: line inside the mortar

(n.) mortar thickness Point 1 mortar coats Point 2 coats (hours/cm) (N/mm') (N/mm')

1 2 / 1 0,08 Inside the undercoat ° Inside the coat

2 2 / 1,5 0,13 Inside the undercoat 0,08 Inside the undercoat

3 2 /2 0,13 Inside the undercoat 0,07 Inside the undercoat

4 2 / 2,5 0,16 Inside the coat 0,20 Inside the coat

5 2 /3 0,15 The coat came of! 0,14 Inside lhe undercoat lhe undercoal

6 4 / 1 0,10 The coat carne of! 0,15 Inside lhe undercoal the undercoal

7 4 / 1,5 0,15 Inside lhe undercoat 0,13 The coaI carne of! lhe undercoal

8 4 / 2 0,10 Inside lhe undercoal 0,13 Inside the undercoat

9 462,5 0,05 The coat carne of! 0,05 Inside lhe undercoat the undercoal

10 4/3 0,15 Inside the undercoat 0,17 Inside lhe undercoal

11 8 / 1 0,08 Partly separation 0,11 Inside the undercoat undercoat/coal and

partly breaking

12 8 / 1,5 0,04 Partly separalion ° The coaI carne of! the undercoal/coal and undercoat

partly breaking

13 8 /3 ° Partly separation undercoat/base and partly undercoall

coat

14 24 / 1 ° Inside the undercoat

15 24 / U 0,19 Inside the undercoal

16 24 / 2 0,12 Inside the undercoal

17 24 12,5 0,10 Inside the undercoat

18 24/3 0,14 Separation 0,10 Inside the undercoat undercoat/base

19 72 / 1 0,08

20 72 /3 Separalion undercoal/base

21 168 / 1 0,14

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showed some eraekings on the surfaee. This phenomenon did not oecur for higher thiekness, that means starting from 2 em.

After the euring period, samples were subjeeted to the adhesion test in order to eheek the aetual separation between the different mortar layers. The test was ear­ried out in two points for eaeh plastered serena stone bloek. Moreover the bloeks, plastered with the undereoat only, were subjeeted to the same adhesion test in order to evaluate the adhesion to the stony base material. It was not possible to obtain the mortar adhesion results for ali the bloeks: in faet, samples plastered starting from 8 hours on showed many adhesion problems between the eoat and the undereoat; and samples plastered starting from 72 hours on showed a clear separation, deteetable by hand, between the eoat and the undereoat. After 168 hours this separation was mueh more evident. Some results are shown in table n. 2. In eonclusion the tests earried out eonfirmed that the mortar laying fresh on fresh, with at least three thin layers, seemed to be optimal for non porous base materiais . Moreover a 2 em eoat thiekness appeared to be the most suitable. Be­low this value some eraekings and eavities eould oeeur, probably due to the strong shrinkage aseribable to the loss of water whieh is not eontrasted by a fast tensile strength increase. Above 2 em of thiekness adhesion problems between layers risk to be overstressed . The present results eannot be extende to other kinds of mortar or base material, but this speeifie experimental proeedure is deemed to be effeetive if implemented taking the neeessary preeautions. In particular sam­pies preparation and laying proeedures must be seriously taken into aeeount. Fur­ther tests on plastered masonry walls essentially eonfirmed the results obtained on small samples.

Figure 8. Final coat erosion due to acid rain tes to

4.3. On wallets

Tests carried out on wallets provided both qualitative indications, supported by photografic images, and quantitative data based on instrumental measure­ments.

4.3.1. Determination of water penetrotion and leakage through masonry

Two samples were subjected to the testo At the end of the test (4 hours under pression of 500 Pa with a water film on the sample of about 3,5 I min/mq) no damp areas were observed on the other side of the wallets. In order to obtain fur­ther characterization data on the analysed plastering mortar, both samples were subjected to the water permeability under low pressure test and to the adhesion test. Comparing the permeability results of the wallets before and after the water penetration test, no relevant differences were found.

4.3.2. Acid roin test

As far as the surface appearance is concerned, an increasing erosion of the final coat could be observed as the test went on. In particular at the end of the first 75 cycles, the middle coat started to become visible and some small crackings, due to the already mentioned shrinkage phenomenon, were observed (figure 8). For what concerns the variations of the plastering mortar porosity and the adhesion between layers, see the following points.

4.3.2.1. Water absorption

An increase in water permeability values was recorded, for both mortar typolo­gies, already after the first 75 cycles of the acid rain test (figure 18).

Figure 78. Wallette befare and after 75 cicie af acid rain testo

12 Ü 10 ~ c 8 o R 6 o (/) 4 n cu Oi 2

after

. -:.:: ~ .--__ _ ..:~~ _ _ _ before

ro O 3 O 20 40 60 80

time (min .)

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4.3.2.2. Adhesion of the mortar to the base material

A certain degree of damage on the plastered surfaces of both samples, caused by the acid rain test, was noticed. In particular the break deepness was halved in consequence of the acid rain test (figure 19).

Figure 79. Some results from adhesive strength tests before and after acid rain test on wallettes.

5. CONCLUSIONS

[J bOfldSlrtngllt:ltfrllcidramlnl (Nlmml) obond stlllrogth b.f:lre <,cid r:110 IUI ( Nhnm'2)

The implementation of the experimental procedure implied relevant work as far as the survey of reference standards and the frequent development of new tests apparatus. The latter needs further research and improving anyway. Identyfing ad hoc procedures always implies some criticai phases, such as the preparation of the test samples: unless this passage is carried out properly and ali the necessary pre­cautions are taken, the prepared samples may show faults which are likely to in­terfere with the data liabelity. In particular, for what concerns small samples it would be better if they were the outcome of the cutting of large surface sample previously plastered as in real buildings. The ad hoc tests here described will be soon repeted (watertightness, air permeability and determination of the coating time), to confirm liability of procedure and to give detailed intructions for sample preparation. Both the standard tests and the experimental procedures here pro­posed are believed to be an useful contribution towards the definition of operat­ing tools, suitable for the evaluation of plastering systems in terms of initial per­formances and durability.

REFERENCES

1. Acid rain test TNO/9502/2 1996.

2. Determinazione della consistenza delle malte cementizie mediantre I'impiego di tavola a scosse UNI 7044 - 72.

3. Determination of the permeability of concrete to oxygen by Cembureau method.

4. Determination of the resistance of wallettes against sulphates and chlorides TNO document.

5. Determination of water vapour permeability of hardened rendering and plastering mortars prEN 1015 -19.

6. Essais recommandés pour mesurer I'altération des pierres et évaluer I'efficacité des method­es de traitement: absorption d'eau sous basse pression (à la pipe) RILEM Essai n. 11 4.

7. Essais recommandés pour mesurer I'altération des pierres et évaluer I'efficacité des method­es de traitement: coefficient d'absorption d'eau (capillarité) RILEM Essai n. 11.6.

8. Essais recommandés pour mesurer I'altération des pierres et évaluer I'efficacité des method­es de traitement: courbe d'évaporation RILEM Essai n. 11.5.

9. Essais recommandés pour mesurer I'altération des pierres et évaluer I'efficacité des method­es de traitement: cristallisation par immersion partiale RILEM Essai n. V.2 .

10. Essais recommandés pour mesurer I'altération des pierres et évaluer I'efficacité des method­es de traitement: cristallisation par immersion totale RILEM Essai n. V.1 .

11. Essais recommandés pour mesurer I'altération des pierres et évaluer I'efficacité des method­es de traitement: dilatation linéaire par absorption d'eau RILEM Essai n. 11.7.

12. Essais recommandés pour mesurer I'altération des pierres et évaluer I'efficacité des method­es de traitement: dureté superficielle mesurée par rebondissement RILEM Essai n. IV. 3.

13. Hydraulic shrinkage determination UNI 6687 -73 .

14. Membrane per impermeabilizzazione: determinazione dei la impermeabilità all'acqua - UNI 8202/21.

15. Methods of test for mortar for masonry: determination of adhesion of hardened rendering and plastering mortars pr EN 1015 - 12.

16. Methods of test for mortar for masonry: determination of freeze/ thaw resistance of clay ma­sonry units Pr EN 1338/ 96 ali C.

17. Methods of test for mortar for masonry: determination of service life of fresh mortar prEN 1015 - 9.

18. Metodi di prova dei cementi, determinazione delle resistenze meccaniche. UNI EN 196/1 Luglio 1991 - Ente Nazionale di Unificazione.

19. Ministerial Decree. Norme per la progettazione, esecuzione, e collaudo degli edifici in mu­ratura e per il consolidamento. D.M 20-11-87.

20. Ministerial Decree. Norme sui requisiti di accettazione e modialità di prova dei cementi . D.M 3-6-68.

21 . Standard Test Method for Water Penetration and Leakage Through Masonry - ASTM E 514-90.

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