12TH INTERNATIONAL

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

Bos

SHEAR TESTS OF THE URM PANElS MADE FROM DIFFERENT TYPES OF MORTAR

- AN EXPERIMENTAL STUDY

v. Bosiljkov1, R. Zarnié2 and v. Bokan Bosiljkov3

1 PhD, 510venian National Building and Civil Engineering Institute,

Dimiceva 12, 51-1000 Ljubljana, Slovenia

2 Professor, University of Ljubljana, Faculty of Civil Engineering and Geodesy,

Jamova 2, 51-1000 Ljubljana, 510venia

] Assistant Professor, University of Ljubljana, Faculty of Civil Engineering and Geodesy,

Jamova 2, SI -1 000 Ljubljana, 510venia

ABSTRACT

The effect of the modification of the mortar on the behaviour of the URM (UnReinfor­ced Masonry) solid brick single leaf masonry panels under shear loading were experi­mental/y investigated. The tests were performed on the device that was designed for tests of shear bearing capacity of cantilever wal/s under the constant vertical and cy­clic horizontal loading. In the first part of the testing programme the shear bearing capacity of the masonry made with three different types of ordinary mortar were eva­luated. Further modification of the mortar included the micro and macro reinforce­ment of the one chosen type of the ordinary mortar. For each type of the mortar 3 masonry panels were tested under the same leveI of pre-compression. The results of the testing are showing the benefits for shear bearing capacity of the URM that can be achieved just through different modifications of the mortar.

Key words: shear tests, URM panel, mortar, solid brick, mortar modifications, fibre, mesh.

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INTRODUCTION

A variety of additives that are available at the market today generate ideas how to improve mortars that are traditiona lly composed of mineral binders and sand. The lack of data on the influence of modifications of mortars may lead to misuse of additives. Short polymer fibres are somet imes used to improve mor­ta r toughness and flexibility, but their prime role is to reduce cracks induced by the process of mortar hardening . Our previous investigations of the role of poly­mers as binder and different lengths of polypropylene fibres (Bosiljkov 1996) showed that the ignorance of the behaviou r of these additives within the ma­sonry could provoke some further problems, which can effect the mortar-unit junction.

Another approach to improve masonry is to introduce non-metal reinforcement embedded in bed joint mortar. This way of reinforcement w ith in the bed joint is much more convenient for solid brick masonry because by using glass meshes w ith square openings (5x5 mm2) we can avoid the problems which arise from rus­ting and slippage which occurs when using steel bars as reinforcement of the bed joints. On the other hand the function of the mesh reinforcement is to relieve the bricks from stresses arising because of t he inhibition of lateral expansion (lateral strain) by the mortar, and thus to reduce the transverse tensile stresses in the brick. Previous research of the influence of that so-called 'soft' approach of rein­forcing bed joints (Jung, 1991; Bosiljkov, 1998 and Zarnié, 1998) with glass mes­hes and Sofronie, 1998 with plastic meshes) have showed some of the benefits which can be gained through compressive and diagonal testing of masonry ele­ments.

An extensive program of testing the influence of different mortar compositions was initiated in the mainframe of an international collaborative project. In the cu­rrent phase the investigation is focused on the influence of three different type of basic masonry mortars on the mechanical properties of biaxially loaded masonry. An extension was made by micro-reinforcing ordinary cement-lime mortar with 6mm polypropylene fibres (Figure 1-b) and macro-reinforcing cement-lime mor­tar with glass-f ibre meshes embedded with in its bed joint (Figure l-c).

Figure 7. Ordinary, micro and macro-reinforced masonry.

a) ord inary ma 50 nry b) micro· reinfo rced ma sonry c) macro-reinfo rced maso nry

TESTING PROGRAMME

The tests were divided into two parts: the preliminary testing of the constituents of the masonry (mortar, unit and their junction) and the main program of shear testing of masonry panels. In the ma in programme of shear testing of masonry panels, the influence of five different mortars on the mechanical properties of the solid brick masonry were evaluated.

The basic mortars and two modifications were composed in volume proportions of the following materiais:

• cement: sand in volume proportion of 1:4 (MIX 1),

• cement : lime: sand in volume proportion of 1:1 :6 (MIX 2),

• lime : sand mortar in volume proportion of 1 :3 (MIX 3),

• cement : lime: sand in proportion of 1 :1 :6 with addition of polypropylene fi­bres (MIX 4), and cement : lime: sand in volume proportion of 1 :1 :6 reinfor­ced by glass-fibres mesh embedded within the bed joint (MIX 5).

Binding materiais which were used are the Portland cement PC 30dz 455 accor­ding to the former Yugoslav codes and dry hydrated lime. As micro reinforcement commercial polypropylene fibres "Krenit" with a fibre length of 6 mm, cross-sec­tion size 35x250-600 11m, ultimate stress 340-500 MPa, elastic modulus 8.5-12.5 epa and ultimate strain of 8-10% were used. Commercial synthetic resin-im­pregnated glass-fibres mesh with square-shaped openings 5x5 mm2 was used as mortar bed joints macro-reinforcement. Ultimate tensile force of such twisted glass fibres in both longitudinal and perpendicular directions is higher than 1500 N and the ultimate strain does not exceed 3.5 %.

Figure 2. Boundary conditions for shear tests of URM pane/s.

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306

For each mortar mixture 3 masonry panels with dimensions 95x140 cm' and thickness of 12 cm were prepared. The shear tests of masonry panels were per­formed on the device that was designed for the tests of shear bearing capacity of cantilever walls with different dimensions, where rotation and horizontal displa­cement are released on the lower edge of the panel (Figure 2) . The vertical force was applied first and the horizontal cyclic displacement controlled load was then applied . The design of the testing machine enables the constant vertical load du­ring the testing. The levei of constant vertical load (precompression) was chosen as a 1/6 of the mean compressive strength of the masonry from the chosen type of mortar. The compressive strengths were derived through compressive tests of wallets (Bosiljkov, 1998).

The preliminary testing programme encompasses the tests of the constituents in the means of flexural and compressive tests of the mortar specimens according to prEN 1015-11 (prEN 1015-11 1993) and compressive tests of the units accor­ding to prEN 772-1 (prEN 772-1 1992), splitting tensile test and determination of IRA (Initial Rate of Absorption) of the units according to the prEN 772-11 (prEN 772-11 1992) and IRA of the pre-wetted unit ready for bricklaying. In the first part of the test programme the horizontal mortar joints were tested by means of bond wrench test of two -stack high masonry prisms. Ali the preliminary tests were ca­rried out approximately at the same time as the shear tests of masonry panels.

Preparing the specimens

Ali the masonry specimens were made with the thickness of bed joints between 12 and 14 mm. The bricks used for specimens had standard dimensions accor­ding to the former Yugoslav codes: 250 mm in length, 120 mm in width and 65 mm in height. They were extruded, solid and taken from the same batch. Ali bricks were pre-wetted before bricklaying . The pre-wetting procedure was water immersion of bricks for 30 minutes and their drying in the laboratory ambient conditions for 30 minutes. The masonry prisms and panels were for the first 24 hours additionally loaded with two courses of brick on the top of the specimens and cured under PVC foil and after that exposed to laboratory ambient condi­tions. Ali the specimens were prepared by the same qualified bricklayer. The mortar was batched by weight to assure consistent mix properties. After the water content had been adjusted in order to obtain the desired mortar workabi­lity, which was judged by the bricklayer, the consistency of the fresh mortar was measured by flow table and no re-tempering of the mortar during the brick la­ying was perm itted. From each mortar batch at least 3 mortar prisms (4x4x16 cm 3

) were prepared for flexural and compressive tests.

Test set-up and instrumentation

The test set-up is shown on the Figure 3. The testing sample (4) in the testing ma­chine presents a cantilever turned upside down inserted into a frame structure (3)

at the upper edge, and resting on a trolley (5), through which the vertical and horizontal loads (7) are introduced into it, on the lower edge. Constant vertical load is applied, with weight (1), which act through a lever (2) as a vertical load of the testing sample (4). The magnitude of the vertical load can be controlled either through the weight (1) or changing the position of the hinge (8) of the le­ver armo The free horizontal displacement and the rotation of the lower edge of the cantilever are provided by a hinge mechanism, which consists of a free rota­ting beam (6) and a trolley (5), which can freely slide over the rotating beam (6). The horizontal load (7) was applied through servo-hydraulic actuator with the ca­pacity of (250 kN.

Instrumentation of shear tests (Figure 4) was designed in such a manner that ali boundary conditions were carefully monitored. Before putting the specimen into the testing machine the steel plates were glued with epoxy resign to the upper and bottom surface of the specimen. With help of the plates the specimen was fi­xed (by screwing the steel plates) with the upper end into the frame structure and with the bottom end to the trolley.

The in-plane deformations of the wall panel were measured and monitored with 12 deformeters with the accuracy of 1 /-lm and 11 LVDT's with the accuracy of 10 /-lm. With deformeters U1 and U2 the overall vertical deformations were monito­red. On the record of these deformeters the opening of the flexural crack were monitored. With U3-U6 the boundary conditions were monitored as well as po­tential de-bonding of the masonry panel from the steel plates. With the defor­meters U7-9 in the combination with LVDT's LV4-6 the potential slippage and the

Figure 3. Test Set-Up.

.. ..

.. .. . . .. . . .. . . ..

.. . . .. o. " .. ..

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308

Figure 4: /nstrumentation of shear tests of masonry pane/s.

TLV11 LV6

~ jjll7 11 F c:::J Ir

li\. c:::J[Z ~c:::J " 11

11 ..1. J III i= ~CJ \. 11 .r U2i=

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IV 11" 11 LV4 11 " 11\.

I ZJc:::J \.11

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f:~('~ lo.l~obF I

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LV1 95an

FRONTSIDE BACK SIDE

Figure 5. Disp/acement histories.

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30 - - - - - -,- - - - - - T - - - - - - ,- - - - - - r - - - - - -

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O 1000 2000 3000 4000 5000 Time [s]

opening of the shear cracks were monitored. Vertical deformations in the middle third of the specimens were monitored with the deformeters U1 0-12. With those measuring also the changes of the boundary conditions to the axis of symmetry of the panel were captured very well. With LVDT's LVl-6 the in-plane curvature of the specimen were captured very precisely. The difference between LV1 and

LV2 was indicator for potential slippage between the panel and steel plate. The measuring pair of devices LV7-8 and LV9-10 is standard measuring position for capturing shear deformation of the masonry. The only difference was that the first pair (LV7-8) was put for measuring masonry on the local levei, while the other pair (LV 9-10) were put to measure global shear behaviour of masonry panel.

Each specimen was subjected to a prescribed lateral displacement history under a constant axial load (Figure 5).

After the first three cycles which were repeated at three different levei (elastic 10-ading) and were the same for each type of masonry the increasing step of the la­teral displacement was each time adjusted according to the type of the mortar mixture.

Each time when some new crack pattern were formed the same lateral displace­ment were repeated twice.

During the testing the crack pattern were carefully observed and sketched, so that the later on it was possible to compare them with the recorded deformations which were gained through measuring devices. With such approach we could re­latively precisely appraise the appearance of the flexural and shear cracks as well as beginning of rocking of the specimens.

ANAL YSIS OF TEST RESUL TS

Preliminary tests

The results of preliminary tests of the hardened mortar (Table 2) are showing that with the modification using the polypropylene fibres (MIX 4) both the compres­sive and tensile strength of the mortar prisms slightly decrease in compare to the reference cement-lime mortar (MIX 2). On the other hand the toughness of such modified mortar was increased (Bosiljkov, 2000). The relation between the values for the basic mortars (MIX1,2 and 3) was as expected. Cement mortar (MIX 1) had for 46% higher compressive strength in compare to the cement-lime mortar and for 34% higher flexural strength. The results for lime mortar (MIX 3) were as we had expected at least ten times lower in comparison to the cement mortar.

Table 7. Results of testing of the hardened mortar.

MIX 1 MIX 2 MIX3 MIX 4 MIX 5

Number 01 specimens 9 9 9 9 9

Age 180 180 300 180 180

Compressive strenght I~ (MPz) 13.85 9,47 1,13 7.69 9.57

C.O.V. 4% 6% 10% 6% 8%

Flexural strenght Im. (Mpa) 3.72 2.76 0.37 2.31 2.85

C.o.v. 5% 13% 27% 9% 5%

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3 10

Table 2. Results of testing of the brick.

Tesllype Number 01 specimens Mean value c.o.v. Compressive strength f" (MPa) 15 19.52 19%

Splitting tensile slrength f", (MPa) 6 1.89 8%

IRA of brick (prEN 772·11) (kg/(m' min) 10 2.57 5%

IRA of prewetted brick (kg/(m' min) 10 0.12 2%

Table 3. Results of the Bond Wrench testing.

MIX 1 MIX 2 MIX 3 MIX4 MIX 5

Number of junctions 8 8 8 8 8

Bond strength fjtb (MPa) 0.431 0.342 0.127 0.404 0.369

C.O.V. 21% 16% 24% 9% 18%

The results of testing brick (Table 2) are showing that the ratio of the compressive and tensile strength of the brick was as it was expected about 10%. The chosen pre-wetting procedure of the brick before bricklaying had significantly influenced the IRA, so from that point of view we can say that the chosen way of pre-wetting the brick had diminished the influence of the IRA on the brick-mortar junction.

The test results of testing the brick-mortar junction by means of Bond Wrench tests have opened some new perspectives of the influence of different mortar modifications on the strength of the bond. Some previous assumptions that we had in mind were that due to the presence of the polypropylene fibres in the interface between brick and mortar, and therefore smaller interfacial zone between brick and binder, a lower fle­xural strength would be expected for the specimens made with MIX 4. The obtained results did not confirm this assumption (Table 3). Obviously, in this kind of mortar the polymeric fibres had taken over the early tension stresses which arose during the first days of curing the specimens, caused mainly by shrinkage of the mortar. Also the fai­lure of bond was not as sudden as it was observed for the other mortar mixes. The fai­lure propagated in a more gradually manner. Our other concern that the presence of glass fibre mesh within the joint can provoke failure in the contact zone between mor­tar and mesh and thus worsen the results of Bond Wrench testing also were not justi­fied. Not in the one single case we have got a failure in the contact zone between mor­tar and mesh. The results of Bond Wrench testing of macro-reinforced morta r (MIX 5) were almost the same as for reference mortar (MIX 2). It is worth to mention that in the contrast to other mortar mixtures, the failure mechanisms of the mortar-brick junc­tion for the lime mortar (MIX 3) was not in the contact between mortar and brick but through the mortar joint. Obviously for the lime mortar mixture the weakest point is not the mortar-brick junction but the mortar tensile strength within the bed joint.

Shear panels

According to the observation and measurements we have defined some basic crack patterns which can occur for the case of cantilever laterally loaded shear pa­nels (Figure 6).

Figure 6. Modes of fai/ure for a shear pane/o

/ ~~ ~

C !T! II " A

/ CJ

IL 11 I 11

CJ [==:J

" -H +H

ttittittti .. =:>

A - Flexural cracking (H,) which does not involve collapse but for moderate levei of precompression it can provoke a variation of the stiffness and the formation of hysteresis loops. It can be stabilised in one single course or it can be spread th­rough the height of the specimen.

B - Shear diagonal cracking (H,), which for moderate levei of precompression do­es not always present an ultimate limit state if only one direction of loading is con­sidered. For higher levei of precompression it can represent a limit state.

c - Rocking (toe crushing), can represent a limit state but for moderate levei of precompression. Together with the shear crack it can provoke an explosive fai­lure of the specimen.

On the basis of the test results of shear tests and the observations and monitoring of the developing of the crack pattern we have tried to summarised some basic conclusions of the behaviour of shear panels in dependence from the used mor­tar mixtures.

MIX 1 - The shape of the hysteresis loop is characteristic for rocking behaviour. Flexural cracking at this levei of precompression does not provoke the change of stiffness of the specimen. The flexural crack is situated in the first course and af­ter its occurrence it is very quickly localised (does not spread through the height or length of the specimen) . The shear crack usually start to form together with beginning of the rocking, which after a while provoke the failure of the specimen with widely opened shear crack and crushed masonry on both ends of the dia­gonal shear crack. The direction of the shear crack was in the direction of the main compressive stresses with the cracks, which were passed both through the units and mortar. The mortar in the head joints had a stiff behaviour, so that the cracks, which were passed through head joints, were situated on the brick-mor­tar junction.

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MIX 2 - The shape of the hysteresis loop is characteristic for rocking behaviour but with some differences in comparison to the masonry panels made from cement mortar (MIX 1). The occurrence of the flexural cracks did not change the stiffness of the panels. But for a difference from the previous case flexural cracks were not localised. With increasing loading they were spreading through the length of the specimen and thus changing the stiffness of the specimen. Shear cracks were pre­dominantly opened before the beginning of rocking . The shape of the shear crack was in the middle third of the specimen linear and it passed both through the units and mortar in the direction of the main compressive stresses. Towards the corner it has turned into zigzag shape and has passed mainly through unit-mor­tar junction. Behaviour of the mortar within head joint was the same as for pre­vious case.

MIX 3 - The shape of the hysteresis loops is more characteristic for the shear be­haviour of the panels with strong dissipation of energy. Very important for lime based masonry is the crushing of the mortar from the joints, which were presen­ted ali through the testing . The appearance of the flexural cracks has induced the change of stiffness of the panels. Flexural cracks were not localised and they we­re spread both through the length and the height of the specimens. The shape of the shear cracks were zigzag ali through the specimen, but for a difference from previous two cases the orientation of the cracks through the units were not in the direction of the main compressive stresses but they were mostly concen­trated through the units in that direction. Low tensile strength and soft behaviour of the mortar within the joints (both bed and head joint) have provoke that the cracks which were passed through joints were not situated in the brick-mortar junction but within the joints themselves.

MIX 4 - Overall behaviour of those panels were very compact. The shape of the hysteresis loops were characteristic for rocking . For a difference from MIX 1 and MIX 2, the first f lexural cracks have occurred in the second course of the panels. With the increasing the load the flexural cracks were spreading through the length of the specimens and thus provoke the changes in the stiffness of the spe­cimen. Despite the ductile behaviour of the micro-reinforce mortar, which was observed during the Bond Wrench tests such behaviour, were not noticeable du­ring the opening of the flexural cracks. The failure of the specimens was predo­minantly because of rocking. The shear cracks, which were occurred shortly be­fore the rocking where oriented in the direction of the ma in compressive stresses but without, distinguish one. Instead of it there were many closely spaced shear cracks passing both through the unit and the bed joints in the direction of the main compressive stresses. After the fa ilure of the specimens it was observed that the head joints were not properly fulfilled due to the problems of workability of fresh micro-reinforced mortar.

MIX 5 - Overall behaviour of masonry panels made f rom macro-reinforced ce­ment-lime mortar were up to the beginning of opening of shear cracks almost the same as it was observed in the case for the reference mortar MIX 2. It is worth to mention that the shear cracks opened in both cases at the same levei of lateral

force. But in the case of macro-reinforced masonry panels the shape of the shear cracks were much more alike as it was observed for the MIX 4. It is obvious that the presence of either polypropylene fibres or glass mesh which have prevented propagation of the crack through the height of the specimens are inducing the higher tensile strains within the units itself which have for the consequences the dense crack pattern within the units. The macro-reinforced mortar has provoked much more ductile behaviour of the specimens with strong dissipation of the energy. The beginning of the rocking mechanisms did not provoke the failure of

Figure 7. Experimental lateral displacement -lateral resistance hysteresis loops.

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a) MIX 1

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c) MIX 3

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e) MIX 5

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the specimens. The failure was a consequence of the softening of the masonry material within the middle third of the specimen, which sometimes provoke an explosive collapse.

Some characteristic types of hysteresis behaviour of laterally loaded masonry pa­nels in dependence from the mortar mixture are represented in the following fi­gures (Figure 7).

In order to quantify the influence of different mortar types on the overall behaviour of biaxially loaded masonry first we had to idealise the experimental envelopes. The bilinear idealisation of the experimentally gained hysteresis envelope was evaluated by taking into account the equal energy dissipation capacity of actual and idealised panels: the areas below the actual and bilinear idealised curves were equal.

To idealise the experimental envelope a three limit states in the observed beha­viour of the tested panels were defined as follows:

• Crack limit, determined by displacement b" and resistance H" at the formation of the flexural crack H, in the panel, which change the slope of the envelope.

• Maximum resistance determined by maximum resistance Hma" attained during test, and corresponding displacement bHma< '

• Ultimate state determined by maximum displacement attained during test bma< and corresponding resistance H.ma<'

The bilinear idealised curve is thus defined by its idealised resistance Hu and its ef­fective stiffness K.,. The effective stiffness of the panel, which represent the initial slope of the idealised envelope, is defined as a secant stiffness at the formation of flexural cracks. And it is calculated as the ratio between the resistance and dis­placement of the panel at crack limit as K., = H, / b".

Figure 8. Hysteresis envelope and its bilinear idealisation.

Hmax ,--------=,....,.-=::-----,

Hu

ómax

The results of testing and calculation of the basic parameters of shear tests of the URM panels are presented in the following table (Table 4), where value !J,uk repre­sent ultimate ductility factor and is defined as !J,uk= bm., / b •. The parameter (Jo re­present the levei of precompression.

On the basis of the experimental results presented in the table (Table 4) we can see that there exist statistically significant differences which approve the influen­ce of the different mortar modifications on the mechanical and deformation cha­racteristics of the laterally loaded masonry which are ma de from stiffer mortar mixtures (MIX 1,2,4 and 5) and a lime based mixture (MIX 3).

The following conclusions are made on the basis of the analysis of variance (ANO­VA method).

By using cement mortar instead of cement-lime mortar (MIX 1 vs. MIX 2), we can gained up to 40% higher shear resistance with almost the same stiffness of the specimens. On the other hand by modifying cement-lime mortar either by micro ar 'soft' macro-reinforcing we can gained up to 25% higher shear resistant ma­sonry with lower stiffness and higher deformation characteristics. The last state­ment should be taken with reserves beca use beside that we had at least two or three specimens for each type of masonry the levei of significance was too high for comparison of the displacement characteristics among different types of ma­sonry.

The trend among the results of the flexural resistance (Hf) for different types of masonry is almost the same as it was observed at the Bond Wrench tests: the hig-

Tab/e 4. Resu/ts af shear testing af URM pane/s.

No (l. H_ ô,.,. o~ H, H, K. õe ~~ H,

sp. (MPa) (kN) (mm) (mm) (kN) (kN) (kN/ mm) (mm) (kN)

MIX 1 2.72 mean

96.6 8.3 11.7 90.0 59.5 39.2 2.7 4.5 65.6 value

c.o.V, 39 46 40 51 56 12

(%)

MIX 2 2.00 mean

71.6 10.4 12.0 63.8 33.5 39.8 1.6 7.5 67.5 value

c.o.v. 33 32 17 30

(%)

MIX3 1.16 mean 44.6 9.5 12.5 39.8 23.3 18.4 2.6 5.9 27.9 value

c.o.v. 10 15 18 13 35 53 45 63 13

(%)

MIX4 2.42 mean

87.8 13.9 15.5 80.0 47.2 33.6 2.4 6.7 81.1 value

c.o.v. 8 39 38 14 21 14 72

(%)

MIX5 2.54 mean 92.2 13.4 20.5 81.7 51.5 33.4 2.5 8.5 67.6

value

c.o.v. 20 10 11 51

(%)

315

37 6

hest flexural resistance for cement mortar (MIX 1) and the lowest for lime mortar (MIX 3). By using micro-reinforced mortar mixture we can improve the flexural resistance up to 40% and the resistance of the masonry to the shear cracking (H,) up to 20% in comparison to the reference mortar MIX 2. By macro-reinforcing there are no improvement in the resistance to the shear cracking but the flexural resistance can be improved up to 50%.

There are not statistically significant differences among the different types of ma­sonry for the ultimate ductility facto r !luk (levei of significance >10%). The only thing that we can conclude is that the ultimate ductility factor for cantilever she­ar walls varies between 4.5 for cement mortar MIX 1 and 8.5 for macro-reinforced cement-lime mortar MIX 5.

CONCLUSIONS

The main conclusions can be summarised as follows:

• Just by testing the constituents of the masonry we can not gain the right im­pression of the influence of different mortar modifications on the mechanical and deformation characteristics of the masonry. On the other hand by testing the brick-mortar junction by means of Bond Wrench test we can get a valua­ble tool for estimation of the influence of different mortar modifications on the quality of the mortar-brick junction and thus the overall quality of the masonry as a composite material.

• By modifying the cement-lime mortar, which is the most common mortar in our earthquake prone areas, we can gain almost the same shear resistant pro­perties of the masonry as we had gained by using the very stiff cement mortar. Hence by different modifications we have got lower stiffness of the specimens and better ability for dissipation of energy. The influence of those modifications are also reflecting through different mechanisms of failure of the masonry for such modified mortars in comparison to the masonry made from basic stiff mortars (cement and ordinary cement-lime mortar) .

• Both micro and macro reinforcement of the mortar have their advantages and disadvantages. Working with macro-reinforced mortar takes much more time for the bricklayer, because he has to fulfil the bed joint with two layers of mortar with embedded mesh between them. On the other hand working with micro-reinforced mortar has its d isadvantages due to worse workability of such modified mortar. This problem can be solved by using additional plasticiser but in the amount, which will not harm the quality of the brick­mortar junction. The impact of both modifications on the overall behaviour of shear loaded masonry are almost the same with slightly better performan­ce of the macro-reinforced mortar masonry. On the other hand by micro­reinforcement of the mortar we can increase the homogeneity of masonry as a material.

ACKNOWLEDGEMENTS

The paper presents the results of the research work at University of Ljubljana, fi­nanced by the European Community through the project COPERNICUS CIPA - CT 94 - 0174 - ATEM and by The Ministry of Science and Technology of the Repu­blic of Slovenia. Their support is gratefully acknowledged.

REFERENCES

Bosiljkov, v., 1996, "On Modelling Mechanical Properties of the Masonry", M.Sc. Thesis, Univer­sity of Ljubljana, 510venia, October

Bosiljkov, V., Zarnié, R. & Bokan-Bosiljkov, V., 1998, "5trength and deformation properties of the URM brick wallettes under compression", The 8th North American Masonry Conference, Austin, Te­xas, June 3-6

Bosiljkov, V., 2000, "Experimental and numerical research on the influence of the modified mor­tars on the mechanical properties of the brick masonry", PhO Thesis, University of Ljubljana, 510-venia, March

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