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Strengthening of brick masonry with PVA fiber reinforced cement stucco
Construction and Building Materials 79 (2015) 255–262
Contents lists available at ScienceDirect
Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat
Strengthening of brick masonry with PVA fiber reinforced cement stucco Bengi Arisoy a,⇑, Emre Ercan a, Ali Demir b a b
Department of Civil Engineering, Ege University, Bornova, Izmir, Turkey Department of Civil Engineering, Celal Bayar University, Muradiye, Manisa, Turkey
h i g h l i g h t s Shear and compressive tests of brick masonry walls samples were performed. Three different types of brick were used. The effectiveness of PVA fiber reinforced cementitious stucco of masonry walls was investigated.
a r t i c l e
i n f o
Article history: Received 24 June 2014 Received in revised form 17 November 2014 Accepted 27 December 2014 Available online 28 January 2015 Keywords: Masonry Strengthening of masonry
a b s t r a c t This paper presents the behavior of masonry walls externally strengthened by poly vinyl alcohol (PVA) fiber reinforced cement plaster. Tensile weakness of masonry wall is improved by simply applying fiber reinforced cement (FRC) plaster on masonry surface. Strengthening by ductile materials, in order to maintain ductile behavior of masonry to resist shear forces would provide reduction in the crack development and crack width providing delay in failure. FRC was applied to surfaces of the masonry wall as stucco to prevent crack growth under shear effect. An experimental program was performed to study the response of unreinforced and retrofitted masonry walls with externally applied fiber reinforced cement mixture, under shear and compressive loading. The experimental results indicate that retrofitting masonry walls with PVA fiber reinforced cement stucco increases the shear strength of the wall approximately half times in solid and high strength brick walls, 2.5 times in regular brick walls. Ó 2015 Elsevier Ltd. All rights reserved.
1. Introduction Unreinforced masonry buildings cover a large proportion of the building stock in Turkey. Especially in rural areas, brick masonry buildings are still the main building stile and a large portion of the population live in masonry buildings. In possible earthquake hazards, these buildings are likely to be damaged by causing life and property losses. Lately, upgrading such buildings in Turkey has become important. Many earthquake experiences show that masonry buildings are weak structures under seismic excitation, demonstrate poor performance, and are likely to develop cracks that are consequences of masonry failure. By suppressing crack development and/or crack progress, the failure of the masonry walls may be prevented [1]. There are various techniques to prevent crack progress by retrofitting masonry with ductile materials and there are many studies performed about these techniques, few resent ones are sited here
⇑ Corresponding author. E-mail address: [email protected] (B. Arisoy). http://dx.doi.org/10.1016/j.conbuildmat.2014.12.093 0950-0618/Ó 2015 Elsevier Ltd. All rights reserved.
[2–6]. One of the methods is to plaster the masonry wall by fibrous cementitious material. Although the idea of having fibrous material in the mortar goes well back in history, both the properties of fibrous materials and the properties of mortar are not sufficient to hold back large crack development. In order to successfully prevent crack formation and progress, suitable fibrous materials are needed to achieve a better bond between fibers and cementitious material [1]. Studies on fiber reinforced cementitious materials exhibit that such materials may be sufficiently ductile and are adequate to use as stucco in masonry. The presented study is an application of strengthening brick masonry wall using PVA fiber reinforced cement stucco. Cement retrofitted with fiber has increased flexural and tensile strength [1]. Tensile weakness of masonry can be lessened by using a material having better tensile strength like fibrous cementitious materials. Cement based mortar is much stronger than lime based mortar, and its use is important because the bond between the fibers and the mortar must be sufficient. The studies show that in order to provide adequate ductility, there should be enough bond strength between fibers and mortar [1]. Furthermore, cement based materials would hold surface of masonry better.
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2. Research significance The significance of the study mentioned in Section 1 has two main aspects: first, to prevent crack development under shear forces; second, in case of any failure in masonry wall, the collapse of the wall would be prevented by retrofitting FRC stucco, which is extremely important to prevent loss of life.
3.2.1. Mortar stucco In many local masonry buildings, masonry walls are usually plastered on both inside and outside surfaces to protect the masonry from environmental effects and to provide insulation. Regular mortar used to bind both the masonry blocs together and to cover the masonry wall is composed of Portland cement, lime, and sand. Material tests were performed to obtain the mechanical properties of the mortar. Composition, material and mechanical properties of regular mortar are given in Table 3. For the material properties EN-12390-3 [7] code was used. The testing set up is shown in Fig. 5.
3. Experimental program The experimental study consisted of 42 masonry wall samples. The masonry wall samples were build up with three different types of masonry bricks, testing for two different types of stucco, and testing under shear and compressive loads. The bricks used for samples were classified as solid bricks (Fig. 1a), hollow bricks (Fig. 1b) and high strength hollow brick (Fig. 1c). Although all these types of bricks are common and have a wide range of use in the construction industry in Turkey, solids bricks have not been used since the 1970’s, yet there are many masonry buildings built up using solid brick constructed earlier than the 1970’s. Material properties of the bricks used in the presented study are provided by the manufacturer and are given in Table 1. Wall samples were subjected to both axial compression and diagonal tension tests. The sample types and testing methods are presented in Table 2.
3.1. Test specimens The masonry wall specimens prepared for testing were 500 500 mm (19.68 19.68 in). The thickness of the specimens was limited by the width of the masonry bricks. Brick wall samples prepared using three different types of bricks are shown in Figs. 2–4. While the thickness of the wall sample manufactured using solid bricks is 10 cm (3.93 in), the others are 13.5 cm (5.31 in). Although variations in the thickness of the samples have effects on performance of the walls, the results for each type of wall is discussed separately so that the performances are considered for each kind of brick wall. In all samples, regular mortar was used as binding material for holding bricks together. Although the thickness of the mortar joints should be kept uniform, in some cases it cannot be uniform. This issue was ignored because the experimental study was intended to meet field application conditions. On the other hand, the stucco thickness may have a significant effect on the performance of the sample. Wall samples were plastered on both sides with the same type of stucco.
(a) Solid brick
3.2.2. Fiber reinforced cement stucco Fiber reinforcement is used to improve ductile behavior of the cementitious materials and mortar. Fiber reinforced concrete, both regular and lightweight, has been used selectively in the construction industry as exterior siding, interior wall panels, blocks, flooring, roofing, curtain walls, girders and columns, piers, pavement, bridge and road paving, earth retaining, tunnel lining and back filling, insulation (including pipe insulation), sewer systems, irrigation systems, void filling in dams and replacement of poor quality earth underneath an infrastructure. Although a lot of research about effects of fibers on cementitious composites has been performed, only a few are cited here [8–20]. These research results indicate that an increase in the tension strength of the composite is closely related with the material mechanical properties and the fiber amount. Fibers used in this study were polyvinyl alcohol fibers with diameter 37 lm, length 15 mm (0.59 in), density 1.30 g/cm3 (81.16 lb/ft3) and modulus of elasticity 40 GPa (5800 ksi). Material tests were performed to obtain mechanical properties of fiber reinforced mortar according to EN-12390-3 [7]. Fiber reinforced cement mortar composition used in this study is also given in Table 2.
3.2.3. Effect of fiber reinforcement in cement The tensile behavior of fiber reinforced composites can be divided into three stages: (1) basically linear up to first cracking, after first crack, progress of crack would be slowed down by fibers [21]; (2) multiple-cracking stage, also referred to as strain-hardening stage; (3) strain-softening stage also referred to as failure [22–23]. Generally failure would occur growing of microcracks. In the present study, the layer of fiber reinforced cement stucco over surface of the wall encounters tensile effect after the wall is loaded diagonally and diagonal cracks have occurred. The fracture modeling of the fiber reinforced cement stucco layer in respect to diagonal shearing loads of the wall may be studied future research.
(b) Hollow brick
(c) High strength brick Fig. 1. Brick samples: (a) solid brick, (b) hollow brick, and (c) high strength hollow brick.
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B. Arisoy et al. / Construction and Building Materials 79 (2015) 255–262 Table 1 Dimensions, material and mechanical properties of masonry bricks.
Solid Hollow High strength hollow *
Dimensions (length width height) cm (in)
Density g/cm3 (lb/ft3)
Compression strength* Pa (psf)
19 10 5 (7.5 4 2) 19 19 13.5 (7.5 7.5 5.3) 29 19 13.5 (11.4 7.5 5.3)
1.44 (90) 0.8 (50) 0.8 (50)
6–8 (0.12–0.16) 3–8 (0.06–0.16) 8–10 (0.16–0.2)
By manufacturer.
Table 2 Type of samples and applied tests descriptions.
DT reference NT reference YT reference DTS LDTS NTS LNTS YTS LYTS
Sample definition
Total number of sample
Number of samples undergo diagonal tension test
Number of samples undergo compression test
Solid brick wall sample without stucco Regular hollow brick wall sample without stucco High strength brick wall sample without stucco Solid brick wall sample with regular stucco Solid brick wall sample with fiber reinforced stucco Regular hollow brick wall sample with regular stucco Regular hollow brick wall sample with fiber reinforced stucco High strength brick wall sample with regular stucco High strength brick wall sample with fiber reinforced stucco
2 2 2 6 6 6 6 6 6
1 1 1 3 3 3 3 3 3
1 1 1 3 3 3 3 3 3
Fig. 2. (a) Solid masonry brick wall sample (b) brick assemblage.
Fig. 3. (a) Hollow masonry brick wall sample (b) brick assemblage.
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Fig. 4. (a) High strength hollow masonry brick wall sample (b) brick assemblage.
Table 3 Mix compositions and mechanical properties of mortar.
Regular mortar FR* mortar * **
Cement:lime:sand
Fiber**
Water/cement
Density g/cm3 (lb/ft3)
Cube sample compression strength MPa (ksi)
1:0.5:4.5 1:0:4.5
– 0.01
1.4 1.6
2.1 (131) 2.2 (137)
4 (0.6) 22–24 (3.2–3.5)
Fiber reinforced. By volume.
Fig. 5. Material test set up for regular mortar. 3.2.4. Bricks Three types of clay bricks were used to build up the wall samples. Dimensions, material and mechanical properties of the bricks were obtained from the manufacturer. Information about the bricks is given in Table 1.
4. Testing Each type of specimen was tested for compression and shear. All details of the performed tests are explained below. In addition, descriptions of the type of specimen tested and testing methods are given in Table 2. 4.1. Uniaxial compression tests The compression tests were performed according to EN 1052-1 [24]. The compression tests were carried out at a constant loading
Fig. 6. Solid brick wall sample plastered with regular stucco (NTS) under compression test.
rate equal to 0.1 mm/s, (0.0039 in/s) using a 250 kN (56.2 kips) loading capacity testing machine. Loads were measured by a 200 kN (44.96 kips) load cell and displacements were obtained using external potentiometers. Samples were loaded until complete failure. A sample under compression test is shown in Fig. 6, and a compression test result of sample is given in Fig. 7. The compressive strength (fcomp) of the wall is calculated as follows [2]:
f comp ¼
P A
ð1Þ
where P is diagonal shear load, A is cross section area of the wall.
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Fig. 7. Sample compression test result. Fig. 9. Diagonal shear test result of high strength brick wall plastered with regular stucco (YTS).
Fig. 10. Shear damage in bricks. Fig. 8. High strength brick wall sample plastered with regular stucco (YTS) under diagonal tension test.
5. Test results and discussion 4.2. Diagonal tension (shear) tests The diagonal tension tests were performed by same loading system mentioned above. ASTM E 519-02 [25] was used to configure the testing. A sample under compression test is shown in Fig. 8, and a diagonal test result sample is given in Fig. 9. Diagonal shear strength (fshear) of the wall is calculated as follows:
f shear ¼
0:707P An
ð2Þ
Failure pattern of the masonry walls without stucco, with regular stucco and with fiber reinforced stucco under compression loads were similar. Any effect of the fiber reinforced stucco on compression strength was not observed. On the other hand, the effect of fiber reinforced stucco in the diagonal tension test was exceeded expectations. In both, means of increase in load carrying capacity and failure pattern, the fiber reinforced stucco exhibits noteworthy success. Average shear loads and displacements and average compression load and displacements for each type of masonry wall samples are given in Tables 4 and 5, respectively. 5.1. Wall samples with regular mortar stucco
ðw þ hÞ An ¼ tn 2
ð3Þ
where P is diagonal shear load, An is net area, w is width, h is height, t is thickness of the specimen. n is percent of the gross area of the unit. n is adapted 1 for both solid and hollow bricks [26].
The overall behavior of the samples with and without regular mortar stucco exhibits approximately the same pattern. In both sample types, with and without stucco, failure occurred in bricks unexpectedly as seen in Figs. 10 and 11. In reality, cracks should progress in grouts without damaging bricks as seen in Fig. 12.
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B. Arisoy et al. / Construction and Building Materials 79 (2015) 255–262 Table 4 Shear load carrying capacity of the masonry wall samples. Diagonal tension test
DT reference NT reference YT reference DTS LDTS NTS LNTS YTS LYTS
Diagonal tension load kN (kips)
Displacement in shear mm (in)
Shear strength MPa (ksi)
71.6–77.4 (16.1–17.44) 31.1–36.9 (7.03–8.34) 68.3–72.8 (15.4–16.4) 72.3–76.7 (16.3–17.3) 94.6–137.8 (21.31–31.05) 32.9–35.6 (7.4–8.02) 89.1–94.7 (20.08–21.33) 69.3–71.8 (15.6–16.2) 106.8–112.6 (24.05–25.4)
0.083–0.165 (0.0032–0.0066) 0.075–0.143 (0.003–0.057) 0.09–0.12 (0.0036–0.048) 0.089–0.155 (0.0036–0.062) 0.61–1.27 (0.024–0.051) 0.098–0.21 (0.0039–0.084) 0.052–0.741 (0.021–0.029) 1.38–1.71 (0.055–0.068) 3.53–4.91 (0.14–0.2)
0.53–0.57 (0.077–0.083) 0.23–0.28 (0.033–0.041) 0.51–0.54 (0.074–0.078) 0.54–0.57 (0.078–0.083) 0.704–1.03 (0.102–0.15) 0.25–0.27 (0.036–0.039) 0.67–0.71 (0.097–0.103) 0.52–0.54 (0.075–0.078) 0.8–0.84 (0.116–0.121)
Table 5 Compression load carrying capacity of the masonry wall samples. Compression test
DT reference NT reference YT reference DTS LDTS NTS LNTS YTS LYTS
Comp. load kN (kips)
Disp. in comp. mm (in)
Comp. strength MPa (ksi)
112.5–116.1 (25.29–26.1) 108.9–113.3 (24.48–25.47) 113.24–117.8 (25.46–26.48) 113.1–115.9 (25.43–26.06) 113.8–115.82 (25.58–26.04) 108.5–114.1 (24.4–25.65) 110.6–116.8 (24.86–26.26) 128.42–132.1 (28.87–29.7) 147.53–152.1 (33.17–34.2)
0.05 0.05 0.05 0.05 0.05 0.05 0.05 0.05 0.05
1.18–1.22 (0.17–0.18) 1.15–1.19 (0.17–0.172) 1.19–1.24 (0.172–0.18) 1.19–1.22 (0.172–0.176) 1.2–1.22 (0.17–0.176) 1.14–1.23 0.165-(0.18) 1.16–1.23 (0.17–0.18) 1.35–1.39 (0.195–0.201) 1.55–1.6 (0.224–0.232)
(0.002) (0.002) (0.002) (0.002) (0.002) (0.002) (0.002) (0.002) (0.002)
Fig. 11. Brick failure due to shear. Fig. 12. Shear crack progress in grouts.
The solid brick wall sample without stucco (DT reference) and the solid brick wall sample with regular stucco (DTS), in Table 4, exhibited the same shear strength as 0.56 MPa (0.081 kips). On the other hand, the solid brick wall samples (DT reference and DTS) have higher shear strength than the hollow brick wall samples (NT reference and NTS), because solid bricks have higher compressive strength than hollow bricks (refer to Table 1). High strength bricks already have higher strength (Table 1) so that the wall samples (YT and YTS) produced with high strength bricks also have higher shear strength. As a result, regular stucco has no effect on the strength of the samples.
Regarding compressive strength of the masonry wall samples, all samples, except the samples produced with high strength bricks, have approximately the same compressive strength regardless of whether they have regular or fiber reinforced stucco. In Table 5, compressive strength of YTS and LYTS differs by 14%, but this difference may not originate from the effect of the fiber. 5.2. Wall samples with fiber reinforced mortar stucco As is seen from Table 4, the samples plastered with fiber reinforced stucco have 50–150% higher shear strength than the
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The experiment results indicate that compressive strength of the brick masonry walls are closely related with the strength of the brick. External retrofitting such as applying ductile stucco would not increase the compressive strength of the wall. On the other hand, ductile fiber reinforced cement stucco that is the subject of this present study would increase shear strength of the wall. The results obtained from diagonal tension tests indicate that retrofitting masonry walls with fiber reinforced cement stucco increases the shear strength of the wall approximately 0.5 times in solid and high strength brick walls, 2.5 times in regular brick walls. This outcome implies that strongly built masonry walls need more effective retrofitting in order to provide larger strength gain. Another observation in the diagonal tension test is that while brittle failure occurs in unreinforced masonry, exhibited ductile failure occurs in reinforced masonry, and this is considered an important issue in the overall behavior of any masonry structure. Fig. 13. Shear failure in fiber reinforced plastered samples.
Acknowledgments This study was supported by Ege University Research Foundation with research project number 2010MUH020. The authors also wish to thank Celal Bayar University, Faculty of Engineering, Department of Civil Engineering for permission to use their Structural Lab. facilities. References
Fig. 14. Diagonal shear test result of high strength brick wall plastered with fiber reinforced stucco (LYTS).
samples plastered with regular stucco. Fig. 13 shows an example of shear failure of the fiber reinforced concrete plastered samples. Fibers played a bridge role in transferring the shear load on two sides of the crack, exhibiting ductile behavior in a direction perpendicular to the crack pattern as seen in Fig. 13. As is seen from the graphic in Fig. 14, displacement perpendicular to the crack growth (in the figure mentioned as ‘‘Horizontal Displacement’’) is 5 mm (0.2 in) until complete failure which is considerably high compared to displacements in the samples with regular plastered stucco. Results indicate that the use of fibers is an effective way to prevent crack growth in shear in masonry walls.
6. Result This paper presents an experimental investigation on the retrofitting of brick masonry walls using fiber reinforced cement stucco. The relative ease of applying such retrofitting on masonry walls may provide significant use among other strengthening techniques. The use of stucco or plaster reinforced with fibers may provide a simple and effective way to protect masonry buildings from ruinous failure under lateral loads.
[1] Arisoy B. Development and fracture evaluation of high performance fiber reinforced lightweight concrete [Ph.D. thesis]. Detroit, MI, USA: Wayne State University; 2002. [2] Zimmermann T, Strauss A, Bergmeister K. Numerical investigation of historic masonry walls under normal and shear load. Constr Build Mater 2010;24:1385–91. [3] Luccioni B, Rougier CV. In-plane retrofitting of masonry panels with fibre reinforced composite materials. Constr Build Mater 2011;25:1772–88. [4] Papanicolaou C, Triantafillou T, Lekka M. Externally bonded grids as strengthening and seismic retrofitting materials of masonry panels. Constr Build Mater 2011;25:504–14. [5] D’Ambrisi A, Mezzi M, Caporale A. Experimental investigation on polymeric net-RCM reinforced masonry panels. Compos Struct 2013;105:207–15. [6] D’Ambrisi A, Mezzi M, Feo L, Berardi VP. Analysis of masonry structures strengthened with polymeric net reinforced cementitious matrix materials. Compos Struct 2014;113:264–71. [7] EN-12390-3. Testing hardened concrete – Part 3: Compressive strength of test specimen. [8] Bentur A, Mindess S. Fiber reinforced cementitious composites. London: Elsevier Science Publishers Ltd.; 1990. [9] Gopalartnam VS, Shah SP, Batson GB, Criswell ME, Ramakrishan V, Wecharatana M. Fracture toughness of fiber reinforced concrete. ACI Mater J 1991;88(4):339–53. [10] Weshatarana M, Lin S. In: Reinhardt HW, Namaan AE, editors. Tensile properties of high performance fiber reinforced concrete. RILEM. London: E & FN Spon; 1992. [11] Li VC, Mishra DK, Wu HC. Matrix design for pseudo-strain hardening fiber reinforced cementitious composites. Mater Struct 1995;28:586–95. [12] Banthia N, Dubey A. Measurement of flexural toughness of fiber reinforced concrete using a novel technique – Part 1: Assessment and calibration. ACI Mater J 1999;96(6):651–6. [13] Li VC, Wang S. Flexural behaviors of glass fiber reinforced polymer (GFRP) reinforced engineered cementitious composite beams. ACI Mater J 2002; 99(1):11–21. [14] Kayali O, Haque MN, Zhu B. Some characteristics of high strength fiber reinforced lightweight aggregate concrete. Cement Concr Compos 2003;25(2): 207–13. [15] ElGawady M, Lestuzzi P, Badoux M. A review of conventional seismic retrofitting techniques for URM. In: Proceedings of the 13th international brick and block masonry conference. Amsterdam; 2004. [16] Turco V, Secondin S, Morbin A, Valluzzi MR, Modena C. Flexural and shear strengthening of un-reinforced masonry with FRP bars. Compos Sci Technol 2006;66:289–96. [17] El-Dakhakhni WW, Hamid AA, Hakam ZHR, Elgaaly M. Hazard mitigation and strengthening of unreinforced masonry walls using composites. Compos Struct 2006;73:458–77. [18] Farooq SH, Ilyasb M, Ghaffarb A. Technique for strengthening of masonry wall Panels using steel strips. Asian J Civil Eng (Build Hous) 2006;7(6):621–38. [19] Seim W, Pfeiffer U. Local post-strengthening of masonry structures with fiberreinforced polymers (FRPs). Constr Build Mater 2011;25(8):3393–403 [Original Research Article].
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[20] Konthesingha KMC, Masia MJ, Petersen RB, Mojsilovic N, Simundic G, Page AW. Static cyclic in-plane shear response of damaged masonry walls retrofitted with NSM FRP strips: an experimental evaluation. Eng Struct 2013;50:126–36. [21] Shah SP. Do fibers increase tensile strength of cement based matrices. ACI J Mater 1991;88(6):595–602. [22] Marikunte S, Shah SP. Cement matrix Composites. In: Mallick PK, editor. Composites engineering handbook. Marcel Dekker Inc Publications; 1997. p. 1039–66. [23] Evans AG, Faber KT. On the crack growth resistance of microcracking brittle materials. In: Evans AG, editor. Fracture in ceramic materials toughening mechanisms, machining damage, shock. Noyes Publications; 1984. p. 109–36.
[24] EN 1052–1. Methods of test for masonry – Part 1: Determination of compressive strength. [25] ASTM E 519-02. Standard test method for diagonal tension (shear) in masonry assemblages. Philadelphia: ASTM standards; 2002. [26] The Brick Association. Technical Notes 39A – Testing for engineered brick masonry – determination of allowable design stresses, July/Aug. 1981 (Reissued December 1987). Technical notes on brick construction Centennial Park Drv. Suite 301, reston, VA; 1850.
Contents lists available at ScienceDirect
Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat
Strengthening of brick masonry with PVA fiber reinforced cement stucco Bengi Arisoy a,⇑, Emre Ercan a, Ali Demir b a b
Department of Civil Engineering, Ege University, Bornova, Izmir, Turkey Department of Civil Engineering, Celal Bayar University, Muradiye, Manisa, Turkey
h i g h l i g h t s Shear and compressive tests of brick masonry walls samples were performed. Three different types of brick were used. The effectiveness of PVA fiber reinforced cementitious stucco of masonry walls was investigated.
a r t i c l e
i n f o
Article history: Received 24 June 2014 Received in revised form 17 November 2014 Accepted 27 December 2014 Available online 28 January 2015 Keywords: Masonry Strengthening of masonry
a b s t r a c t This paper presents the behavior of masonry walls externally strengthened by poly vinyl alcohol (PVA) fiber reinforced cement plaster. Tensile weakness of masonry wall is improved by simply applying fiber reinforced cement (FRC) plaster on masonry surface. Strengthening by ductile materials, in order to maintain ductile behavior of masonry to resist shear forces would provide reduction in the crack development and crack width providing delay in failure. FRC was applied to surfaces of the masonry wall as stucco to prevent crack growth under shear effect. An experimental program was performed to study the response of unreinforced and retrofitted masonry walls with externally applied fiber reinforced cement mixture, under shear and compressive loading. The experimental results indicate that retrofitting masonry walls with PVA fiber reinforced cement stucco increases the shear strength of the wall approximately half times in solid and high strength brick walls, 2.5 times in regular brick walls. Ó 2015 Elsevier Ltd. All rights reserved.
1. Introduction Unreinforced masonry buildings cover a large proportion of the building stock in Turkey. Especially in rural areas, brick masonry buildings are still the main building stile and a large portion of the population live in masonry buildings. In possible earthquake hazards, these buildings are likely to be damaged by causing life and property losses. Lately, upgrading such buildings in Turkey has become important. Many earthquake experiences show that masonry buildings are weak structures under seismic excitation, demonstrate poor performance, and are likely to develop cracks that are consequences of masonry failure. By suppressing crack development and/or crack progress, the failure of the masonry walls may be prevented [1]. There are various techniques to prevent crack progress by retrofitting masonry with ductile materials and there are many studies performed about these techniques, few resent ones are sited here
⇑ Corresponding author. E-mail address: [email protected] (B. Arisoy). http://dx.doi.org/10.1016/j.conbuildmat.2014.12.093 0950-0618/Ó 2015 Elsevier Ltd. All rights reserved.
[2–6]. One of the methods is to plaster the masonry wall by fibrous cementitious material. Although the idea of having fibrous material in the mortar goes well back in history, both the properties of fibrous materials and the properties of mortar are not sufficient to hold back large crack development. In order to successfully prevent crack formation and progress, suitable fibrous materials are needed to achieve a better bond between fibers and cementitious material [1]. Studies on fiber reinforced cementitious materials exhibit that such materials may be sufficiently ductile and are adequate to use as stucco in masonry. The presented study is an application of strengthening brick masonry wall using PVA fiber reinforced cement stucco. Cement retrofitted with fiber has increased flexural and tensile strength [1]. Tensile weakness of masonry can be lessened by using a material having better tensile strength like fibrous cementitious materials. Cement based mortar is much stronger than lime based mortar, and its use is important because the bond between the fibers and the mortar must be sufficient. The studies show that in order to provide adequate ductility, there should be enough bond strength between fibers and mortar [1]. Furthermore, cement based materials would hold surface of masonry better.
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2. Research significance The significance of the study mentioned in Section 1 has two main aspects: first, to prevent crack development under shear forces; second, in case of any failure in masonry wall, the collapse of the wall would be prevented by retrofitting FRC stucco, which is extremely important to prevent loss of life.
3.2.1. Mortar stucco In many local masonry buildings, masonry walls are usually plastered on both inside and outside surfaces to protect the masonry from environmental effects and to provide insulation. Regular mortar used to bind both the masonry blocs together and to cover the masonry wall is composed of Portland cement, lime, and sand. Material tests were performed to obtain the mechanical properties of the mortar. Composition, material and mechanical properties of regular mortar are given in Table 3. For the material properties EN-12390-3 [7] code was used. The testing set up is shown in Fig. 5.
3. Experimental program The experimental study consisted of 42 masonry wall samples. The masonry wall samples were build up with three different types of masonry bricks, testing for two different types of stucco, and testing under shear and compressive loads. The bricks used for samples were classified as solid bricks (Fig. 1a), hollow bricks (Fig. 1b) and high strength hollow brick (Fig. 1c). Although all these types of bricks are common and have a wide range of use in the construction industry in Turkey, solids bricks have not been used since the 1970’s, yet there are many masonry buildings built up using solid brick constructed earlier than the 1970’s. Material properties of the bricks used in the presented study are provided by the manufacturer and are given in Table 1. Wall samples were subjected to both axial compression and diagonal tension tests. The sample types and testing methods are presented in Table 2.
3.1. Test specimens The masonry wall specimens prepared for testing were 500 500 mm (19.68 19.68 in). The thickness of the specimens was limited by the width of the masonry bricks. Brick wall samples prepared using three different types of bricks are shown in Figs. 2–4. While the thickness of the wall sample manufactured using solid bricks is 10 cm (3.93 in), the others are 13.5 cm (5.31 in). Although variations in the thickness of the samples have effects on performance of the walls, the results for each type of wall is discussed separately so that the performances are considered for each kind of brick wall. In all samples, regular mortar was used as binding material for holding bricks together. Although the thickness of the mortar joints should be kept uniform, in some cases it cannot be uniform. This issue was ignored because the experimental study was intended to meet field application conditions. On the other hand, the stucco thickness may have a significant effect on the performance of the sample. Wall samples were plastered on both sides with the same type of stucco.
(a) Solid brick
3.2.2. Fiber reinforced cement stucco Fiber reinforcement is used to improve ductile behavior of the cementitious materials and mortar. Fiber reinforced concrete, both regular and lightweight, has been used selectively in the construction industry as exterior siding, interior wall panels, blocks, flooring, roofing, curtain walls, girders and columns, piers, pavement, bridge and road paving, earth retaining, tunnel lining and back filling, insulation (including pipe insulation), sewer systems, irrigation systems, void filling in dams and replacement of poor quality earth underneath an infrastructure. Although a lot of research about effects of fibers on cementitious composites has been performed, only a few are cited here [8–20]. These research results indicate that an increase in the tension strength of the composite is closely related with the material mechanical properties and the fiber amount. Fibers used in this study were polyvinyl alcohol fibers with diameter 37 lm, length 15 mm (0.59 in), density 1.30 g/cm3 (81.16 lb/ft3) and modulus of elasticity 40 GPa (5800 ksi). Material tests were performed to obtain mechanical properties of fiber reinforced mortar according to EN-12390-3 [7]. Fiber reinforced cement mortar composition used in this study is also given in Table 2.
3.2.3. Effect of fiber reinforcement in cement The tensile behavior of fiber reinforced composites can be divided into three stages: (1) basically linear up to first cracking, after first crack, progress of crack would be slowed down by fibers [21]; (2) multiple-cracking stage, also referred to as strain-hardening stage; (3) strain-softening stage also referred to as failure [22–23]. Generally failure would occur growing of microcracks. In the present study, the layer of fiber reinforced cement stucco over surface of the wall encounters tensile effect after the wall is loaded diagonally and diagonal cracks have occurred. The fracture modeling of the fiber reinforced cement stucco layer in respect to diagonal shearing loads of the wall may be studied future research.
(b) Hollow brick
(c) High strength brick Fig. 1. Brick samples: (a) solid brick, (b) hollow brick, and (c) high strength hollow brick.
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Solid Hollow High strength hollow *
Dimensions (length width height) cm (in)
Density g/cm3 (lb/ft3)
Compression strength* Pa (psf)
19 10 5 (7.5 4 2) 19 19 13.5 (7.5 7.5 5.3) 29 19 13.5 (11.4 7.5 5.3)
1.44 (90) 0.8 (50) 0.8 (50)
6–8 (0.12–0.16) 3–8 (0.06–0.16) 8–10 (0.16–0.2)
By manufacturer.
Table 2 Type of samples and applied tests descriptions.
DT reference NT reference YT reference DTS LDTS NTS LNTS YTS LYTS
Sample definition
Total number of sample
Number of samples undergo diagonal tension test
Number of samples undergo compression test
Solid brick wall sample without stucco Regular hollow brick wall sample without stucco High strength brick wall sample without stucco Solid brick wall sample with regular stucco Solid brick wall sample with fiber reinforced stucco Regular hollow brick wall sample with regular stucco Regular hollow brick wall sample with fiber reinforced stucco High strength brick wall sample with regular stucco High strength brick wall sample with fiber reinforced stucco
2 2 2 6 6 6 6 6 6
1 1 1 3 3 3 3 3 3
1 1 1 3 3 3 3 3 3
Fig. 2. (a) Solid masonry brick wall sample (b) brick assemblage.
Fig. 3. (a) Hollow masonry brick wall sample (b) brick assemblage.
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Fig. 4. (a) High strength hollow masonry brick wall sample (b) brick assemblage.
Table 3 Mix compositions and mechanical properties of mortar.
Regular mortar FR* mortar * **
Cement:lime:sand
Fiber**
Water/cement
Density g/cm3 (lb/ft3)
Cube sample compression strength MPa (ksi)
1:0.5:4.5 1:0:4.5
– 0.01
1.4 1.6
2.1 (131) 2.2 (137)
4 (0.6) 22–24 (3.2–3.5)
Fiber reinforced. By volume.
Fig. 5. Material test set up for regular mortar. 3.2.4. Bricks Three types of clay bricks were used to build up the wall samples. Dimensions, material and mechanical properties of the bricks were obtained from the manufacturer. Information about the bricks is given in Table 1.
4. Testing Each type of specimen was tested for compression and shear. All details of the performed tests are explained below. In addition, descriptions of the type of specimen tested and testing methods are given in Table 2. 4.1. Uniaxial compression tests The compression tests were performed according to EN 1052-1 [24]. The compression tests were carried out at a constant loading
Fig. 6. Solid brick wall sample plastered with regular stucco (NTS) under compression test.
rate equal to 0.1 mm/s, (0.0039 in/s) using a 250 kN (56.2 kips) loading capacity testing machine. Loads were measured by a 200 kN (44.96 kips) load cell and displacements were obtained using external potentiometers. Samples were loaded until complete failure. A sample under compression test is shown in Fig. 6, and a compression test result of sample is given in Fig. 7. The compressive strength (fcomp) of the wall is calculated as follows [2]:
f comp ¼
P A
ð1Þ
where P is diagonal shear load, A is cross section area of the wall.
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Fig. 7. Sample compression test result. Fig. 9. Diagonal shear test result of high strength brick wall plastered with regular stucco (YTS).
Fig. 10. Shear damage in bricks. Fig. 8. High strength brick wall sample plastered with regular stucco (YTS) under diagonal tension test.
5. Test results and discussion 4.2. Diagonal tension (shear) tests The diagonal tension tests were performed by same loading system mentioned above. ASTM E 519-02 [25] was used to configure the testing. A sample under compression test is shown in Fig. 8, and a diagonal test result sample is given in Fig. 9. Diagonal shear strength (fshear) of the wall is calculated as follows:
f shear ¼
0:707P An
ð2Þ
Failure pattern of the masonry walls without stucco, with regular stucco and with fiber reinforced stucco under compression loads were similar. Any effect of the fiber reinforced stucco on compression strength was not observed. On the other hand, the effect of fiber reinforced stucco in the diagonal tension test was exceeded expectations. In both, means of increase in load carrying capacity and failure pattern, the fiber reinforced stucco exhibits noteworthy success. Average shear loads and displacements and average compression load and displacements for each type of masonry wall samples are given in Tables 4 and 5, respectively. 5.1. Wall samples with regular mortar stucco
ðw þ hÞ An ¼ tn 2
ð3Þ
where P is diagonal shear load, An is net area, w is width, h is height, t is thickness of the specimen. n is percent of the gross area of the unit. n is adapted 1 for both solid and hollow bricks [26].
The overall behavior of the samples with and without regular mortar stucco exhibits approximately the same pattern. In both sample types, with and without stucco, failure occurred in bricks unexpectedly as seen in Figs. 10 and 11. In reality, cracks should progress in grouts without damaging bricks as seen in Fig. 12.
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B. Arisoy et al. / Construction and Building Materials 79 (2015) 255–262 Table 4 Shear load carrying capacity of the masonry wall samples. Diagonal tension test
DT reference NT reference YT reference DTS LDTS NTS LNTS YTS LYTS
Diagonal tension load kN (kips)
Displacement in shear mm (in)
Shear strength MPa (ksi)
71.6–77.4 (16.1–17.44) 31.1–36.9 (7.03–8.34) 68.3–72.8 (15.4–16.4) 72.3–76.7 (16.3–17.3) 94.6–137.8 (21.31–31.05) 32.9–35.6 (7.4–8.02) 89.1–94.7 (20.08–21.33) 69.3–71.8 (15.6–16.2) 106.8–112.6 (24.05–25.4)
0.083–0.165 (0.0032–0.0066) 0.075–0.143 (0.003–0.057) 0.09–0.12 (0.0036–0.048) 0.089–0.155 (0.0036–0.062) 0.61–1.27 (0.024–0.051) 0.098–0.21 (0.0039–0.084) 0.052–0.741 (0.021–0.029) 1.38–1.71 (0.055–0.068) 3.53–4.91 (0.14–0.2)
0.53–0.57 (0.077–0.083) 0.23–0.28 (0.033–0.041) 0.51–0.54 (0.074–0.078) 0.54–0.57 (0.078–0.083) 0.704–1.03 (0.102–0.15) 0.25–0.27 (0.036–0.039) 0.67–0.71 (0.097–0.103) 0.52–0.54 (0.075–0.078) 0.8–0.84 (0.116–0.121)
Table 5 Compression load carrying capacity of the masonry wall samples. Compression test
DT reference NT reference YT reference DTS LDTS NTS LNTS YTS LYTS
Comp. load kN (kips)
Disp. in comp. mm (in)
Comp. strength MPa (ksi)
112.5–116.1 (25.29–26.1) 108.9–113.3 (24.48–25.47) 113.24–117.8 (25.46–26.48) 113.1–115.9 (25.43–26.06) 113.8–115.82 (25.58–26.04) 108.5–114.1 (24.4–25.65) 110.6–116.8 (24.86–26.26) 128.42–132.1 (28.87–29.7) 147.53–152.1 (33.17–34.2)
0.05 0.05 0.05 0.05 0.05 0.05 0.05 0.05 0.05
1.18–1.22 (0.17–0.18) 1.15–1.19 (0.17–0.172) 1.19–1.24 (0.172–0.18) 1.19–1.22 (0.172–0.176) 1.2–1.22 (0.17–0.176) 1.14–1.23 0.165-(0.18) 1.16–1.23 (0.17–0.18) 1.35–1.39 (0.195–0.201) 1.55–1.6 (0.224–0.232)
(0.002) (0.002) (0.002) (0.002) (0.002) (0.002) (0.002) (0.002) (0.002)
Fig. 11. Brick failure due to shear. Fig. 12. Shear crack progress in grouts.
The solid brick wall sample without stucco (DT reference) and the solid brick wall sample with regular stucco (DTS), in Table 4, exhibited the same shear strength as 0.56 MPa (0.081 kips). On the other hand, the solid brick wall samples (DT reference and DTS) have higher shear strength than the hollow brick wall samples (NT reference and NTS), because solid bricks have higher compressive strength than hollow bricks (refer to Table 1). High strength bricks already have higher strength (Table 1) so that the wall samples (YT and YTS) produced with high strength bricks also have higher shear strength. As a result, regular stucco has no effect on the strength of the samples.
Regarding compressive strength of the masonry wall samples, all samples, except the samples produced with high strength bricks, have approximately the same compressive strength regardless of whether they have regular or fiber reinforced stucco. In Table 5, compressive strength of YTS and LYTS differs by 14%, but this difference may not originate from the effect of the fiber. 5.2. Wall samples with fiber reinforced mortar stucco As is seen from Table 4, the samples plastered with fiber reinforced stucco have 50–150% higher shear strength than the
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The experiment results indicate that compressive strength of the brick masonry walls are closely related with the strength of the brick. External retrofitting such as applying ductile stucco would not increase the compressive strength of the wall. On the other hand, ductile fiber reinforced cement stucco that is the subject of this present study would increase shear strength of the wall. The results obtained from diagonal tension tests indicate that retrofitting masonry walls with fiber reinforced cement stucco increases the shear strength of the wall approximately 0.5 times in solid and high strength brick walls, 2.5 times in regular brick walls. This outcome implies that strongly built masonry walls need more effective retrofitting in order to provide larger strength gain. Another observation in the diagonal tension test is that while brittle failure occurs in unreinforced masonry, exhibited ductile failure occurs in reinforced masonry, and this is considered an important issue in the overall behavior of any masonry structure. Fig. 13. Shear failure in fiber reinforced plastered samples.
Acknowledgments This study was supported by Ege University Research Foundation with research project number 2010MUH020. The authors also wish to thank Celal Bayar University, Faculty of Engineering, Department of Civil Engineering for permission to use their Structural Lab. facilities. References
Fig. 14. Diagonal shear test result of high strength brick wall plastered with fiber reinforced stucco (LYTS).
samples plastered with regular stucco. Fig. 13 shows an example of shear failure of the fiber reinforced concrete plastered samples. Fibers played a bridge role in transferring the shear load on two sides of the crack, exhibiting ductile behavior in a direction perpendicular to the crack pattern as seen in Fig. 13. As is seen from the graphic in Fig. 14, displacement perpendicular to the crack growth (in the figure mentioned as ‘‘Horizontal Displacement’’) is 5 mm (0.2 in) until complete failure which is considerably high compared to displacements in the samples with regular plastered stucco. Results indicate that the use of fibers is an effective way to prevent crack growth in shear in masonry walls.
6. Result This paper presents an experimental investigation on the retrofitting of brick masonry walls using fiber reinforced cement stucco. The relative ease of applying such retrofitting on masonry walls may provide significant use among other strengthening techniques. The use of stucco or plaster reinforced with fibers may provide a simple and effective way to protect masonry buildings from ruinous failure under lateral loads.
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