2. EXPERIMENTAL PROGRAME

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1 F1A04 The Study of FRP Sheet Effectiveness on Structural Behavioral of AAC Blocks Asghar V. Oskouei Department of Civil Engineering, Shahid Rajaee University, Tehran, Iran Shahed Rasouli Department of Civil Engineering, Shahid Rajaee University, Tehran, Iran ABSTRACT This article presents the experimental study on Autoclaved Aerated Concrete (AAC) specimens retrofitted by Fiber-reinforced polymer (FRP) sheets to improve the structural properties like compressive and tensile strength of elements that made of AAC. In this study, FRP sheets that are used to strengthen concrete structures are two types: Carbon and Glass. There are no sufficient studies for FRP application on AAC. Autoclaved Aerated Concrete is one such material that applied in recent years in the world. There is an interest in evaluating the feasibility of application of FRP to retrofit existing structures or elements made of AAC (e.g., beams, columns, etc.). The specimens used in this study include tensile specimens without FRP and with a scheme of FRP applied to the external surfaces for flexural specimens. The measured test data provide a basis for evaluating the accuracy of existing strength-design equations to predict the capacity of such specimens. Test results shows that the application of FRP at the bottom and top of the tensile specimens, increases the load and deflection capacities. Comparison of test results and calculated strengths shows that the existing guidelines such as ACI 440.2R and ACI 523.4R give safe estimates of flexural strength for AAC-FRP structural elements. KEYWORD Autoclaved Aerated Concrete (AAC), FRP, retrofitting, Reinforcing, Bending, tensile

2 1. INTRODUCTION According to premiums of Autoclaved Aerated Concrete (AAC) like lightweight that against earthquakes causes to reduce anticipated forces, so have a good temperature and acoustic isolation adapted with nature. Today s, Usage of produced parts of AAC as non-structural elements grows up. Using of AAC in structural members is rare Because of weak structural properties like little strength and brittle failure modes. Although more of constructed building in our country (Iran) (especially in towns and villages) have few stories, in this study tried to use retrofitted elements of AAC as structural parts. To do so, we applied fiber reinforced polymers (FRP) to strengthen compressive and tensile specimens. Autoclaved aerated concretes have percent weight of ordinary concretes and have compressive strength between 2 and 7 MPa. According to the required density and strength, AAC have about % air voids of its weight. In recent years broad studies were accomplished about using AAC structural members. Nasim Uddin and partners [1] in Alabama University, by wrapping carbon FRP in different templates by suction procedure around sandwich panels of AAC, tested them and resulted that rigidity and bending capacity of specimens increased. In that research flexural strength about 50% and shear strength about 300% relative to simple specimens (beams without FRP) increased but this procedure is expensive. Ali M.memari [2] in the state University of Pennsylvania had similar study to Nasim Uddin by wrapping Glass FRP to bending specimens increases flexural capacity about 70%. Tanner [3] in the Texas University has study about shear walls. Argudo [4] by constructing a model of two-story building with shear wall of AAC parts pay to seismic behavior of it and resulted that the shear walls conformed to the predictive models for flexural cracking and web-shear cracking. Damage did not occur in the AAC floor slabs or their connections to the walls, verifying that the proposed design provisions based on adhesion would produce a structure whose behavior was governed by the behavior of the shear walls. A comprehensive testing program at the University of Alabama at Birmingham (UAB) by Snow (1999) and Dembowski (2001) revealed the behavior of reinforced AAC. The floor panels and lintels were tested by four-point bending, and the wall panels were concentrically or eccentrically loaded to failure. Some of the results that are interesting to this research are as follows:1.the load at first crack or the cracking load ranged, on average, 30% of the failure load for the floor panels and lintels; 2.For the floor panels, Snow (1999)[6]reported all the failure modes to be brittle, sudden, and in shear mode. Dembowski (2001)[7], however, observed all failure modes to be brittle. Snow (1999) also noted that for the floor panels, the steel does not even begin to yield when the ultimate load has been reached; and3. For the wall panels, Snow (1999) observed a brittle and a sudden failure localized at the top of the panels. Dembowski (2001), however, described a failure due to the concrete shell around the reinforcement mat cracking randomly at the top or bottom of the panel under the axial load. Dembowski (2001) also stated that there were no signs of steel buckling. Moreover, according to Snow (1999), the steel has a very little role to play apart from holding the AAC together. The first cracking load is always very small and the load-deflection curves show negligible ductility. In This article trying to find effectiveness of FRP sheets on structural behavioral of AAC blocks like beams and columns by making specimens of them. 2. EXPERIMENTAL PROGRAME In this study, a total of 42 tensile specimens were tested. Tensile specimens divided into four different sets of specimens, According to the table 1 we have different template of retrofitting that in it: AAC: Autoclaved Aerated Concrete Numbers: Length of beam (cm) O: Original specimen (no reinforcing) C: Carbon FRP G: Glass FRP B: bottom face of specimens T: Top face of specimens H: specimens with hobnail Table 1 Simple tensile specimen s specifications specimens No. Length Reinforcing template AAC-40-O 3 40 O AAC-60-O 3 60 O Total 6

3 Table 2 Speciation of tensile specimens wrapped by FRP specimens No. Length Reinforcing template AAC-40-C-B 3 40 B AAC-40-C-B&T 3 40 B&T AAC-40-C-B&T&H 3 40 B&T&H AAC-60-C-B 3 60 B AAC-60-C-B&T 3 60 B&T AAC-60-C-B&T&H 3 60 B&T&H AAC-40-G-B 3 40 B AAC-40-G-B&T 3 40 B&T AAC-40-G-B&T&H 3 40 B&T&H AAC-60-G-B 3 60 B AAC-60-G-B&T 3 60 B&T AAC-60-G-B&T&H 3 60 B&T&H Total specimens 6 Figure 2 Perspective view of type B Figure 3 Perspective view of type B&T Figure 1 shematic figure of wrapping specimens by FRP According to table 1 we have two simple tensile specimens without any reinforcing. One of sets has 40 cm length and another set have 60 cm. In the table 2 we have three kind of retrofitted AAC tensile specimens that wrapped by CFRP and GFRP. For example AAC-60-C-B&T&H means that this case have 60 cm length and in this case uses CFRP (C) in the both sides bottom and top (B&T) with using hobnails of FRP (H)for more anchoring sheet to specimen surface. For others we can understand the template of retrofitting by attention to both table 2 and figure 1.By attention to figures 2, 3 And 4 another schematic perspective of specimens is shown. Figure 4 Perspective view of type B&T&H FRP sheets and resin specification that are used in this study had shown in table 3 and 4. Fiber Type CFRP GFRP Table 3 Fibers specifications Commercial Tensile Stiffness Name strength (GPa) (MPa) SK-N SK-G Thickness (mm)

4 Item YC-CP A10 Table 4 Resin specifications Temp ( ) Pot Life ) Setting Time ) Mixing Ratio (Sub: Hardener) 3. DESCRIPTION OF EXPERIMENTS Standard Usage (kg/m2) 15~ : Most studies involving the testing of FRP strengthening beams have used variations of applying two concentrated loads on specimens (four-point loading test). In this study we use one concentrated load (three-point loading test). The apparatus of this test shown in figure 5. Three vertical linear variable differential transformers (LVDT) were used to measure deflections, one at mid span and the others at each load point were applied. The applied total load was recorded by Load Cell. Fiber strains were recorded by strain gauges that are applied to the bottom face of beams (specimens).the load was applied slowly and continuously until the specimen reached its ultimate load. The dead load of the load cell about 9 Kg and was calculated and the deflection of the test apparatus was measured and proven to be negligible. Figure 5 Setup and apparatus of tensile test (Unit of measurement: cm) 4. RESULTS AND DISSCUSSIONS OF OBSERVATION FROM THE EXPERIMENTS In the following figures the stress-strain of specimens were shown. By attention to Diagrams of figure 6we found that by using one layer Of CFRP at the bottom-type B (tensile side) of specimen the tensile (flexural) strength is increased about 4.6 times and longitudinal strain (along loading) grows up from 27 in simple manner to 60.this is shows that ductility is increased and failure mode that is brittle in simple cases changed to bending-compressive failure mode. Tensile strength of another reinforcing template type B&T about 5 times greater than type O and longitudinal strain receives to 65. By comparing the above diagrams (figure 6) it is obvious that Tensile strength of specimens that using Carbon FRP (CFRP) in the equal retrofitting type relative to specimens that is reinforced by Glass FRP sheets is about percent greater. But longitudinal strain in GFRP cases is 50% greater than CFRP specimens. The reason maybe depend on tensile strength of GFRP sheets that is less than CFRP sheets and causes greater strains on GFRP specimens (table2). According to stress-strain diagrams of specimens with length equal to 60cm (figure 7) we found that bending capacity increase in these specimens reduces to 50% of specimens with 60cm length. For example in specimens type C-B&T that is reinforced by Carbon FRP in both sides (top and bottom) tensile capacity increase is about 2.8 times greater than tensile capacity of type O. we can find that for thicker specimens we must use two or more layers of FRP sheets required for get higher capacity.complete results of all specimens were shown in table 5.FRP strains in all tests is between 100 to 250 and it is noted that FRP sheets receives to yielding point before AAC starin. It must note that using hobnails for anchoring sheets on specimens has little effect on flexural capacity. Table 5 Results summary of flexural tests Percent of Flexural Specimen Max capacity increase relative to type(o) AAC-40-O AAC-40-C-B AAC-40-G-B AAC-40-C-B&T AAC-40-G-B&T AAC-40-C-B&T&H AAC-40-G-B&T&H AAC-60-O AAC-60-C-B AAC-60-G-B AAC-60-C-B&T AAC-60-G-B&T AAC-60-C-B&T&H AAC-60-G-B&T&H

5 Figure 6 Stress-strain diagram of tensile specimen (length = 40 cm)

6 Figure 7 Stress-strain diagram of tensile specimen (length = 60 cm)

7 5. SUMMARY AND CONLUSIONS This study has provided a better understanding of the behavior of typical reinforced AAC members such as lintel beams strengthened with FRP composites. The observations from the tests have helped characterize the behavior of AAC lintels with different CFRP and GFRP strengthening options. Experimental results have shown that strengthening concrete beams with externally bonded FRP improves both shear and flexural capacities depending on how the FRP fabric is applied. The pattern and form of FRP sheet application plays a major role in the mode of failure and ultimate strength. Attaching FRP on the tensile face of the lintel (Type B) in order to improve flexural capacity may increase the load capacity. Results shows that using CFRP sheets is more effective than GFRP because CFRP have greater tensile strength than GFRP and is more flexible but CFRP is more expensive than GFRP and it is not having commercial feasibility to use CFRP sheets in the AAC elements. It is better to use GFRP systems to improve the structural elements of buildings. And finally results summarized in following items: Using Carbon FRP sheets in tensile side of specimens (length=40cm) increases bending capacity about 362 percent. Using Glass FRP sheets in tensile side of specimens (length=40cm) increases bending capacity about 300 percent. Using FRP sheets in both tensile and compressive sides have no very difference with specimens that have FRP sheets only on tensile side. There is no enough effect while using hobnails in specimens. We found that for retrofitting AAC blocks using glass sheets is effective and have economic feasibility. The optimum template of reinforcing for AAC blocks that is use of sheets on tensile side. In elements with thickness more than 10cm it is better to use more than one layer. ACKNOWLEDGEMENT The AAC materials for this study were donated by Silic Ara Plant in Zanjan, Iran. Omran sanaat ava Company provided the composite materials. The contribution by these material suppliers is gratefully acknowledged. REFERENCES [1] Nasim Uddin, Mohammed A. Mousa, Experimental and analytical study of carbon fiber-reinforced polymer (FRP)/autoclaved aerated concrete (AAC) sandwich panels Journal of Engineering Structures, University of Alabama at Birmingham, Civil, Construction and Environmental Engineering Department, United States [2] Ali M Memari, Andres Lepage and Jarin Setthachayanon An experimental study of autoclaved aerated concrete lintels strengthened with externally bonded glass FRP Journal of Reinforced Plastics and Composites published online 9 August 2010 [3] Jennifer E.Tanner DESIGN PROVISIONS FOR AUTOCLAVED AERATED CONCRETE (AAC) STRUCTURAL SYSTEMS PhD thesis The University of Texas [4] Jaime ARGUDO SEISMIC PERFORMANCE AND DESIGN OF UTOCLAVED AERATED CONCRETE (AAC) STRUCTURAL SYSTEMS 13th World Conference on Earthquake Engineering Vancouver, B.C., Canada August 1-6, 2004 Paper No. 541 [5] Snow, C., 1999, A Comprehensive Study of the Material Properties and Structural Behavior of AAC Products, MS thesis, CEE Department, University of Alabama at Birmingham, Birmingham, AL. [6] Dembowski J. A Study of the material properties and structural behavior of Plain and Reinforced AAC components. M.S. thesis. CCEE Department, University of Alabama at Birmingham; [7] A. Laukaitis, Influence of fibrous additives on properties of aerated autoclaved concrete forming mixtures and strength characteristics of products Construction and Building Materials 23 (2009)