FIBER GLASS REINFORCED PLASTIC REBARS FOR CONCRETE STRUCTURES

Abstract

An experimental program was conducted to develop Glass Fiber Reinforced Plastic (GFRP) reinforcing bars (rebars) for the first time in Pakistan using available local resources, with tensile and bond strengths closely conforming to the international standards. The average bond strength of locally developed GFRP rebars was evaluated using normal strength concrete through direct pullout and beam bond tests by varying the bonded length, rebar diameter, concrete cover, surface texture as well as the concrete strength. Sequence and methodology of research work was divided into three distinct phases, in which first two were related with the development of GFRP rebars. The optimum composition of resin mixture was determined first of all basing on barcol hardness criterion through hit and trial approach using standard pultrusion process. Fifty trial productions of GFRP rebars with barcol hardness tests were executed for this purpose, and the optimum composition of resin mixture was finalized. The next stage of experimental program was to achieve the optimized combination of three process parameters namely, fiber content, pull speed and heating die temperature for 9.5mm, 13mm, 16mm, 19mm, 22mm and 25mm diameter rebars. It was achieved initially through hit and trial approach using the optimum composition of resin mixture for 9.5mm and 25mm diameter rebars and production models were developed for these two rebar diameters relating the tensile strength of rebar with fiber content, pull speed and heating die temperature. These production models helped to reduce the trials for two comparable diameter rebars of 13mm and 22mm respectively. Similarly optimum combinations of process parameters were determined for remaining diameter rebars based on their production models developed on same analogy thus reducing the time and cost of GFRP rebars. Total 165 trial productions along with simple tension tests were executed for this purpose. Finally a single and comprehensive model named as ‘unified production model’ was developed in which fiber content, pull speed, heating die temperature, rebar diameter and its square were the main parameters. The experimental tensile strength results were validated using the unified production model. The unified model is recommended as a comprehensive guideline for the development of GFRP rebars in future where patent details are not available. iii ABSTRACT

GFRP rebar surface texture was finalized through preliminary bond study with plain GFRP rebars by conducting 16 direct pullout tests using four diameter, 9.5mm, 13mm, 19mm and 25mm rebars, two bonded lengths, 5.0 d b & 7.0 d b with concrete strength of 41.4 MPa, to check for comparable bond strength as per American reference GFRP rebars, Aslan-100 TM , developed by Hughes Brothers Inc. USA. The bond stress of plain rebars was found quite low, therefore, deformed uncoated rebars were next developed and subjected to simple direct pullout tests. A set of 24 simple direct pullout tests (without recording the stroke or slip values) was conducted using 27.0 MPa concrete by combining four diameter rebars of 9.5mm, 13mm, 19mm, & 25mm and three bonded lengths of 3.0 d b , 5.0 d b and 7.0 d b . Two pullout specimen sizes, Ø150mm x 300mm and Ø100mm x 200mm, were used. These deformed rebars exhibited the bond stress well comparable with the above reference GFRP rebars. The final production of deformed uncoated and sand coated GFRP rebars was made in six diameter rebars of 9.5mm, 13mm, 16mm, 19mm, 22mm and 25mm using optimum composition of resin mixture and optimum combinations of process parameters. Each lot of final production was tested for quality assurance tests including barcol hardness, tensile strength, tensile modulus of elasticity and the average bond strength. The average bond stress of locally developed deformed GFRP rebars was evaluated through 48 direct pullout tests using 41.4 MPa concrete, four diameter rebars of 9.5mm, 13mm, 19mm, & 25mm and three bonded lengths of 3.5 d b , 5.0 d b & 7.0 d b . Two pullout specimen sizes, Ø150mm x 300mm and Ø100mm x 200mm, were used for this purpose. The bond study was carried out by varying the bonded length, rebar diameter, concrete cover/confinement and surface texture of GFRP rebars. Average bond stress of locally developed deformed GFRP rebars in flexure was evaluated through six beams using 41.4 MPa concrete, two diameter rebars of 13mm and 19mm with above three bonded lengths by varying the bonded length as well as rebar diameter. The effect of joint action on average bond stress of primary beams of junctions was also studied using the same parameters as of individual beams. The bond evaluation studies were carried out to ensure the bond performance of locally developed GFRP rebars for their effective composite action in RC members. A model for predicting the average bond stress was developed basing on the direct pullout experimental results; half of which were used to calibrate the model and remaining half to validate. The proposed pullout bond model was further validated using the published data iv ABSTRACT

of direct pullout results by several researchers for the rebars whose surface textures were comparable to the developed rebars. The model prediction agreed closely with the experimental results. The beam bond experimental results were also in close agreement with the published beam bond results by several other researchers. Basing on the barcol hardness, tensile strength, tensile modulus of elasticity, bond strength comparisons with the ACI/ASTM requirements, reference GFRP rebars as well as experimental results of several researchers, it may safely be claimed that the successful development of GFRP rebars in Pakistan has been achieved, which is a major breakthrough considering the poor to moderate technological facilities available in Pakistan. The indigenous development process will help the country to economically develop and use the GFRP rebars in RC flexure members for special applications as well as to maintain the safety and durability of theses members.