Axial Compressive Behavior Of CFRP-confined Lightweight Aggregate Concrete Reinforced With Hybrid Fibers

Lightweight aggregate concrete(LWAC)shows advantages on high specific strength,good thermal isolation,and environmental characteristic.It is a promising green material for construction.The addition of fibers is capable of improving the mechanical properties of lightweight aggregate concrete,adding that the toughness and the ductility can be modified,furthermore,the fatigue resistance and the durability of structural LWAC can be enhanced.Carbon fiber reinforced polymer(CFRP)has been extensively applied to the field of concrete structures’ repair.The brittleness,crack of shrinkage and dead load of structural LWAC can be reduced by using confinement of CFRP accompanied with enough strength and ductility.This paper investigated the axial compressive performance of CFRP confined LWAC by experimental program and theoretical analysis,the following main conclusions can be drawn:(1)9groups of prisms made of LWAC with different types and contents of fibers were cast and tested under axial compression.The failure process and the failure mode of hybrid fiber reinforced LWAC subjected to axial compression were studied,and the axial compressive stress-strain curves were obtained,by which the influences of fibers’ type and content on the compressive strength,peak strain,elastic modulus,and secant modulus were discussed,and the strengthening effect of fibers on the LWAC was also analyzed.Test results showed that the peak stress,peak strain and ultimate strain of LWAC can be improved by carbon fiber and hybrid fiber,while the presence of polypropylene fiber had a negative effect.Fibers decreased the elastic modulus and the secant modulus of LWAC,where specimens with single type of fiber was reduced by about 6.28%～25.65%,and specimens with hybrid fibers showed 9.42%～21.99%reduction in relevant indices.The hybrid of carbon and polypropylene fibers gave rise to best modification on the toughness of LWAC,single carbon fiber showed less one,and polypropylene had the relative worst effect.(2)30 standard cylinders were tested under axial compression considering experimental parameters including the type of CFRP sheet(jacket and wrap),type of fibers(carbon and polypropylene fiber),and(0,0.2%,and 0.4%)content of fibers,the failure process and failure mode of specimens were observed and analyzed,and the mechanical characteristics of CFRP confined LWAC under axial compression was studied.The effectiveness of CFRP sheet on the concrete strength and deformation was determined,and the effects of confining ratio,type of fibers and content of fibers on the axial compressive behavior of confined LWAC reinforced with hybrid fibers were discussed.The test results showed that the compressive strength and deformation capacity of LWAC were significantly improved by using CFRP confinement,and the increase of strength was about 5.5% ～ 58.4%,while the increase of axial deformation was about 62.8% ～ 492.7%.The effect of CFRP jacket on the compressive strength of specimens was significant,but the improvement effect on the deformation capacity of specimens was weaker than that of CFRP wrap;the addition of fibers reduced the strength of LWAC specimens,deformation capacity of specimens was also affected.With the same amount of CFRP sheet,better confining effect of CFRP wrap was obtained on the ductility of LWAC,and and the greater the strip width is,the better the improvement effect of ductility is.(3)The calculation of effective lateral strength of CFRP confined LWAC with different type of confinement was analyzed and determined.Existing test data related to FRP confined LWAC was reviewed and used to derive models of peak stress and peak strain.The analytical iteration model for axial compressive stress-strain relationship of CFRP confined LWAC was proposed based on Spoelstra’s work accompanied with the modification on the concrete elastic modulus,efficiency factor of CFRP,confinement of fibers,and the peak stress and strain.Typical constitutive models of FRP confined concrete were compared to evaluated the proposed model,it was found that the established model showed better precision to the axial compressive stressstrain curve of CFRP confined LWAC.The study on the axial compression test of hybrid fiber reinforced LWAC and CFRP confined LWAC,and established the stress-strain relationship model of CFRP confined LWAC,which can enrich the axial compression test data of CFRP confined LWAC.It is of great significance for CFRP confined LWAC in engineering design and application.