Preparation And Properties Of Strain Hardening Cementitious Composites Reinforced With Non Surface Modified PVA Fibers

Strain hardening cementitious composites(SHCC)have the characteristics of high toughness and high ductility,and can be used to improve the earthquake resistance,impact resistance,and corrosion resistance of buildings.The fibers currently used for the preparation of SHCC are usually polyvinyl alcohol(PVA)fibers produced by Kuraray Co.,Ltd in Japan.PVA fibers are oil-coated on the surface to reduce chemical bond of PVA fibers and cement matrix,thereby improve SHCC ductility.This study is devoted to studying the effect of different domestic non-surface-modified PVA fibers and different cement matrixes,preparing SHCC reinforced with non-surface-modified PVA fibers,and further reducing economic and environmental costs of SHCC production while maintaining their high toughness and ductility.Firstly,with a type of PVA fiber without surface modification as the reinforcement at2% by volume,and using high volume fly ash in combination with superplasticizer,the possibility of preparing SHCC with PVA fibers was investigated.The results of compressive strength test and three-point bending test showed that the workability and compressive strength of matrix can be controlled by adjusting fly ash content and waterbinder ratio,combining with the effect of superplasticizer,so as to obtain the proper matrix mix ratio which is beneficial to fiber dispersion and meets the strength requirement of designing SHCC.In addition,the results of three point bending test also showed that the composites with PVA fiber without surface modification exhibited significant multiple cracking phenomenon and deflection hardening characteristic,and had excellent ductility and toughness.Secondly,the toughening and strengthening effect of different PVA fibers without surface modification within a fixed matrix material was investigated,and SHCC reinforced with several kinds of PVA fibers without surface modification were produced.Three matrices were selected,whose fly ash content was 0,50% and 67%,respectively.The five types of fibers include one PVA fiber with oil coated on the surface and four PVA fibers without surface treatment.Through three point bending test and uniaxial tensile test,with SHCC with oil-coated PVA fiber as a reference,the performance of composites containing fly ash and reinforced with four kinds of PVA fiber without surface treatment was compared and analyzed.The influence of fiber volume content was also studied for two fibers with high aspect ratio.Experimental results show that domestic PVA fiber without surface modification showed desirable toughening effect,and the bending performance of the composites with these fibres without surface treatment is similar to that of the composites with PVA fibers with oil coated surface.Finally,this study investigated the reinforcing effect of various kinds of PVA fibers within an alkali-activated matrix,and strain hardening alkali-activated composites were manufactured.Within a matrix of slag-fly ash alkali-activated cement cured at room temperature,the strengthening and toughening effect of five kinds of PVA fibers was examined by auniaxial tensile test.The uniaxial tensile test results showed that four kinds of PVA fibers including three without surface led to composites materials with multiple cracking and strain hardening characteristics under direct tension,and exhibiting high ductility.That is,these illustrated that we can to prepare high ductility strain hardening alkali-activated cementitious composites materials could be produced by using PVA fibers without surface modification.