Preparation And High Temperature Of PVA Fiber Toughened Cement-based Composites Study On Mechanical Properties

At present,ordinary concrete is limited in engineering application due to its brittleness,poor toughness and easy cracking and other shortcomings.In the future,engineering materials will be optimized in the direction based on high ductility and durability.In order to meet this demand,this paper prepared PVA fiber tougheningcement based composite material(PVA-FRCC).Meanwhile,in the face of frequent building fires,its heat resistance needs further study.Combined with the research status at home and abroad,This paper studied the preparation of PVA-FRCC,the influence of three influencing factors(fly ash content,fiber volume rate and water-binder ratio)on its mechanical properties,dynamic mechanical properties,degradation law of PVA-FRCC mechanical properties under high temperature(200℃,400℃,600℃ and 800℃)and the relationship between mechanical properties deterioration and temperature.The main research contents and conclusions are summarized as follows:(1)Through the compression and prismatic flexural tests on the PVA-FRCC cube,the results show that: With the increase of water-binder ratio,the compressive strength and flexographic strength of PVA-FRCC decrease,and the increase of fiber volume percentage and fly ash content is conducive to improving the toughness of materials.The specimens have better integrity under load,and the increase of fiber volume percentage significantly improves the compressive strength and flexographic strength of PVA-FRCC.But the increase of fly ash content reduces the compressive strength and flexural strength of PVA-FRCC.(2)Through uniaxial tensile tests on PVA-FRCC,the results show that both PVAFRCC specimens with water-binder ratio of 0.26 and 0.28 have good tensile properties,and there is little difference in ultimate tensile strain between the two specimens,but the initial cracking strength of the latter is lower than that of the former.The specimens with60% fly ash content have good strain-hardening characteristics and multi-crack cracking characteristics,while the specimens with 70% fly ash content show better strainhardening characteristics,but the initial crack strength decreases.With the increase of fiber volume percentage,the tensile property of the specimen is improved,and the optimum value is reached when.(3)the fiber volume percentage is 2.0%.The specimen has good and stable tensile property and high tensile strain.The measured stress-strain curve is fitted with the constitutive equation of the simplified model of cement-based composites,and the fitting results are good.Combined with the previous part of the test to determine the optimal mix of PVA-FRCC,fly ash content of 60%,water-binder ratio of 0.26,fiber volume rate of 2.0% is appropriate.(4)The optimal ratio group was tested for compressive strength,flexural strength and uniaxial tensile properties after high temperature,and the degradation mechanism was analyzed to establish the relationship between temperature and mechanical properties after high temperature.Finally,basalt fiber and PVA fiber were mixed to optimize the compressive strength and flexural strength of cement-based composites.The results show that,when the temperature exceeds 200℃,PVA-FRCC no longer has the strain-hardening characteristics and presents a brittle failure mode,and its compressive strength and flexural strength deteriorate seriously.X-ray diffraction test results show that the hydration products affecting the strength of the matrix gradually decompose when the specimen exceeds 200℃,the mass loss rate increases,and the working performance loss of the specimen is serious.The mixing of 1.0vol% basalt fiber and 1.0vol% PVA fiber can better optimize the compressive strength and flexural strength of the cement-based composite at high temperature.