| Engineering cement based composite materials have excellent ductility,crack resistance,and energy absorption capabilities,and have been used in the repair of earthquake resistant structures,bridge structures,dams,and retaining walls.However,due to the low melting point of PVA fibers(200℃ ～ 300℃),they are prone to failure in high-temperature(fire)environments,and their performance degradation is severe.Therefore,in this paper,fiber reinforced potassium magnesium phosphate cement based composites(MS/PVA MKPC)are prepared using potassium magnesium phosphate cement(MKPC)instead of ordinary cement and blended fibers to ensure that MS/PVA MKPC has certain strain strength characteristics at room temperature,while reducing its degradation after high temperature.The research team has completed the static performance research of MS/PVA MKPC in the early stage.This article focuses on the dynamic performance of materials at room temperature and after high temperature,and specifies indicators such as residual dynamic compressive strength after high temperature.The impact resistance of Brazilian disc(φ72 × 36 mm)was studied by split Hopkinson pressure bar(SHPB).The test parameters included temperature(20°C,100°C,150°C,200°C,500°C,800°C,1100°C),fiber content(single steel fiber: 1%,2%,3%;mixing: 0.5%PVA + 1.5%MS,1.0%PVA + 1.0%MS),water-binder ratio(0.2,0.25,0.3).The effects of various parameters on the failure mode,dynamic compressive strength,dynamic peak strain,dynamic elastic modulus,dynamic growth factor(DIF)and stress-strain curve of MS/PVA MKPC were discussed.The mechanism analysis was carried out by SEM-EDS,XRD and MIP.The main conclusions of the study are as follows :(1)At room temperature,with the increase of steel(MS)fiber content from 1% to 3%,the dynamic compressive strength of MS/PVA MKPC increases first and then decreases,and its dynamic peak strain increases.When the content of MS fiber is 2%,the improvement effect of dynamic compressive strength is the best.Under different strain rates,the dynamic compressive strength of M2.0 is 18.02% ～ 26.1% higher than that of M0.For M2.0 specimens,after experiencing 100°C,150°C,200°C,500°C,800°C and 1100°C respectively,the average dynamic peak strain increased by 128.2%,90.4%,28.3%,15.3%,53.1% and 62.5% respectively compared with M0.(2)Under the premise of controlling the fiber content to be 2%,the mixed PVA fiber can improve the deformation ability of MS/PVA MKPC at room temperature,and the effect is optimal when the PVA content is 0.5% and the MS fiber content is 1.5%.At different strain rates,the dynamic compressive strength of mixed fiber P0.5M1.5 is 2.9% ～ 7.4% lower than that of M2.0,but its dynamic peak strain is 1.1% ～ 10.8% higher than that of M2.0.(3)After high temperature,the residual dynamic compressive strength of MS/PVA MKPC with different fiber content decreased first and then increased with the increase of temperature.The strength loss rate of the specimen reached the maximum at 500°C ～ 800°C,and the loss range was 62.37% ～ 68.85%.After the temperature rose to 1100°C,the residual dynamic compressive strength of the specimen increased by 18.54% ～66.32% compared with 800°C.(4)After high temperature,proper blending of PVA fiber helps to reduce the strength loss rate after high temperature and increase the strength residual rate.For M2.0 specimens,after experiencing 100°C,150°C,200°C,500°C,800°C and 1100°C,the average dynamic compressive strength residual rates were 90.85%,58.79%,46.42%,32.53%,34.08% and 46.54%,respectively.For P0.5M1.5 specimens,after experiencing 100°C,150°C,200°C,500°C,800°C and 1100°C,the average dynamic compressive strength residual rates were 93.02%,59.57%,47.41%,29.94%,36.18% and 48.72%,respectively.(5)Considering the strain rate,fiber content,temperature and other factors,the DIF prediction formula and dynamic constitutive prediction model at room temperature and after high temperature are established.The experimental values are in good agreement with the predicted values,which provides a theoretical basis for the dynamic mechanical response of MS/PVA MKPC materials at room temperature and after high temperature. |
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