基于NSGM(1,N)模型的RTSF/PVA矿渣混凝土高温后力学性能分析及预测

Analysis and Prediction of Mechanical Properties of RTSF/PVA Slag Concrete after High Temperature Based on NSGM(1,N)Model

为改善混凝土高温后的力学性能,以RTSF和PVA体积掺量以及矿渣替代率为变量,设置四因素三水平的正交试验,测试RTSF/PVA矿渣混凝土在200℃、400℃、600℃以及800℃后的残余抗压强度;结合电镜扫描分析高温后RTSF/PVA矿渣混凝土的微观结构;并采用一种新结构的多变量灰色模型对RTSF-PVA/矿渣混凝土进行高温后的强度预测。结果表明:RTSF-PVA/矿渣混凝土对裂缝的把控能力明显优于素混凝土,600~800℃后的最大裂缝宽度仅为素混凝土的1/3~1/4,但裂纹分布较广;RTSF-PVA/矿渣混凝土的残余抗压强度随温度升高,总体上呈降低趋势,当掺量组合为RTSF掺量0.6%、PVA掺量0.05%以及GBFS替代率25%时,800℃后的抗压强度残余率为56.64%,较素混凝土提高了14.44%;通过电镜扫描观测到RTSF-PVA/矿渣混凝土基体结构更加致密,混凝土劣化主要是因为胶凝物质的分解和骨料膨胀,导致ITZ出现缺陷,以及纤维与基体粘结力降低,两者共同作用导致强度降低;建立NSGM(1,4)模型对RTSF-PVA/矿渣混凝土进行高温后的强度预测,平均相对误差控制在6.3%以内,模型精度达到Ⅱ级,根据发展系数判断模型可以对RTSF-PVA/矿渣混凝土进行高温后强度的长期预测。

To improve the mechanical properties of concrete at high temperatures,orthogonal tests with four factors and three levels were set to investigate the residual compressive strength of RTSF/PVA slag concrete at the temperatures of 200℃,400℃,600℃and 800℃,with the volume fraction of RTSF and PVA and slag replacement rate as variables.At the same time,the microstructure of RTSF/PVA slag concrete after high temperature exposure was analyzed using a scanning electron mi-croscope.A new structure multivariable grey model is used to predict the strength of RTSF-PVA/slag concrete at high temperatures.The results show that RTF-PVA/slag concrete has better crack control ability than plain concrete,and the maximum crack width at temperatures ranging from 600℃to 800℃is only 1/3~1/4 of that found in plain concrete,but the crack distribution is wider.The re-sidual compressive strength of RTSF-PVA/slag concrete decreases as the temperature increases.When the mixture of RTSF 0.6%,PVA 0.05%and GBFS 25%,the residual compressive strength of RTSF-PVA/slag concrete is 56.64%after 800℃exposure,which is 14.44%higher than plain concrete.Scanning electron microscope revealed that the matrix structure of RTSF-PVA/slag con-crete is denser.The concrete deterioration is mainly due to the decomposition of cementitious sub-stances and aggregate expansion,resulting in defects in ITZ,and the reduction of the adhesion be-tween fiber and matrix,resulting in the reduction of strength.The NSGM(1,4)model was estab-lished to predict the strength of RTSF-PVA/slag concrete after high temperature exposure.The aver-age relative error was controlled within 6.3%,and the accuracy of the model reached levelⅱ.The long-term strength prediction of RTSF-PVA/slag concrete after high temperature could be carried out according to the development coefficient judgment model.