高温对混凝土孔隙结构改变和抗压强度降低作用的规律研究

Characteristics of Pore Structure Change and Compressive Strength Reduction of Concrete Under Elevated Temperatures

混凝土内部的孔隙结构会显著影响其力学性能。本工作的主要目的是建立高温下孔隙结构变化和抗压强度的对应关系。将标准养护12个月的混凝土在不同温度(40℃、105℃、150℃、200℃和250℃)下干燥至恒重,并测定其抗压强度与孔隙结构。混凝土的孔隙结构通过压汞法(MIP)和氮吸附结果定量描述。结果表明:随着温度的升高,混凝土的孔隙率不断增大,孔隙结构逐渐被破坏。同时,混凝土的抗压强度随温度的升高逐渐降低。混凝土抗压强度与孔隙率的关系同Schiller提出的抗压强度-孔隙率方程符合较好,相关系数达到了0.994。因此,高温条件下,可通过Schi-ller方程定量反映混凝土抗压强度的变化。

The pore structure of concrete exert critical impact on its mechanical properties.In this work,we aimed to describe the correspondence between the compressive strength and the pore structure of concrete.Concrete specimens undergoing standard curing in water for 12 months were dried at diverse temperatures(40℃,105℃,150℃,200℃and 250℃)until their weight maintained unchanged.Then,the effects of temperature on concrete pore structure and compressive strength were investigated.Compressive strength tests were carried out to characterize the mechanical properties of the concrete specimens.The pore structure were quantitatively characterized by mercury intrusion porosimetry(MIP)and N2 adsorption.The results implied that the temperature rise leaded to the ever-increasing porosity and gradual damage of the pore structure,while the compressive strength of concrete specimen declined as the temperature rose.The relationship between compressive strength and porosity is in good accordance with the strength-porosity Logarithmic relation proposed by Schiller,showing a correlation coefficient as high as 0.994.It can be concluded that Schiller function is capable of describing the variation of compressive strength under elevated temperature quantitatively.