This study aimed to investigate the influence of low temperature ranging from 20
C to 0
C on the compressive strength and pore structure of a certain pile foundation concrete in the permafrost regions in China. This study analyzed concrete microstructure by low-temperature SEM. To quantify the influence of freezing amount, the relationship model of the compressive strength of concrete in a low-temperature environment was established based on the theory of accumulative curve of liquid saturation. Compressive strength increased with decreasing temperature. This finding was due to the gradual decrease in the pore radius of the water–ice phase transformation of concrete, and the amount of ice increased. This condition forms a complete and compact ice body and concrete bond, which gradually reduces concrete porosity. The calculated value of concrete compressive strength model established under pore icing is consistent with the experimental value.

Introduction

The Qinghai-Tibet Railway, also known as the ‘‘Road to the Sky,” crosses the world’s largest distance of permafrost area at 550 km [1]. The average and minimum temperatures in the permafrost area are below 0
C and ranging from 16
C to 20
C [2,3]. The total length of the bridge and tunnel is approximately 8% of the total length of the railway. The pile foundation of bridge engineering has been in the permafrost area for a long time. Thus, concrete is required to reach the design strength under low temperature conditions and permafrost regions. The strength of the pile foundation in the permafrost area is greatly significant to the safe use of the Qinghai-Tibet Railway. Therefore, the strength of the bridge pile foundation structure in the permafrost region in China is studied in this paper. Compressive strength is an important basis for evaluating concrete strength. The strength of concrete exposed to different temperatures from 0
C to 20
C needs to be studied, and the results provide a reliable basis for evaluating the performance of low temperature concrete structure of the pile foundation of the Qinghai-Tibet Railway Bridge Project. At present, concrete is an excellent low-temperature building material [4,5] that has good mechanical properties [6]. For example, Lee GC [7], Hideo Kasami [8], and Chuanxing Wang [9] considered that the compressive strength and elasticity modulus of concrete with different strengths have been improved to some extent at low temperatures (in the range 100
C to 0
C).