Influences of short-term heavy rainfall on interlayer properties and microstructure of concrete dam

Rainwater adversely affects the interlayer bonding quality of layered concrete. This study tested the influences of different treatment measures (i.e., discharging the rainwater accumulated on the layer and covering the insulation quilt) on the interlayer mechanical properties of concrete under the condition of short-term heavy rainfall, including compressive strength (CS), splitting tensile strength (STS), and shear strength (SS). Meanwhile, the influence of short-term heavy rainfall on the interlayer microstructure of concrete was analyzed using a scanning electron microscope (SEM) and mercury intrusion porosimetry (MIP). In addition, the ultrasonic non-destructive testing method was employed to quantify the deterioration degree of the concrete layer under the condition of short-term heavy rainfall. The results show that short-term heavy rainfall can reduce the CS, STS, and SS of concrete by 50%, 70%, and 37%, respectively. Meanwhile, the porosity and damage degree near the concrete interlayer were also increased by short-term heavy rainfall. This is mainly because rainfall increases the water-binder ratio (w/b) of concrete, resulting in the deterioration of concrete microstructure. The increase of w/b is not conducive to the development of concrete mechanical properties. Concrete with a large w/b will retain more water after hydration. The water not involved in hydration leaves more pores after evaporation, increasing the total porosity of concrete. Moreover, there is a linear relationship between the concrete damage degree and the interlayer STS and SS loss rate, as well as the correlation coefficients are 0.959 and 0.983, respectively. The porosity of concrete is linearly correlated with the interlayer STS and SS, and the correlation coefficients are 0.973 and 0.909, respectively. Draining the rainwater accumulated on the layer and covering the insulation quilt can improve the interlayer CS, STS, and SS of concrete. This is mainly because the above measures reduce the influence of rainwater on the interlayer.