Strength Characteristics of Foamed Concrete under Coupling Effect of Constant Compressive Loading and Freeze-Thaw Cycles

In cold regions, foamed concrete used for the tunnel reserved deformation layer is usually subjected to environmental factors, such as the groundwater erosion, peristaltic pressure of surrounding rock, and freeze-thaw cycles. In this research, experiments considering single-factor (i.e., water immersion, constant compressive loading, and freeze-thaw cycles) and coupled multi-factor effects (the coupling of water saturated - constant loading and constant loading - freeze thaw cycles) were conducted on foamed concretes with different densities to examine the strength variation under different conditions. The results show that under the effect of singlefactor environment, the average compressive strength of saturated foamed concrete is about 10% lower than the dry foamed concrete. The compressive strength of foamed concrete significantly decreases at the beginning of constant compressive loading but gradually increases with the loading time. Furthermore, the strength loss of foamed concrete after 30 freeze-thaw cycles can exceed 10%. Under the multi-factor coupled environment, the hydraulic effect accelerates the degradation of foamed concrete, particularly in terms of water saturation constant loading coupling. Furthermore, for loading - freeze thaw cycles coupling, the compressive loading of 0.3 fc (fc is the unconfined compressive strength at 28 days) can improves the frost resistance of foamed concrete. In addition, the results of orthogonal analysis prove that the density has the most important influence, followed by the freeze-thaw cycle and the slightest effect of constant compressive loading. Additionally, a prediction equation of compressive strength as a function of density, freeze-thaw cycles, and the constant pressure value was established to describe the strength variation of foamed concretes under coupled-loading effects.