Porous concrete is an energy absorption material, which has been widely used in civil engineering, traffic engineering and disaster reduction engineering. However, the effect of pore structure on the impact behavior of the porous concrete is lacked. In this study, a series of drop-weight impact tests were carried out on three typical types of porous concrete, i.e., concrete hollow brick (CHB), autoclaved aerated concrete (AAC) and foamed concrete (FC), to investigate the effect of pore structures on their impact behavior. For comparison, static load tests were also conducted as references. According to the damage to the samples, the developments of impact force, strain, contact stress–strain relationship and absorbed energy during drop-weight during the impact test were measured and analyzed. The results show that the ratio between the peak impact stress and compressive strength of CHB was 0.44, while that of AAC and FC increased to about 0.6, indicating that the small and uniform pore structure in AAC and FC had a higher resistance against impact load than the hollow cavity of CHB. In addition, the elastic recovery strain in AAC increased by about 0.2% and its strain at peak contact stress increased by about 160% for a comparison of CHB, implying that a small open pore structure could enhance ductility. Besides, the peak contact stress of FC was close to that of AAC during impact loading, while the strain at peak contact stress of FC increased by about 36% compared with AAC, revealing that the closed-pore structure could further enhance the deformation potential. Correspondingly, the energy absorption rates of CHB, AAC and FC were 85.9 kJ/s, 54.4 kJ/s and 49.7 kJ/s, respectively, where AAC decreased by about 58% compared with CHB, and FC decreased by about 10% compared with AAC.

Foam concrete, as an important construction and building material, mainly consists of small inner pores (produced by preformed foam) and foam walls (i.e., the concrete surrounding the small inner pores). The effect of density and air volume quantity on compressive strength has been investigated in many previous studies. However, the findings on the relationship between compressive strength and water-to-cement ratio (Rwc) are controversial from different studies. The possible reason may be the effect of sand-to-cement ratio (Rsc), which has not been considered in pervious studies. In this study, a series of compressive tests on foam concrete with various Rwc and Rsc were conducted at a fixed air volume quantity. The results show that when Rwc was 0.5–1.0, the compressive strength increased along Rwc, different from the change of the concrete without foam. The enhance effect from the foam walls was dominant. When Rwc was larger than 1, the slurry was too thin to preserve the bubble for the Rsc of 2. However, for the Rsc of 5, the slurry performed well and its compressive strength remained constant, which was different from the increase stage with Rwc of 0.5–1.0. It was because of the enhanced effect caused by the decrease in the number of small holes, which almost offset the weakening effect for the Rwc on the strength. The enhance effect due to the decrease in the number of small holes can be normalized by the water-to-solid ratio (Rws). Except the results in the constant stage, the compressive strength increased with the increase of Rws, irrelevant to the Rsc. It indicates that the sand and cement had the same function on the decrease in the number of small holes. In order to get the same compressive strength, the cement can be replaced by the sand in the increase stage. The research results are expected to improve the quality control and the engineering efficiency of foam concrete.