Experimental and Theoretical Studies on Effect of Height-to-Diameter Ratios on Failure Forms and Mechanical Characteristics of Foamed Concrete

The response of concrete under uniaxial loading is dependent on its density and the height-to-diameter ($\mathrm{H}:\mathrm{D}$) ratio of the specimen, and this phenomenon has received wide attention in research on normal concrete. However, few studies have paid attention to foamed concrete. The objective of this study is to investigate the effects of height-to-diameter ($\mathrm{H}:\mathrm{D}$) ratios on the failure forms and mechanical characteristics of foamed concrete at different densities. For the purposes of this study, four different densities (300, 450, 600, and $800\mathrm{kg}/{\mathrm{m}}^3$) of foamed concrete were prepared. The specimens were all cut to the same diameter (50 mm) but had different $\mathrm{H}:\mathrm{D}$ ratios (0.5, 1.0, 1.5, and 2.0). A series of uniaxial compressive tests were carried out, and the effects of $\mathrm{H}:\mathrm{D}$ ratios on failure forms, compressive strength, and elastic modulus were determined. The results showed that the failure forms of foamed concrete mainly correlated with its density; it was less influenced by $\mathrm{H}:\mathrm{D}$ ratio. The failure forms can be divided into three categories: local crushing failure, splitting failure, and shear failure. The compressive strength ratio decreased with the increase of $\mathrm{H}:\mathrm{D}$ ratio for foamed concrete with densities of 450, 600, and $800\mathrm{kg}/{\mathrm{m}}^3$, while the elastic modulus followed an opposite trend. The variation of the effects of $\mathrm{H}:\mathrm{D}$ ratio on compressive strength ratio and elastic modulus was similar: the higher the density was, the greater the effect. However, it is interesting to note that the $\mathrm{H}:\mathrm{D}$ ratio seemed to have little influence on either of them for the foamed concrete with a low density of $300\mathrm{kg}/{\mathrm{m}}^3$. A prediction model that reflects the variation of compressive strength ratio with the densities and $\mathrm{H}:\mathrm{D}$ ratios was deduced. Two other prediction results were prepared for comparison. Furthermore, a prediction model to reflect the variation of the elastic modulus ratio with the densities and $\mathrm{H}:\mathrm{D}$ ratios is proposed.