Effect of w/c ratio on air-void system of foamed concrete and their influence on mechanical properties

A study was undertaken to investigate the effect of water to cementitious material (w/c) ratio (ranging from 0·22 to 0·60) on the air-void system (air content ranging from about 10 to 70%) of foamed concrete, and their effects on the mechanical properties of foamed concrete without sand. The cementitious material used in this study was blended cement with 50% ordinary Portland cement (OPC) and 50% ground granulated blastfurnace slag (ggbs) by weight. The linear traverse method was used to characterise the air-void system, referring to air content, average air-void size, air-void frequency and spacing factor. The results show that although the same quality of foam was introduced, the air-void size and frequency, and hence spacing factor, of the foamed concrete varied with different w/c ratios and air contents, which in turn affected the mechanical properties of the concrete. For the different w/c ratios and air contents adopted, it was found that an air-void system with a spacing factor of about 0·05 mm, air-void size of 0·15 mm and air content of 40% was optimal in terms of achieving a high strength to weight ratio. The compressive strength of foamed concrete seems to be influenced by the spacing factor, w/c ratio and air content in relation to density. The results also indicated that the inclusion of air-voids in foamed concrete had a greater effect on compressive strength than the modulus of elasticity and it increases with increase of w/c ratio. The results of a numerical analysis concurred with the experimental observations.