Bubble Structure, Stability and Rheology of Foamed Concrete

Foamed concrete has been identified as a versatile construction material with excellent properties that include being highly flowable, light, and durable, which are mainly own to its large volume of spherical bubbles. However, improper bubble structure in foamed concrete could result in stability problem unexpectedly on-site during its application and cause it to collapse. In this study, the bubble structure of foamed concrete was examined to establish links with its stability and rheology properties. Mixes with plastic densities ranging from 300 to 1400 kg/m³ were produced with CEM I, CSA and fine fly ash cement combinations. Water/cement (w/c) ratios varied from 0.4 to 0.8 and two types of surfactant were used. The bubble size of foamed concrete was found to be a function of its density, w/c ratio, the material fineness and surfactant types. The bubble diameters were shown to range between 0.1 to 0.5 mm. The stability was improved with increase in density. Reducing w/c ratio and fineness of constituent materials was also beneficial. The hardening time had a significant effect for stability of low density mixes and stable mixes with 300 kg/m³ density were achieved by using cement combinations of CSA with CEM I R or CSA with fine fly ash. A relationship was also established between bubble structures and the rheological values. Bubble sizes reduced when the yield stress increased. Changing the densities exhibited significant variance in the rheological values due to the changes in total bubble content. Altering the w/c ratio also had a considerable variation in the rheological values due to the changes in consistence of base mixes.