Material characteristics of recycled aerated limestone blocks

Abstract

Limestone was highly used because it was easily found on the island. Nowadays, globigerina limestone is no longer used as extensively as it was in the past, since quarries consisting of good stone are now nearly exhausted. Consequently, concrete building products have taken their place. Certain areas around the island have a higher number of buildings constructed with concrete than those built with Globigerina limestone. The availability of Malta's limestone has decreased, while hollow concrete blocks are preferred for building due to their lighter nature. Nonetheless, autoclaved aerated concrete blocks are preferred due to their lighter nature, as well as for their thermal and acoustic insulation, and durability, making them a greener building material. Once the calcium hydroxide in the cement reacts with the aluminium powder, the mixture rises in the mould, producing hydrogen bubbles that provide the aerated effect in the concrete. The proportions in the mix will affect the thermal properties and the strength of each block. This dissertation aims to investigate the volume increase, density and compressive strength of aerated concrete under six varying conditions. Five of these studies focus on the use of aluminium powder as a reactive agent, assessing; different percentages of aluminium powder in the samples, curing at various temperatures, the use of lime as a replacement for cement, the replacement of cement with varying percentages of limestone powder, and the containment of a sample. The sixth study focuses on the use of a foaming agent (MasterAir 160) instead. Based on the experimental results, it was concluded that the higher the volume increase, the lower the density of the sample, and the lower the compressive strength.