Lightweight masonry blocks from fly ash pellets

Abstract

A process for making lightweight building/masonry blocks from fly ash is described, essentially consisting of pelletizing a mixture of fly ash with smaller quantities of lime and sand, pouring the clusters of wet pellets into a suitable mould, and steam curing the resultant blocks. Pre-grinding of the fly ash and lime mixture and addition of an accelerator/activator (calcium chloride) lead to significant improvement in the strength. The novel features of the process are: (i) the intrinsic pozzolanic activity of fly ash is exploited to generate strength both within the pellets and in the interpellet neck bonds; no additional binder or cement is required, and (ii) the low bulk density of the blocks is derived from large interpellet void volume in the randomly packed bed of porous pellets having relatively narrow size distribution. In this respect, the blocks are similar to the standard "no-fines" concrete blocks made from nominally single size lightweight aggregates bonded with Portland cement. The compressive strength, and compressive strength to bulk density ratio data compare favourably with conventional masonry blocks.