Physicochemical characteristics of cementitious building materials derived from industrial solid wastes

- Lime rich sludge (LRS) can act as an alkaline activator for ground granulated blast furnace slag (GGBFS).
- Addition of fine kaolinite sand (FKS) results in marked improvement in the hydraulic properties of GGBFS-LRS-FKS mixes.
- GGBFS, LRS and FKS wastes can be used for the production of building materials of strong hydraulic properties.
- The main hydration products are nearly amorphous and microcrystalline CSH.

In this study the possibility of using alternative waste materials with cementitious properties was studied. Lime rich sludge (LRS) (solid waste of acetylene industry), ground granulated blastfurnace slag (GGBFS) and fine kaolinite sand (FKS) (by-product during kaolin mineralization) were used in the production of cementitious building materials. Different mixes were prepared using percentage weight ratios 80/20, 75/25, 70/30 of GGBFS and LRS, respectively, at water/cement ratio of 0.20 by weight. Fine kaolinite sand (5 wt%) was used as addition in these mixes. The mechanical and hydration characteristics of the prepared pastes were studied at various time intervals up to 90 days. The results showed that LRS acts as an alkaline activator for GGBFS and the optimum mix composition for activation was 75% GGBFS and 25% LRS. Addition of fine kaolinite sand (FKS) to these mixes resulted in a marked improvement in the hydraulic properties especially in the early hydration ages; this is related to the higher rate of pazzolanic interaction between the lime in LRS and the aluminosilicate constituents in fine kaolinite sand leading to formation of excessive amounts of calcium silicate hydrates (CSH) which act as binding centers between the remaining unhydrated parts of GGBFS and FKS. XRD patterns and DSC thermograms obtained for all pastes showed that the main hydration products are nearly amorphous and microcrystalline calcium silicate hydrates as well as minor amounts of calcium aluminosilicate hydrates.