Hydration characteristics of boiler calcium carbonate scales blended cement pastes

Abstract EN

The aim of this investigation is to study the utilization of waste boiler calcium carbonate scales waste as a blending material in comparison with limestone filler in the preparation of filled cement The boiler scales sample used in the present study was collected from the boilers of a local sugar factory.

It is mainly composed of aragonite mineral (CaCO3), whereas limestone is mainly composed of calcite mineral as confirmed by the XRD analysis.

The crystal size range calculated from XRD analysis of both materials indicate that its fineness is nearly the same.

The hydration characteristics of hydrated OPC and filled cement pastes containing 5, 10, 15 and 20 wt % of boiler scales or limestone fillers were evaluated by measuring the combined water content, bulk density and compressive strength up to 90 days.

The phase composition and microstructure of some selected samples were analyzed by XRD, DSC and FTIR techniques.

It was observed that the presence of the metastable aragonite mineral enhances the hydration of C3S and forms CSH, whereas the calcite mineral reacts mainly with C3A to form calcium carboaluminate hydrates, which contain higher amount of water than CSH.

Hence, the combined water content of boiler scales filled cement pastes decreases, while the bulk density as well as compressive strength increases compared to limestone cement pastes at all ages of hydration.

Accordingly, it may be concluded that the boiler scales filler improves the physicochemical properties of cement pastes more than the limestone and can be used as a filler in the preparation of blended cement instead of its disposal to open landfills.