Newer Cementitious Binder from Thermo-Chemically Activated Lime Sludge and Its Use in Mortar

Abstract

The lime sludge from pulp and paper industry was thermo-chemically activated at 850 oC in the presence of alkali. The lime reactivity of activated sludge was evaluated (as per IS: 1727) in terms of compressive strength (varies from 3.61 MPa to 4.36 MPa) for its use with Portland cement clinker. Various mixes comprising of cement clinker, fly ash, calcined clay and ground granulated blast furnace slag (GGBFS) and thermo-chemically activated lime sludge were formulated. The Blaine’s surface area and particle size distribution of the resulting mixes was found in the range of 500 m2/kg -561 m2/kg and 1.678 x 10-5 m to 4.177 x 10-5 m, which are finer than Portland cement (285 m2/kg Blaine’s surface area). All the mixes exhibited lime absorption value below the saturation line in lime solubility curve plotted between calcium oxide concentration and hydroxyl ion concentration showing their adequate pozzolanicity. Hydration behaviour of various mixes were studied with the help of isothermal conduction calorimetry. It was found that total heat of lime sludge binders were higher than the Portland cement. Addition of activated lime sludge into mix resulted intense acceleration peak indicated the possibility of higher strength development than the Portland cement in the hardened pastes. The binders were also tested for setting time and compressive strength by preparing the mortars. Based on findings of all these tests, it is concluded that cementitious binder containing GGBFS, calcined clay and 15% thermo-chemically activated lime sludge gives optimum results. Life cycle analysis of lime sludge based binder was carried out using SIMA PRO software. It was observed that global warming in terms of CO2 emission was reduced by 51% when compared with the Portland cement.

Keywords: Thermochemical activation, lime sludge, cementitious binder, mortar