The effect of including biomass on the rheological and pozzolanic properties of Portland limestone cement- case study

Various investigations have been presented on the possibility of using agro-allied industry waste in concrete, with the goal of achieving a cleaner environment and environmentally friendly construction. Biomass fly ash (BFA) and limestone clinker are waste from steam/power plants and the cement industry, respectively, and are of high relevance to economic and environmental problems. The effect of including biomass on the rheological and pozzolanic properties of Portland limestone cement (PLC) pastes are presented. The BFA was used as partial replacement for PLC as supplementary cementitious materials (SCMs). The rheological properties (yield stress, viscosity and thixotropy) of the cement paste were determined using a parallel-plate rotational rheometer. The pozzolanic properties were determined using thermogravimetric analysis (TGA) by measuring the amount of calcium hydroxide (CH), and calcium silicate hydrate (CSH) of the hydrated paste, as well as the reaction kinetics. Different characterization techniques including X-ray diffraction (XRD), X-ray fluorescence spectroscopy (XRF), and scanning electron microscopy (SEM) were used to study the microstructure and mineralogy of the BFA. It was observed that the mineral composition of the biomass fly ash is like class C fly ash. At 15% of cement replacement the paste exhibits better rheological properties: lower yield stress and lower viscosity up till 120 min after mixing, which is an important factor in ready-mix concrete plants. However, a better pozzolanic behavior was observed at 20% cement replacement. From the results obtained, the properties of the paste containing BFA is very sensitive to water/binder ratio (w/b). Above 20% cement replacement, it is suggested to use viscosity modifying agent (VMA) to get a better rheology and pozzolanic behavior.