Calcined Clay as a Clinker Substitute for Sustainable Cement Production

Sofia Marques Mota

Key information

Authors:

Sofia Marques Mota (Sofia Marques Mota)

Supervisors:

Carla Isabel Costa Pinheiro (Carla Isabel Costa Pinheiro); Diana Lara Matos Correia

Published in

12/02/2021

Abstract

The present research work focused on the partial substitution of clinker by calcined clay (CL) and limestone filler (L1) as a sustainable short-term strategy to reduce CO2 emissions in the cement industry. The clay was submitted to thermal activation at a temperature range between 700°C and 850°C. The raw and calcined clays were characterized by XRD, TGA and N2 adsorption techniques to study the calcination temperature influence on the mineralogical composition, dehydroxylation degree, and textural properties. Calcined products pozzolanic reactivity was assessed by the production of calcined clay cement (75% Ordinary Portland Cement, OPC, and 25 %CL) and limestone calcined clay cement mortars (50% OPC, 30% CL and 20% L1) with superplasticizer addition, by evaluating mortars mechanical performance through compressive strength tests. Specific surface and total pore volume were negatively affected by the increase in activation temperatures, justified by particles agglomeration and pores closure due to sintering. The dehydroxylation degree of the calcined products was higher at 800°C and 850°C and the best compressive strength results were obtained for all mortars with incorporation of clays calcined at 800°C, at 28 days, showing the best equilibrium regarding dehydroxylation degree and particles’ specific surface area, even surpassing OPC reference mortars. Superplasticizer addition enabled a clinker substitution of 50% while maintaining the water-to-cement ratio (w/c) and consistency at normal conditions, with 37.0 MPa compressive strength value at 28 days. Finally, limestone calcined clay cement production enabled a 50% reduction in CO2 emissions considering the calcination stage, when compared to OPC.