Physical-chemical characterization of construction and demolition waste powder with thermomechanical activation for use as supplementary cementitious material

Abstract

Cement production is responsible for large anthropogenic CO2 emissions into the atmosphere, partly through the decarbonization of limestone rock. Reducing the clinker/cement ratio is a viable alternative to reducing the environmental impact of construction. To achieve this, the continued exploration of additional cementitious materials is necessary. With adequate particle size and chemical composition, construction and demolition waste powder (CDWP) can be used as supplementary cementitious material (SCM). In this sense, the present work aims to evaluate the CDWP physical-chemical characteristics when subjected to thermomechanical treatment (calcination and milling), aiming for application as SCM. The powders (fraction smaller than 150 µm) were subjected to different calcination temperatures (600, 700, 800, and 900°C) without milling and milled for 5 hours. The physicochemical characterization was carried out using laser granulometry, X-ray diffraction (XRD), thermogravimetry (TG), X-ray fluorescence (XRF), BET, scanning electron microscopy (SEM), specific mass, pozzolanic activity index (PAI) and Portlandite consumption. The results indicate that thermomechanical activation made it possible to obtain a powder with physical-chemical characteristics of interest for application as SCM. The amount of Si2O, Fe2O3, and Al2O3 is greater than 70 %, making them suitable. Calcination from 700°C presents a loss of ignition of less than 6 %, meeting regulatory requirements for pozzolanic materials. Milled for 5 hours leads to a 75 % reduction in particle mean diameter. With the combination of thermal and mechanical treatments, a PAI of 97 % was obtained, and a decrease in the quantity of Portlandite of 12 %. Analysis of variance (ANOVA) indicated a significant influence of thermal and mechanical treatment on the compressive strength of mortars. Based on the data found, it can be stated that CDWP has the potential to be used as an SCM, decreasing CO2 emissions from the cement industry and contributing to the circular economy of the construction sector.