The investigation into the potential of ceramic waste powder as a pozzolanic material and inert cement filler in concrete

Abstract

The construction industry is increasingly seeking sustainable alternatives to Portland cement (PC) due to its high carbon footprint. Ceramic waste powder (CWP) offers potential as either a supplementary cementitious material or an inert filler. However, its role in cement hydration is uncertain due to conflicting reports on its pozzolanic reactivity. This study investigates the potential of CWP as a partial replacement for both pozzolanic material (Ground Granulated Blast Furnace Slag, GGBS) and inert filler (limestone powder, LSP) in concrete. The CWP was incorporated into Portland-slag and Portland-limestone cement blends at varying levels. Its chemical compositions were analysed using X-ray fluorescence (XRF). Scanning electron microscopy with energy dispersive spectroscopy (SEM-EDS), and X-ray diffraction (XRD) were use to better understand its microstructure. Workability (slump), strength, and durability were evaluated at water-binder ratios of 0.45, 0.50, and 0.55. Compressive and splitting tensile strength tests were conducted at 7, 28, 56, and 90 days. Durability performance was determined using the Oxygen Permeability Index (OPI), Water Sorptivity Index (WSI), and Chloride Conductivity Index (CCI). Additionally, SEM analysis was used to examine hydration products, pore distribution, and interfacial transition zones (ITZ) in concrete microstructures. Results indicated that CWP has limited pozzolanic reactivity, leading to lower early-age (7 days) strength compared to GGBS. However, it outperformed LSP in both early-age and long-term strength, as well as in durability. CWP reduced the slump in GGBS mixes, requiring more superplasticizers, but improved the slump in LSP-based mixes. Durability tests confirmed that CWP enhances resistance to permeability, moisture ingress, and chloride penetration. Microstructural analysis revealed improved densification, reduced porosity, and better hydration over time. Compared to LSP, CWP demonstrated similar filler effects but also generated minor secondary hydration products, suggesting partial pozzolanic activity. However, its hydration rate, as indicated by strength development over time, was lower than that of GGBS. Overall, CWP primarily acts as an inert filler with limited pozzolanic reactivity.