Development of a Low-Carbon Building Material Based on Mechanically Processed Brick and an Alkali-Aktivated Binder

Abstract

The construction industry faces urgent demands to reduce carbon dioxide emissions, mainly due to the environmental impact of Portland cement production. Alkali-activated materials (AAMs), known as geopolymers, offer a promising low-CO₂ alternative to traditional cement-based systems. This study investigates the partial replacement of metakaolin (MK) with crushed brick powder (CBP) in alkali-activated mortars, aiming to improve workability while maintaining sufficient mechanical performance. Two types of CBP and two waterglass moduli (WGM 1.7 and WGM 2.0) were tested across various mix designs. The fresh and hardened properties of the mortar samples were evaluated through flow tests, a custom-developed penetration method, and compressive and flexural strength testing over a 28-day period. The results demonstrate that CBP can successfully replace 25–50% of MK without compromising compressive or flexural strength. While WGM 1.7 accelerates early strength development, WGM 2.0 results in more stable and consistent long-term performance. Including CBP significantly improves workability, reducing viscosity and enhancing flowability without negatively affecting density. The findings confirm that crushed brick powder performs similarly to other recycled materials, such as concrete fines, and supports its application in sustainable, CO₂-reduced mortar systems for future construction.