Valorizing the use of recycled fine aggregates in masonry cement production

Abstract

The recycled fine aggregate (RFA) fraction generated during crushing of waste hardened concrete is hardly recyclable in new construction and building materials. This paper assesses the suitability of grinding RFA for use as filler materials during masonry cement (MC) production, which helps valorizing this fraction and conserving natural limestone (LS) resources. For given Blaine fineness of 3100 ± 200 cm2/g, test results showed that the RFA requires about 38% less grinding energy than LS, given the porous and weakly bonded natures of the adhered cement paste. The air content, water retention, setting time, and compressive strength for LS and RFA-based MC mortars were pretty close to each other; i.e., all complying to EN 413-1 and ASTM C91 requirements. This practically reveals that the LS and RFA materials can be exchanged with each other during MC production, with limited effects on the fresh and mechanical cement properties. Nevertheless, the various MC components (i.e., clinker, LS, and RFA) should be ground separately in the grinding mill, and then blended together according to the specified MC strength class. This allows adjusting the comminution energy to each component hardness and avoids the formation of excessive fines that could result from the inter-grinding process.