Role of lime, fly ash, and slag in cement pastes containing recycled concrete fines. (20th March 2019)

• Record Type: Journal Article
• Authors: Prošek, Z.; Nežerka, V.; Hlůžek, R.; Trejbal, J.; Tesárek, P.; Karra'a, G.
• Is Part Of: Construction & building materials. Volume 201(2019)
• Page Start: 702
• Page End: 714
• Publication Date: 2019-03-20
• Subjects: Demolition waste -- Concrete recycling -- Alkali activation -- Fly ash -- Slag; Building materials -- Periodicals; 624.18
• DOI: 10.1016/j.conbuildmat.2018.12.227
• Languages: English
• ISSNs: 0950-0618

Abstract

Highlights: Cementitious pastes with large amounts of recycled concrete fines were examined. Thermal activation of recycled concrete was avoided by using additives. Addition of fly ash and slag resulted in higher tensile strength in bending. Presence of recycled concrete in cement pastes resulted in shrinkage mitigation. Abstract: Construction and demolition waste recycling for production of new concrete is usually limited to the use of coarse aggregates, and efficient utilization of fine subsieve fractions remains an unresolved issue. In the presented research, Portland cement pastes containing 50% finely ground recycled concrete, blended with lime, fly ash, or blast furnace slag, were studied. SEM-BSE microscopy, EDX analysis, and porosimetry were employed for investigating their microstructure, individual stages of hydration were detected using calorimetry, shrinkage was optically monitored in the early stages of hardening, the evolution of Young's modulus was assessed using the resonance method, and strength was determined from destructive tests. The study suggests that recycled concrete fines can be incorporated into cementitious composites in large amounts and even improve their properties, especially when blended with fly ash or blast furnace slag. Substitution of Portland cement in the studied pastes by recycled concrete led to a compressive strength deterioration, but also a reduction of shrinkage, and an increase of the tensile strength in bending by up to 26%.