Sustainable Zero-Slump Concrete Containing Recycled Aggregates from Construction and Demolition Waste of a 63-Year-Old Demolished Building

Abstract

In this study, recycled concrete aggregate (RCA) from construction and demolition waste (CDW) was utilized in zero-slump concrete (ZSC) to produce M-40 grade paver blocks. Initially, coarse RCA (4.75 to 10 mm in diameter) replaced natural coarse aggregate (NCA) and fresh (slump, compaction factor, density) and hardened (compressive strength, water absorption, abrasion resistance) properties were investigated to optimize its replacement percentage. Then, the feasibility of incorporating RCA (<4.75 mm) was determined based on fresh and hardened properties, i.e., bulk density, compressive strength, flexural strength, split tensile strength, water absorption, void ratio, abrasion resistance, ultrasonic pulse velocity, and dynamic modulus of elasticity. Four samples of each formulation were tested, and the average was recorded with the standard deviation as the error bar. Microstructural analysis [thermogravimetric analysis (TGA), Fourier transform infrared (FTIR) spectroscopy, and scanning electron microscopy (SEM)] was conducted to validate the findings. The effects of RCA incorporation with respect to environmental impact [global warming potential (GWP) and primary energy (PE) consumption] of 1 m3 optimized ZSC mixes were assessed. As per observation, mechanical as well as durability properties degraded with increase in RCA content. Compressive strength decreased 17% at a combined replacement of 45% coarse and 100% fine RCA. Based on TGA analysis, portlandite content decreased with increasing RCA concentration, as confirmed by FTIR spectroscopy. SEM results also confirms the findings as pore counts, total area, average size, and percentage area increases with increase in RCA. Incorporation of 45% coarse and 100% fine RCA resulted in 4% and 8.8% decrease in GWP and PE, respectively. The optimized ZSC mixture (coarse 45% and 40% fine RCA) was based on an optimized compressive strength/GWP ratio. The production cost of 1 m3 concrete mix (45% coarse and 100% fine RCA) was 75% higher than the control mix because of the associated higher cost of RCA. Based on these findings, RCA can replace up to 45% NCA and 40% river sand without having a significant impact on its properties. Therefore, CDW can be viewed as a resource, not a waste, which can save natural resources and pave the way to sustainable development.