Development of Cement-Less Recycled Aggregate Concrete Mixes: A Step Towards Sustainable Construction

Muhammad Numan, Qasim S. Khan, Asad U. Qazi, Syed Minhaj Saleem Kazmi and Muhammad Junaid Munir ()
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Muhammad Numan: Assistant Director Academics, University of Sialkot, Sialkot 51040, Pakistan
Qasim S. Khan: Civil Engineering Department, University of Engineering and Technology, Lahore 54890, Pakistan
Asad U. Qazi: Civil Engineering Department, University of Engineering and Technology, Lahore 54890, Pakistan
Syed Minhaj Saleem Kazmi: School of Mechanics and Construction Engineering, Jinan University, Guangzhou 510632, China
Muhammad Junaid Munir: School of Mechanics and Construction Engineering, Jinan University, Guangzhou 510632, China

Sustainability, 2025, vol. 17, issue 6, 1-22

Abstract: This study investigates the potential of cement-less recycled aggregate concrete (C.R.A.C.) as an eco-friendly alternative to traditional ordinary Portland cement (OPC) concrete, using industrial waste (fly ash) and construction and demolition waste (recycled coarse aggregates). This research explores the effects of mixes of varying sodium hydroxide (NH) molarities and percentage substitutions of natural coarse aggregates (N.C.As.) with recycled coarse aggregates (R.C.As.) on the mechanical properties of C.R.A.C. A total of eighteen ambient-cured C.R.A.C. mixes, using Thar Coal fly ash with varying NH molarities (12 M, 14 M, and 16 M), and percentage substitutions of N.C.As. with R.C.As. (0%, 20%, 40%, 60%, 80%, and 100%), were prepared and tested under axial compression and flexure. It was observed that the compressive strength increased by about 76% with an increasing NH molarity, whereas the compressive strength decreased by about 52.9% with an increasing percentage substitution of N.C.As. with R.C.As. The flexural strength increased by about 78.3% with an increasing NH molarity, whereas the flexural strength decreased by about 50.5% with an increasing percentage substitution of N.C.As. with R.C.As. The SEM analysis of the C.R.A.C. mixes highlighted the heterogeneous morphology of fly ash particles (e.g., irregular shape, rough surface texture, and porous regions), which negatively influenced the overall performance of the concrete matrix. The environmental assessment exhibited that the C.R.A.C. mixes exhibited about 45% lower CO 2 emissions than OPC concrete; however, the cost of the C.R.A.C. mixes was about 21% higher than that of OPC concrete mixes.

Keywords: cement-less recycled aggregate concrete; recycled coarse aggregates; NH molarity; compressive strength; flexural strength; embodied CO 2 (search for similar items in EconPapers)
JEL-codes: O13 Q Q0 Q2 Q3 Q5 Q56 (search for similar items in EconPapers)
Date: 2025
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