Alkali Activation of Construction and Demolition Waste

Date

2025-9-1

Author

Israf, Javed

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As cities grow and skylines expand, the construction industry has emerged as one of the most resource-intensive and polluting sectors, generating a third of the world’s waste, consuming over 40% of raw materials, and emitting nearly 40% of global CO2 emissions. Each year, over two billion tons of construction and demolition waste (CDW) are produced worldwide, with the majority ending up in landfills. To address this challenge, the present study examines the potential of repurposing CDW into alkali-activated mortars (AAMs), utilizing sodium hydroxide (NaOH) as an activating agent. Eleven CDW-based mortar mixes were developed by varying the BW/TW ratios (0 to 1), NaOH concentrations (0%, 5%, 7%, and 10%), and curing periods (7, 28, and 60 days). The AAMs were assessed for mechanical properties (UCS, G0), durability (wet/dry and freeze/thaw cycles), and microstructure (SEM and XRD). The results indicated that mechanical performance, durability, and microstructural development improved consistently with increasing NaOH concentration, BW/TW ratios up to 0.9, and longer curing durations. The optimum formulation (10% NaOH, BW/TW ratio of 0.9, and 60 days of curing) achieved a compressive strength of 28.7 MPa and a shear modulus of 30 GPa. This mix also demonstrated superior durability, with accumulated mass loss (ALM) limited to below 2% under freeze-thaw cycles and below 3% under wet-dry conditions. Microstructural analysis revealed denser pores and increased gel formation, supporting these trends. A dimensional analysis based on the Buckingham π theorem enabled the development of a scalable empirical model capturing the influence of material composition, alkaline activation, and curing on mechanical performance. This study confirms the potential of CDW-based AAMs as a sustainable, low-carbon alternative that supports circularity in the construction sector.

Subject Keywords

Alkali Activated Mortars, Brick Waste, Construction and Demolition Waste, Concrete Waste, Durability

URI

https://hdl.handle.net/11511/116646

Collections

Northern Cyprus Campus, Thesis