Cement-Less Recycled Aggregate Concrete: A Sustainable Solution for Future Constructions in Pakistan

Climate change as a result of global warming has become one of the worlds’ most pressing concerns. The release of greenhouse gases (GHG), primarily carbon dioxide (CO2) emissions into the atmosphere increases global warming. The concrete is the second most used material and cement is the key element in concrete. The cement production releases GHG in the atmosphere, which increases global warming and consequently results in climate change. This research utilizes, fly ash (FA) as 100% replacement of cement in concrete, which will reduce the reliance of construction industry on the cement production and will help to reduce the adverse impacts of climate changes. Moreover, recycled aggregates (RA) prepared from construction and demolition (C&D) wastes are used as varying percentage replacements of natural aggregates (NA) in cement-less recycled aggregate concrete (CRAC), which will help to reduce the depletion of natural resources. This research investigates the influences of varying percentage replacements of NA with RA (0%, 25%, 50%, 75% and 100%) and molarity of NaOH solution (12 M, 14 M and 16 M) on the compressive strength (CS) and flexural strength (FS) of CRAC mixes. A total of 15 CRAC mixes were prepared. Each mix comprised three 100 mm cube specimens and three prism specimens sized 75 mm x 75 mm x 300 mm. The research concluded that the CS and FS decreased with the increase in percentage replacements of NA with RA. Moreover, the CS and FS increased as the molarity of NaOH solution was increased from 12 M to 16 M. The CS and FS was reduced by 29.1% and 31.1% respectively at 100% replacement of NA with RA at 16 M compared to 12 M NaOH solution. The CS and FS increased by 30% and 31.9% respectively at 16 M NaOH solution compared to 12 M NaOH solution at 25% replacement of NA with RA.