Modeling the strength and economic parameters involved in recycling waste concrete material in fresh concrete

The economic and strength implications of concretes made from virgin and recycled waste concrete aggregate in fresh concrete production was examined using concrete mixes of different water cement ratios. The properties investigated were the physical properties and compressive strengths of both concretes and the results of compressive strength showed that the strength of concrete made from recycled aggregate were lower than that made from virgin aggregate but a more important observation was that the rates of gain in strength of concrete made from recycled aggregate approached that of concrete made from virgin aggregate when the free water cement ratio increased from 0.4, 0.45 up to 0.5. But as the water cement ratio increased from 0.55, 0.6 up to 0.65, the difference between the strengths of concrete made from both types of aggregates increased continually with curing age. An economic analysis showed that where a compressive strength in excess of 25N/mm2 is not needed, the use of recycled aggregate is more economical as Three Thousand Six Hundred Naira can be saved per cubic meter of concrete. Finally, very good fits were obtained for water cement ratios of 0.45, 0.5 and 0.65 using a least square optimization of Scheffe’s 2nd degree polynomial.