Fresh properties of concrete prepared withrecycled aggregates and class-F fly ash

Concrete mix design and production

This paper presents the fresh properties such as slump, slump loss, air content and bleeding of concrete prepared with recycled aggregate and class-F fly ash. Bleed tests were performed in accordance with ASTM C232-92 on the concretes in which up to 100% of the natural aggregate was replaced with recycled aggregate. In parallel, concrete mixtures with the replacement of cement by 25% fly ash were prepared for comparison. All concretes mixtures were prepared at a water/cementitious material ratio of 0.45. Test results showed that the use of recycled aggregate as a partial replacement of natural aggregate lead to slight increases in slump. The slump loss rate was increased with an increase in recycled aggregate content. The replacement of natural granite with up to 100% recycled aggregate increased the bleed capacity and bleed rate by 21.2% and 28.6% respectively. Delaying the start of the bleed test from 30 to 120 min reduced the bleed capacity of the natural aggregate mix by more than 55% compared with 55% for concrete mixes with 100% recycled aggregates. Moreover, the replacement of cement by 25% fly ash increased initial slump and decreased both the bleed capacity and bleed rate of the concrete mixtures.

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