The Influence of Freezing and Thawing Cycles on Recycled Concrete Incorporating Mineral Slag

This paper aims to study the freeze-thaw resistance of various proportions of the recycled aggregate concrete (RAC) prepared using local recycled aggregates supplied by a Kuwaiti Recycled Aggregates factory. The recycled concrete was prepared with partial replacement of Portland cement by mineral slag (GGBS) of 25%. Six different mixtures were used to cast the concrete specimens. The water-binder ratio (w/b) was kept constant at 0.35 in all mixtures. Three different ratios of recycled aggregates (0%, 50% and 100%) were utilized, with or without 25% slag as cement replacement. Mixes were tested for workability, compressive strength and freeze and thaw resistance, which is considered a good indication for concrete durability.

For the freeze and thaw test, specimens were inserted in the Freeze-Thaw machine The duration of each freeze-thaw cycle was 4 hours. Specimens were tested after every completed 30 freeze-thaw cycles. The compressive strength, mass loss, length change, transverse frequency and relative dynamic modulus of concrete mixtures were determined. In general, the incorporation of 25% slag improved the compressive strength of the RAC and had a positive effect on them when subjected to freeze-thaw cycles. Mass, ultrasonic pulse velocity (UPV) and freeze–thaw resistance of concrete decreased in recycled aggregate concrete and enhanced by the introduction of 25% GGBS as partial cement replacement. The durability factor for concrete mixes that contain slag was decreased as the amount of recycled aggregates increased. A lower frost resistance and deterioration due to freeze-thaw cycles when using 25% GGBS combined with 100% RA was noticed compared to other recycled aggregates ratios.

Author(s): Moetaz El-Hawary

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