Plastic Concrete Reuse Using Extended Set-Retarding Admixtures

Abstract

This paper reports a preliminary experimental study on the effect of extended setretarding admixture or ‘stabiliser’ on the plastic and hardened properties of grouts and concretes containing general purpose Portland cement, blended cement and low heat cement. The effect of stabiliser on efflux time or ‘flow time’ of GP cement grout was studied and the dosage required to achieve an efflux time of 35 seconds was estimated. The results showed a linear relationship with increasing stabiliser dosage extending the holding time of the grout. The effect of stabiliser on the timing and measure of peak hydration temperature was then assessed and the results showed that for GP cement and GB cementitious grouts, peak temperatures were lower after adding stabiliser, and for all three grouts the time to peak hydration was significantly increased. Finally, the effect of stabiliser on the plastic and hardened properties of fresh concrete, stabilised concrete, and a blend of fresh and stabilised concrete was assessed. The results showed that the initial one hour slumps and the final slumps of the blended concretes were all within tolerance. The results also showed that adding stabiliser to the concretes did not a significantly reduce compressive strength when compared to the original, non-stabilised concretes.