Influence of High Volume Fly Ash and Recycled Aggregates in Chloride and Carbonation Resistance of Concrete

This paper deals with the evaluation of the influence of recycled concrete aggregate (RCA) and the employment of high volume of fly ash (FA) on the physical, mechanical and durability (chloride ion penetration and carbonation) properties of concretes. The obtained values of which, being compared to those of conventional concretes. Concrete was produced using 0%, 25% and 50% FA in replacement of Portland cement, and 0% and 50% of RCA in substitution of natural aggregates. All the concretes were produced employing an effective water-cement ratio of 0.50. The physical properties at 28 days and the compressive strength at 7, 28 and 90 days were determined in all the concretes produced as well as the assessment of durability (penetration of chlorides and depth of carbonation) on all concrete mixtures. The depth of the carbonation was determined after submitting every concrete sample to a series of accelerated tests at 20% of CO2 concentration during 7, 14 and 28 days after the curing period in the humidity room and pre-condition in the laboratory. The chloride penetration was determined at 28 and 90 days of curing. It was concluded that the employment of 50% of un-carbonated RCA increased the early strength of concrete produced using FA, and at late ages, RCA concretes achieved similar strength when 25% of FA was employed. The concrete produced with 50% of FA achieved the highest resistance to chloride ion penetration also when RCA was employed. Although the use of FA increased the carbonation depth of the concrete samples, the employment of the un-carbonated RCA reduced that effect. The employment of RCA with CEM II or binder with 25% of FA caused the lowest carbonation