Treatments for the Improvement of Recycled Aggregate

Abstract

The microstructure of recycled aggregate prepared from the crushing of old concrete was studied. It was found that the recycled aggregate is covered with loose particles that may prevent good bonding between the new cement matrix and the recycled aggregate. The old cement paste that remained on the natural aggregate was porous and cracked, leading to weak mechanical properties of the recycled aggregate. Treatment of the recycled aggregate by impregnation of silica fume solution and by ultrasonic cleaning was studied with the objective of overcoming the above-mentioned limitations. An increase of ϳ30 and ϳ15% in the compressive strength at ages 7 and 28 days was observed after the silica fume treatment. Ultrasonic treatment led to an improvement of ϳ7%.

Enhancement of Recycled Aggregate Concrete Properties by a New Treatment Method

“…4, At the early age, with the support of treatment solution type S, the compressive strength of RAC strongly soared up about 23-50% compared to untreated RAC, and it was around 1.7-6.9% higher than that of NAC. This observation indicated that the combination between solution type S and pozzolanic materials promoted the increase of the compressive strength of RAC at the early age more effectively than other methods [29]. At 28 days (see Fig.…”

“…In addition, the results revealed that RAC treated with 20SSF had the highest value in compressive strength of concretes in comparison with other specimens and was comparable with that of NAC. Therefore, the combination between sodium silicate and silica fume created a good treatment solution for RCA which was higher than the existing method [29]. It could be explained that silica fume contained the high percentage of amorphous silica which was useful for the development of concrete strength [32] and silica fume in concrete gave the higher strength compared to that of fly ash [33].…”

Feasibility of Using Nanoparticles of SiO2 to Improve the Performance of Recycled Aggregate Concrete

“…Weak interfacial transition zone (ITZ) between the recycled concrete aggregate (RCA) and the cement matrix has also been identi ed [1,9,10]. Moreover, the presence of more than one ITZ in the RAC is another reason for the low quality of the RAC [1,9,11].…”

Effect of Sand Replacement and Silica Fume Addition on Chloride Ion Permeability of Lightweight Concrete

“…Silica fume acts as a micro filler, filing the transition zone between the aggregate surface and the bulk cement matrix, followed by pozzolanic reaction at the same place [13] . When porous aggregate is involved, as in lightweight aggregate used in this study, the interfacial transition zone extends from a certain distance below the surface of the aggregate particle out to the bulk cement [14] . Finally, it can be concluded that incorporating silica fume in structural lightweight concrete mixes significantly reduces the chloride ion penetration dye to the above mentioned mechanism (filler and pozzolanic effects) of concrete.…”