Testing and Prediction of the Strength Development of Recycled-Aggregate Concrete with Large Particle Natural Aggregate

Abstract

In this paper, a new recycled aggregate concrete (RAC) was produced with composite coarse aggregate and fine recycled aggregate. The composite coarse aggregate was mixed into continuous gradation by large particle natural aggregate with small particle recycled aggregate. To explore the time-dependent developments of the compressive strength and splitting tensile strength of this new RAC, 320 groups of cubic specimens were tested at different curing ages from 3 days to 360 days to measure the compressive and splitting tensile strengths. The amount of large particle natural aggregate varied from zero to 70% in mass of the total coarse aggregate. The water/cement ratio was taken as 0.60, 0.49, 0.41 and 0.36 to represent four strength grades of the RAC at about C20, C30, C40 and C50. Based on the tested results, the curves of the compressive and tensile strengths of the RAC that changed with curing age are plotted, which clearly exhibit that the amount of large particle natural aggregate had a rational range in different strength grades of the RAC which had better aging strength. When the RAC was no larger than C30 with a water/cement ratio of 0.60 and 0.49, the amount of large particle natural aggregate should be no more than 30%; when the RAC was no less than C40 with a water/cement ratio of 0.41 and 0.36, the amount of large particle natural aggregate should be no less than 50%. Along with the general prediction of the strength development of all the tested RAC, the optimal predictive formulas are proposed for the strength development of RAC with a rational amount of natural aggregate. Meanwhile, the strength developments of RAC with a rational amount of natural aggregate are assessed by the time-dependent models proposed by the ACI Committee 209 and CEB-FIP MC 2010.

Environmental Assessment of Two Use Cycles of Recycled Aggregate Concrete

“…This could lead to better mechanical and permeability properties of the concrete. The use of fine and coarse RCA also influences the strength development of RAC [42].…”

Shear Performance of Reinforced Concrete Beams Affected by Satisfactory Composite-Recycled Aggregates

“…The mix proportion design of concrete has been adjusting by using mineral admixtures [9,10], and different approaches of recycled aggregates replacing natural aggregates. These approaches include coarse natural aggregate being partially replaced by recycled coarse aggregate, natural sand partially or all replaced by recycled fine aggregate, and full use of recycled fine and coarse aggregates [2,6,11,12]. The absolute volume method has been generally accepted in the design of mix proportion to deal with the difference of density among raw materials.…”

“…The absolute volume method has been generally accepted in the design of mix proportion to deal with the difference of density among raw materials. The mixing procedure attains perfection by adding the step of pre-soaking the recycled aggregates with additional water, or pre-wrapping recycled coarse aggregates with a certain amount of cement paste [10][11][12][13][14]. Different properties of concrete with recycled aggregates are given out due to the different approaches applied in the investigations.…”

“…Following the worldwide research steps, the authors' research team draw inspiration by absorbing the successful experiences in the investigations of recycled aggregate concrete. The purpose is to fully use the recycled fine and coarse aggregates without byproduct emission [11,12,[19][20][21][22]. A three-stage-recycling-technology is formed to produce recycled aggregate with rational morphology.…”

“…This forms a composite-recycled aggregate. Combined with the perfecting of the mixing process, a new concrete with composite-recycled aggregate (abbreviated as CRAC) is produced [11]. As the composite technology overcomes the shortcomings of large particle recycled coarse aggregate with rough surface attached old mortars, the mechanical properties of CRAC are similar to those of conventional concrete [25,26].…”