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.
Highlights
With the awareness of sustainable social development and strengthened measures to protect natural resources and the environment, the usage of recycled aggregate derived from construction and demolition waste and dismantled concrete structures becomes increasingly important
Lotfi et al [4] discovered that the properties of recycled aggregate concrete (RAC) were less influenced by the replacement rate of recycled aggregate, while they were directly affected by the grade of cement and the water/cement ratio; Yao et al [10] revealed that when the replacement rate of coarse recycled aggregate with a particle size of 19–26.5 mm varied from 0% to
100%, only the cases of 0% and 60% led to the maximized compressive and splitting tensile strengths of RAC; Liu et al [11] explained by numerical analyses that the compressive and flexural strengths of RAC decreased gradually with the increase of the amount of coarse recycled aggregate, and the flexural strength decreased with the increasing maximum particle size of coarse recycled aggregate
Summary
With the awareness of sustainable social development and strengthened measures to protect natural resources and the environment, the usage of recycled aggregate derived from construction and demolition waste and dismantled concrete structures becomes increasingly important. This leads to a new research area to reuse recycled aggregate as a substitute for natural aggregate to produce a new concrete, commonly called recycled aggregate concrete (RAC) [1,2,3]. The structural behaviors of RAC members are generally weaker in comparison to those of structures made of natural aggregate concrete, RAC can be used through proper design from the view point of loading capacity behavior This can be attributed to ignoring the special morphology of recycled aggregate with a different particle size
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