Abstract
This paper aims to experimentally investigate the effects of high volume cement replacement of blast furnace slag (BFS) on the bond, strength and durability of recycled aggregate concrete (RAC). Concrete mixtures were prepared containing 0%, 15%, 30%, 45%, 60% and 75% BFS with each of recycled aggregate and natural aggregate. Measurements of the compressive and bond strength, the resistance to chloride-ion penetration and the water permeability of concrete are reported. In addition, a microhardness test was also performed to evaluate the quality of interfacial transition zone (ITZ) in concrete. Test results of the bond strength and the compressive strength of RAC mixtures, in spite of the cement replacement amount with BFS, show that the concretes result in reduced strength when compared to natural aggregate concrete (NAC) mixtures, while the strength gains for the BFS-based concrete are higher than that of the reference mixtures without BFS at long-term ages. Incorporating BFS in concrete can inherently improve the durability properties by increasing higher resistance to chloride-ion penetration and lower water permeability. This improvement in the mechanical and durability properties of the BFS-based RAC mixture may be due to the additional pozzolanic reaction of BFS, which enhances the properties of ITZ in concrete, resulting in an improvement of the strength of concrete.
Highlights
Cement and aggregate are the two main components in concrete
The results revealed that the enhancement in the mechanical properties of blast furnace slag-based recycled aggregate concrete (RAC) mixes were found to be in the range of 14.02–19.61%, 10.74–14.71%, 9.33–14.07% and 6.65–14.17% for compressive, flexural and bond, and splitting tensile strength, respectively
These results indicate that the RAC mixtures prepared for test can exhibit adequate properties of fresh concrete
Summary
Cement and aggregate are the two main components in concrete. the procedures of their production emit much CO2 and consume a large amount of energy, which is unfriendly to the natural environment. Many researchers intended to find an effective method for producing sustainable concrete with a low amount of cement or recycled aggregate. The general measure is to crush waste concrete as coarse aggregate for producing concrete, which was regarded as recycled aggregate concrete (RAC) [1,2,3]. The surface of recycled coarse aggregate is generally full of pores, presenting high water absorption, which affects the interfacial transition zone (ITZ) property in concrete, leading to negative effects for the durability of concrete [4,5,6,7]. In order to improve the durability of the RAC, pozzolans such as fly ash and blast furnace slag were added to concrete; there are restrictions on the dosages of the pozzolans in many national standard codes [8,9,10]
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