# Feasibility of Developing Sustainable Concrete Using Environmentally Friendly Coarse Aggregate
## 1 Introduction
However, the negative effect of recycled aggregates on the mechanical properties of concrete is higher when using mixed recycled aggregates than when using recycled coarse aggregate [27]. Replacing 50% of natural aggregate by mixed recycled aggregates produces a decrease in compressive strength up to 20% [28; 29; 30] whereas 100% mixed recycled aggregates replacement produces a decrease in compressive strength up to 45% [30; 31; 32]. However, replacing coarse aggregates up to 30% with recycled concrete aggregates have marginal effect on compressive strength development [33]. Further, even with 100% of coarse recycled concrete aggregate replacement, the compressive strength reduction is only 20 to 30% [34; 35]. The reduction percentage of compressive strength depends on the quality of recycled aggregate used [36; 37]. Recycle aggregate concrete has shown comparable long term strength development to normal aggregate concrete [33; 38]. A possible alternative source of the recycled coarse aggregate is that of the waste concrete that is unused in construction projects. At present this is discharged from the mixer, allowed to set and then crushed to produce recycled coarse aggregate. This process requires both time and energy in detouring to discharge the unused concrete, the setting time and then the crushing and grading. An alternative approach has been developed which directly treats the wet mix. Using a patented hygroscopic chemical formula, a powder is added to the wet concrete. Due to the hygroscopic property it absorbs virtually all of the water and moisture in the mix. Once the mix is dry it allows the fine and the coarse aggregate to be separated and stored for later use. This process does not require the concrete to harden as in most concrete recycling techniques, and therefore significantly reduces the time needed in traditional concrete recycling. In addition, the procedure does not require heavy machinery to crush any concrete, nor does it require transportation to storage sites, hence conserving energy and fossil fuel usage. Furthermore, due to the highly hygroscopic nature of the powder, when used in sufficient amounts it will absorb the majority of the water and moisture in the mixer, leaving the interior almost dry with no sticky residue, this makes it significantly easier to clean the trucks potentially using only one tenth of the usual amount of water to clean the mixing equipment compared to a mixer used for traditional concrete. [PERSON] et al. [39] used a similar approach to produce recycled aggregate from fresh concrete waste without employing mechanical crushing. The authors [39] used a superabsorbent polymer and an ettringite forming compound to produce the recycled aggregates. This recycled aggregate was used in concrete, with up to 30% replacement of the natural aggregates. However, this technique is significantly different from the other fresh concrete waste recycling techniques commonly reported in the literature [40; 41; 42]. In this study a novel methodology to reclaim unused aggregate from wet mix concrete was employed to produce recycled coarse aggregate. An investigation was undertaken to determine the effect of replacing standard quarried coarse aggregate with the recycled concrete aggregate while maintaining a similar aggregate grading. Two different standard concrete design strengths, i.e., 25 MPa and 40 MPa, corresponding to Australian concrete code AS 3600 [43] were employed to produce recycled coarse aggregates. This paper presents the key engineering properties, such as compressive strength, flexural strength, splitting tensile strength, elastic modulus, water absorption and drying shrinkage of concrete produced. The observed test results up to 90 days of age are reported, and the variations in properties observed are then explained in conjunction with the microstructure development.