Page 22 - Demo

CONCRETE TECHNOLOGY22 CPI %u2013 Concrete Plant International | India Edition %u2013 5 | 2025 www.cpi-worldwide.comThis study investigated the effect of replacing natural dune sand with fine recycled concrete aggregates (fRCA) produced using real concrete construction and demolition waste (CDW) and with a maximum particle size of 1.18 mm on the fresh and hardened properties of concrete. Concrete with w/b ratios of 0.45 and 0.60 was produced. Natural fine aggregates comprised of a 50/50 mix of dune sand and crusher dust. fRCA replaced the dune sand portion of the natural fine aggregates by 0%, 30%, and 50% of total natural fine aggregates by mass. Results showed that workability of fresh concrete was reduced as fRCA replacement level increased while hardened properties of concrete, including compressive strength and various durability indicators - gas permeability, sorptivity, and water-penetrable porosity - were comparable at all replacement levels for each w/b. Sand, through supporting habitats and acting as the foundation of many ecological processes, plays a pivotal role in the healthy function of ecosystems. Moreover, as a key input in the production of commonly used construction materials such as concrete, asphalt, and glass, sand is also important in urbanization and infrastructure development. Consequently between 47 and 59 billion tons of sand and other aggregate materials are extracted per annum [1]. This exceeds the rate of renewal [1]. The Sand and Sustainability report issued by the United Nations [2] recommends reducing the consumption of virgin sand resources and using alternative materials such as recycled aggregates in its place. An example of a recycled aggregate material that has been successfully used to replace fine natural aggregates (such as sand) is fine recycled concrete aggregates (fRCA) [3]. fRCA is produced through crushing recovered concrete waste and sieving the crushed material at 4.75 mm, as per fine aggregate requirements stipulated in EN 12620:2013. As reported in EN 206:2016, coarse recycled concrete aggregates can replace up to 50% of natural coarse aggregates in the production of structural concrete. The use of fRCA, however, is currently prohibited due to concerns about the potential negative effects on the fresh and hardened properties of concrete produced [3]. According to the review of characterization and structural applications of fRCA by [3], experimental investigations into the use of fRCA in concrete as a natural fine aggregate replacement show that performance may improve, worsen, or remain the same depending on fRCA physico-chemical properties and how fRCA is treated during concrete manufacture. Performance may be limited by fRCA properties such as high water absorption due to the presence of porous hardened cement paste (HCP) phases. The proportion of HCP phases has been found to increase as the size fraction of recycled concrete aggregate decreases [4]. To limit the potential negative effects of these fine fractions, several studies have focused on the use of fRCA with fine fractions screened out or with fine aggregate gradings altered to limit the presence of these fractions [3]. However, this practice does not address the issue of limiting sand consumption in concrete production as sand particles often fall within this size range. Therefore, this study aims to investigate the effect of using fRCA sieved at 1.18 mm as a sand replacement on the fresh and hardened properties of concrete. Experimental methodologyMaterialsCEM II/A-L 42.5 N, comprised of Portland cement blended with approximately 9% limestone extender, was used as a binder. Greywacke aggregate with a nominal size of 19 mm was used as a coarse aggregate. Natural fine aggregates used include crushed greywacke rock and natural dune sand. fRCA was produced by crushing real concrete CDW produced during a regional highway construction project. Further information about the physical properties and grading characteristics of the fine aggregates used can be found in Table 1 and Figure 1, respectively. It was found that the natural sands largely lay outside of the recommended ASTM grading limits. However, the various blends, including the natural fine aggregate Fine recycled concrete aggregates as a replacement for natural sand in concrete production Circular economy n Areej Gamieldien, Bhooshay Dookee, Hans Beushausen and Mark Alexander, Department of Civil Engineering, University of Cape Town, South Africa