Alternative cleaner production of sustainable concrete from waste foundry sand and slag
N. T. Sithole
<p><span class="fontstyle0">The objective of this study was to synthesize a sustainable concrete material from readily available waste and byproducts; Ground Granulated blast furnace slag (GGBFS) and waste foundry sand (WFS). GGBFS was alkaliactivated using NaOH solution and used as a binder to completely replace Ordinary Portland cement (OPC). Concurrently, WFS was used as fine aggregate to replace natural sand in concrete production. An optimization experimental program of various conditions was used to get the best concrete specimens in terms of high strength and low metal leachability. The GGBFS, WFS, and crushed stones mix design formulations used were; 20:40:40, 25:37.5:37.5, 30:35:35, and 40:30:30 respectively. The specimens were cured for 7, 14, 28, 56, and 90 days, respectively. The liquid to solid (L/S) ratio was varied from 15% to 30%. The concrete specimens</span><span class="fontstyle2">’ </span><span class="fontstyle0">with a mix design formulation; 40% GGBFS binder, 30% WFS, and 30% crushed stones with 15% L/S ratio cured for 90 days yielded the highest Unconfined Compressive Strength (UCS) of 12.7 MPa. The best concrete specimen was evaluated for durability, structural performance, and long-term metal leachability. The XRD results showed that hydration products (CSH) play a crucial role in the strength development of the concrete. The metal leachability and durability results show that the metals were successfully immobilized in the concrete specimens with acceptable durability properties. Thus, the synthesized concrete specimens can be used for loadbearing concrete masonry units as per ASTM </span><span class="fontstyle0" style="color:rgb(33,150,209);">C90 </span><span class="fontstyle0">and other building and construction applications as per ASTM </span><span class="fontstyle0" style="color:rgb(33,150,209);">C34</span><span class="fontstyle0">- 03, ASTM </span><span class="fontstyle0" style="color:rgb(33,150,209);">C62-10</span><span class="fontstyle0">. Furthermore, the study demonstrated that a sole alkaline activated GGBFS can completely replace OPC and concurrently use WFS as fine aggregate to replace natural sand in concrete production. As a result, the reutilization rate of WFS can be increased from 20% to 30%.</span>
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