Utilizing basic oxygen furnace slag and fly ash to stabilize wet flue gas desulfurization gypsum for construction applications

Dumisane Mahlangu , Keletso Mphahlele , Nomcebo Mthombeni , Bridjesh Pappula , Seshibe Makgato
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Abstract

Gypsum production in South Africa has surged due to the country’s dependence on coal-fired power plants, resulting in increased generation of fly ash (FA), wet flue gas desulfurization gypsum (WFGDG), and basic oxygen furnace slag (BOFS). This study proposes a sustainable solution for repurposing these industrial by-products into eco-friendly construction materials. A novel binder was developed by blending varying proportions of WFGDG, FA, and BOFS. In these composite blocks, up to 50 wt% of WFGDG was substituted with FA and BOFS. The blends were evaluated for compressive strength, durability, resistance to wet-dry cycles, and environmental impact. The optimum mix-containing 10 wt% FA and 40 wt% BOFS - achieved a compressive strength of 4.4 MPa after 90 days of ambient curing at 40 °C, exceeding the SANS 10145 requirement for Class III mortar. Compaction tests showed that increasing FA content reduced reactivity, with the best performance observed at the mentioned ratio. Microstructural analysis using Scanning Electron Microscopy (SEM) and X-ray Diffraction (XRD) revealed the development of new hydration products and confirmed crystallinity. Despite FA's pozzolanic potential, it does not self-activate due to the absence of alkalis and sulfates. Environmental compliance was verified through the Toxicity Characteristic Leaching Procedure (TCLP), meeting the safety criteria of SANS 227:2007 and ASTM C34–13. The study highlights the potential of these waste-derived composite bricks for load-bearing applications, offering an environmentally and economically sustainable alternative for the construction sector.
利用碱性氧炉渣和粉煤灰稳定湿法建筑烟气脱硫石膏
由于南非对燃煤电厂的依赖,该国的石膏产量激增,导致粉煤灰(FA)、湿法烟气脱硫石膏(WFGDG)和碱性氧炉渣(BOFS)的产量增加。这项研究提出了一个可持续的解决方案,将这些工业副产品转化为环保建筑材料。通过不同比例的WFGDG、FA和BOFS的共混,研制出一种新型粘合剂。在这些复合块中,高达50% wt%的WFGDG被FA和BOFS取代。评估共混物的抗压强度,耐久性,抗干湿循环和环境影响。在40°C环境养护90天后,最佳混合物(含10 wt% FA和40 wt% BOFS)的抗压强度达到4.4 MPa,超过了SANS 10145对III类砂浆的要求。压实试验表明,增加FA含量可降低反应活性,且在该比例下表现最佳。利用扫描电子显微镜(SEM)和x射线衍射仪(XRD)进行微观结构分析,发现了新的水化产物,并证实了结晶度。尽管FA具有火山灰潜能,但由于缺乏碱和硫酸盐,它不能自激活。通过毒性特性浸出程序(TCLP)验证了环境合规性,符合SANS 227:2007和ASTM C34-13的安全标准。该研究强调了这些由废物产生的复合砖在承重应用方面的潜力,为建筑部门提供了一种环境和经济上可持续的替代方案。
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