Abstract
Each year, about 730 million tons of bottom ash is generated in coal fired power plants worldwide. This by-product can be used as partial replacement for Portland cement, favoring resource conservation and sustainability. Substantial research has explored treated and processed coal bottom ash (CBA) for possible use in the construction industry. The present research explores using local untreated and raw CBA in mitigating the alkali–silica reaction (ASR) of reactive aggregates in concrete. Mortar bar specimens incorporating various proportions of untreated CBA were tested in accordance with ASTM C1260 up to 150 days. Strength activity index (SAI) and thermal analysis were used to assess the pozzolanic activity of CBA. Specimens incorporating 20% CBA achieved SAI greater than 75%, indicating pozzolanic activity. Mixtures incorporating CBA had decreased ASR expansion. Incorporating 20% CBA in mixtures yielded 28-day ASR expansion of less than the ASTM C1260 limit value of 0.20%. Scanning electron microscopy depicted ASR induced microcracks in control specimens, while specimens incorporating CBA exhibited no microcracking. Moreover, low calcium-to-silica ratio and reduced alkali content were observed in specimens incorporating CBA owing to alkali dilution and absorption, consequently decreasing ASR expansion. The toxicity characteristics of CBA indicated the presence of heavy metals below the US-EPA limits. Therefore, using local untreated CBA in concrete as partial replacement for Portland cement can be a non-hazardous alternative for reducing the environmental overburden of cement production and CBA disposal, with the added benefit of mitigating ASR expansion and its associated costly damage, leading to sustainable infrastructure.
Highlights
Alkali–silica reaction (ASR) is a common deterioration process in concrete structures incorporating reactive aggregates
This study investigates the physical and chemical properties of local untreated coal bottom ash (CBA), its concentration of heavy metals and compares the results with previous studies (CBA produced in different countries), the pozzolanic activity of untreated local CBA and its possible role in controlling alkali–silica reaction (ASR) damage in concrete
Sandstone was fine to medium grained (0.10 to 0.60 mm) and grayish to brown in color
Summary
Alkali–silica reaction (ASR) is a common deterioration process in concrete structures incorporating reactive aggregates. Alkalis present in the pore solution react with siliceous phases in reactive aggregates and produce alkali–silica gel This ASR gel absorbs moisture and swells, leading to distress and cracking, possibly compromising the structural integrity and durability of concrete structures [1,2,3]. It has been posited that the availability of calcium ions is important for preserving desirable alkalinity levels in the pore solution [4]. Various reactive aggregates such as Spratt, opaline silica, strained quartz, cristobalite, chalcedony, volcanic glasses and ferronickel slag were found to accelerate ASR [5,6]. Other factors that cause adverse ASR in concrete structures include the presence of moisture, type of alkali constituents and exposure to higher temperature [1]
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