Abstract
Alkali-activated concrete (AAC) could be a solution to use a cement-less binder and recycled materials for producing concrete reducing the carbon dioxide emission and the demand for raw materials, respectively. In addition to the environmental aspect, AACs can achieve mechanical characteristics higher than those of ordinary Portland concrete (OPC) but also an improvement of the thermal insulation capacity. Despite the positive results available in the scientific literature, the use of AACs in construction practice is still limited mainly due to the absence of codification for the mix design and consequently of specific design rules. In this paper, AAC produced by ground-granulated blast-furnace slag (GGBFS) and silica fume is investigated for the production of structural elements and to discuss the reliability of formulations for evaluating mechanical properties, necessary for structural design. The mechanical strengths (compression strength, tensile strength, flexural strength) are evaluated by experimental tests according to different curing times (7, 14, 28, 90 days) in ambient conditions and the thermal conductivity is measured to understand the effect that the material could have on thermal losses for a sustainable building perspective. The results showed that AAC strengths depend on the curing time and the exposure conditions, and the insulation properties can be improved compared to the traditional Portland cement with the proposed composition.
Highlights
The environmental and economic concerns associated with conventional cement-based building materials have led the scientific and technical community to explore possibilities in the use of alternative materials.Currently, the concrete industry faces two main challenges that are the increasingly limited limestone reserves and the carbon taxes increase because of the growing demand for Portland cement (OPC) and the greenhouse gas emissions resulting from the production of ordinary Portland concrete (OPC), respectively [1]
The mechanical and thermal properties of alkali-activated concrete produced by silica fume and ground-granulated blast-furnace slag (GGBFS) were investigated by experimental tests
A rapid setting of the mixture has been observed during the manufacturing process, the difficult workability can be a challenge to face during casting; The compression strength of alkali-activated concrete is affected by test age and significant performance is obtained already in the early days of curing; The long-term measured properties showed a degradation of the strength probably due to the curing conditions in humid environments that could favor the development of the sub fluorescence phenomenon and the carbonatation causing internal damage to the material
Summary
The environmental and economic concerns associated with conventional cement-based building materials have led the scientific and technical community to explore possibilities in the use of alternative materials.Currently, the concrete industry faces two main challenges that are the increasingly limited limestone reserves and the carbon taxes increase because of the growing demand for Portland cement (OPC) and the greenhouse gas emissions resulting from the production of OPC, respectively [1]. Approximately 5–7% of global CO2 emissions originate from the manufacturing of Portland cement [2,3], and its production consumes a high amount of energy that is accounting for 50–60% of the plant production costs [4] These issues require the development of alternative binders, such as alkali-activated cement (AAC), with the aim of reducing the environmental impact of buildings, the use of a greater percentage of pozzolan waste and improving concrete performance [5]. From this point of view, they are considered an ecological binder whose production involves CO2 emissions lower than those necessary to produce OPC [6,7], with a reduction of greenhouse gas emissions up to 64% [8]. Based on a life cycle assessment (LCA), it was reported that the global warming potential of fly ash-based AAC is about 70%
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