# Binary Mixes of Self-Compacting Concrete with Municipal Solid Waste Incinerator Bottom Ash
## 1 Introduction  
The concentration of CO\({}_{2}\) in the atmosphere has been increasing progressively, with reported values of increase from 324 ppm in 1969 to 415 ppm in 2020 alone [1]. According to experts, to avoid climate change in the second half of the 21 st century, CO\({}_{2}\) emissions must be reduced by 90% by 2030 [2]. Today, the World's annual concrete production is approximately 1 \(\times\) 10\({}^{10}\) tonnes. This results in large amounts of CO\({}_{2}\) emissions mainly due to the production of Portland cement. This binder currently accounts for 74-81% of the total CO\({}_{2}\) emissions of concrete manufacture [3]. The production of one tonne of Portland cement emits about 0.94 tons of CO\({}_{2}\) and the cement industry is responsible for about 8% of all CO\({}_{2}\) emissions from all economic sectors [4]. It is estimated that 1.5 to 1.7 tons of natural resources are used as raw material per tonne of Portland cement [5]. Given the current status, there is an urgent need to change the methods and principles of Portland cement manufacturing and to evaluate in detail the use of various industrial wastes as cement replacement in the production of cementitious composites. The use of certain wastes, such as municipal solid waste incinerator bottom ash (MIBA), can prevent the excessive consumption of natural resources, is capable of reducing energy expenditure, can reduce the cement and/or concrete cost of manufacturing and can be beneficial for the environment due to the reduction of air pollution, landfill space, among other environmental impacts [6, 7]. In addition to the problem of CO\({}_{2}\) emissions into the atmosphere, the production of municipal solid waste is also expected to increase by approximately 2.2 billion tonnes per year by 2025 [8], which will consequently lead to an increase in by-products resulting from their combustion. In waste management policies, the priority is to prevent the production of waste; however, when this does not happen, the next steps include recycling, recovery, incineration and, as a last resort, the landfilling of wastes. Due to the scarcity of space available for the disposal of waste in landfills, the costs of this process tend to increase, which, together with issues like water contamination and public health, strengthen the need to find more technically, economically and environmentally friendly solutions. Currently, MIBA is commonly used for the construction of unbound layers for road pavements [9]. However, to respond to the demand for new materials that minimize the environmental impact of the construction sector, some studies have been developed to validate the use of MIBA in the production of concrete [7]. These have essentially focused on the mechanical behaviour of composites using MIBA as cement replacement. [PERSON] et al. [10] expressed the possibility of MIBA having pozzolanic or hydraulic behaviour due to their composition being similar to that of cement, but observed a decrease in compressive strength with the increase of MIBA in concrete. Other researchers found a similar decline in performance with increasing replacement levels [11; 12; 13]. [PERSON] et al. [14] used MIBA in combination with fly ash and cement in the production of ternary self-compacting concrete mixes; despite the decline in performance with increasing MIBA content, all mixes demonstrated adequate levels of workability according with existing regulations. Promising results are likely to be observed in mixes with relatively high replacement levels if MIBA is adequately treated before use. A pre-drying and milling process is fundamental to achieve a particle size distribution close to that of cement. There are few (and little in-depth) studies on, for example, its durability. Therefore, it is clear that there is a need for further studies on the incorporation of these ashes in cementitious composites.