# Evaluation of Workability and Mechanical Properties of Bottom Ash Aggregate Concrete
## 1 Introduction  
In South Korea, the amount of industrial waste has been increasing exponentially for decades due to rapid growth and industrial expansion. In this context, many studies have contributed to improvement of the physical and mechanical properties of concrete by adding recycled industrial waste. As a result, a number of industrial byproducts (e.g., fly ash (FA), silica fume, and blast furnace slag) have been recognized as concrete admixture additives, and are widely used [1]. On the other hand, byproducts from marine sediment, municipal solid waste incinerator (MSWI), and bottom ash (BA) show noticeably low rates of utilization due to their respective drawbacks [2; 3]. Among them, the use of BA, which accounts for 10-15% of the total amount of cinders generated, shows significantly less improvement in the mechanical characteristics of concrete compared to FA [4]. Thus, the demand for it is low, and most BA beyond storage capacity is buried or discarded [5; 6]. BA contains heavy metals and arsenic as part of its chemical composition, and is classified as an environmental hazard in the majority of countries [7; 8]. Therefore, it is necessary to accurately evaluate the mechanical properties of BA-incorporated concrete in order to achieve a concrete structure that is safe, durable, and sustainable. BA is generally considered to be most appropriate for use as an alternative to fine aggregate in concrete. In a considerable number of studies, the use of BA as an alternative to fine aggregate revealed very encouraging results in terms of strength and pore structure [9; 10; 11; 12]. Some studies have reported that there is an increase in strength compared with plain concrete according to the replacement ratio of fine bottom ash aggregate (BAA) [13; 14; 15], and indicate that this is most probably caused by the pozzolanic reaction of particles 600 \(\upmu\)m or less in size among the BAA [16]. Coarse BAA is porous, irregular, angular, and rough-textured, and is characterized by being lighter than natural aggregate [17; 18]. These physical properties may be suitable for the application of coarse BAA as concrete aggregate; however, its excessively porous structure and rough-textured properties act as disadvantages that may lower the mechanical properties of concrete, including fluidity and strength development. In particular, BAA shows a lower density than natural aggregate at about 2.0 kg/m\({}^{3}\) (although it varies according to producing countries and manufacturing technologies), and so is classified as lightweight aggregate (LWA), but it is a relatively heavy LWA. In general, concrete containing bottom ash (CCBA) has a relatively higher density than the range of oven-dried density (\(\rho_{c}\)) (1600-1840 kg/m\({}^{3}\)) for lightweight aggregate concrete (LWAC) suggested by LWAC-related design codes (ACI Committee 213 [19], ASTM C 330 [20], and Comite Euro-International du Beton [21]). For the reliable design of structures, specific data and rational estimation regarding the mechanical properties of materials are required. In general, LWAC is known to show inferior mechanical performance compared to normal weight concrete (NWC) with similar compressive strength. If the strength of the aggregate itself is low, the transmission velocity of the cracks becomes high because cracking in the case of maximum load mostly penetrates the aggregate, and a large decrease in strength occurs in parts of the same member because of the generation of localized failure zones [17]. The biggest obstacle to the use of CCBA for structures is that there are relatively few studies on its mechanical properties. Accordingly, it is difficult to clearly determine its adherence to the existing structural design codes. These concerns are greater when BA is applied as coarse aggregate than as fine aggregate [12; 22].