Effective Recycling of Surface Modification Aggregate using Microwave Heating

Abstract

In this study, Author present a quantitative review of the mechanical performance, as well as the separation from the matrix and the recovery performance of surface modification coarse aggregate (SMCA) that was produced using aggregate, whose surface was modified using fine inorganic powder. Therefore, experiments were conducted to measure the compressive strength, microwave heating characteristics, distribution of the void volume, and chemical changes in SMCA concrete, as well as the recovery rate of the aggregate. The results of the experiments showed that reinforcing the interfacial transition zone, which is a weak part in concrete, by coating the surface of the original coarse aggregate with cement paste, can help suppress the occurrence of microcracks and improve the mechanical performance of the aggregate. Further, microcracking and the decomposition of hydrates were observed as a result of microwave heating. In other words, an increase in void size distribution and weakening of the hydrated cement paste led to the effective recovery of recycled coarse aggregate.

Using Microwave Heating to Completely Recycle Concrete

“…For the mechanical properties, the compressive and splitting tensile strengths of each SMCA concrete specimen were higher than those of the OCA concrete specimens by 5% -12%, as shown in Figure 16 and Figure 17 improved strength of the modified aggregate concrete was due to the reinforced physical and chemical bonding between the modified paste and cement matrices, which was caused by the increased mechanical friction resulting from the particle size and shape of the iron oxide and the SMCP coating effect on the ITZ [5]. In addition, the SMCA concrete using pozzolanic materials (silica fume and fly ash) showed an increase in strength of approximately 8% after 7, 14, and 28 days of curing compared to the SMCA concrete using only cement ( Figure 16).…”

“…In the mixing design, the amount of coarse aggregate coated with an admixture can be increased. Thus, the amount of SMCP coated on the coarse aggregate can be excluded from the amounts of cement and water in the mixing ratio, and the amounts of cement, water, and OCA for the OCA and SMCA concretes can be the same [5]. In this experiment, OCA and SMCA concrete specimens with a water-cement (W/C) ratio of 55% were compared.…”

“…Thus, recycled coarse aggregate (RCA) can be recovered for concrete structures because the mechanical performance of the concrete is improved, as shown in Figure 2(a) and Figure 2(b). This technique involves coating the OCA with iron oxide (Fe 2 O 3 ), which has a high dielectric constant, as a binder and then selectively heating and weakening the aggregate interface with microwaves to manufacture RCA following the dismantling of a structure, as shown in Figure 3(a) and Figure 3(b) [5]. This technique allows almost complete recycling of the aggregates by recovering high-quality RCA while using a small amount of energy [21] [22].…”

“…The accumulation and storage of concrete in huge piles cannot be a long-term solution because of the reduced natural resources and lack of space. Moreover, decreases in road construction work, which is the main use for recycled concrete, are expected to lead to less demand for sub-base coarse material for roads [3] [4]; in the long term, this calls for measures to expand and diversify the use of recycled concrete waste and to use recycled aggregates for concrete manufacture [5]. Thus, research on recycled aggregates is being conducted from various angles worldwide, and the Japanese Industrial Standards (JIS) has been revised for recycled aggregates [6].…”

Evaluation on the Surface Modification of Recycled Fine Aggregates in Aqueous H2SiF6 Solution

“…In general, the reason that RAs are lower in quality than natural aggregates is because mortar adheres to the surface of RA (cement matrix). Low-quality RAs having a high absorption rate and low weight have limitations in terms of being reused for concrete (Behera et al 2014;Choi et al 2014;Ismail and Ramli 2014). Accordingly, most RAs are not used as concrete aggregates, but as roadbed and sub-base materials; however, this demand is gradually decreasing, while the demand for their use in concrete is continuously required.…”