Using Microwave Heating to Completely Recycle Concrete

Abstract

The aim of this study was to develop a technique for the complete recycling of concrete based on microwave heating of surface modification coarse aggregate (SMCA) with only inorganic materials such as cement and pozzolanic materials (silica fume, fly ash). The mechanical properties of SMCA, which was produced using original coarse aggregate (OCA) and inorganic admixtures, as well as its separation from the cement matrix and recovery performance were quantitatively assessed. The experimental results showed that micro structural reinforcement of the interfacial transition zone, which is a weak part of concrete, by coating the surface of the OCA with cement and admixtures such as pozzolanic materials can help suppress the occurrence of micro-cracks and improve the mechanical performance of the OCA. Microwave heating was observed to cause micro-cracking and hydrate decomposition. Increasing the void volume and weakening the hydrated cement paste led to the effective recovery of recycled coarse aggregate.

A review of alternative approaches to the reduction of CO2 emissions associated with the manufacture of the binder phase in concrete

“…[34] recently reported a technique for easy separation of aggregate from cement paste by applying inorganic materials such as cement and pozzolanic materials to the aggregate surfaces and employing microwave heating to manufacture recycled aggregate. This technique enables reducing CO 2 emissions from aggregate recycling to about one third those by conventional methods.…”

Evaluation on the Mechanical Performance of Low-Quality Recycled Aggregate Through Interface Enhancement Between Cement Matrix and Coarse Aggregate by Surface Modification Technology

“…The bonding failure load was then measured at a loading speed of 1 mm/min. In the tensile-shear bonding test, an epoxy adhesive was used on the tension test device to perform the loading using a ring without causing eccentricity (Choi et al 2014b). Moreover, for a more quantitative examination of the mechanism in which the strength of modified aggregates is improved, through a microscopic analysis of the ITZ, the specimens shown in Fig.…”

“…using an inorganic material, thereby improving the ITZ and enhancing the mechanical characteristics of the resulting concrete (Tsujino et al 2007(Tsujino et al , 2010(Tsujino et al , 2011Choi et al 2014b). Figure 2 shows a schematic diagram of the bonding mechanism at each interface after surface modification, while Fig.…”

“…In order to assess the chemical and physical bonds of the modified aggregate, general aggregates, and the cement matrix, specimens simulating coarse aggregates, modification paste, and mortar were fabricated as shown in Fig. 4, based on the modification paste and mortar mix reported in an earlier study on surface modification (Choi et al 2014b). Compressive-and tensile-shear bonding tests were performed to assess the effect of surface modification on the chemical and physical bonding characteristics of the aggregate and cement matrix.…”

“…Choi et al (2014a, b) conducted a study on surface modification (Noguchi and Tamura 2001;Tsujino et al 2010Tsujino et al , 2011 through the use of an inorganic material on crushed stone aggregates; they reported its effect on improving the mechanical characteristics of crushed stone aggregates and recovering high-quality recycled aggregates. Of particular note, based on the method using sand enveloped by cement (SEC), in which fine aggregates are coated with a cement paste with low water-to-cement (W/C) ratio, while the mixing water is added in steps (Tazawa 2002), a surface-modification technique was developed for the enhancement of concrete performance by improving the interfacial transition zone (ITZ), which is the weak region in concrete (Tsujino et al 2007;Choi et al 2014b).…”