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Abstract Recycled aggregates (RAs) production techniques are essential for the material circulation society because RAs from demolished concrete waste can sustainably be reused as a concrete material. However, RAs can bring about several performance decreases when they are used for recycled aggregate concrete (RAC) because of the low qualities (i.e., high water-absorption rate and low density) caused by the attached hydrated cement paste on the RA surface. Therefore, both the production of high-quality RAs and the surface modification of RAs are significantly important for the extension of RAC utilization. This paper focuses on the surface modification of RFA to reduce the water absorption rate and increase density. Hydrofluorosilicic acid (H2SiF6), which is one of the by-products in phosphoric acid manufacture, is used herein for the surface modification of the RFA. The physical properties and mechanical performance of mortar using RFA were evaluated after RFA modification. Consequently, the proposed method is effective in reducing water absorption rate and increasing density of RFA. The density of RFAs was slightly increased by 0.5–2.6% after modification. On the other hand, the water absorption rate decreased by 4–18% after modification. The compressive strengths of mortar at 28 days ages showed 18.1 MPa with modified RFA and 16.2 MPa with RFA.

Abstract Calcium acetate, which can be used in concrete to shorten the construction period and to improve productivity, was manufactured using limestone sludge and acetic acid. Calcium acetate contains a carboxyl group, and it can provide anticorrosive properties by forming a complex with the steel surface. We evaluated the basic performance of a carboxylic early-strength agent produced from industrial by-products (limestone sludge and acetic acid) as a corrosion inhibitor. A comparative evaluation was performed using calcium nitrate, which is a conventional early-strength agent; the corrosion area ratio, corrosion state, and electrochemical performance of a steel plate immersed in aqueous solutions were evaluated. A steel plate immersed in calcium acetate was not substantially corroded. The electrochemical investigations showed a high corrosion potential based on the impedance characteristics. The corrosion current showed anodic values, and no corrosion occurred on the surface of the steel plate because of the adsorption of carboxyl groups. Scanning electron microscopy indicated that the steel plate was covered by a crystalline coating, which suppressed corrosion. We show that it is possible to develop an environmentally friendly recycling method as an early-strength agent and corrosion inhibitor when manufacturing calcium acetate using limestone sludge.

Ready mixed acrylic paste (RMAP) is a material used in exterior insulation systems of buildings; it consists of liquids and aggregates. However, it is considerably difficult to use an admixture to control the physical properties of the RMAP owing to problems associated with strength and workability. Thus, to improve the properties of RMAP, this study evaluates the properties of a mortar produced with RMAP as well as pozzolanic materials and atomizing slag, which is a by-product from the steelmaking industry. It was observed that if the density difference is large, a liquid RMAP may experience segregation. Through our experiments, we confirm that segregation resistance could be achieved even at 20% atomizing slag, which has a high density, by increasing the viscosity by approximately 1000 cP through the use of 10% fly ash and 3% metakaolin in the RMAP. Despite the increase in viscosity with the addition of the atomizing slag, the flow of the RMAP increased from 160 to 175 mm due to the spherical particle shape of the slag; in addition, the strength and water absorption coefficient also improved. In particular, the adhesion tension increased from 1.8 N/mm2 to 2.4 N/mm2 or higher.

Concrete is one of the most widely used construction materials. There are several methods available to improve its performance, with one of them being the use of high-early-strength admixtures (HESAs). Typical HESAs include calcium nitrate, calcium chloride, and calcium formate (CF). Industrial by-products, such as acetic acid and lime stone sludge (LSS), can be used together to produce calcium acetate (CA), which can subsequently be used as a cementitious HESA. In this study, calcium carbonate and LSS were mixed with cement in weight ratios of 1 : 1, 1 : 1.5, and 1 : 2, and the properties of the as-produced CA were evaluated. CA and CF were mixed with cement in different weight ratios (0, 1, 2, and 3 wt%) to obtain CA- and CF-mortars, respectively. The flow behavior, setting time, pH, and compressive strength of these mortars were evaluated, and their X-ray diffraction patterns were also analyzed. It was found that as the CF content in the CF-mortar increased, the initial strength of the mortar also increased. However, it impaired its long-term strength. On the other hand, when 1% CA was mixed with cement, satisfactory early and long-term strengths were achieved. Thus, CA, which is obtained from industrial by-products, can be an effective HESA.