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This study focused on the performance of hardener-free epoxy-modified mortar (HFEMM) with pyrolysis tar (PT), a by-product of the green wood industry. HFEMMs were prepared with amounts of 1, 3, and 5% epoxy resin. For the HFEMM with a 1% epoxy resin mixing rate, 5, 10, 15, and 20% of the epoxy resin were replaced with PT. The highest hardening rate was observed for the HFEMM with 1% epoxy resin, whereas the amounts of hardened and unhardened epoxy resin were the largest at 5%. When 1% epoxy resin was replaced with PT, the hardening rate increased to 10%. When 10% PT was substituted with 1% epoxy resin, the compressive, flexural, and adhesive strengths increased because of the higher hardening rate. X-ray diffraction result showed that an increase in the epoxy resin content and the PT replacement rates resulted in lower amounts of calcium hydroxide and lower semi-adiabatic and maximum exothermic temperatures. These results showed that the use of PT in the HFEMM could improve its performance while providing an avenue to recycle PT.

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.

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.

In the case of fire, surface treatment agents used in external insulation finishing methods are substances that are vulnerable to fire. This study examined the incorporation and applicability of expandable graphite in surface preparation mortar so that heat transfer to the surface part can be suppressed even when the cementitious surface preparation mortar is thinly constructed in the external insulation method. Experimental results showed that the mechanical properties of surface preparation mortar were improved by using the fly ash and silica fume. Surface treatment materials using expanded graphite have a characteristic of expanding when a fire occurs. It was experimentally confirmed that incorporating expanded graphite can reduce the phenomenon of heat penetration to the rear surface when the surface preparation mortar is exposed to high temperatures such as a flame.