As a measure to reduce CO₂ emissions during cement production, a special formulation of ordinary Portland cement (OPC) was prepared with the content of minor additional constituents increased up to 10%, and physical properties of the concrete using the cement were evaluated by laboratory testing and also in the exposure to natural environments.
　The cement, named "10 OPC", contains 10% limestone and has an increased amount of the aluminate phase (C₃A). Both in cement and concrete evaluations, 10 OPC demonstrated comparable performance to conventional OPC which typically contains 5% limestone. The exposure tests which were conducted at three different locations across Japan revealed no signs of deterioration or visible damage in any of the concrete specimens over the course of one year. Furthermore, no significant differences were found in compressive strength between the two types of cement. Additional evaluations included indoor saline immersion tests and exposure tests in environments containing stagnant seawater. The results of these tests confirmed that the chloride penetration resistance of 10 OPC was equivalent to that of conventional OPC.

View full abstract

 For the purpose of determining efficient thermal carbonation treatment conditions for waste concrete, trying evaluated the effects of sample particle size, water content, CO₂ concentration in the gas and temperature/humidity on the amount of CO₂ fixation which are assumed to be factors affecting CO₂ fixation in waste concrete. As a result, the increase in specific surface area due to smaller particle size or the increase CO₂ gas concentration was effective for CO₂ fixation, since the thermal carbonation process progressed from the surface to the interior of the sample. It was also found that the thermal carbonation reaction was accelerated when the sample water content of the sample was less than 6% and not dry. An experiment with 20% CO₂ gas was carried out, assuming using cement kiln exhaust gas with a low CO₂ concentration directly. It was revealed that the same amount of CO₂ as that with pure CO₂ gas could be fixed when the samples with particle sizes of 20 mm or less (excluding fine particles) were allowed to react with the gas equivalent to cement kiln exhaust gas at a temperature of 90°C and a relative humidity of 40% for about 2 hours, with the water content kept at 3% to 6%.

View full abstract

 Waste rocks generated during tunnel construction contain naturally occurring heavy metals, sometimes in amounts incompatible with the soil elution standards. Insolubilization is a common measure to reduce future elution by adding materials that chemically immobilize the heavy metals. However, it has been reported that crushing or slaking occurring after the construction can change the elution characteristics of the heavy metals.
　In this study, sedimentary rock and igneous rock samples which were obtained from excavation and found incompatible with the soil elution standards were examined by the short-term elution test, which was a laboratory test commonly used for evaluation, and the rainwater exposure test by the method of the Public Works Research Institute of Japan.
　The effectiveness and duration of the insolubilization using DENITE were investigated, and the changes in elution characteristics of heavy metals associated with crushing and slaking were measured. It was found that the addition of DENITE at 15 kg/m³ or more could reduce leaching concentrations of heavy metals for a long term, even with waste rocks liable to fragmentation by slaking or crushing.

View full abstract

 To achieve carbon neutrality, efforts are being made to reduce greenhouse gas emissions. Our company has developed CARBOFIX^Ⓡ cement, which has a low CO₂ emission during manufacturing and reacts with CO₂ during curing to enhance strength. We are currently considering its practical application in concrete products. To apply CARBOFIX^Ⓡ cement to pour-in concrete products, we manufactured actual products at our production facility and evaluated various properties. The manufactured products fully satisfied the required performance and were adopted in real projects. Furthermore, it was demonstrated that the concrete products using CARBOFIX^Ⓡ cement could reduce CO₂ emissions by approximately 43 kg/m³-concrete, compared to those using ordinary Portland cement (OPC). These efforts contribute to the realization of carbon neutrality by reducing greenhouse gas emissions. We will continue to research, develop, and work towards practical implementation to achieve a sustainable society.

View full abstract

 Curing is an essential process for achieving the required quality of concrete; however, it may be challenging to achieve proper curing under certain conditions on a construction site.In such cases, there are instances where coating-type curing agents are employed as an alternative curing method. In this study, a performance evaluation was conducted on a newly developed coating-type high-performance curing agent, "Clean Saver", with respect to strength characteristics and durability, through comparative analysis with the conventional method using moisture-retaining curing tapes. The results demonstrated that the application of Clean Saver provided a sustained and effective suppression of moisture evaporation, thereby contributing to enhanced strength development, reduced drying shrinkage, and improved surface quality. Moreover, it was revealed that the application of Clean Saver mitigated the deterioration of surface appearance through the inhibition of mold growth.

View full abstract