ABSTRACT
Human survival is threatened by the rapid climate change due to global warming caused by the increase in CO2 emissions since the Second Industrial Revolution. This study developed a secondary cement product production technology by replacing cement, a conventional binder, with calcium silicate cement (CSC), i.e., CO2 reactive hardening cement, to reduce CO2 emissions and utilize CO2 from the cement industry, which emits CO2 in large quantities. Results showed that the carbonation depth, compressive strength increase rate, and CO2 sequestration rate increased as the CSC content increased, suggesting that CSC can be applied as a secondary cement product.
ABSTRACT
To prevent drastic climate changes due to global warming, it is necessary to transition to a carbon-neutral society by reducing greenhouse gas emissions in all industrial sectors. This study aimed to develop carbon utilization sequestration technology that uses the concrete slurry water generated during the production of concrete as a new CO2 sink to reduce CO2 emissions from the cement industry. This was achieved by performing supercritical CO2 carbonation by varying the concrete slurry waste (CSW) ratio. The study's results confirmed that, according to the CSW ratio (5 to 25%), complete carbonation occurred within only 10 min of the reaction at 40 °C and 100 bar.
ABSTRACT
This study aims to develop highly durable, mineral carbonation-based, resource-recycling, secondary cement products based on supercritical carbon dioxide (CO2) curing as part of carbon capture utilization technology that permanently fixes captured CO2. To investigate the basic characteristics of secondary cement products containing concrete sludge waste (CSW) as the main materials after supercritical CO2 curing, the compressive strengths of the paste and mortar (fabricated by using CSW as the main binder), ordinary Portland cement, blast furnace slag powder, and fly ash as admixtures were evaluated to derive the optimal mixture for secondary products. The carbonation curing method that can promote the surface densification (intensive CaCO3 formation) of the hardened body within a short period of time using supercritical CO2 curing was defined as "Lean Carbonation". The optimal curing conditions were derived by evaluating the compressive strength and durability improvement effects of applying Lean Carbonation to secondary product specimens. As a result of the experiment, for specimens subjected to Lean Carbonation, compressive strength increased by up to 12%, and the carbonation penetration resistance also increased by more than 50%. The optimal conditions for Lean Carbonation used to improve compressive strength and durability were found to be 35 °C, 80 bar, and 1 min.
ABSTRACT
To prevent drastic climate change due to global warming, it is necessary to transition to a carbon-neutral society by reducing greenhouse gas emissions in all industrial sectors. This study aims to prepare measures to reduce the greenhouse gas in the cement industry, which is a large source of greenhouse gas emissions. The research uses supercritical CO2 carbonation to develop a carbon utilization fixation technology that uses concrete slurry water generated via concrete production as a new CO2 fixation source. Experiments were conducted using this concrete slurry water and supernatant water under different conditions of temperature (40 and 80 °C), pressure (100 and 150 bar), and reaction time (10 and 30 min). The results showed that reaction for 10 min was sufficient for complete carbonation at a sludge solids content of 5%. However, reaction products of supernatant water could not be identified due to the presence of Ca(HCO3)2 as an aqueous solution, warranting further research.
ABSTRACT
When a concrete structure is exposed to fire, its structural safety is significantly compromised due to the spalling of members and scaling of concrete. In addition, its durability is substantially reduced due to certain chemical changes such as the dehydration of Ca(OH)2, the main hydration product of concrete, and the rehydration of CaO. Therefore, when fire damage occurs to a reinforced concrete (RC) building, rapid diagnosis and evaluation techniques are required for immediate repair and reinforcement, requiring a crucial step of quantitatively determining the heating temperature. This study aims to demonstrate a method of estimating the heating temperature experienced by fire damaged RC buildings. The experiments utilized two short RC column specimens with embedded titanium strips. The discoloration characteristics of titanium at high temperatures provided a quick, accurate, and simple mechanism for the estimation of the heating temperature by depth. Empirical equations were derived to estimate the heating temperature as a function of the discoloration characteristics of titanium. Thereafter, a comparison of this estimated temperature with the actual heating temperature measured using thermocouples revealed an average error of less than 20 °C, thereby demonstrating a significantly good correlation and an extremely high reliability of the proposed method.