A study on the development of compressive strength and carbonation depth of cementitious materials incorporating CO2 reactive materials subjected to CO2 curing

Abstract

Much economic development and growth of industry have been progressed, in contrast, CO2 emission has been caused sea level rise and global warming. It has been an important issue internationally. Among that, because amount of CO2 from cement concrete industry is occupied with 5～7% of all industry, much efforts such as development of additives to reduce CO2 emission have been proceeded. Despite these efforts, more CO2 emission is happening, and it causes pH reduction and thus steel corrosion. Therefore, various researches about prevention and prediction of carbonation using carbonation depth have been proceeded. However, if CO2 is invaded into concrete, it makes CaCO3 as results of reaction with Ca(OH)2, C-S-H of hydration products, and then compressive strength can be improved with reduction of porosity. Based on this theory, many researches about CO2 as one of the curing methods has been investigated, and to maximize the effect of CO2 curing, researches are using CO2 reactive material like MgO. However considering varieties of CO2 reactive materials, no research about CO2 curing using various CO2 reactive materials has been reported. Therefore, this study carried out CO2 curing using various reactive materials in powder type and liquid type to compare carbonation depth and compressive strength for each type of materials. MgO, zeolite and desulfurized slag were used as powder type, and lithium silicate and DMEA were used as liquid type. Water-binder ratio was set to 50%, replacement ratio of powder type materials were 90% of cement weight and for liquid type, 5% was added. After cast into mold, sealing curing had been proceeded for 2 days, none CO2 cured specimens were cured under air dry curing, CO2 specimens were cured under CO2’s concentration 20%. Carbonation depth was measured through phenolphthalein spray method, compressive strength was conducted at 3, 7 and 28 day. As a result of carbonation depth, when CO2 curing while using CO2 reactive materials; carbonation depth was higher, especially, zeolite and desulfurized slag were recorded the highest carbonation depth for powder type as liquid type, lithium silicate had the highest carbonation depth. However, in case of liquid type, lithium silicate and DMEA showed similar and lower depth compared to Plain, it is judged that because small amount of liquid type has led rapid reaction with CO2 at early ages, it made dense surface, invasion of CO2 was difficult at later ages. As a result of compressive strength, except for zeolite, higher compressive strength was shown. Especially, the material that showed the highest strength was MgO for powder type, and lithium silicate for liquid type. As a result of chemical products through TG-DTA and XRD analysis, hydration products such as Ca(OH)2, Mg(OH)2 were shown on none CO2 cured specimens, but on CO2 cured specimens, CaCO3, MgCO3, Li4CO4 were measured. Porosity was analyzed to investigate the influence of products from reaction of CO2 curing using MIP. CO2 cured specimens showed reduction of porosity, among that, the material that had the lowest porosity was MgO for powder type, and lithium silicate for liquid type. It is judged that because CaCO3, MgCO3, Li4CO4 from CO2 curing were contributed to lowest porosity for each type materials, it influenced the highest compressive strength for each type materials.