This paper presents a set of the investigation of corrosion of steel bars in autoclaved concrete pile containing γ -2CaO ·SiO2 (γ -C2S) with carbonation curing. OPC, γ -C2S, and fine silica powder were used as the binders; the replacement ratio of OPC by γ -C2S was 0%, 40%, and 80% by mass. Autoclaved concrete pile after carbonation was submerged in real marine environment at Kurihama Bay for two years. After immersion, visual observation of steel bars was conducted to confirm the corrosion state of steel inside the concrete pile. Furthermore, to evaluate the corrosion of steel bars -weight loss, corrosion current density, and anodic polarization curve were measured ; various corrosion substances also were measured to evaluate the permeability of corrosion factors. In addition, cement past sample with same mixed proportion and curing condition was made for explaining the permeable characteristics of corrosion substances. As the results, the steel bars in the 80% γ -C2S replacement ratio did not corrode while steel bars in the other mixed proportions had corroded. The weight loss of steel bar in the 80% γ -C2S replacement ratio after carbonation reduced by 39% and corrosion current density reduced more than 95% compared with the 0% γ -C2S replacement ratio. Furthermore, the corrosion substances in concrete pile -carbonation depth, total chloride ion content, and oxygen diffusion rate, reduced significantly at the 80% replacement ratio of γ -C2S. Based on the overall results of this study, we suggest that, when using γ -C2S with an autoclave curing, accelerated carbonation curing is able to do to densify the concrete surface preventing the steel from corrosion for the long-term exposure.Key words : γ-2CaO ·SiO2
Sulfate attack on concrete structures is a serious problem around the world, particularly in the Middle East, where sulfate is abundant in soil. Design of a cementitious material with high sulfate resistance is thus required, leading to research on the high durability of cementitious materials containing γ-Ca 2 SiO 4 (γ-C 2 S). The authors have proposed the following material design for high durability: a cementitious material mixed with γ-C 2 S and subjected to autoclaving and accelerated carbonation, to give 1.1nm tobermorite in the autoclaved hardened body, and densification at the surface. However, the sulfate resistance of this new material has not been investigated. Therefore, the purpose of the present research is to understand the effect of adding γ-C 2 S, autoclaving and accelerated carbonation on the permeability of sulfate ions (crucial for sulfate resistance), from the viewpoint of the reaction products and porosity. The smallest sulfate ion penetration was a sample with 80% replacement ratio of OPC with γ-C 2 S. Generation of vaterite following accelerated carbonation suppressed sulfate ion penetration. In addition, dissolution of 1.1nm tobermorite in the hardened body was inhibited. Also, low-Ca/Si C-S-H at the surface may reduce the porosity of this surface and thus contribute to the suppression of sulfate ion penetration.
Aggregate size and its source are crucial for concrete properties. This paper presents the evaluation of the properties of self-compacting concrete (SCC) which mixed with coarse aggregate from different sources. Coarse aggregate from three sources which are commonly available in Vientiane Capital, Mekong River (MK), Ngum River (NG) and Crushed Mountain Stone (MT) were used for this study. Six different mixed proportions with two maximum aggregate size 19mm and 12.5mm for each aggregate source were prepared. Ordinary Portland Cement Type I and Fly ash class C were used as binders. The replacement ratio of fly ash to cement was fixed at 20% and w/p ratio was 0.36. Sika Viscocrete-3180MR was used as water reducing admixture with 0.95% by weight of binders. The results show that, for the fresh concrete properties, the coarse aggregate with maximum size of 12.5mm from Mekong River is the most suitable aggregate comparing to other sources. For the hardened concrete with 28-day curing, the highest compressive strength is the mixed proportion MK12 for aggregate size 12.5mm. As seen, the coarse aggregate with 12.5mm of Mekong River is the most appropriate aggregate among three sources which has a flow-ability and higher compressive strength.
SiO 2 Permeability of Sulfate Ions in Cementitous Materials with Autoclave Curing and Accelerated Carbonation Curing Using γ -2CaO • SiO 2 by Tsuyoshi SAITO , Nobuaki OTSUKI , Tatsuya YUMOTO and Saphouvong KHAMHOUNowadays, in the middle east region where sulfate is abundantly found in soil, the sulfate attack on concrete structures is one of the serious problem. For this purpose, a material design of cementitous material is expected to obtain high sulfate resistance, leading to the research on the high durability of the cementitous material using γ -2CaO • SiO2 (hereafter "γ -C2S"). The authors have proposed the material design as follows : the cementitous material mixed with γ -C2S and conducted with autoclave and accelerated carbonation curing to obtain high durability performance due to the generation of tobermorite in the hardened body by autoclave curing, and densification at the surface of hardened body by accelerated carbonation curing. However, its sulfate resistance has not been investigated yet. Therefore, the purpose of this research is to evaluate the effect of using γ -C2S, autoclave curing and accelerated carbonation curing to permeability of sulfate ions related to the sulfate resistance, and clarify the mechanism of sulfate resistance from the view point of the reaction product and sulfate ion penetration. As a result, in the case of 80% γ -C2S substitution ratio with autoclave and carbonation curing, the sulfate ion penetration was the smallest due to the generation of vaterite. In addition, dissolution of tobermorite in the hardened body could be inhibited. Also, low-Ca/Si C-S-H at the surface of hardened body could possibly contribute to the resistance of sulfate ion penetration.
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