Toyoharu Nawa

The Influence of Leaching on the Ion Adsorption Ability of Hardened Cement Paste

The durability of the concrete structure is determined by transport properties of concrete. The transport of chloride ions greatly changes by the amount of adsorption by hydrates. However, there are few studies on change of the amount of adsorption with the calcium leaching. In this study, the purpose is to investigate a change of the amount of adsorption of the chloride ion with the calcium leaching of hardened cement pastes. The amount of chloride ion adsorption increased with the increase of the replacement ratio of the blast furnace slag. The authors established an equation to predict the amount of chloride ion adsorption on C-S-H and Afm. It was clarified that the amount of chloride ion adsorption on C-S-H of leached hardened cement paste depends on Ca/Si and Al/Si.

Chloride penetration into concrete using various cement types under flexural cyclical load and tidal environment

Presented herein is a model to simulate the chloride ingress into plain concrete, using four common cement types, under flexural cyclical load and tidal environment. Flexural cyclic load was applied from 50 to 80% ultimate bending load, stress ratio (SR) = 0.5; 0.6; 0.7 and 0.8. Fictitious crack model was adopted to predict fatigue deformation of concrete beam under flexural fatigue. The four cement types used were Ordinary Portland cement (OPC), modified cement (MC), rapid hardening cement (RHC) and low heat cement (LHC). The proposed model and experimental results showed that the flexural cyclical load, in terms of the number of cycles, N, and the load level, SR, accelerated chloride penetration into concrete, especially with SR of 0.7 and 0.8. Of four common cement types, OPC is the best cement to retard the chloride penetration into concretes. The model predictions fitted well with experimental results when the crack density parameter, μ, and the tortuosity parameter, τ, were introduced.