Use of blast-furnace slag fine powder blended cement is an important option for lowering carbon emission in the concrete construction sector. However, concrete with blended cement (hereafter denoted as BFS concrete) has been believed vulnerable to shrinkage cracking and its use in building construction has been avoided except for underground structural elements in Japan. To develop the use of BFS concrete in building construction, quantitative evaluation of its shrinkage cracking resistance is necessary. The scope of this study included experimental verification of shrinkage resistance of BFS concrete, in which the effects of ambient temperature were emphasized, and restraint shrinkage cracking tests with BFS concrete subjected to three levels of ambient temperatures of 10, 20 and 30°C compared with normal concrete. To improve crack resistance, an improved BFS concrete using additives such as water retaining shrinkage reducing agent (SRA) was added to the experiments. As a result, the following two major conclusions were obtained: 1) The crack resistances of BFS concrete deteriorated due to increasing free shrinkage strain at high temperatures, while this was not the case for the normal concrete, and 2) water retaining type SRA dramatically improved the crack resistance of BFS concrete at high temperatures.
After fire, the decrease in load capacity of reinforced concrete (RC) structure will take place and may lead to a damage. This research brings out a method to repair flexural reinforced concrete members after fire by using near-surface mounted (NSM) carbon fiber reinforced polymer (CFRP) rods. In this study, a series of slabs were conducted to evaluate the flexural behavior of fire-damaged RC structures strengthened with NSM CFRP rods and repairing material. The arrangement or the location of NSM CFRP rods were the main factor that had been considered to evaluate the effectiveness of this method. Besides, the direct bond test of C-shaped specimens was carried out to investigate the bond behavior between CFRP rods and concrete in three different embedding positions of CFRP rods. Based on the experimental databases, it is clear to conclude that the strengthened slabs not only improved endurance limits but also improved load-carrying capacities and stiffness values as compared to control slab and fire-damaged slab. Especially, the test results showed that slabs with CFRP rods embedded in repairing material overlay had more load-carrying capacity than slabs with CFRP rods embedded inside concrete or between concrete and repairing material overlay.
In this paper, a comprehensive investigation regarding the loading effects on chloride diffusion in saturated concrete is reported. It involves both theoretical and experimental aspects, towards contributing to the service-life prediction of infrastructure under chloride attack. A revised chloride diffusion model is proposed based on the modified Fick' s second law with an emphasis on the loading effects. In particular, this influence is quantified using a newly-introduced damage effect factor defined by tortuosity and constrictivity of damaged concrete. This model is capable of predicting the chloride profiles in concrete under different loading states, regardless of whether it is damaged or undamaged. Meanwhile, a series of experimental studies were extensively operated in order to analyze the influence of loading on chloride diffu-sion process. Two types of mixtures (i.e. ordinary concrete and ordinary concrete mixed with slag) were investigated for chloride diffusion tests under different natures (i.e. compressive and tensile loads) and magnitudes of loads. Totally four levels of loads were applied to further correlate the relation between chloride diffusivities and associated strain values. Finally, two groups of test data with different tensile strain were adopted to validate the theoretical model. It shows that the model is reasonable and the numerical result is adequately accurate.
The objective of this research was to develop a method for the rapid estimation of the quantity of residual cement in sludge water and to control its hydration reaction using sodium gluconate in order to enable the residual cement in sludge water to be effectively utilized. The quantity of residual cement in sludge water can be estimated by measuring the heat of hydration liberated in 24 h using a conduction calorimeter. It is possible to recommence sodium gluconate-controlled cement hydration using magnesium nitrate. A method was developed to simulate the rate of the hydration reaction, which makes it possible to estimate the quantity of residual cement in sludge water by measuring the rate of heat liberation of hydration over 10 h.