The purpose of this study is to clarify the enhancement in self-compactability of self-compacting concrete with entrained air with respect to the size of entrained air bubbles. Air bubbles entrained with a simple mixing method in which all the materials were poured at once was not suitable for enhancement in self-compactability. The authors developed a new mixing method called water-dividing mixing method, which enabled entrained air bubbles to be suitable for enhancement in self-compactability. The water-dividing method with excessive dosage of air entraining agent (AE) entrained high proportion of smaller air bubbles. The larger total surface area of bubbles due to high amount of fine entrained air reduced internal friction of fresh mortar during deformation, resulted in higher level of self-compactability of self-compacting concrete. This usefulness leads to the successful achievement of self-compacting concrete (SCC) with lower cement content with the air content of approximately 10%. The authors have named the concrete “air-enhanced self-compacting concrete (air-SCC).”
Aggregate radiation-induced volumetric expansion (RIVE) is a predominant mechanism in the formation of mechanical damage in the hardened cement paste (hcp) of irradiated concrete under fast-neutron flux (Giorla et al. 2015). Among the operating conditions difference between test reactors and light water reactors (LWRs), the difference of irradiation flux and temperature is significant. While a temperature increase is quite generally associated with a direct, or indirect (e.g., by dehydration) loss of mechanical properties (Maruyama et al. 2014), it causes a partial annealing of irradiation amorphization of α-quartz, hence, reducing RIVE rate. Based on data collected by Bykov et al. (1981), an incremental RIVE model coupling neutron fluence and temperature is developed. The elastic properties and coefficient of thermal expansion (CTE) of irradiated polycrystalline quartz are interpreted through analytical homogenization of experimental data on irradiated α-quartz published by Mayer and Lecomte (1960). The proposed model, implemented in the meso-scale simulation code AMIE, is compared to experimental data obtained on ordinary concrete made of quartz/quartzite aggregate (Dubrovskii et al. 1967). Substantial discrepancy, in terms of damage and volumetric expansion developments, is found when comparing irradiation scenarios assuming constant flux and temperature, as opposed to more realistic test reactor operation conditions.
The transport properties of hardened cement paste (HCP) have been investigated in many studies; the AC impedance method (ACI) is a non-destructive technique employed for this purpose and has been used in investigations of the elec-trical characteristic and mass transport properties of HCP. However, there are relatively fewer studies investigating chloride ingress in HCP and using the ACI. In this study, the relationship between the electrical conductivity measured by the ACI and chloride ingress was investigated. Backscattered electron image analysis and mercury intrusion porosimetry and water porosity were used to measure the pore structure of HCP, and the chloride ingress depth was measured by an electron probe microanalyzer. There was a high correlation between the porosity and conductivity and between the conductivity and diffusion coefficient of the chloride ions in HCP. This implies that the diffusion coefficient of chloride ions could be estimated by the conductivity measurements.
When concrete is being pumped through a pipe, a lubrication layer is formed at the interface between the concrete and pipe, which plays a dominant role in determining the pumpability. In the present study, a method to improve the properties of the lubrication layer was suggested by imposing ultrasound on the pipe. To examine the effects of ultrasound on the formation of lubrication layer, three different intensities of ultrasonic energy were applied while conducting 170 m long full scale pumping tests. When ultrasound was applied, the lubrication layer thickness increased, which led to a decrease in pumping pressure. Therefore, the application of ultrasound can be an effective method for improving pumpability.
The crystallization of ettringite at very early cement hydration (hydration period - 10 s) was studied under normal and zero gravity condition utilizing SEM microscopy. Furthermore, the impact of two polycarboxylate superplasticizers (one methacrylate ester-, one methallyl ether - based) on ettringite crystallization was investigated. It was found that under microgravity attained on parabolic flights, generally smaller, but a larger amount of ettringite crystals is formed resulting from the absence of convection and ion diffusion limited crystal growth. Furthermore, the PCE polymers were found to act as morphological catalysts for ettringite even under zero gravity condition.