An extensive experimental study of the mechanical properties and fracture properties of heavy concrete used mostly in the construction of radiation shielding structures is presented. The mixtures considered herein are developed according to the one adapted in the Kuosheng nuclear power plant in Taiwan; tests of the basic mechanical characteristics properties conform to the ASTM and the fracture properties are determined by the method proposed by Karihaloo and Nallathambi [RILEM Report 5, Fracture Mechanics Test Methods for Concrete (1991) 1]. A crack analysis using pre-cracked specimens and a dye technique was also conducted to examine the crack fronts and the corresponding residual strengths of heavy concrete. Test results indicated that the elastic modulus of heavy concrete is higher than that of regular mortar and increase with iron ore content. The compressive strength of heavy concrete also increases with iron ore content, while the tensile strength declines. The concrete including 40% metallic aggregate content by volume performs higher compressive strength and fracture toughness in this study.
This study aims to assess the performances of reactive powder concrete, RPC, as a new repair and retrofitting material and evaluate its durability in concrete members. One accelerated aging environment, namely a freeze-thaw cycle acceleration deterioration test, was selected for the durability study of the repair materials. Before and after aging, the samples were evaluated by the bond strength (slant shear test), rebar pull out strength, and relative dynamic modulus NDT tests.The test results show that the RPC displayed excellent repair and retrofit potentials, as it possessed high strengthening effect, bond strength, dynamic modulus and durability, as compared with other concretes. Using RPC or CFRP (carbon fiber reinforced plates) for strengthening concrete members one can obtain specific retrofit effects, but the costs are extremely different for these two materials.
This study focuses on evaluating the effects of the fineness of fly ash on the strength, fracture toughness, and fracture resistance of concrete. Three fineness levels of fly ash that respectively pass sieves—no. 175, no. 250, and no. 32—were used. In addition to the control concrete mixture without fly ash, two fly ash replacement levels of 10% and 20% by weight of the cementitious material were selected for the concrete mixture. The experimental results indicate that the compressive strength of the fly ash concrete decreases with the increase in the replacement ratio of fly ash but increases in conjunction with the fineness level of fly ash. The presence of finer fly ash can have beneficial effects on the fracture energy (GF) of concrete at an early age (14 days) and attain a higher increment of GF at a later age (56 days). The concrete containing finer fly ash was found to present larger critical stress intensity factors (KSIC) at various ages, and the KSIC also increases in conjunction with the fineness levels of fly ash.
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