Abstract
The research reported herein studied the permeability of concrete containing recycled-concrete aggregate (RA), superfine phosphorous slag (PHS), and ground granulated blast-furnace slag (GGBS) with and without stress. Test results showed that the chloride diffusion coefficient of RA concrete (RAC) without external loads decreased with time, and the permeability of RAC is much lower than that of the reference concrete due to the on-going hydration and the pozzolanic reaction provided by the PHS and GGBS additives in the RAC mixture. The permeability of chloride under flexural load is much more sensitive than that under compressive load due to the differences in porosity and cracking pattern. At low compressive stress levels, the permeability of chloride decreased by the closing of pores and microcracks within RAC specimens. However, in a relatively short time the chloride diffusion coefficient and the chloride content increased rapidly with the increase of compressive stress when it exceeded a threshold stress level of approximate 35% of the ultimate compressive strength. Under flexural stress, the chloride transport capability increased with the increase of stress level and time. At high compressive and flexural stress levels, creep had a significant effect on the permeability of chloride in the RAC specimens due to the damage from the nucleation and propagation of microcracks over time. It is apparent that mortar cracking has more of a significant effect on the chloride transport in concrete than cracking in the interfacial transition zone (ITZ).
Highlights
Recycling discarded concrete as new concrete aggregate has been proven to be a commercial and effective way for the sustainable development
Various methods have been suggested to compensate for the shortcomings in RA concrete (RAC), and incorporating pozzolanic materials have been accepted as effective ways to improve the performance of RAC [4,5]
ground granulated blast-furnace slag (GGBS) decreases the permeability of RAC significantly
Summary
Recycling discarded concrete as new concrete aggregate has been proven to be a commercial and effective way for the sustainable development. One purpose of this study is to identify the permeability of RAC with PHS and GGBS materials before applying it to marine structures During their service life, concrete structures are always subjected to various types of loads and aggressive environments, so it is essential to evaluate the transport properties of RAC under a simultaneous application of stress [7,8]. Several experimental studies on the water and chloride permeability of stressed normal concrete have shown that the applied loads can promote the growth of microcracks and interconnectivity, which in turn results in an increase of permeability of structural concrete [7,9,10,11,12,13] It seems that the design service life of concrete structures will be overestimated if this effect is not taken into account.
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