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Abstract: An experimental program was carried out to study the effect of water absorption of lightweight aggregate on the pore size distribution at the interfacial zone of lightweight aggregate concrete. Properties of lightweight expanded clay aggregates with absorption of 8.9%, 9.4% and 11% were compared. In order to do the study, three lightweight concrete mixes of water to cement ratio of 0.4, 0.44 and 0.48 were batched. The pore area percentage and pore size distribution in the cement paste and at the interfacial zone of the concretes cured for 28 days were examined using a high resolution optical microscope and image analysis software. The findings indicated that the pore area percentage at the interfacial zone was much higher than that at the hardened cement paste. The effect of W/C ratio of concrete on the pore area percentage at the interfacial zone was not significant. The aggregate of larger water absorption produced greater pore area percentage at the interfacial zone of concrete. For aggregates with absorption ranging from 8.9% to 11%, the pore area percentage ranged between 14.4% and 21.7%. [Copyright &y& Elsevier]

Abstract: Air entraining agent is used to control the floatation of lightweight aggregate (LWA) in lightweight aggregate concrete (LWAC), therefore reducing the segregation of LWAC. At the same time, using an air entraining agent will affect the water sorption of the concrete. In this paper, two lightweight concrete mixes of density 1000 kg/m3 and air content of 13.5% and 31.9% were compared and the effects of entrained air on the strength, surface sorptivity, and chloride permeability of LWAC are presented. Results show that the use of porous LWA would not lower the permeability resistance of concrete. Entrained air had little effect on sorptivity but a major effect on chloride permeability. The weaker pores'' network in the cement paste is the basic cause for the high chloride permeability of concrete than the use of porous LWA. Although chloride permeability of low density LWAC concrete decreased with age of concrete, it was found that the concrete was not dense enough to stop the chloride ion to penetrate through the concrete before the concrete mature at 90 days. [Copyright &y& Elsevier]

Fourier Transform Infrared spectrum analysis was employed to study the phase transformation characteristics of the Interfacial Zone. In this research, three groups of infrared spectra with regular patterns were determined. These corresponded with three parts of the concrete, i.e. the aggregate core, the aggregate shell and the hardened cement paste. The transition between two zones corresponded to a remarkable change in the characteristic peak, either with the absence of a peak or a shift in the peak. The outcome of the spectrum analysis employed in this research shows that the cement paste diffuses into the aggregate shell through the interface between lightweight aggregate and cement paste. The water absorption by the dense hardened cement paste is also greater than the materials in the interface and inside the lightweight aggregate. The use of Fourier Transform Infrared spectrum analysis could become a good means for measuring the cement paste diffusion across the interface. [Copyright &y& Elsevier]

An abstract of the article "Interfacial-Zone Microstructure of Lightweight Aggregate Concrete" by Tommy Y. Lo and H.Z. Cui is presented.

Abstract: Making use of industrial by-product or waste clay to partially replace cement in concrete has greatly contributed to sustainable development of environment. This study investigated the optimal activation condition for producing high reactivity metakaolin (MK) by using kaolin by-products (KB) from paper industry. Initially, the material properties of KB were analyzed in this study and the results indicated its great potential to be treated by calcination to be a very effective pozzolan. Afterwards, MK samples produced from different activation treatments of KB, including different calcining temperature, calcining duration, initial temperature rise rime and grinding particle size, were applied in mortar to determine their pozzolanic effect. Results indicated that the optimal activation condition for KB to high reactivity MK conversion is 2-h calcining duration at 750°C and with 7μm grinding particle size. Finally, compressive and flexural strengths of mortar samples produced by replacing cement with 0–25% MK content were tested and the results showed that 15% was the optimal cement replacement level of MK and the mortar so produced exhibited 20% improvement in compressive strength compared to control mortar. [ABSTRACT FROM AUTHOR]

River sand (RS) has been overly exploited to meet demand in the construction industry, particularly in China. Chloride salt in dredged marine sand (DMS) is the primary concern that limits the use of DMS in reinforced-concrete (RC) structures. This paper developed an interaction model between the carbonation behaviour and chloride ions in DMS concrete compared with RS concrete. In this research, the test results indicated that the chloride ions introduced by DMS can reduce 20–50% carbonation of the DMS concretes. A higher carbonation resistance can reduce the possibility of steel bar corrosion in the concrete. The process of concrete carbonation can alter the state of chloride ions in the concrete and their concentrations. During the carbonation process, the bound chloride ions would become free, and their concentration in carbonated concrete could increase by up to 200% compared to that of uncarbonated concrete when the chloride ion concentration was less than 3% by cement mass. Therefore, the effect of carbonation on chloride ions must be considered with respect to the durability when DMS concrete is designed for use in RC structures. [ABSTRACT FROM AUTHOR]