International Concrete Abstracts Portal

The X-ray diffraction analysis and mercury intrusion porosimetry were employed to investigate the hydration process of calcium sulfoaluminate (CSA)- portland cement blends with C4A3S mass concentration, C3S/C4A3S, and CS/C4A3S mass ratios ranging from 7.7 to 22.0%, 1.0 to 6.5, and 0.5 to 1.2, respectively. Owing to the hydration of adequate C4A3S contents and the generation of sufficient quantities of expansive ettringite, blends with C4A3S amounts as well as C3S/C4A3S and CS/C4A3S values comprised between 17.6 and 22.0%, 1.0 and 1.7, 0.5 and 1.0, respectively, showed high-early strengths and low drying-shrinkage when compared to normal portland cements. The formation of expansive ettringite was associated with concentrated pore distributions and most preferred pore radii ranging from either 47 to 225 or 367 to 896 nanometers, depending on both C3S/C4A3S and CS/C4A3S ratios.

The influence of paste quality [water-cementitious material ratio (w/cm), binder type, admixtures, etc.] on concrete properties has been extensively studied. However, there is only a few data on how the volume fraction of paste in concrete may or may not affect these properties. This paper reviews existing data on this subject. Apart from workability, most engineering properties as well as durability characteristics are not negatively affected by a reduction of the paste volume. Low paste volume concrete therefore represents an interesting option to produce economical concrete, both from ecological and economical point of view. This nevertheless requires compensating the workability loss by proper usage of admixtures. The general advantages and limitations of this approach are discussed.

An analysis method for histories of hydration heat and autogenous shrinkage at early ages is suggested in this study. The early age properties and the relation between hydration heat and autogenous shrinkage of high-strength concrete were investigated. In the results, most autogenous shrinkage of high-strength concrete occurred in a few days after casting. The shape of autogenous shrinkage history corresponded well to the shape of hydration temperature history at early ages. There was a close relation between hydration heat and autogenous shrinkage at early ages, especially between hydration heating velocity (HHV) and autogenous shrinking velocity (ASV). And it is noted that HHV can affect the ultimate autogenous shrinkage.

Self-consolidating concrete (SCC) is designed to exhibit high deformability and moderate viscosity to maintain homogeneity and adequate stability to fill the formwork, and encapsulate the reinforcement without any mechanical vibration. Any concrete should have high impermeability and low chloride diffusion to reduce the risk of corrosion and enhance service life. In this study, the effect of the replacement content of cement by supplementary cementing materials (SCM) and fillers. Limestone powder (LSP) replacement of 15% to 30%, ground granulated blastfurnace slag (GGBS) of 40% to 60%, and pulverized fly ash (PFA) of 20% to 35% are evaluated on the durability of SCC of grade C40/50. Fresh concrete properties and development of compressive strength were also evaluated. For the durability performance, all mixtures were tested at 28 days for the air permeability, water permeability, sorptivity, and chloride diffusion which were assessed by Autoclam, and Permit tests. The chloride migration coefficient was dependent on the type SCM and filler in use. The most durable SCC mixture, taking into consideration overall properties, was found to be the one containing 20% PFA, which showed low capillary water absorption, water and air permeation, and lower ionic diffusivity in comparison to the other mixtures. In general, SCC mixtures containing GGBS exhibited inferior performance regarding air and water permeability and sorptivity, but had satisfactory chloride resistance. SCC with 50% of GGBS demonstrates the lowest chloride diffusivity.

In recent years, it has been pointed out that many concrete structures are likely to accrue the initial defects in construction work because of the massive and complicated configuration and function of concrete structures. The service life of concrete structures and the structural performance will be lowered due to loading and environmental attack such as carbonation, frost action, and drying shrinkage. In the last few decades, various types of chemical admixtures have been developed, with emphasis on making highly durable concrete and on producing highly flowable concrete for self-compacting. In this paper, a new cement dispersing agent for retempering, denoted as CDA was examined to confirm its effect on fundamental properties of concrete. This chemical agent is used not only to improve the performance on vibrating consolidation of fresh concrete, but also to increase the resistance to segregation of concrete. The addition of agent will promise the dispersion of cement particles and the reduction of bleeding of concrete. The CDA is a negative ion type cement dispersing agent having a main component of Polyester fiber. The benefit of CDA is given in the dosage of a small amount of agent (0.5~1.0g/m3). The improvement in vibrating consolidation of fresh concrete was depended on late addition for retmpering. It was observed by the vibrating table-type consistency meter. From the tests for bleeding, setting, mechanical properties, durability, and micro structures of concrete such as Vickers hardness and pore size distribution, the benefit of CDA was also confirmed.