International Concrete Abstracts Portal

This paper discusses a new method for the determination of the optimum W/C plus FA for maximum compaction of no slump concrete made with high volumes of fly ash. It explores the effect of fly ash fineness and particularly, carbon content on the explores the effect of fly ash fineness an particularly, carbon content on the compressive strength of the mixtures made with 50% and 70% replacement of normal portland cement with fly ash. By using an appropriate surfactant the no slump concrete mixtures are rendered workable and suitable for structural applications. The strength attained at 28 days is 60 Mpa or more, and therefore these mixtures are considered to yield high-strength concrete. The performance of the high-volume fly ash concrete is assessed in terms of abrasion and fatigue resistance that are the most appropriate performance indicators for concrete that will be used for the construction of pavements.

One of the limitations of high-performance concrete is its susceptibility to autogenously shrinkage, which can considerably compromise its durability and mechanical strength despite diligent cure during the hardening stage. Although calcium-sulfoaluminate admixture (CSA) and shrinkage-reducing admixture (SRA) can play a role in reducing autogenously shrinkage, rapid set and low effectiveness have been associated with their use in concrete with low water content/ Recently, an innovative type of CSA admixture based on pre-hydrated high-alumina cement (H-HAC) has been developed, but its potential in reducing autogenous shrinkage has not yet been evaluated. In this paper, the effects of H-HAC expansive admixture in decreasing the shrinkage during the early hardening and hardening stages are described. It was hoped that the expansion generated from hydration of the expansive components would offset the volume reduction due to autogenous shrinkage. The influences of particle size distribution, dosage and type of H-HAC hydrates in determining expansion are evaluated and discussed. Microstructural and chemical aspects are studied through XRD and SEM techniques. Tests on the evaluation of the H-HAC admixture to offset autogenous shrinkage are described and preliminary results are presented. The results show that in specific dosage and particle size distribution, H-HAC is a suitable admixture for compensating shrinkage, although autogenous shrinkage in high-performance concrete has not been prevented by the use of this admixture.

A total of 15 repaired and unrepaired reinforced concrete beams was tested under static loading in this study. The beams were of rectangular cross-section, 100 by 120 mm, and tested in flexure in simply supported mode on a span of 600 mm under a line load at mid-span. These include control beams, which were unrepaired, and beams repaired by shotcreting prepacked materials, shotcreting mortar, casting prepacked materials and casting prepacked material with steel fibres. The performance of the repaired beams statically-loaded to failure was monitored. The influence of differential shrinkage between repair material and substrate, bonding strength, casting method and the presence of steel fibres on the mechanical behaviour of repaired beams are discussed in this paper. The test results indicated that the mechanical properties of the repaired properties and the mix proportions of the repair materials used, and the repairing methods employed. The flexural stiffness of the repaired beams could be increased by using steel fibres, improving the bond quality between substrate and repair materials, and selecting appropriate repair method.

The generation of solid residues and an adequate final destiny for them is a subject that have attracted more and more researches. The recycling of solid by-products as construction materials can be an alternative to reduce costs of the latter and the impact on the environment. Nevertheless, it is fundamental that the characteristics of these new materials be equivalent to the traditional ones or even better, if possible. In this context, the use of electric steel slag and copper slag can be a potential alternative to the admixtures used in concrete and mortars. Results of physical, chemical and physical-chemical characterizations of electric steel lags from Rio Grande do Sul and copper slags from Bahia, both in Brazil, are presented in this work. Also presented are results of compressive tests, flexural tests and Brazilian tests in concrete specimens with these admixtures, indicating the viability of their use.

In the Velenje Lignite Mine, Slovenia, the panel substructures are in sue. Fiber reinforced concrete panels are used because of their advantages which they have in the construction of mine railway lines over other types of substructures. In a development project, a fibre reinforced panel with much better carrying capacity and ductility in comparison with reinforced concrete panels has been developed. The panels, with high-performance fiber reinforced concrete (HP-FRC), which resist greater rock formation pressures have been developed also. These properties are input data for analysis of panel at the outside loading. Because the crack propagation in the length direction as well in the width direction is prevented by the presence of fibres in concrete, energy absorption capacity, toughness and ductility of concrete respectively are increased.