International Concrete Abstracts Portal

In current construction practice, discontinuous fibers are added to cementitious matrices at relatively low volume fractions (usually < 1 .O%), mostly in order to improve the toughness, or the post-cracking ductility, of the composite. At these addition rates, there is relatively little improvement in strength. Moreover, there are no generally accepted methods of characterizing the improvements in other mechanical properties which the fibers may impart to the concrete. As a result, the various national structural design codes do not recognize fiber reinforced concrete (FRC) as a distinct material, and this inhibits its use in structural applications. However, there is continued research on the use of fibers in conjunction with conventional continuous steel reinforcement to improve the structural behaviour of concrete. In addition, a new generation of micro-fibers is being developed, which can be used at higher addition rates to bring about major improvements in the mechanical properties of FRC. In this review, current FRC technology is described. Likely future developments of FRC are also considered, such as applications in the design of concrete structures subjected to dynamic (blast, impact or earthquake) loading. The next generation of FRC materials will have the capacity of being tailored for a wide range of specific applications, and should be able to compete with other structural materials in a variety of applications.

Developments in the use of fly ash and silica fume in portland cement concrete are critically reviewed. Concrete properties, both in the fresh and hardened states, that are influenced by the addition of fly ash and silica fume are discussed. The effects on workability, segregation, bleeding, air entrainment, heat of hydration, and plastic shrinkage cracking are reviewed relative to fresh concrete. The influence on strength, permeability, drying shrinkage, creep, steel-to-concrete bond, alkali-silica reactivity, resistance to reinforcing steel corrosion, and resistance to sulfate attack are documented for hardened concrete. The curing requirement of fly ash and silica fume concrete is identified as one of the important areas that needs further investigation to utilize the full potential of these concretes. The literature contains a reasonable amount of data concerning the curing requirement of fly ash concretes. However, very limited data on the curing requirements of silica fume concrete are available. A significant amount of confusion exists in the construction industry regarding the curing of silica fume concrete. In the absence of adequate specifications, overcuring of silica fume concrete is the general practice. A brief review of the available literature concerning the curing requirements of fly ash and silica fume concretes is presented.

A new model of the K-slump tester was developed that can be used to evaluate the slump of concrete in 40 sec. The new apparatus features an electronic digital readout giving the slump value to the nearest 1 percent. Experimental studies were performed in accordance with ASTM C 670 and C 802 using the new K-slump tester to determine its reliability and precision. The results indicate that the new apparatus is accurate and reliable in evaluating concrete slump.

There are many methods for determining the mixture proportions of concrete when compressive strength is the design criterion. However, there is not much information when other criteria, such as fracture energy, elastic modulus, or durability aspects, are specified. For these cases, a new mix design nomogram developed from well-established concrete relationships is reported. The application of this method is demonstrated by showing the influence of cement content, water-cement ratio, and aggregate-cement ratio on the compressive strength, modulus of elasticity, fracture energy, depth of carbonation, and permeability. The mixture design nomogram, apart from being a practitioner's tool, can also help the researcher select the most appropriate parameters for experimental studies.

Polymers, once used historically in natural form, are today synthetically manufactured. Polymers are used in concrete in varying amounts or may be impregnated into hardened concrete. They interact with cement hydration products and create complexes, influencing the crystallization process during cement hydration and hindering the formation of large calcium hydroxide crystals during C 3S hydration. The mechanism of interaction is extensively reviewed. Polymers produce hydrophobicity in concrete and reduce its permeability. Because of this, the absorption of water, salt solution, and the like are substantially reduced. Subsequently, the corrosion resulting from salt ingress is decreased, extending the service life of the concrete. Durability properties such as freeze-thaw resistance and chemical resistance to inorganic acids are also significantly improved. Use of polymers is well known in the repair of bridges and parking decks, as well as in the restoration and conservation of monuments and historical buildings. Applications of polymer mortar and concrete and their recent developments are reviewed.