International Concrete Abstracts Portal

In this study, the use of a new permeable sheet was evaluated in making the surface layer of concrete denser, thus improving the performance and durability of the concrete. The application of permeable sheet was confirmed effective in the lowering of water-cement ratio corresponding to the decrease of pore volume; this resulted in the increase of pull-off of tensile strength, rebound number, pulse velocity, and pin penetration resistance in the surface layer. It was also observed that the air bubbles were likely to move from the internal portion to the surface with the expelled flow of water, remarkably reducing bugholes on the concrete surface. The use of new type of permeable sheet improved resistance to freezing and thawing cycling and reduced the depth of carbonation and the ingress of chloride ions. Furthermore, the water tightness was also improved.

In recent years, there has been an increasing demand for high- performance concrete with better workability, higher strength, and greater durability to meet current structural design needs. In Japan, studies of highly flowable concrete with self-compacting properties have been undertaken with the goal of improving reliability of concrete compaction in forms having complicated shapes or densely arranged reinforcement. To produce highly flowable concrete, it is necessary to create high-fluidity concrete by adding a superplasticizer and to eliminate segregation by adding a viscosity-controlling admixture or a large volume of powdered material. It is also necessary to provide the concrete with the ability to pass between the steel reinforcing bars to make it self compacting; this is achieved by controlling the rheological properties of mortar and volume of coarse aggregate. In this paper, the properties of self-compacting concrete are described.

Describes improvements in the performance characteristics of cement- based matrices when reinforced with pitch-based carbon fibers. Under tension and flexure, increases both in strength and strain capacity were reported as a result of fiber reinforcement. Carbon fiber reinforced cement composites were also much more impact resistant that the parent matrix. Under compression, however, no increases either in the compressive strength or in the elastic modulus were noticed. Crack propagation in these composites was characterized using crack growth resistance curves (R-Curves) in which it was demonstrated that carbon fibers lead to a higher resistance to both nucleation and growth of cracks. This paper emphasizes the desired durability characteristics of these composites and discusses their current and future applications.

The Japanese economy has been highly developed through foreign trade. Port facilities have been supporting this economic growth; many concrete port structures have been constructed and maintained during the past few decades. Recently, various social and economical demands have required port facilities to be multi-functional. New facilities are being constructed to meet this trend. These changes include new types of breakwaters, revetment, and undersea tunnels which improve aesthetics and reduce cost, labor, and construction time. Fresh concrete used in the construction of these new types of structures is often required to have high flowability and to be self-compactible because of the complicated shape and densely arranged reinforcements of these structures. To meet these demands, the authors have developed super workable concrete using viscous admixture (segregation-reducing admixture) and super plasticizer. In this paper, the mix design and material properties of this supe rworkable concrete and examples of its application to new port concrete structures are presented.

Over the last 50 years, many researchers have investigated the subject of sulfate attack of concrete and special cements have been formulated to combat the problem. However, recent site investigative work and laboratory- based studies carried out by the Building Research Establishment have shown that a particular form of sulfate attack can proceed even in some concretes which were specifically designed to provide good sulfate resistance. In this type of attack, the main mechanism of deterioration is the breakdown of the calcium silicate hydrate phases in the hardened cement paste in the presence of an available supply of sulfate and carbonate ions to produce the mineral thaumasite (CaSiO3CaSO4CaCO315H2O). A microstructural overview incorporating three examples of the thaumasite form of sulfate attack is presented in this paper. The combination of optical and electron microscopy has proved to be a very powerful technique for examining the processes of deterioration in carefully selected site samples