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.

To improve durability, it is necessary to find remedial solutions to counteract the embrittlement process of natural fiber reinforced composite materials. One solution to alleviate fiber degradation is to reduce the alkalinity of the pore fluid in the cement paste. This can be achieved by replacing a part of the normal portland cement with a highly reactive pozzolanic material. The purpose of this research study was to investigate experimentally the mechanical behavior of sisal pulp-mortar composites containing cement blended with a modified rice husk ash (MRHA). The main variable was the pulp volume fraction. The results of sisal pulp-mortar composites were compared to those using bamboo and pine pulps. The water-cementitious and sand cementitious ratios by weight were kept constant. The dosage of superplasticizer was fixed. The tests on the composites included strengths under direct tension, axial compression, anticlastic, and bending. The material performance tests were conducted for moisture content, water absorption, expansion, drying shrinkage, and impact resistance. he durability of the composites was investigated by simulating aging cycles. The results showed that after being subjected to 48 simulated aging cycles, the sisal pulp- mortar containing five percent pulp volume fraction showed the highest modulus of toughness. Other tests showed that pulp-mortar composites were impervious, durable, possessed high strength and good impact resistance and, therefore, can be considered as suitable substitutes for asbestos-fiber board.

Reports the results of an investigation of the effect of using ground granulated blast furnace slag to prevent alkali-aggregate reaction damage to concrete. The authors discuss the effectiveness of the blast furnace slag on the dilution, stabilization, and fixation of alkali. The relationship between the replacement ratio of blast furnace slag and prevention of the expansion due to the alkali-aggregate reaction in concrete is reported.