International Concrete Abstracts Portal

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.

Disintegration of many concrete pavements (D-cracking, popouts, etc.) exposed to freezing and thawing is often connected with poor physical quality of aggregates used in the concrete. Inability to differentiate between good and poor quality aggregates is due to the lack of appropriate laboratory techniques for aggregate evaluation. A growing shortage of easily available sources of good quality aggregates highlights the need for aggregate classification. A new rapid laboratory test, called RAO-Method, as well as a new pore size distribution index based on the mercury intrusion porosimetry (MIP) analysis, has been proposed to meet engineers' expectations in the field of aggregate classification. An analysis of some research data of the RAO and MIP tests is presented in this paper to illustrate practical usefulness of the techniques. Results of long-term observations of concrete blocks subjected to outdoor conditions and the results of the new laboratory tests of the aggregates previously used in the blocks were compared. The new tests seem to provide means for more successful evaluation of coarse aggregates for purposes of diagnostics, design, and prediction of service life of concrete.

Economic solutions for production of high-strength concrete in Vietnam require use of locally available indigenous resources. Proportioning of gap graded mixtures in Northern Vietnam is therefore based on broken rock and very fine Red River sand. Additionally, normal portland cement blended with fine-grained rice husk ash (RHA) is employed in combination with a superplasticizer. This paper discusses results obtained in a Dutch-Vietnamese research cooperation program. RHA was incinerated in a specially constructed oven under temperatures up to 750 C, yielding amorphous silica with a relatively high carbon content (23 percent). Ash was ground for 18 hours in a laboratory ball mill in combination with or without use of a naphthalene type of superplasticizer. Dutch sand and gravel were used, simulating as closely as possible the Vietnamese aggregate. Particularly promising data was obtained for 19 percent sand content in the aggregate and a paste content of 500 kgf/m 3, in which the RHA content amounted to 100 and 200 kg/m 3 with a corresponding water to paste ratio of 0.3 and 0.35, respectively. RHA ground with the superplasticizer was used in such cases (yielding 75 percent of particles to be smaller that 5 micro-m). Compressive strength was found to exceed 50 MPa at seven days and 70 MPa at 28 days.

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.