International Concrete Abstracts Portal

This paper outlines the historical developments in the use of fly ash in Australia, Malaysia and Thailand. The slow but marked change in the philosophical approach to the use of fly ash concretes is discussed. With more focused research into the durability performance of fly ash concretes for specific environments in Malaysia and Australia, fly ash concretes in both countries are gaining acceptance into this new area of applications. This is also reflected in some of the most advanced specifications. It has been found that for concretes of equal 28-day strength, the use of fly ash in concretes resulted in a better resistance to chloride ingress. This was also shown in the lower coulomb values in the ASTM C 1202. Higher strength grade portland and fly ash concretes gave lower coulomb values. Other related work had shown that the use of fly ash could result in a lower corrosion rate of steel reinforcement in concretes. Hence a significantly longer service life could be expected from fly ash concretes compared with portland cement concretes of equal strength. In high-performance concretes, it has been found that the use of triple blends of either a slag or a silica fume added to the fly ash/Portland chloride resistance of the concretes. cement system could further enhance the

The corrosion resistance of reinforced concrete, containing fly ash and calcium nitrite-based corrosion inhibitor, under sea water attack was studied in this research. Aggressive and normal construction conditions were simulated. Test results indicate that the use of calcium nitrite-based corrosion inhibitor is an effective way to protect reinforcing steel from corrosion in aggressive environments. No serious detrimental effect was found for the corrosion inhibitor on concrete properties. Replacement of 20% cement by fly ash gives no apparent improvement in preventing the corrosion of steel in sea water exposure.

This research was carried out to evaluate the effects of source and amount of fly ash on s,trength and durabil ity properties of concrete. Mechanical properties considered were compressive strength, tensile strength, tlexural strength, and modulus of elasticity. The durability-related properties considered were: shrinkage, abrasion resistance, air and water permeability , chloride permeability and salt scaling resistance of concrete. A reference concrete was proportioned to attain the 28-day compressive strength of 41 MPa. Three sources of Class C fly ash were used in this work. Fly ash from each source was used at three levels of cement replacements (40, SO, and 60% ) in producing, concrete mixtures. The water-to-cementitious materials ratio was maintained at 0.30 + 0.02 for all mixtures. In general strength and durability-related properties of concrete were considerably affected by both the tly ash source and amount of fly ash. Also, the strength properties and durabi lity for the 40% fly ash mixture were either comparable or superior to the no-tly ash concrete. The salt scaling resistance of fly ash concrete was either comparable to or better than the no-fly ash concrete, except for one source of fly ash at 60% cement replacement level. All the mixtures, with and without tly ash, tested in this investigation conformed to the strength and durability requirements for excellent quality structural grade concretes.

Converter slag is a metallurgical waste material for which there are utilisation problems. The phase composition of the material includes, beside the phases which are not reactive, mineral phases typical for portland clinker -tricalcium silicate (C3S), dicalcium silicate (C2S) and calcium oxide are always present in the converter slag. The authors have found that special preparation of the converter slag can strongly influence the durability of the concretes containing this material. The results concerning the resistance of the mortars containing converter slag to the corrosive solutions are presented. Microstructure of the mortars (SEM) has been analysed. Very low porosity and extremely low water permeability of the samples containing converter slag are the most important reasons for the high chemical resistance of this material.

Permeability is now recognized to be one of the key properties influencing the durability of concrete structures. The focus of this paper is the determination of the role and effectiveness of combinations of pozzolanic and cementitious cement replacement materials on the air/gas permeability of concrete. The apparatus used to determine the gas permeability consisted of a permeability cell, and air was forced to flow only in the vertical direction. Six different concrete mixtures were used; all the mixtures had the same water-binder ratio of 0.45, but two different total cementitious contents of 350 kg/m3 and 450 kg/m3 were investigated. Fly ash or slag was used in combination with silica fume. The test specimens were exposed to three different curing conditions prior to carrying out the permeability test. The results show that air permeability of concrete is highly dependent on the curing history of the concrete. There was no well-defined correlation between air permeability and compressive strength, but a reasonable correlation existed between air permeability and the threshold pore parameter obtained from pore structure studies.