International Concrete Abstracts Portal

Metakaolin-blended cements were used to stabilize two kinds of wastes: municipal incinerator fly ash and latex waste coming from the carpet industry. The physical and chemical properties of wastes were investigated and mortars containing these wastes were cast. A blended cement containing 20 % metakaolin was utilized to immobilize the incinerator fly ash which was introduced as a sand substitute in mortars. Leaching tests and microstructural investigations were carried out as well as mechanical tests. The results obtained show that metakaolin plays a beneficial effect in the stabilization of chlorides contained in such fly ash. Cements containing from 10 to 30 % metakaolin were used to cast mortars, in which latex was introduced as a sand substitute. Metakaolin reacted with the calcite contained in the latex and the C3A of portland cement to form carboaluminate. Leaching tests showed a good immobilization of this waste.

This paper presents a research carried out to convert paper sludges from de-inking and water-treatment processing plants into a pozzolanic product usable in the cement and concrete industries. Paper sludges contain inorganic fillers like ground limestone, kaolinite, clay, and organics. The process consists in heat treatment in the range of 600 to 700°C in order to transform the kaolinite present in the sludge into metakaolinite, a very reactive pozzolan, without the formation of large amounts of free lime (due to the decarbonation of the calcite also present in the sludge). In addition, the organic compounds in the sludge must be burned off and their presence reduces the use of fossil fuels to reach the temperature needed for processing. The results of both laboratory and field tests show the feasibility of the process. A reactive pozzolan is obtained when the amount of kaolinite present in the sludge is higher than 20 % of the dry inorganic phase. This metakaolin is sometimes more reactive than that obtained by calcining pure kaolinic clays, and can be used to enhance the durability of concrete in severe environments.

Concrete in contact with a sulfate environment can severely degrade due to expansion accompanying the formation reaction products such as ettringite. The use of Portland-pozzolan cement has been successful in mitigating this expansion. However, it is important to study the effectiveness of natural pozzolans to improve the resistance to attack by sulfates. This paper reports results of different portland-pozzolan cements containing different natural pozzolans and ASTM Types I, II, and V portland cements. The pozzolanic activity and composition of each pozzolan was evaluated. The susceptibility to sulfate attack was studied by measuring the expansion in mortar bars at different ages according to ASTM Method 1012 for 78 weeks. It was found that cements containing pozzolans with high activity or low alumina content improved the sulfate resistance. Also, the pozzolan content in the cement was found to be important.

This paper reports the findings from a laboratory evaluation of a metallurgical slag as a pozzolanic admixture for concrete. Lead blast-furnace slag is fumed in a batch process to remove base metal values after which the molten barren slag is water-quenched to produce a glassy, granular product. Chemical analysis shows the principal components of the slag to be silica, iron and calcium with lesser amounts of alumina, zinc and copper. Semi-quantitative x-ray diffraction analysis revealed the slag to be largely amorphous (> 60% glass), the crystalline phases being apparently confined to mineral varieties of iron oxide and cuprite (Cu2 O). The slag was ground to produce three samples with different Blaine fineness values and tested for compliance with the Canadian Standard for Supplementary Cementing Materials (CSA A23.5). The effect of the slag on a range of fresh and hardened concrete properties was then determined. Concrete mixtures were also cast using commercially available fly ash from a sub-bituminous coal source in Western Canada for comparison. The slag meets all the requirements of Type N, F and C materials and failed only the 45-microns sieve retention maximum of Type G. The results of concrete tests (setting time, compressive strength development, drying shrinkage and rapid chloride permeability) are very encouraging. The incorporation of slag slightly retarded the early strength gain of concrete, but after 28 days the strength of the slag concrete exceeded that of the control concretes of the same W/CM, regardless of the level of slag (in the range 20 to 40%). The strength of slag concrete was higher than that of concrete containing the same level of fly ash and the same W/CM at all ages. The coulomb ratings of the concretes containing slag were lower than those obtained on equivalent control concretes but were higher than those of the fly ash concretes. The results from these preliminary tests indicate that the lead blast-furnace slag is suitable as a pozzolanic admixture for concrete.

Soil stabilisation with cement or lime, is a well established technique for use in highway or foundation construction. Extensive laboratory investigations and a full-scale trial have been carried out to evaluate the performance of ground granulated blastfurnace slag (ggbs) in combination with lime, for stabilising soils. This paper reports the results of laboratory tests for strength and swelling, and also describes the full-scale trial. The applicability of lime / ggbs combinations has been demonstrated. In addition laboratory tests have shown a previously undemonstrated advantage where the incorporation of ggbs combats the deleterious swelling which can occur when sulphate-containing soils are stabilised with cement or lime.