International Concrete Abstracts Portal

ASTM C 672 scaling tests were carried out on normal concretes and concretes containing 5 percent silica fume, with air-void spacing factors in the 100 to 200 æm range. Five curing methods were compared: a 24 hr heat cycle with a maximum temperature of 70 C, 2 and 14 days moist curing, and two different curing compounds. Results indicate that the use of silica fume does not improve the scaling resistance of concrete. Concretes cured with one particular curing compound were found to have a scaling resistance similar to that of those cured in water for 14 days, weight losses after 50 cycles being lower than 1 kg/mý for all mixes. Concretes cured with the other curing compound had a lower and more variable scaling resistance. As expected, specimens cured for only two days in water also had a lower scaling resistance. All mixes cured using the heat cycle exhibited a poor performance, although, in this case only, silica fume reduced very significantly, but not sufficiently, the damage due to the freeze-thaw cycles in the presence of deicing salts.

The use of supplementary cementing materials for reducing harmful alkali-aggregate reactions (AAR) in concrete is being studied at the Canada Centre for Mineral and Energy Technology (CANMET). One investigation involves the use of three types of reactive aggregate and supplementary cementing materials that include fly ash, slag, silica fume, and natural pozzolans. This report covers the part in which ground granulated blast furnace slags (one from the U.S. and two from Canadian sources) were used to partially replace cement in concrete containing the three reactive aggregates. Test data include characterization of the materials used, their proportions in mixtures, concrete strengths, and 2-year expansion measurements of mortar bars and concrete prisms containing these materials. Test results show the effectiveness of the slags in reducing deleterious AAR and their optimum replacement levels. These slags are all effective in controlling such reactions, particularly with the highly reactive Kingston dolostone.

A study of the effects of beneficiation on the performance and properties of fly ash from Lingan Generating Station, Nova Scotia, has been conducted. A pilot scale high-efficiency air classifier was used successfully to separate the fly ash into product grades with nominal sizes of -45æm, -10æm, and -45/ + 10æm. Overall recovery of the -45æm fraction from the raw ash was 66 percent. Beneficiation was found to generally improve the quality of the fly ash by increasing both the glass content and the proportion of spherical particles. The raw fly ash and the process fractions were all acceptable pozzolans complying with the requirements of CSA Standard A23.5-M1982. Beneficiated ashes showed improved pozzolanic activity, reduced water demand, and enhanced ability to reduce alkali-aggregate reactivity. In ASTM C 109 mortars, approximately twice the quantity of the -45æm fraction compared to the raw ash could be substituted for portland cement without loss of strength at 28d. This indicates that considerable cement savings would be realized from beneficiation of the ash. The -10æm fraction was an even more effective pozzolan with improved strength development and higher ultimate strength (110 percent of control). The hydration of control and portland cement-fly ash pastes (85:15 and 70:30) was investigated at w/c = 0.5 and curing ages from 2 hr to 28 days. In the early stages of hydration, fly ash substitution increased both the rate and extent of ettringite precipitation. At 28 days, the major ions in pore solutions were Na+, K+, and OH- with concentrations similar to the control. Mechanisms for the apparent net depletion of Na+ and K+ with increasing curing age are discussed in terms of a general theory of the chemistry of pore fluids. In general, the ash-containing systems showed less dissolved total alkali than the control. The pore structures of the portland cement-fly ash pastes were investigated by mercury intrusion porosimetry and their permeability to water at 500 psi. While permeability was not uniquely related to the pore structure parameters, it is clear that the fly ash particles in the pastes serve to close the pore structures in a way that generally restricts water intrusion. Whether this is attributable to reduced permeability of the matrix material (possibly as a result of improved nucleation and phase growth) or increased tortuosity remains to be established.

The Japan Society of Civil Engineers (JSCE) studied the use of ground granulated blast furnace slag in concrete as an admixture. Various properties of fresh concrete and hardened concrete containing ground slag were examined. Ground slags included 13 samples on the market and 18 samples with different fineness and gypsum content especially prepared for the experiment from two kinds of water-granulated blast furnace slags. Based on the experimental results, the JSCE Standard "Ground Granulated Blast-Furnace Slag for Concrete" and the JSCE Recommendation "Recommendation for Design and Construction of Concrete Containing Ground Granulated Blast-Furnace Slag" were prepared and published in 1986 and 1988, respectively. This paper introduces the essential parts of both the JSCE Standard and the JSCE Recommendation, showing some of the representative experimental results.

Paper reports the accelerated carbonation test results to investigate the effect of replacement ratio of fly ash, initial curing period in water, and air content on the carbonation phenomena in concrete. Using these test results, equations for the prediction of carbonation depth of concrete with and without fly ash are proposed, and these effects are also evaluated by these equations. Furthermore, the accelerated carbonation test results are compared with natural exposure test results for 15 years, and a method to predict the carbonation depth of concrete with and without fly ash exposed to natural indoor conditions is proposed. Concrete with fly ash is affected by initial curing period in water rather than concrete without fly ash from the viewpoint of depth of carbonation and compressive strength. The higher the fly ash content of concrete is, the deeper is the depth of carbonation. Depth of carbonation can be evaluated by compressive strength of concrete cured in water for 28 days, irrespective of the fly ash content of concrete. Carbonation depth of concrete with and without fly ash naturally exposed indoors can be predicted by the equation obtained by the accelerated carbonation tests.