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The compressive strength of blast furnace slag concrete containing slag/(cement + slag) ratios of 0, 0.3, 0.5, and 0.7 was followed by changing the curing conditions. The specimens were cured in air or water at 10, 20, or 40 C, and the strength development after 1, 4, 8, 13, and 26 weeks was determined. Equations were developed for strength based on maturity, curing, method, age of concrete, and amount of slag.

Portland cement was mixed with slags at different fineness and replacement levels and hydrated at 10, 20, 35, 50, and 65 C. The temperature rise of concrete containing slag was reduced when the slag replacement level was 70 percent. The hydration of slag was accelerated at temperatures between 20 and 35 C. The amount of heat liberated by the mixtures was greater than that of the reference portland cement at temperatures 35 C or higher. It is therefore evident that in mass concrete containing slag, the adiabatic temperature rise need not be lower than that of the concrete containing only portland cement.

A study was conducted to determine whether pulverized fuel ash, granulated blast furnace slag, and natural pozzolana contribute effective alkalies and whether such alkalies lead to alkali-silica reaction (ASR) damage. Mortar bars were prepared in accordance with ASTM C 227 but stored at 20 C, and using three factory-produced cements, three Type F pulverized fuel ashes, three blast furnace slags, and four natural pozzolans at three or four different levels of substitution. The reactive aggregate component was Beltane opal substituted at the pessimum level, as well as zero and three near-pessimum levels. The selection of the materials and their substitution levels were adjudged to represent as wide as possible present-day usage. Deleterious expansion defined as > 0.0 percent within 4 years was taken as the criterion of failure. The results have been applied to demonstrate the deduction of practical guidelines for the use of composite hydraulic binders in situations in which ASR is a consideration. Limiting total alkali contents of composite hydraulic binders as function of the substitution ratio of the three mineral additives are suggested. The analysis of the results demonstrates that if the effective alkalies derived from portland cement are taken as 100 percent, then those derived from pulverized fuel ash and natural pozzolana can be taken as 17 percent and those derived from blast furnace slag as 50 percent of total alkalies. There is also evidence of somem mineral additives, particularly at high substitution levels, not simply acting as dilutents but exhibiting a positive ASR-suppressive effect.

Tests were carried out on a series of concrete mixes, designed to equal workability and 28 day compressive strength and with a range of pulverized fuel ash (pfa) levels, to study the effect of curing on the strength and permeability of pfa concrete. Concrete specimens were subjected to a range of moist-curing periods prior to air storage. Compressive strength was determined at various ages and permeability to oxygen and water was determined at 28 days. Results confirm the importance of curing, with reductions in the curing period resulting in lower strength, more permeable concrete. The strength of the pfa concretes appears to be more sensitive to poor curing than ordinary portland cement (opc) concrete, the sensitivity increasing with increasing pfa content. However, despite exhibiting lower strengths, pfa concretes moist-cured for only one day were, generally, no more permeable to water and substantially less permeable to oxygen than similarly cured opc concretes. As the period of curing increased, the pfa concretes became considerably more impermeable to water and oxygen than the opc concretes. These results are discussed in the context of the minimum periods of curing and protection recommended in BS 8110. It is argued that although the increased curing periods suggested for pfa concrete are justified on the basis of concrete strength, pfa concrete may require no more curing than opc concrete to achieve equal durability, as measured by oxygen and water permeability.

Zinc coatings, applied mainly by galvanizing, have been widely used to provide supplementary corrosion protection to reinforcing steel in concrete exposed to aggressive media. Their performance, particularly in concretes contaminated with chloride salts, has been variable; this is believed to be due, at least in part, to the effects of differences in cement alkalinity on the rate of zinc dissolution. To investigate this, specimens were made in which well characterized zinc coated steel electrodes were embedded in cement pastes containing various proportions of silica fume and sodium chloride. They were exposed to moist air for several months, during which time the pore electrolyte compositions were analyzed and the corrosion rates of the embedded electrodes were monitored by linear polarization. It was found that the major influence on the corrosion rate of the zinc coatings was the pH of the pore electrolyte phase, so that quite modest levels of silica fume were capable of reducing corrosion rates by orders of magnitude when compared with those sustained in the unblended pastes. The implications regarding the effective service lives of the coatings are believed to be considerable. Analysis of the relationship between corrosion potential and corrosion rate for the embedded electrodes revealed that the rates of corrosion were generally subject to anodic control, except at very high values when oxygen diffusion became the rate-limiting process.