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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.

Provides data from an investigation of the behavior of a range of concrete mixes made with blended cements stored in seawater. Three cements were used at binder contents of 280, 350, 420, and 550 kg/m3. Ground granulated blast furnace slag was used as a

Presents results of investigations forming part of a long-term study of concrete incorporating low quantities of cement and high volumes of low-calcium (ASTM Class F) fly ash. Two types of low-calcium fly ashes from sources in Nova Scotia and Alberta were studied. For comparison purposes, a control concrete containing only ASTM Type I cement was also investigated. A large number of concrete test cylinders and prisms were subjected to determinations of strength, modulus of elasticity, drying shrinkage, freezing and thawing durability, carbonation, and permeability to chloride ions. The test results up to 1 year corroborate the results of previous investigations on concrete incorporating high volumes of low-calcium fly ash. At 7 and 28 days, the compressive strength and the modulus of elasticity were about 47 MPa and 37 GPa, respectively. Air-curing of test specimens did not seem to affect the compressive strength development significantly up to the testing period of 91 days. Resistance of all concretes to repeated cycles of freezing and thawing was found to be excellent with durability factors > 99, when tested after 14 days of the initial moist curing. The drying shrinkage strains of the fly ash concretes were comparable to or lower than that of the control concrete. Further, permeability tests carried out on one of the fly ash concretes indicated exceedingly low permeability to chloride ions at 1 year.

The effect of different curing conditions on the performance of alkali-activated slag (AAS) pastes, mortars, and concrete has been investigated. The temperature range is from -15 to 105 C. The storing conditions were underwater and at relative humidities of 100, 70, and 50 percent. After storing under these conditions, the compressive strengths were determined, and some microscopic and x-ray diffraction analyses were made on the tested samples. The AAS mortars and concretes perform very well even after an extremely strong heat treatment followed by storing at a low relative humidity. At normal temperature, the drop from 100 to 70 percent relative humidity does not affect the strength properties of the concrete. The AAS concrete can be heat-treated immediately after casting without any detrimental losses in strength. Storage in a dry climate does not have a strong influence on the strength development because the AAS binders form a very dense matrix with a large part of closed pores. Some results from industrial production of concrete with AAS binders are also presented. The results prove the suitability of AAS for the precast industry.

Blast furnace slags and pulverized fly ash have been used extensively as additives to ordinary portland cement (OPC) to make low-permeability pastes with adequate long-term strengths. These properties are a consequence of phase development in the matrix that proceeds nonuniformly because the OPC clinker and blending agent react at different rates. Also, sheaths of hydration products forming around anhydrous grains inhibit reaction. This complicates our interpretation of the properties of blended cement systems because phases observed as products on laboratory time scales are not necessarily representative of the steady state assemblages. The aqueous chemistry is also subject to time-dependent changes since solution composition is related to that of the coexisting solids. In some applications, it is necessary to predict long-term physicochemical properties. This can be achieved through modeling, based on sound scientific principles, and using as much information as realistic from immature systems. Paper describes progress in model development and verification.