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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.

Effects of alkalies in Class C fly ash on Alkali-aggregate reaction were studied by using two cements, a type I high-alkali cement and a type II low-Alkali cement, and three Class C fly ashes. Mortar bar expansion was measured according to ASTM C 441. Reaction products of alkali-aggregate reaction were examined n by XRD, SEM, and EDAX. were to study: The purposes of this research (1) the significance of the standard mortar bar test in determining the degree to which high and low-alkali cement could be replaced by Class C fly ashes, and (2) effect of fly ash alkali contents on alkali reactivity. Expansion of mortar bars prepared using high-alkali cement increased at low replacement levels but decreased at high replacement levels for curing periods up to 12 weeks at 38 C; whereas expansion of mortars prepared using low-alkali cement increased at all Levels of fly ash replacements up to 40% by volume. A critical equivalent Na20/Si02 mole ratio was identified and found to characterize alkali reactivity. No crys-talline reaction products could be identified by XRD. Results of SEM and EDAX showed that the reaction product was an alkali-silicate gel, composed mainly of silica, sodium, potassium, and calcium, with their relative amounts varying within the gel.

The specific creep and shrinkage of five high-strength concrete mixtures were monitored for 400 days at the University of Michigan, Ann Arbor. One 52.6 MPa (7630 psi) silica fume (SF) concrete was compared with a fly ash concrete of similar compressive strength, and SR concrete and fly ash concrete having compressive strengths of approximately 69 MPa (10,000 psi) were compared. A 106.6 MPa (15,450 psi) SF concrete was also studied. The creep of SF concretes was not significantly different from that of the fly ash concretes. Furthermore, the relationship between creep and compressive strength was consistent with that reported in the open literature for high-strength portland cement concretes. Several other concrete properties were studied, including slump retention, time of setting, compressive strength development for one year, split-tensile strength, modulus of rupture, and for the nominal 69 Mpa concretes only, rapid freezing and thawing durability and the hardened concrete air-void system.

The results of studies on the contributions of alkalies in fly ash, slag, and silica fume to the expansion of concrete due to alkali-silica reaction are presented and discussed. A wide range of concrete mixtures was made. Each mixture contained a different amount of cement and different proportions of one type of fly ash, one type of slag, or one type of silica fume. All mixtures were made with amorphous-fused silica as a synthetic reactive aggregate. The alkalilevel of some mixtures was increased by sodium hydroxide to study the effects of pozzolans or slag mixtures at higher concentrations of alkalies. Concrete prisms were made and stored in water at 38 C. The test results indicate that the effectiveness of these supplementary cementing materials in reducing or increasing expansion due to alkali-silica reaction varies widely. The results also indicate that the supplementary cementing materials can contribute significant quantities of alkalies to the reaction, under particular replacement and test conditions employed.

Paper presents extensive test data on the shrinkage and creep behavior of high fly ash-content concrete made with ordinary portland cement and 50 percent by weight cement replacement with low-calcium Type F fly ash. The concrete mixes were designed to have 20, 40, and 60 MPa 28 day cube strength with high workability and low water-to-composite cement ratio. The other variables were the exposure condition for the shrinkage tests and stress-strength ratio for the creep tests. The results showed that for structural concrete of 40 to 60 MPa, the ultimate shrinkage strain ranged from 400 to 500 x 10-6 m/m. The swelling strain amounted to 40 to 55 percent of the shrinkage value and indicated the importance and continued water curing for effective realization of full pozzolanic action of the fly ash. For the same concrete strength of 40 to 60 MPa, the specific creep and the creep coefficient were remarkably low ranging from 40 to 100 x 10-6 /MPa and 1.20 to 2.50, respectively. The data clearly confirm that the time-dependent deformations of well-designed high fly ash-content concrete compare extremely well with those of portland cement concrete.