International Concrete Abstracts Portal

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.

Presents experimental results on the use of concrete incorporating condensed silica fume and fly ash to reduce cement content, to lower temperature rise due to hydration, and to enhance early strength, and gives a case history on the application of this type of concrete in the construction of turbine shells in China. Studies were done on the effect of adding different amounts of silica fume and fly ash on strength, the effect of addition of both silica fume and fly ash on the total heat of hydration, and properties of concrete, including setting time, slump loss, modulus of elasticity, ultimate elongation, impermeability, and resistance to abrasion. Experimental and field studies indicated that the concrete mixture containing condensed silica fume and fly ash helped save 38 percent cement, lower the heat of hydration by 40 percent, and showed a slight increase in strength and durability. In placing over 200 mý of concrete of this type in hot weather, no abnormal phenomena occurred during the operation. A 90-day compressive strength of 30 MPa and a 98 percent strength were obtained, meeting the design strength requirements. No crack has been found in the surface of the shells since they were completed half a year ago.

In the Federal Republic of Germany, adequate pozzolanic activity of fly ash as a concrete additive has so far been insured by requiring cement mortars containing fly ash to reach a certain compressive-strength ratio as compared to a reference mortar. Test results are known to be sensitive to other influencing factors, especially composition and properties of cement. A series of tests was conducted to establish the usefulness of various testing methods. Under investigation were the respective influences of cement, fly ash content, and preparation on the basis of constant water content or constant workability. Mortars were stored according to the German test guideline, to BS 3892, and to ASTM C 311. Certain physical and chemical properties of the fly ashes were also determined. This paper discusses the effects of cement, i.e., alkali content, fineness, and slag content, on the pozzolanic activity index at different ages. Also demonstrated is the suitability of accelerating strength testing methods. Finally, the strong influence of fly ash fineness on workability and strength is shown.

Usability of rice husk ash was investigated as a siliceous material for calcium silicate products manufactured by hydrothermal reaction. It is concluded that rice husk ash can be used as a superior siliceous material for manufacture of calcium silicate insulating materials with good thermal durability up to 1000 C. Characteristics of rice husk ash, namely, high SiO2 content, reactive silica phase comprising amorphous silica, cristobalite and/or tridymite, and high surface area, are favorable to the formation of well-grown xonotlite which forms bodies of insulating materials. Trial products with bulk densities ranging from 0.11 to 0.41 g/cm3 prepared from rice husk ash using glass fiber for reinforcement not only satisfied all the requirements in the industrial standards (JIS A9510) but also gave 1.4 to 2 times higher bending strength than commercial products prepared from conventional siliceous materials, such as finely ground quartz sand, silica fume, and diatomaceous earth. A variety of rice husk ashes with different crystallinity are usable for manufacture of calcium silicate products, but the hydrothermal reaction condition should be optimized according to the crystallinity or amorphousness of the ash.

Presents data on selected properties of cement pastes and concretes containing peat fly ash as a supplementary cementing material. Reference concretes and cement pastes with pure portland cement and with coal fly ash were used. The tests were performed as comparison tests on pastes and concretes with or without an air-entraining agent. In addition, a superplasticizer and a water reducer were used in the pastes and concretes containing fly ashes. The fly ash contents used varied between 20 and 60 percent by mass of the total amount of binder. Tests on cement pastes showed that using peat fly ash or coal fly ash decreases the cracking tendency of a portland cement paste as measured by a shrinkage ring test method. No differences were observed between the pastes with peat fly ash or coal fly ash in this experiment. Drying shrinkage results show that concretes containing peat fly ash developed somewhat lower shrinkage values than the control mixtures containing coal fly ash. The strength, impermeability, and frost-resistance properties of concretes with peat fly ash did not essentially differ from those of coal fly ash concretes. The test data indicate that with proper mix design and choice of admixtures, peat fly ash could be used as a supplementary cementing material to produce a high-quality, frost-resistant concrete.