Although 37 million tons of concrete wastes have been generated annually in Japan, the use of recycled aggregate for concrete is limited because of low density and high absorption due to adhered cement paste and mortar. A new method to produce high qualty recycled aggregate by heating and grinding concrete rubbles to separate cement portions adhering to aggregate was developped recently. In this process by-product powder with the fineness of 400 m/kg is generated. By-product recycled concrete powder consists of fine particles of hydrated cement and crushed aggregate. To utilize the recycled concrete powder as concrete additives two series of experiments were performed to make clear of the effect of recycled powder. Self-compacting concrete with recycled concrete powder, ground blast-furnace slag and ground limestone were tested for slump-flow, compressive strength, modulus of elasticity and drying shrinkage. Reduction in super-plasticizing effect of high-range water reducer was found for concrete with recycled concrete powder. Compressive strength of concrete with recycled concrete powder were the same as those with ground limestone, and lower than those with ground slag. Concrete with recycled concrete powder showed lower elastic modulus and higher drying shrinkage than those with ground slag and ground limestone. The recycled concrete powder is usable for self-compacting concrete without further processing, despite the possible increase in dosage of high-range water reducer for a given slump-flow and in drying shrinkage. The addition of ground blast-furnace slag together with recycled concrete powder to self-compacting concrete improved superplasticizing effect of high-range water reducer and properties of concrete .

The effects of metakaolin and silica fume on the creep and shrinkage of concrete were investigated. Compared with the control concrete, the concrete containing the mineral admixtures had lower early age autogenous shrinkage measured from the time of initial set, but the long-term autogenous shrinkage measured from the age of 24 hours was increased. The total shrinkage (autogenous plus drying shrinkage) measured from 24 hours was reduced. Drying shrinkage was less than for the control concrete. The basic creep of sealed concrete and total creep of drying concrete were significantly reduced due to metakaolin and silica fume particularly at higher replacement levels.

This paper describes a five-year Electric Power Research Institute (EPRI) program directed toward increasing ash utilization in the cement and concrete market within the United States, in the face of the impacts on ash quality due to more aggressive Nox controls. EPRI is undertaking this program to provide the technical basis for protecting the bulk sale of coal ash in high-volume applications in cement and concrete and other high volume civil engineering applications. In addition to higher carbon levels in ash from NOx control systems, problems associated with ammoniated ash have become a major concern for coal-fired facilities in recent years as a result of the increased use of ammonia-based environmental control technologies. Many coal-fired power producers have become concerned that post-combustion Nox controls could lead to fly ash containing high levels of ammonia. Therefore, EPRI conducted a research program designed to assist power producers evaluate and mitigate the impacts of high carbon and ammoniated ash.

Experimental and analytical studies on High Strength Concrete (HSC) columns subjected to biaxial bending are presented. The experimental work consisted of testing of twelve HSC columns. The primary test variables were load eccentricities about both the axes and the longitudinal steel ratio. All the columns were loaded to failure. The analytical work comprised development of a computer-based numerical algorithm to predict the strength of columns. The numerical analysis calculated the strength of the column in uniaxial bending separately about both the axes and applied the Bresler’s reciprocal load formula to predict the strength of the column in biaxial bending. The analysis applies to all grades of concrete. Good correlation between the test and calculated results is observed.

bleeding; bottom ash; CLSM; compressive strength; deterioration; durability; flowability; fly ash; freezing and thawing; frost heaving; mix proportioning; slump flow; used foundry sand