International Concrete Abstracts Portal

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.

Effect of rice husk ash addition on the chloride diffusivity of concrete is investigated in the present paper. The concrete specimens, having water-cementitious materials ratio of 0.30, 0.36 and 0.53, with and without rice husk ash are subjected to accelerated chloride penetration using the following two methods: i) Immersion in saturated NaCl at 20°C. ii) Exposure to alternate cycles of 3days immersion in 3% NaCl solution at 20°C and 4days drying at 50% R.H. After the accelerated chloride penetration, the total chloride content of concrete specimens at various depths was determined. Consequently, using the chloride content distributions, the chloride diffusion coefficient of concrete is evaluated by applying Fick’s second law. In addition, the pore size distribution of concrete is determined in order to assess the effect of concrete microstructure on chloride diffusivity. From the experimental results, the total chloride content of concrete incorporating rice husk ash was shown to be lower than that of the control concrete after accelerated chloride penetration. The concrete specimens incorporating rice husk ash had chloride diffusion coefficients 57% to 25% lower than the control concrete. The effect of rice husk ash on pore refinement in concrete was observed, especially in the pore radii larger than 50nm. The pore size distribution of concrete tended to shift towards the smaller pores with the addition of rice husk ash. The decrease of the chloride diffusion coefficient of concrete incorporating RHA may therefore be attributed to the pore-refinement effect.

Self-compacting concrete, recycled concrete as aggregate, calcium nitrate accelerators—these are just a few of the topics covered in the 47 papers included in ACI SP-200, Fifth CANMET/ACI International Conference on Recent Advances in Concrete Technology. You’ll be able to compare the structural performance of full-scale columns using ordinary and self-compacting concretes and with stirrup configurations representing differing degrees of confinement. You’ll also learn about a procedure that improves the quality of concrete made using aggregate produced from recycled concrete, and about experiments showing that, at 5 °C, calcium nitrate is a much more effective accelerator than calcium chloride. Note: The individual papers are also available as .pdf downloads.. Please click on the following link to view the papers available, or call 248.848.3800 to order. SP200

High strength concrete mixtures containing 10% metakaolin replacement and 10% metakaolin addition, water/cementitious material ratio of 0.3 and 1% super-plasticizer were studied.. Similar mixtures incorporating silica fume were also prepared. The effect of mineral admixtures on the fresh and hardened properties of concrete was investigated. Mixtures with mineral admixture exhibited lower workability, less bleeding, and slightly lower air content. Metakaolin resulted in a higher loss of workability compared with silica fume. Mixtures incorporating mineral admixture developed greater compressive strength and elastic modulus at all ages. The enhancement was more pronounced at early ages and in the addition mixtures. The study concludes that the performance of metakaolin is equivalent to silica fume in terms of contribution to the enhancement of strength and elastic modulus. The metakaolin addition mixture attained 70% and 50% strength improvement while the metakaolin replacement mixture achieved 67% and 39% strength increment at the respective ages of 3 and 28 days.

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