Self-compacting concrete was first developed in 1988 to achieve durable concrete structures. Since then, various investigations have been carried out and this type of concrete has been used in practical structures in Japan, mainly by large construction companies. Investigations for establishing a rational mix-design method and self-compactability testing methods have been carried out from the viewpoint of making selfcompacting concrete a standard concrete.

Self-compacting concrete was first developed in 1988 to achieve durable concrete structures. Since then, various investigations have been carried out and this type of concrete has been used in practical structures in Japan, mainly by large construction companies. Investigations for establishing a rational mix-design method and self-compactability testing methods have been carried out from the viewpoint of making selfcompacting concrete a standard concrete.

Self‐compacting concrete was first developed in 1988 in order to achieve durable concrete structures. Since then, various investigations have been carried out and the concrete has been used in practical structures, mainly by large construction companies. Investigations for establishing a rational mix‐design method and self‐compactability testing methods have been carried out from the viewpoint of making it a standard concrete.

The effect of superplasticizer on the balance between flowability and viscosity of mortar in self-compacting concrete was investigated quantitatively. From experimental results, the ratio of funnel speed to flow area of mortar with a fixed amount of superplasticizer was found to be almost constant, independent of the water-powder ratio. A higher amount of superplasticizer resulted in a lower ratio of funnel speed to flow area. The ratio is proposed as an index for the effect of superplasticizer on mortar flowability and viscosity from the viewpoint of achieving self-compactability. This index is convenient for evaluating the amount of superplasticizer for proper flowability and viscosity of mortar using only one set of experimental results. The relationship between superplasticizer amount and its effect was found to differ depending on the type of powder or superplasticizer. The difference can be indicated quantitatively by the proposed index.

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The objective of this paper is to determine the critical size of air bubbles, which harmfully affects the stability of air in mortar of self-compacting concrete (SCC). Mortar samples produced by different type of mixing procedures and mixing time with various dosage of air-entraining agent (AE) were tested. Air diameter distribution of these mortar samples was measured at fresh stage with air-void analyzer (AVA). With AVA machine, size of air bubble measured is considered as the chord length, which is assumed to be 2/3 of the diameter of air bubble (according to ASTM C 457). It was assumed that air bubbles with over the critical size were easily to escape either by collapsing or floating upward. It was found that instability in volume of air in fresh mortar of SCC was caused mainly by the existence of air bubbles with chord length of over 1000 µm and partially by 500 to 1000 µm due to unification between air bubbles with chord length of less than 1000 µm.

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