Research for Development of Flowing concrete

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In order to develop flowing concrete mixed with delayed-type superplasticizer, fundamental research based on labolatory experiments and verification of field performances in actual scale have been conducted.Verious properties of fresh concrete, mechanical properties and durability of hardened concrete have been experimentally investigated so that the most suitable method of ulitization could be determined. Seven brands of superplasticizer of new type have been compared by each partaker with some additional brands being selected on private basis. The following results have been obtained.1) Delayed-type superplasticizer is effective in reducing slump loss of flowing concrete.2) For some brands of superplasticizer, air entraining agent should be carefully selected to avoid its ill effect on durability evaluated as resistance to freezing and thawing.3) Mixing conditions such as delayed dosage (referred to time lag up to the end of mixing), postponed dosage and double-mixing have a great influence on the required amount of superplasticizer and the degree of slump loss. The amount of superplasticizer can be minimized by choosing mixing conditions, but for the cases where the amount is reduced more slump loss has been observed.Method of dosage, types of mixer, and atmospheric temperature have been selected as main variables of field performance tests. Delayed type-superplasticizer has been proved to be effective also in practical scale application. But degree of effectiveness for reducing slump loss has become different for different types of mixer. Compressive strength and bleeding characteristics have not influenced by superplasticizer as observed also in laboratory tests. For some brands of superplasticizer relative dynamic modulus of elasticity after freezing and thawing cycle is decreased more than in laboratory tests. This behavior has been supported by air spacing factor obtained from microscopic observation.