Research for Development of Flowing concrete

为了研制掺延型高效减水剂的流动混凝土，开展了基于室内试验和实际规模现场性能验证的基础研究。对新拌混凝土的各种性能、硬化混凝土的力学性能和耐久性进行了实验研究，从而确定了最合适的利用方法。7个新型高效减水剂品牌由每个参与者进行比较，并私下选择一些额外的品牌。得到了以下结果：1)延迟型高效减水剂对降低流动混凝土坍落度损失是有效的。2)对于某些品牌的高效减水剂，应慎重选择引气剂，以免对耐久性（抗冻融性）产生不良影响。3)延迟加量（指混合结束前的时间滞后）、延迟加量、二次混合等混合条件对高效减水剂所需用量和坍落度损失程度影响较大。通过选择混合条件可以使高效减水剂的掺量最小化，但在掺量减少的情况下，坍落度损失更大。选取掺量方法、混频器类型和大气温度作为现场性能试验的主要变量。延迟型高效减水剂在实际的规模应用中也被证明是有效的。但不同类型的混合器对降低坍落度损失的效果不同。抗压强度和出血特性不受高效减水剂的影响，在实验室试验中也观察到。对于某些品牌的高效减水剂，冻融循环后的相对动态弹性模量比室内试验值下降得更大。微观观察得到的空气间距因子支持了这种行为。

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.