Research for Development of Flowing concrete

为了研制掺延迟型高效减水剂的流态混凝土，进行了室内试验和现场实际规模性能验证的基础研究，对新拌混凝土的各项性能、硬化混凝土的力学性能和耐久性进行了试验研究，以确定最合适的固化方法。7个品牌的新型高效减水剂已由每个参赛者进行了比较，并在私人基础上选择了一些额外的品牌。结果表明：1)延迟型高效减水剂对减少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，以避免其对耐久性的不良影响，如抗冻性和抗冻性。3)延迟量(指搅拌结束前的滞后时间)、延迟量和双掺等搅拌条件对减水剂的需求量和坍落度损失程度有很大影响。通过选择掺加条件可以使高效减水剂的掺量降到最低，但随着掺量的减少，坍落度损失较大。选择了掺量方法、搅拌器类型和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应用中也被证明是有效的。但是，对于不同类型的混合器，降低坍落度损失的有效程度是不同的。在实验室试验中也观察到，高效减水剂对抗压强度和渗漏特性没有影响。对于某些品牌的高效减水剂，冻融循环后的相对动弹模数比实验室试验时的下降幅度更大。这一行为得到了从显微镜观察中获得的空气间隔系数的支持。

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.