超早强聚羧酸对低坍落度混凝土流变与气泡结构经时变化的影响

Influence of Super Early Strength Polycarboxylate Superplasticizer on Time-dependent Behavior of Rheological Properties and Air-VoidStructure of Low Slump Concrete

分别采用两种超长侧链聚羧酸减水剂与一种常规聚羧酸减水剂制备低坍落度混凝土,通过测试分析湿筛砂浆流动度、流变性、气泡结构参数以及三维重构气泡形态,对比研究了超长侧链聚羧酸减水剂对混凝土工作性能与气泡特征经时变化的影响。结果表明:低坍落度混凝土湿筛砂浆符合宾汉姆流体特征,流动度与屈服应力具有强线性相关性,减水剂种类对其影响较小,但超长侧链聚羧酸对砂浆流动度的经时保持作用明显弱于普通聚羧酸。超长侧链聚羧酸在砂浆中的引气数量和小孔径气泡占比均低于普通聚羧酸,并且超长侧链聚羧酸加速了砂浆中小孔径气泡向大孔径气泡的转变。CT三维重构试验直观地证实了砂浆中相邻小气泡聚并成大气泡现象的存在,超长侧链聚羧酸使得砂浆中气泡聚并发生的时间比普通聚羧酸更早。

Polycarboxylate(PCE)comb-like copolymers with super-length side chains(i.e.,one with ether-type side chains and the other with ester-type side chains)and normal-length side chains were employed to prepare low slump concrete in this paper.Influence of the superplasticizers on the time-dependent behavior of fresh properties and air-void structure of low slump concrete were investigated by fluidity test,rheological analysis,air-void parameters measurement of wet-screened mortar and air bubble shape 3D reconstruction in the mortar during hardening.The results showed that a strong linear relationship between fluidity and yield stress of the wet-screened mortar as Bingham fluid was revealed,regardless of PCE types.Superplasticizers with super-length of side chains weakened the fluidity retention of mortar in comparison with superplasticizer of normal molecular structure.The two PCEs with super-length side chains presented less initial air-entraining efficacy and amount ratio of small air bubbles than the normal one,and advanced the process of reduction of small air bubbles and growth of large air bubbles.The 3D reconstruction analysis of air bubble shape visually proved the coalescence of adjacent bubbles exists,and PCEs with super-length side chains led to an earlier coalescence.