装配式结构接缝微膨胀自密实混凝土收缩和力学性能研究

Study on Shrinkage and Mechanical Properties of Micro-Expansion Self-Compacted Concrete for Joint of Precast Concrete Structures

现浇混凝土接缝的质量控制和补偿收缩是预制装配整体式混凝土结构的关键问题之一.本文选取粉煤灰和石灰石粉作为矿物掺合料,总掺量为胶凝材料总量的30%;选取硫铝酸钙型膨胀剂,按照胶凝材料总量的8%、10%和12%等量取代水泥,制备了拌合物工作性能满足规范要求的自密实混凝土.实验研究了自密实混凝土收缩性能(自收缩、干缩)和基本力学性能(立方体抗压强度、轴心抗压强度、劈裂抗拉强度和弹性模量)的影响规律.结果表明:掺加膨胀剂自密实混凝土的自收缩呈先膨胀后收缩规律;随着膨胀剂掺量增加,自收缩和干燥收缩均持续减小,立方体和轴心抗压强度以及劈裂抗拉强度降低,但弹性模量没有明显变化.从控制自密实混凝土早期收缩防止早期开裂考虑,膨胀剂掺量不宜低于10%;从控制自密实混凝土长期收缩防止后期裂缝考虑,可选取膨胀剂掺量不低于8%.

The quality control and the shrinkage-compensating are the issues of cast-in-situ concrete for joints of precast concrete structures.In this paper,the self-compacting concrete(SCC)with satisfactory fresh workability was prepared by using fly ash and stone powder as the mineral admixtures with dosage of 30%total binders,and replacing cement by calcium sulphoaluminate expansive agent with dosage of 8%,10%and 12%total binders,respectively.The experimental studies were carried out for the autogenous and drying shrinkages as well as the mechanical properties including cubic compressive strength,axial compressive strength,splitting tensile strength and modulus of elasticity of the SCC.Results indicate that the SCC with expansive-agent presents a regulation of first expansion and last shrinkage for autogenous shrinkage.With the increasing content of expansive agent,the SCC is continuously reduced in autogenous shrinkage and drying shrinkage,and the cubic and axial compressive strengths as well as splitting tensile strength are decreased,but there is no obvious change in the modulus of elasticity.The content of expansive agent should not be less than 10%from the point of controlling the earlier shrinkage to prevent the earlier cracking,while it should not be less than 8%in view of controlling the later shrinkage to avoid the later cracks.