Compressive strength values dispersion of side-mixed and ready-mixed concretes

Abstract Compressive strength testing method has been widely used as indirect way for evaluate the concrete quality, due to it simplest execution, reliability of the results achieved and low cost of execution. Independently, if the concrete was side or ready-mixed, it is necessary to achieve the compressive strength requirements stated during structure design, essentially because this parameter allows the obtainment of the average strength of the reinforced concrete structure analyzed. Following, as for ready-mixed, as for side-mixed concretes, it is need to ensure the correspondence between the concrete design parameters and the concrete mixed, namely these parameters are summarized in terms of the compressive strength and homogeneity in the different phases of the construction. This way, the present work aims to do the analysis of the dispersions of the compressive strength of concretes mixtures (corresponding to compressive strength classes of 20, 25, 30, 35 and 40 MPa), and identify some influence factors, in this case, the influence of the workers team variation. Two mixtures (35 MPa and 40 MPa) were ready-mixed, while five of the concrete mixtures were side-mixed, by five different worker’s group with same time of experience on concrete’s manufacture. The results demonstrate that the variation of the workers team presents a high influence for the homogeneity of the compressive strength of the concrete.摘要：抗压强度试验方法因施工简便、测试结果可靠且成本低廉，已被广泛用作评估混凝土质量的间接手段。无论混凝土为现场搅拌（side-mixed）还是预拌（ready-mixed），均需满足结构设计阶段规定的抗压强度要求，究其本质，该参数可用于获取所分析钢筋混凝土结构的平均强度。无论是预拌混凝土还是现场搅拌混凝土，均需确保配合比设计参数与实际拌制混凝土的参数相匹配，而这些参数可概括为抗压强度与施工各阶段的匀质性。 鉴于此，本研究旨在分析抗压强度等级为20、25、30、35及40 MPa的混凝土拌合物的抗压强度离散性，并识别相关影响因素，本次研究考察的具体影响因素为作业班组差异。本次研究中，2组混凝土拌合物（抗压强度等级35 MPa和40 MPa）为预拌混凝土，其余5组由5个混凝土拌制经验时长相同的不同作业班组分别现场拌制。试验结果表明，作业班组差异对混凝土抗压强度的匀质性具有显著影响。