超小直径芯样检测混凝土抗压强度的实验研究

发布时间：2018-10-20 17:29

【摘要】：钻芯法作为检测混凝土抗压强度的直接方法被广泛应用。随着实际工作对检测要求的提高，现有钻芯技术已不能完全满足需要。本文针对比目前允许使用的直径70mm芯样更小的直径为50mm的超小芯样展开研究，用于解决实际问题。目前对直径为50mm的超小芯样应用上的主要障碍是小芯样的尺寸效应及离散性问题。本文分析了国内外大量的研究资料并制作了522个芯样进行不同直径芯样间的强度比对。可以看出芯样不同于浇筑成型的立方体试块，受多种因素的影响，一般不随直径的减小而增大，尺寸效应没有浇筑成型的试块明显。芯样直径与粗骨料最大粒径之比及粗骨料被切割的位置对抗压强度有较大影响，混凝土芯样与粗骨料最大粒径之比宜大于等于2。高径比不同体现出来的尺寸效应对混凝土抗压强度的影响更显著，故不建议采用短芯样来评定薄构件。钻芯法检测结果的不确定性源于系统、随机和检测操作三个方面。钻芯法检测混凝土强度的系统偏差较小；检测操作过程中的偏差会对芯样强度值降低，对小芯样的影响将更为显著应严格控制，对于50mm直径超小芯样不宜含有钢筋。泵送混凝土和喷射混凝土粗骨料最大粒径可得到控制，混凝土匀质性较好，可减小样本的离散性，符合超小芯样的研究条件。泵送和喷射混凝土50mm小芯样抗压强度值服从正态分布，可以运用统计学中的知识进行分析统计。通过统计学中显著性假设检验，泵送混凝土抗压强度用50mm小芯样测得的平均值与用标准试件测得的平均值没有显著差异，而喷射混凝土则存在显著差异，但同时喷射混凝土50mm小芯样与100mm直径芯样测得的抗压强度存在显著相关性。可认为泵送混凝土50mm小芯样与标准试件抗压强度平均值基本相当，，喷射混凝土可采取0.9的换算系数。因50mm小芯样受各种因素干扰更明显，离散性偏大，在小样本的情况下，不建议采用50mm的芯样按最小值法进行单个评定。根据试验数据计算并结合工程实体取样的客观条件，50mm直径超小芯样批量检测的取样数量可定为：当设计等级不大于C50时，批量检测数量不少于25个；当设计等级大于C50时，批量检测数量不少于20个。
[Abstract]:The core drilling method is widely used as a direct method to measure the compressive strength of concrete. With the improvement of testing requirements, the existing core drilling technology can not fully meet the needs. In this paper, the ultra-small core sample with a diameter of 50mm that is smaller than the diameter 70mm core sample which is allowed to be used at present is studied to solve the practical problem. At present, the main obstacle in the application of ultra-small core sample with diameter 50mm is the size effect and dispersion of small core sample. In this paper, a large number of research data at home and abroad were analyzed and 522 core samples were made to compare the strength of different diameter core samples. It can be seen that the core sample is different from the cube sample in pouring molding, which is affected by many factors, and generally does not increase with the decrease of diameter, and the size effect is not obvious. The ratio of the diameter of core to the maximum diameter of coarse aggregate and the position where coarse aggregate is cut have great influence on the compressive strength. The ratio of the maximum diameter of concrete core to coarse aggregate should be greater than or equal to 2. The dimension effect of different aspect ratio is more significant to the compressive strength of concrete, so it is not recommended to use the short core sample to evaluate the thin members. The uncertainty of the test result of drilling core method originates from three aspects: system, random and test operation. The system deviation of testing concrete strength by drilling core method is small, and the deviation during testing operation will decrease the strength value of the core sample, and the influence on the small core sample should be strictly controlled, and the reinforcement should not be included in the ultra-small core sample of 50mm diameter. The maximum particle size of pumping concrete and shotcrete coarse aggregate can be controlled, the homogeneity of concrete is better, the dispersion of samples can be reduced, and the research conditions of ultra-small core samples are satisfied. The compressive strength of pumping and shotcrete 50mm core samples is normally distributed and can be analyzed by using the knowledge of statistics. Through statistical significance hypothesis test, the average value of compressive strength of pumping concrete measured by 50mm small core sample is not significantly different from that of standard specimen, but there is significant difference between shotcrete. But there is a significant correlation between the compressive strength of shotcrete 50mm core sample and 100mm diameter core sample. It can be considered that the average compressive strength of pumping concrete 50mm core sample is basically equal to that of standard specimen, and the conversion coefficient of shotcrete can be taken as 0.9. Because the small core sample of 50mm is more obviously disturbed by various factors, the dispersion is larger. In the case of small sample, it is not recommended that the core sample of 50mm be evaluated by the method of minimum value. According to the test data and the objective conditions of engineering solid sampling, the sampling quantity of 50mm diameter ultra small core sample can be determined as: when the design grade is not greater than C50, the number of batch detection is not less than 25, and when the design grade is greater than C50, the quantity of batch detection is not less than 25, when the design grade is greater than C50, The quantity of batch inspection is not less than 20.
【学位授予单位】：清华大学
【学位级别】：硕士
【学位授予年份】：2013
【分类号】：TU528.07

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