Estimation of Concrete Strength by Nondestructive Methods

从1989年开始，我们对大体积混凝土试件的无损强度估算进行了研究和试验。在1995年和1996年，我们进行了以下两个实验：[)高*宽*深= 70*60*40、70*40*40、70*20*40cm的试件在龄期7、14、28、56 d时的大体积混凝土强度超声脉冲速度估算。在龄期结束时，测量了从大块试件中钻孔的混凝土芯的抗压强度。[][)试件直径和长度对超声脉冲速度的影响。试件尺寸为3种直径（10、15、20cm）和5种长度（20、30、40、50、60cm）。分别于7、14、28天时测定超声脉冲速度。从这些实验中，得到以下结果：(1)采用超声脉冲法较准确地估计了与实际构件尺寸相近的大体积混凝土试件的强度发展情况。(2)估算大体积混凝土试件的抗压强度和密度时，直径为7.5 cm的钻孔混凝土芯要优于直径为10cm的钻孔混凝土芯。(3)超声脉冲穿过混凝土试件的速度随试件直径和长度的增加而减小。与试件长度相比，直径对超声脉冲速度的减小影响较大。

We have studied and carried out the experiments on the estimation of strength of massive concrete test piece by non-destructive methods from 1989. In 1995 and 1996, we carried out the following two experiments ;(]SY.encircleda.[) The estimation of massive concrete strength by ultrasonic pulse velocity for the massive test pieces with height*width*depth = 70*60*40,70*40*40 and 70*20*40cm at the ages 7,14,28 and 56 days. And at the end of age, the compressive strength of concrete cores bored from massive test pieces were measured.(]SY.encircledb.[) The influences of diameter and length of test piece on the ultrasonic pulse velocity. The sizes of test piece were 3 diameters (10,15,20cm) and 5 lengths (20,30,40,50,60cm). At the ages 7,14,28 days, ultrasonic pulse velocity was measured.From these experiments, the following results were obtained ;(1) The strength development in a massive concrete test piece with nearly same size of actural structural member is estimated by ultrasonic pulse method fairly accurately.(2) To estimate the compressive strength and the density in a massive concrete test piece, the bored concrete cores with 7.5 cm diameter is fairly better than those with 10cm.(3) The ultrasonic pulse velocity through the concrete test piece decreases with the increasing of diameter and length of test pieces. As compared with the length of test piece, the diameter greatly influences the decreasing of ultrasonic pulse velocity.