大坝混凝土凝结过程的超声波联合测定方法

Ultrasonic combined determination method for setting process of dam concrete

新拌混凝土的凝结状态测定对大坝混凝土施工质量控制至关重要。传统的混凝土凝结时间测定方法是贯入阻力法,该方法为有损监测且难以实现对混凝土凝结过程的连续、实时监测。新兴的超声波无损监测主要采用单一的透射法或反射法,然而,反射法受入射角度影响较大、透射法存在波速的计算需要人工精准确定首波出现时间的问题。针对上述问题,本文提出了超声波透射-反射联合测定方法,并以此开展混凝土凝结状态的监测试验研究,构建基于L-M(Levenberg-Marquaredt)算法的神经网络模型,并以能量指标确定的时间点数据集进行训练,用以精确计算大坝混凝土凝结时间。将该方法用于C25大坝混凝土的凝结试验中,并同基于能量分析的反射法、透射法和基于波速分析的透射法进行了对比。结果表明:本文所提的方法相比上述方法计算所得凝结时间的最大相对误差降低了2.5%~18.7%,且计算所得初凝时间和终凝时间与真实值的相关系数分别为0.89和0.96,验证了超声波透射-反射联合法的准确性。本文提出的“透射-反射”联合法能够准确监测大坝混凝土凝结过程,可为大坝混凝土施工质量控制提供新的有效手段,具有重要的理论意义与实用价值。

How to determine the setting state of fresh concrete is crucial to the quality control of dam concrete construction.The traditional measurement of concrete setting time uses the penetration resistance method,which is detrimental and difficult to achieve real-time continuous monitoring of the setting.Most of the emerging ultrasonic nondestructive monitoring is a method that adopts a single transmission or reflection,but its measurement is affected greatly by the incident angle,and its calculation of wave velocity requires an accurate determination of the arrival time of the first wave through manual calculations.Aimed at these problems,this paper develops a method of ultrasonic transmission-reflection joint measurement to accurately calculate the setting time of dam concrete.We conduct an experimental study of monitoring concrete setting state,construct a neural network model based on the Levenberg-Marquaredt(L-M)algorithm,and train it using the time point data set determined by energy index.This new method has been applied to the setting test of dam concrete C25 and compared with the reflection method and the transmission method both based on energy analysis,and the transmission method based on wave velocity analysis.The results show the maximum relative error of its setting time calculations is reduced by 2.5%-18.7%.The correlation coefficients of its calculated initial setting time and final setting time with the real values are 0.89 and 0.96 respectively,verifying its accuracy and theoretical and practical significance in the quality control of dam concrete construction.