The homogeneity of the structure of the boired pile shaft has been studied based on the results of four-channel inter-well ultrasonic (US) monitoring. The actual lengthy of the piles has been determined with the detection of defragmentation of the pile shaft, the compressive defects have been determined, and continuity defects have been identified based on a joint analysis of data from the method of interwell ultrasonic monitoring. The use of four channels allows to control separately the peripheral and central areas of the pile in six directions. The data of the seismoacoustic method coincided with the parameters of ultrasonic monitoring in terms of identifying zones of concrete heterogeneity, reducing the pile cross section, etc. For all of the listed piles, data are not registered by the named test methods indicating defragmentation of the pile shaft – the presence of sections in the cross sections of which there is no concrete at all. These test methods for all piles confirmed the compliance of their actual length with the design values. A significant defect in the continuity of the concrete of the 40op pile, according to the data of ultrasonic monitoring and seismoacoustic method, was registered in the interval of marks – (17.5–18) m, manifesting itself a sa decrease in the propagation velocity of the ultrasonic pulse from 25 to 50 % in two sounding directions, inclu-ding diametrical. This defect can be interpreted as a decrease in the effective section of the pile to 25–50 % of the average value. Defective sections of piles were found in their upper part at depth marks from 0 to –1.5 m, counting from the end surface of the head. At the same time, differences in the physical and mechanical parameters of concrete at these marks were also observed within the cross section of piles [1–5].
Sclerometric methods of testing concrete, in particular, the rebound hammer testing, retain their positions as the most common indirect methods for concrete strength determining in situ. They are used as a means for technological testing during the buildings construction, as well as during their inspection during maintenance. Indirect parameters of current sclerometric devices are usually point-values: the rebound index, the diameter and depth of the print, the duration of the indenter insertion process, and the maximum interaction force. However, the lack of an unambiguous relationship between these parameters and the strength of concrete leads to additional uncertainty of the test result, which is one of the problems of sclerometric methods of concrete control. The instability of the calibration dependencies of the method is also observed. Even strict compliance with the requirements of the procedure does not guarantee the repeatability of the obtained dependencies.The article considers the possibility of improving metrological indicators of calibration dependencies of sclerometric methods by introducing an additional parameter-concrete humidity. The possibility of combining two sclerometric methods – the elastic rebound method and the shock pulse method is also considered. Data were obtained on concrete samples with a curing time of 25..60 days. Two-parameter calibration dependencies, including concrete humidity as an additional parameter, allowed for all experimental series of samples to reduce the residual mean square deviation of the calibration dependence of elastic rebound and shock pulse methods by 10%..16%, and to consistently provide the minimum acceptable value of the correlation coefficient r = 0.7 for the studied concrete compositions. The influence of concrete heterogeneity on the readings of sclerometric test methods is considered.The developed method of constructing two-parameter calibration dependencies can be recommended for inclusion in the current standards governing the determination of the strength of concrete structures under construction.
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