The article presents an attempt to identify the particles of bentonite in the concrete structure derived from the diaphragm wall. The aim of the research was to demonstrate that during the performance of diaphragm walls, bentonite suspension is mixed with the concrete mix – what causes the significant decrease in technical concrete parameters. The distinction of bentonite particles in the concrete would confirm the above thesis. Markings were carried out on samples taken from the existing object.After appropriate preparation sampleswere subjected to scanning electron microscope test and quantitative phase composition test using X-ray diffractionmethod. The thermogravimetry marking (TG) as well as the differential thermal analysis (DTG) and (DTA) were also performed. The presence of bentonite in the tested samples was not stated. Then, an attempt was made to determine the detection of bentonite in the concrete. The marking was performed using (TG), (DTA) and (DTG) methods. The conducted research indicated that a slight (a fewpercent) bentonite content in the concrete is not possible to the detection by the presented researchmethods. The presence of bentonite in themonolith of the diaphragm walls can therefore be stated only symptomatically on the basis of the technical characteristics research of concrete.

Keywords: bentonite suspension, bentonite, diaphragm wall, concrete.