Проведены исследования по определению температуры и времени нагрева строительных конструкций на основе цементного камня методами термического анализа в целях установления очага пожара при производстве пожарно-технических экспертиз. Результаты исследований показали, что методами термоанализа можно установить температуру и время нагрева образцов, определить соотношение компонентов в смеси, начало и степень их разложения, наличие веществ, обладающих огнестойкостью, остаточную массу образца в зависимости от времени и температуры прогрева, влияющих на свойства строительных материалов. Установлено, что в отличие от применяющихся в настоящее время методов исследований метод синхронного термического анализа позволяет использовать малые количества материала, отобранного с места пожара. В работе также были применены общепринятые методы определения прочности цементного камня с использованием молотка Кашкарова и комплекса "Ультратерм" для получения объективных результатов исследования.
The scientific department of Expert-Criminalistic Center of the Ministry of Internal Affairs of Russia has observed cement bricks after the heat impact in order to evaluate the possibility of usage of thermal analysis to study concretes after the fire accidents. The samples of M200 and M400 (Russian cement types) cement bricks were prepared for the observation (the river sand was added to the M400 cement mixture). The obtained samples were annealed in the muffle roaster under 200-1000 °C with 100 °C interval for 15, 30 and 60 minutes. These samples were tested with a hammer of Kashkarov. It is discovered, that the changes are not significant at the opening phase with the temperature rising from 200 to 500 °C. However, under the temperature between 500 and 700 °C essential decrease of the samples' resistibility and their destruction afterward are observed. The results of through and dilatational sonic test have similar regularity and prove that the speed of the ultrasonic wave going through the sample decreases with rising of the stone thermal damage. The time of the ultrasonic wave going through the sample depends remarkably on the duration of the annealing process. The thermally damaged samples of the cement bricks were tested with the SDT-Q600 instrument. The synchronous thermal analysis (STA) provided the temperatures, under which the mass of the samples reduces, defined the processes, going in the studied sample, and the duration of the heat impact. The result of the current research concludes that the thermal analysis (alternatively to the nondestructive testing and testing by Kashkarov hammer) allows to explore microquantity of the substance, provides the regularity of the cement bricks alternations, which permits to differentiate the level and the duration of the heat impact. During the expertise of the cement stone, the loss of the remaining mass can be used as the differentiating grade of the material thermal damage. The appliance of the STA allows to define the different components presence in the system, the beginning and the level of the material decompounding, the remaining mass of the sample depending on the time and temperature of the heat-up. Altogether they influence the constructional materials characteristics.
The authors declare that there are no conflicts of interest present.