The Polish Patent Office granted the IPPT PAN a new patent. The creators work at the Department of Experimental Mechanics, IPPT PAN: Michał A. Glinicki, Maciej Sobczak, Daria Jóźwiak-Niedźwiedzka, Karolina Gibas-Bogusz, and Mariusz Dąbrowski.
Title: Device for measuring the change in the length of elements containing aggregate, in particular concrete, subject to alkali-aggregate reaction.
The invention aims at modifying the classic device for measuring the length of mortar and concrete specimens, which secures better precision and measurement repetitiveness, and which is of particular importance in high-temperature tested specimens reaching 80°C, characteristic for accelerated reactivity of mineral aggregates tests in a cement matrix in a strongly alkaline environment.
The essence of the invention lies in the use of materials with a low thermal conductivity coefficient (α < 2-10-6/K) in these elements of the measuring device which have direct contact with a high-temperature specimen, as well as in the introduction of an additional crossbar equipped with a rotation-protected adapter bar with a measuring socket. The proposed material solution, based on the Invar alloy and consisting of 54–64% iron and 36–46% nickel, plus an addition of carbon and chromium, reduces the elongation error generated by the changing temperature of the elements of the length measurement device after placing a specimen with increased temperature (up to 80°C) in it under the conditions of measurement (20±2°C). The additional crossbar equipped with a rotation-protected adapter bar increases the stiffness of the mounting system in the measuring sockets and reduces the stress on the displacement sensor in a direction other than movement along the measurement axis, resulting in greater measurement accuracy.
The device is especially dedicated to alkaline reactiveness tests of mineral aggregates in accelerated tests at 80°C and to elongation measurements of mortar and concrete specimens with the required resolution of 0,001 mm and measurement accuracy of 0,003 mm.
Figs. Mariusz Dąbrowski and device for measuring the change in the length of mortar and concrete specimens with the calibration bar made of Invar (A) with the concrete specimen (B)
Fig. Schematic design of the device for measuring the change in the length of elements containing aggregate and concrete, composed of a base (1), column (2), measuring plugs sockets (3) and (6), crossbar for the rotation-protected adapter bar (4), crossbar (5), measure sensor (7), pressure spring (8), calibration bar with a marked end (9)
The device was designed for the realization of a research project carried out in cooperation with the Instytut Ceramiki i Materiałów Budowlanych Sieci Badawczej Łukasiewicz (Łukasiewicz Institute of Ceramics and Building Materials) and made at the Laboratory Services Center IPPT PAN. A dozen devices were bought by other laboratories which specialize in testing concrete road infrastructure. Measurements made with the device have already been used in many scientific publications of the authors and a doctoral thesis by dr inż. Aneta Antolik.
