STUDIES ON THE STRESS-STRAIN RELATIONSHIP IN COMPRESSION OF CONCRETE AT HIGH TEMPERATURES (I) : Apparatus and Test Procedure

Various experiments were attempted on the stress-strain relationship in compression of concrete at high temperatures in many countries in the past. But results by these experiments are not suffisient, since accuracy of extensometers designed for these experiments were not complete. Author designed the special extensometer for high temperatures and could record sufficiently perfect stress-strain curves in the 0 to 700℃ temperature range. In this paper, the theoretical and experimental investigation for principal and accuracy of this extensometer is explained. This extensometer and testing assembly were shown in Fig. 1 to 5. Tipical force deformation curve records were shown in Fig. 6 to 8. This extensometer is very exact and far better than other extensometers such as marten's extensometer, wire strain gage and so on. As the tensil strength of concrete is very small than compressive strength, concrete specimens may be broken due to thermal stress, when they are heated rapidly, so that care must be taken to heat concrete specimens. Theoretical and experimental investigation to heat concrete specimens homogeniously and without spoilling was done, and proper heating procedure was established.