HTR concrete experiments - high-temperature strength experiments

It is reported on high-temperature strength investigations on unsealed HTR concrete samples of basalt concrete and Rhenish gravel concrete. These investigations had become necessary, because only temperatures up to 3000C have been considered in the framework of the previous R + D concrete programme, but the consideration of hypothetic breakdowns requires to have corresponding strength and deformation data at least up to temperatures of 6000C available. The tests were carried out on a high-temperature test stand on cylindrical test specimens of a diameter of 8 cm and a length of 24 cm. Three different courses of experiment were realized: 1) 'slow' heating with a constant heating rate of 5 K/h, 2) 'rapid' heating with a constant heating rate of 20 K/h, 3) 'stepped' heating with the samples heated up to 1200C at 5 K/h, then kept at this temperature for approx. 24 h and finally heated up to 400, 500 resp. 6000C at 20 K/h. The samples were installed in the testing machine with a low load required. After installing the samples were at first loaded and relieved three times with max. 15 N/mm2 at room temperature, thus determining the modulus of elasticity. Then a creep stress of 15 N/mm2 was applied and the heating up to 4000C, 5000C resp. 6000C took place according to the temperature programmes mentioned before. After reaching the corresponding test temperature the samples were thermally homogenized up to 2 hours. Finally the modulus of elasticity was determined in a hot state by loading and relieving the samples three times. (orig./MM)