MECHANICAL PROPERTIES OF STEEL FIBER REINFORCED CONCRETE AT HIGH TEMPERATURE

Abstract

 This paper presents results of high temperature compression tests of steel fiber reinforced concrete. The influence of steel fiber on the mechanical properties at high temperature was investigated from the difference of the test results between steel fiber reinforced concrete and plain concrete. Although research on prevention of concrete spalling by means of mixing steel fibers has been conducted, there is no report on mechanical properties of steel fiber reinforced concrete at high temperature in Japan, and there are few such reports in foreign countries.

 In this study, high temperature compression tests were performed using two types of concrete, i. e. steel fiber reinforced concrete (SF) and plain concrete (P). The tests consisted two kind of tests. One was load increasing tests under steady state at constant high temperatures (steady state tests, ST tests). Other was temperature increasing tests under constant stress (transient tests, TR tests) . In case of ST tests, the parameter was specimen temperatures ranging from ambient temperature to 800 °C. While concrete was heated to the target temperature, heating rate was controlled at 1.5 °C/minute. While stress or strain of concrete increased, the concrete temperature was kept the target temperature. From ST test results, stress-strain relationship, compressive strength, Young's modulus and absorbed energy were compared between SF and P. In case of TR tests, the parameter was level of the constant compressive stress ranging from 0 to 0.7.After applying the target stress, specimen was heated and the relative displacement was measured. From TR test, the thermal strain and total strain were obtained.

 Main findings of this paper were summarized as follows:

 (1) Compressive strength ranging from 200 °C to 400 °C was higher for SF than for P, meanwhile both the compressive strengths were approximately same above 500 °C. There was no significant difference in Young's modulus at high temperatures due to the presence or absence of steel fibers.

 (2) The absorbed energy of SF was larger than that of P between 100 °C and 500 °C, and the difference was the largest at 500 °C. On the other hand, the difference above 600 °C was relatively low.

 (3) The thermal strain ranging from 600 °C to 800 °C was lower for SF than for P.

 (4) Under stress level of 0.7 in TR tests, SF supported the load up to 477 °C, meanwhile P fractured at 78 °C. Under high load condition, the effect of steel fiber may be considerable.