Purpose The behavior of high-performance concrete (HPC) at high temperatures is very complex and also affects the global behavior of heated HPC-based structures. Researchers have also reported how various types of fibers affected the mechanical properties of cement-based materials at high temperatures. This study aims to discuss the effects of high temperatures on the compressive strength and elastic modulus of HPC with polypropylene (PP) and jute fiber. Design/methodology/approach Adding synthetic fiber (especially the PP type) to HPC is a widely used and effective method of preventing explosive spalling. Although researchers have experimentally determined the permeability of heated PP-fiber-reinforced HPC, few studies have investigated how adding natural fiber such as jute to this type of concrete might prevent spalling. In this study, the effects of high temperatures on the compressive strength and elastic modulus of HPC with PP and jute fiber (jute fiber addition ratio: 0.075 vol.%; length: 12 mm; PP fiber addition ratio: 0.075 vol.%; length: 12 mm) were experimentally investigated. Findings The work was intended to clarify the influence of elevated temperatures ranging from 20°C to 500°C on the material mechanical properties of HPC at 80 MPa. HSC with jute fiber showed a compressive strength loss of about 40 per cent at 100°C before recovering to full strength between 200°C and 300°C. Originality/value The elastic modulus of high-strength concrete decreased by 10-40 per cent between 100°C and 300°C. At 500°C, the elastic modulus was only 30 per cent of the room temperature value. The thermal expansion strain of all specimens was 0.006 at 500°C.

In construction field, it used various technique for concrete formwork. Part of them, non-destructive test has been conducted to estimate a compressive strength of concrete easily such as rebound method and ultrasonic pulse velocity method etc. Former research has recommend proposed equation based on experimental data to investigate strength of concrete but it was sometimes deferent actual value of that from in field because of the few of data in case of early strength concrete. In this study, an experiment was conducted to analyze strength properties for early strength concrete using cylinder mold and 1,000mm×1,000mm×200mm rectangular specimen. And compressive strength of concrete was tested by non-destructive test, and calculated by the equation proposed former research. As a result, the non-destructive test results showed approximately 70 percent of the failure test value for all conditions, and worse reliability was obtained for high strength concrete samples when the ultrasonic pulse velocity method was used. Based on the scope of this study, the experimental equation for estimating compressive strength of early strength concrete from 24MPa to 60MPa was proposed.