دانلود رایگان مقاله خواص مکانیکی کامپوزیت سیمان فوق العاده سبک و در دماهای پایین از 0 تا -60 ° C

Abstract

This paper presents an experimental study on mechanical properties of an innovative ultra-lightweight cement composite (ULCC) at low temperatures down to −60 °C in comparison with those at ambient temperature. Those properties include stress-strain curve, ultimate strength, elastic modulus, Poisson ratio, and flexural tensile behavior. Effect of curing condition is also evaluated. In addition, the performance of the ULCC is compared with that of a normal weight concrete (NWC) and a lightweight concrete (LWC) with similar 28-day compressive strength. The cylindrical compressive strength of the NWC and LWC was increased generally with the reduction in temperature. However, the same phenomenon was not observed for the ULCC. The elastic modulus of the ULCC did not change much, whereas the elastic modulus of the NWC increased significantly with the reduction of temperature from 30 °C to −60 °C. Strain of the ULCC at the peak load was generally much higher than that of the NWC and LWC, and was generally not affected by the temperature. The flexural strength of the three concretes was increased with the reduction in temperature. Duration of the moist curing did not affect the performance of the ULCC under compression significantly, but influenced its flexural strength significantly.

4. Conclusions

Compressive and flexural behavior of the ULCC under low temperatures of 0 C, -30 C, and
60 C are investigated in comparison to those at an ambient temperature of about 30 C. Effect of moist curing of 7 and 28 days on its mechanical performance is also evaluated. The results are also compared with those of a NWC and a LWC with similar 28-day compressive strength. Based on experimental results, following conclusions can be drawn:  The stress-strain curves of the ULCC and LWC were almost linear in the ascending branch, whereas those of the NWC were not linear except for the one obtained at
60 C.  Compressive strength of the NWC and LWC increased generally with the reduction in temperature. However, the same phenomenon was not observed for the ULCC. This might be due to the “strength limit” of the cenospheres. For design purpose, therefore, the compressive strength of the ULCC under subzero temperatures may be conservatively estimated by using its compressive strengths at ambient temperature of 30 C or at 0 C.  The ULCC had significantly lower elastic modulus than the NWC and LWC. The elastic modulus of the ULCC(D) increased slightly from 14.0 to 15.6 GPa whereas that of the NWC increased significantly from 27.8 to 45.3 GPa with reduction of temperature from 30 C to
60 C. The elastic modulus of the LWC was not affected by the temperature significantly in the same range.  Strain at the peak load of the ULCC was generally much higher than that of the NWC and LWC, and was generally not affected by the temperature. No consistent trend of the strain at the peak load vs temperature was observed for the LWC and NWC.  Poisson's ratio of the ULCC was not changed with temperature drop from 30 to 0 C, but was decreased with further temperature reduction to
30 and
60 C. The Poisson's ratios of the NWC and LWC were not affected by the reduction in the temperatures.  The flexural strength of the three concretes was increased with the reduction in temperature. At various temperatures, the ULCC and LWC had comparable flexural tensile strengths which were much lower than those of the NWC.  Moist curing durations of 7 and 28 days did not affect the performance of the ULCC under compressive loading significantly. However, the flexural strength of the ULCC moist cured for 28 days was about 25e38% higher than that of the ULCC moist cured for 7 days and dried for 21 days in lab air, possibly due to drying shrinkage effect on specimen surface.