Compressive and splitting tensile strength of autoclaved aerated concrete (AAC) containing perlite aggregate and polypropylene fiber subjected to high temperatures
This paper presents the results of an experimental study on the residual compressive and splitting tensile strength of autoclaved aerated concrete (AAC) containing perlite and polypropylene (PP) fiber subjected to high temperatures. Cylinder specimens were subjected to various temperature ranges of 100, 200, 400, 800, and 1,000°C. The mixtures were prepared with AAC cementitious materials containing perlite at 15%, 20%, and 30% sand replacement. The polypropylene fiber content of 0, 0.5%, 1%, 1.5%, and 2% by volume was also added to the mixture. The results showed that the unheated compressive and splitting tensile strength of AACs containing PP fiber were not significantly higher than those containing no PP fiber. Furthermore, the presence of PP fiber was not more effective for residual compressive strength than splitting tensile strength. The 30% perlite replacement of sand gave the highest strength. Based on the results, it can be concluded that addition of PP fiber did not significantly promote the residual strength of AAC specimens subjected to high temperatures.
An experimental investigation of the thermal spalling of polypropylene-fibered reactive powder concrete exposed to elevated temperatures
Polypropylene fibers are embedded to prevent reactive powder concrete (RPC) from spalling failure under high temperatures. This paper probes the influence of embedded fibers at various volumetric dosages on the thermomechanical properties of polypropylene-fibered reactive powder concrete (PPRPC) exposed to high temperatures up to 350 °C and on the spalling performance and characteristics up to 600 °C. The thermomechanical properties include the characteristic temperature for spalling, and residual strengths, such as the compressive strength, split tensile strength, and flexural tensile strength. A high-definition charge-coupled device camera and scanning electron microscope technology were employed to capture the spalling processes and to detect the microstructural changes in the materials with various fiber dosages. To understand and characterize the mechanism by which polypropylene fibers influence the thermal spalling of RPC, a numerical model to determine the moisture migration and vapor pressure transmission during spalling was developed in this paper. It showed that there was an optimal volumetric dosage of fibers to prevent PPRPC from explosive spalling. The relationships between the mechanical characteristics of PPRPC and the fiber dosages were derived based on experimental data.摘要聚丙烯纤维可用于改善活性粉末混凝土(RPC)的高温爆裂,本文实验研究了不同掺量聚丙烯纤维对活性粉末混凝土热物理力学性质以及高温爆裂特征的影响,测试并分析了聚丙烯RPC的抗压、劈裂和弯折强度随温度和纤维掺量的变化规律;利用自主研制的高温实验装置及高清摄像机观测了聚丙烯RPC高温爆裂的全过程,获取了起止温度、持续时间等爆裂特征。利用SEM分析了聚丙烯纤维熔化前后的微观结构变化及其对内部蒸汽压作用的影响,结合内部蒸汽压和含湿量的数值计算, 定量分析了RPC爆裂破坏的蒸汽压机理。实验发现:改善聚丙烯RPC高温力学性能和缓解其爆裂破坏的聚丙烯纤维最优掺量为0.9 %。
ROOM- AND HIGH-TEMPERATURE MAGNETIC PROPERTIES OF Sm(CobalFexCu0.088Zr0.025)7.5 (x=0.30) SINTERED MAGNETS
The effect of Fe content on room- and high-temperature magnetic properties of Sm(CobalFexCu0.088Zr0.025)7.5 (x=0-0.30) sintered magnets, prepared by the conventional powder metallurgy method, has been systematically studied. With increasing Fe content, the remanences BT and maximum energy products (BH)max at room temperature gradually increase and reach optimal values of 1.055 T with x=0.27 for BT, and 205 kJ/m3 with x=0.21 for (BH)max, respectively, and then drop sharply with further Fe increase. An excessive addition of Fe (x≥0.24) results in rapid deterioration of permanent magnetic properties due to the formation of a considerable amount of FeCo soft magnetic phase. It was found that the effect of Fe content on high temperature stability is huge. The lower the Fe content, the smaller the temperature coefficient of coercivity. When x=0.07, a temperature coefficient of coercivity of -0.14%/K (293-723 K) can be achieved, as compared with -0.23%/K for x=0.21. BT of 0.725 T, bHc of 517 kA/m, iHc of 764 kA/m, and (BH)max of 95 kJ/m3 at 723 K were obtained, and the B-H demagnetization curve remains a straight line.