Jiang Feifei, Deng Wencong, Wang Qi, Wang Jialei, Mao Zhongyang
School of Civil Engineering, Nantong Institute of Technology, Nantong 226000, China.
China State Construction Engineering (Macau) Co., Ltd., Macau 999078, China.
Materials (Basel). 2024 Nov 13;17(22):5530. doi: 10.3390/ma17225530.
Low strength and low impact toughness are two of the main issues affecting the use of lightweight aggregate concrete in harsh cold environments. In this study, the strength of concrete was improved by adding high-strength fibers to bear tensile stress and organize crack propagation. Four sets of comparative experiments were designed with freeze-thaw cycles of 0, 50, 100, and 150 to study the mechanical properties of fiber-reinforced lightweight aggregate concrete under freeze-thaw conditions. A detailed study was conducted on the effects of freeze-thaw on the compressive strength, flexural strength, impact toughness, and microstructure of concrete with different fiber contents (3, 6, and 9 kg/m). The results show that for ordinary lightweight aggregate concrete, under the freeze-thaw cycle, the internal pore water of the concrete froze and generated expansion stress, resulting in tensile cracks inside the concrete. The cracks gradually accumulated and expanded, ultimately leading to cracking and damage of concrete structures. After 150 cycles, the strength loss rate exceeded 25%. When adding a reasonable amount of fiber (6 kg/m), the fiber took on the tensile stress and hindered the development of internal cracks, significantly enhancing the splitting tensile strength, flexural strength, and impact toughness of lightweight aggregate concrete. And the failure pattern of concrete was significantly improved. At the beginning of the freeze-thaw cycle, the internal tensile stress was less than the fiber tensile strength and the fiber-matrix bonding strength, and the strength reduction rate of the concrete was slow. Relying on the friction absorption capacity between the fiber and the matrix, the fiber used its own deformation to resist the tensile stress. In the late stage of the freeze-thaw cycle, due to the destruction of the fiber-matrix transition zone structure, the bond strength decreased, the crack resistance and toughening effect decreased, and the strength of the concrete decreased rapidly. Moreover, the reduction in impact toughness was greater than the compressive strength and flexural strength under static load.
强度低和冲击韧性差是影响轻质骨料混凝土在严寒环境中应用的两个主要问题。在本研究中，通过添加高强度纤维来承受拉应力并阻止裂缝扩展，从而提高混凝土强度。设计了四组对比试验，冻融循环次数分别为0、50、100和150次，以研究冻融条件下纤维增强轻质骨料混凝土的力学性能。详细研究了冻融对不同纤维含量（3、6和9kg/m）混凝土的抗压强度、抗折强度、冲击韧性和微观结构的影响。结果表明，对于普通轻质骨料混凝土，在冻融循环作用下，混凝土内部孔隙水结冰并产生膨胀应力，导致混凝土内部出现拉裂缝。裂缝逐渐累积和扩展，最终导致混凝土结构开裂和破坏。150次循环后，强度损失率超过25%。当添加适量纤维（6kg/m）时，纤维承担拉应力并阻碍内部裂缝发展，显著提高了轻质骨料混凝土的劈裂抗拉强度、抗折强度和冲击韧性。且混凝土的破坏模式得到显著改善。在冻融循环初期，内部拉应力小于纤维抗拉强度和纤维-基体粘结强度，混凝土强度降低速率缓慢。依靠纤维与基体之间的摩擦吸收能力，纤维利用自身变形抵抗拉应力。在冻融循环后期，由于纤维-基体过渡区结构破坏，粘结强度降低，抗裂增韧效果减弱，混凝土强度迅速降低。此外，冲击韧性的降低幅度大于静载下的抗压强度和抗折强度。
