Yuan Zhu, Jia Yanmin
School of Civil Engineering, Northeast Forestry University, Harbin 150040, China.
Materials (Basel). 2022 May 24;15(11):3760. doi: 10.3390/ma15113760.
The main objective of this study is to better understand the performance changes of naturally aged glass fiber-reinforced concrete (GFRC) and polypropylene fiber-reinforced concrete (PPFRC), especially the degradation of fibers, which is of great significance for evaluating the durability of structures using these two types of composite materials. The mechanical properties, water absorption, and microstructures of GFRC and PPFRC at a curing age of three years, including their compressive strength, full curves of water absorption, fiber-matrix interaction, and fiber degradation, were systematically studied, and the related properties were compared with those at the curing age of 28 days. The degradation of fibers after freeze-thaw cycles was also studied. The results revealed the following. The water/binder ratio (w/b) affects the rate of increase of the long-term compressive strength of naturally aged concrete. In general, the water absorption of fiber-reinforced concrete (FRC) at the curing age of three years was found to be significantly reduced, but with the increases of w/b and the fiber content to the maximum values, the water absorption of the specimens cured for three years was higher than that of the specimens cured for 28 days. Moreover, with the increase of the curing age, the optimal glass fiber (GF) contents for reducing the water absorption decreased from 1.35% to 0.90% (w/b = 0.30), and from 0.90% to 0.45% (w/b = 0.35), respectively. The GF surface was degraded into continuous pits with diameters of about 200 to 600 nm, and the surface of the pits was attached with spherical granular C-S-H gel products with diameters of about 30 to 44 nm. The freeze-thaw cycles were found to have no significant effect on the pits on the GF surface and the granular C-S-H gel products attached to the pits, but caused a portion of the cement matrix covering the GF to fall off. The interfacial bonding between the polypropylene fiber (PPF) and the cement matrix exhibited almost no change in the PPFRC after three years of curing as compared with that after 28 days of curing. Furthermore, the cement hydration gel on the PPF surface was not significantly damaged by 150 freeze-thaw cycles.
本研究的主要目的是更好地了解自然老化的玻璃纤维增强混凝土（GFRC）和聚丙烯纤维增强混凝土（PPFRC）的性能变化，尤其是纤维的降解情况，这对于评估使用这两种复合材料的结构耐久性具有重要意义。系统研究了养护龄期为三年的GFRC和PPFRC的力学性能、吸水性和微观结构，包括其抗压强度、吸水全曲线、纤维-基体相互作用和纤维降解，并将相关性能与养护龄期为28天的情况进行了比较。还研究了冻融循环后纤维的降解情况。结果表明如下。水胶比（w/b）影响自然老化混凝土长期抗压强度的增长速率。一般来说，发现养护龄期为三年的纤维增强混凝土（FRC）的吸水率显著降低，但随着w/b和纤维含量增加到最大值，养护三年的试件的吸水率高于养护28天的试件。此外，随着养护龄期的增加，降低吸水率的最佳玻璃纤维（GF）含量分别从1.35%降至0.90%（w/b = 0.30），以及从0.90%降至0.45%（w/b = 0.35）。GF表面降解为直径约200至600 nm的连续凹坑，凹坑表面附着有直径约30至44 nm的球形颗粒状C-S-H凝胶产物。发现冻融循环对GF表面的凹坑和附着在凹坑上的颗粒状C-S-H凝胶产物没有显著影响，但导致覆盖GF的部分水泥基体脱落。与养护28天后相比，养护三年后的PPFRC中聚丙烯纤维（PPF）与水泥基体之间的界面粘结几乎没有变化。此外，PPF表面的水泥水化凝胶在150次冻融循环后没有受到显著破坏。
