高温低湿下砂浆力学性能及微结构的变化

Mechanical properties and microstructure of mortar under the hot-dry environment

为初步掌握高温低湿环境下水泥基材料力学性能改善的技术方法,测试不同养护条件下,组成参数不同的砂浆力学性能变化,并采用SEM,XRD以及TG等方法测试砂浆微结构的变化。研究结果表明:相比标准养护,高温低湿养护导致砂浆力学性能大幅度降低。与直接高温低湿养护比较,高温低湿下初期的短期覆膜养护能显著提高砂浆强度。粉煤灰掺量25%的砂浆在高温低湿下早期覆膜1 d养护后,28 d抗压和抗折强度均大于标养试件。掺入聚丙烯纤维和内养护材料可以改善高温低湿下砂浆的力学性能,但需要结合适合的早期养护制度。高温促进了水泥早期水化,但所生成的水化产物不能及时扩散,堆积在未反应的水泥颗粒表面,造成水化产物不均匀,阻碍了进一步水化反应,水分在低湿下蒸发,水化速率迅速降低甚至停止,内部结构疏松,孔隙率增大,强度严重降低。

In order to primarily understand the method to improve the mechanical properties of cement-based materials under hot-dry environment,the mechanical properties of mortar with different composition parameters were tested under different curing systems.The mechanical properties of mortar under the condition of hot-dry environment were tested,and the microstructure of mortar was also analyzed by means of SEM,XRD and TG.Results show that compared with the standard curing,the hot-dry curing results in a great decrease in the mechanical properties of mortar.Compared with direct hot-dry curing,early short-term cover curing under hot-dry environment can significantly improve the strength of the mortar.When the mortar with 25%fly ash was cured in the condition of cover and hot-dry environment for 1 d,the compressive and flexural strength of 28 d were both higher than that of the standard curing specimens.The addition of polypropylene fiber and internal curing materials could improve the mechanical properties of mortar under hot-dry environment,but a suitable early curing system is needed.High temperature promoted the early hydration of cement,but the generated hydration products could not spread in time,piled up on the surface of unreacted cement particles,resulting in uneven hydration products and hindering further hydration reaction.Water evaporates at low humidity and the rate of hydration rapidly decreases or even stops.The internal structure becomes loose,the porosity increases and the strength decreases seriously.