Abstract The crystallization induced blockage defect in tunnel drainage system is closely related to groundwater seepage in shotcrete. In order to ascertain the correlation between the curing age of shotcrete and crystallization induced defect, a home-built indoor simulation device is used to simulate the seepage-crystallization process of tunnel shotcrete. The mass of crystal and the pH value and calcium ion concentration of effluent solution from drainage pipe have been measured, and XRD, thermogravimetric analysis, electron microscope scanning and mercury injection test have been conducted, so as to reveal the deterioration process of the shotcrete of different ages and the crystallization pattern in drainage pipe under groundwater seepage conditions. As the results indicate: (1) The curing age of shotcrete is a key factor that affects the crystallization induced defect of tunnel, and the early age affects it particu? larly significantly. Under seepage conditions, the crystal mass in drainage pipe in the concrete with 2 h age is essentially 30 times that in the concrete with 28 d age; (2) Longer concrete curing age means the pH value will decrease faster, pH value will stabilize sooner and calcium ion concentration will stabilize sooner; (3) After 60 d of internal seepage in the concrete of different ages, only very small amount of ettringite and C-S-H gel are observed inside the concrete, the structure is uneven, and the concrete has high total porosity; The interior of concrete contains calcium hydroxide crystal, and as the curing age increases, the crystal changes from small amount of flocculent crystal in unstable state to large amount of lumpy crystal in stable state; Longer curing age means less concrete hydration products are dissolved out. According to the thermogravimetric analysis, the calcium hydroxide content of the concrete with 28 d age is 5.9 times that of the concrete with 2 h age.
Abstract：
The crystallization induced blockage defect in tunnel drainage system is closely related to groundwater seepage in shotcrete. In order to ascertain the correlation between the curing age of shotcrete and crystallization induced defect, a home-built indoor simulation device is used to simulate the seepage-crystallization process of tunnel shotcrete. The mass of crystal and the pH value and calcium ion concentration of effluent solution from drainage pipe have been measured, and XRD, thermogravimetric analysis, electron microscope scanning and mercury injection test have been conducted, so as to reveal the deterioration process of the shotcrete of different ages and the crystallization pattern in drainage pipe under groundwater seepage conditions. As the results indicate: (1) The curing age of shotcrete is a key factor that affects the crystallization induced defect of tunnel, and the early age affects it particu? larly significantly. Under seepage conditions, the crystal mass in drainage pipe in the concrete with 2 h age is essentially 30 times that in the concrete with 28 d age; (2) Longer concrete curing age means the pH value will decrease faster, pH value will stabilize sooner and calcium ion concentration will stabilize sooner; (3) After 60 d of internal seepage in the concrete of different ages, only very small amount of ettringite and C-S-H gel are observed inside the concrete, the structure is uneven, and the concrete has high total porosity; The interior of concrete contains calcium hydroxide crystal, and as the curing age increases, the crystal changes from small amount of flocculent crystal in unstable state to large amount of lumpy crystal in stable state; Longer curing age means less concrete hydration products are dissolved out. According to the thermogravimetric analysis, the calcium hydroxide content of the concrete with 28 d age is 5.9 times that of the concrete with 2 h age.
TONG Yueping1 TIAN Chongming1 YE Fei1 JIANG Yin1 ZHANG Junyuan1 WU Bowen1WANG Han1 LI Wenhui2
.Study on Seepage Crystallization Pattern of Tunnel Shotcrete of Different Ages[J] MODERN TUNNELLING TECHNOLOGY, 2024,V61(1): 272-282
2024, Vol. 61 