The long term stability of silica nanoparticle gels in waters of different ionic compositions and pH values

Journal article, 2018

The use of silica nanoparticles for grouting underground tunnels offers an environmentally friendly option compared to organic grouting materials. Silica sols are commercially available and when mixed with an accelerator (salt) they form gels in a predetermined time. While much research has been focused on the practical implementation of silica sols in grouting as well as on the development of physical parameters such as viscosity and strength development, little is known about the long term stability of the resultant silica gels. When placed in rock fractures, parameters such as pH and ionic composition of groundwater may affect the long term stability and functionality of the gels. In this article we use a newly designed test equipment to simulate the behaviour of silica gels when water passes through the gel structure for up to 488 days. The pH and ionic composition of the water is varied to simulate environments that can be experienced by gels used for grouting applications. Results in the form of ionic composition, volume, and pH of leached water were used to evaluate and predict the lifetime of silica gels. The overall results show that several factors such as water flow and the nature of salt, so called accelerator used for gelling have significant effect on the gel life time. Furthermore, it is shown that the accelerator ions leach from the gels; however, the extent to which they are released from the gel depends upon the salt type. From these results we have predicted the lifetime of the 100 mL gels used in our experiments by using a simple numerical model. The predictions show that the total dissolution time for 100 mL gels are up to hundreds of years.