Solidification of Two-Component Grouts by the Use of Superabsorbent Polymers as Activator

In mechanized shield tunneling, the annular gap between the tunnel structure and the surrounding soil needs to be filled with an adequate grouting mortar to ensure a rapid and safe bedding of the segment rings and to minimize settlements on the surface above the tunnel lining. After mounting of the segment rings and filling of the annular gap, a rapid solidification of the used grout must prevent possible displacements or a floating of the tunnel. In the case of nearly impermeable soils, two-component grouts are necessary, which develop an adequate strength and stiffness in a short period of time by the use of powerful activators like water glass (component B). In addition to the commonly activated cementitious materials, it is feasible to ensure an immediate and sufficient bedding by physical effects. Therefore, the use of superabsorbent polymers (SAP) as component B has been investigated. Experimental studies have been carried out in a systematic way in order to determine the type of the SAP, which leads to a sufficient absorption rate in the alkaline pore water of a cementitious grout. After identification of a suitable “alkali-stable” polymer, tests were carried out in order to examine the necessary amount of SAPs in a slightly modified one-component grout (component A) to cause a sufficient solidification of the whole system within a short period of time. Next to this, the short and long term strength development like shear strength or compressive strength of the combined system (component A and B) were determined. Considering the state of the art of the structural design of the grouting technology on a tunnel boring machine and the generally used liquid activators, a permanent pre-suspension of the SAP was tested and also the strength development of the activated system was examined.