Waterproofing sprayed concrete Linings -Existing Methods and Potential Developments

Sprayed concrete tunnel linings are a popular solution to the increasing need for fast and efficient transport systems in urban environment worldwide. Achieving an acceptable level of watertightness in sprayed concrete linings with a view to increasing the speed of construction, reducing costs and improving the carbon footprint remains a significant challenge for the construction industry. Sheet and sprayed membranes and, to a lesser extent, integral waterproofing admixtures are currently being used for achieving the required level of watertightness. Each of these technologies have advantages and disadvantages, which determine their suitability and ease of use in a particular project. This paper examines the existing technologies and outlines emerging technologies in the concrete admixtures that have the potential to control the water penetration in a sprayed concrete tunnel lining. It describes the laboratory work carried out using integral waterproofing admixtures as part of research in the UK towards the development of a one-pass watertight sprayed concrete tunnel lining, where different admixtures were tested using conventional tests normally performed in the industry and a modification of a standard test to reveal the benefits of the use of technologies such as crystalline and Polymer Latex additives to reduce the permeability of the joints over time