Innovative Geopolymer Coating for Road Tunnels
Having a key role in the today’s transportation network, tunnels are an essential part of the infrastructure and affect the development of regional economies. Concrete linings in the tunnels also have a key role for ensuring structural safety and security which is essential for driving safety. These linings do not only structurally support the tunnel itself but also create an isolated and safe driving space for vehicles. But as very well known, concrete is a vulnerable construction material and it may not always be able to contribute to better tunnel interior visibility due to its natural grey color which gets quickly much darker over time by the exhaust fumes released in the tunnel. A significant amount of the existing tunnel stock has been already started aging since most of them were built in 60s and 70s. Poor concrete quality and lack of proper waterproofing systems accelerated the deterioration process in the tunnel linings and already become a significant threat on driving safety. As a result of compromised safety in the tunnels, possible accidents and particularly fires, can have dramatic consequences, which could be extremely costly in terms of human life. However, finding sustainable solutions to overcome these general problems with tunnels linings by using existing technologies has been a difficult task for many years. Several refurbishment and protection technologies are being used to improve the condition of the tunnel linings for increased structural and driving safety. Cementitious, acrylic and epoxy coatings have been widely used to protect tunnel linings and increasing visibility. Geopolymers, an existing technology, provides a new approach to solving many problems with existing tunnel linings – both in terms of enhanced durability and tunnel interior visibility. Geopolymers are synthetic alkali aluminosilicate materials, derived by alkaline activation, e.g. using aqueous alkaline solution or waterglass to activate the reactive raw materials containing silicate and aluminate. These reactive raw materials like silica fume, blast furnace slag, fly ash, metakaolin, pozzolans, are activated by using an alkaline based activator (e.g. waterglass, MeOH) to form intermediate monomers and oligomers and finally form alumosilicate composites after poly-condensation process. The new tailor-made geopolymer coating for tunnels, is a coating which has a unique formulation that brings a perfect compromise of different benefits carried out from geopolymer chemistry. Geopolymers inherently provide a wide range of properties and characteristics, such as;• controlled hardening,• high-temperature resistance,• low dirt pick up• easy to clean property,• low permeability to fluids and chloride ions,• chemical resistance (especially against fuels).