Application of TRC for the crack repair of a silo
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Report in the yearbook 2012
Sugar Without Sand
Exterior view of the sugar silo strengthened by TRC
Everyone knows sugar as a means to sweeten tea or biscuits – sand, however, should not play a role in neither tea nor cake. Normally, this is the fact without saying. Nonetheless, it was the main question in one of the projects in 2012. After the production process, sugar is stored in so-called sugar silos until further processing or until the sugar is bagged into customary packages. These silos are usually made of reinforced or pre-stressed concrete. They are coated on the inside to guarantee that sugar and concrete do not come into contact. However, these coatings only fulfil their function properly as long as cracks in the concrete remain small. Yet, this is not the case for many older silos. The existing cracks are regularly exposed to variable loads due to the filling and emptying of the silos. As a result, the cracks are being washed out and cause spalling of the concrete. This, in turn, may lead to sand in the sugar.
Such cracks also occurred in a twin compartment silo which dates back to 1962 and can contain 20,000 t of sugar. So far, this problem was solved by applying a reinforced concrete layer of at least 10 to 15 cm thickness. While being well established, this method is very expensive and leads to a reduced storage capacity. As a result, an alternative was searched for and found in textile reinforced concrete (TRC) strengthenings.
It was the task of the institute to survey the strengthening measures in advance of the construction works, offer expert advice, quality control of the used materials and the construction supervision. Following the building analysis, the strengthening was designed. The construction process was started with grouting the cracks whose width exceeded 0.3 mm and roughening the concrete surface (approximately 3,500 m²). Then, a textile reinforced concrete cover consisting of four layers was applied and, subsequently, coated. The textile reinforced concrete cover bridges the existing cracks and contributes to crack distribution. As a result, the width of the cracks, which will nonetheless develop in the textile reinforced concrete layer due to the changing load, will be reduced to a significant degree. Consequently, the coating will not be damaged in the future and, thus, the serviceability can be restored. In the next step, the durability of textile reinforced concrete strengthenings in the field of application of sugar silos shall be proven by repeated filling and emptying of the silo. Once this has been successfully completed, textile reinforced concrete strengthenings shall become the preferred option for the redevelopment of a number of other silos.