JEC COMPOSITES MAGAZINE - Issue #44 - October 2008 - Special Asia - 33

Fibre grids can be produced. • Carbon textile reinforcements have a much larger surface area than traditional steel-bar reinforcements. Thus, very high bond forces can be introduced into the concrete. This, in practice, is evidenced by both the ability to use short anchoring lengths and the presence of very dense crack patterns. • TRCs produced from carbon possess distinctly higher strength than standard steel-bar reinforcements. The current generation of textile reinforcements has reached strengths well over 1,500 N/mm². In addition to increasing the ultimate loading capacity of reinforced concrete, TRC is also suitable for other repair applications. • The use of additional TRC strengthening layers in RC structures has proved to have a positive influence on subsequent concrete cracking. The number of cracks increases while crack spacing decreases, and crack width is simultaneously reduced (Figure 3). bar reinforcement or externally bonded carbon fibre-reinforced polymers (CFRP). Advantageous properties of externally bonded CFRP include: high tensile strength, low weight, easy handling, and high corrosion resistance. Disadvantages include high cost, sensitivity to moisture and UV radiation, low ductility, lack of fire resistance, cross-pressure sensitivity, and soaking. The repassivation of uncovered steel reinforcement – as a result of damage – requires additional measures. The use of shotcrete, which is based on a cementitious matrix, is a suitable rehabilitation method that provides fresh protection against corrosion for existing reinforcement. Its primary advantage is the re-passivation of existing reinforcement, as influenced by the alkaline conditions of a new shotcrete layer while ruling out any sensitivity to soaking and UV radiation. However, the use of traditional steel reinforcement in combination with shotcrete has several drawbacks, including: 1) the costly production and installation of strengthening layer(s), 2) enlarged dimensions of the original total cross-section and required concrete covering, and 3) high dead weight of the concrete added to the structure. Tab. 1: Performance comparison of shotcrete RC, CFRP lamellas and TRC for strengthening concrete structures RC Load capacity Stiffness Ductile failure mode Layer thickness/ weight Handling UV resistance Fig. 3: Concrete slab strengthened with TRC in laboratory loading test. Fire resistance ++ + ++ + ++ + CFRP + + ++ -- TRC + + + ++ ++ ++ + • Concrete elements become stiffer due to the application of additional material but also to the demonstrated fact that parts remain longer in an un-cracked state. • More advanced repairs can be produced using a mineral-based matrix. In addition, pure re-profiling, re-passivation and the provision of a new or additional dense concrete cover are valuable options. Building and infrastructure strengthening In recent years, the need to strengthen and retrofit existing RC structures has increased. Over the course of normal building use, many situations may arise that require the strengthening of RC structures. Examples of such situations are structural damage, increased loads, design and construction faults, and system changes. A variety of methods can be used to increase the load-carrying capacity. The use of TRC can be an ingenious alternative, particularly since it is closely related to traditional, established strengthening procedures like shotcrete with steel The advantages of both externally bonded carbon fibrereinforced polymers and shotcrete with steel reinforcement are incorporated in the use of TRC strengthening (Table 1). The combination of textile reinforcement and concrete results in a composite material with prime qualities – high tensile strength, minimal layer thickness, low weight, high corrosion resistance, and additional corrosion protection for existing concrete reinforcement. TRC strengthening with carbon grids can improve the performance in different directions, such as bending or flexural strength, shear strength, torsion stiffness and axial forces. Moreover, the flexibility of textile reinforcement makes it possible to strengthen complex and curved geometries such as shell structures and columns. Before the strengthening material can be applied, the surface of the RC member must be prepared, for example by sandblasting. The surface must be sufficiently rough to ensure that an adequate bond will form between the existing concrete and the No44 October 2008 / JEC Composites Magazine

JEC COMPOSITES MAGAZINE - Issue #44 - October 2008 - Special Asia

Table of Contents for the Digital Edition of JEC COMPOSITES MAGAZINE - Issue #44 - October 2008 - Special Asia