2.2.2. Layout

SMART-DECK is a supplementary TRC layer, which is applied on top of the existing concrete and subsequently covered by the road surface (Figure 3). It is to be processed along the entire width of the bridge deck, but the textiles are to be laid in sections in longitudinal direction of the bridge at a defined distance from each other in order to obtain electrically separated fields. SMART-DECK consists of a high-performance mortar and a textile reinforcement made of carbon fibres impregnated with epoxy resin. The textiles are installed in two layers with a mutual centre distance of 15 mm and an edge distance to the concrete interface and to the upper side of 10 mm, resulting in a total layer depth of approximately 35 mm.

The bond between strengthening layer and existing concrete in this system is not achieved by mechanical connectors but relies on concrete-to-mortar adhesion. This greatly reduces application time and cost but requires proper surface preparation prior to casting as well as a close quality control on site. The basic material carbon of the TRC layer offers the electrical conductivity required for monitoring and pCCP on the one hand. On the other hand, in combination with epoxy resin impregnation, it has good bonding properties to the surrounding concrete and is very efficient due to its high axial tensile strength (5 to 6 times the value of reinforcing steel). The corrosion resistance of the material allows the execution of thin layers with small concrete covers. Especially in combination with a massive existing

supporting structure, which provides high stiffness, these advantageous properties of TRC can be used optimally and high increases in load-bearing capacity can be achieved with a minimum use of material.

**Figure 3.** Virtual saw cut as schematic sketch of the strengthening layer on a RC slab.

### *2.3. Previous Investigations*

As stated before, the flexural strength of regular RC components with small longitudinal reinforcement ratios can be significantly increased by TRC strengthening in the flexural tension zone [57,61–63]. Investigations on the influence of web strengthening with TRC showed that shear capacity of reinforced concrete beams can also be significantly increased by TRC strengthening [23,24,52]. Here, in addition to the high tensile strength of the textile reinforcement, the reduction of the crack width plays an important role, since this can prevent an early confinement of the flexural compression zone and delay the propagation of the shear crack into the compression zone. Furthermore, it could be shown that web strengthening with TRC can also be a useful alternative to existing strengthening methods for cyclically stressed components [23,53,64].

Prior to the start of the project, tests were conducted to estimate whether promising degrees of strengthening for the main failure modes in transverse direction of the bridge can be achieved in the ultimate limit state [65]. It was shown that a supplementary TRC layer can increase shear capacity of the bridge deck. However, different materials and different boundary conditions were applied in those tests compared to the investigation presented in this paper. Therefore, these results only allowed for tendentious statements.

The strengthening effect of SMART-DECK itself was already experimentally examined during realisation of the project demonstrator. For this purpose, a slab of approximately 100 m<sup>2</sup> was built which also met the demands resulting from the other two intended functionalities. It featured a height of *h* = 28 cm and a change of slope was produced to represent realistic conditions for fabrication with respect to an existing bridge slab. The additional TRC layer was applied to 80% of the area, whereby the implementation of the cross-sectional supplement itself and the manufacturing of the measuring device for the monitoring system were tested. Subsequently, the monitoring system (see above) and the achievable increases in capacity were investigated. The latter was done by extracting saw-cuts from the strengthened and non-strengthened areas of the demonstrator slab, which were then tested in a total of eight load tests at IMB until failure. Bending and shear were investigated in the same way as in the series of tests presented here: 24–56% shear strengthening and 90–174% flexural strengthening were achieved [64].
