**3. Experimental Programme and Results of Small-Scale Tests**

## *3.1. General*

Material and small-scale tests were carried out to characterise the materials intended for SMART-DECK and their interaction with each other. The goal was to select a suitable combination of mortar and textiles for strengthening (I. and II., according to Figure 4). The small-scale tests were divided into three groups: uniaxial yarn tensile tests as well as flexural and uniaxial tensile tests on composite strips. In the uniaxial yarn tensile tests, individual fibre strands extracted from the mesh were investigated, while in the bending and other uniaxial tensile tests, composite components with textile cut-outs embedded in concrete were tested. Also, mortar testing was performed on each batch that was used for SMART-DECK on prisms *W* × *H* × *L* = 40 × 40 × 160 (mm) in accordance with Reference [66].

**Figure 4.** Overview of the experimental programme (photographs by IMB, RWTH Aachen University).

The quadratic textile reinforcement meshes were provided by the project partner solidian. The mesh size (centre-to-centre distance of the fibre strands) was either 21 or 38 mm. Depending on the knitting method, different bond properties can occur which not only differ among the various grids but also depend on the direction [38] since weft and warp vary in cross-sectional shape and surface characteristics (Figure 5).

**Figure 5.** Textile grids made of carbon with epoxy impregnation with a mesh size of 38 mm (**a**) and 21 mm ((**b**), photographs by IMB, RWTH Aachen University).

With the findings from the small-body tests, in which various parameter combinations were investigated, the materials for the final SMART-DECK system were pre-selected. This optimised combination was then used as a strengthening layer in the large-scale tests. Small-body tests are particularly suitable for this purpose, as multiple repetitions with the same combination of properties and a large number of different specimens can be tested in a comparatively short time. The tests were labelled X-YZ based on the type of experiment and the materials used as follows:


For some tests, another abbreviation was added to the end in order to mark a more specific property. Table 1 shows the materials used in the course of the investigations on the strengthening effect of SMART-DECK. The notation A-B-C of the materials results from the project consortium's definitions, where A is the material (M: mortar, T: textile), B is a consecutive number for each material and C is a specification (maximum aggregate size, in mm, for mortar and mesh size, in mm, for textiles).


**Table 1.** Details of mortars and textiles.

\* CNT: Carbo Nano Tubes.

Due to the production process, the weft direction of the textiles is limited to the width of the textile machines. For this reason, the weft direction is positioned in longitudinal direction and the warp direction in transverse direction of the bridge (main load transfer direction of the roadway slab) since separated segments of textile are required in longitudinal direction by means of electrically insulated areas (Figure 2). While the flexural and tensile tests on the composite material were therefore tested in warp direction, the yarn tensile tests were carried out for both fibre strand directions in order to obtain comparative values. Figure 4, Step I, shows the test setups and measuring technology used for the tensile tests on individual fibre strands and an example after failure.
