# Study of Basalt Fibers and Graphene Enriched Polymers on Bond Behavior of FRP Bars in Concrete
## 2 Experimental Study
### Materials  
Three types of bars are considered in this work: BFRP and GFRP with vinyl-ester matrix and GFRP with polyester matrix where GNP was added. In the latter case the cheaper polyester polymer was enriched with a minimum weight of GNP in order to keep costs at the same level of the more traditional and more expensive vinyl-ester polymer. These cases will be referred as GFRPg. Two diameters are considered for the bars: 8.0 and 12.5 mm. In GFRP and GFRPg cases, surface treatment is helically wrapped while BFRP 8.0 mm bars have smooth surface and 12.5 mm bars have helically wounded surface treatment, see Figure 1 (nomenclature according to definition in [PERSON] et al. [39]). FRP applications are relatively common in footing, slabs on grade applications, which in general requires lower concrete strength grades, such as C20. Another typical FRP applications are industrial pavements, residential slabs and beams which requires at least C30 concretes [40]. This is the main reason these concretes were chosen here and also by other relatively recent publications [30]. For the identification of the combinations tested, the nomenclature \(C\ xx-\phi N-yy\) was defined, where \(xx\) corresponds to the compressive strength class of the concrete; \(\phi\) is the nominal diameter of the reinforcement (8 = 8.0 mm diameter and 12 = 12.5 mm diameter); N represents the type of bar (G = GFRP, Gg = GFRPg and B = BFRP) and yy is the test temperature in degree Celcius, which is omitted in case of room temperature tests. Table 1 indicates geometrical and mechanical properties of the bars. Geometrical properties (_rh_, _rs_ and _rw_) are defined according to Figure 1. The average roughness of the bars (Ra) was based on the ISO 21920-1 [41] Standard. Fiber fraction is measured by weight fraction through resin burn-off. Values obtained are higher than the minimum values established by ASTM D7957 [42]. The tensile strength (\(\sigma_{t}\)) and longitudinal elasticity modulus (\(E\)) of the bars were determined according to ASTM D7205 [43] and are related  
only to axial direction. Poisson coefficient is 0.2 in all cases. \(T_{g}\) is the glass transition temperature. In this temperature there is a substantial degradation of the polymer, so the bars loose most of their bond capabilities. Regarding test temperatures, the fundamental information is how the bars behave before and after glass temperature transition. So, besides room temperature, other two are considered based on \(T_{g}\)s. One below \(T_{g}\) (60 \({}^{\circ}\)C) and another above \(T_{g}\) (120 \({}^{\circ}\)C). As bond tends to drop significantly after \(T_{g}\) and then keeps approximately constant, there is no reason to test different higher temperatures.For the cases above room temperature only concrete C30 and 12.5 mm bars are considered. Concrete mix proportions are presented in Table 2. High-early-strength Portland cement of 3.00 g/cm\({}^{3}\) specific mass and Blaine finesses of 5001 cm\({}^{2}\)/g was used for the concrete mixes. Fine aggregates were quartz sand of natural origin, with a 4.8 mm maximum grain diameter and 2.49 g/cm\({}^{3}\) specific mass, determined according to the ABNT NBR 17054 [44] and ABNT NBR 16916 [45], respectively. Basalt-based coarse aggregates with a 25 mm maximum size, 2.79 g/cm\({}^{3}\) specific mass and 1.03% water absorption were utilized, determined according to the ABNT NBR 17054 [44] and ABNT NBR 16917 [46]. Throughout the research, supplied tap water was used for both mixing and curing purposes.The evaluation of the concrete compressive strength at 28 days of age was made according to ABNT NBR 5739 [47] recommendations. Based on the 28 day compressive strength of the concrete, its elasticity modulus was estimated using the _FIB_ Model Code 2010 [48] and the results are presented in Table 3. In all cases, 3 samples were considered.