Issue 42

A. Jadidi et alii, Frattura ed Integrità Strutturale, 42 (2017) 249-262; DOI: 10.3221/IGF-ESIS.42.27 254 2 minutes > ---------- Aggregate 2 minutes > ---------- Cement 1 minutes > ---------- Micro silica 4 minutes > ---------- Super plasticizer + 70% Water 4 minutes > ---------- 30% remaining water Figure 4 : Mixing process. Cement matrix Cement (kg) Micro silica (kg) Aggregate (kg) Water (kg) Super Plasticizer (L) Weight ratio 1.0 0.1 1.58 0.35 0.006 Table 4 : Cement matrix final mixture design. Materials Mass (kg) cement 944.86 Aggregate (0.0- 0.1 mm) 111.96 Aggregate (0.1- 0.3 mm) 111.96 Aggregate (0.3- 1.0 mm) 320.96 Aggregate (1.0- 2.0 mm) 291.113 Aggregate (2.0- 3.0 mm) 238.855 Aggregate (3.0- 5.0 mm) 418.007 Micro silica 94.481 Super plasticizer 6.238 Water 330.702 Table 5 : Final mixture design (kg/m 3 ). E XPERIMENTAL RESULTS n this research, three samples from each mentioned range were made with 0%, 1.5%, 2% and 2.5% fibers which were tested based on compressive strength, splitting tensile test, bending test and the results were evaluated against each other and fibreless samples. The tensile strength of cylindrical samples was determined using sample splitting test (Brazilian test) through applying diagonal force on cylindrical concrete samples placed horizontally between the two plates of testing machine. To test the tensile strength in this study, the constructed samples were tested at the ages of 3, 7 and and 28 days. As shown in Fig. 5, the 28-day tensile strength of mixture design has to large extent changed. It is worth noting that application of steel fibers has increased long-term tensile strength of concrete in all cases. According to Fig. 5, the 28-day tensile strength of all samples has increased. Based on these results, the highest 28-day tensile strength exists in samples reinforced with 2.5% hybrid steel fibers (hooked steel fibers L/D=30 and crimped steel fibers L/D=50) with 7.11 MPa and 80% tensile strength increase. I