Issue 42

A. Jadidi et alii, Frattura ed Integrità Strutturale, 42 (2017) 249-262; DOI: 10.3221/IGF-ESIS.42.27 250 the first 7 days [ 3 ] . Rodrigues et al., studied the behavior of concrete columns reinforced with fibers on fire. In this research, four columns, 0.25 m long, 0.25 m wide and 3 m high, strengthened with different longitudinal steel reinforcements were investigated. Columns 1 to 3 contained 38.8 kg, 27.24 kg and 16.56 kg steel fibers and 1.5 kg polypropylene fibers per cubic meter respectively, without any fibers in column 4. Tests indicated that steel and polypropylene fibers used in concrete improve the behavior of columns on fire. Polypropylene fibers can control concrete flaking. Moreover, steel round bars are needed in columns to resist against fires. Therefore, to replace steel bars by steel fibers is not a good option when concrete is on fire [ 4 ] .Vandewalle, did some experiments on hybrid fiber-reinforced concrete. He used three types of fiber: very short fibers with a length of 6 mm, short fibers with a length of 13 mm and long hooked-end fibers with a length of 35 mm. Beams 550 mm to 600 mm long and 150 mm wide and high were used in the experiments. The amount of fibers used varied from 0 to 90 kg per cubic meters, added to the concrete mix separately as well as a combined with two or three types of fiber. The results of measuring changes of the openings in cracks show the 3 mm and 13 mm fibers are very effective at the openings of tiny cracks, while 35 mm fibers provide appropriate plasticity at big and wide cracks. Tiny cracks grow, come together and join big cracks. Long hooked end fibers become very active in joining these cracks [5]. Milind V mohod et al., in this experimental investigation for M30 grade of concrete to study the compressive strength and tensile strength of steel fibers reinforced concrete containing fibers varied by 0.25%, 0.50%, 0.75%, 1%, 1.5% and 2% by volume of cement cubes of size 150mm × 150mm × 150mm to check the compressive strength and beams of size 500mm × 100mm × 100mm for checking flexural strength were casted. All the specimens were cured for the period of 3, 7 and 28 days before crushing the result of fibers reinforced concrete 3 days, 7 days, and 28 days curing with varied percentage of fiber were studied and it has been found that there is significant strength improvement in steel fiber reinforced concrete. The optimum fiber content while studying the compressive strength of cube is found to be 10% and 0.75% for flexural strength of the beam [6]. Carneiro et al., conducted experimental investigations on the mechanical properties of construction and demolition waste concrete with hooked-end steel fibers. Recycled aggregate concrete with hooked-end steel fibers exhibited a better mechanical performance with a 0.75% volume fraction than natural aggregate concrete. Ahsana Fathima et al. [7], presented the experimental study on the effect of steel fibers and polypropylene fibers on the mechanical properties of concrete, experimental program consisted of compressive strength test, split tensile strength test and flexural strength test on steel fiber reinforced concrete polypropylene fiber reinforced concrete three types of fibers used of length 30mm crimped steel fibers of length 25mm and endure 600 polypropylene of length 50mm with aspect ratio 50. The main aim of this experiment is to study the strength properties of steel fibers and polypropylene. Fibers reinforced concrete of M30 grade with 0%, 0.25%, 0.5% and 0.75% by volume of concrete [8]. Graybeal, attributed the increase in the flexural behavior of UHPC to the particle packing and the addition of fibers which hold the cement matrix together after cracking has occurred. UHPC exhibits ductility because as the specimen begins to micro crack the small scale fibers reinforce the matrix causing smaller, less damaging cracks to form [9]. S TEEL FIBER - REINFORCED CONCRETE iber concrete (steel fibers) consists of a concrete body composed of cement, aggregates, water, and some percentage of short steel fibers scattered randomly and disorderly into the mix in various directions. The steel fibers improve concrete properties compared to its normal state. Steel fiber-reinforced concrete is cast and agglomerated like plain concrete. Mixture designs for steel fiber reinforced concrete are basically similar to those of plain concrete. However, measures should be adopted for the even distribution of fibers and preventing them from being separated and intertwined into balls, so as to produce an efficient mix to cast, agglomerate and smoothen [ 2 ] . E XPERIMENT DESIGN AND RESEARCH APPROACH he present study, by doing experiments with various fiber weights in steel fiber-reinforced concrete, aims at investigating the impact of fiber content on strength parameters of this type of concrete. In this research, 381 of specimens have been examined. Numerically, 69, 189, 123 samples of these number have been employed based on compressive strength, splitting tensile test and bending test. Indirect tensile test, known as the Brazilian test To assess tensile strength, sample splitting test (Brazilian test) was carried out on cylindrical samples of steel fiber- reinforced concrete, and the results were evaluated against each other and fibreless samples. Tensile strength measurement F T