ADDITIONAL STEEL FIBERS IN CONCRETE MIXTURE STUDIES OF COMPRESSIVE AND TENSILE STRENGTH OF CONCRETE Budi Witjaksana* Civil Engineering, 17 Agustus 1945 University Surabaya, Semolowaru 45 Surabaya, Indonesia *[email protected] Test results for average compressive strength at 3-day concrete age were obtained from the proportion of fiber steels 2.5%, of 200.81 kg / cm2, 7 days obtained from the proportion of 2.5% fiber steels mixture of 263.97 kg / cm2, 14 days obtained from the proportion 7.5% steels steels mixture, 183.84 kg / cm2, 21 days obtained from the proportion of 7.5% steels fiber mixture, amounting to 345.99 kg / cm2. The test result for average tensile strength at concrete 3-day concrete age was obtained from proportion of 2.5% fiber steels mixture, 40.46 kg / cm2, 7 days obtained from proportion of 2.5% fiber steels mixture, 48.95 kg / cm2, 14 days obtained from the proportion of 5% fiber steels mixture, amounting to 54.38 kg / cm2, 21 days obtained from the proportion of 7.5% steel steels mixture, amounting to 56.27 kg / cm2. Keywords: fiber concrete, fibre steel, compressive strength, tensile strength 1. Introduction Starting from the researcher's concern about the start of cracks / damage to the structure of the college building where the researcher devoted himself as a lecturer in the Civil Engineering Study Program, the researchers moved to conduct research to improve the properties or characteristics of the concrete so that stronger, more resilient and has a lifespan which is longer and more reliable in cost. One of the development efforts is to improve the nature of the weakness of the concrete that is not able to withstand tensile strength, where the value of tensile strength of concrete ranges from 9% -15% of its strong urges [1]. Every effort to improve the quality of compressive strength is accompanied by a small increase in tensile strength. The value of the approach obtained from the test results repeatedly reaches the strength of 0,50-0,60√fc ', so for normal concrete used value 0,57√fc' [2]. Other assumptions say that in structural planning, concrete is considered to be able to withstand the stress urges, even though concrete is capable of withstanding tensile stress of 27kg / cm2 (Suhendro, 1991), so it is considered inefficient, especially in tensile and plastered plastering. The drag on the beam will experience a crack even if only get a voltage that is not so large. This is due to the cracking of the hair which is the nature of the concrete. Structurally this kind of condition is often ignored because the tensile stress has been fully supported by the reinforcement in sufficient quantities and placed correctly. Rapid development of technology at this time increasingly demanded an alternative that was born from some research that essentially is to create a new finding or at least can develop previous research, so it is expected to produce concrete technology products that are more qualified and efficient. One of the alternative materials used that is physics is steel fibers (stainless fibers). The basic idea is to repeat (reinforce concrete) with uniformly dispersed steel fibers into concrete with random orientation. So that concrete does not experience cracks that are too early due to loading or heat hydration [3]. Thus it is expected that the ability of concrete to support internal voltages (axial, flexural, and shear) will increase. 2. Experimental The method applied in this research is experimental method, that is research which aims to investigate causal relationship between each other and compare the result. Tests conducted in this study include material testing, compressive strength testing, and tensile strength testing. The research materials used in this research are as follows: water, cement, agregat, serat Fliber Steel (Dramix®3D). Material properties: Tensile strength: Rm, nom: 1.345 N / mm2, Tolerances: ± 7.5% Avg, Young's Modulus: ± 210,000 N / mm2, Geometry Fiber family Length (l) 35 mm, Diameter (d) 0.55 mm, Aspect ratio (l / d) 65 Variables are everything that will be the object of research observation. Variables can also be interpreted as factors that play an important role in the events or symptoms to be studied. The variables in this study were to use cement weight 350 kg / m3 with f.a.s 0,5 and 0% fiber content of bendrat; 2.5%; 5%; 7.5%; 10% (of the weight of cement). Variables in this study can be seen in Table 1 below: Table 1. Research Variable Cement weight (kg/m3) 350 Long fiber Dramix®3D (mm) 35 mm Fiber content (%) of the weight of cement 0 0,5 2,5 5 7,5 10 Number of specimens Water factor cement Number of specimens For test For test (fc&Ec) (ft) 3 3 3 3 3 3 3 3 3 3 15 15 The test specimen under study is cylindrical in size. 150 mm and 300 mm height are tested for compressive strength and tensile strength. The number of test objects 30 pieces, each composition of 3 samples. For a compressive test use the same test object, which is 15 pieces. While the other 15 test objects are used for tensile testing. Strong Concrete Press (f'c) The compressive strength of concrete according to SNI 03-1974-1990 [4] is the large burden of unity. The compressive strength of the concrete identifies the quality of a structure. The amount of compressive strength of concrete can be calculated by Equation (1): f'c = Pmax/A ................................................................................................................. 1 f’c = Strong press (N/mm2) P = maximum compressive load (N) A = Surface area of the test object (mm2) Strong Tensile (ft) Tensile strength becomes an important part in the concrete to resist cracks due to moisture content and temperature so as to affect the ability of the concrete in overcoming the initial crack before being burdened. Roughly normal concrete tensile strength values are only about 9% -15% of the compressive strength and can be computed by Equation (2) : ft = 2P/.l.d .................................................................................................................. 2 ft = tensile strength (N/mm2) P = load at concrete time split (N) l = The length of the cylindrical test object (mm) d = diameter of cylindrical test object (mm) Melting Point Determination The melting point is the point at which the gradient changes from the incline become almost flat on the load and deflection diagram on the reinforced concrete. Based on Figure 1., the first stage of the diagram is the strain that occurs is still small so the diagram is almost vertical. After that the slope of the diagram will be few reduced because the concrete is not stiff enough as in the early stages before the concrete starts to crack. After that, the diagram will experience gradient changes from tilted to almost straight horizontal. In order for reinforced concrete to melt, additional large burden is required to increase the reinforced concrete deflection. More details can be seen in Figure 1. Fig. 1. The moment-curve diagram for the reinforced concrete beam Strong Bending The bending of the beam is caused by strains arising from external loads. This test uses SNI 03-6861.1-2002 [5] and ASTM C-78 [6] standards, that is, the testing of tensile strength with two split loads acting on a beam cross section with the point being 3 parts. The magnitude of concrete bending strength for testing with the placement of two load points can be calculated by Equation [3]. σl = P/l/bh2 .................................................................................................................. 3 1 = modulus of rupture (MPa) P = Loads given on object blocks uji (N) l = Length of span ( mm) b = The width of the specimen (mm) h = Height of specimen (mm) 3. Result and Discussion Research results can be seen in table 2 and table 3 Table 2. Average Compressive Strength Fig. 2. Graph of test result of concrete compressive strength Table 3. Average Tensile Strength Fig. 3. Graph of test result of concrete tensile strength Fig. 4. Photo testing of concrete tensile strength 4. Conclusions Test results for average compressive strength at 3-day concrete age were obtained from the proportion of fiber steels 2.5%, of 200.81 kg / cm2, 7 days obtained from the proportion of 2.5% fiber steels mixture of 263.97 kg / cm2, 14 days obtained from the proportion 7.5% steels steels mixture, 183.84 kg / cm2, 21 days obtained from the proportion of 7.5% steels fiber mixture, amounting to 345.99 kg / cm2. The test result for average tensile strength at concrete 3-day concrete age was obtained from proportion of 2.5% fiber steels mixture, 40.46 kg / cm2, 7 days obtained from proportion of 2.5% fiber steels mixture, 48.95 kg / cm2, 14 days obtained from the proportion of 5% fiber steels mixture, amounting to 54.38 kg / cm2, 21 days obtained from the proportion of 7.5% steel steels mixture, amounting to 56.27 kg References [1] Dipohusodo, Istimawan, Struktur Beton Bertulang, Gramedia Pustaka Utama,Jakarta, 1994. [2] Dipohusodo, Istimawan, Struktur Beton Bertulang, Gramedia Pustaka Utama,Jakarta, 1999: 10 [3] Soroushian P and Z. Bayasi, 1987, Concept of Fiber Reinforced Concrete, Dept Of Civil and Environmental Engineering, Michigan State University,Michigan,1987. [4] SNI 03-1974-1990 [5] SNI 03-6861.1-2002 [6] ASTM C-78
