Issue 42

A. Jadidi et alii, Frattura ed Integrità Strutturale, 42 (2017) 249-262; DOI: 10.3221/IGF-ESIS.42.27 253 research consist of two types of hooked steel fiber and one type of crimped steel fiber, the characteristics of which are shown in Tab. 2. Aggregates 0.0 – 0.1 mm 0.1- 0.3 mm 0.3 - 1.0 mm 1.0 - 2.0 mm 2.0 – 3.0 mm 3.0 – 5.0 mm Table 1 : Dimensions of quartz aggregates used. Fiber Mechanical anchors Diameter (mm) Length (mm) Specific Gravity (kg/m 3 ) Tensile Strength (MPa) Elasticity Modulus (GPa) Fiber Coating HE Hooked-End Steel 1.0 50 7850 800 210 - HE Hooked-End Steel 1.0 30 7850 800 210 - Crimped Crimped 1.0 50 7850 850 212 copper Table 2 : Characteristics of fibers used in the research. Figure 3 : General scheme of fibers used in research. Mixture design Maximum amount of fibers used in the mixture was estimated to be 2.5%. The fibers were added at the end of mixing process. To control the efficiency of the mixture, the fibers were divided into 5 equal parts, i.e. each part contained 0.5% of the entire fibers. Each part was gradually added to the mixture. After adding all parts and ensuring even distribution of the fibers, the mixture is checked for efficiency. The process of mixing the material is shown in Fig 4. The mixing process starts with mixing the dry aggregates and micro silica for about 2 minutes. When this mixing process is done, cement will be added to them and all the dry materials will be completely mixed together for about 2 minutes. The super plasticizer will be mixed by 70 percent water. Using this method of distribution, makes it possible to have a better performance in having the same distribution in all areas and increasing the cement efficiency. After completing the process of mixing the dry materials, the mixing of super plasticizer and water will be added gradually over a period of 4 minutes. Finally, by adding 30 percent of the remaining water over a period of 4 minutes, the quality and efficiency needed for adding the fibers, will be reached. The final mixture design hence obtained is presented in Tabs. 4 and 5.