الفهرس 
IntroductionOnly 14 pages are availabe for public view
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Abstract
There are many kinds of fibers, no matter metallic or polymeric, widely used in concrete engineering for their advantages. In fact, no single fiber-reinforced concrete has the perfect mechanical and durability properties. Recently, many researches have an orientation to discuss the mechanical and durability properties of the hybrid fiber-reinforced concrete especially polypropylene fibers because polypropylene fibers are chemically resistant to acids and alkalis and can be used with any type of Portland cement, don‘t require much workmanship in its production, easy to apply, not rust, low weight, high toughness, resistance to corrosion ,enhancing fire performance of concrete at elevated temperatures through reducing pore pressure and spalling hazard and improves mechanical properties of concrete.2) Study scope: The performance of high strength concrete (HSC) incorporating hybrid polypropylene fibers (staple, monofilament).3) Study objective: Determining the optimum content of hybrid polypropylene fibers which achieves the optimal mechanical and durability properties.4) Steps of the study: In this investigation an introduction to concrete, HSC, and polypropylene fibers followed by a studies review on fresh and hardened properties, mixing proportions, testing methods, and statically models for proportion and optimizing of polypropylene fibers on HSC. The materials used in this investigation were selected due to their locality and availability. The methodology of experimental program along with the tests is discussed. The analysis and discussion of the whole test results, and the statically models are presented. This follows by conclusions of the whole project and suggestion for further work. 5) Summary of the study: The results of this study showed that Central Composite Design (CCD) can reduce the number of experiments required to obtain significant data, Response
Surface Methodology (RSM) can develop strong relationships between responses and HPFRC
concrete’s constituent materials, analyses of variance (ANOVA) can be used to test the effects
of variables and their interactions on responses, and it is possible to determine the optimum
values of variables, which achieve the optimal properties. The results indicated that concrete mixtures reinforced with hybrid polypropylene fibers have significantly improved in terms of compressive strength, flexural strength ranged, impact resistance, and resistance to elevated temperature while the workability slightly decreased. The compressive strength and flexural strength of hybrid polypropylene fiber reinforced concrete increased by (1.96% to 12%) and (14.28% to 41.9%) respectively at age 56 days compared to control mixture without fibers. The hybridization of 5 kg monofilament and 0.75 kg staple fibers achieved the highest compressive strength (84.6 MPa), flexural strength (14.9 MPa), and the optimum impact resistance at age 56 days. The increase of coarse monofilament fibers significantly improved the spalling resistance performance. The residual compressive strength of mixture containing 5 kg monofilament and 0.75 kg staple fibers up to 63.8% of the initial strength after exposure to 800 0C. Investigations using (SEM) technology demonstrated that adding hybrid polypropylene fibers to concrete could enhance interfacial transition zones and the matrix between aggregates and the polypropylene matrix. Subsequently, improved the mechanical properties. Using RSM, the regression model offers a detailed analysis of the hybrid mpolypropylene fibers reinforced concrete properties over the selected range of fiber volume fraction. The results of the lack-of-fit test along with the high values of the coefficients of multiple determinations (R2 ) demonstrated that the polynomial regression model was enough to forecast the necessary performance of hybrid polypropylene fiber concrete. The ANOVA results
also confirmed, based on a very low P-value, that the inclusion of all model parameters is
statistically significant.