Studies On The Engineering Performance Of Modified Polypropylene Fiber Concrete

The necessity for the use of chemical fiber in concrete engineering was shown and the related fundamental research on polypropylene fiber concrete, advantages of adding polypropylene fiber and development trend of modified profiled polypropylene fiber in all engineering fields were summarized. Polypropylene fiber concrete properties and strengthening theory of fiber concrete were described, as references for further exploiting fiber concrete engineering function and the explanation of improvement mechanism at the beginning of the thesis.By putting the additive agent into PP, combining with profile and spinning technology, two kinds of polypropylene fiber were obtained, which are modified profiled polypropylene fiber and rigid-rod polypropylene fiber; The main function of the fiber in concrete and the selection principle of test fiber were described, and an experimental study on the weathering aging for the modified profiled polypropylene fiber was also made. The mechanical model for fiber filament pull-out was discussed by testing the pulling out of the modified profiled PP fiber from concrete, analyzing the effects of embedded length,water cement ratio, and ageing on pull-out strength. The theory for modified fiber pulled out and micro-mechanism for rupture were preliminary discussed.Regarding the performance requirements of the pavement concrete,the abrasion and impact tests of polypropylene fiber concrete were carried out. The effects of the adding of polypropylene fiber on impact and abrasion performance of concrete, the effects of ageing and fiber content on abrasion, abrasion mechanism,and the abrasion surface morphology of fiber concrete were studied. It was found that a high impact and abrasion performance could be achieved by adding certain amount of modified polypropylene fiber.The laboratory test on hydraulic characteristics of polypropylene fiber concrete demonstrated the relations between the micro mechanism and the performance of erosion, permeability and freeze-thaw resistant. The engineering practice showed that polypropylene fiber reinforced concrete possessed good impact and abrasion ability,impermeable crack and anti-freeze-thaw damage performance. The using of polypropylene fiber concrete could give construction projects full benefits of low cost and good mechanical properties. The related study was valuable in practice for the development of fiber reinforced concrete technology and to increase construction concrete durability, since the anti-freezing and water disaster difficulties of road cement pavements in frozen earth area could be overcome.The foreign standards,characteristics and calculation methods for concrete toughness test in academia were introduced. The bending toughness of modified profiled polypropylene fiber concrete was studied based on the experimental results. The effects on the strength and toughness of concrete as well as the improvement of concrete bending toughness with the addition of the modified profiled polypropylene fiber were analyzed. Furthermore, the effects of fiber contents, cross-section shape, and elastic modulus on concrete bending toughness were also studied. The comparative test with monofilament polypropylene fiber concrete was carried out, which may be used as reference in research of fiber concrete toughness test and in the related engineering design.In this paper rigid-rod polypropylene fiber is used to enhance the strength and to improve the durability of the water pervious concrete. It helps to overcome the shortcomings of steel fiber's strength deterioration caused by easily rusting and porous concrete's lower water permeability and lower effect on the restricting the concrete's shrinkage, but also to improve the concrete's matrix water permeability. The different main performances of the rigid-rod fiber enhanced water permeability concrete caused by using different kinds of fiber, additive silica powder and polymer, different proportions, different construction methods and different agitation technics are studied in the issue. Based on the study, it presents the investigation on the application of the vertical three-dimensional virescence concrete, comprehensive analysis of the pervious concrete technique system's research and application prospect, and reference for the further research and application.The law of the influence of freeze-thaw cycle on damage characteristics of fiber concrete material was also studied through the fast freeze-thaw cycle test of concrete. A constitutive model of freeze-thaw and damage of fiber concrete was established by analyzing the micro-mechanism of freeze-thaw damage of concrete and integrating with microscopic damage mechanics. The test, research and computation on damage parameters of concrete samples by ultrasonic wave method showed that the computed value from the model of freeze-thaw and damage of fiber concrete was basically consistent with the measured value.The predicted damage characteristics of concrete by constitutive model were well agreed with practical condition of freeze-thaw damage. The variation of ultrasonic damage parameters could be used to explain the law of freeze-thaw damage. The degree of inferiority of freeze-thaw damage of concrete could be effectively reduced by the adding of modified polypropylene fiber. To some strength extent, the anti-freezing performance of concrete would be optimal with 10 percent of fiber contents.The conclusions on the engineering application properties and mechanism of modified polypropylene fiber as well as concrete through the study in test, theory and practice were as follwings:1.The development of polypropylene fiber:(a)The early-age shrinkage property, bending and compressing strength of concrete could be effectively improved with the addition of multiple micro-voids PP fiber, and the strength of the pavement concrete and hydraulic concrete could be enhanced with the modified profiled polypropylene fiber; (b) A rigid-rod polypropylene fiber that can improve the toughness of concrete was developed, with which the strength of the water pervious concrete and other kinds of concrete that requiring additional toughness could be enhanced.2. About the pull-out strength of the polypropylene fiber:(a) The pull-out strength of the fiber was improved with the increase of embedded length. The selective preference length of the fiber is better from 9 to 13mm. (b) The pull-out strength of fiber was almost the same with the water cement ratio of concrete in the range of 0.28-0.44. (c) The pull-out strength of the fiber could be improved by fiber modification, because the roughness of the fiber surface was increased after the surface modification, which is good for the interfacial adhesive property between concrete matrix and fiber would be strengthened. (d) The pull-out strength of fiber could be increased with the increase of the age. This was because the strength of the concrete was improved with the increase of the age, and the hydration product at interface was helpful to the cementation between the fiber and the cement with the continuous progress of cement hydration.3.Impact and abrasion property of polypropylene fiber concrete:The main factor controlling the abrasion was the strength of concrete. An improved impact and abrasion properties of modified polypropylene fiber with surface modifying was comparatively good because of a good cementation with cement matrix. Since the breakaway of fiber from cement matrix in abrasion needed the consuming of considerable energy, it could therefore promote the performance of abrasion and impact of concrete materials. In brief, the adding of polypropylene fiber would provide concrete remarkable toughness and anti-crack ability. Modified polypropylene fiber could not only restrain the development of concrete cracks, but also maintain the internal continuity and integrity of concrete matrix therefore improved abrasion and anti-impact of polypropylene fiber concrete could be achieved.4.Hydraulic property of polypropylene fiber concrete:The modified polypropylene fiber reinforced concrete could be used as a kind of functional materials for anti-crack, seepage, eroding, freeze-thaw and denudation. The results provided the references for the repair and protection engineering of hydraulic concrete buildings. Therefore the polypropylene fiber concrete could be used in projects with above requirements, and could also give a full play for concrete buildings many advantages.5.Bending toughness of polypropylene fiber concrete:There was a better toughness for profiled modified polypropylene fiber concrete. The adding of fiber to concrete could substantially increase the bending toughness, and the ductility and toughness of concrete were obviously increased with the increase of fiber amount to certain extent.As the concrete strain range was comparatively larger, it could make little effect on anti-compression strength. Bending toughness with modified polypropylene fiber concrete was imcreased by 96%, and bending strength was increased by 38%. The profiled fiber with suitable elasticity module could be used to control the contraction cracks of plasticity as non-structural strength improving material. It could also be considered as structural strength improving material in design to improve ductility and bearing-capacity of the component. In engineering applications, modified polypropylene fiber could be used for spray concrete too, for its low price and good cementation with matrix. The fiber would be distributed uniformly in concrete matrix and resulted in an improved performance both in mechanics and in construction applications.6.The rigid-rod polypropylene fiber can be used to enhance the strength and to improve the durability of the water pervious concrete. It helps to overcome the shortcomings of steel fiber's strength deterioration caused by easily rusting and porous concrete's lower water permeability and lower effect on the restricting the concrete's shrinkage, but also to improve the bending and compressing strength of the water pervious concrete and the concrete's matrix water permeability. The research results can develop the pervious concrete technology. The study on the vertical three-dimensional virescence concrete technology system which based on the permeable matrix research has practical value.7.Freeze-thaw and damage model of polypropylene fiber-concrete: The calculated results with the built freeze-thaw and damage model of fiber concrete was in basic well agreed with experimental data. The damage property of concrete predicted by the model was also in agreement with test results. The supersonic method was used to directly testing of concrete structure against freeze-thaw damage, and the change of ultrasonic damage content could well reflect the law of freeze-thaw damage. The property of freeze-thaw of fiber concrete was optimal at 0.9kg/m3 polypropylene fiber, with smallest freeze-thaw damage extent and largest predicted freeze-thaw times. The tensile strength and strain of concrete could also be remarkably increased by the adding of modified polypropylene fiber. More polypropylene fiber in a certain extent could increase the strength of the concrete's anti-stretching more effectively. Modificative polypropylene fiber could effectively restrain the formation, development and freeze thaw deterioration degree of damage of the cracks in concrete caused by freeze-thaw cycle.