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Characteristics of High-toughness Cement Concrete Paving Material and the Structural Analysis

Author: HeRui
Tutor: ChenShuanFa
School: Chang'an University
Course: Road and Railway Engineering
Keywords: Cement Concrete High Toughness Multiple Cracking Hydrid Fiber Theory Model Structural Analysis
CLC: U414
Type: PhD thesis
Year: 2013
Downloads: 67
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Abstract

Due to its low tensile strength, poor toughness and cracking potential, ordinarycement concrete has caused a great influence to the durability of concrete structures,which is more prominent with the increase of concrete strength. As the construction ofChina’s transportation infrastructures develops, the traffic flow with heavey axle loadand high speed has put forward higher requirements to the flexural strength anddeformation performance of concrete. Considering the multi-dimensional factors fromworkability to macroscopic mechanical properties, hybrid fiber were adopted toprepare high-toughness cement concrete paving material featuring the characteristicsof strain hardening and multiple cracking, the material properties and structuralfeatures of which was analyzed intensively in this paper with the combination ofindoor experiment and numerical simulation.This paper was started from analyzing the performance of raw materials. Thechemical stability of polyethylene (PE) and coarse polypropylene fibers (CPP) wastested, with the results showing that the employed fibers have good resistance tochemical corrosion. A fiber dispersing agent (M1) and a functional composite powder(M2) was invented to enhance the flowability of concrete mixture and improve thebond strength between fiber and matrix. It’s shown that the addition of M1cansignificantly improve the dispersion of fibers, while M2causes better interface bondto fiber and matrix. The flowability and fiber dispersion are preferable with the use ofM1or compound M1and M2.For the detection of the dispersion properties of these two fibers, digital imageprocessing and analysis technology was employed to establish a recognition anddispersion evaluation system of CPP fiber, with the evaluation index presented. Theevaluation method is not only suitable for coarse synthetic fiber, but also suitable forsteel fiber. The qualitative evaluation of PE fiber was conducted with the use of SEMobservation. Results show that the compound use of M1and M2can promote theuniform dispersion of PE fiber, and the dispersion of CPP and PE fibers have the samerules. Four point bending test and impact test were adopted to evaluate the toughnesscharacteristics of prepared high-toughness concrete. Obvious strain hardeningcharacteristics were observed under the flexural load and large amounts of fine cracksCPPeared near the opening surface. The initial crack and failure impact numbers ofprepared concrete are far higher than that of normal concrete under impact load. Theimpact toughness index was proposed according to the development of impactcracking, which has a good correlation with the deformation performance of fiberreinforced concrete.The cracking development law of high-toughness concrete was analyzed basedon the bridging law of fiber reinforced cementitious composites. SEM method is usedto analyze the microstructure of the interface between CPP fiber and matrix. Theobservation results show that the adhesion is poor, and there are a small number ofpores and micro-fractures in the interface zone with a large number of plate-likeaggregations of C-H crystals. The addition of M2leads to a large number of C-S-Hgel and improve the compactness of the interfacial zone. Thus, the stress anddeformation of the transfer effect can be improved, the mechanical characteristics ofinterface transform from brittle into toughn, and fiber toughening effect rangeincreases, leading to the significantly improvement of toughness in concrete.The uniaxial performance of high-toughness of concrete was evaluated inuniaxial tensile and compression tests. The elastic modulus is approximately the2/3of ordinary concrete with the same compressive strength, and the compressive andtensile strain capacity is greatly improved. The unique multiple cracking and strainhardening phenomenon occur for the six recommended mix proportion. According tothe features of stress-strain curve of high-toughness concrete, the constitutive modelwas built which can accurately fitting the deformation characteristics of concrete bothbefore and after the peak load. In the combination of bending and tensioncharacteristics, the inverse formula for determining the tensile strength and straincapacity of high-toughness concrete was recommended.Two-dimensional numerical models were established for the bending,compression and tensile concrete specimens at the mesoscopic level. The three kind of test process was simulated. The simulation results can better reflect the stress-straincharacteristics and the law of cracking damage development for the high-toughnessconcrete.The fatigue performance of high-toughness concrete was evaluated by bendingfatigue test. The curves of mid-span deflection-cycle ratio under fatigue load alsoaccord with the3stage model. The double logarithm fatigue equations with0.05and0.50of the failure probability were established based on the Weibull distributionmodel. The formula of fatigue stress coefficient in high-toughness slab is also derived.A three-dimensional finite element model was established for the analysis of thecharacteristics of high-toughness concrete pavement structure. It’s shown that thevariation of design parameters in the conventional range has less influence on themechanics characteristics of high-toughness concrete pavement which has superioranti-fatigue performance to the combination action of load and temperature fatigueeffect than that of ordinary concrete. According to the calculation results, combinedwith the engineering practice, the slab length and thickness under different trafficlevels were recommended for the high-toughness concrete pavement.

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