CT Image-based Analysis on the Defect of Polypropylene Fiber Reinforced High-Strength Concrete at High Temperatures

With the application of X-ray computed tomography（CT） technology of C80 high-strength concrete with polypropylene fiber at elevated temperatures, the microscopic damage evolution process observation and image building could be obtained, based on the statistics theory and numerical analysis of the combination of concrete internal defects extension and evolution regularity of microscopic structure. The expermental results show that the defect rate has changed at different temperatures and can determine the concrete degradation threshold temperatures. Also, data analysis can help to establish the evolution equation between the defect rate and the effect of temperature damage, and identify that the addition of polypropylene fibers in the high strength concrete at high temperature can improve cracking resistance.

Properties and Mechanism on Flexural Fatigue of Polypropylene Fiber Reinforced Concrete Containing Slag

Properties and mechanism were investigated on flexural fatigue of concrete containing polypropylene fibers and ground granulated blast furnace slag（GGBFS）.Four polypropylene fibers’volume fractions and five slag proportions were considered.An experiment was conducted to obtain the fatigue lives at three stress levels in 20 Hz frequency and at a constant stress level of 0.59 in four frequency respectively.Mechanism and evaluation were investigated based on the experimental data.Fatigue life span models were established.The results show that the addition of polypropylene fibers improves the flexural fatigue cumulative strength and fatigue life span.It is proposed that the slag particles and hydrated products improve Interfacial Transition Zone（ITZ）structure and benefit flexural fatigue performance.A composite reinforce effect is found with the incorporation of slag and polypropylene fibers.The optimum mixture contents 55%slag with 0.6%polypropylene fiber for the cumulative fatigue stress.Fatigue properties are decreased as the stress level increasing,the higher frequency reduces the fatigue strength more than lower frequency at a constant stress level.

The damage evolution behavior of polypropylene fiber reinforced concrete subjected to sulfate attack based on acoustic emission

To study the damage evolution behavior of polypropylene fiber reinforced concrete(PFRC)subjected to sulfate attack,a uniaxial compression test was carried out based on acoustic emission(AE).The effect of sulfate attack relative to time and fiber hybridization were analyzed and the compression damage factor was calculated using a mathematical model.The changes to AE ringing counts during the compression could be divided into compaction,elastic,and AE signal hyperactivity stages.In the initial stage of sulfate attack,the concrete micropores and microcracks were compacted gradually under external load and a corrosion products filling effect,and this corresponded with detection of few AE signals and with concrete compression strength enhancement.With increasing sulfate attack time,AE activity decreased.The cumulative AE ringing counts of PFRC at all corrosion ages were much higher than those for plain concrete.PFRC could still produce AE signals after peak load due to drawing effect of polypropylene fiber.After 150 d of sulfate attack,the cumulative AE ringing counts of plain concrete went down by about an order of magnitude,while that for PFRC remained at a high level.The initial damage factor of hybrid PFRC was-0.042 and-0.056 respectively after 150 d of corrosion,indicating that the advantage of hybrid polypropylene fiber was more obvious than plain concrete and single-doped PFRC.Based on a deterioration equation,the corrosion resistance coefficient of hybrid PFRC would be less than 0.75 after 42 drying-wetting sulfate attack cycles,which was 40%longer than that of plain concrete.

Research on Concrete Preparation for the Steel-concrete Composite Segment of Jingyue Yangtze River Bridge

To improve the quality of the steel-concrete composite segment of the box girder,to ensure the compactness of concrete to avoid debonding and to enhance the fatigue strength of concrete are critical to the concrete preparation for such site. Furthermore,the coordination ability to deformation between steel and concrete is also important because of great difference of the elastic modulus between them. Concrete for the steel-concrete composite segment with high fluidity,excellent crack resistance and low shrinkage was prepared by adding efficient poly-carboxylic water-reducing agent,high quality fly ash and expansion agent to it. The quality of the concrete of the half partial testing block showed that the optimal mix proportion of polypropylene fiber reinforced concrete had achieved expected effect,ensured high quality,thus meeting the requirements of construction.