【作者】 李长永；

【导师】 陈淮；

【作者基本信息】 郑州大学 ， 结构工程， 2014， 博士

【摘要】 轻骨料混凝土具有轻质、高强、抗震性能和耐久性能好等优点，越来越多地被应用于土木工程中。在轻骨料混凝土中掺入钢纤维配制的钢纤维轻骨料混凝土(简称SFRLC)，不仅具有轻骨料混凝土的各种优点，而且能显著提高轻骨料混凝土的抗拉、抗裂性能和韧性，改善混凝土结构的延性、抗疲劳性能和耐久性能。因此，开展钢纤维轻骨料混凝土材料与构件性能试验与理论研究具有重要的应用价值与理论意义。为充分利用钢纤维轻骨料混凝土和普通混凝土的优点，作者提出了一种新型结构形式：在下部一定高度的钢纤维轻骨料混凝土上同期现浇普通混凝土组成的叠浇梁。本文采用不同配合比方法进行钢纤维轻骨料混凝土配合比设计，通过系列试验研究了不同参数对钢纤维轻骨料混凝土基本性能的影响，对所提出的新型钢纤维轻骨料混凝土叠浇梁（简称SFRLCB）开展了系统试验研究和理论分析，所完成的主要工作和取得的结论：（1）采用松散体积法对钢纤维机制砂轻混凝土和钢纤维全轻混凝土(简称SFRFLC)进行配合比设计，系统研究了水灰比、水泥用量、砂率及钢纤维体积率等参数对混凝土性能的影响。结果表明：机制砂轻混凝土的抗压强度及弹性模量、劈裂抗拉强度和轴心抗拉强度均随水灰比的增大而减小，但抗弯强度受水灰比的影响不明显；当水泥用量较高时，砂率对混凝土轴心抗拉强度和抗弯强度的影响较小；当水泥用量较低时，混凝土的轴心抗拉强度和抗弯强度受砂率和水泥用量的关联影响，砂率对混凝土劈裂抗拉强度的影响不明显。全轻混凝土的强度受砂率、水灰比及水泥用量的关联影响，其强度值主要取决于水泥砂浆及陶粒强度的强弱；存在使混凝土各强度指标达到最佳值的水泥用量、水灰比及砂率。掺加钢纤维显著增强了机制砂轻混凝土的劈裂抗拉强度和轴心抗拉强度，明显提高了全轻混凝土的抗弯强度。（2）采用考虑钢纤维裹浆厚度的直接设计方法进行高强钢纤维全轻混凝土配合比设计，系统研究了钢纤维体积率、水灰比、钢纤维裹浆厚度及砂率对高强钢纤维全轻混凝土性能的影响。结果表明：按考虑裹浆厚度的直接设计方法配制的高强钢纤维全轻混凝土，能满足拌合物工作性能、干表观密度和强度的要求。随着钢纤维体积率的增加，高强钢纤维全轻混凝土立方体抗压强度、轴心抗压强度和轴心抗拉强度均有所提高，劈裂抗拉强度显著提高。经综合分析，确定钢纤维全轻混凝土最佳钢纤维裹浆厚度为1.0mm。（3）对试验中采用不同配合比方法的钢纤维轻骨料混凝土的劈裂抗拉强度和轴心抗拉强度的关系进行了分析研究，结果表明：该类轻骨料混凝土劈裂抗拉强度与轴心抗拉强度的比值随轻骨料性质和钢纤维特征含量的变化而变化，建议轻骨料混凝土和钢纤维轻骨料混凝土抗拉强度采用轴心抗拉强度法测定。（4）考虑水泥用量、水灰比及钢纤维体积率变化，进行了钢纤维全轻混凝土抗冻性能试验研究。结果表明：钢纤维全轻混凝土的抗冻性能受水泥用量及水灰比的影响，掺入钢纤维可显著提高全轻混凝土的抗冻性能。与相对动弹性模量相比，抗弯强度损失率对冻融循环更为敏感。建议对承受弯曲作用为主的钢纤维轻骨料混凝土构件，采用抗弯强度损失率作为抗冻性能的1个评价指标。（5）系统进行了42根钢筋钢纤维全轻混凝土叠浇梁、12根钢筋混凝土梁和4根钢筋钢纤维全轻混凝土梁的受弯性能试验。结果表明：3类试验梁的破坏形态基本相似，均为适筋破坏；钢纤维掺量、叠浇高度对试验梁极限承载力具有较大影响，且变化规律与配筋率相关；纵筋配筋率显著影响试验梁的极限承载力，受压区混凝土强度等级对叠浇梁的极限承载力影响较小。根据理论分析和试验结果，建立了钢筋钢纤维全轻混凝土叠浇梁受弯承载力的计算模型和计算方法，提出了叠浇梁钢纤维全轻混凝土最小高度和最佳高度计算公式。（6）结合试验梁的研究成果，分析了钢纤维体积率、普通混凝土强度等级、纵向受拉钢筋配筋率和钢纤维全轻混凝土截面高度等参数对叠浇梁正截面抗裂弯矩的影响规律。结果表明：叠浇梁受压区混凝土与受拉区钢纤维全轻混凝土的截面高度存在较优值，受压区高强混凝土保障了叠浇梁正截面的较高抗裂弯矩；适当的纵向受拉钢筋配筋率有利于提高叠浇梁的正截面抗裂弯矩；钢纤维对叠浇梁正截面抗裂弯矩的提高与其对全轻混凝土抗拉强度的提高是一致的。结合理论计算分析，提出了钢筋钢纤维全轻混凝土叠浇梁正截面抗裂计算方法以及充分发挥钢纤维全轻混凝土抗拉能力的截面高度计算公式。（7）根据叠浇梁在正常使用荷载作用下的裂缝分布情况，明确了叠浇梁裂缝分类统计原则，进行了各类裂缝数量、平均裂缝间距、平均裂缝宽度及最大裂缝宽度分布规律的统计分析，建立了叠浇梁纵向受力钢筋重心水平位置处平均裂缝间距、平均裂缝宽度和最大裂缝宽度的计算模型和计算方法。更多还原

【Abstract】 Structural lightweight concrete has the advantages of lightweight, high-strength,anti-seismic and good durability, it has been widely used in civil engineering. Steelfiber reinforced lightweight concrete (SFRLC) made by lightweight concrete mixingsteel fiber has not only the advantages of lightweight concrete, but also theremarkable tensile strength and cracking resistance as well as toughness, which canimprove the ductility, fatigue resistance and durability. Therefore, the experimentaland theoretical researches on performance of materials and members for SFRLC haveimportant practical value and theoretical significance. The new type superposingcomposite beam, i.e. SFRLC beam superposing with partial ordinary concrete, is thecast-in-place composite beam formed by ordinary concrete superposed on steel fiberlightweight concrete casted firstly in certain height (SFRLCB), which combines thegood performances of steel fiber lightweight concrete in lightweight and tensileresistance, and ordinary concrete in compression. This paper carried out the mixdesign of SFRLC by different method and studied the influences of differentparameters on the basic properties of SFRLC by a series of experiments, andconducted systematically experimental study and theoretical analysis on the SFRLCB.The main contents and conclusions are as follows:(1) the loose volume method was used to do mix design of the SFRLC withmachine-made sand and expanded-shale, and the steel fiber reinforced fulllightweight concrete (SFRFLC). The effects of water to cement ratio, cement dosage,sand ratio and fraction of steel fiber by volume on the properties of these two kinds ofSFRLC were systematically studied. The results show that for SFRLC withmachine-made sand and expanded-shale, the compressive strength, elastic modulus,splitting tensile strength and axial tensile strength increase with the increase of waterto cement ratio, but the flexural strength has no obvious change; the axial tensilestrength and flexural strength are affected in some extent by the sand ratio while thecement dosage is greater; when the cement dosage is lower, the axial tensile strengthand flexural strength are jointly affected by the sand ratio and cement dosage, the splitting tensile strength is not obviously affected by the sand ratio. The strengths ofSFRFLC are affected jointly by the sand ratio, water to cement ratio and cementdosage, and controlled by the strength of cement mortar and expanded-shale; theoptimum values are there for the sand ratio, water to cement ratio and cement dosage;the splitting tensile strength, the axial tensile strength and the flexural strength areobviously enhanced by the adding of steel fiber.(2) the mix design of high-strength SFRFLC was made by the direct designmethod considering the cement paste wrapping steel fibers, the properties ofhigh-strength SFRFLC were systematically experimental studied with the view ofinfluencing parameters of the fraction of steel fiber by volume, the water to cementratio, the thickness of cement paste wrapping steel fiber and the sand ratio. the resultsshow that the high-strength SFRFLC satisfies the requirements of workability of freshconcrete, dry apparent density and strength; with the increase of fraction of steel fiberby volume, the cubic compressive strength, axial compressive strength and axialtensile strength are all improved in some extent, while the splitting tensile strengthincreases obviously. After comprehensively analysis, the optimum thickness ofcement paste wrapping steel fibers is determined as1.0mm.(3) the relationship of splitting tensile strength and axial tensile strength forSFRLC on different mix proportion method was analysed. Results showed that theconversion coefficient of splitting tensile strength to axial tensile strength changewith the lightweight aggregate and characteristic value of steel fiber. It isrecommended that the testing method of axial tensile strength is suit to determine thetensile strength of lightweight concrete.(4) considering the changes of cement dosage, water to cement ratio and fractionof steel fiber by volume, experimental study was carried out on the freeze-thawresistance of SFRFLC. The results show that the freeze-thaw resistance of SFRFLC isaffected by the cement dosage and water to cement ratio, which can be obviouslyenhanced by the steel fibers. Compared with the relative dynamic elastic-modulus,the loss rate of flexural strength has more sensitivity to the freeze-thaw cycle.Therefore, it is suggested that for the member mainly subjecting to flexural actions,the loss rate of flexural strength of SFRFLC may be better as one of the evaluation indexes to the freeze-thaw resistance.(5) systematical experimental study was carried out on42SFRFLC beamssuperposed with ordinary concrete,12reinforced concrete beams and4reinforcedSFRFLC beams. The results show that the failure states of these three kinds of beamswere similar with the yield of proper reinforcement and compressive crush ofconcrete; larger influences of fraction of steel fiber by volume and depth of SFRFLCare on the ultimate resistance, which are related to the reinforcement ratio; thereinforcement ratio obviously affects to the ultimate resistance of beams; thesuperposed concrete strength has a little effect on the ultimate resistance of SFRFLCbeams superposed with ordinary concrete. Based on the theoretical analysis and withthe comparison of experimental results, the calculation model and computationmethod of bending resistance are established for the SFRFLC beams superposed withordinary concrete, the formulas for calculating the minimum and optimum depths ofSFRFLC are proposed.(6) combined with the experimental results of42SFRLC comparing with12reinforced concrete beams and4SFRFLC beams, the effects of such parameters asthe fraction of steel fiber by volume, the strength grade of ordinary concrete, thereinforcement ratio of longitudinal tensile rebar and the sectional depth of SFRFLCon the anti-cracking moment of normal section of SFRLCBs are analyzed. The resultsshow that the optimal value is there for the section depths of ordinary concrete incompressive zone and SFRFLC in tensile zone, the high-strength ordinary concreteprovides the larger anti-cracking moment of SFRLCB, the proper reinforcement ratioof longitudinal tensile rebar benefits to improve the anti-cracking moment ofSFRLCB, the enhancement of steel fiber to the anti-cracking moment of SFRLCBcoincides with the strengthening to the tensile strength of SFRFLC. Combining withthe theoretical analysis, the method for calculating the anti-cracking moment ofnormal section of SFRLCB is proposed, the formula is suggested to determine thesectional depth of SFRFLC giving full play to resisting tension.(7) based on the crack distribution of SFRFLC beams superposed with ordinaryconcrete under normal service load, the principle of classified statistical analysis forthe cracks is determined. The statistical analyses are carried out on the number of cracks, the average crack space, the average crack width and the distribution ofmaximum crack width. The calculation models and computation method are proposedfor the average crack space, average crack width and maximum crack width at thehorizontal level of longitudinal reinforcements of the SFRLCBs.更多还原