【作者】 谢海波；

【导师】 邵旭东；

【作者基本信息】 湖南大学 ， 桥梁与隧道工程， 2017， 博士

【摘要】 应变硬化水泥基材料(Strain Hardening Cementitious Composite(SHCC))是一种具备有类似金属材料的拉伸应变特征和细微裂缝的高韧性水泥基材料,具有显著韧性和优越的耐久性能,是非常适合加固的一种复合材料,但SHCC材料还存在着弹性模量和强度偏低等问题,导致加固结构承载力提升并不明显,因此本文采取致密化方法对SHCC进行改进,通过一系列试验和理论分析,研究出适用于混凝土加固的致密应变硬化水泥基复合材料(Densified Strain Hardening Cementitious Composite(DSHCC))。本文针对新型加固材料展开了如下研究工作:1.DSHCC配合比和材料基本力学性能的研究根据材料和易性和力学性能要求,对DSHCC材料配比进行了试验研究。首先基于对SHCC和UHPC材料配合比和力学性能差异进行了分析,并以DSP理论为基础,得到了 DSHCC的配比范围;进一步根据和易性能试验,进一步确定水胶比、硅胶比等材料配合比范围,;再由轴心受拉试验确定满足材料性能的PVA纤维含量;最后通过轴心受压试验,取得材料的受压强度和弹性模量等参数。与普通SHCC材料相比,DSHCC材料的极限抗拉强度提高了 38%,极限抗压强度提高了 56%,弹性模量提高了 59%。2.加固材料DSHCC的抗渗性能和收缩性能试验研究采用Torrent气压法和温纳电阻率法相结合的列阵图法研究了水胶比、硅灰含量对材料抗渗性能影响,还通过多种材料对比验证了 DSHCC材料具备了非常优越的抗渗性能;试验还研究了材料的收缩性能,研究了水胶比、硅灰含量、纤维含量和浸水养护四个参数对材料收缩性能影响,提出了增加纤维含量和掺入膨胀剂,并改善养护条件来控制材料收缩的具体措施。3.DSHCC增强混凝土梁受弯性能试验和理论研究试验证明DSHCC加强梁的初裂荷载、屈服荷载和极限荷载均比复合砂浆加强梁有显著提高,而且加强层出现细微裂缝特性,DSHCC材料大幅度提高了结构强度和耐久性;试验也发现随着加强层厚度增加,加强梁的延性越差;界面层的裂缝致使DSHCC加强层顶部出现应力集中,局部应力超越其极限抗拉强度而出现过早的断裂破坏,致使加强梁容易发生脆性破坏;通过在DSHCC加强层加入少量钢筋的方法提高其变形能力,增强加强结构延性;通过试验和数值分析研究了加筋DSHCC层加固RC梁受弯承载过程,分析DSHCC加强混凝土梁正截面抗弯性能,并将试验结果与计算值进行对比分析;最后推导DSHCC加固RC梁极限承载简化计算公式。4.DSHCC加固钢筋混凝土梁抗剪性能试验研究对剪跨比分别为3.2和2.2两组共6根试验梁进行了试验研究,对比分析了加固梁和RC基准梁剪切破坏模式、承载力、变形能力以及裂缝分布等方面的不同,DSHCC剪切加强能有效地提高钢筋混凝土梁的开裂强度和极限强度,特别是开裂强度。DSHCC材料能有效地延缓构件开裂,增加构件抗裂性提高加强梁的耐久性。基于试验得到的DSHCC本构关系,采用非线性有限元分析方法,进一步研究了 DSHCC抗剪加强梁的受剪承载过程;最后基于桁-拱模型和材料应力-应变关系,推导的DSHCC加强梁斜截面极限承载力简化公式,并将试验结果与计算值进行对比研究,实验结果吻合较好。更多还原

【Abstract】 Strain Hardening Cementitious Composites(SHCC)has exhibit tensile strain hardening similar with metal material and multiple fine cracks.This material offers superior performance over other reinforcement material for reinforced concrete.Due to the issues of SHCC with low Young’s modulus and tensile strength,RC structure’s ultimate bearing capacity using SHCC strengthening were not obvious,so densified Strain Hardening Cementitious Composite(DSHCC)were developed using the densification method.The selection of new compositions and optimizing was based on the fresh characteristics properties and uniaxial tensile test,air permeability tests and shrinkage behavior tests;then tests and theoretical analysis were carried out to find the effectiveness of applying DSHCC for bending and shear resistance of RC beams.Therefore the main research contents of this paper are as follows:1.Experimental study on the mix proportion and the basic mechanical properties of DSHCCMix proportion tests of DSHCC were carried out according to fresh characteristics and mechanical property.Firstly SHCC and UHPC were compared with material mix proportion and mechanical property,then based on DSP theory,approximate range of new material have been developed.Water cement ratios and silica/binder ratios and so on were established based on workability property test.The choosing of PVA fiber ratio was mainly depended on tensile mechanical properties for repairing demand.Finally the compressive strength and elastic modulus of the material are obtained by axial compression test.Compared with SHCC materials,the mechanical properties of DSHCC materials have been greatly improved,and the tensile and compressive strengths and Young’s modulus has been raised by 38%,56%,and 59%respectively.DSHCC layer can make the ductility of strengthened RC beams increase 40%and 100%2.Experimental study on permeability and shrinkage of DSHCCDSHCC has excellent anti-permeability with combination diagram method including Torrent pressure method and the combination of Wenner resistivity method.Research on shrinkage properties of materials,the water cement ratio,silica fume content,fiber content and curing conditions of four parameters on the material shrinkage effect,It was proposed to increase the fiber content and expansion agent,and improve the curing conditions to control concrete shrinkage.3.Experiment and theoretical analysis on flexural behavior of RC beams strengthened with DSHCCThe experimental results show that the DSHCC reinforced beams the first crack load,yield load and ultimate load was improved than those of composite mortar reinforced beam,and durability of RC beams was greatly improved because of DSHCC behavior of formatting multiple fine cracking.The tests also found that with the strengthening layer thickness increases,the ductility of the strengthened beams got worse because of the crack interface layer which causes DSHCC to strengthen the top layer of stress concentration,then local stress exceed the ultimate tensile strength and premature fracture,the strengthened beams cause brittle failure.Deformation capacity was greatly improved by a small amount of steel in DSHCC,which enhance the ductility of the strengthened beams.Experiments and numerical analysis for RC beams with the reinforced DSHCC strengthened was carried out,which show the strengthened beams flexural performance;the calculated values and tests was compared.Finally a simplified formula for calculating the ultimate bearing capacity of RC beams strengthened with DSHCC was proposed in this study.4.Experimental Study and theoretical analysis on Shear Performance of Strengthened RC Beams with DSHCCSix test beams in two groups which are respective with shear span ratios of 3.2 and 2.2 are studied;the differences of the shear failure mode,bearing capacity,deformation and fracture distribution between RC beam and DSHCC strengthened beam were analyzed;Based on finite element analysis and the Truss-Arch theory,a simplified ultimate shear strength formula of the DSHCC strengthened beam is derived and verified by the test results.This investigation proves that the DSHCC is also an excellent material for shear strengthening and the proposed simplified ultimate shear strength formula will give reference for the design of DSHCC strengthened beams.A simplified ultimate shear strength formula of the DSHCC strengthened beam is derived and verified by the test results.更多还原