【作者】 田冬梅；

【导师】 邓德华；

【作者基本信息】 中南大学 ， 土木工程， 2013， 博士

【摘要】 摘要：水泥乳化沥青砂浆(日本简称CA砂浆,德国简称BZ砂浆,本文统称SL砂浆)是板式无砟轨道结构中关键工程材料之一,其长期服役性能对轨道结构的平顺性、耐久性和列车运行的安全性、舒适性至关重要。对我国早期建设的试验段和施工现场考察发现,砂浆充填层主要发生层间离缝、表面冲蚀、开裂、剥落与碎裂等劣化破坏现象,分析认为雨水、动荷载与温度变化是导致砂浆充填层的劣化与破坏的主要因素。本文采用阳离子型(A1)、阴-阳复合离子型(A2)、和阴离子型(A3)3种乳化沥青、P.Ⅱ型硅酸盐水泥、细砂和常用添加剂,分别制备了不同沥灰比(沥青/水泥质量比,A/C)的A1、A2和A3等3种SL砂浆试件,围绕水、荷载与温变等3个主要因素,分别研究单一因素和水-荷载耦合作用下硬化SL砂浆的劣化与失效机理。主要完成以下试验内容并得出相关结论：(1)采用SL砂浆层和混凝土层粘结叠合试件进行高低温循环模拟试验,研究板式轨道结构中砂浆充填层与混凝土轨道板层间离缝的原因。试验结果证明：经过一定高低温循环次数后,叠合试件中砂浆层与混凝土层周边出现离缝,层间剪切强度逐渐降低,砂浆层表面开裂,这表明温度变化是层间离缝和开裂的主要原因。分析认为,因沥青相的存在与沥青材料特性,使得SL砂浆与混凝土材料的热变形行为存在较大差异,前者热变形较大且对温度、时间依赖性较大,后者热变形较小；当温度交替变化时,叠合试件中混凝土层对SL砂浆层有较强的约束作用,使得SL砂浆层内产生较大压或拉应力；在压或拉应力的交替反复作用下,砂浆充填层表面出现裂缝,层间界面粘结强度逐渐降低,最终导致界面脱粘离缝。所以,环境温度变化和SL砂浆与混凝土热行为差异是轨道结构出现层间离缝、砂浆充填层开裂等劣化现象的两个重要原因。(2)通过接触角、毛细吸水试验,研究了硬化SL砂浆的吸水特性。试验结果表明：硬化砂浆成型面与水的接触角<90°,且随砂浆中A/C增加而增大,这表明硬化SL砂浆具有一定亲水性；SL砂浆有一定毛细吸水性,其单位面积毛细吸水量与t1/2呈线性关系,且毛细吸水速率与乳化沥青类型、A/C、毛细孔隙率及孔特征等有关,随A/C增加、毛细孔隙率减小、孔隙弯曲程度增大,毛细吸水速率减小；配比相同时,A1砂浆试件的毛细吸水速率高于A3砂浆试件。分析认为：硬化SL砂浆中分布较多的沥青凝聚相和毛细孔,毛细孔壁表面存在富沥青膜。尽管石油沥青是憎水性材料,但因硬化砂浆中沥青相是由乳化沥青颗粒凝聚而成,其表面定向排列一层憎水基指向沥青而亲水基指向空气的乳化剂分子层,毛细孔壁具有一定亲水性,导致外部水易于通过毛细孔向砂浆内部迁移,产生毛细吸水现象。(3)通过静压力吸水试验可得：在静压力作用下SL砂浆的吸水速率增大,且单位而积吸水量与t1/2关系曲线上存在明显拐点,拐点前的压力吸水速率比毛细吸水速率高两个数量级,拐点后比毛细吸水速率高一个数量级。无论拐点前后,相同条件下,3种砂浆试件的压力吸水速率与A/C和乳化沥青种类有关。因为静压力不但加速毛细吸水,而且可使水进入SL砂浆中沥青一水泥相和沥青一砂子等有机-无机相界面,A/C比越大,界面数量越多；乳化沥青种类既影响砂浆试件中界面数量又影响界面结合力,所以,砂浆试件的抗渗能力随A/C增加而减小,A/C比相同时,3种砂浆试件的压力吸水速率大小的顺序为：A1>A3>A2,抗渗能力大小的顺序为：A2>A3>A1。(4)为研究水对SL砂浆静态力学性能的影响,测量了不同种类SL砂浆试件在不同饱水度时的力学性能。试验结果表明：硬化SL砂浆的抗压强度和弹性模量均随其饱水度的增加而降低,抗压强度降低幅度最大可达40%以上。这是由于水对SL砂浆中有机-无机相界面的侵害作用,引起硬化SL砂浆发生“软化”,“软化”程度与A/C和乳化沥青种类有关,A/C值越大,其力学性能降低幅度也越大,抗水性越差；A/C相同时,A2抗水性较好,A3次之,Al乳化沥青砂浆的抗水性较差。因此增强SL砂浆中有机-无机相界面抗水侵害的能力是改善SL砂浆抗水性的有效途径。(5)为研究动荷载一水耦合作用下SL砂浆力学性能的变化,对不同饱水度的SL砂浆试件进行了疲劳试验。试验结果表明：吸水后,砂浆试件的极限疲劳强度显著降低,且饱水度越大,极限疲劳强度降低幅度越大；未吸水的基准试件的疲劳破坏形式为劈裂破坏,大多数为竖向裂缝,而在动荷载作用下吸水试件孔隙水形成超孔隙水压,对孔隙周围结构产生剪切作用,使其发生剪切破坏,裂缝呈倾斜状。另一方面,当饱水砂浆试件表面有一层水膜时,动荷载使这层水产生水力劈裂作用,使孔隙或缝隙尖端快速开裂并迅速扩展,导致饱水砂浆在较低的动荷载作用下就会产生贯穿裂缝。所以,在水-动荷载耦合的不断作用下,硬化SL砂浆试件的极限疲劳强度显著降低,并发生破坏通过上述试验研究,得出板式轨道结构中砂浆充填层劣化与失效机理是：环境温变和SL砂浆与混凝土热行为差异导致SL砂浆充填层与轨道板间层间离缝、砂浆充填层竖向开裂；雨水沿这些缝隙渗入砂浆内部,并滞留在砂浆充填层表面,在列车运行中的冲击荷载不断作用下,砂浆孔隙内产生的超孔隙水压力作用和层间界面高速处水流产生的水力劈裂作用,最终导致板式轨道结构中砂浆充填层劣化破坏而过早失效。更多还原

【Abstract】 Abstract:as one of key engineering materials in slab ballastless track, the long-term service performance of cement emulsified asphalt mortar (SL mortar) plays important role on the smoothness and durability of slab track, and the safety and ride comfort of passenger train. Such degradation and invalidation phenomena as interfacial opening gaps between SL mortar and concrete slab, vertical cracks, surface erosion and crush in SL mortar were observed in early testing section and construction site. Rainwater, dynamic load and temperature variation were determined as the primary influence factors on the degradation and invalidation of SL mortar.Some SL mortar specimens with different mass ratio of asphalt to cement (A/C) were prepared using cation emulsified asphalt (Al), compound ion emulsified asphalt (A2) and anion emulsified asphalt (A3), P.Ⅱ. silicate cement, fine sand and some additive. To obtain the effect of rainwater, dynamic load and temperature variation on the degradation and invalidation mechanism of SL mortar, the major experiments and conclusions are as follows:(1) The simulated test result of high-low temperature cycling on superposed specimen of SL mortar layer bond with concrete lay shows that under a certain high-low temperature cycling, surface crack in SL mortar and interfacial opening gaps are occurred, as well as interfacial bonding strength of superposed specimen decreases. It is indicated that temperature variation is the primary cause of interfacial opening gaps in superposed specimen. Because SL mortar thermal behavior is obviously differeent from concrete due to asphalt material characteristic. SL mortar has higher thermal deformation dependent on time and temperature, and that of concrete is lower. Under alternate temperature variation, concrete layer has constraint effect to SL mortar layer leading to reciprocating compressive or tensile stress. So some degradation phenomena appear including cracks on SL mortar surface, interfacial adhesive strength dropping and interfacial debonding and opening gaps. Hence, it is the two primary reasons for degradation and invalidation of SL mortar that environment temperature variation and thermal behavior differences between SL mortar and concrete material.(2) The absoption of SL mortar was studied by contact angle test and capillary absorption test. Results show that the contact angle of SL mortar former surface is less than90°, increasing with increase of A/C, which presents some degree hydrophilicity of SL mortar. Besides, SL mortar has considerable capillary absorption and per area mass of capillary absorption of SL mortar and t1/2demonstrates linear correlation. Its capillary absorption velocity depends on emulsified asphalt type, A/C, capillary porosity and capillary pore characteristic etc. The capillary absorption velocity decreases with increase of A/C, decrease of capillary porosity and increase of capillary pore tortuous. With the same proportion, the capillary absorption velocity of Al mortar specimen is higher than that of A3mortar specimen. It is analysed that there is lot of condensate of asphalt particles and capillary pores distributing inside hardened SL mortar. The matter of capillary pore wall is rich asphalt membrane, on which emulsifier molecular layer with hydrophobic group toward asphalt and hydrophibic group outside orienting. Surface wettability effect of emulsifier molecular leads to certain hydrophilicity of capillary pore wall, and easily transportation of water into SL mortar through capillary pores.(3)The static compression absorption test indicates that the static compression absorption velocity is higher, and an obvious inflection point exists in per area mass of static compressive absorption and t1/2relation curve. The compressive absorption velocity before the inflection point is hundreds times more than capillary absorption velocity, and the one after that are orders of magnitude greater. No matter before and after the inflection point, under the same condition, the static compression absorption velocity of the3type SL mortar are all relation to A/C and asphalt type. Due to the static compression quickens the compressive absorption velocity and drives water intrude into asphalt-cement interface and asphalt-sand interface. The interface number increases with the increase of A/C. Asphalt type plays effect on the interface number and interface adhesion strength, which results in the permeability-resistance decreases with increase of A/C. With the same proportion, the compressive absorption velocity order is A1>A3>A2, and the anti-permeability time order is A2>A3>A1.(4) The experiment results from influence of water on static mechanical properties demonstrates that the compressive strength and elastic modulus of hardened SL mortar decreases with increase of saturation, and the maximum reducing degree of compressive strength is up to40%. On account of water invading into organic-inorganic interface, the hardened SL mortar is weakened, the degree of which is correlation to A/C and the type of emulsified asphalt. The greater A/C of a mortar specimen is, the more reducing degree of its mechanical properties and the worse its water resistance are. With the same proportion, the water resistance of SL mortar with A2asphalt emulsion occupies first, then anion emulsified asphalt of A3comes and finally cation asphalt emulsion of A1takes place. So, the water resistance of SL mortar efficiently improves by advancing prevention interface from water intruding.(5) Fatigue experiment results of reference specimen and various saturation specimen show that the ultimate fatigue strength of suction specimens badly decreases, with increase of saturation. Vertical fatigue cracks can appear in reference specimen meaning splitting failure, but sloping cracks appear in most various saturation specimens meaning shear failure. Results obtained from hydrodynamic fatigue testing indicate that water detained on SL mortar surface will produce hydraulic fracture effect under alternate load of high frequency, which makes cracks quickly emerge and movement in the tips of pores or gaps. So under water-dynamic load coupling effect, the ultimate fatigue strength notably reduce and harden SL mortar damage.In conclusion, both environment temperature variation and thermal behavior differences between SL mortar and concrete are the primary reason to cause interfacial opening gaps and crack. When rainwater penetrates into SL mortar meanwhile exists on its surface, excess pore pressure of capillary water and hydraulic fracture of high velocity flow result in premature degradation and invalidation of SL mortar under alternate load of passenger train.更多还原