级配碎石压实特性的研究

级配碎石的研究和应用,主要在于通过取得高质量的碎石,获得高密度的良好级配以及良好的施工压实手段来提高级配碎石的强度和稳定性。分析了级配碎石物理性能指标和影响级配碎石性能的因素,从材料选择、级配设计、不同机械组合及碾压方式方面入手,研究了级配碎石施工的压实特性和提高压实强度的方法,并通过具体试验路段进行了验证,总结了级配碎石的压实特性。     

沥青混合料压实特性影响因素研究

压实是沥青路面生产建设中的关键环节,为了研究沥青混合料压实特性及其影响因素,文中结合沥青混合料旋转压实(SGC)曲线,分析了沥青混合料压实特征不同参数(压实能量指数CEI,混合料旋转压实曲线两个平均斜率K1、K2)的物理意义,并且进一步研究了混合料压实特征参数与沥青混合料材料组成(级配、沥青用量)及成型温度之间的关系。研究发现,中值级配的混合料在施工过程中较其它级配更容易被压实,而随着油石比的增加,混合料的可压实性表现出线性增长的趋势,另外,研究也发现混合料只有在合适的温度范围才有较好的可压实性,并非温度越高越好。     

沥青混合料旋转压实效果的数字图像分析

针对旋转压实法，利用不同压实功作用成型试件模拟压实过程，采用数字图像处理技术，研究沥青混合料的压实成型特性，提出了以集料颗粒的取向特性描述沥青混合料的稳定性，以集料颗粒的分布特性来反映混合料的密实程度，定义了集料颗粒主轴方向、沥青砂胶膜厚及颗粒面积比等参数来进行评价。实验表明效果良好。     

不同成型方法级配碎石的抗变形性能

为研究不同成型方法对不同级配的级配碎石抗变形性能的影响,选取了振动压实法和静压法2种成型方法,悬浮密实结构(GD)和多级嵌挤骨架密实结构(TK)2种不同级配的级配碎石,利用回弹模量表征级配碎石的弹性变形特性,提出了稳定指数(SI)来评价级配碎石的塑性变形特性.采用2种方法成型试件后,在最佳含水量下测定其回弹模量;借鉴沥青混合料车辙试验来研究级配碎石的抗塑性变形能力,根据最大干密度和最佳含水量,按98%的压实度,利用振动压实法和静压法成型级配碎石试件,测定试件含水量为W_0、0.5 W_0和0的动稳定度.研究发现,不同成型方法下级配碎石的弹、塑性变形相差较大,且振动压实法级配碎石回弹模量为静压成型法的1.56~1.77倍,稳定指数为1.52~1.56倍.     

压实填土随浸水时间增长强度降低规律研究

水利、交通、建筑等土木工程建设中,压实填土是经常遇到的建设内容,压实填土遇降雨、水浸时,含水率逐渐增大,颗粒间结合水逐渐增厚,结晶盐类逐渐溶解,压实填土粘聚力逐渐减小,土体强度逐渐降低,严重时导致工程破坏.使用不同级配土体,按各自最优含水率击实,制备多组试样,分批次在不同条件下浸水,测定土体强度随浸水时间的变化数值,分析其变化规律、土体级配与土体强度随浸水时间降低的关系、产生原因,给出了较好的压实土种类,为水利、交通、建筑工程压实填土浸水后预防工程事故提供参考.     

级配和压实次数对沥青混合料性能的影响分析

以混合料的高温动稳定度、低温小梁弯曲应变、浸水马歇尔残留稳定度、劈裂强度、冻融劈裂强度以及AASH-TO T283劈裂强度比为评价指标,探讨集料级配和旋转压实次数对沥青混合料路用性能的影响。研究选取Sup13、Sup20粗、Sup20细3种级配和100次、125次的压实次数,用Tukey-Kramer方法对级配和设计旋转压实次数等水平的试验结果进行均值比较。结果表明:增加设计压实次数可以显著提高沥青混合料的高温动稳定度、低温弯曲破坏应变、劈裂强度和浸水劈裂强度,对混合料的水稳定性提高不显著。在相同设计压实次数下,粗级配相比细级配具有更显著的高温稳定性、低温抗裂性、劈裂强度和浸水劈裂强度,水稳定性相当。在混合料设计时,应优先考虑粗级配进行混合料设计。     

SAMPAVE混合料压实特性研究

SAMPAVE混合料具有抗裂、防渗、粘结等特性,为了研究其压实特性,采用旋转压实(SGC)法及马歇尔方法对SAMPAVE混合料级配和体积参数进行了系统研究。分析了SGC曲线,得出宜采用旋转压实50次进行试验分析,并分别推荐了SGC法和马歇尔法体积参数的控制指标。进行了SGC法和马歇尔法各体积参数的对比分析,得出将马歇尔法设计的最佳用量下调0.2%,即可得到工程所需的最佳沥青用量。     

沥青路面现场压实细观特性分析

为研究沥青路面现场压实细观特性,基于离散元PFC3D(particle flow code in 3-dimensions)根据均布荷载-时间等效原则建立了考虑集料形态特征和温度影响的三维沥青路面压实模型,通过动态模量试验利用时间-温度等效原理确定了热态沥青混合料的细观参数,分析压实过程中路面厚度、集料运动、接触力及能量演化机制等.结果表明:沥青路面位移表现出非连续和不对称性,集料的运动位移、应力与压实荷位及其方向有关;压实区域与非压实区域集料的运动规律不同,在压实区域与非压实区域的过渡带集料运动方向形成了类似"涡流"状结构;压实区域材料内部以接触压力为主;外力做功和应变能在压实初期增加速率较大,后期逐渐变小;动能在初始阶段因压实应力未稳定导致集料运动速度较大发生异常,当进入稳定阶段后,动能减小.该研究结果与前期成果基本一致,表明采用离散元法建立的路面压实模型分析沥青路面压实过程的细观行为是合理可行的,离散元法是研究沥青路面细观特征的重要工具.     

关键筛孔对多碎石沥青混凝土压实功的影响分析

针对多碎石沥青混凝土SAC-20,统计分析27个试验级配的压实功与关键筛孔通过率关系后,得出1.18mm通过率对压实功影响最大,0.075mm通过率居其次,细料级配及含量(包括填料)极大地着影响压实功。平均压实次数随1.18mm和0.6mm通过率的增加都有减小的趋势,若两个筛孔通过率进一步增大而进入Superpave相应细集料级配限制区时,压实次数应更少,混合料更容易压实压密,将对抗车辙性能不利,禁区具有一定的合理性,在级配设计时应尽可能保证细集料关键筛孔通过率在限制区下方。     

压实钢渣-膨润土覆盖防渗材料试验研究

为了实现钢渣在工业固废堆场覆盖层中的应用,采用膨润土改良钢渣的防渗性.通过柔性壁渗透试验,测量压实钢渣-膨润土混合材料的饱和渗透系数k_s.结合压汞法、X射线衍射和扫描电镜技术,分别观察试样的孔隙分布、蒙脱石矿物层间距和矿物形态,从微观尺度分析k_s的影响机理.提出满足防渗层渗透性要求(k_s≤10-9 m/s)的配方与制备方法.结果表明,膨润土预水化处理使试样的k_s降低至未处理试样的1/2.改良钢渣级配后,钢渣颗粒间的大孔隙比例降低,使试样的k_s降低至不良级配试样的1/5.钢渣掺和怀俄明膨润土试样的k_s和孔隙分布与掺和钠化钙基膨润土试样的相似.钢渣的高盐浸出液使蒙脱石层间距增大、结合水减少,对膨润土的渗透溶胀起抑制作用;钢渣水洗处理可以缓解该抑制作用,减少蒙脱石团簇的产生,使试样的k_s降低至未处理试样的1/10.     

级配碎石混合料及其基层的抗剪性能

为了研究级配碎石基层在路面结构中能否发生剪切破坏,对级配碎石基层材料抗剪强度及在路面结构中的剪应力进行了对比研究;应用高精度静三轴仪对选定的级配碎石进行振动成型和击实成型的抗剪强度研究,揭示不同成型方法对抗剪强度的影响,采用有限元分析典型路面结构在标准荷载作用下剪应力的大小,明确级配碎石基层发生剪切破坏的可能性;三轴试验表明振动成型级配碎石过渡层的抗剪强度为0.17 MPa,击实成型的为0.14 MPa,振动成型试样比击实的抗剪强度提高20%;剪应力分析表明:水平荷载在级配碎石基层中产生的最大剪应力在0.04~0.05 MPa;级配碎石的抗剪强度是最大结构剪应力的3.5倍,级配碎石基层在高等级沥青路面结构中产生剪切破坏的可能性很小.     

Densification mechanism of warm compaction and powder mixture designing rules

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The compaction characteristics of hot mixed asphalt mixtures

The quality of compaction is important to the performance of hot mixed asphalt(HMA) pavement. Most premature failures of asphalt pavement are concerned with poor compaction. Compaction characteristic of HMA mixtures were studied. Compaction tests were done with typical widely used HMA mixtures, including dense gradation asphalt mixtures with different nominal maximum aggregate size(AC13,AC20,AC25), and mixtures with different gradation(AC13, SMA13,Sup13 and OGFC13). HMA mixtures were sampled at different compaction temperature and Marshall blow numbers, varying between 60 and 175 ℃ and between 15 and 75 lows, respectively. The compaction characteristics of these mixtures were evaluated. The results showed that the Marshall stability and volumetric properties were significantly affected by the compaction temperature. Mixtures with the same NMAS but different type of gradation need different compaction energy to get the designed density.     

Degradation behavior of aggregate skeleton in stone matrix asphalt mixture

The degradation behavior of aggregate skeleton in stone matrix asphalt mixture was investigated based on theoretical analysis, laboratory test and field materials evaluation. A stress-transfer model was established to provide the fundamental understanding of the stress distribution and degradation mechanism of stone matrix asphalt (SMA) aggregate skeleton. Based on the theoretical analysis, crushing test and superpave gyratory compactor (SGC) test were used to evaluate the degradation behavior of aggregate skeleton of SMA. To verify the laboratory test results, gradation analysis was also conducted for the field materials extracted from SMA pavements after long-time service. The results indicate that the degradation of SMA aggregate skeleton is not random but has fixed internal trend and mechanism. Special rule is found for the graded fine aggregates generated from coarse aggregate breakdown and the variation of 4.75 mm aggregate is found to play a key role in the graded aggregates to form well-balanced skeleton to bear external loading. The variation of 4.75 mm aggregate together with the breakdown ratio of aggregate gradation can be used to characterize the degradation behavior of aggregate skeleton. The crushing test and SGC test are proved to be promising in estimating the degradation behavior of SMA skeleton.     

The Low-Voltage Electromagnetic Compaction of Powder Materials

The low-voltage-electromagnetic forming was applied to powder compaction,A series of experiments was performed to compact aluminum,copper and tin powders in an indierect working way ,Haing compacted high-density powder parts successfully ,the authors analyzed the the effects of voltage,capacitance ,friction,compaction times,powder size and other factors on the densitis of compacted specimens,The experimental results show that lower voltage but larger capacitance are benficial to increasing the density and homogeneity of the compacted specimens,if the loading velocity and discarging energy are suitable,The higher the voltage,the greater the percentage of energy consumed by friction ,If the equipment energy is liminted,the iterative compction is an efficinet way to manufacture homogeneous and high-density powder parts.     

辉绿岩在高速公路沥青路面表面层的应用

进行了粗、细集料不同类型组合、不同成型压力、不同旋转压实次数比较等试验,研究了辉绿岩作为高速公路沥青表面层的可行性.     

掺再生集料的水泥稳定碎石路面基层施工与应用

对废弃混凝土进行循环再利用,可以减小废弃混凝土对城市环境带来的负担,是发展绿色混凝土的主要措施之一.再生集料与天然集料相比有着其特殊的物理力学特性.针对由废弃水泥路面混凝土破碎而成的再生集料用于水泥稳定碎石基层,对其生产、施工、养护过程进行了分析.对于再生集料外观不平整、比表面积大的特性,采用振动压实的工艺能取得比较好的摊铺效果;但是碾压遍数、含水量、养护等方面的差异对水泥稳定碎石的影响非常大;合理的级配和水泥剂量对水泥稳定碎石抗裂性能有较大的影响.     

Reducing the Compaction Segregation of Hot Mix Asphalt

This paper presented the methods of reducing the compaction segregation of asphalt layer by improving the operating characteristics of roller and paver. The fit formula, which expresses the compaction rule of the paving layer after passing different rolling passes of the steel wheel roller, was also put forward. The measured results of test road show that when some technical methods are adopted, the compaction segregation can be controlled.     

Vibration compaction characteristics of rock filling embankment

The dynamic model experiment of the rock filling embankment was carried out to investigate the vibration compaction mechanism. The rock filling materials were compacted by the plate-vibrated compactor, and the characteristics of the rock filling materials, such as settlement, pressure change and response waveform, were measured by the dynamic earth pressure gauge and accelerometer. Moreover, a new method for detecting the compactness of the rock filling embankment was proposed based on the maximum dry density and modulus of deformation. The results show that the process of vibration compaction includes compact, elastic deformation and loose stages, and the vibratory pressure transfers to the surroundings from the vibration center in non-linear rule. Furthermore, the test results obtained by the present method are basically in agreement with those obtained by the traditional method, and the maximum relative error between them is about 0.5%.