Laboratory fatigue models for recycled mixes with bitumen emulsion and cement

The role of cement in cold recycled mixes with bitumen emulsion (CRME) have been extensively investigated. In most cases it is affirmed that cement will stiffen the mix and will decrease its moisture sensivity and temperature susceptibility and will increase its resistance against permanent deformation. Nevertheless the effect of cement on the fatigue properties of these mixes is not clearly understood. Because of crystalline nature of the pozzolanic bonds, cemented materials tend to be brittle which can reduce the flexibility and fatigue life of recycled mixes. In this research in order to develope fatigue models for these mixes, extensive indirect tensile fatigue and resilient modulus tests were performed at different temperatures (varying from −10 to 25 °C) and curing times (varying from 7 to 120 days). Test results showed that the effects of cement on fatigue life of mixes is related to the initial strain level assumed in testing. At 300 microstrain level and above, the addition of cement caused a reduction in fatigue life, whereas below 300 microstrain the reverse was true. Finally based on laboratory testing results distinct models were established for different boundary strain levels.     

冷再生混合料疲劳性能的室内试验研究

对两种级配的泡沫沥青和乳化沥青冷再生混合料的疲劳性能展开室内试验研究,运用疲劳统计学原理对试验结果进行了分析,在此基础上得到了可靠的疲劳方程,并就冷再生混合料与热拌沥青混合料的疲劳性能进行了对比分析。     

A parametric study on the laboratory fatigue characteristics of recycled mixes

There are not enough information about the fatigue characteristics of cold recycled mixes with bitumen emulsion and cement. In this research with the purpose of studying the fatigue characteristics of these mixes and determining the effects of different parameters, several laboratory recycled specimens containing CSS-1h bitumen emulsion and two types of cements (type I and I (PM) pozzolanic cement) have been prepared and tested. The main laboratory tests consisted of resilient modulus and indirect tensile fatigue test. After curing specimens in laboratory conditions, specimens were tested at three different temperatures and curing times. For each recycled specimen, studied parameters consisted of cement type, cement content, test temperature and curing time. According to obtained results, by increasing cement content and decreasing temperature, the slope of fatigue line will be decreased but no considerable change in fatigue behavior was occurred upon increasing the curing time. Furthermore, in comparison with reference specimens (i.e. specimens with no cement) and type I cement specimens, I (PM) cement had the mean fatigue behavior. At low initial strain levels, the fatigue life of I (PM) cement specimens were more than reference specimens and less than type I cement, whereas at high initial strain levels, the fatigue life of I (PM) cement specimens were more than type I cement and less than the reference specimens.     

泡沫沥青冷再生混合料配合比设计浅谈

通过海南一小时交通圈西线高速公路改建工程所用泡沫沥青厂拌冷再生混合料的配合比设计的实例,根据室内试验,确定基质沥青的最佳发泡条件、混合料级配组成、最佳含水量、最佳泡沫沥青用量,最终确定泡沫沥青混合料最佳配合比。     

Effect of Portland cement and lime additives on properties of cold in-place recycled mixtures with asphalt emulsion

Due to lack of previous research on applying additives in Cold In-Place Recycling (CIR) mixes in this study, Portland cement and lime were used as additives. The Portland cement was introduced in powder form and lime was utilized as hydrated lime in powder form and lime slurry, and the effects of each additive on properties of CIR mixes has been evaluated. The results showed that both lime and Portland cement can increase Marshall stability, resilient modulus, tensile strength, resistance to moisture damage and resistance to permanent deformation of CIR mixes. Use of Portland cement and lime slurry had better results than hydrated lime but due to the difficulties in producing lime slurry in practice, the use of Portland cement is recommended.     

再生混凝土框架抗震性能的试验研究

在保持竖向荷载恒定的情况下,对3榀再生骨料掺量为30%、50%和100%的再生混凝土框架和1榀天然混凝土框架进行了水平低周反复荷载试验,研究了再生混凝土框架的破坏机制、承载力、滞回特性、延性、强度退化、刚度退化和耗能等性能,并和普通混凝土框架进行对比分析。试验发现再生混凝土框架为“强柱弱梁”的破坏类型,最大水平承载能力比普通混凝土框架低2.3%～15.7%,位移延性系数在3.91￣4.54之间,和天然混凝土框架相比耗能能力没有明显降低。试验结果表明再生混凝土框架具有良好的抗震性能,应用于工程实际是完全可行的。     

A model for resilient modulus determination of recycled mixes with bitumen emulsion and cement from ITS testing results

Typically, resilient modulus (M_r) of recycled mixes, containing bitumen emulsion and cement, will increase upon curing. Hence, assigning a design M_r for these mixes will be more complex than the case of conventional hot mixes. Furthermore, M_r testing facilities are not generally available in many project sites. Therefore, developing a model that could estimate M_r from ordinary testing methods would be quite appropriate. In this research, upon performing indirect tensile strength test (ITS) and determining M_r of specimens at different testing temperatures (−10, 5 and 25 °C) and curing times (7, 28 and 120 days), two models have been developed to estimate the M_r of recycled mixes with bitumen emulsion and two types of cements (type I and pozzolanic cement). The results showed that increased curing time and cement content and decreased testing temperature led to increased ITS and M_r values. For both tests the effect of temperature was more pronounced than two other parameters. The models were developed by two steps. First the relationship between ITS and M_r at similar testing conditions was determined for each cement type. This was done by a linear relationship. In the second step, the relationship was adjusted to consider the effects of temperature and curing time. Using the final model, M_r of studied mixes could be estimated from ITS testing results at similar or different testing conditions.     

高温作用对再生粗集料性能影响的试验研究

为了研究高温对再生粗集料性能的影响,将高温作用后的废弃混凝土经破碎、分解作为混凝土的再生粗集料,进行了一系列的试验研究。试验表明：作用温度对再生粗集料的吸水率、压碎指标有显著影响,而对其表观密度、堆积密度及空隙率等性能的影响不很显著,该研究结果对配制再生混凝土有一定的参考价值。     

钢筋-中高强度再生混凝土黏结滑移性能梁式试验研究

为研究钢筋与再生混凝土黏结滑移性能,进行了13个梁式试件的钢筋-中高强度再生混凝土黏结性能试验。研究了钢筋外形、锚固长度、混凝土强度、再生骨料取代率对钢筋-再生混凝土黏结滑移性能的影响。结果表明：再生粗骨料混凝土取代率为33%~66%、细骨料为天然砂时,钢筋-再生混凝土黏结强度与普通混凝土接近;再生粗骨料取代率100%、再生细骨料取代率50%以上时,钢筋-再生混凝土黏结性能明显退化;与普通混凝土相比,再生粗骨料混凝土的相对混凝土强度黏结效率系数有所提高;变形钢筋与再生混凝土的黏结强度明显好于光圆钢筋;钢筋与再生混凝土的黏结强度随钢筋相对锚固长度增大而减小;拟合所得的黏结-滑移本构模型,其计算值与试验值吻合良好。     

随机变幅疲劳荷载下预应力混凝土梁疲劳寿命的试验研究

基于实测的钢筋混凝土吊车梁疲劳荷载谱,经过适当的简化得到试验用随机变幅疲劳荷载谱,并通过MTS疲劳试验机实现了该随机变幅疲劳荷载谱作用下部分预应力混凝土梁的疲劳试验。试验结果表明,由随机变幅疲劳试验得出的构件疲劳寿命远低于由疲劳荷载上限值取为荷载谱均值的等幅疲劳试验得出的疲劳寿命,因此如果采用后者的试验结果去估算实际服役中的预应力混凝土构件的疲劳寿命是非常危险的。然后分别利用Miner准则、相对Miner准则和Corten-Dolan累积损伤准则对承受随机变幅疲劳荷载作用的试件疲劳寿命进行了估算。计算结果表明,改进的Corten-Dolan累积损伤准则精度最高,相对Miner准则也具有较高的精度,Miner准则的精度最低且偏于不安全。建议对预应力混凝土受弯构件进行随机变幅疲劳分析时采用改进的Corten-Dolan累积损伤准则或相对Miner准则。     

泡沫(乳化)沥青冷再生混合料力学性能的试验研究

研究了不同水泥剂量、不同养生条件和不同龄期对泡沫(乳化)沥青冷再生混合料劈裂强度和无侧限抗压强度的影响。研究表明,水泥含量对冷再生混合料的强度影响很大,直接影响冷再生混合料早期强度的形成;通过对比不同养生条件和不同龄期下冷再生混合料的强度发展规律,建立了室内养生条件与现场施工之间的关系。     

就地热再生沥青混合料疲劳寿命试验研究

通过马歇尔试验确定了施工现场取样就地热再生沥青混合料新旧料比为2:8的AC-13配合比.并测试不同温度、应变环境时的疲劳寿命.结果表明就地热再生沥青混合料的疲劳寿命较短,但仍具有良好的疲劳寿命,疲劳寿命与初始弹性模量和应变大小具有良好的双对数线性回归关系,并以此可建立三种沥青混合料的修正疲劳方程.     

泡沫热态稳定的探索性试验研究

通过观察在热油面上泡沫状态和油品温度的变化,研究了泡沫热态稳定性及泡沫性能对油温的影响因素。试验证明,油品温度决定泡沫的热态稳定性,泡沫在油面上稳定停留的临界油温为125 ℃;当油温＞135 ℃时,随着油温增加,泡沫消失速度越来越快。油温降速与油品温度、泡沫析液速度、油品黏度有关,而与发泡倍数无关。油温越高、泡沫析液速度越快、油品黏度越低,油品降温速度越快。     

自密实再生混凝土配合比设计及力学性能试验研究

按改进的全计算法,参考CCES 02-2004《自密实混凝土设计与施工指南》和CECS 203-2006《自密实混凝土应用技术规程》,对再生粗骨料与天然碎石C40自密实混凝土配合比进行了设计及相关性能试验研究.试验结果表明：自密实再生混凝土砂率宜控制在50％～ 55％之间,浆体体积宜为0.4 m3/ m3左右;再生粗骨料能够配制出符合CECS 203-2006《自密实混凝土应用技术规程》中新拌混凝土工作性能要求的自密实再生混凝土,其28天立方体抗压强度最高达52.3 MPa,轴心抗压强度最高达36.8 MPa;自密实再生混凝土的强度、弹性模量均低于天然碎石自密实混凝土.     

WEP改性泡沫沥青冷再生混合料的强度特性及耐久性

为提高泡沫沥青冷再生混合料的早期强度、抗松散性能、水稳定性和耐久性能,将水性环氧树脂(WEP)应用于泡沫沥青冷再生混合料,研究了WEP掺量对泡沫沥青冷再生混合料性能的影响,通过SEM分析了影响机理。结果表明,掺加WEP能显著提高泡沫沥青冷再生混合料的力学性能、水稳定性和抗疲劳耐久性能,同时降低疲劳寿命对应变水平的敏感性。WEP对泡沫沥青冷再生混合料的改性机理在于其界面增强作用、加箍锁作用及加筋阻裂作用。推荐泡沫沥青冷再生混合料中WEP的适宜掺量为2%~3%。     

透水混凝土物理力学性能试验研究

针对透水混凝土的抗压强度与抗折强度、劈裂强度之间的相关性,以及孔隙率对它们的影响和无砂透水混凝土与普通混凝土的收缩性能进行了试验研究;对透水混凝土与普通混凝土破坏的不同之处和对无砂透水混凝土与普通混凝土的收缩特性进行了分析。     

再生粗骨料取代率对混凝土基本性能的影响

系统研究了相同水灰比情况下再生粗骨料取代率对混凝土基本性能的影响。试验中再生粗骨料取代率分别为0，30％，50％，70％和100％，保持混凝土的水灰比不变。主要研究了再生粗骨料取代率对混凝土立方体坍落度、抗压强度、棱柱体抗压强度、峰值应变和泊松比、弹性模量、劈裂抗拉强度以及抗折强度的影响。试验结果表明，再生粗骨料取代率对上述各性能指标均有一定影响，但程度不同。同时发现，除抗折强度外，普通混凝土各基本力学性能指标问的关系均不适用各种再生骨料取代率混凝土。     

寒冷地区再生混凝土抗冻性能试验研究

再生混凝土的研究意义重大,其抗冻性则是影响其应用的重要指标.主要通过冻融循环试验研究了不同粗骨料取代率的再生混凝土的抗冻性,从冻融循环过程中混凝土试件的表面现象、质量损失及相对动弹模量3个方面进行阐述.     

再生砂水泥砂浆力学性能试验研究

通过测定再生砂水泥砂浆的胶砂流动度、抗压强度、抗折强度和韧性,探究了再生砂取代率及养护龄期对再生砂水泥砂浆力学性能的影响。研究结果表明：增大再生砂取代率,胶砂流动度会降低0.95%～10.00%,再生砂水泥砂浆的抗压强度、抗折强度整体表现为下降趋势,当取代率超过15%时,再生砂水泥砂浆的韧性会增加;增大养护龄期,再生砂水泥砂浆的抗压强度和抗折强度会增大,但韧性会减小。     

自密实再生混凝土柱轴压性能的试验研究

通过对两个自密实再生混凝土柱的轴压试验,记录了试件的荷载—变形曲线,通过理论计算与试验结果对比,分析了自密实再生混凝土柱的轴压性能和在工程中的适用性,研究表明:在柱尺寸、混凝土和钢筋强度相同的条件下,自密实再生混凝土柱轴压承载能力可以达到自密实普通混凝土柱的承载能力。