Performance of RAP in the system of cold inplace recycling of asphalt pavement

The property of reclaimed asphalt pavement(RAP) mixture will be affected mainly by composition of old asphalt/soil and cement content in CIR system. We studied the relationship between A/S and cementitious materials. It showed that if there was no soil in RAP, the unconfined compressive strength was only from 0.18 MPa to 1.07 MPa even if adding cement was from 2% to 6%, and RAP samples collapsed during conserving in water. The optimum water content rose from 6.5% to 11% with the declining of A/S from S=0 to A/S=1/5. Five RAP samples all got the maximum compressive strength when A/S=5/5, and the maximum compressive strength of the samples adding 6% cement was 3.17 MPa. It showed that the capacity of RAP was not only affected by A/S, but also by the content of cement. The dynamic modulus of RAP will increase with the rise of loading frequency and decrease with the temperature rising. SEM test showed that C-S-H interlacing formed the netted structure, and it enwrapped the aggregate and improved the strength of RAP.     

The influence of mineral admixtures on bending strength of mortar on the premise of equal compressive strength

The influence of mineral admixtures on bending strength of mortar on the premise of equal compressive strength was investigated. Three mineral admixtures (fly ash, ground granulated blast-furnace slag and steel slag) were used. The adding amount of mineral admixture in this study ranges from 22.5% to 60%, and the water-to-binder ratio ranges from 0.34 to 0.50. With equal compressive strength, different mortars can be arranged in such a descending order with their bending strength: cement-fly ash mortar, cement mortar, cement-GGBS mortar, and cement-steel slag mortar. With the same compressive strength, the higher the steel slag content and water-to-binder ratio, the lower the bending strength of mortars. However, the effect of mineral mixture content and water-to-binder ratio on the bending strength of cement-fly ash mortar and cement-GGBS mortar is far inconspicuous.     

沥青道路冷再生系统中水泥基胶结效应

设定不同配比的再生沥青混合料（RAP）和不同水泥掺量,通过标准击实、无侧限抗压强度、水稳定性、模量性能以及SEM测试,研究了水泥在RAP中的胶结效应。结果表明：RAP中沥青含量与稳定土的质量比（A／s）为0．4时,随着水泥掺量的增大,RAP的最大干密度从1．91g／cm。增加到2．00g／cm^3。水泥掺量一定时,随着废旧沥青含量的增加,RAP的最大干密度随随之增大;掺6％水泥的RAP无侧限抗压强度从1．48MPa增加到2．63MPa,随之减小到2．28MPa。使用的材料体系中,A／S=0．4,掺6％水泥,用水量9．5％时,再生料获得最好性能。试件浸水后抗压强度普遍降低,但与干燥试件无侧限抗压强度变化趋势一致。对RAP的模量试验表明高温状态下RAP混合料的路用性能最差。SEM测试表明：水泥的水化使得混合料中有针状钙矾石和纤维状C—S—H凝胶相互交织搭接,形成网络结构,将集料颗粒包裹起来,这是RAP产生强度的主要因素。     

改性再生骨料对自密实混凝土性能的影响

为提高再生骨料的性能,使之适用于自密实混凝土,使用4种强化手段对简单破碎后的两种来源再生骨料进行改性处理,研究其对新配RA-SCC工作性能和硬化后物理力学等性能的影响.结果发现:骨料来源和原生混凝土强度对再生骨料的品质有较大影响,而经过改性处理以后,不同来源的再生骨料品质都有所提升,所制成的RA-SCC性能差异变小;裹浆法以及水玻璃浸泡的方法能够较大程度地改善新拌RA-SCC的自密实性能;高温煅烧法、酸性溶液浸泡法、水玻璃分散技术可使硬化后的RA-SCC内部结构更加致密,从而明显改善了RA-SCC的抗拉强度、抗干燥收缩性能和抗冻性能,但大部分骨料增强技术对RA-SCC的抗压强度和弹性模量的影响较小.     

Early age properties of cementitious materials by electrical resistivity measurement

Three cement pastes were prepared with the fixed water-binder ratio and different fly ash contents. The compression test and electrical resistivity measurement of the paste mixes were conducted during 48 h. The changes of the CH content and the non-evaporable water content in the cement-fly ash hydration systems with time were obtained by the thermal gravimetric analysis. The experimental results show that dilution effect of fly ash as micro-filler is dominant mechanism before 48 h, which appears to decrease in the CH content and the non-evaporable water content, also in compressive strength and electrical resistivity, with the increase of fly ash replacement. The relationships between CH content, non-evaporable water content and electrical resistivity show that electrical resistivity can be the indicators of hydration products CH and non-evaporable water. The correlation of the compressive strength f _c and the electrical resistivity ρ can be obtained as f _c =8.3429 ρ = 6.7088 for the period of 48 h. The early age compressive strength can then be predicted by electrical resistivity measurement.     

Experimental research on inorganic solidified foam for sealing air leakage in coal mines

In order to efficiently seal air leakages and control spontaneous combustion of coal, solidified foam was developed by adding a certain compound additive to fly coal ash and cement as the main materials. It was prepared basing on the foaming characteristic through physical and mechanical system. We studied the effects of the different types of foaming agents, the mass ratio of cement to fly ash, and the mass ratio of solid to water and content of cellulose on the performance of solidified foam. The results show that when adding the composite protein, surfactant and cellulose foaming agents. The cement-fly ash ratio of 0.75:1, the water solid ratio as large as 2:1, and the solidified foam with high properties and density of only 516 kg/m³ and compressive strength of up to 12.68 MPa were prepared. But the initial setting time, identity and compressive strength may be changed by varying the water solid ratio and/or the additives. We theoretically analyzed the influence mechanism of foam density, compressive strength and water solid ratio. The solidified foam is especially suitable for sealing surface leakage channels and filling the goaf with a wide application prospects.     

阻燃剂对SBS改性沥青混合料路用性能影响

采用阻燃剂与SBS改性沥青复合制备了阻燃SBS改性沥青,测试了不同阻燃剂掺量下SBS改性沥青的阻燃性能和物理性能,研究了阻燃剂掺量对SMA沥青混合料路用性能的影响。结果表明:阻燃剂可显著提高SBS改性沥青的阻燃性,在阻燃剂掺量为8%时,改性沥青的氧指数可达到24.5%;阻燃剂的加入,增大了改性沥青的粘度,导致SMA沥青混合料空隙率增大,降低了沥青混合料的马歇尔稳定度,浸水残留稳定度比和冻融劈裂强度比也减小,但车辙动稳定度提高。     

混凝土修补砂浆力学性能的研究

本文通过正交试验,对添加可再分散乳胶粉、高效减水剂、硅灰和膨胀剂的聚合物砂浆的抗压强度及抗拉强度进行了测试．经结果分析,得到各种外加剂掺量对聚合物砂浆力学性能影响的规律,并取得最佳配比．     

粉煤灰混合料的力学特性

以细磨粉煤灰、水泥和粉细沙为主要材料组成混合料,采用正交试验方法,研究胶沙比、灰胶比和龄期对混合料的抗压强度和抗拉强度等力学性能的影响.研究表明,灰胶比对混合料的抗拉强度有显著影响;其次是龄期和胶沙比,但二者影响不显著.各因素对粉煤灰混合料抗压强度的影响程度按自大到小的顺序依次为胶沙比、灰胶比和龄期,但均无显著影响.采用低胶沙比和灰胶比组合确定混合料的配合比,既可满足强度要求,又能达到经济性目的.     

承重粉煤灰砖材料配合比及其力学性能的研究

用湿排粉煤灰、水泥、骨料等材料,适当加入外加剂和激发剂以激发粉煤灰的活性,采用模压成型,自然养护制成双免粉煤灰砖,测定粉煤灰砖的抗压强度等各项指标.通过调整粉煤灰砖各材料的掺量,利用正交设计的方法,共进行了9组计81个不同配合比的试件和试块的物理和力学性能试验,通过实验,找出了各种材料配合比与粉煤灰砖抗压强度的关系,得到了各项指标均达到或超过目前粘土砖的模压成型、自然养护的粉煤灰砖最佳配比.     

高温作用对大掺量粉煤灰混凝土力学性能影响

研究了高温作用对大掺量粉煤灰混凝土(HFCC)立方体力学性能的影响,探讨了不同加热温度、不同粉煤灰掺量与HFCC残余强度的关系.将粉煤灰掺量30%、40%和50%的混凝土立方体试块加热至250,450,550和650℃进行强度测试,并与素混凝土(不掺粉煤灰)试块进行对比.研究结果表明,随着温度升高,HFCC残余抗压、劈裂抗拉强度均出现明显退化,劈裂抗拉强度退化尤为明显;随着粉煤灰的掺入,粉煤灰掺量对强度退化率的影响具有复杂性:高温后HFCC抗压强度退化率均低于普通混凝土强度退化率;劈裂抗拉强度退化率除粉煤灰掺量30%外均低于普通混凝土退化率.在试验基础上建立HFCC高温后立方体残余抗压强度、残余劈裂抗拉强度与温度、粉煤灰掺量的定量关系,为高温后HFCC材料强度评估及修复提供依据.     

稻草纤维增强泡沫混凝土物理力学性能试验研究

为了研究稻草纤维增强泡沫混凝土的性能,以普通硅酸盐水泥为主要胶凝材料,硅灰、偏高岭土和粉煤灰为辅助胶凝材料,稻草纤维为增强材料,采用物理发泡法制备纤维增强泡沫混凝土;通过全因子试验,研究在不同水胶比和发泡剂掺量下,稻草纤维掺量对泡沫混凝土的密度、吸水率、抗压强度、抗折强度、劈裂抗拉强度和抗冻性能的影响。结果表明：对于不同水胶比和发泡剂掺量,泡沫混凝土的密度、抗压强度和劈裂抗拉强度均随纤维掺量的增加呈现出先增加后降低的变化规律;抗压强度随密度增加呈幂函数增加关系;劈裂抗拉强度随抗压强度的增加呈指数函数增加关系;当水胶比为0.45时,抗折强度随纤维掺量的增加先增加后降低,当水胶比为0.50时,抗折强度随纤维掺量的增加而增加;纤维的掺入增大了泡沫混凝土的泡孔尺寸和吸水率,降低了其抗冻性能。     

酸性水环境下桥梁桩基混凝土的配制与耐久性研究

针对酸性水环境下桥梁桩基混凝土的配制,研究了矿物掺合料、水胶比以及侵蚀溶液pH值对混凝土抗酸侵蚀性能的影响。混凝土的粉煤灰掺量从20%～50%变化,矿粉掺量从35%～65%变化,水胶比分别取0.35、0.39、0.43,酸性水侵蚀环境通过pH值分别为1、2、4的硫酸溶液模拟,抗酸性能通过测定1年龄期的混凝土抗压强度变化率表征。结果表明,降低水胶比有利于提高混凝土的抗酸侵蚀性能;矿物掺合料对混凝土耐酸性能的改善作用与其品种、掺量及模拟侵蚀溶液的pH值大小有关。大掺量粉煤灰混凝土比大掺量矿渣粉混凝土具有更好的耐酸性能。     

改性多孔沥青混合料水稳定性与损伤规律

为了提高季冻区多孔沥青路面的使用质量、减轻路面冻融损伤,采用玻璃纤维、硅藻土与沥青路面旧料以改善多孔沥青混合料性能。分析不同材料掺量的多孔沥青混合料在冻融循环下的抗压强度、空隙率及应变变化,并考虑不同材料与不同材料掺量对多孔沥青混合料水稳定性的影响;基于损伤力学理论以抗压强度为指标表示强度率,研究改性多孔沥青混合料的冻融损伤演化规律;基于CT无损检测与数字图像处理技术,分析玻璃纤维多孔沥青混合料冻融前后空隙数量与空隙面积的变化规律。结果表明：混合料抗压强度随冻融循环次数的增加而降低,而空隙率与应变呈上升趋势;具有玻璃纤维掺量0.7%、沥青路面旧料掺量15%、硅藻土掺量25%和掺量15%沥青路面旧料及20%硅藻土的4种多孔沥青混合料水稳定性能最好,其中玻璃纤维的改性效果最佳;掺入玻璃纤维、15%掺量硅藻土与15%掺量沥青路面旧料能减轻多孔沥青混合料的冻融损伤,但硅藻土再生多孔沥青混合料损伤程度均较大,损伤前期强度较高,更适用于短时冻土区;与硅藻土再生多孔沥青混合料相比,玻璃纤维多孔沥青混合料、再生多孔沥青混合料与硅藻土多孔沥青混合料经历了长时间的快速损伤期、短时间的损伤稳定期与损伤发展期;玻璃纤维掺量较低的试样空隙数量增加,平均单个空隙面积减小,而掺量较高的试样表现相反。     

Evaluation on Moisture Resistance of Asphalt Mixture with Active Mineral Powder

A new type of filler named 'active mineral powder' (AMP) was introduced and applied in asphalt mixture in order to improve the adhesive property of gneiss or granite aggregates and asphalt. The treated mixtures contained 2% AMP by weight of the total aggregates as filler. The moisture stabilization properties of various combined mixtures were analyzed using the adhesive test,Marshall stability and indirect tensile strength tests. Five frost-thaw cycles test was conducted to further investigate the effect of active filler on asphalt mixtures in the indirect tensile strength experiment. The results show that active filler improves the moisture stability of mixtures with gneiss and granite. The active mechanism of AMP was also discussed in this paper.     

SBS改性沥青厂拌热再生混合料力学性能分析

针对SBS改性沥青厂拌热再生混合料,通过测量不同RAP用量及旧料加热温度下的抗压强度、劈裂强度,对再生混合料的力学性能变化规律进行了分析.试验结果表明：RAP含量在20%以内时,再生混合料性能与新料性能并无明显差别;随着RAP比例增加,再生混合料强度逐渐提高.当温度条件满足要求时,可以适当提高RAP用量.     

中热水泥-粉煤灰体系的贫钙问题

为了提高水工大体积混凝土中的粉煤灰掺量,研究了中热水泥 粉煤灰体系的贫钙问题.通过抗折和抗压强度试验研究了粉煤灰掺量对中热水泥-粉煤灰体系的强度的影响，通过水化率测定和XRD分析研究了中热水泥-粉煤灰体系的水化特性.结果表明：在强度实验中，粉煤灰存在一个允许掺量，这个掺量随着养护龄期的增长而提高0.3 d和28 d时，允许掺量小于10%， 而在3.5a时，允许掺量高达65%以上；体系中粉煤灰的水化速率很慢，粉煤灰明显降低了体系中的Ca(OH)₂，随着粉煤灰掺量增加和龄期延长，Ca(OH)₂减少.在中热水泥-粉煤灰体系中并不存在贫钙问题.     

刺槐豆胶改良黏土强度抗压抗拉力学特性试验研究

为了研究刺槐豆胶改良黏土强度的效果,对不同养护龄期、刺槐豆胶掺量的改良黏土分别进行无侧限抗压强度试验以及抗拉试验研究。结果表明:刺槐豆胶的掺入可以显著改善黏土的抗压和抗拉性能。当养护龄期一定时,随着刺槐豆胶掺量的增加,改良黏土的抗压和抗拉强度均呈增长趋势,通过对比可知,刺槐豆胶的最优掺量为2%,试样的抗压和抗拉强度的最大值分别提升至425.74及234.61 kPa,与素土相比均提高约1.8倍;当刺槐豆胶掺量一定时,养护龄期对改良黏土的抗压、抗拉强度也有一定的影响。在刺槐豆胶掺量相同的条件下,养护龄期为7 d时,试样抗压、抗拉强度提升量最大,最大提升量分别为68.12 和34.39 kPa。刺槐豆胶在土体表层形成一层胶质薄膜,并利用自身延展性填充土颗粒间孔隙,改善了土体的粒间结构,增强土体的稳定性,从而提升黏土的强度特性。随着养护龄期的增加,胶质薄膜逐渐收缩,使土体颗粒排列更加紧密,进而提高改良黏土体的无侧限抗压强度及抗拉强度。     

Compressive Strength, Pore Size Distribution and Chloride-ion Penetration of Recycled Aggregate Concrete Incorporating Class-F Fly Ash

The effects of fly ash on the compressive strength, pore size distribution and chloride-ion penetration of recycled aggregate concrete were investigated. Two series of concrete mb：tures were prepared. The concrete mixtures in series I had a water-to-binder ratio and a cement content of 0.55 and 410 kg/ m^3 , respectively. The concrete rnixtures in series II had a water-to-binder ratio and a cement content of 0.45 and 400 kg/ ml respectively. Recycled aggregate was ased as 20% , 50% , and 100% replacements of natural coarse aggregate in the concrete mixtures in both series. In cutdition, fly ash was used as 0% , 25% and 35% by weight replacements of cement. The results show that the compressive strengths of the concrete decreased as the recycled aggregate and the fly ash contents increased. The total porosity and average porosity diameter of the concrete increased us the recycled aggregate content increased. Furtherrruore , an increase in the recycled aggregate content decreased the resistance to chloride ion penetration. Nevertheless, the replacement of cement by 25% fly ush improved the resistance to chloride ion penetration and pore diameters and reduced the total porosity of the recycled aggregate concrete.     

INFLUENCE OF MINERAL ADMIXTURES ON MECHANICAL PROPERTIES OF HIGH-PERFORMANCE CONCRETE

The improvements of the mechanical properties, including bulk density of fresh mixtures, elastic modulus, and compressive strengths of four high - performance concrete mixtures, made with the addition of fly ash, refined ground blast - furnace microslag(microslag) and silica fume are studied. The concrete mixtures were determined based on the dispersion testing results. The study indicates that the elastic modulus at 28 and 91 days, and compressive strengths of the concretes are improved a lot when fly ash and microslag by 25 percent by weight of ce-