高性能混凝土制备及其耐久性性能的试验分析

为研制高性能沥青混凝土,以聚丙烯纤维和玄武岩纤维为掺入变量,测试沥青混凝土的7d及28d后的抗压强度和抗拉强度、冻融循环50次后的沥青混凝土抗压强度,并结合扫描电镜方法分析两种纤维对冻融循环后的沥青混凝土的影响。通过试验得出：随着纤维掺量的增加沥青混凝土的抗拉强度、抗压强度及冻融循环50次后的沥青混凝土抗压强度先增加而后逐渐降低。根据试验结果建议优先选用2%的玄武岩纤维或3%的聚丙烯纤维制备高性能沥青混凝土。     

玄武岩短切纤维对环氧沥青及其混合料性能的影响

为了将环氧沥青混合料应用于高寒地区钢桥面铺装层,基于黏度试验、直接拉伸试验、贯入剪切试验研究玄武岩纤维对环氧沥青的增柔增韧作用,采用路用性能、疲劳性能试验与SEM试验研究了玄武岩纤维对环氧沥青混合料耐候性、抗裂性能与微观形貌的影响,并将玄武岩纤维改性环氧沥青混合料应用于高寒地区钢桥面铺装大中修工程.结果 表明,掺加玄武岩纤维显著改善了环氧沥青的柔韧性与变形特性,玄武岩纤维的加筋、阻裂和增韧作用,阻止或延缓了裂缝的产生与扩展,显著改善了重载、高温作用下环氧沥青混合料的抗车辙能力,显著改善了环氧沥青混合料的低温柔韧性与抗疲劳耐久性.实体工程应用表明,将6wt％玄武岩纤维改性沥青混凝土应用于高寒地区钢桥面铺装取得了良好使用效果.     

混杂废旧纤维对乳化沥青冷再生混合料的性能优化研究

为提高含再生剂乳化沥青冷再生混合料的性能,选用木质素纤维及废旧玻璃纤维作为混杂纤维进行配比优化设计.采用室内车辙试验、低温弯曲试验、间接拉伸模量以及疲劳试验,研究了两种纤维的混杂比例及掺量对乳化沥青冷再生混合料路用性能和力学性能的影响.基于主成分分析方法分析了混杂纤维乳化沥青冷再生混合料的综合性能,并建立了相应的综合得分评价模型.结果 表明,相对于使用单一纤维,混杂纤维的应用进一步提高了乳化沥青冷再生混合料的高温抗车辙能力以及低温抗裂能力,改善了其疲劳性能.此外,纤维的混杂比例因素对乳化沥青冷再生混合料的性能影响占到80.114％,而混杂纤维掺量对其综合性能的影响占到14.002％,定量说明两种纤维的混杂比例对乳化沥青冷再生混合料的综合性能有着更显著影响.推荐混杂纤维掺加量为0.3％,M玻璃纤维∶ M木质素纤维为7∶3时,乳化沥青冷再生混合料的综合性能最佳.     

不同纤维透水沥青混合料的路用性能影响分析

选择玻璃纤维和玄武岩纤维2种不同纤维透水沥青混合料进行室内试验,并对比分析了不同纤维掺量对沥青混合料路用性能的影响规律。结果表明,2种纤维均可有效增强透水沥青混合料的路用性能,但纤维掺量不宜过大,其中掺入0.2%玻璃纤维的沥青混合料混合料的高温性能、水稳定性能及透水性能更好,而掺入0.3%玄武岩纤维沥青混合料的低温抗裂性能更好,在实际透水沥青混合料制备中应根据施工需求选择纤维种类及合理掺量。     

混杂粗纤维轻骨料混凝土的力学性能及耐久性的试验研究

为了改善轻骨料混凝土的力学性能和耐久性能,在轻骨料混凝土中混合掺加了两种粗纤维,即高模量的钢纤维和低模量的辅特维.本文通过辅特维掺量的改变,研究混杂纤维对轻骨料混凝土抗压强度、抗折强度及抗渗性能和抗碳化性能的影响.结果表明:两种纤维混杂后的轻骨料混凝土的抗压强度明显降低,抗折强度略有降低.在适当掺量条件下,对抗渗性能及抗碳化性能有一定的加强作用.     

玄武岩纤维沥青混凝土高温性能研究

为研究玄武岩纤维对沥青混凝土高温性能的影响,对普通沥青混凝土和玄武岩纤维沥青混凝土进行了配合比试验和高温车辙试验研究.试验采用AC-13型沥青混合料,玄武岩纤维长度选用3 mm,6 mm和9 mm,掺量为0.1％,0.3％和0.5％.通过车辙试验研究最佳沥青用量条件下不同纤维长度和不同纤维掺量沥青混凝土的动稳定度(DS),进行高温性能及增强机理分析.试验结果表明玄武岩纤维显著得提高了沥青混凝土的高温稳定性能,其中纤维长度3 mm,纤维掺量0.1％的纤维增强效果最好.进一步研究表明,玄武岩纤维具有各项有利于提高沥青混凝土高温性能的物理力学指标,在沥青混凝土中具有广阔的应用前景.     

复合纤维对严寒地区混凝土抗冻性能的影响研究

为了研究严寒地区混凝土的抗冻性能,制备了5种不同聚丙烯纤维和钢纤维掺加的混凝土试件,测试了混凝土试件的抗压强度、抗折强度、质量损失率和动弹性模量,分析了不同冻融循环次数影响混凝土力学强度的变化规律.结果表明:复掺聚丙烯纤维和钢纤维能够在单掺一种纤维的基础上再进一步提高混凝土的抗压强度以及抗折强度;复合纤维混凝土的抗压强度、抗折强度、质量以及动弹性模量损失随着冻融循环次数的增大而增大;相同冻融次数下,复掺聚丙烯纤维1.0 kg·m-3和钢纤维40 kg·m-3条件下混凝土的抗冻性能最佳.     

冻融循环条件下玄武岩纤维改性桥面沥青混凝土抗裂性能研究

为改良我国寒区低温条件下桥面沥青混凝土的工作性能,利用玄武岩纤维制备了玄武岩改性沥青混凝土(BFAC),并对不同纤维长度、不同纤维掺量的BFAC开展了浸水马歇尔试验、三点弯曲试验以及冻融循环力学试验。研究发现：不掺BF的沥青混凝土在的残留稳定度为80.21%;当掺入0.2%的BF后,沥青混凝土的残留稳定度产生了不同程度的增大;不掺BF的沥青混凝土抗弯强度为7.02MP,而掺入玄武BF后,沥青混凝土试件的抗弯强度大幅提高,当BF长度为2mm、掺量为0.2%时,BFAC试件的抗弯强度为7.58MPa,较普通沥青混凝土高出7.98%;当BF的长度为4mm、掺量为0.4%时,BF改性沥青混凝土的综合工程性能最好。此时,BFAC试件的动稳定度为2163.26次·mm^-1,残留稳定度为83.65%,抗弯强度为8.31MPa,冻融循环强度损失率为5.26%。研究成果为我国寒区桥面沥青混凝土的设计施工提供了一定的借鉴作用。     

盐渍土路基混凝土配合比设计研究

针对盐渍土具体工程要求,通过掺加防腐剂,改变SL、FA、SF的掺量与掺加方式等手段,优选出最佳的SL、FA、SF掺量与掺加方式.试验分别制备了C25、C30、C35、C40等4个标号的混凝土,分析混凝土的抗SO42-侵蚀性能、抗Cl-侵蚀性能.     

不同纤维对新型生态排水沥青混合料性能影响评价

以提高排水沥青路面的稳定性、抗变形能力以及抗水损害性能为目标,选取三种不同纤维(聚合物纤维、木质素纤维、玄武岩纤维)作为排水沥青混合料增强稳定剂;通过不同指标确定纤维最佳掺量,并采用残留稳定度试验、冻融劈裂试验、车辙试验、渗水试验评价不同纤维对新型生态排水沥青混合料路用性能的影响.结果表明:三种纤维的最佳掺量均为0.1％(质量分数),其对排水沥青混合料的体积指标影响较小;玄武岩纤维对混合料稳定度和抗飞散性能提高程度最为明显,抗飞散性能提高35％左右,动稳定度提高2倍左右;在抗水损害性能方面,玄武岩纤维也优于其他两种纤维,不同纤维对沥青混合料渗水能力影响程度差距不大,数据随机性较强.综上所述,玄武岩纤维对新型生态排水沥青混合料路用性能提高最为显著.     

混杂纤维增强高强混凝土性能研究

为研究钢纤维、聚乙烯醇纤维混杂比例对高强混凝土性能的影响,通过合理设计坍落度试验、力学强度试验、收缩试验、抗裂试验、抗氯离子侵蚀试验,对比评价了纤维混杂比例对高强混凝土工作性、抗折强度、收缩性、抗裂性能以及氯离子渗透系数的影响。结果表明,钢纤维和聚乙烯醇纤维降低了新拌混合物的工作性。与单掺纤维相比,混杂纤维对高强混凝土力学性能改善效果不明显,但可明显改善混凝土抗裂性能,开裂面积抑制率最大为95.8%,同时能使高强混凝土收缩率和氯离子分别降低27.7%和66.5%,明显提高高强混凝土的耐久性能。通过扫描电镜试验分析探讨了纤维增强混凝土的作用机理,结果表明混杂纤维对基体内部结构的改善实现了对混凝土宏观性能的提升,最终推荐采用0.75%(体积分数)钢纤维和0.25%(体积分数)聚乙烯醇纤维。     

Performance of polyurethane-coated concrete in sewer environment

Polyurethane-based coatings are used to protect concrete facilities against corrosive environments. The performances of two commercially available polyurethane coatings were evaluated under sulfuric acid environment (representing sewer condition) for over 5 years. Both dry (representing new construction) and wet (representing rehabilitation) concretes were used in this study. A combination of the full-scale hydrostatic test, bonding test, and chemical resistance tests were performed to evaluate the coatings to protect concrete structures below ground water. The full-scale hydrostatic test was used to evaluate the application and performance of coatings under hydrostatic pressure to simulate underground concrete structures below ground water. Visual inspections and in situ bonding tests were performed on coated concrete under a hydrostatic pressure of 105 kPa. Test results showed that bonding strength of one coating was affected by the moisture condition and hydrostatic water pressure in the full-scale test. Coated cement concrete specimens with pinholes were used to study the chemical resistance of the coated concrete in sulfuric acid to represent the worst sewer condition. Change in weight of coated concrete specimens was measured at regular intervals. Types of failures in coated concrete under acidic environment have been identified. Test results showed that the performance of the two coatings were noticeably different and one coating with pinholes extended the service life of concrete by 14 times while the other coating extended the service life of concrete by 57 times. There was no direct correlation between bonding strength and chemical resistance of the polyurethane-coated concrete. Although both coatings were polyurethane-based, their performances were different under the testing conditions adopted in the study.     

保护剂对清水混凝土抗碳化性能的影响

清水混凝土保护剂具有优异的防水性能,极大地提升了清水混凝土建筑的使用寿命。为精确确定清水混凝土保护剂对清水混凝土抗碳化性能的影响,本文研究了水溶性有机硅类渗透型保护剂和丙烯酸类成膜型保护剂对清水混凝土抗碳化性能的影响。结果表明:成膜型保护剂和渗透型保护剂均可有效降低清水混凝土碳化深度,成膜型保护剂降低效果更为显著;涂抹两种类型保护剂试件的碳化深度均随养护龄期的增加而降低,养护龄期和渗透型保护剂独立发挥作用,而养护龄期和成膜型保护剂相互促进,两者作用可进一步降低清水混凝土碳化深度;建立了清水混凝土碳化深度预测模型,该模型考虑了保护剂种类和厚度对清水混凝土抗碳化性能的影响。     

冻融循环下再生混凝土孔隙分布变化及其对抗冻性能的影响

为研究冻融循环下再生混凝土孔隙分布变化对抗冻性能的影响,选取再生骨料取代率为0%、50%、100%的三组混凝土进行冻融循环试验,基于核磁共振(NMR)技术,监测混凝土冻融破坏过程中内部孔隙结构的分布和变化情况.结果表明:冻融循环试验中,普通混凝土和50%取代率的再生混凝土抗冻性能相近,孔隙扩展不明显,而全取代再生混凝土内部孔隙扩展情况显著,混凝土抗冻性能明显降低;核磁共振测得的混凝土内部孔隙分布变化和孔隙体积变化率参数,能够很好的反映混凝土的抗冻性能,可以作为评判混凝土结构抗冻性的重要指标之一.     

改性混凝土试验及性能研究

针对废弃混凝土中的再生骨料表面附着大量残留的水泥浆,以及新老砂浆之间缝隙过大,进而导致再生混凝土的耐久性能出现问题,结合粉煤灰的特点,提出对再生骨料进行改性处理,在混凝土中掺入一定量的粉煤灰,从而填充再生骨料存在的缝隙过大的问题。最后,利用电通等试验方法对改性混凝土试件的抗氯离子渗透性能进行测试,并通过实验结果表明粉煤灰可改善再生混凝土结果,提高抗渗透性能,并当掺量在28%时,抗氯离子渗透性能最佳。     

Characteristics of a thermally activated alumino-silicate pozzolanic material and its use in concrete

This paper presents the results of the physical and chemical properties of a thermally activated alumino-silicate material (MK), and deals with the properties of fresh and hardened concrete incorporating this material. The properties of fresh concrete investigated included workability, bleeding, setting time, and autogenous temperature rise. The properties of the hardened concrete investigated included compressive, splitting-tensile and flexural strengths, Young's modulus of elasticity, drying shrinkage, resistance to chloride-ion penetration, freezing and thawing, and saltscaling resistance. The properties of the MK concrete were also compared with those of the control portland cement concrete and the silica fume concrete.

The test results indicate that the MK material is highly pozzolanic and can be used as a supplementary cementing material to produce high-performance concrete. Although it requires a higher dosage of the superplasticizer and air-entraining admixture compared with that of the control concrete, the MK concrete can be produced with satisfactory slump, air content, and setting time. The concrete incorporating 10% MK had higher strength at all ages up to 180 days compared with the control concrete; in comparison with the silica fume concrete the MK concrete showed a faster strength development at early ages, but had lower strength after 28 days. At 28 days, the MK concrete had somewhat higher splitting-tensile and flexural strengths, Young's modulus of elasticity, and lower drying shrinkage compared with that of the control and the silica fume concretes. The resistance of the MK concrete to the chloride-ion penetration was significantly higher than that of the control concrete, but similar to that of the silica fume concrete. The MK concrete showed excellent performance in the freezing and thawing test. The performance of the MK concrete subjected to the de-icing salt scaling test was similar to that of the silica fume concrete, but marginally inferior to the control concrete.     

自养护路面混凝土抗盐冻性能及疲劳特性

为有效增强路面混凝土耐久性能,基于盐冻试验、盐冻前后的断裂性能试验及弯拉荷载疲劳试验,探索了高吸水性聚合物(SAP)自养护路面混凝土抗盐冻性能及疲劳特性随SAP掺量、粒径的变化规律,并结合自养护水泥浆体孔隙参数、微观形貌及骨料-水泥石界面过渡区(ITZ)特征,揭示了性能影响机理。结果表明:小粒径SAP形成的残留孔洞能有效释放拉应力,降低结冰点,细化孔结构,从而增强路面混凝土抗盐冻性能;当SAP粒径为100目(150 μm),掺量为0.145%(质量分数)时,路面混凝土在冻融30次时的断裂韧度损失率、断裂能损失率分别比基准组降低了25.25%、10.51%;小粒径SAP对疲劳寿命的提升程度随应力水平的提高而增大,当应力水平为0.80时,自养护组的疲劳寿命相比基准组提升了2.65倍;SAP能够有效提升水泥混凝土结构内部密实度,吸持ITZ区域部分水分,增强水泥石和骨料之间的粘结性,从而改善混凝土抗盐冻性能和疲劳特性。     

Performance of spalling resistance of high performance concrete with polypropylene fiber contents and lateral confinement

This paper presents an experimental study on the spalling resistance of high performance concrete with polypropylene (PP) fibers and fabric or sheet material for lateral confinement subjected to fire. According to the test results, spalling occurred on all specimens that did not contain PP fiber in the concrete mixture. However, spalling did not occur on specimens containing PP fibers above 0.05% by volume. A metal fabric showed beneficial effect on spalling resistance, but glass or carbon fiber fabrics do not show the same effect on the spalling resistance due to reduction of bond strength at high temperatures. Spalling did not occur on all specimens in which PP fibers and metal fabric were applied at the same time, and hence spalling resistance performance was significantly improved. The residual compressive strength was maintained at about 90% of its original strength, and this can be considered as an improved performance against fire damage.     

Response of concrete to accelerated physical salt attack exposure

Various concrete structures/elements are at risk of physical salt attack (PSA) during service; however, there is currently no standard test method in North America for PSA of cement-based materials. Therefore, an accelerated laboratory test, based on sodium sulfate, was developed in this research to assess the resistance of concrete to PSA. The effects of w/cm, fly ash and two types of nanoparticle (nano-silica [NS] and nano-alumina [NA]) addition on the resistance of concrete to PSA were also investigated. The assessment criteria were based on physical properties (visual appearance, mass loss and penetrability), and the alteration of microstructure by microscopy, thermal and mineralogical analyses. The results showed that the proposed procedure can successfully reflect the performance of concrete under PSA within a relatively short time interval (120 days). Also, adverse effects of higher w/cm (0.5) and nanoparticle addition on the resistance of concrete to PSA were captured.     

掺合料对再生混凝土强度和耐久性的影响

对掺入磨细掺合料的再生混凝土的抗压强度及抗渗性、抗冻性、抗碳化等耐久性能进行了研究。结果表明,适量磨细粉煤灰掺入再生混凝土中对混凝土抗压强度及耐久性能影响不大;将磨细粉煤灰与矿渣混掺可以发挥复合效应,提高掺合料的活性,改善再生混凝土的性能。