含钢渣的低熟料混凝土耐久性及水化机理研究

研究了不同钢渣掺量对C40低熟料胶凝材料混凝土的碳化、电通量、抗冻等耐久性的影响,结果表明,钢渣掺量为15%时,混凝土碳化深度最小,抗碳化等级为T-Ⅳ;抗氯离子渗透和抗冻性能在钢渣掺量为10%时最佳,分别达到Q-Ⅴ和F275等级。采用XRD、IR和SEM等手段分析了10%钢渣掺量的低熟料胶凝材料水化机理,结果表明,胶凝体系主要水化产物是水化硅酸钙(C-S-H)凝胶和钙矾石(AFt);水泥熟料和钢渣先后水化,产生的OH-维持体系的碱性环境,使矿渣中的硅(铝)氧四面体逐渐解离,在SO2-₄的共同作用下形成C-S-H凝胶和AFt;矿渣和钢渣的水化相互促进,使胶凝体系在后期仍然产生大量水化产物,为混凝土后期强度和密实度的提高起到了重要作用。     

橡胶改性陶粒混凝土抗氯离子渗透性和抗冻性试验研究

通过直流电量法和慢冻法试验,研究了橡胶改性陶粒混凝土的抗氯离子渗透性和抗冻性,并分析了橡胶掺量对这两个方面的影响。     

高炉水渣用作混凝土细骨料的可行性研究

研究了高炉水渣和天然黄砂的区别,水渣代砂配制混凝土的新拌混凝土性能,混凝土强度及抗渗、抗碳化和抗氯离子渗透等耐久性能。研究发现水渣符合2级配区砂,水渣具有一定的胶凝活性,但不会对混凝土结构产生危害。随着水渣代砂率的增大,水泥砂浆干缩性减小,混凝土坍落度逐渐降低;混凝土达到相同坍落度所需减水剂掺量逐渐增大;混凝土抗压强度和抗折强度均缓慢增大;混凝土的抗渗性能、抗氯离子渗透性能、抗碳化性能均得到了改善。     

高性能混凝土在工程中的应用

文章针对中宝8万t镍铁项目回转窑基础工程特点,选用本地优质原材料,利用绝对体积法设计配合比并进行调配,最终设计适合回转窑基础工程的配合比。并对现场混凝土的工作性、强度、抗冻性能、抗渗性能、抗氯离子渗透性能进行试验。试验数据表明:混凝土坍落度、试块抗压强度、抗冻等级、抗渗透性能、抗氯离子侵蚀性能均满足设计要求。     

高钛重矿渣纤维混凝土力学性能试验研究

考虑纤维掺量、水胶比和粉煤灰掺量3个主要因素,采用正交试验设计20组高钛重矿渣纤维混凝土试件,结合SEM分析研究纤维掺量、水胶比等因素对高钛重矿渣纤维混凝土力学性能的影响。试验结果表明:水胶比对高钛重矿渣混凝土的抗折与抗压强度影响最大;玄武岩纤维可以显著提高高钛重矿渣混凝土抗折强度,塑钢纤维可以明显提高高钛重矿渣混凝土抗压强度。当水胶比为0.32,玄武岩纤维掺量1 kg,粉煤灰掺量5%时,高钛重矿渣纤维混凝土抗折强度为5.61 MPa,比未掺纤维的高钛重矿渣混凝土提高10%。当水胶比为0.34,塑钢纤维掺量2 kg,粉煤灰掺量5%时,高钛重矿渣混凝土的抗压强度为60.45 MPa,达到GB50010—2010《混凝土结构设计规范》规定的C55等级。     

高炉矿渣微粉在极端环境下的应用研究

对高炉矿渣微粉(GGBS)混凝土在海岸、撒盐道路及污染严重的工业区等极端环境中的氯盐渗析、碳化、耐蚀性等耐久性能进行了研究,在海水环境中矿粉混凝土有较好的抗蚀性,比相同强度等级的普通水泥混凝土有更好的抵抗海水侵蚀的能力.这种特性增加了混凝土的耐久性,通过对电位、氯化物、抗蚀性的测试也证明以上观点.通过对在海水环境下相同强度等级混凝土试块的测试可知,掺矿粉70%的混凝土抗氯盐侵蚀的能力要远好于普通水泥混凝土.海边的暴露环境对混凝土影响最大,其次是道路环境和工业区环境.     

高钛重矿渣再生混凝土耐久性试验研究

将再生高钛重矿渣粗、细骨料按50%、75%、100%的取代率取代高钛重矿渣粗、细骨料制备强度等级为C20、C25、C30的高钛重矿渣再生混凝土并测定其28 d强度,采用抗氯离子渗透试验、快速冻融试验、抗硫酸盐干湿循环侵蚀试验研究其耐久性能。试验结果表明:再生混凝土实测强度随再生骨料取代率的增大而减小,各个强度等级混凝土的实测强度均能达到设计强度,但强度富余小;再生混凝土D_(RCM)值随骨料取代率及强度等级的提高而降低,最小及最大D_(RCM)值分别为2.3×10~(-12) m~2/s和3.3×10~(-12) m~2/s,耐久性推荐水平分别为好和较好;再生混凝土抗冻性能随再生骨料取代率及强度等级的提高逐渐增强,但仅有再生骨料取代率为75%、100%的C25再生混凝土及取代率为100%的C30再生混凝土达到100次冻融循环的抗冻等级;30次硫酸盐干湿循环侵蚀对再生混凝土的强度影响很小,在同一强度等级下,再生混凝土抗硫酸盐侵蚀性能随再生骨料取代率的升高而减小,强度等级越小,减小幅度越大。     

煤矸石复合生态纤维混凝土抗冻性能研究

本文针对结构物早期受冻开裂、导致混凝土劣化问题,选择自然煤矸石、粉煤灰和生态纤维为主要试验材料,对混凝土的力学性能、抗冻性能展开研究.文中以煤矸石、粉煤灰和生态纤维单掺、复掺为研究思路,展开了对混凝土抗压和劈拉强度的基本力学性能的研究,并对经250次冻融循环前后的混凝土抗压和劈拉强度进行测试和分析.最后通过SEM和XRD物相检测手段,针对纤维掺合料混凝土的微观结构与宏观结构试验结果做出了具体的评价,分析了生态纤维与矿物掺合料联掺对混凝土抗冻性能的影响.     

如何提高混凝土的耐久性

提高混凝土的强度主要是研究混凝土的耐久性.混凝土的耐久性又包括抗冻性、抗渗性、抗侵蚀性及抗碳化能力.本文从工程角度分析了混凝土耐久性问题,并总结了提高混凝土耐久性的几个措施.     

如何提高混凝土的耐久性

提高混凝土的强度主要是研究混凝土的耐久性。混凝土的耐久性又包括抗冻性、抗渗性、抗侵蚀性及抗碳化能力。本文从工程角度分析了混凝土耐久性问题,并总结了提高混凝土耐久性的几个措施。     

硫酸盐侵蚀作用下纤维锂渣混凝土裂缝的分形特征

为探究新型混凝土受硫酸盐侵蚀后的力学性能,采用质量分数为5%的硫酸盐溶液全浸泡加速侵蚀法,对11组聚丙烯纤维混凝土（PC）试块、11组聚丙烯纤维锂渣混凝土（PLiC）试块、8根PC大偏心受压柱和8根PLiC大偏心受压柱进行侵蚀试验,得到了不同侵蚀时间下混凝土的力学性能。基于分形理论分析了试块及构件破坏时表面裂缝分布的分形特征,详细讨论了试块及构件表面裂缝分形维数与其侵蚀时间、抗压强度、极限承载力之间的关系。研究表明,PC和PLiC立方体抗压强度随侵蚀天数先增加后降低,在120 d达到最大;试块及构件破坏时表面裂缝分布具有分形特征,试块表面裂缝分形维数随侵蚀天数的增加呈现先增加后减少再增加的规律,随试块抗压强度的提高而减少;PC及PLiC混凝土大偏心柱极限承载力随侵蚀天数的增加先增加后减少,锂渣的掺入可以提高聚丙烯纤维混凝土柱的抗硫酸盐侵蚀能力,构件破坏时表面裂缝分形维数随硫酸盐侵蚀天数呈现震荡上升的趋势;因此混凝土表面裂缝的分形特征可作为判定构件损伤程度的指标之一,可为今后对在役混凝土结构承载力和寿命预测提供参考。      

早龄期冻结土压力与负温耦合作用的井壁混凝土性能

研究了早龄期冻结压力等荷载、负温及早龄期荷载和负温耦合作用对冻结竖井井壁C60混凝土抗压强度、氯离子扩散系数和声发射特征的影响,并通过扫描电镜分析其内部微裂缝.结果表明:早龄期荷载加载时间越早对混凝土28d抗压强度的影响越大,当外部荷载作用时间在3d以后且荷载水平在混凝土当天强度40%以内时,混凝土28d强度几乎不受影响;冻结井井帮负温环境会延缓井壁混凝土早期水化,防冻剂的加入利于加快混凝土水化和强度的发展;在早龄期荷载及负温耦合作用下,混凝土28d抗压强度降低明显,氯离子扩散系数大大增加,混凝土的渗透性由"中"变为"高",内部产生了缺陷和微裂缝导致声发射"活跃阶段"提前,且混凝土呈现明显的塑性变形.      

模拟冻结法施工环境对大体积混凝土的性能影响

模拟大体积混凝土在冻结法施工环境的状态,将混凝土浇筑7 h后施加?5/60 ℃和?5/70 ℃温差,测试施加模拟环境后混凝土的超声波参数、抗压强度、劈裂抗拉强度、氯离子扩散系数和冲击倾向性,分析混凝土的扫描电镜微观形貌。结果表明,冻结施工环境对于混凝土内部会造成一定的损伤,且平行于加温方向的损伤要大于垂直方向,C50混凝土的损伤大于C70混凝土,温度梯度会加剧混凝土内部的损伤。模拟冻结环境会对混凝土抗压强度、劈裂抗拉强度、氯离子渗透性能和冲击倾向性造成不利影响,温差与性能降低率正相关,且这种影响对于低强度混凝土更加显著。模拟冻结环境造成混凝土试块的内部微观结构不均匀,低温端混凝土结构比较疏松,高温端结构比较致密,导致部分混凝土性能的降低。      

电化学修复后钢筋混凝土黏结性能演变规律

针对电化学修复技术导致修复后结构内钢筋混凝土黏结性能退化问题,通过中心拉拔实验获取电化学修复后钢筋混凝土黏结滑移曲线,研究电化学修复参数（电流密度和通电时间）对钢筋混凝土黏结性能的影响规律,通过实验结果进行模型参数分析,建立基于电流密度和通电时间两个控制变量的黏结强度劣化模型。研究结果表明:电通量较小的情况下,钢筋混凝土黏结性能损失较小;不控制通电参数的电化学修复技术导致黏结强度下降明显,采用5 A·m–2的电流开展28 d的恒电流通电,试件的最大黏结力损失量高达56.9%;本文提出的劣化模型可以定量表征电化学修复后试件黏结强度折减情况,模型的数值模拟结果与本文及其他文献的实验结果均有较好的一致性,相关系数分别为0.9606和0.9745。      

Dynamic Deformation Behavior of Zr-Based Amorphous Alloy Matrix Composites Reinforced with STS304 or Tantalum Fibers

The Zr-based amorphous alloy matrix composites reinforced with stainless steel (STS) or tantalum (Ta) continuous fibers were fabricated without pores or defects by liquid pressing process, and their dynamic deformation behaviors were investigated. Dynamic compressive tests were conducted by a split Hopkinson pressure bar, and then the test data were analyzed in relation to the microstructures and the deformation modes. In the STS-fiber?Creinforced composite, the STS fibers could interrupt the propagation of cracks initiated in the matrix and promoted the continuous deformation without fracture according to the strain-hardening effect of the fibers themselves. The Ta-fiber?Creinforced composite showed the higher yield strength than the STS-fiber?Creinforced composite, but the cracks were not interrupted properly by the Ta fibers according to the lower ductility and strain hardening of the Ta fibers. Both the Ta and STS fibers favorably affected the strength and ductility of the composites by interrupting the propagation of cracks formed in the amorphous matrix, by dispersing the stress applied to the matrix, and by promoting deformation mechanisms such as fiber buckling. The STS-fiber?Creinforced composite showed the higher compressive strength and ductility than the Ta-fiber?Creinforced composite because the STS fibers were higher in the resistance to deformation and fracture than the tantalum fibers.     

Neutron attenuation characteristics of polyethylene, polyvinyl chloride, and heavy aggregate concrete and mortars

Polyethylene and polyvinyl chloride pellets were introduced into concrete to improve its neutron attenuation characteristics while several types of heavy coarse aggregates were used to improve its gamma ray attenuation properties. Neutron and gamma ray attenuation were studied in concrete samples containing coarse aggregates of barite, pyrite, basalt, hematite, and marble as well as polyethylene and polyvinyl chloride pellets in narrow-beam geometry. The highest neutron attenuation was shown by polyethylene mortar, followed by polyvinyl chloride mortar; barite and pyrite concrete showed higher gamma ray attenuation than ordinary concrete. Broad-beam and continuous (infinite) medium geometries were used to study the neutron attenuation of samples containing polymers at different concentrations with and without heavy aggregates, the fitting equations were established, and from these the neutron removal coefficients were deduced. In a radiation field of neutrons and gamma rays, the appropriate concentration of polymer and heavy aggregate can be selected to give the optimum total dose attenuation depending on the relative intensities of each type of radiation. This would give much better design flexibility over ordinary concrete. The compressive strength tests performed on mortar and concrete samples showed that their value, in general, decreases as polymer concentration increases and that the polyvinyl chloride mortar showed higher values than the polyethylene mortar. For general construction purposes, the compression strength was considered acceptable in these samples.     

Effects of Mixed Corrosion, Freeze-Thaw Cycles, and Persistent Loads on Behavior of Reinforced Concrete Beams

The effects of mixed corrosion and freeze-thaw cycles on the mechanical properties of concrete prism specimens and the effects of mixed corrosion, freeze-thaw cycles, and persistent loads on the structural behavior of reinforced concrete beams were experimentally studied. A mixed solution of NaCl and Na2SO4 was used as a corrosive medium. Results show that under alternating actions of freeze-thaw and mixed corrosive agents, increasing the number of freeze-thaw cycles decreases the compressive strength and the elastic modulus of concrete and increases the compressive strain corresponding to the maximum compressive stress. The degradation of concrete material properties accelerates with the increase of water-cement ratio. For reinforced concrete beams, a 4% reduction in the loading capacity is found when these are subjected to freeze-thaw cycles and mixed corrosion only. However, if these actions are coupled with persistent loading, as expected during the service life of reinforced concrete structures in cold regions, a more rapid drop in the strength and deformation capacity of the beams is identified. The degradation is enhanced by a larger persistent-loading ratio. The significance of an accurate simulation of service conditions in the durability study of reinforced concrete structures in cold regions is highlighted.     

基于3参数Weibull分布钢筋混凝土盐腐蚀环境中可靠性寿命分析

为研究钢筋混凝土在耦合盐环境中的腐蚀劣化规律及寿命分布,将钢筋混凝土试件置于0.32 mol·L?1 NaCl和0.4 mol·L?1 MgSO₄盐溶液中,利用电化学工作站定期无损检测,以极化曲线、交流阻抗图谱及电化学参数指标进行耐久性分析,选择3参数Weibull进行可靠性建模,通过Anderson-Darling法（A-D）进行先验假设检验,采用相关系数优化法(CCOM)、极大似然法(MLM)及矩估计法(MEM)进行参数估计,综合可靠度曲线、密度曲线、失效率曲线对钢筋混凝土在氯盐、硫酸盐、镁盐腐蚀环境中的寿命进行分析,研究结果表明:腐蚀离子综合作用下,极化曲线逐渐向腐蚀电流密度增大和负电位方向移动,交流阻抗图谱不断左移并向阻抗实部收缩,钢筋锈蚀发生的阻力逐渐减小,概率逐渐增大。可靠性寿命曲线初期保持不变,后期加速下降,密度曲线呈单峰对称状,失效率曲线初始基本保持不变,后期线性增加。3种参数估计方法中,CCOM和MLM参数估计值相近且稳定准确,所得可靠性寿命曲线相似,MEM参数估计值误差较大,对于钢筋混凝土加速试验得到的小样本失效数据建议用CCOM和MLM进行参数估计,并进行可靠性寿命分析。C35钢筋混凝土在硫酸镁及氯化钠腐蚀环境中的可靠性寿命周期约为760 d。