N型高效泵送剂在高强流态混凝土中的应用

随着高层建筑的不断发展,混凝土强度由C30为主提高到C40为主,重要部位采用C50、C60混凝土。能否生产高质量、高强度泵送混凝土是考察施工单位技术实力的重要指标。铁道部建厂局深圳工程处近两年在特区施工的近50万m~2高层建筑中,选用优质硅酸盐525＃水泥。掺加N型高效泵送剂及蛇口妈湾电厂干排原状Ⅱ级粉煤灰,现场生产了6万m~3C40-C60高强泵送混凝土,砼工程包括1-1,5m厚底板,高层建筑墙柱梁板等。一次浇筑泵送混凝土的最大量为3700m~3,单机泵送最大高度110m,保证了混凝土质量,加快了工程进度。     

用常规工艺配制流态性高强混凝土

随着我国建筑业的飞跃发展,人们对混凝土的品质愈加注重。开发新型优质高强混凝土是节能节材最有效途径之一。有资料表明,18m跨孤形标准屋架,用C60强度等级的混凝土代替C3(?)混凝土,则减轻自重40％(即节约混凝土量40％),可降低造价16％左右。     

用优质KSF材料配制流态高强混凝土的研究

研究了以优质粉煤灰为基材的ＫＳＦ活性矿物掺和材料,并以此作为主要组分,配制了坍落度为１８０ｍｍ以上,５６ｄ平均抗压强度可达１００ＭＰａ左右的流态高强混凝土,通过实验证实了该混雍土具有优异的物理力学性能和耐久性能。     

流态超高强混凝土的配制及性能分析

通过使用超细粉煤灰、矿粉、硅灰及高效减水剂进行了流态超高强混凝土的配制研究。试验结果表明：超细粉煤灰具有优良的减水效果,并且对混凝土的增强效果显著,能使混凝土的强度达到１００ＭＰａ以上;超细矿粉在细度较低时无减水效果,但对混凝土的增强效果和超细粉煤灰相当;将少量硅灰和超细粉煤灰、矿粉复合使用可进一步提高混凝土强度至１２０ＭＰａ左右。     

高强碱矿渣（JK）流态混凝土研究

新型碱矿渣混凝土具有高强，快硬，低热，高抗渗，高抗冻，高抗蚀等一系列优异性能，而且工艺简单，基建设资少，成本较廉，是极有发展前途的新型结构材料，但由于混凝土的凝结时间短，施性性能较差，影响着这种混凝土的工程应用，作者针对碱矿渣混凝土这一弱点，研究成功了高强碱矿矿混凝土的特效缓凝剂，在此基础上研制成功了高强碱矿渣流态混凝土，混凝土抗合物坍浇度达１８～２２厘米，坍落度可以作到２小时内无损失，３小时内损     

硅灰对150MPa超高强高流态混凝土的强度及流动性的贡献

采用硅酸盐水泥＋高效减水剂＋硅灰的技术路线和通用工艺研制成功９０天抗压强度达１５０ＭＰａ的超高强高流态混凝土,分析了硅灰对提高１５０ＭＰａ超高强混凝土的强度及流动性的巨大作用。表明：在掺入高效减水剂的同时,用掺量１０％￣１５％的硅灰等量取代水泥,可将坍落度为０的无硅灰干硬性混合料转化为坍落度为２３０ｎｍ￣２４０ｎｍ的高流态混凝土混合料,硅灰的火山灰效应所贡献的强度达１５０ＭＰａ级混凝土总强度的１／     

高强流态混凝土的研究与工程应用

本文介绍了针对河北省重点工程－燕都大酒店设计采用的高性能混凝土的技术和施工要求,用石家庄地区５２５＃普通硅酸盐水泥、当地常用的砂石,配制Ｃ６０、Ｃ６５级高强流态混凝土的试验研究结果。     

纳米SiO2改性陶粒混凝土冻融损伤规律及模型研究

为研究纳米SiO2改性陶粒混凝土在不同溶液冻融环境下的抗冻性能,设计了四种溶液(水、硫酸盐、碳酸盐、复合盐)冻融环境,采用快速冻融法,以质量损失率及相对动弹性模量为指标对其冻融损伤规律进行了研究,并基于试验数据建立了抗冻性能退化模型。结果表明:在盐溶液冻融环境下,陶粒混凝土质量损失及相对动弹性模量高于水冻环境;当盐溶液浓度相同时,硫酸盐溶液冻融环境对混凝土的质量及动弹性模量的损伤较碳酸盐溶液强,复合盐类溶液冻融损伤居中;基于试验数据建立的抗冻性能模型可较好地反映纳米SiO2改性陶粒混凝土在不同冻融溶液环境下的冻融损伤规律。     

强度92MPa,坍落度20cm,2小时内无坍落度损失的高强高流态混凝土的研制及应

本研究利用中热５２５＃硅酸盐水泥４５０公斤，硅粉５０公斤，Ｗ／Ｃ＋Ｆ＝２６％，高效减水剂ＦＤＮ１．０％，Ｃ．Ｆ．Ａ１．４％，混凝土２８天强度９２．４ＭＰａ，坍落度可达２０ｃｍ，且２小时无坍落度损失。     

纳米SiO2改性粉煤灰混凝土力学性能及吸水特性研究

为了探索粉煤灰混凝土的高性能,开展了纳米SiO₂改性粉煤灰混凝土的力学和吸水试验,研究了粉煤灰取代率和纳米SiO₂掺量对混凝土力学性能(抗压强度、劈拉强度、动弹性模量)和吸水特性的影响。结果表明：粉煤灰混凝土的力学性能指标均随纳米SiO₂掺量的增加先增大后减小;当纳米SiO₂掺量从0%增加至2%时,粉煤灰混凝土28 d抗压强度、劈拉强度和动弹性模量分别提高了12.90%、7.53%和5.85%,可见纳米SiO₂对抗压强度影响更显著;当粉煤灰取代率从10%增加至30%时,混凝土28 d抗压强度、劈拉强度和动弹性模量分别降低了7.24%、2.61%和9.87%,可见粉煤灰对动弹性模量影响更显著;随纳米SiO₂掺量增加,粉煤灰混凝土的毛细吸水系数呈现出先下降后上升的趋势;随粉煤灰取代率增加,混凝土毛细吸水系数增大,且纳米SiO₂对混凝土毛细吸水系数影响也越显著;粉煤灰取代率和纳米SiO₂掺量对混凝土力学性能与毛细吸水系...     

纳米SiO2对橡胶混凝土断裂行为的影响

为改善橡胶混凝土的力学性能,以纳米SiO₂为改性剂,研究了纳米SiO₂增强橡胶混凝土的断裂行为,采用数字图像相关方法,分析了纳米SiO₂增强橡胶混凝土断裂性能,并结合微观结构分析探讨了其增强机理.结果表明：纳米SiO₂的掺入对橡胶混凝土的断裂性能和强度提高效果显著;纳米SiO₂与橡胶的协同作用提高了混凝土裂缝扩展稳定性,延长了断裂过程起裂到失稳的时间;纳米SiO₂对橡胶混凝土断裂性能的提升归结于其对水泥基质的改善,从而提高了混凝土的承载能力.     

铁质渣球超高强高耐磨混凝土材料的研究

研究铁质渣球的物理、力学性质;通过正交试验设计,确定了超高强、高耐磨混凝土最佳配比:铁质渣球与胶凝材料的体积比掺量(Ai/B)为0.5、高效减水剂(液体)掺量为3%、钢纤维掺量(体积率)为4%、硅灰掺量(占胶凝材料总量)为10%、水胶比0.18。通过多元回归分析确定模型方程,并进行方差分析,经过试验优化,得到28d抗压强度为129.3MPa、抗折强度为28.87MPa、弹性模量最高可达53GPa、断裂能可达3198J/m2的超高强、高耐磨混凝土。     

100MPa超高强高性能混凝土的研配及其性能研究

采用常规的材料及通用的工艺方法,通过低水胶比、低胶结材料用量,研制成功了流动性优良,抗压强度超过100MPa,耐久性优异的超高强高性能混凝土材料.研究内容包括超高强高性能混凝土材料的配合比,超高强高性能混凝土材料的抗压强度、劈裂抗拉强度、抗折强度、轴心抗压强度、静力弹性模量等力学性能;同时进行了电通量、抗氯离子渗透、SEM电子扫描等研究.     

Al2O3 nanoparticles in concrete and different curing media

In the present study, the effect of limewater on strength and percentage of water absorption of Al₂O₃ nanoparticles blended concrete has been investigated. Portland cement was partially replaced by Al₂O₃ nanoparticles with the average particle size of 15 nm with different amount and the specimens were cured in water and saturated limewater for specific ages. Utilizing up to 2.0 wt% Al₂O₃ nanoparticles could produce concrete with improved strength and water permeability when the specimens cured in saturated limewater while this content is 1.0 wt% for the specimens cured in tap water. The high action of fine nanoparticles substantially increases the quantity of C-S-H gel. Although the limewater reduces the strength of concrete without nanoparticles when compared with that cured in water, curing the specimens in saturated limewater results in more strengthening gel formation around Al₂O₃ nanoparticles and causes improved permeability together with high strength. In addition, Al₂O₃ nanoparticles are able to act as nanofillers and recover the pore structure of the specimens by decreasing harmful pores. Accelerated peak appearance in conduction calorimetry tests, more weight loss in thermogravimetric analysis and more rapid appearance of peaks related to hydrated products in X-ray diffraction results, all indicate that Al₂O₃ nanoparticles could improve mechanical and physical properties of the specimens.     

Greywater treatment by UVC/H2O2

Greywater treatment by UVC/H₂O₂ was investigated with regard to the removal of chemical oxygen demand (COD). A COD reduction from 225 to 30 mg l⁻¹ (overall removal of 87%) was achieved after settling overnight and subsequent irradiation for 3 h with 10 mM H₂O₂. Most of the contaminants were removed by oxidation since only 13% COD was removed by settlement.The removal of COD in the greywater followed a second-order kinetic equation, r = 0.0637[COD][H₂O₂], up to 10 mM H₂O₂. A slightly enhanced COD removal was observed at the initial pH of 10 compared with pH 3 and 7. This was attributed to the dissociation of H₂O₂ to O₂H⁻. The treatment was not affected by total concentration of carbonate (c_T) of at least 3 mM, above which operation between pH 3 and 5 was essential. The initial biodegradability of the settled greywater (as BOD₅:COD) was 0.22. After 2 h UVC/H₂O₂ treatment, a higher proportion of the residual contaminants was biodegradable (BOD₅:COD = 0.41) which indicated its potential as a pre-treatment for a biological process.     

Arsenic sorption on TiO2 nanoparticles: Size and crystallinity effects

Single solute As (III) and As (V) sorption on nano-sized amorphous and crystalline TiO₂ was investigated to determine: size and crystallinity effects on arsenic sorption capacities, possible As (III) oxidation, and the nature of surface complexes. Amorphous and crystalline nanoparticles were prepared using sol-gel synthesis techniques. For amorphous TiO₂, solute pH in the range of 4-9 had a profound impact on only As (V) sorption. As (III) and As (V) sorption isotherms indicated that sorption capacities of the different TiO₂ polymorphs were dependent on the sorption site density, surface area (particle size) and crystalline structure. When normalized to surface area, As (III) surface coverage on the TiO₂ surface remained almost constant for particles between 5 and 20 nm. However, As (V) surface coverage increased with the degree of crystallinity. X-ray absorption spectroscopic analysis provided evidence of partial As (III) oxidation on amorphous TiO₂ rather than crystalline TiO₂. The data also indicated that As (III) and As (V) form binuclear bidentate inner-sphere complexes with amorphous TiO₂ at neutral pH.     

Experimental study on bond performance between high strength steel rebar and ultra-high performance concrete

为研究超高性能混凝土(UHPC)与高强钢筋的黏结性能，设计并制作69个试件，通过拔出试验研究UHPC强度、纤维体积率、纤维尺寸形状、保护层厚度、黏结长度、加载方式和黏结段位置对黏结性能的影响。结果表明：试件的主要破坏形态包括拔出破坏、钢筋拉断和劈裂破坏，高强钢筋与UHPC界面的黏结强度随UHPC抗压强度、纤维体积率和长径比以及保护层厚度的增加而增大；纤维的掺入对高强钢筋与UHPC黏结强度提高作用明显；当纤维体积率从1%增长至3%，长径比从35增加到100时，黏结强度分别提高了23%和16%；但纤维形状的变化对黏结强度没有明显影响；黏结强度随着UHPC抗压强度和保护层厚度的增大而显著增加，随着黏结长度增大而降低，当保护层厚度超过4倍钢筋直径时，增幅基本不变；当黏结段位于加载端时，受拉拔出加载试件黏结强度仅为受压加载的77%，黏结段越靠近试件中部，加载方式对黏结强度影响越小。基于试验结果，确定临界锚固长度计算式，提出高强钢筋与UHPC的黏结强度计算式，同时建立黏结应力-滑移本构关系模型。通过试验结果及公式计算结果对比可得，现有的普通混凝土黏结强度公式低估了高强钢筋与UHPC的黏结强度，建议的简化公式预测结果与试验结果吻合良好。     

高强钢筋与超高性能混凝土黏结性能试验研究

为研究超高性能混凝土(UHPC)与高强钢筋的黏结性能,设计并制作69个试件,通过拔出试验研究UHPC强度、纤维体积率、纤维尺寸形状、保护层厚度、黏结长度、加载方式和黏结段位置对黏结性能的影响。结果表明：试件的主要破坏形态包括拔出破坏、钢筋拉断和劈裂破坏,高强钢筋与UHPC界面的黏结强度随UHPC抗压强度、纤维体积率和长径比以及保护层厚度的增加而增大;纤维的掺入对高强钢筋与UHPC黏结强度提高作用明显;当纤维体积率从1%增长至3%,长径比从35增加到100时,黏结强度分别提高了23%和16%;但纤维形状的变化对黏结强度没有明显影响;黏结强度随着UHPC抗压强度和保护层厚度的增大而显著增加,随着黏结长度增大而降低,当保护层厚度超过4倍钢筋直径时,增幅基本不变;当黏结段位于加载端时,受拉拔出加载试件黏结强度仅为受压加载的77%,黏结段越靠近试件中部,加载方式对黏结强度影响越小。基于试验结果,确定临界锚固长度计算式,提出高强钢筋与UHPC的黏结强度计算式,同时建立黏结应力-滑移本构关系模型。通过试验结果及公式计算结果对比可得,现有的普通混凝土黏结强度公式低估了高强钢筋与UHPC的黏结强度,建议的简化公式预测结果与试验结果吻合良好。     

Atmospheric NH3 and NO2 concentration and nitrogen deposition in an agricultural catchment of Eastern China

To assess the atmospheric environmental impacts of anthropogenic reactive nitrogen in the fast-developing Eastern China region, we measured atmospheric concentrations of nitrogen dioxide (NO₂) and ammonia (NH₃) as well as the wet deposition of inorganic nitrogen (NO₃⁻ and NH₄⁺) and dissolved organic nitrogen (DON) levels in a typical agricultural catchment in Jiangsu Province, China, from October 2007 to September 2008_. The annual average gaseous concentrations of NO₂ and NH₃ were 42.2 μg m⁻³ and 4.5 μg m⁻³ (0 °C, 760 mm Hg), respectively, whereas those of NO₃⁻, NH₄⁺, and DON in the rainwater within the study catchment were 1.3, 1.3, and 0.5 mg N L⁻¹, respectively. No clear difference in gaseous NO₂ concentrations and nitrogen concentrations in collected rainwater was found between the crop field and residential sites, but the average NH₃ concentration of 5.4 μg m⁻³ in residential sites was significantly higher than that in field sites (4.1 μg m⁻³). Total depositions were 40 kg N ha⁻¹ yr⁻¹ for crop field sites and 30 kg N ha⁻¹ yr⁻¹ for residential sites, in which dry depositions (NO₂ and NH₃) were 7.6 kg N ha⁻¹ yr⁻¹ for crop field sites and 1.9 kg N ha⁻¹ yr⁻¹ for residential sites. The DON in the rainwater accounted for 16% of the total wet nitrogen deposition. Oxidized N (NO₃⁻ in the precipitation and gaseous NO₂) was the dominant form of nitrogen deposition in the studied region, indicating that reactive forms of nitrogen created from urban areas contribute greatly to N deposition in the rural area evaluated in this study.     

Splitting tensile strength of concrete using ground granulated blast furnace slag and SiO2 nanoparticles as binder

In the present study, split tensile strength together with pore structure, thermal behavior and microstructure of concrete containing ground granulated blast furnace slag and SiO₂ nanoparticles have been investigated. Portland cement was replaced by different amounts of ground granulated blast furnace slag and the properties of concrete specimens were measured. Although it negatively impacts the properties of concrete at early ages, ground granulated blast furnace slag was found to improve the physical and mechanical properties of concrete up to 45 wt% at later ages. SiO₂ nanoparticles with the average particle size of 15 nm were partially added to concrete with the optimum content of ground granulated blast furnace slag and physical and mechanical properties of the specimens were studied. SiO₂ nanoparticle as a partial replacement of cement up to 3 wt% could accelerate C-S-H gel formation as a result of increased crystalline Ca(OH)₂ amount at the early age of hydration and hence increase split tensile strength of concrete specimens. The increased the SiO₂ nanoparticles’ content more than 3 wt% causes the reduced the split tensile strength because of the decreased crystalline Ca(OH)₂ content required for C-S-H gel formation. SiO₂ nanoparticles could improve the pore structure of concrete and shift the distributed pores to harmless and few-harm pores.