氧化石墨烯对水泥基自流平砂浆性能的影响

通过氧化和超声波分散制备了浓度为7. 4 g/L的氧化石墨烯(GO)分散液,研究了不同GO掺量条件下硅酸盐体系自流平砂浆及其硬化体的流动度、凝结时间、力学性能和耐久性能,并借助XRD、SEM和MIP等手段分析其改性机理。实验得出GO的最佳掺量是0. 04%(质量分数)。在该掺量下,相比未掺GO的空白样,水泥基自流平砂浆的流动度与凝结时间稍有降低,28 d抗折、抗压强度和耐磨性能分别提高38. 9%、27. 7%和48. 8%。28 d试样的氯离子渗透性能较空白样降低了98. 5%。微观测试结果表明,氧化石墨烯能够促进硅酸盐水泥的水化进程,调控水泥水化产物的微观结构,从而提高水泥基自流平材料的力学性能和耐久性能等。     

砒砂岩对硅酸盐和硫铝酸盐水泥性能的影响

为了研究砒砂岩对硅酸盐水泥和硫铝酸盐水泥物理性能的影响,采用单因素多水平梯度实验,通过不同砒砂岩掺量的对比,测定硅酸盐水泥和硫铝酸盐水泥的凝结时间、标准稠度用水量和胶砂强度等性能。结果表明:砒砂岩对硅酸盐水泥和硫铝酸盐水泥皆有促凝作用,当砒砂岩掺量质量分数为5%时硅酸盐水泥的初凝时间会缩短30%,硫铝酸盐水泥初凝时间缩短47%,硅酸盐水泥和硫铝酸盐水泥的标准稠度用水量分别增加6.6%和21.7%;砒砂岩掺量质量分数为10%时,硅酸盐水泥的3 d和28 d的强度分别增加7.2%和6%,对其力学性能有较大影响;掺入砒砂岩后,硫铝酸盐水泥强度降低,且随掺量增加,抗压强度降幅增大。     

硫铝酸盐水泥基高性能混凝土的制备及性能研究

采用硫铝酸盐水泥,根据设计配比,配制了硫铝酸盐水泥基高性能混凝土,探究了硫铝酸盐水泥不同掺量(0,3%,6%和9%(质量分数))对高性能混凝土力学性能(抗压强度)和耐久性能(侵蚀性)的影响。通过XRD、SEM、热分析和力学性能分析等对硫铝酸盐水泥基高性能混凝土进行了表征。结果表明,随着硫铝酸盐水泥掺量的增加,钙矾石(AFt)的衍射峰逐渐增强,水化反应加快,高性能混凝土的结构变得更加致密;所有试样中的六方板状的Ca(OH)_2均比较厚,且呈现出片层状,整体结构的致密性比较接近,而随着硫铝酸盐水泥掺量的增加,整体的密度有变得蓬松的趋势;随着硫铝酸盐水泥掺量的增加,CH的含量增加,前期的水化放热能力得到提高,所有试样在3和28 d时的抗压强度均呈现出逐渐增大的趋势,当硫铝酸盐水泥的掺量为9%时,试样的抗压强度在28 d达到了最大值41.1 MPa,相比3 d增加了19.83%;随着硫铝酸盐水泥掺量的增加,高性能混凝土试样的强度损失逐渐增加,耐久性变差,当硫铝酸盐水泥的掺量为9%时,腐蚀90 d的强度损失率达到了最大值10.3%。     

常温下硝酸铵钙对硫铝酸盐水泥的早强作用

研究了常温下硝酸铵钙对硫铝酸盐水泥浆体的流动度、凝结时间、抗压强度、电阻率及浆体内部温度、水化热、水化产物和孔结构的影响,对硝酸铵钙的早强作用机理进行了分析。结果表明,当硝酸铵钙的掺量从0增大到5%时,水泥浆体的初始流动度明显增大,凝结时间显著缩短,6 h,1,3,7和28 d抗压强度均显著提高,电阻率变化速率曲线峰值出现的时间逐渐提前,水泥浆体内部温度逐渐升高,温峰出现时间提前;其掺量在2%以内时,水泥水化放热速率明显加快,1 d累积放热量略有增大,钙矾石的生成速率及生成量均增大,硬化水泥浆体的平均孔径、总孔体积和孔隙率减小。由于硝酸铵钙能够明显加快硫铝酸盐水泥的水化进程,使其早期强度显著提高,因此可用作早强剂。     

硅酸盐水泥与铝酸盐水泥混合体系的研究和应用

介绍了由硅酸盐水泥与铝酸盐水泥组成的二元体系,以及掺石膏后三元体系的凝结时间、力学性能、体积变形等,水化硬化机理和应用方面的国内外研究现状,并提出了今后的研究重点。     

调凝剂对物理发泡水泥性能的影响

采用物理发泡制备泡沫混凝土,以普通硅酸盐水泥为基材,为了让其凝结时间与泡沫的稳定时间相匹配,研究采用硫酸铝与快硬硫铝酸盐水泥作为调凝剂以调整普通硅酸盐水泥凝结时间。研究发现:随着调凝剂(Al2(SO4)3·18H2O和快硬硫铝酸盐水泥)掺量的逐渐增加,普通硅酸盐水泥净浆凝结时间逐渐缩短,泡沫混凝土容重呈降低趋势,并且气孔尺寸逐渐减小;调凝剂的掺加会提高低容重(425Kg/m3)泡沫混凝土的早期强度,而使其后期(28d)强度有所降低;但是,随着调凝剂掺量的逐渐增加,高容重(725Kg/m3)泡沫混凝土的抗压强度逐渐降低;并用XRD方法对其水化产物进行表征,并分析了调凝剂促凝和后期强度降低的原因。结果表明:在低容重泡沫混凝土的制备过程中可以适当掺加调凝剂,而在高容重泡沫混凝土的制备过程中应避免调凝剂的使用。     

普通硅酸盐-硫铝酸盐复合胶凝体系水化性能和机理研究

对普通硅酸盐(P·O)-硫铝酸盐(R·SAC)复合胶凝体系的凝结时间、胶砂强度进行了分析,利用等温量热仪、综合热分析仪(TG-DSC)、扫描电镜(SEM)、X射线衍射仪(XRD)等从水化速率及水化产物微观形貌等方面分析了复合胶凝体系的水化机理。结果表明:当R·SAC掺量约为10%时,复合胶凝体系的凝结时间相比P·O明显缩短,早期强度提高幅度较大,同时也能获得较大幅度的后期强度增长,力学性能较纯组分水泥性能优越。复合胶凝体系的早期水化速率和放热量高于单组分水泥。随着R·SAC的掺入,复合胶凝体系的水化产物中钙矾石(AFt)增多,Ca(OH)₂晶体减少,且AFt的生成量越多,越有利于早期强度的发展,当R·SAC掺量超过30%时,Ca(OH)₂消失。     

高性能硫铝酸盐-硅酸盐复合胶凝体系的制备及性能研究

根据实验配比,制备了硫铝酸盐-硅酸盐复合胶凝体系,通过XRD、SEM、TG-DTG和力学性能分析等对复合胶凝体系进行了表征,探究了不同硫铝酸盐掺量下复合胶凝体系的物相结构、显微形貌、热性能和力学性能。结果表明,硫铝酸盐-硅酸盐复合胶凝体系中主要检测到Ca(OH)_2、Mulite、钙矾石(AFT)、水硫铝钙石(Kuzelite)、单硫型硫铝酸钙(AFm)和Ca_3SiO_5等产物相,随着硫铝酸盐掺量的增加,体系水化产物中Ca(OH)_2的峰均有降低趋势;不同硫铝酸盐掺量的复合胶凝体系的结构致密性相差不大,随着硫铝酸盐掺量的增加,大量针状的钙矾石(AFT)的含量明显增加,块状的Ca_3SiO_5含量减少;所有复合胶凝体系的失重曲线规律较为相似,且掺杂硫铝酸盐水泥的体系的失重率均明显高于不掺杂的试样;随着硫铝酸盐掺量的增加,复合胶凝体系在1,3和28 d的抗压强度均呈现逐渐增大的趋势,当硫铝酸盐的掺量为25%(质量分数)时,复合胶凝体系在28 d的抗压强度达到了最大值49.3 MPa,相比在1 d时36.5 MPa,增加了35.1%。     

硫铝酸盐水泥增强建筑石膏的力学性能与耐水性能机理

石膏基胶凝材料的力学性能低、耐水性能差是限制其应用的主要原因.本工作通过复掺硫铝酸盐水泥,研究其对建筑石膏水化硬化进程及石膏硬化体力学性能与耐水性能的影响.结果表明,随着硫铝酸盐水泥掺量的增加,建筑石膏标准稠度需水量小幅降低,水化进程加速;10％水泥掺量时,石膏硬化体2 h与3 d的绝干抗折、抗压强度均大幅提升,2 h增幅高达34.8％、29.0％,3 d增幅高达28.8％、34.7％;同时饱水抗折强度由2.35 MPa提升至3.38 MPa,增幅高达43.8％,吸水率相应降低.XRD、SEM、MIP微观结构分析表明:硫铝酸盐水泥与建筑石膏复掺,水化生成针尖状的钙矾石(AFt)与无定形铝凝胶(AH3),AFt与针棒状二水石膏(DH)交织、穿插生长,在晶体之间发挥架桥、连接作用,同时AH3紧密填充在孔隙之间形成致密的晶胶结构中,石膏硬化体孔隙率降低,孔径明显细化,力学性能与耐水性能得到显著改善.     

硫铝酸盐复合水泥体系水化特征研究

通过正交试验研究了硫铝酸盐复合水泥中不同掺量的普通硅酸盐水泥、石膏、硅灰及粉煤灰对其强度、自收缩以及水化热的影响。结果表明:普通硅酸盐水泥及石膏的掺入显著改变了硫铝酸盐复合水泥水化进程,硅灰及粉煤灰是影响后期强度的主要因素;自收缩试验结果表明普通硅酸盐水泥和石膏是影响硫铝酸盐复合水泥水化早期自收缩的主要因素;水化热测试结果表明粉煤灰和普通硅酸盐水泥在水化前6 h起到显著作用,粉煤灰降低了水化放热,而普通硅酸盐水泥增加水化放热;硅灰及石膏对6~24 h水化放热影响显著。结合XRD及SEM测试结果,表明普通硅酸盐水泥和石膏的存在加速了硫铝酸盐复合水泥水化早期钙矾石生成,随着石膏浓度的下降,发生转晶(AFm),随着后期硫铝酸盐水泥中β-C₂S的水化以及硅灰、粉煤灰的火山灰反应产生C-S-H凝胶,使得体系致密化。     

水泥品种对水泥基材料热膨胀性能影响的研究

针对不同品种水泥基材料在高温下体积稳定性问题,采用差示热膨胀仪对普通硅酸盐水泥、高铝水泥和硫铝酸盐水泥分别制成的水泥石的热膨胀性能进行了测试,并用DTA/TG对影响水泥石高温热性能的原因和机制进行了分析。结果表明:3种水泥石的热膨胀率均随着温度的升高先增加后显著降低,到达一定温度后趋于稳定。分析热膨胀随温度变化的规律获知,3种水泥在高温状态下应用时,高铝水泥体积稳定性最佳、硫铝酸盐水泥次之、普通硅酸盐水泥石最差。水泥石的热膨胀均是由其固相组分的受热膨胀与主要水化产物的脱水收缩共同作用的结果,而水泥品种不同,其水化产物中主要脱水组分截然不同。     

Apatite and Portland/apatite composite cements obtained using a hydrothermal method for retaining heavy metals

Apatite and Portland/apatite composite cements containing steelwork dusts have been prepared using a low temperature hydrothermal method (200 degrees C, 48h). The produced solids were characterized by means of XRD, IR, and SEM-EDX, and the remaining liquid was analyzed by ICP. The results clearly show the capability of these cements to inertise the heavy metals contained in steelwork dusts, that is Fe, Pb, Mo, Cr, Mn, Ni, and Zn. In the case of apatitic cements, Fe, Mg, Cr, Mn, and Pb coming from steel dust replaced Ca in the divalent cation position of the apatite structure, while Si and Mo replaced P in tetrahedral position. The average crystal size of the apatite-containing dust is smaller than in pure apatite synthesized using the same procedure, which is related to the magnesium content of the dust, since magnesium seems to inhibit the crystal growth. XRD diagrams of composite cements show only peaks corresponding to phases observed in the single cements, and in that no new phases are found. However, EDX analysis reveals the introduction of cations coming from Portland cement into the apatite structure. From the results of water analysis it could be concluded that the capability of retention is higher in composite matrices than in the pure apatite one. In conclusion, the obtained data allow stating that the proposed method, the hydrothermal synthesis of steelwork dust containing cement, is a reliable one for immobilization of toxic residues containing heavy leachable cations.     

Carbonation of calcium sulfoaluminate mortars

This study investigated potential physical and chemical parameters that could govern the carbonation rate of calcium sulfoaluminate (CSA) mortars and endeavored to elucidate the microstructural and chemical factors that govern CSA cement's carbonation rate. Experiments included: water absorption, oxygen diffusion, mercury intrusion porosimetry, quantitative X-ray diffraction, thermogravimetric analysis, accelerated carbonation, compression and flexure tests. Additionally, the carbonation process was investigated using thermodynamic modeling. The results show that CSA mortars carbonate much faster than Portland cement mortars and at approximately the same rate as calcium aluminate cement mortars. Additionally, CSA mortars carbonate slower with decreasing w/c, and the anhydrite content of the CSA mortars strongly affects the ye'elimite reaction kinetics which plays an important role in imparting carbonation resistance in CSA mortars. Finally, calcium sulfate additions to CSA clinker to produce CSA cement dilutes the clinker content and reduces the amount of CO₂ that the CSA cement can ultimately bind.     

水泥材料研究动向

环境负荷小的高性能低钙水泥和水泥代用材料的研究越来越热,有机高聚物和水泥的复合使用是水泥砼行业减耗,增效和改性的必要手段,国际标准的采用把各国水泥的研究、生产和贸易联在一起。中国水泥研究应不忘自身特点和自主产权。     

Flow Behavior of Fresh Portland Cement Pastes

Portland cement pastes prepared at various water/cement ratios were studied using the rate-controlled coaxial cylinder viscometer Rotovisko-Haake 20, system M5-oscillatory measuring device MV2P with serrated surfaces. The tests were performed under both continuous and oscillatory flow conditions. In this article, experimental shear stress and shear rate data were fitted very satisfactorily with a model proposed by the authors. Excellent results were achieved also by applying the Quemada equation. Oscillatory flow data gave further information on the workability of the pastes investigated. In addition, the influence of two different commercial superplasticizing agents (Concretan RX and Ergomix 1000, the first based on polycyclic copolymers with modified structures carrying hydroxylated side chains, the second on a modified polyacrylic resin) was studied with the aim of determining their optimum dosage. In the case of Ergomix 1000, agreement between the optimum dosage determined rheologically and that recommended by the producer was obtained.     

纳米技术在水泥领域中的应用研究

介绍了纳米技术及纳米材料的的概念,指出纳米技术在自然科学世界已进入全盛时代,纳米技术和纳米材料正逐步扩展应用于军事、医药、化工、环保、信息、机械等各领域。综述了近年来在水泥领域中纳米技术的国内外应用研究现状,探讨了在传统材料水泥、混凝土领域中应用纳米技术的前景。     

Flow Behavior of Fresh Portland Cement Pastes

Portland cement pastes prepared at various water/cement ratios were studied using the rate-controlled coaxial cylinder viscometer Rotovisko-Haake 20, system M5-oscillatory measuring device MV2P with serrated surfaces. The tests were performed under both continuous and oscillatory flow conditions. In this article, experimental shear stress and shear rate data were fitted very satisfactorily with a model proposed by the authors. Excellent results were achieved also by applying the Quemada equation. Oscillatory flow data gave further information on the workability of the pastes investigated. In addition, the influence of two different commercial superplasticizing agents (Concretan RX and Ergomix 1000, the first based on polycyclic copolymers with modified structures carrying hydroxylated side chains, the second on a modified polyacrylic resin) was studied with the aim of determining their optimum dosage. In the case of Ergomix 1000, agreement between the optimum dosage determined rheologically and that recommended by the producer was obtained.     

氧化石墨烯对水泥净浆流动度及水泥石结构和性能的影响

采用Hummers法及超声破碎分散法制备了氧化石墨烯(GO)纳米相分散液,研究了GO对水泥净浆流动度和水泥石微观结构的影响,用FT-IR、AFM、XRD及SEM对GO及水泥石结构进行了表征。结果表明GO的掺入降低了净浆流动性,每增加0.01%的GO需要增加0.02%的聚羧酸系减水剂(PCs)以保持水泥净浆流动度在3 h内在200 mm以上,GO的掺入能够使水泥石的微观结构发生明显的变化,当GO/PCs掺量为0.01%/0.24%~0.03%/0.28%时,水化龄期7 d的水泥石出现了大量分散均匀的花状微晶体,当GO/PCs掺量为0.05%/0.32%~0.07%/0.36%时,同龄期水泥石中出现大量的片状晶体,在水化龄期延长到28 d时有转化为密实结构的趋势,结果说明GO具有调控水泥水化产物形貌的能力及增强增韧的作用,此研究结果对于提高水泥基材料的力学性能具有重要意义。     

粉体改性与水泥的高性能化

建筑技术的进步对水泥的性能和品质提出了越来越高的要求,为了满足这些需求,水泥本身的改性是重要的技术措施。本文中介绍了水泥粉体改性的主要方法和对提高水泥性能的作用,提出了粉碎机械力化学法和球形水泥技术在水泥基材料中的应用研究,并认为这是应该关注的水泥粉体改性问题。