石灰石粉对硅酸盐水泥水化的影响

石灰石粉被广泛应用到水泥混凝土中,其在水泥体系中是否能产生活性效果仍存在争议。本文通过掺入30%石灰石粉与不掺石灰石粉组进行对比试验,采用扫描电镜(SEM)、能谱分析(EDS)以及X射线衍射分析(XRD)进行微观分析,结果表明:石灰石粉能够加速水泥中C3S的水化,以及能够与C3A反应生成水化碳铝酸钙,并且会阻止钙矾石向单硫型水化硫铝酸钙的转变。     

冶金渣制备高强人工鱼礁结构材料的试验研究

为了研究钢渣粉磨时间和矿渣钢渣复掺比例对矿渣-钢渣-熟料-石膏体系胶凝材料强度的影响,采用一次线性回归得到胶凝材料强度的变化趋势,并利用XRD和SEM方法分析钢渣粉磨和净浆的水化过程.试验表明:矿渣与钢渣的复合比为7∶1,钢渣和矿渣的比表面积分别为550和480 m2/kg,且与质量分数10%的水泥熟料和质量分数10%的脱硫石膏复合的胶凝材料具有较高的强度.以优化后的胶凝材料代替水泥,并以热闷法稳定化的钢渣颗粒为骨料,可以制备出抗压强度达到60 MPa以上,水泥熟料总用量为2%的高强人工鱼礁混凝土.研究表明,对钢渣适度粉磨能改善钢渣性能,适量加入钢渣对促进体系的水化有积极作用.     

石灰石粉和含铝相辅助性胶凝材料的协同作用对混凝土抗碳化性能的影响

为了研究石灰石粉和含铝相辅助性胶凝材料的协同作用对混凝土抗碳化性能的影响,选取了两种含铝相辅助性胶凝材料和石灰石粉以不同比例取代水泥,并采用差热分析、XRD和压汞法测试了其水化产物和微观结构。研究结果表明,单掺石灰石粉降低了混凝土的抗碳化性能,当石灰石粉掺量约为10%时,混凝土的碳化深度最低。当复掺石灰石粉和含铝相辅助性胶凝材料时,两者反应生成了碳铝酸钙,增大了固相体积,优化了孔结构,它们的协同作用提高了混凝土的抗碳化性能。当石灰石粉掺量为5%~15%,粉煤灰掺量小于10%,或者矿粉掺量为10%~30%时,混凝土的碳化深度最低。     

含石灰石粉水泥砂浆在低温环境中的硫酸盐侵蚀

分析了掺30%石灰石粉砂浆与纯水泥砂浆在(5±1)℃的2%MgSO4溶液中浸泡不同时间后试件表面层的矿物成分变化与微观结构,研究了强度与外观的变化.结果表明:掺入石灰石粉使水泥水化产物中的单硫型水化硫铝酸钙转变为稳定的单碳水化铝酸钙,物理填充作用使水泥石结构更加致密,因而在短期的低温硫酸盐侵蚀环境下掺石灰石粉砂浆比纯水泥砂浆表现出更好的耐腐蚀性.在经受低温硫酸盐侵蚀后纯水泥砂浆生成大量的石膏和钙矾石,而掺石灰石粉砂浆在经受同条件210 d侵蚀后的腐蚀产物中除了石膏、钙矾石外,还有少量的硅灰石膏生成,表明水泥石中的CSH凝胶体也受到侵蚀.     

钢渣粉性能优化及制备无熟料混凝土的试验研究

为提高固体废弃物综合利用率,通过钢渣分段除铁优化试验和钢渣粉对无熟料混凝土抗压强度影响试验,研究以钢渣-矿渣-脱硫石膏作为胶凝材料制备无熟料全固废混凝土。结果表明,经分段磁选可获得金属铁含量低于0.5%的高性能钢渣粉;当钢渣粉比表面积为640m~2/kg,m(钢渣)∶m(矿渣)=1∶2.5时,无熟料混凝土同时获得较优的3d和28d强度。XRD、TG-DSC、IR和FE-SEM分析表明,在脱硫石膏的激发作用下钢渣和矿渣可以相互促进水化,水化产物以AFt(钙矾石)和C-S-H(水化硅酸钙)凝胶为主。早期钢渣水化促进矿渣的解聚并结合脱硫石膏生成AFt网状结构,随着水化反应的进行胶凝体系生成的C-S-H凝胶充填于AFt网络中使硬化浆体结构致密从而保证强度的增长。     

环境极性对水泥基材料抗低温硫酸盐侵蚀性能的影响

通过分析甘油对水泥-石灰石粉胶凝材料在低温(5℃)、5%硫酸钠溶液中侵蚀的影响,研究了环境极性对水泥基材料抗低温硫酸盐侵蚀性能的影响。结果表明,水泥-石灰石粉试件腐蚀程度随时间增加而加重,腐蚀产物主要为碳硫硅钙石,未掺甘油的试件棱角发生明显脱落;掺甘油降低了腐蚀产物中碳硫硅钙石的生成量,随甘油掺量增加腐蚀产物中碳硫硅钙石的生成量减少,腐蚀程度减轻。甘油可以抑制水泥基材料中碳硫硅钙石的生成,降低环境极性能提高水泥基材料抗低温硫酸盐侵蚀性能。     

硫铝酸钙改性硅酸盐水泥应用研究进展

硫铝酸钙改性硅酸盐水泥熟料兼具硅酸盐水泥熟料和硫铝酸盐水泥熟料的优良性能,同时该种水泥熟料对粉煤灰等火山灰类材料具有超强的活性激发效果,这使得硫铝酸钙改性硅酸盐水泥具有广阔的应用前景。主要概括了硫铝酸盐改性硅酸盐水泥的性能及水化特性,综述了该种水泥与不同矿物掺合料的复合性能以及与化学外加剂的适应性,提出了硫铝酸钙改性硅酸盐水泥存在的问题及改善措施。     

新型胶凝材料体系的抗裂性能

结构开裂问题一直困扰着现代混凝土工程,引起混凝土结构开裂的因素有很多,其中水泥的"三高"问题,即高硅酸三钙、高铝酸三钙、高细度是引起开裂的主要原因.本通过降低胶凝材料中水泥熟料的比例、采用粗磨而成的水泥熟料以及提高胶凝材料中矿物掺和料比例的方法配制出低碳胶凝材料这种新型胶凝材料体系,并将其与现行搅拌站常用胶凝材料体系进行抗裂性能的对比,应用自主研发设计的"方圆抗裂模具"研究两种胶凝材料体系的抗裂性能,同时结合水化热做进一步的分析.研究表明:低碳胶凝材料这种新型胶凝材料体系所体现的抗裂性能和当前搅拌站所采用的胶凝材料体系进行比较具有非常大的优势;此外对于低碳胶凝材料而言,它的水化放热量和水化放热速率低于现行搅拌站常用胶凝材料体系;掺加一定量的钢渣、膨胀剂能够显著提高低碳胶凝材料的抗裂性;SO3含量低会增加低碳胶凝材料的开裂敏感性.     

梯级粉磨铁尾矿制备超高性能混凝土的研究

展开了梯级粉磨工艺粉磨铁尾矿、石膏、矿渣及水泥熟料生产铁尾矿-矿渣基高性能胶凝材料(简称TSBC)及其性能的研究,探讨了不同粉磨工艺的粉体粒径特征及胶凝性能,对比了TSBC材料与PO52.5水泥的制备超高性能混凝土强度及耐久性差异。研究结果表明,三级粉磨较二级粉磨能更好发挥颗粒的"微磨球"效应,所得粉体材料粒径更小;粉磨中应将铁尾矿砂作为第一级粉磨材料,第一级粉磨时间不宜过长,否则导致粉体过细大量覆盖粗颗粒材料表面,降低后期粉磨效率;TSBC制备的UHPC不仅具有常规UHPC的强度甚至有更优良的耐久性能。     

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.     

Microstructure and mechanical properties of accelerated sprayed concrete

Considering the different hydration processes of concrete without accelerator, sprayed concrete with low-alkali accelerator not only presents short setting times and high early-age mechanical properties but also yields different hydration products. This study presents an analysis of the mechanical properties of concrete with and without accelerator and sprayed concrete with three water–binder (w/b) ratios and four dosages of fly ash (FA) after different curing ages. It also examines the setting time, mineral composition, thermogravimetric–differential scanning calorimetry curves and microscopic images of cement pastes with different accelerator amounts. Furthermore, the setting time and microstructure of accelerated sprayed concrete with different w/b ratios and FA contents are examined. Results show that the retarded action of gypsum disappears in the accelerated cement–accelerator–water system. C₃A is quickly hydrated to form calcium aluminate hydrate (CAH) crystals, and a mesh structure is formed by ettringite, albite and CAH. A large amount of hydration heat improves the hydration rate of the cement clinker mineral and the resulting density, thereby improving mechanical properties at early curing ages. The setting times of the pastes increase with increasing w/b ratio and FA dosage. Thus, the hydration level, microstructure and morphology of the hydration products also change. Models of mechanical properties as functions of w/b, FA and curing age, as well as the relationship between compressive strength and splitting tensile strength, are established.     

High-volume natural volcanic pozzolan and limestone powder as partial replacements for portland cement in self-compacting and sustainable concrete

A laboratory study demonstrates that high volume, 45% by mass replacement of portland cement (OPC) with 30% finely-ground basaltic ash from Saudi Arabia (NP) and 15% limestone powder (LS) produces concrete with good workability, high 28-day compressive strength (39 MPa), excellent one year strength (57 MPa), and very high resistance to chloride penetration. Conventional OPC is produced by intergrinding 95% portland clinker and 5% gypsum, and its clinker factor (CF) thus equals 0.95. With 30% NP and 15% LS portland clinker replacement, the CF of the blended ternary PC equals 0.52 so that 48% CO₂ emissions could be avoided, while enhancing strength development and durability in the resulting self-compacting concrete (SCC). Petrographic and scanning electron microscopy (SEM) investigations of the crushed NP and finely-ground NP in the concretes provide new insights into the heterogeneous fine-scale cementitious hydration products associated with basaltic ash-portland cement reactions.     

Ettringite and calcium sulfoaluminate cement: investigation of water content by near-infrared spectroscopy

Calcium sulfoaluminate (CSA) cement is a sulfate-based binder whose high-performance hydraulic behavior depends on the rapid formation of ettringite, when grinded clinker is hydrated in presence of gypsum. Ettringite is a calcium aluminum sulfate mineral characterized by high water content, estimated as 32 water molecules per formula unit. Three examples of utilization of near-infrared (NIR) spectroscopy are here shown. First of all, information on water distribution in pure ettringite was deduced and compared with infrared analyses. Then its thermal behavior has been followed up to 400 °C, allowing to improve the knowledge about water loss and thermal decomposition of this hydrated phase. Finally, the obtained results have been employed in order to follow hydration of CSA cement sample, demonstrating thus that NIR spectroscopy, being highly sensitive to water amount and distribution, can be an extremely useful tool for hydration studies.     

An investigation on the recycling of hydrated cement from concrete demolition waste

Construction and demolition waste (CDW) recycling is generally limited to the use of the coarser fraction as aggregate for new concrete. The recovery of fine aggregates requires a cleaning by removing the hydrated cement waste (HCW). In this paper, the possibility to use HCW extracted from CDW as alternative component for the production of new clinker is explored.A pure HCW sample was prepared and used in partial replacement of natural materials in raw admixtures for new clinker production. At a replacement degree of 30%, a new Portland clinker containing almost 50% of C₃S could be produced with a huge spare in the release of CO₂ (about 1/3 less). At higher HCW dosage a non-Portland clinker containing almost 80% of C₂S has been obtained: its use as supplementary cementing material in blended cements revealed satisfying long term performances.     

The effect of clinker and limestone quality on the gas permeability,water absorption and pore structure of limestone cement concrete

In this paper the effect of clinker and limestone quality on the air permeability, water absorption and pore structure of limestone cement concrete is investigated. Portland limestone cements of different fineness and limestone content have been produced by intergrinding clinker, gypsum and limestone. Two clinkers with different chemical composition, mineralogical composition and strength development as well as three limestones, differing by their calcite, dolomite, quartz and clay contents, have been used. It is shown that the clinker quality significantly affects the gas permeability and sorptivity of the limestone cement concrete. Limestone cements with high C₃A and alkalis content seem to be more appropriate for improving the permeability properties of concrete. In addition, the effect of the limestone quality on the concrete permeability is not well established. The pore size distribution and more specifically the mean pore size affects the gas permeability and the sorptivity of the concrete. Finally it is concluded that, depending on the clinker quality and the cement fineness, limestone cement concrete, with an optimum limestone content, can give lower gas permeability and water absorption rate as compared with pure cement concrete.     

矿物外加剂对丁苯聚合物/水泥复合胶凝材料凝结硬化过程的影响及机制

为了比较沸石、纳米二氧化硅和稻壳灰这3种矿物外加剂对丁苯聚合物/水泥复合胶凝材料凝结硬化过程作用的差异,分别采用这3种矿物外加剂为调凝材料,并从凝结时间、早期强度、水化进程以及水化产物等角度比较3种矿物外加剂对丁苯聚合物/水泥复合胶凝材料的影响。结果表明,3种矿物外加剂都能促进复合胶凝材料的凝结硬化,大幅缩短凝结时间,提高早期强度。但3种矿物外加剂的调凝效果互不相同,调凝机理也有差异:沸石对AFt的生成有较大的促进作用,它不仅能促进C3A的水化,自身也能与Ca(OH)_2反应生成AFt和CSH凝胶;而纳米二氧化硅和稻壳灰对C3S水化的促进作用较强,自身也会与Ca(OH)_2反应生成CSH凝胶。     

A hydration study of various calcium sulfoaluminate cements

The present work studies the hydration process and microstructural features of five calcium sulfoaluminate (CSA) cements and a ternary mixture including also ordinary Portland cement (OPC). The pastes were studied with simultaneous differential thermal-thermogravimetric (DTA-TG) analysis, mercury intrusion porosimetry (MIP), scanning electron microscopy (SEM), and expansion/shrinkage tests. The DTA-TG analysis confirmed the role of the hydration reactions involving the main CSA clinker constituent, tetracalcium trialuminate sulfate, which produced (i) ettringite when combined with lime and calcium sulfate, (ii) ettringite and aluminum hydroxide in the presence of calcium sulfate alone, and (iii) monosulfate and aluminum hydroxide in the absence of both lime and calcium sulfate. The MIP and SEM were able to discriminate between expansive (ternary mixture and CSA cement containing 50% gypsum) and non-expansive cements. Expansive cement pastes had (i) a nearly unimodal pore size distribution shifted toward higher radii and (ii) ettringite crystals smaller in size during the first day of curing. In a SEM image of a hardened paste of the CSA cement containing 50% gypsum, a stellate ettringite cluster was observed.     

Carbonation of ternary building cementing materials

The carbonation processes of ettringite and calcium aluminate hydrates phases developed by hydration of calcium aluminate cement, fly ash and calcium sulphate ternary mixtures have been studied. The hydrated samples were submitted to 4% of CO₂ in a carbonation chamber, and were analysed, previous carbonation and after 14 and 90 days of carbonation time, by infrared spectroscopy and X-ray diffraction; the developed morphology was performed with the 14 days carbonated samples. The results evidenced that ettringite reacts with CO₂ after 14 days of exposition time and evolves totally at 90 days; the developed hydrated phases C₃AH₆ in samples with major CAC content, also reacts with CO₂. Due to carbonation, calcium carbonate – mainly vaterite but also aragonite-, depending on the initial formulation, aluminium hydroxide and gypsum were detected.     

Analysis of cubic and orthorhombic C<Subscript>3</Subscript>A hydration in presence of gypsum and lime

Field emission scanning electron microscopy (FE-SEM) and X-ray diffraction (XRD) have been used to study the microstructural changes and phase development that take place during the hydration of cubic (pure) and orthorhombic (Na-doped) tricalcium aluminate (C₃A) and gypsum in the absence and presence of lime. The results demonstrate that important differences occur in the hydration of each C₃A polymorph and gypsum when no lime is added; orthorhombic C₃A reacts faster with gypsum than the cubic phase, forming longer ettringite needles; however, the presence of lime slows down the formation of ettringite in the orthorhombic sample. Additional rheometric tests showed the possible effects on the setting time in these cementitious mixes.