用低硅铁尾矿制备贝利特水泥

以湖北某地铁尾矿为主要原料进行了制备贝利特水泥的研究,考察了原料配比、煅烧温度和活化剂石膏掺量对水泥熟料性能的影响。结果表明：以质量分数为30.90%的铁尾矿和69.10%的石灰石为原料,在1 350 ℃煅烧1 h,再添加相当于熟料质量0.60%的活化剂石膏,制得的贝利特水泥3、28 d的强度指标达到了PI42.5R水泥的要求,且其主要矿物种类与传统硅酸盐水泥相一致,但贝利特矿物的含量明显超过传统的硅酸盐水泥。     

Aluminum-rich belite sulfoaluminate cements: Clinkering and early age hydration

Belite sulfoaluminate (BSA) cements have been proposed as environmentally friendly building materials, as their production may release up to 35% less CO₂ into the atmosphere when compared to ordinary Portland cements. Here, we discuss the laboratory production of three aluminum-rich BSA clinkers with nominal mineralogical compositions in the range C₂S (50-60%), C₄A₃$ (20-30%), CA (10%) and C₁₂A₇ (10%). Using thermogravimetry, differential thermal analysis, high temperature microscopy, and X-ray powder diffraction with Rietveld quantitative phase analysis, we found that burning for 15 min at 1350 ºC was the optimal procedure, in these experimental conditions, for obtaining the highest amount of C₄A₃$, i.e. a value as close as possible to the nominal composition. Under these experimental conditions, three different BSA clinkers, nominally with 20, 30 and 30 wt.% of C₄A₃$, had 19.6, 27.1 and 27.7 wt.%, C₄A₃$ respectively, as determined by Rietveld analysis. We also studied the complex hydration process of BSA cements prepared by mixing BSA clinkers and gypsum. We present a methodology to establish the phase assemblage evolution of BSA cement pastes with time, including amorphous phases and free water. The methodology is based on Rietveld quantitative phase analysis of synchrotron and laboratory X-ray powder diffraction data coupled with chemical constraints. A parallel calorimetric study is also reported. It is shown that the β-C₂S phase is more reactive in aluminum-rich BSA cements than in standard belite cements. On the other hand, C₄A₃$ reacts faster than the belite phases. The gypsum ratio in the cement is also shown to be an important factor in the phase evolution.     

HBC低热高抗裂大坝混凝土的开发研究

在“九五”国家科技攻关项目“高贝利特（HBC）新型胶凝材料研究”的基础上,进行了HBC低热高抗裂大坝混凝土的开发研究,通过与三峡二期大坝中热水泥（MHC）混凝土的平行对比试验,初步论证了HBC大坝混凝土具有良好的工作性、力学性能和耐久性能。HBC大坝混凝土在相同配合比下的绝热温升将降低3－5℃;抗裂性分析表明,HBC大坝混凝土具有良好的抗裂能力,是一种可以在水工大体积混凝土工程中推广应用的新型低热高抗裂大坝混凝土。     

Synthesis of belite sulfoaluminate-ternesite cements with phosphogypsum

Phosphogypsum (PG) is an industrial byproduct from phosphoric acid production. In order to facilitate the use of PG, belite sulfoaluminate-ternesite cements were produced with high amounts of PG. This work regards the laboratory production of belite sulfoaluminate-ternesite cements by using a new synthesis method. Using a secondary heat treatment step, the method achieves the coexistence of ye'elimite and ternesite. Quantitative X-ray powder diffraction and electron microscopy were used to analyze the phase composition of clinkers. The secondary heat treatment between 1100 and 1200 °C can significantly facilitate the formation of ternesite in the clinkers. The presence of large amount of ternesite results in a decrease in early strength, but the hydration of ternesite at later ages can increase the strength after 56 days of hardening. The hydration products of pure ternesite and the clinker containing ternesite were also investigated. The results show that pure ternesite can hydrate at a slow rate, and the addition of ye'elimite promotes the hydration of ternesite and the formation of ettringite. The ettringite formation for the clinker containing ternesite mainly depends on the dissolution of gypsum originating from the hydration of ternesite.     

Dicalcium silicate (2CaO·SiO2) synthesized through flame spray pyrolysis and solution combustion synthesis methods

Synthesis of dicalcium silicate (2CaO.SiO₂ or C₂S) through flame spray pyrolysis and a solution combustion method was investigated by the variation of flames and fuels. The synthesized powders were characterized by X-ray diffraction (XRD), Fourier transform infrared (FT-IR) and scanning electron microscopy (SEM). X-ray diffraction analysis revealed the formation of dicalcium silicate polymorphs with presence of calcium oxide, calcium carbonates and amorphous materials as impurities. Results suggest that some flames and fuels favor the formation of calcite during the synthesis process due to an excess of carbon atoms in the combustion. Fourier transform infrared spectra of all samples showed the main silicates reflections located near to 500?cm^?1 and 1000?cm^?1 and scanning electron microscopy showed the formation of spherical agglomerates of nanoparticles in both methods. By these two alternative methods of synthesis it was possible to obtain C₂S with nanometric particle size.     

高贝利特水泥混凝土的抗拉性能

通过劈裂抗拉试验和轴心抗拉试验,比较了不同水灰比、不同龄期的高贝利特水泥混凝土与硅酸盐混凝土的抗拉强度、极限拉伸值,研究了高贝利特水泥抗拉性能对开裂的影响。采用界面过渡区显微硬度试验、电子扫描电镜和X射线能谱分析,分别对高贝利特水泥和硅酸盐水泥混凝土界面过渡区进行了表征。结果表明:相同水灰比和龄期的高贝利特水泥混凝土的抗拉强度和极限拉伸值均大于硅酸盐水泥的;高贝利特水泥混凝土后期抗拉强度增长率大,强度高;高贝利特水泥混凝土界面过渡区厚度比硅酸盐水泥混凝土小25μm,显微硬度大8.9MPa,钙硅比低,界面黏结好。高贝利特混凝土的界面结构和抗拉性能均优于硅酸盐水泥混凝土。     

铬渣的利用研究

利用粉煤灰、石灰石、铬渣等为原料煅烧生产新型贝利特水泥可以去除铬渣毒性。本文进行了去除铬渣毒性稳定性试验；讨论了去除铬渣毒性的机理与影响去除铬渣毒性的因素。试验结果表明，该法去除铬渣毒性彻底，社会效益十分显著，是铬渣利用的一种有效途径。     

Microstructure and mineral composition of Roman cements produced at defined calcination conditions

As a part of a major study on 19th century Roman cements a laboratory optimisation study of the calcination of two marls has been conducted within the temperature range 730 to 1100 °C. Strength assessment has shown that the optimum kiln conditions lie towards lower temperatures and differ for the two marls by no more than some 50 °C.This paper discusses the clinker properties in terms of phase composition and microstructural features. The textural and mineralogical characteristics of the marl fractions significantly influence the nature and amount of phases formed during solid-state reactions under non-equilibrium conditions.At low to intermediate calcination temperatures it is mainly the fine-grained matrix of the marls which reacts, while coarse particles remain largely un-reacted. The major reactive crystalline phases identified in the optimum cements are belite in two polymorphs and free lime, while a number of other compounds remain unclear because of their non-crystalline nature.     

New waste based clinkers: Belite and lime formulations

This work describes the formulation of new belite-based (CR2) and lime-based (CR3) cementitious materials derived from industrial wastes, such as sludges (generated in the Al-anodising and surface coating industrial processes, potable water filtration/cleaning operations and in marble sawing processes) and foundry sand.Powder mixtures were prepared and fired at different temperatures. For comparison, similar formulations were prepared with pre-treated and commercially available natural raw materials and processed in similar conditions. The thermal process was followed by differential scanning calorimetry (DSC) and high-temperature powder X-ray diffraction (HT-XRD) studies.The CR2 clinker was found to contain belite as the main cementitious phase, the main polymorph being identified by NMR. The CR3 clinker contained common cementitious phases, such as C₃A and C₃S, but free lime and calcium aluminium oxide sulphates were also identified by high temperature XRD and NMR.Then the corresponding cement was prepared and the evolution of the mechanical strength with time was evaluated. The lime-based cement obtained from wastes shows a stronger hardening character than the standard material, which tends to show dusting phenomena due to the presence of a reasonable amount of free lime (as the result of its expansive reaction with ambient moisture). Some fluxing impurities (e.g. alkalis) present in the waste materials improve the overall reactivity of the mixture and induces the combination of the lime in CR3. Raman, XPS and FIB techniques were used to fully characterise the aged cements.     

固废制备高贝利特硫铝酸盐水泥的研究进展

高贝利特硫铝酸盐水泥具有早期强度高、后期强度发展好的特点,生产能耗低且CO2排放量少。从固废原料的利用、水泥制备工艺与水泥性能3个层面,综述了固体废弃物制备高贝利特硫铝酸盐水泥的研究现状;并提出固废制备高贝利特硫铝酸盐水泥需进一步研究和解决的问题,如大宗固废原料的利用、全固废制备技术及固废重金属固化、溶出评价等,亦为今后理论研究与实践发展的新路径。