In order to effectively manage large quantities of discharged iron ore tailings (IOTs), this investigation studied the application of calcareous IOTs in cement production with the analysis of clinker phases and hydration products using X-ray diffraction, thermogravimetric analysis, and scanning electron microscopy. Furthermore, the influence of the addition of calcareous IOTs on the physical strengths of the prepared cement was evaluated. The results showed that the clinker phases were C3S, C2S, C(3)A, and C(4)AF, and the cement hydration products were claviform ettringite, granular C-S-H gels, and flaky Ca(OH)(2). In addition, the maximum amount of IOTs added for a 52.5 grade cement production was 6 wt.%. This investigation is beneficial in both reducing the use of conventional cement materials and the management of IOTs.

利用矿渣-CaO-脱硫石膏为胶凝材料、海砂为骨料,制备出了较高强度的新型人工鱼礁.借助力学性能测试、X射线衍射、热重分析和扫描电镜考查了脱硫石膏对新型人工鱼礁材料的抗压强度和水化产物的影响.结果表明:适量脱硫石膏的掺加能够显著提高CaO激发矿渣胶凝材料的胶结强度,促进钙矾石(AFt)在水化过程的优先生成,较佳石膏掺量条件下3 d强度可提高51.4％,7 d强度提高35.7％,28 d强度提高25.2％;重金属离子溶出检测结果表明,浸泡试样的海水水质符合国家一类海水水质标准;表面浸出液pH值检测显示,人工鱼礁材料试块海水浸泡初期,表层有少量OH-溶出,使浸泡液pH值由新鲜海水的8.0升至8.5,但60 d后恢复到正常值;此外,海域实地挂板实验表明,制作出的鱼礁海水相容性良好,有大量水生生物附着.低碱度生态型人工鱼礁能够满足鱼礁的基本性能要求,具有广阔的应用前景,为矿渣及海砂的资源化综合利用提供了一条新的途径.

To investigate the variation in the degree of polymerization calcium aluminium silicate hydrate (C-A-S-H) gel and its role in the evolution of the strength of waterglass slag binders,the compressive strength,hydration products,degree of hydration of the slag,and the degree of polymerization of C-A-S-H gels of binders were examined.The experimental results indicate that the pH of the pore solution increased with an increase in the Na 2 O concentration.However,mortar with an optimum compressive strength value of 81.0 MPa at 28 d was obtained when water glass modulus was 1.5.The main hydration product is a C-A-S-H gel for which the quantity and the degree of polymerization depend strongly on the Na 2 O concentration;for a given range,both increase with increasing Na 2 O concentration,thus yielding an enhanced strength.A further increase in the Na 2 O concentration continuously increases the quantity of C-A-S-H gels while drastically reducing the degree of polymerization.The positive effect of the former is counteracted by the adverse effect of the latter,ultimately,leading to a decreased strength.Furthermore,we reveal that the degree of polymerization for C-A-S-H gels may be affected by pH,through a series of complex chemical reactions.

海砂混凝土是指采用海砂为骨料制备而成的混凝土.随着河砂资源的日趋减少,致使建筑用砂逐渐短缺,利用海砂来制备混凝土,可以一定程度缓解建筑用砂短缺的压力.介绍了海砂中氯离子、硫酸根离子和贝壳类等有害物质对混凝土耐久性能的影响.针对目前海砂混凝土在开发利用方面存在的问题,概述了海砂淡化、钢筋保护法和采用新型耐腐材料(FRP)3种改进措施.最后就海砂混凝土研究现状提出了3点建议,以期为未来的研究方向提供参考.

地聚物泡沫混凝土是一种新型轻质多孔材料,具有轻质高强、吸声隔热、吸能抗震、节能利废、耐酸耐腐等优良性能.本文综合介绍了地聚物泡沫混凝土的制备工艺及研究现状,并对其性能和应用现状进行了探讨,最后指出了其应用中常见的问题,展望了未来地聚物泡沫混凝土的应用前景与发展方向.

The harm caused by mine tailings has become increasingly problematic in recent years, so efforts are needed to dispose of or reutilize them in environmentally friendly ways. The objective of the present study was to find out if the hydration properties of muscovite contained in mine tailings are suitable for it to be used as a pozzolan in cement, after undergoing mechanical activation. Aqueous suspensions of mechanically activated muscovite were blended with 10, 20, or 30 wt.% calcium oxide and then allowed to harden. The hardened paste samples were analyzed by X-ray diffraction (XRD), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), and energy dispersive X-ray spectroscopy (EDS) techniques. The results revealed that the mechanically activated muscovite exhibited pozzolanic reaction activity in the alkaline environment provided by calcium oxide, and the activated muscovite possessed a capacity to react with calcium hydroxide to form hydration products. The calcium oxide content affected significantly the quantities and kinds of hydration products, non-evaporable water content, and the compressive strength development of the paste samples. The hydration products of the 10% calcium oxide-activated, mechanically activated muscovite pastes were Al-containing hydrated calcium silicate (C-A-S-H) gel, stratlingite, and, upon addition of 20% and 30% calcium oxide, Ca-Al hydrotalcite-like (Ht) phases. The present study was helpful in evaluating the hydration properties of the mechanically activated muscovite and also provided a research basis for evaluating the hydration properties of mine tailings containing muscovite after mechanical activation. The results provided a theoretical basis for muscovite-containing mine tailings to be used as a cement additive, and was conducive to the large-scale utilization of mine tailings.

为进一步明确水玻璃在矿渣基胶凝材料(SCM)水化过程中的作用机制,借助力学性能测试、X射线衍射和热重分析考察了水玻璃模数对SCM抗压强度和水化产物的影响.同时,采用等温量热法和Krstulovic-Dabic动力学模型,讨论了SCM结晶成核与晶体生长(NG)、相边界反应(I)和扩散(D)过程的水化动力学参数与水玻璃模数之间的相关性.结果表明,在水玻璃模数为0.7～2.5范围内,SCM的主要水化产物均为水化硅(铝)酸钙凝胶,其生成量随水玻璃模数的增加逐渐降低.低水玻璃模数(Ms=0.7)条件下,大量低聚合度硅(铝)酸钙凝胶的生成造成了SCM抗压强度的降低.动力学研究表明,SCM的水化过程符合Krstulovic-Dabic动力学模型,控制历程均表现为NG→I→D.水玻璃模数对SCM水化过程的作用机制在于对各阶段反应速率常数的影响,NG、I和D过程的反应速率常数均随水玻璃模数的增加逐渐降低,导致了SCM水化反应速率下降.

The harm caused by mine tailings to human society has become increasingly prominent and the utilization of mine tailings has become the focus of research in recent years. The pozzolanic reaction activity of iron ore tailings (IOTs), which is of great significance for the effective treatment of the tailings and their efficient utilization as supplementary cementitious material was investigated in this study. The reactivity of IOTs was characterized by comparing the pozzolanic activity and hydration properties of mechanically activated IOTs obtained by mechanical activation in a vertical planetary mill and amorphous ground granulated blast furnace slag (GGBFS) with the similar specific surface area as IOTs. The results demonstrated that the mechanically activated IOTs exhibited similar hydration properties to GGBFS, but their pozzolanic activity was lower. The major hydration products of the CaO-activated mechanically ground IOTs/GGBFS pastes were both amorphous C-S-H gel, as well as ettringite crystals in the presence of natural anhydrite, differing only in amounts. The compressive strength of the activated IOTs-based paste sample was lower, but had a long-term strength development trend than GGBFS based past sample. In addition, the elemental compositions of the C-S-H gel in the activated IOTs-based paste exhibited a lower atomic ratio of Ca/Si than GGBFS based past at the same curing time. The aluminosilicate minerals in activated IOTs have positive effects on the reaction activity, and the pozzolanic activity index (28 d) of the activated IOTs was tested to be qualified for usage as active mixture in cement. This study provides an innovative approach for the utilisation of crystalline IOTs in an environmentally friendly manner.