Rietveld全谱拟合方法对磷酸镁水泥水化产物的定量分析研究

在X射线衍射定性分析的基础上,结合Rietveld全谱拟合方法对不同龄期磷酸镁水泥样品的水化产物晶相含量进行了定量研究。结果表明,龄期为10 min、1 h及1 d的磷酸镁水泥样品中水化产物MgKPO4·6H2O的相对含量分别为12.39%、15.77%和18.38%,拟合的Rwp因子为9.73%～12. 8%,说明该方法能准确、直观、快速的确定不同龄期样品中各晶相的组成及相对含量,并获得各相的相关晶体学结构参数,同时结合相关理论对磷酸镁水泥的水化及性能作出客观分析,为加深对水泥材料的认识提供了一种可行的研究方法。     

氯氧镁水泥胶凝材料的研究进展

氯氧镁水泥是由轻烧菱镁石粉和氯化镁水溶液按一定比例混合而成的一种新型镁质气硬性胶凝材料。它有很多优于普通硅酸盐水泥的性能,但其耐水性差等缺点也很突出。为了使氯氧镁水泥得到更好的应用,总结和分析了氯氧镁水泥的研究进展,包括水化行为、水化产物组成和结构、耐水性以及生产应用方面。指出了氯氧镁水泥在当前的发展过程中存在的不足和问题,以期为后续氯氧镁水泥的进一步研究提供参考。     

Microstructures of magnesium oxychloride

The well-crystallized phases of magnesium oxychloride (MOC) cement have been described as scroll-tubular whiskers and compared to the tobermorite crystals for a long time. However, sporadic evidence of the acicular crystals without enough and consistent detail has befuddled researchers in the microstructural studies of the cement. With the modern technology and powerful computational capability, more detailed and clarified microstructure of the MOC crystalline phases including morphology, crystal habit, grain size, and elemental composition could be revealed. This paper reports the work on microstructural examination of MOC cement providing practical information for further study of the crystal structure of the different reaction phases. The experimental results show that the crystalline phases of MOC cement are in general needle shaped crystals with a granular surface and bundled in different forms. Imprints of bundled needle shaped crystal can also be scrutinized in the massive and dense microstructure of the cement paste with high compressive strength.     

Strength and hydration products of reactive MgO–silica pastes

The reaction between MgO and microsilica has been studied by many researchers, who confirmed the formation of magnesium silicate hydrate. The blend was reported to have the potential as a novel material for construction and environment purposes. However, the characteristics of MgO vary significantly, e.g., reactivity and purity, which would have an effect on the hydration process of MgO–silica blend. This paper investigated the strength and hydration products of reactive MgO and silica blend at room temperature up to 90 days. The existence of magnesium silicate hydrate after 7 days’ curing was confirmed with the help of infrared spectroscopy, thermogravimetric analysis and X-ray diffraction. The microstructural and elemental analysis of the resulting magnesium silicate hydrate was conducted using scanning electron microscopy and energy dispersive spectroscopy. In addition, the effect of characteristics of MgO on the hydration process was discussed. It was found that the synthesis of magnesium silicate hydrate was highly dependent on the reactivity of the precursors. MgO and silica with higher reactivity resulted in higher formation rate of magnesium silicate hydrate. In addition, the impurity in the MgO affects the pH value of the blends, which in turn determines the solubility of silica and the formation of magnesium silicate hydrate.     

Influence of curing temperature on the evolution of magnesium oxychloride cement

Hardening behaviour and strength of oxychloride cement strongly depend on the formation of Phase 3 and Phase 5 from MgO and magnesium chloride water solution, and the initial composition can be chosen accordingly within the corresponding phase diagram. A certain number of reactions occur before the final formation of P5 or P3 crystals, and several parameters influence the transformations kinetic, such as MgO reactivity and temperature. Several articles deal with the first aspect, while no indications can be found with regard to the curing temperature’s effect on the formation of noble phases. In this article the evolution of magnesium oxychloride cement pastes is analysed at various curing temperatures between 5 and 40 °C. The study is carried out to simulate typical industrial processing conditions and indicate optimal conditions for the production of high chemical and mechanical resistance oxychloride cement. It is shown that at low temperature, Phase 3 is produced in place of Phase 5, and a certain amount of MgO remains non-reacted. The corresponding cement is characterised by lower mechanical strength and higher water solubility.     

MgO晶须增强磷酸镁水泥力学性能的研究

MgO 晶须弹性模量高,长径比大,掺加到磷酸镁水泥(MPC)中可以产生增强增韧作用。研究了水料比、缓凝剂掺量不同时 MgO 晶须对 MPC 力学性能的影响,采用 SEM 和重量法研究了 MgO 晶须在 MPC 中的分布及水化,分析了 MgO 晶须增强 MPC 的机理。结果表明,掺加3%~5%的 MgO 晶须使 MPC 在水料比和缓凝剂掺量较高时获得良好的早期强度;MgO 晶须在 MPC 中搭接形成网络结构,并通过晶须桥联、裂缝偏转等作用,使 MPC 的早期力学性能显著增强;MgO 晶须参与水化,提高了晶须与 MPC 基体的握裹力和相容性;随着龄期延长,晶须水化程度加深,使 MPC 基体更加致密,后期抗压强度增长明显,但晶须的桥联作用逐渐减弱,MPC 的后期抗折强度增长幅度较小。     

Enhanced hydrated properties of α-tricalcium phosphate bone cement mediated by loading magnesium substituted octacalcium phosphate

A novel Mg-containing α-tricalcium phosphate (α-TCP) bone cement with excellent wetting compressive strength and suitable setting time has been developed in this work. Mg-substituted octacalcium phosphate (Mg-OCP) crystals with the special morphology was prepared by homogeneous precipitation method, and used to modify the α-TCP bone cement. Mg²⁺ was successfully introduced into OCP structure, and the filaments/sheet-like morphologies of OCP were obtained by changing the Mg²⁺ concentration. As added in the α-TCP cement matrix, the effects of Mg-OCP on the wetting compressive strength, setting time and microstructure of the cement system were studied. The addition of Mg-OCP shortened the setting time of cement pastes with the minimum setting time of 15 min, and enhanced the wetting compressive strength of the hydrated cement products with the highest wetting compressive strength of 36.86 MPa. This work highlights the special morphologies of Mg-OCP induced by Mg²⁺ substitution, which made an effect on the hydration reaction of α-TCP cement; Furthermore, Mg-OCP was supposed to improve the condensation capacities and mechanical properties of α-TCP cement system as a novel cement admixture.     

含Q相高铝水泥水化性能的研究

在实验室内采用化学原料烧制Q相-CA(CaO·Al2O3)-C12A7(12CaO·7Al2O3)高铝水泥,对所烧制的水泥进行水化性能研究.研究结果表明:Q相-CA-C12A7高铝水泥早期强度高,中后期强度仍在发展且不倒缩.XRD和DTA分析表明,其早期水化产物为铝胶、CAHio和C2AH8,中后期为铝胶、CAH1o、C2AH8和C3AH6.     

Strength and hydration properties of reactive MgO-activated ground granulated blastfurnace slag paste

Ground granulated blastfurnace slag (GGBS) is widely used as a partial replacement for Portland cement or as the major component in the alkali-activated cement to give a clinker-free binder. In this study, reactive MgO is investigated as a potentially more practical and greener alternative as a GGBS activator. This paper focuses on of the hydration of GGBS, activated by two commercial reactive MgOs, with contents ranging from 2.5% to 20% up to 90 days. The hydration kinetics and products of MgO–GGBS blends were investigated by selective dissolution, thermogravimetric analysis, X-ray diffraction and scanning electron microscopy techniques. It was found that reactive MgO was more effective than hydrated lime in activating the GGBS based on unconfined compressive strength and the efficiency increased with the reactivity and the content of the MgO. It is hence proposed that reactive MgO has the potential to serve as an effective and economical activator for GGBS.