矿物掺合料改性磷酸镁水泥研究进展

在总结磷酸镁水泥水化产物、水化速度、孔结构、流动性和物理力学性能等的基础上,综述了粉煤灰、矿渣、硅灰、赤泥和偏高岭土等矿物掺合料对磷酸镁水泥的改性效果和作用机理。矿物掺合料改性磷酸镁水泥具有优异的物理力学性能和经济性,耐水性、严苛条件下耐久性、负温下水化硬化特征和矿物掺合料改性机制等课题尚待深入研究,以期为促进磷酸镁水泥及其修补砂浆在重点工程中的应用提供参考。     

粉煤灰和矿粉对磷酸镁水泥性能的影响

磷酸镁水泥(magnesium phosphate cement,MPC)是一种新型气硬性胶凝材料,在其中掺入矿物掺合料可改善其性能.本文采用高纯度死烧MgO、磷酸二氢铵及硼砂配制了磷酸镁水泥,掺人一定量粉煤灰或矿粉,研究了这两种矿物掺合料对磷酸镁水泥凝结时间、力学性能及耐水性能的影响.结果表明:随着粉煤灰和矿粉掺量的增加,MPC凝结时间缩短;砂浆试件抗压强度呈先升高后降低趋势,当掺量为10％时,抗压强度最高,同等掺量的矿粉对MPC早期和后期强度的贡献均优于粉煤灰的贡献;粉煤灰的掺入提高了MPC的耐水性,而矿粉的掺入却有降低MPC的耐水性的趋势;XRD测试表明,不掺掺合料、掺粉煤灰、掺矿粉的MPC的主要反应产物均为MgNH4 PO4·6H2O和一些非晶相,掺矿粉的MPC试件浸水28 d后,表面浸出物主要为MgNH4 PO4·6H2O.     

磷酸镁水泥的研究与工程应用

分析阐明了磷酸镁水泥（MPC）的凝结硬化作用机理,指出MPC是在酸性条件下通过化学反应形成以磷酸镁为主要黏结相的水泥质陶瓷材料,并对MPC凝结时间的控制技术进行了探讨;概述了MPC材料的性能特点,并对其处理固体废物进行了试验研究;同时结合MPC的性能特点,对其工程应用做了简单介绍。     

磷酸镁水泥的研究进展

磷酸镁水泥凝结时间短、早期强度高，在机场跑道、隧道、矿井等民用建筑和国防工程的抢修等方面具有广阔的前景。但磷酸镁水泥水化极快，凝结时间非常短，导致工程施工无法进行。综述了现阶段磷酸镁水泥凝结时间受原材料、缓凝剂、掺合料等因素影响的新成果，以及提高磷酸镁水泥密实性、粘结性、抗冻性性能的新措施，展望了磷酸镁水泥的发展前景。     

偏高岭土改性磷酸镁水泥

磷酸镁水泥具有快硬早强特性,但使用缓凝剂延长凝结时间会导致早期强度下降。采用偏高岭土部分替代氧化镁对磷酸镁水泥进行改性,研究了偏高岭土取代量对磷酸镁水泥砂浆凝结时间、水化热、小时强度和粘结强度的影响,并采用扫描电镜对水化产物进行了分析。结果表明:偏高岭土部分取代氧化镁可显著延长磷酸镁水泥砂浆凝结时间,且大幅提高其1 h强度和粘结强度;偏高岭土中的活性Al_2O_3参与反应并形成AlH_3(PO_4)_2·H_2O和AlPO_4等非晶态凝胶,有效改善了其力学性能。     

磷酸镁水泥耐水性研究进展

磷酸镁水泥(MPC)是一种快凝快硬的新型胶凝材料,具有干缩小、抗冻性好、早期强度高等优良特性,应用于工程修补和有害物质的固化。从磷酸镁水泥的水化产物出发,分析了磷酸镁水泥耐水性的机理,讨论了其耐水性的影响因素,包括原料配比、MgO颗粒细度、养护湿度和温度、缓凝剂和水胶比,提出了通过使用防水剂、增加预养护时间、掺入外加剂和掺合料等措施改善磷酸镁水泥的耐水性。     

粉煤灰对磷酸镁水泥早期性能的影响

磷酸镁水泥具有早强快硬性的特点,导致了其制备的混凝土存在长距离运输不易搅拌、难以泵送等施工问题.针对这一问题,采用粉煤灰对磷酸镁水泥进行改性,研究了不同粉煤灰掺量对磷酸镁水泥流变性的影响.采用布氏粘度计测定了磷酸镁水泥浆体在不同剪切速率下的流变参数,使用宾汉姆流体模型拟合了磷酸镁水泥流变曲线.利用冷场发射扫描电镜与X射线衍射仪研究了粉煤灰对磷酸镁水泥微观结构与水化产物的影响,并探讨了粉煤灰对磷酸镁水泥流变性的改性机理.结果 表明,粉煤灰可以有效地改善磷酸镁水泥的流变性并延长凝结时间;“形貌效应”是粉煤灰提高磷酸镁水泥流变性的主要原因;粉煤灰的掺入不会改变磷酸镁水泥水化产物的物相组成,但会对磷酸镁水泥的部分力学特性产生不良影响.     

低温下粉煤灰改性磷酸镁水泥性能研究

磷酸镁水泥(MPC)是以重烧氧化镁、磷酸二氢钾为主要原料,掺入一定量的粉煤灰作为掺合料,硼砂与磷酸氢二钾作为缓凝组分制备而成.本文对低温(-10±2)℃条件下,磷酸镁水泥的力学性能与收缩率进行了测试、使用MIP、SEM等测试手段对磷酸镁水泥低温下性能进行了研究;分析了低温对MPC材料影响的机理.结果表明,一定量的粉煤灰掺入,可以提高低温养护下MPC材料的性能.     

磷酸镁水泥性能试验研究

采用过烧镁砂与磷酸镁二氢钾为主要原料,按照一定配比制备出可工业化生产的磷酸镁水泥。研究了磷酸镁水泥的凝结硬化时间、不同龄期的强度、干缩率、耐腐蚀性及粉煤灰对其性能的改性,并采用X射线衍射分析和扫描电镜等手段对其水化产物进行了分析。研究结果表明,磷酸镁水泥凝结时间受水灰比、成型温度影响较大,早期强度发展迅速,干缩率较小,耐腐蚀性好,掺加适量的粉煤灰可有效地提高其后期强度。该体系水化产物主要是六水磷酸镁钾晶体和一些无定形物质。     

矿物掺合料对氯氧镁水泥早期水化行为的影响

研究了矿物改性氯氧镁水泥前期水化行为,绘制了各矿物掺合料氯氧镁水泥水化电阻率-时间曲线,测试终凝时间以及1 d抗弯与抗压强度。结果表明,矿物掺合料能够延缓氯氧镁水泥水化速度,并随着矿物掺合料掺量的提高,其水化速度逐渐变慢。同等掺量下硅灰延缓反应时间的作用最为明显,其次是石粉与粉煤灰。硅灰的掺入延缓氯氧镁水泥水化速度,大幅度提高其初终凝时间,降低早期强度,其掺量不宜超过20%。粉煤灰与石粉氯氧镁水泥初终凝时间均在规范要求以内,对早期抗弯拉强度与抗压强度影响幅度相对较小。添加粉煤灰与石粉试样晶体较掺硅灰试样结晶程度更高。     

矿物掺合料对混凝土徐变影响研究进展

掺加矿物掺合料是改善混凝土性能的主要措施之一,受到研究者的广泛关注。当前,已有大量研究表明矿物掺合料对混凝土徐变性能具有积极的作用,但缺少文献系统回顾和比较不同类型矿物掺合料对混凝土徐变的影响。本文从徐变机理、单掺和复掺不同类型矿物掺合料对混凝土徐变的影响等方面,对已有文献进行总结分析,以便为进一步研究提供参考和借鉴。     

超快硬磷酸镁水泥研究进展

概述了制备磷酸镁水泥所使用的原料和水泥的制备方法。探讨了磷酸镁水泥的水化机理和缓凝机理,并对主要水化产物磷酸镁铵（MgNH4PO4·6H2O）的晶体化学结构进行了分析。综述了磷酸镁水泥的研究进展和应用前景。指出：磷酸镁水泥基础性研究不够深入,特别是水化机理和水化产物等方面存在争议;在磷酸镁水泥中采用较多的化学原料时会造成成本偏高;磷酸镁水泥在水化反应过程中释放氨气会造成空气污染;中国对磷酸镁水泥的研究报道较少,应用领域也较有限。以上种种因素限制了磷酸镁水泥的规模化生产和应用。因此,在深入开展磷酸镁水泥基础理论研究的同时,仍需对其应用领域进行推广,特别是寻求廉价的矿物和岩石原料或工业废弃物作为替代原料（如菱镁矿替代轻质碳酸镁等镁盐）或填料,这是磷酸镁水泥大量规模化生产和应用的关键。     

半柔性路面用水泥基灌浆材料的矿物掺合料协同优化研究

矿物掺合料是半柔性路面用水泥基灌浆材料的重要组成部分,各矿物掺合料协同优化对灌浆材料流动性能和力学性能的提升发挥重要作用。本文选用矿粉、微珠和硅灰三种矿物掺合料,通过正交试验研究了三种矿物掺合料协同优化对路面用灌浆材料流动性能和力学性能的影响规律,并借助XRD、SEM等表征方法分析了灌浆材料硬化浆体的水化产物组成与形貌。结果表明,三种矿物掺合料协同优化对灌浆材料流动性能和力学性能的影响顺序为微珠、硅灰和矿粉,其中微珠对灌浆材料流动性能改善效果最为显著,硅灰和矿粉对灌浆材料力学性能提升效果明显。以灌浆材料的流动性能和早期强度为评价指标,微珠、硅灰和矿粉协同优化灌浆材料的最佳掺量分别为15%、1.5%和5%(均为质量分数)。此外,三种矿物掺合料协同掺加对灌浆材料早期水化产物组成与形貌影响较小,表明矿物掺合料协同主要是通过物理填充作用提高了硬化浆体材料的密实度,从而改善灌浆材料早期力学性能。     

Effect of superplasticizer and shrinkage-reducing admixtures on alkali-activated slag pastes and mortars

This paper shows how several superplasticizers (polycarboxylates, vinyl copolymers, melamine and naphthalene-based) and shrinkage-reducing (polypropylenglycol derivatives) admixtures affect the mechanical and rheological properties and setting times of alkali-activated slag pastes and mortars. Two activator solutions, waterglass and NaOH, were used, along with two concentrations—4% and 5% of Na₂O by mass of slag. All admixtures, with the exception of the naphthalene-based product, lost their fluidifying properties in mortars activated with NaOH as a result of the changes in their chemical structures in high alkaline media. The difference in the behaviour of these admixtures when ordinary Portland cement is used as a binder is also discussed in this paper.     

Durability of self-consolidating concrete incorporating high-volume replacement composite cements

Self-consolidating concrete (SCC) decreases construction time, labor and equipment on construction sites, makes the construction of heavily congested structural elements and hard to reach areas easier, reduces noise- and vibration-related injuries, and helps in achieving higher quality finish surfaces. However, because it usually requires a larger content of binder and chemical admixtures compared to ordinary concrete, its material cost is generally 20-50% higher, which has been a major hindrance to a wider implementation of its use. There is growing evidence that incorporating high volumes of mineral admixtures and microfillers as partial replacement for portland cement in SCC can make it cost effective. However, the durability of such SCC needs to be proven. This research investigates the rapid chloride ion penetrability, sulfate expansion and deicing salt surface scaling resistance of SCC mixtures made with high-volume replacement binary, ternary, and quaternary cements. The fresh concrete properties and compressive strength at 1, 7, 28 and 91 days of such SCC mixtures were measured. Moreover, rapid chloride ion penetrability was investigated for the various SCC mixtures at 28 and 91 days, while the deicing salt surface scaling under 50 freezing-thawing cycles and sulfate expansion after up to 9 months of immersion in a 5% Na₂SO₄ solution were investigated as per the ASTM C-672 and ASTM C1012 guidelines, respectively. Results indicate that SCC can be made with high-volume replacement composite cements and achieve good workability, high long-term strength, good deicing salt surface scaling resistance, low sulfate expansion and very low chloride ion penetrability.     

喷射3D打印磷酸镁水泥与混凝土界面粘结性能研究

本文结合喷射3D打印全角度智能建造与磷酸镁水泥(MPC)快硬早强、高粘结性能,研究喷射3D打印MPC与混凝土界面粘结性能。通过掺加偏高岭土(MK)和粉煤灰(FA)调控MPC凝结时间、流变和力学性能,研发可喷射3D打印MPC,分析喷射3D打印MPC与混凝土界面粘结强度和微观结构变化规律。结果表明:MK通过降低MPC水化放热速率可明显提高MPC凝结时间,FA可缩短MPC初凝与终凝时间差,进而提高喷射3D打印MPC稳定性;MPC抗折强度随MK掺量先增大后降低,FA可进一步提高MPC抗折强度;随MK掺量增加,MPC静态屈服应力逐渐提高,FA对MPC屈服应力作用不明显,但可显著降低MPC塑性粘度,当掺加30%MK和15%FA时,可保证MPC良好可喷射3D打印建造性和泵送性;喷射3D打印通过高速喷射挤压作用,提高MPC与混凝土界面以及MPC层间粘结强度,使喷射3D打印MPC层间及其与混凝土微观界面粘结密实。     

Properties of fresh and hardened concrete

The present paper reviews the literature related to the properties of fresh and hardened concrete published after the previous (12th) International Congress on the Chemistry of Cement held in Montreal in 2007.Workability and fundamental rheological properties, reversible and non-reversible evolution, thixotropy, slump loss, setting time, bleeding, segregation and practical issues related to formwork filling and pressure, are addressed among the properties of fresh concrete.Among hardened concrete properties compressive strength and other mechanical and physical properties of hardened concrete, such as tensile strength, elastic properties, shrinkage, creep, cracking resistance, electrical, thermal, transport and other properties are covered. Testing, interpretation, modeling and prediction of properties are addressed, as well as correlation with properties of fresh concrete and durability, effects of special binders, recycled and natural aggregates, fiber reinforcement, mineral and chemical admixtures. Special attention is given to the properties of hardened lightweight and self-compacting concrete.     

Influence of mineral admixtures on mechanical properties of self‐compacting concrete under elevated temperature

Self‐compacting concrete (SCC) is a form of concrete that is capable of flowing into the congested interior of formwork and consolidating under the action of its own weight without segregation and bleeding. In the present investigation, an attempt has been made to study the effect of elevated temperature on mechanical properties of SCC specimens made with different mineral admixtures that were heated from 27 to 900 °C and cooled by air or water. Silica fume, flyash, metakaolin were used as mineral admixtures. Master Glenium was used as superplasticizer, and Glenium Stream 2 was used as viscosity modifying agent. Mechanical properties of the cooled specimens such as compressive strength, tensile strength, flexural strength, and modulus of elasticity were found. Compressive, tensile, and flexural strengths of specimens were found to decrease by 73.18%, 65.05%, and 63.2%, and 85.2%, 83.52%, and 83.56% for the specimens with metakaolin that were heated and cooled by air and water, respectively. Similar reductions were found for the SCC specimens made with silica fume and flyash. Microstructure investigation has been carried out on SCC samples using scanning electron microscope and X‐ray diffraction analytical techniques to understand the effect of temperature on decrease in strength. Copyright © 2016 John Wiley & Sons, Ltd.     

多元矿物掺合料对珊瑚砂混凝土性能的影响

因珊瑚砂混凝土成型初期吸水量大,引起强度波动,影响混凝土耐久性,本文采用矿物掺合料对其进行改性研究.将5wt％偏高岭土(MK)、15wt％粉煤灰(FA)、15wt％矿粉(GGBS)分别以单掺、复掺和三掺形式加入珊瑚砂混凝土中,研究多元矿物掺合料对其抗压强度、抗氯离子渗透性能及体积稳定性的影响,利用XRD、SEM对其机理进行研究.结果表明,矿物掺合料能优化水泥浆体的水化产物组成与亚微观孔结构,增强浆体与骨料间的结合,通过不同的组合方式加入到珊瑚砂混凝土中,其28 d抗压强度提高17.7％～21％;氯离子渗透系数降低66.7％～71.0％;干燥收缩率降低36.7％～57.0％.