Characteristic and optimization of ferrite-rich sulfoaluminate-based composite cement suitable for cold region tunnels

To develop suitable grouting materials for water conveyance tunnels in cold regions,firstly,this study investigated the performance evolution of ferrite-rich sulfoaluminate-based composite cement(FSAC grouting material)at 20 and 3℃.The results show that low temperature only delays the strength development of FSAC grouting material within the first 3 d.Then,the effect of four typical early strength synergists on the early properties of FSAC grouting material was evaluated to optimize the early(£1 d)strength at 3℃.The most effective synergist,Ca(HCOO)_(2),which enhances the low-temperature early strength without compromising fluidity was selected based on strength and fluidity tests.Its micro-mechanism was analyzed by XRD,TG,and SEM methods.The results reveal that the most suitable dosage range is 0.3 wt%−0.5 wt%.Proper addition of Ca(HCOO)_(2)changed the crystal morphology of the hydration products,decreased the pore size and formed more compact hydration products by interlocking and overlapping.However,excessive addition of Ca(HCOO)_(2)inhibited the hydration reaction,resulting in a simple and loose structure of the hydration products.The research results have reference value for controlling surrounding rock deformation and preventing water and mud inrushes during the excavation in cold region tunnels.

Effects of fibers on expansive shotcrete mixtures consisting of calcium sulfoaluminate cement,ordinary Portland cement,and calcium sulfate

The mining industry often uses shotcrete for ground stabilization. However, cracking within shotcrete is commonly observed, which delays production schedules and increases maintenance costs. A possible crack reduction method is using expansive shotcrete mixture consisting of calcium sulfoaluminate cement(CSA), ordinary Portland cement(OPC), and calcium sulfate(CS) to reduce shrinkage. Furthermore, fibers can be added to the mixture to restrain expansion and impede cracking. The objective of this paper is to study the effects of nylon fiber, glass fiber, and steel fiber on an expansive shotcrete mixture that can better resist cracking. In this study, parameters such as density, water absorption, volume of permeable voids, unconfined compressive strength(UCS), splitting tensile strength(STS), and volume change of fiber-added expansive mixtures were determined at different time periods(i.e. the strengths on the 28 th day, and the volume changes on the 1 st, 7 th, 14 th, 21 st, and 28 th days). The results show that addition of fibers can improve mixture durability, in the form of decreased water absorption and reduced permeable pore space content. Moreover, the expansion of the CSA-OPC-CS mixture was restrained up to50% by glass fiber, up to 43% by nylon fiber, and up to 28% by steel fiber. The results show that the STS was improved by 57% with glass fiber addition, 43% with steel fiber addition, and 38% with nylon fiber addition. The UCS was also increased by 31% after steel fiber addition, 26% after nylon fiber addition, and16% after glass fiber addition. These results suggest that fiber additions to the expansive shotcrete mixtures can improve durability and strengths while controlling expansion.

Ultra High Early Strength Self-compacting Mortar Based on Sulfoaluminate Cement and Silica Fume

The influences of silica fume and aluminum sulfate on hydration process of sulfoaluminate cement were carried out by ring flow, setting time, hydration heat, XRD and DTG analyses. In addition, mortar mixtures with different functional additives have been studied through compressive strength, flexural strength, volume stability at early age and porosity characterization tests. The results show that the addition of silica fume and aluminum sulfate reduces the fluidity and shortens the setting time of sulfoaluminate cement paste, promoting hydration process and increasing hydration products at early age. In the case of appropriate proportion of mortar, the inclusion of hydroxy propyl methyl cellulose, dispersible polypropylene fiber arid organic silicon kind of defoamer can control segregation and bleeding, improve mechanical strength and volume stability at early age, and modify the pore distribution of sulfoaluminate cement mortar, respectively. The sulfoaluminate cement mortar can carry out gravitational grouting in the absence of outside force, the compressive strength of 2 hours and 24 hours have reached 26 and 58 MPa respectively, and have good micro- expansion and tiny.pore distribution characterization.

Effect of Superplasticizers on the Early Age Hydration of Sulfoaluminate Cement

The effects of two types of superplasticizers on the properties of CSA cement pastes during early hydration were studied. The influences of two types of superplasticizers on the properties of cement pastes, including the normal consistency, setting time, fl uidity, and compressive strength, were investigated by using various methods. The hydration products of the cement pastes cured for 1 day and 3 days were studied by X-ray diffraction（XRD） and scanning electron microscopy（SEM）. The results show that the PCE type superplasticizer retards the early age hydration while the FDN type superplasticizer accelerates the early age hydration of the CSA cement. Both types of superplasticizers have no infl uence on the further hydration of CSA cement, confi rmed by the calorimeter tests as well. The ultrasonic pulse velocity measurements were used to probe the influence of two types of superplasticizers on the hydration of CSA cement pastes at a high water-cement ratio（0.45）. The results show that the PCE type superplasticizer retards the early age hydration of the CSA cement while the FDN type superplasticizer has little infl uence on the early age hydration of the CSA cement.

Effect of Natural Zeolite on Performance of Sulfoaluminate Cement-based Planting Cementitious Material

This paper aimed to improve the water-retention performance and basic physical properties of sulfoaluminate cement（SAC）-based planting cementitious material. The effect of natural zeolite on the performance of SAC-based planting material was investigated. The water-retention performance, porosity, compressive strength, and alkalinity had been tested and TG-DSC analysis had been adopted in this paper. Experimental results showed that zeolite was effective to improve the water-retention capacity and 10%, 20% and 30% natural zeolite increased the pore volume of the hardened pastes by 10.6%, 26.0%, and 38.6%, especially pore size below 0.1 μm was increased by 9.7%, 26.2% and 17.5%. And 10% zeolite was beneficial to the compressive strengths of cementitious material and 1, 3, and 28 d compressive strength reached up to 35.9, 55.0, 80.3 MPa. Furthermore zeolite decreased the alkalinity of pore fluid of hardened cementitious material, while the addition of zeolite reached up to 30%, the alkalinity of pore fluid of hardened cementitious material decreased by 8.9%. Therefore zeolite was suitable for improving the performance of SAC-based planting cementitious material.

Thermodynamic data calculation for iron phases in sulfoaluminate cementitious materials prepared using solid wastes

The preparation of sulfoaluminate cementitious materials(SCM)is a promising way to massively utilize solid wastes.Iron phases are significant in SCM system but the thermodynamic data of some key minerals,such as6 CaO·Al2 O3·2 Fe2 O3(C6 AF2)and 6 CaO·2 Al2 O3·Fe2 O3(C6 A2 F),are missing,which greatly hinders the SCM optimization in a theoretical way.This work,for the first time,calculated the standard formation enthalpy,Gibbs free energy of formation,entropy and molar heat capacity for C6 AF2 and C6 A2 F and lowered the errors to the least with the reference of C4 AF data in the literature.By building the function diagram of Gibbs free energy changes with temperature for the basic iron phase formation reactions with the obtained thermodynamic data,it is proved that the formation likeliness of C6 AF2 is higher than that of C6 A2 F,as is accordant to the literatures and verifies the correctness of obtained data.This work provides a good theoretical foundation to optimize SCM mineral system and to study relevant mechanism deeply.

DEVELOPMENT OF COLORED SULFOALUMINATE CEMENT

One process for producing new type colored sulfoaluminate cement is introduced in this paper. The color stability is an important quality index of colored cement products. Kxperimental results show thds cement clinker can be obtained at 1250~1350? by using some industrial refuse as coloration agent, and the products of this cement do not only have a rapid development in strength but also are almost color fast over 3 years.

铁铝酸盐、硫铝酸盐和硅酸盐水泥的水化进程对比研究

铁铝酸盐水泥具有节能、利废、减排优良的工艺性能和环境友好的特点,目前已逐渐引起了国内外学者的研究兴趣。本文通过水化热、XRD、TG-DTG、孔结构分析、SEM等测试手段对比了铁铝酸盐水泥(FAC)、硫铝酸盐水泥(SAC)和硅酸盐水泥(PC)三类不同水泥体系水化过程,分析了三种水泥水化产物和水化机理。结果表明:FAC的1 d强度相比于PC提高了130%,28 d强度超过SAC。FAC和SAC水化放热主要集中在1 d之内,且FAC熟料中的铁相能缩短加速期时间,促进钙矾石的生成。相较于PC和SAC,FAC水化产物不仅含有钙矾石、水化硅酸钙凝胶和铝胶,还含有铁钙矾石和铁胶,其总孔隙率较低,水泥石结构更加致密,强度和耐久性进一步提高。

硫铝酸盐水泥水化产物-铝凝胶的研究进展

硫铝酸盐水泥作为我国第三系列水泥,既是一种低碳绿色水泥,又是一种海工修补加固水泥。铝凝胶(AH_(3))是其最重要的水化产物之一,可有效提升该系列水泥石的宏观力学性能。本文结合化工中AH_(3)的基础研究,阐述了硫铝酸盐水泥石中AH_(3)的形成过程,归纳了AH_(3)的一般性特征,对比了化工中AH_(3)与硫铝酸盐水泥石中AH_(3)的异同点,具体分析了各类因素对AH_(3)微纳结构及含量的影响,总结了目前AH_(3)研究的不足之处,提出了未来研究的方向和思路。

可溶性P_(2)O_(5)对超细硫铝酸盐水泥基双液注浆材料早期水化性能的影响及机理

为了指导磷石膏在超细硫铝酸盐水泥基双液注浆材料(SCBGM)中的高效应用,研究了可溶性P_(2)O_(5)对大水灰比下SCBGM早期水化性能的影响及作用机理。结果表明,可溶性P_(2)O_(5)的加入不显著影响SCBGM浆体的凝结时间。可溶性P_(2)O_(5)掺量为0%~1.5%时,随着其掺量的增加,SCBGM早期强度逐渐增大。在1.5%最佳掺量下,可溶性P_(2)O_(5)可显著提高早期SCBGM中钙矾石的生成量,还可以显著优化硬化体中钙矾石的分布特征,使其由团簇状转变为显著的搭接交错分布状态,进而充分发挥钙矾石晶体的强度骨架效应。

碱激发矿粉胶凝材料固化高含盐量浓缩液污泥试验研究

采用浸没式燃烧工艺处理生活垃圾填埋场渗滤液产生的浓缩液污泥副产物具有高易溶盐含量的特征。分别采用硫铝酸盐水泥和碱激发矿粉胶凝材料固化浓缩液污泥,对固化试样进行一系列无侧限抗压强度(UCS)试验、水稳定性试验和微观观测试验,分析硫铝酸盐水泥和碱激发矿粉胶凝材料对浓缩液污泥的固化效果和固化机理。研究结果表明:40%水泥掺量的固化试样的28 d无侧限抗压强度为1.95 MPa,浸水28 d后降低至零。30%矿粉掺量的固化试样的28 d无侧限抗压强度为14.8 MPa,浸水28 d后,仍达3.6 MPa,远大于垃圾填埋场的填埋强度要求。碱激发矿粉反应生成的三维网状胶凝材料和钙矾石晶体可对浓缩液污泥颗粒实现有效的包裹和胶结,是碱激发矿粉胶凝材料固化浓缩液污泥的微观固化机制。

基于低标硫铝酸盐水泥熟料的高水材料物理力学性能及应用

为解决高水材料充填成本高、物理力学性能差等问题,选用低标硫铝酸盐水泥熟料为主要原料,通过物理试验探究了低标硫铝酸盐水泥熟料高水材料在不同外加剂剂量、水灰比、水温下的物理力学性能,并通过工艺性试验测试了实际应用效果。研究结果表明:(1)不同条件下高水材料物理力学性能不同的主要原因在于其钙矾石的生成速率及生成量受到影响;(2)以低标型硫铝酸盐水泥熟料作为高水材料原料时,使用一定量外加剂能够改善其样貌并显著提升其强度;(3)降低水灰比能够显著提升高水材料的早期强度及峰值强度,且每提高0.1的水灰比,平均各龄期强度下降约11%;(4)水温对于高水材料初凝时间的影响高于终凝时间,对早期强度起促进作用,水温每上升2℃, 1d强度增加约6.8%;(5)影响高水材料强度的各项因素排序为:外加剂>水灰比>水温;(6)现场应用低标型硫铝酸盐水泥熟料高水材料后,巷道变形量较小,取得较好的留巷效果。

碱激发矿粉-硫铝酸盐水泥砂浆力学性能研究

硫铝酸盐水泥作为一种早强快硬型水泥,其后期强度发展缓慢,甚至会出现强度倒缩的问题,为此提出将矿粉和碱激发剂与硫铝酸盐水泥复合的方法,分别研究了不同掺量的碱激发剂以及不同取代率的矿粉对硫铝酸盐水泥砂浆力学性能和干缩性能的影响。结果表明:在水泥砂浆中添加适量的碱有利于强度发展,在碱与矿粉的协同作用下,水泥砂浆的各龄期强度均有提升,尤其是后期强度,28 d最高强度可达61.3 MPa。碱与矿粉的掺入不仅可以减少水泥的用量,而且矿粉取代水泥带来的强度损失问题也可以通过碱激发剂与矿粉在水化后期发生的二次反应来弥补,且体积稳定性良好。

硫铝酸盐水泥混凝土湿度场试验与模型计算

文中基于湿度场试验研究开发了一种可以同时计算硫铝酸盐水泥(CSA)混凝土自干燥和湿润环境下的综合水分分布模型,在建模中利用混凝土中的含水量与混凝土内部相对湿度的协同关系来模拟水泥水化和水分扩散引起的自干燥,同时,基于此模型求得湿润阶段的等效水分扩散系数。该模型可以将湿润阶段CSA混凝土内部的水分传输分为两个过程:混凝土内部的气态水由于浓度梯度向外扩散的进程和外部的液态水由于毛细作用快速地进入混凝土内部的过程。该模型可用于任何给定养护策略下CSA混凝土湿度场计算。

基于响应面法的UHPC复合胶凝材料体系优化研究

采用基于响应面法(RSM)的D-optimal最优化设计方法设计了超高性能混凝土(UHPC)净浆配合比,研究了复合胶凝材料组分对UHPC净浆湿堆积密实度、力学性能、干燥收缩性能的影响,结合XRD、SEM等微观测试结果分析了复合胶凝材料组分间的相互作用机理。结果表明:粉煤灰和硅灰可有效提高UHPC净浆的湿堆积密实度,优化基体内部颗粒堆积状态;硫铝酸盐水泥和粉煤灰对UHPC净浆的早期强度影响显著,掺入硫铝酸盐水泥可大幅提高UHPC净浆的早期力学性能。

矿渣硫铝酸盐水泥流态固化土的力学性能与固化机理

疏浚工程产生的大量淤泥含水率高且含有重金属等有害物质,对环境构成严重威胁。使用固化剂固化淤泥制备流态固化土是资源化利用淤泥的有效方法。目前常用的普通硅酸盐水泥(Ordinary Portland Cement,OPC)固化淤泥存在强度低、能耗高、碳排放高等问题,而矿渣硫铝酸盐水泥(Slag Calcium Sulfoaluminate Cement,G-CSA)是一种低碳高强的新型胶凝材料,在固化淤泥方面具有潜在的应用前景。采用G-CSA制备流态固化土并设置OPC流态固化土对照组,研究高贝利特硫铝酸盐水泥(High Belite Sulfoaluminate Cement,HB-CSA)熟料对G-CSA流态固化土力学性能的影响,并进行水化产物与孔结构表征,进而深入分析G-CSA的固化机理。结果表明,G-CSA流态固化土的强度随着HB-CSA熟料掺量的增加呈先增大后减小的趋势,在掺量为10%时G-CSA流态固化土力学性能达到最优,其28 d抗压强度和抗折强度分别为OPC流态固化土的2.35倍和2.06倍;G-CSA中的柱状AFt形成了骨架结构,C-S-H凝胶则将土颗粒粘结成一个整体,从而有效填充G-CSA流态固化土内部孔隙;适量的HB-CSA熟料能够减小G-CSA流态固化土的孔隙率,细化孔隙结构,进而提升其力学性能。

高抗折矿渣硫铝酸盐水泥混凝土抗疲劳性能研究

传统水泥混凝土公路路面面临的主要问题是路面易开裂劣化和抗疲劳性能较差,这些问题大大缩短了路面的使用寿命,严重制约了水泥混凝土路面的发展和推广应用。矿渣硫铝酸盐水泥(Slag-Calcium Sulfoaluminate Cement,S-CSA)是一种具有高抗折强度的新型胶凝材料,利用该水泥制备的混凝土路面具有解决现有路面抗疲劳性能差的潜力。通过三点弯曲疲劳试验和声发射试验,对比分析了高抗折S-CSA混凝土和普通硅酸盐水泥(Ordinary Portland Cement,OPC)混凝土的抗疲劳性能。研究结果表明:相同荷载作用下,高抗折S-CSA混凝土粗骨料断裂数量更多;不同强度等级下,高抗折S-CSA混凝土的疲劳寿命均高于OPC混凝土,且提升幅度随着强度等级的提高而显著增加,最高可达到约7.2倍;钙矾石的生成有效改善了界面过渡区,从而提升了高抗折S-CSA混凝土的抗疲劳性能。

石膏对高碱硫铝酸盐水泥性能的影响

针对硫铝酸盐水泥熟料碱含量超标,出现凝结过快、强度降低的问题,本工作研究了石膏对高碱硫铝酸盐水泥物理力学性能以及水化产物的影响。结果表明,石膏的掺入使得高碱硫铝酸盐水泥凝结加快,但是水泥的凝结时间随石膏掺量增加而略微延长。高碱硫铝酸盐水泥砂浆的早期强度随石膏掺量增加有所升高,当石膏掺量从10%提高至20%时,水泥砂浆的后期强度有所提高;当石膏掺量提高至30%时,强度变化不明显甚至后期强度有所降低。随石膏掺量的增加,高碱硫铝酸盐水泥砂浆的膨胀率增大,石膏掺量为35%的水泥砂浆出现开裂现象。石膏掺量的增加促进了高碱硫铝酸盐水泥钙矾石形成,水化28 d时,石膏掺量为20%和30%的水泥浆体中仍存在少量未反应的石膏。

硫铝酸盐水泥基材料抗碳化性能研究进展

碳化是复杂的物理化学过程,主要包括二氧化碳(CO_(2))在水泥混凝土中的扩散、溶解和与可碳化物质的反应,最终造成水泥混凝土碱性的降低和钢筋的锈蚀,显著影响其耐久性能。硫铝酸盐水泥(CSA)具有快硬早强、耐硫酸盐腐蚀性能优异等特点,但其抗碳化性能较差,易导致水泥内部化学组成的改变和微观结构的劣化,最终将严重危害基础设施的正常服役。因此,明晰影响CSA碳化的因素,揭示CSA碳化机理具有重要的工程和科研意义。首先从CSA的水化产物出发,介绍了三硫型水化硫铝酸钙(AFt)、单硫型水化硫铝酸钙(AFm)及水化硅酸钙(C-S-H)的碳化机理;其次分析了材料因素对CSA抗碳化性能的影响;最后综述了CO_(2)矿化养护对CSA性能的提升作用,总结了目前CSA碳化研究的不足,为进一步研究CSA抗碳化性能提升方法和碳化利用方式提出了建议。

锂盐对水泥基快速修补材料性能的影响研究

研究了锂盐种类和添加量对硫铝酸盐水泥凝结时间、抗压强度、耐划伤性能、邵氏硬度的影响规律,并利用扫描电镜揭示了锂盐种类和添加量对硫铝酸盐水泥水化产物微观形貌的作用机制。结果表明:氯化锂、碳酸锂、磷酸锂、硫酸锂4种锂盐的添加均可加速硫铝酸盐水泥的水化过程,其促进效果分别为氯化锂>碳酸锂≈硫酸锂>磷酸锂,且当Li^(+)添加量为0.1×10^(-4)mol/g时,4种锂盐对硫铝酸盐水泥早期强度的提升幅度最高。