Thermodynamic Stability of Sulfate Ions on Calcium Aluminosilicate Hydrate Microstructure

The thermodynamic stability of sulfate ions on synthesized calcium aluminosilicate hydrate(C-A-S-H) microstructure with different Ca/Si ratios and Al/Si ratios was investigated by XRD, SEM-EDS, ~(29) Si and ~(27) Al nuclear magnetic resonance(NMR) and thermodynamic modeling. The results indicate that sulfate attack leads to both decalcification and dealumination for C-A-S-H gels, and the amount of corrosion products(gypsum and ettringite) decreased gradually with decreasing Ca/Si ratios of C-A-S-H. Sulfate ions can also promote the polymerization degree of C-A-S-H gels, improving its resistance to sulfate attack. Moreover, the 4-coordination aluminum(Al[4]) in C-A-S-H, 5-coordination aluminum(Al[5]), 6-ccordination aluminum(Al[6]) in TAH(third aluminum hydrate) and Al[6] in monosulfate or C-A-H(calcium aluminate hydrate) can be transformed into Al[6] in ettringite by sulfate attack. Furthermore, through thermodynamic calculation, the decrease of Ca/Si ratios and increase of Al/Si ratios can improve the thermodynamic stability of C-A-S-H gels under sulfate attack, which agrees well with the experiment results.     

Properties and Acceleration Mechanism of Cement Mortar Added with Low Alkaline Liquid State Setting Accelerator

Low alkaline liquid state setting accelerator(LSA) for Portland cement was prepared in laboratory from aqueous solution of several inorganic sulfate salts and some organic chemical substances. Properties of cement with addition of LSA relating to its setting time and strength development as well as its resistance to sulfate attack for short and long term exposure were experimentally examined. The experimental results showed that 5%-7% addition of LSA significantly accelerated the initial and final setting of Portland cement in the presence or absence of the blending of mineral admixtures, the initial and final setting time being less than 3 min and 6 min respectively. Meanwhile, the early 1 day curing age compressive strength increased remarkably by 20%, while the late 28 th day curing age compressive strength remained almost unchanged as compared with that of the reference accelerator free cement mortar specimen. Furthermore, mortar specimens of cement added with LSA and exposed to 5% Na2SO4 solution showed their excellent resistance to sulfate attack, with their short and long term curing age resistance coefficient to sulfate attack being around 1.04 to 1.17, all larger than 1.0. XRD analysis on hardened cement paste specimens at very early curing ages of several minutes disclosed the existence of more ettringite in specimens added with LSA than that of the reference specimens, meanwhile SEM observation also revealed the existence of well crystallized ettringite at very early hydration stage, suggesting that the accelerated setting of Portland cement can be attributed to the early and rapid formation of ettringite over the whole cement paste matrix due to the introduction of LSA. MIP measurement revealed that hardened cement paste specimens with the addition of LSA presented less medium diameter pores, more proportion of small pores and less proportion of large capillary pores, which is in a very good coincidence with the improvement of strength development of cement mortars added with LSA.     

Investigation of Sulfate Attack Resistance of Shotcrete under Dry-wet Cycles

In order to research the sulfate attack resistance of shotcrete, the sulfate attack of shotcrete in the presence and absence of steel fiber was experimentally studied by using dry-wet cycle method. Meanwhile, compared with ordinary concrete by the same mixture, the difference of sulfate attack resistance of shotcrete was studied. The experimental results showed that, with dry-wet cycles increasing, the changes of loss rate of relative dynamic elastic modulus and mass loss rate of specimens included three stages: initial descent stage, stable stage, and rapid descent stage, respectively. However, the changes of mechanical properties first increased and then decreased. Furthermore, the corrosion products of shotcrete after sulfate attack were observed by using the method of XRD, thermal analysis, and SEM, respectively, and the failure mode of shotcrete turned from ettringite destruction to ettringite-gypsum comprehensive failure. Meanwhile, the contents of ettringite and gypsum increased with increasing dry-wet cycle. Simultaneously, the stratified powders drilled from shotcrete under 150's dry-wet cycle were analyzed for the mineral phase composition and thermal analysis. With the drywet cycle increasing, the content of ettringite first increased and then decreased and tended to stable. However, the determination of gypsum decreased gradually and even to 0 when the depth was more than 12 mm.     

Effects of carbonation and freeze-thaw cycles on microstructure of concrete

The hydraulic concrete durability under the alternation of freeze-thaw and carbonation has been systematically investigated in this work, where both the micro part and the microscopic characteristics of concrete interface were analyzed based on computed tomography (CT) test and scanning electron microscopy (SEM). Average CT numbers of each section, declined at water-cement ratio of 0.35, increased at 0.45, and changed a little at 0.55. The specimen in the absence of fly ash exhibited less types of hydration products and the surface was observed to be a needle-like ettringite, with a relatively dense overall structure. However, with the increase of fly ash content, pores and micro-cracks of specimen structure increased. Hexagonal flake calcium hydroxide, present in the specimen after the first carbonation, was negligible in the test pieces of the first freezethaw where the main hydration products were ettringite and calcium silicate gel. Regular hexagonal plates of calcium hydroxide exhibited in the interior of the specimen in which charring first occurred but calcium hydroxide rarely existed in the interior of the specimen in which freeze-thaw first occurred.     

A binder of phosphogypsum-ground granulated blast furnace slag-ordinary portland cement

A new hydraulic cementitious binder was developed by mainly utilizing industrial byproducts phosphogypsum(PG)and ground granulated blast furnace slag(GGBFS)with small addition of ordinary portland cement(OPC).The hydration process and microstructure were studied by X-ray diffraction(XRD) and scanning electronic microscopy(SEM).OPC hydrated first at early age to form primarily C-S-H gel,ettringite and calcium hydroxide(CH).GGBFS activated by CH and sulfate ions hydrated continuously at later age,producing mo...     

超硫酸盐水泥的水化产物及孔结构特性

采用抗压强度试验、X射线衍射分析、电镜扫描及压汞仪法等测试技术,测试和分析了超硫酸盐水泥在不同龄期的强度、水化产物及孔结构,并将其与普通硅酸盐水泥、矿渣水泥对比,探讨超硫酸盐水泥的水化机理.研究结果表明,超硫酸盐水泥早期强度较低,但后期强度发展快,28 d强度高于42.5普硅水泥;超硫酸盐水泥的主要水化产物为水化硅酸钙、钙矾石及少量石膏晶体,未见普硅水泥及矿渣水泥的主要水化产物氢氧化钙;90 d时,超硫酸盐水泥硬化浆体的阈值孔径、最可几孔径、中孔孔径及平均孔径均小于普硅水泥和矿渣水泥,具有更小的孔隙率和更高的密实度,有效地促进了超硫酸盐水泥后期强度的增长.     

不同CO2养护压力下硫铝酸盐和硅酸盐水泥浆体早期微观结构

研究硫铝酸盐和硅酸盐水泥（CSA-OPC）浆体在不同碳养护压力下的早期碳化过程,通过X射线衍射、红外光谱、热重、压汞和扫描电镜等测试方法,表征碳化前后水泥浆体的物相组成和微观结构. 实验结果表明,CSA-OPC浆体的水化产物主要为钙矾石,碳化作用使钙矾石转变为碳酸钙和硫酸钙晶体;水泥中碳酸钙以3种晶型存在,其中方解石为主要存在形式. 碳化使半碳型的水化硫铝酸钙（Hc-AFm相）逐渐转化为单碳型的水化硫铝酸钙（Mc-AFm相）,碳化程度和碳化深度随着碳化压力的增加而递增. 碳化后CSA-OPC水化产物体积减小,样品总孔隙率增大、孔隙结构变疏松. 研究结果阐明了CSA-OPC浆体在早期碳化养护条件下的微结构变化过程,为制备基于硫铝酸盐水泥的高效碳汇材料提供了技术支撑.     

Influence of cellulose ethers on hydration products of portland cement

Cellulose ethers are widely used to mortar formulations,and it is significant to understand the interaction between cellulose ethers and cement pastes.FT-IR spectra,thermal analysis and SEM are used to investigate hydration products in the cement pastes modified by HEMC and HPMC in this article.The results show that the hydration products in modified cement pastes were finally identical with those in the unmodified cement paste,but the major hydration products,such as CH(calcium hydroxide),ettringite and C-...     

Properties and mechanism of mine tailings solidified and filled with fluorgypsum-based binder material

The properties and microscopic structure of tailings solidification bodies, the hardening mechanism of the fluorgypsum-based binder material (FBBM) and tailings solidification mechanism were investigated. FBBM consisted of 40% fluorgypsum,25%-50% blast furnace slag,10%-35% ordinary Portland cement clinker(OPCC) and 1% activator, which was good material in binding iron ore tailings.XRD analysis showed that the properties of tailings solidification bodies was related to its ettringite content.SEM and XRD analyses of tailings solidification bodies showed that the chemical reaction was produced between FBBM and tailings in the whole hydration process. The hydration of the resulting gel material covered the surface of the tailings particles and formed a gel structure. A large number of ettringite crystals and the remaining board-like gypsum crystals took each end and constituted the structural skeleton. The filamentous network-like calcium-silicate-hydrate(C-S-H) gel bonded firmly together with ettringite crystals, dehydrated gypsum crystals and granular tailings, and formed an extremely dense whole.     

The chloride permeability of persulphated phosphogypsum-slag cement concrete

The chloride permeability and microstructure of persulphated phosphogypsum-slag cement concrete (PPSCC), the Portland slag cement concrete (PSCC) and ordinary Portland cement concrete (OPCC) were investigated comparatively. Some test methods were used to evaluate the chloride permeability and explain the relationship between the permeability and microstructure of concrete. The results show that the resistance to chloride penetration in PPSCC is significantly better than that in OPCC, the reasons are as follows: 1) the slag in PPSCC is activated by clinker (alkali activation) and phosphogypsum (sulfate activation), forming more low Ca/Si C-S-H gel and gel pores below 10 nm than OPCC, improving the resistance to chloride penetration; 2) the hydration products of PPSCC have a much stronger binding capacity for chloride ions; and 3) in the same mix proportion, PPSCC has a better workability without large crystals calcium hydroxide in the hydration products, the interfacial transition zone (ITZ) is smoother and denser, which can cut off the communicating pores between the pastes and aggregates.     

硅灰对水泥净浆抗硫酸盐侵蚀性能的改善作用

将水泥净浆试件在5%Na2SO4溶液中长期浸泡,用试件强度随浸泡时间的变化和试件中物相的XRD分析,研究了硅灰对水泥净浆抗硫酸盐侵蚀性能的影响.在Na2SO4溶液侵蚀下,普通硅酸盐水泥净浆试件强度随浸泡时间先增长,然后急剧降低;外观和XRD相分析表明,其原因是由于形成了膨胀性钙矾石,造成试件开裂破坏;加入硅灰的水泥净浆试件强度损失明显减小,尤其是抗折强度没有降低,其抵抗强度下降系数还略有增加;原因是由于硅灰的稀释作用和火山灰效应减少了水泥净浆中Ca(OH)2的量,从而降低了水泥净浆试件在硫酸盐溶液侵蚀下形成的膨胀性钙矾石的量.因而,硅灰对水泥混凝土抗硫酸盐侵蚀性能有改善作用.     

电石渣—脱硫石膏复合激发充填材料性能及微观结构

针对传统充填材料高碳排放、高成本问题,以“绿色矿山”为理念,选用工业固废电石渣、脱硫石膏和矿渣为胶凝组分,以尾矿砂为骨料制备充填材料。利用X射线（XRD）、扫描电镜（SEM）和能谱分析(EDS)等手段研究充填料水化产物及微观形貌,并开展工作性能、力学性能和重金属固化性能试验。结果表明：所开发的充填材料凝结时间和流动度均满足矿山充填工程要求,充填体7、28 d抗压强度可达4.6、7.9 MPa,充填体浸出液中Pb、Zn浓度低于规定限值。电石渣内的氢氧化钙提供碱性环境,脱硫石膏提供硫酸根离子,两者对矿渣内的硅铝质原料复合激发,生成以钙矾石和C-A-S-H凝胶为主的水化产物。大量针棒状结构的钙矾石晶体及网状结构的C-A-S-H凝胶相互穿插,并且与尾砂颗粒紧密结合,随着龄期延长,结构更加致密,使充填体具有良好的力学性能。     

铝酸钠液体速凝剂性能及作用机理

目的研究不同物质的量比铝酸钠液体速凝剂对水泥性能的影响规律,探讨其促凝机理及存在最佳掺量的原因．方法测试了不同物质的量比的铝酸钠液体速凝剂对水泥的凝结时间和强度,利用差热分析,X-射线衍射和扫面电镜手段分析其作用机理．结果物质的量比为1．2时．铝酸钠液体速凝剂放置1d便产生大量的沉淀．增大物质的量比时,稳定性也增加．不同物质的量比的铝酸钠液体速凝剂均存在最佳掺量,其凝结时间和强度都符合JC477—2005标准．结论铝酸钠液体速凝剂并不是靠生成大量钙矾石相互搭接实现速凝,而是促进各水泥矿物的反应形成大量的凝胶,并有一定量的板状晶体氢氧化钙和柱状晶体钙矾石（AFt）分布在其中．当掺量过大时,形成大量的六方片状晶体水铝石和单硫型水化硫铝酸钙（AFm）,C—S—H凝胶和柱状钙矾石相对较少,导致结构不密实,速凝效果减弱．     

中性钠盐碱矿渣水泥抗化学侵蚀性能研究

研究了中性钠盐碱矿渣水泥在酸性溶液、硫酸盐溶液和海水中的抗化学侵蚀性能。借助X-射线衍射和压汞测孔法考察了中性钠盐碱矿渣水泥的水化产物及水泥石孔结构特征, 并指出高稳定性的水化产物和优良的孔结构是其具有优异抗化学侵蚀性能的主要原因。     

高游离氧化钙水泥的显微结构与膨胀机理研究

运用扫描电子显微镜（SEM）研究了高游离氧化钙（f-CaO）水泥的 经及其在水泥石中氢氧化钙的分布和显微结构特征。讨论了水化早期和后期Ca(OH）2晶体的结晶特性及界面结合关系,指出了熟料中成大堆分布的f－CaO晶体缓慢水化导致Ca（OH）2晶体不断长大是造成水泥安定性不合格的主要原因。     

高渗透压-硫酸盐侵蚀下混凝土时空劣化

为了模拟研究混凝土海水环境下的侵蚀损伤及劣化规律,采用质量分数10% Na₂SO₄溶液对混凝土试样进行不同渗透压和不同时长下的室内侵蚀试验. 结合微米压痕试验、CT扫描试验和电子显微镜扫描试验,对高渗透压-硫酸盐耦合侵蚀作用下混凝土的侵蚀损伤及微观力学性能进行研究. 试验结果显示,渗透压加速了离子迁移,主要起到了促进化学侵蚀作用. 渗透压越大,混凝土化学损伤速率越快,侵蚀深度越深;骨料与砂浆胶结处是易侵蚀、易破坏的薄弱点;混凝土内部孔隙易生成水化产物,高渗透压下容易生成大量短柱状石膏晶体及细密的针状钙矾石晶体.     

复合白云石表面链状纳米CaCO_3的制备

在Ca(OH)_2-H_2O-CO_2反应体系中,根据非均匀成核原理,通过调整体系反应温度、Ca(OH)_2浓度、ZnSO_4添加量等反应参数,控制在白云石颗粒表面生成具有链状结构的纳米Ca-CO_包覆层.利用SEM,XRD等检测表征手段,分析了不同反应参数对纳米CaCO_3晶形的影响.结果表明:当反应温度为25℃,ZnSO_4加入量为Ca(OH)_2的4%,Ca(OH)_2浓度为0.3mol/L时,在白云石颗粒表面生成了长径比为7:1的链状纳米CaCO_3.提高体系的反应浓度能够减少ZnSO_4的加入量.     

海洋大气区蒸养矿粉混凝土内部离子传输与反应

处于滨海大气区的钢筋混凝土结构容易受到氯离子、硫酸根离子等有害离子的侵害，导致结构服役寿命缩短。通过低场核磁等试验研究了蒸养、标养混凝土的孔径分布，揭示了氯离子、硫酸根离子对蒸养混凝土的侵蚀演变规律。结果表明，相比于标养混凝土，蒸养混凝土的无害孔含量降低，有害孔和多害孔含量增大，导致具有更高水化程度蒸养混凝土的抗压强度低于标养混凝土抗压强度。掺入一定量的矿粉可以显著提高蒸养混凝土抗氯离子侵蚀能力，氯离子结合能力越大，氯离子扩散系数越小，表层氯离子浓度越低。当矿粉掺量为25%时，蒸养混凝土的氯离子扩散系数较低，说明矿粉的二次水化作用优化孔径效果达到最佳；随着矿粉掺量的增加硫酸根离子反应系数逐渐降低，当矿粉掺量为50%时，由于混凝土中的钙相物质含量最低，导致硫酸根离子的反应系数最小。     

早强剂对掺硅灰的水泥砂浆强度与结构影响的研究

探讨了不同早强剂对掺硅灰的水泥砂浆强度及微观结构的影响.结果表明：掺入不同的早强剂均可提高掺硅灰的水泥砂浆早期强度,且对其1 d抗压强度的增强效果优于3 d.其中掺入适量的硫酸钠可迅速生成大量的钙矾石晶体,提高水泥砂浆的密实度,同时促进了硅灰的火山灰反应,明显提高了掺硅灰的水泥砂浆的早期强度,但早强剂对掺硅灰的水泥砂浆后期强度影响不大.3种早强剂对掺硅灰的水泥砂浆早期强度增强作用从大到小的顺序依次为硫酸钠、氯化钙、三乙醇胺,其中硫酸钠掺量为3%时增强作用最佳.     

Study on activity evaluation of activated coal-gangue and the hydration process

Chemical compositions,mineral compositions and the activated mechanism of the coal-gangue were analyzed. And pozzolana activities of the coal-gangue were evaluated after activated. Moreover,hydration heat and hydration compositions of activated coal-gangue-calcium oxide system,as well as hydration degree and hardened paste microstructures of activated coal-gangue-cement system were studied. Results show that pozzolana activities of the activated coal-gangue root in amorphous SiO2 and activated Al2O3. With the exciting of gypsum,the reaction of activated coal-gangue and Ca(OH)2 would produce hydration products as ettringite,calcium silicate hydrate,and calcium aluminate. The relationship between the curing age and the content of Ca(OH)2 in coal-gangue-cement system was ascertained. Unhydrated particles in the coal-gangue-cement paste were more than that in the neat cement paste at the same hydration periods,and even existed at the later stage of hydration. Furthermore,the activated coal-gangue could inhibit growth and gathering of the calcium oxide crystal,and improve the structure of hardened cement paste.