大掺量工业废石膏制备石膏基胶凝材料的性能研究

通过热养护的方式,制备了一种废石膏掺量达65%以上的石膏基复合胶凝材料,对材料的力学性能、耐久性能进行了测试.结果表明,大掺量石膏基复合胶凝材料具有良好的力学性能和耐水性,较大的收缩率导致材料抗冻性能不理想.石膏基复合胶凝材料的水化产物主要为钙矾石和C-S-H凝胶,早期生成的钙矾石晶体纰成胶凝材料的基本骨架,通过C-S-H凝胶的小断生成,胶凝材料逐渐致密化,有助于强度的增长和耐久性的提高.     

石膏-矿渣胶凝材料的碱性激发作用

采用扫描电镜、X射线衍射、差示扫描量热分析-热重分析表征了碱激发石膏-矿渣胶凝材料的水化产物.研究表明:添加质量分数为0.5%的碱性激发剂时,石膏-矿渣胶凝材料的各项强度和耐水性能最好.碱激发石膏-矿渣胶凝材料的水化产物主要为二水石膏(CaSO4·2H2O)、水化硅酸钙凝胶(C-S-H)以及少量的钙矾石(ettringite,AFt)和莱粒硅钙石[Ca5(SiO4)2(OH)2].C-S-H凝胶含量越高,材料的强度越高、耐水性能越好.     

钢渣矿渣基全固废胶凝材料的化学活化

为了促进钢铁冶金渣的高附加值应用,以钢渣、矿渣和脱硫石膏为原料制备胶凝材料,研究了不同掺量CaO或Na2SO4对胶凝材料的化学活化作用,并利用XRD、SEM对掺入激发剂胶凝材料的水化产物进行了分析.结果表明,掺入少量CaO或者 Na2SO4的胶凝材料净浆试块早期抗压强度会有一定的提高,后期强度变化不大;但当Na2SO4掺量超过2%时,净浆试块的抗压强度会降低.掺入激发剂对胶凝材料的水化产物种类不会造成影响,其水化产物主要包括钙矾石(AFt)、水化硅酸钙(C-S-H)凝胶和氢氧化钙(CH).     

化学外加剂对粉煤灰-矿渣-水泥胶凝体系的激发作用

为提高粉煤灰-矿渣-水泥充填胶凝体系早期强度,选取10种激发剂,通过单掺及复掺试验,研究激发剂的早强性能,并获得最优配比,利用XRD、SEM、EDS手段分析了胶凝体系的水化产物及复合激发剂作用机理.结果表明:单掺激发剂时,当掺量≤1.4％,早强效果较优的依次为:NaCl>Na2 CO3>CaSO4·2H2 O>Na2 SiO3·9H2 O>三乙醇胺,复掺激发剂最佳配比为:NaCl、三乙醇胺分别为胶凝材料总质量0.9％和0.03％,硫铝酸盐水泥、CaSO4·2H2 O均为水泥熟料质量5％,胶砂试样3 d强度比空白样提高191.7％,28 d强度与空白样相差不大;胶凝体系受激发主要水化产物为C-S-H凝胶、水化氯铝酸钙和钙矾石,C-S-H凝胶构成了试样的强度主体,针状钙矾石与片状水化氯铝酸钙交错生长,具有加筋、填充作用,使微观结构更加密实、紧凑,提高了早期强度.     

高温养护对炉底灰胶凝体系强度及水化产物的影响

为实现炉底灰在大体积混凝土工程中的资源化利用,结合净浆强度测定、X射线衍射、红外光谱及扫描电镜等手段,研究了高温养护对不同龄期炉底灰胶凝体系强度及水化产物的影响,结果表明:炉底灰胶凝体系水化产物主要为羟钙石,红辉沸石,文石以及C-S-H凝胶,高温养护促进了胶凝体系中硅酸钙的水化,生成更多的羟钙石和C-S-H凝胶,提高了试样早期强度;养护后期,胶凝体系水化速率及强度增长速率减小,羟钙石参与碱激发反应被消耗,C-S-H凝胶聚合度降低.高温养护下,胶凝试样的早期微观形貌以密实的网状C-S-H凝胶为主,随着龄期的增长,C-S-H凝胶结构更加致密,包裹于凝胶中的羟钙石在高温作用下产生微裂隙,阻碍了试样强度的发展.     

NaOH激发矿渣胶凝材料的29 Si NMR研究

为研究NaOH激发矿渣胶凝材料的强度演变规律及反应机理,采用抗压强度测试、XRD和29 Si NMR等技术手段探究了NaOH用量对碱矿渣胶凝材料抗压强度、水化产物种类、矿渣水化反应程度、C-S-H凝胶的聚合程度及其Al/Si的影响.研究结果表明:当NaOH用量为6％时,碱激发矿渣胶凝材料的抗压强度达到最大值;XRD谱图显示,NaOH激发矿渣胶凝材料的主要水化产物为C-S-H凝胶;29 Si NMR分析结果表明,NaOH用量的增加促进了矿渣的水化,其最佳用量为6％左右,NaOH用量超过6％,会降低C-S-H凝胶的聚合程度及其Al/Si,对胶凝材料的强度产生不利影响.     

磷石膏-矿渣基胶凝材料的制备及其性能研究

针对磷石膏基胶凝材料强度低、耐水差的缺点,运用碱激发剂改善磷石膏基胶凝材料的力学性能和耐水性。采用扫描电镜、X射线衍射和压汞法分析磷石膏基胶凝材料水化产物和孔结构。结果表明：将磷石膏在140 ℃条件下热活化4 h后得半水石膏,按m（半水石膏）∶m（矿渣）∶m（生石灰）=60∶40∶4配制粉料,水胶质量比为0.6,掺1%（质量分数）的碱激发剂,磷石膏基胶凝材料抗压强度和抗折强度分别为40.6 MPa和11.3 MPa,软化系数为0.84;硬化体中二水石膏和钙矾石为基本骨架,C-S-H凝胶包覆各组分形成致密网状结构,保证材料高强高耐水性。     

碱激发剂浓度及模数对碱矿渣胶凝材料抗压性能及水化产物的影响研究

采用水玻璃(复掺氢氧化钠调整模数)激发粒化高炉矿渣活性制备碱矿渣净浆试样.采用抗压强度测试、X-射线衍射(XRD)、综合热分析(TG-DSC)等技术手段研究了激发剂碱浓度(4%、6%、8%)及模数(0.75、1.00、1.50、2.00)对碱矿渣胶凝材料抗压性能及水化产物的影响.研究结果表明:激发剂模数较低时(0.75和1.00),碱矿渣胶凝材料抗压强度随着碱浓度的增加而呈下降趋势;激发剂模数较高时(1.50和2.00),试件强度在碱浓度为6%时达到最大值.在相同碱浓度下,激发剂模数为1.50时试件抗压强度值最大.碱矿渣胶凝材料主要水化产物为C-S-H凝胶,同时伴有C-A-S-H凝胶生成.另外观测到少量斜方钙沸石(CaAl2Si2O8· 4H2O)的生成.在部分配合比中还观测到水滑石(Mg6Al2(OH)16CO3· 4H2O)的存在.碱浓度较高的碱矿渣胶凝材料中生成了较多的C-S-H水化产物.激发剂模数较高时(1.50和2.00),更有利于碱矿渣中C-S-H水化产物的生成.碱浓度/模数较低时, C-S-H产物结晶度有所提高.相较于C-S-H凝胶结晶度,其生成量对碱矿渣胶凝材料抗压强度的影响更为显著.     

湿选钢渣尾泥制备充填胶凝材料试验研究

钢渣尾泥是转炉钢渣经过湿磨磁选后排出的二次废渣,堆存量大且难以实现大规模资源化利用。以钢渣尾泥为主要原料,协同其他工业固废制备胶凝材料可用于矿山充填。本文开展了钢渣尾泥基充填胶凝材料配合比正交试验、充填材料力学性能测试,利用X射线衍射(XRD)、扫描电镜(SEM)、红外光谱(FT-IR)等多种微观测试手段对钢渣尾泥基胶凝材料的水化机理进行分析。结果表明,钢渣尾泥掺量为55%(质量分数,下同),矿渣掺量为30%,脱硫石膏掺量为15%,胶砂质量比为1:4,料浆浓度为72%时,所制备的充填材料28 d抗压强度可达4.78 MPa,满足矿山充填材料性能的要求。钢渣尾泥基胶凝材料的水化产物主要为C-S-H凝胶和钙矾石,以及少量的Ca(OH)₂,体系内水化产物C-S-H凝胶和钙矾石晶体的数量随着水化龄期的增加而明显增长。     

粉煤灰对碱激发矿渣/粉煤灰体系的作用机理研究

碱激发胶凝材料是以工业固体废弃物为原料制备的一种绿色无机胶凝材料,具有良好的力学性能与耐久性能。粉煤灰因其独特的球体微观结构与其他固废微粉存在本质区别,因此粉煤灰在碱激发胶凝材料体系中的作用机理亟待研究。以矿渣与粉煤灰为原料,利用碱激发剂制备胶凝材料,并对材料进行抗压强度测试,最后采用XRD、FTIR和SEM探究碱激发矿渣/粉煤灰体系的水化反应机理,研究粉煤灰对矿渣/粉煤灰体系的作用机理。结果表明:外掺3%(质量分数)NaOH作为碱激发剂,水固比为0.4时,随粉煤灰掺量减少,抗压强度呈现先上升后下降的趋势;m(矿渣):m(粉煤灰)为4:1时,28 d抗压强度达到峰值(37.1 MPa)。粉煤灰颗粒在不同龄期形成具有不同反应程度与尺寸的嵌入式微观结构,对材料力学性能起到不利影响;但粉煤灰的活化程度随龄期延长逐渐变大,对后期强度发展有持续贡献。碱激发矿渣/粉煤灰体系水化产物中含有Friedel盐、托贝莫来石、钙矾石、C-S-H/C-A-S-H凝胶,以及粉煤灰中残留的α石英相。随粉煤灰掺量增加,托贝莫来石生成量减少,钙矾石向Friedel盐转变,钙矾石生成量减少,Friedel盐生成量增多。     

热活化铅锌尾矿基碱激发胶凝材料的制备及性能

以铅锌尾矿为主要原料,添加由矿渣、钢渣、氟石膏混合而成的辅助胶凝材料,以水玻璃和氢氧化钠为碱激发剂制备铅锌尾矿基碱激发胶凝材料。通过正交试验,探讨了水玻璃模数、水玻璃掺量及尾矿与辅助胶凝材料质量比对胶凝材料抗压强度的影响,并得出最佳原料配比。通过800 ℃、1 000 ℃、1 200 ℃的热处理,制备热活化铅锌尾矿基碱激发胶凝材料,并测试其性能。采用X射线衍射谱、傅里叶红外光谱和扫描电子显微镜对热活化前后尾矿和胶凝材料进行分析表征。结果表明,当水玻璃模数为1.8,水玻璃质量掺比为0.15,尾矿与辅助胶凝材料质量比为7 ∶3时,胶凝材料28 d抗压强度可达到20.68 MPa。胶凝材料内部形成大量水化硅酸钙(C-S-H)与硅铝多聚物构成三维网状结构,覆盖在尾矿晶体表面形成致密整体。当热活化温度为1 000 ℃时,胶凝材料28 d抗压强度达到28.05 MPa。热活化后的尾矿内部结构疏松,利于硅铝质在碱性条件下解聚,同时使得反应体系中生成了更多硅铝多聚体,取代了二聚体为主的C-S-H凝胶,为胶凝材料提供了更优良的抗压强度和早硬特性。此外胶凝材料对Pb、Zn重金属的固定作用极好,大幅降低了尾矿重金属Pb、Zn的毒性浸出浓度,有效解决了尾矿中重金属对周围环境的危害问题。     

C-S-H纳米晶核对矿物掺合料复合胶凝材料水化性能的影响研究

水泥中掺入大量矿物掺合料易造成其早期强度低、施工周期长等问题。本文研究了C-S-H晶核对含矿物掺合料的复合胶凝材料体系水化性能的影响规律;通过热力学计算阐述了C-S-H晶核降低水化产物成核势垒的机理,并通过离子溶出与沉积探讨大掺量矿物掺合料胶凝体系水化机理。结果表明：矿物掺合料复合胶凝材料体系水化能力较弱,这是由于Ca²⁺溶出受到制约,C₃S的水化反应缓慢;当加入晶核后,水泥中硅酸盐相溶解-结晶能力得到大幅提升,使得矿物掺合料水泥体系的水化反应活性接近纯水泥体系。研究表明,C-S-H晶核可解决大掺量矿物掺合料胶凝体系所带来的水化能力严重不足问题。     

高炉镍铁渣粉在水泥基复合胶凝材料中的水化特性研究

通过对不同高炉镍铁渣掺量的水泥-高炉镍铁渣粉复合胶凝材料水化放热速率、高炉镍铁渣粉的反应程度、硬化浆体化学结合水含量以及水化产物中C-S-H凝胶Ca/Si的测定,分别研究了水泥-高炉镍铁渣粉复合胶凝材料的早期、中长期水化进程、浆体微观形貌以及水化产物特点等水化特性.研究结果表明:高炉镍铁渣的掺入会降低水化放热速率,并推迟水化加速期放热峰的出现时间;在复合胶凝体系中,随着高炉镍铁渣粉掺量的增大,其反应程度和硬化浆体中化学结合水含量将降低.复合胶凝材料水化生成的C-S-H凝胶的Ca/Si低于水泥,且随着水化的进行呈降低趋势;高炉镍铁渣粉中的Al,在水化过程中会取代部分Si进入C-S-H凝胶中,形成C-A-S-H凝胶.     

Free-Energy-Based Model of Chemical Equilibria in the CaO–SiO2-H2O System

The chemical equilibrium between the C-S-H gel phase and the aqueous phase in the CaO-SiO₂-H₂O system was modeled using the free-energy-based Thermo-Calc commercial software system. Unlike programs that are based on solubility products, the minimization of free energy allows the composition and solubility of the C-S-H phase to vary, as in real cementitious systems. The C-S-H gel is modeled as a defect tobermorite structure, based on recent compositional data gathered using ²⁹Si NMR. The composition is varied by removal of some of the bridging silica tetrahedra in the SiO layers and by incorporating different amounts of Ca in the interlayer spaces.     

养护温度对凝灰岩基胶凝材料力学性能的影响机理

凝灰岩是经过火山喷出散落在地面,经过压结和水化胶结固化而形成的一种火山灰碎屑岩,具有一定的火山灰活性。本文研究养护温度对凝灰岩基胶凝材料力学性能的影响,并借助FTIR、TG、SEM和MIP等对凝灰岩基胶凝材料水化产物的微观结构进行分析。结果表明,提高养护温度对凝灰岩基胶凝材料的力学性能具有一定的增强作用,提高养护温度不仅能提高早期强度,还可以提高后期强度,凝灰岩基胶凝材料的最佳养护温度为50 ℃。提高养护温度后凝灰岩基胶凝材料中没有生成新的水化产物,AFt和C-S-H等水化产物含量增加,Ca(OH)₂的含量减少。提高养护温度有利于增加凝胶孔和过渡孔占比,细化孔径结构,降低孔隙率,提高基体结构的致密度。     

水泥-粉煤灰-矿粉-偏高岭土四元胶凝材料氯离子固化机理研究

本文在水泥、粉煤灰和矿粉组成的三元胶凝材料基础上掺入第四元矿物掺合料偏高岭土,利用X射线衍射(XRD)和热重分析(TGA/DTG)定性分析了四元胶凝材料水化产物与氯离子固化能力的关系,并在此基础上利用TGA/DTG和Rietveld外标法定量分析不同形态氯离子固化量。研究表明,掺入偏高岭土能够增加体系早期水化反应速率,促进粉煤灰和矿粉早龄期水化,增加了四元胶凝材料水化AFm相(单硫型水化硫铝酸钙)和C-S-H凝胶含量。同时也增加了体系中铝钙摩尔比,使得单硫型硫铝酸钙(Ms)在碳酸盐存在的条件下更加倾向于转化为半碳型碳铝酸钙(Hc)。氯离子等温吸附结果表明,AFm相含量与氯离子固化能力呈正相关。Rietveld外标法结果表明,掺入偏高岭土后四元体系的氯离子化学固化能力提高,物理吸附能力降低,与三元体系相比,氯离子化学固化量提高了94.16%,物理吸附量降低了7.62%,TGA/DTG定量结果表明Rietveld定量分析具有可行性。     

Alteration of fractured cementitious materials

The alteration of cement materials in a fractured repository was investigated by experimental and modelling techniques to predict the long-term evolution of a cementitious repository for the safety assessment of radioactive waste disposal. A flow-through experiment with an artificially fractured cement column sample was carried out, and the evolution of a chemical composition in discharged water and the distribution of mineral components in a solid matrix, which was dominated by the dissolution of portlandite and calcium-silicate hydrate (C-S-H), were observed. A coupling transport and chemical equilibrium calculation code, which includes a thermodynamic incongruent dissolution model of C-S-H, was developed to predict the alteration of the fractured cement materials. The advection transport of a component in a solution within a crack and the diffusion of a component in a solid matrix were modelled in the calculations. With the proposed model, the possible alteration of cement materials along a crack was described.     

Measurement methods of carbonation profiles in concrete: Thermogravimetry, chemical analysis and gammadensimetry

This paper deals with two experimental methods to determine carbonation profiles in concrete. Gammadensimetry is a non-destructive test method able to measure the total penetrated CO₂ and to monitor the carbonation process during laboratory accelerated tests. The second method is thermogravimetric analysis (TGA) supplemented with chemical analysis (CA): as TGA is performed on a small mortar sample not representative of the whole tested concrete, CA is needed to proportion the sample cement content, the sand content and to correct the TGA results becoming thus representative of the concrete mix. Consequently, TGA-CA gives accurate quantitative profiles in carbonated cementitious materials. Results are reported for an ordinary Portland cement paste, and three concrete mixes, containing siliceous or calcareous aggregates. The CO₂ mass loss due to carbonation occurs from 530 to 950 °C, which overlaps the temperature range of the calcareous aggregate dissociation. To solve the problem, the origin of CaCO₃ is carefully analyzed. Calcium carbonate ensuing from C-S-H carbonation dissociates in a lower temperature range than the more stable one ensuing from portlandite carbonation and from limestone, which enables C-S-H carbonation to be distinguished from calcareous aggregates. Therefore, TGA-CA allows the CaCO₃ ensuing from C-S-H carbonation to be measured and to calculate the portlandite degraded by carbonation. Thus, the total calcium carbonates profiles can be deduced even when calcareous aggregates is present in the concrete mix.     

The effect of polycations on early cement paste

This paper studies the possibility for improving the ductility of cement based materials by means of oligocationic additives. Actually, the setting of cement is due to ionic correlation forces between highly negatively charged C-S-H nanoparticles throughout a calcium rich solution. The main drawback of this strong attraction is its very short range that results in low elastic deformation of hydrated cementitious materials. A way to enlarge the attraction range between C-S-H particles would be to add cationic oligomers that would compete with calcium ions modifying the ionic correlation forces via a bridging mechanism of longer range, which could lead to a more ductile material. The studied parameters were the polymerization degree, the separation distance between the charged monomers and the balance between oligocations and monovalent and divalent cations in the solution. The results, both experimental and numerical by Monte Carlo (MC) simulations, demonstrate that cationic oligomers can compete with calcium cations as counterions to the C-S-H surface. The cohesive forces between C-S-H surfaces, calculated by MC simulations, show an interesting behaviour where range and magnitude can be tuned with oligomer concentration, polymerization degree and line charge density. Thus, it seems possible to modulate the ductility and critical strain of cement by addition of cationic oligomers.