纳米水化硅酸钙的制备及对水泥水化影响的研究进展

随着纳米技术的不断发展,纳米材料逐步开始应用于传统混凝土材料中,以提高混凝土的各项服役性能。纳米水化硅酸钙(纳米C-S-H)是一种新型的早强纳米复合材料,可通过晶核效应加快水泥早期水化速率,显著提高水泥基材料的早期力学性能,从而提高施工效率,满足特殊施工要求。本文系统总结了纳米C-S-H的制备方法,及纳米C-S-H对水泥基材料早期和长期性能的影响规律,探讨了其对于水泥水化过程和水化产物的影响机制,其中重点介绍了采用聚合物分散纳米颗粒制备的C-S-H/PCE(聚羧酸型减水剂,简称PCE)纳米复合材料。     

C-S-H/PCE凝胶对掺磷渣水泥的低温促凝早强性能研究

探讨C-S-H/PCE凝胶对掺磷渣硅酸盐水泥的低温促凝早强性能的影响,并通过上清液pH值、Ca2+浓度和化学结合水量分析其对水化的影响机理.低温下(8℃) C-S-H/PCE凝胶能有效缩短混凝土终凝时间,并提高早期强度,当掺量5％时,混凝土终凝时间缩短近6h,16h、24 h和3d抗压强度比分别为160％、150％和1...     

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。     

Microstructural development of early age hydration shells around cement grains

An important microstructural aspect of the early hydration of Portland cement (PC) is the formation of a shell of hydration products around cement grains. There is, at present, limited information on the mechanism of formation of the shell and of the chemistry of the phases that constitute the shells. Through the use of STEM imaging of early age hydrated cement pastes as early as 2 h, the present work shows that the shells correspond to the first C-S-H type product formed which has a distinct morphology compared to C-S-H formed later when the main reaction occurs (nucleation and growth stage at setting time). The shells form only around the silicate part of the grain and are not empty but filled with a fragile fibrous C-S-H which appears to have a lower (packing) density than the rest of the hydration products. The cement grains underneath the shells are seen to react unevenly and the hydration seems to follow a reaction front, leaving striations up to 1 µm deep on the grains. Over the long term, the original fragile product seems to densify and gives rise to the usual inner C-S-H. High resolution EDS chemical analysis and mappings were used to get insight into the chemistry associated with the formation of these early age products. The C/S ratio of all C-S-H (inner and outer shell) is the same (within the limits of the analysis accuracy) and evolves insignificantly over the first 24 h of hydration. High concentrations of sulfate are associated with the C-S-H formed during the early development of the microstructure, but these decrease later, the sulfate being mainly incorporated into ettringite.     

无机外加剂中各离子对水化硅酸钙的影响研究进展

近年来,随着混凝土技术的发展,外加剂已成为制备混凝土的重要辅助材料,但外加剂引入的各种离子对水化硅酸钙(C-S-H)的结构及形貌有较大影响。因此综合评述了无机外加剂中不同离子对C-S-H组成、结构及微观形貌的影响:Al^(3+)能够直接参与C-S-H结构的构建;Na^(+)、K^(+)、Cl^(-)可以加速水化反应,促进C-S-H凝胶的生成;适量的SO_(4)^(2-)有助于C-S-H结晶,而过量的SO_(4)^(2-)则会降低C-S-H的稳定性。详细分析了上述各离子对C-S-H硅氧四面体聚合度、层间距及平均分子链长的影响和研究进展,并在此基础上研究了无机外加剂中多离子共存对C-S-H结构的影响。无机外加剂对C-S-H硅氧四面体聚合度、层间距及平均分子链长的影响还需进一步研究。     

The effects of nano-C-S-H with different polymer stabilizers on early cement hydration

A promising approach to accelerate cement hydration known as “seeding technology” has been discovered using nano-particles to provide additional nucleation sites for growing of C-S-H. Two different types of polymer, polycarboxylate (PCE) and polysulfonate (PSE) were used as stabilizer to synthesize nano-C-S-H via co-precipitation process. The obtained C-S-H-polymer composites were characterized by means of XRD, FTIR, thermogravimetric analysis (TGA), TEM, dynamic laser scattering (DLS), and BET. DLS measurement shows that the particle size of the obtained C-S-H-polymer suspension ranges from 82.6 to 589.9 nm. The results of DLS and BET show that the particle size of the C-S-H particles synthesized using PCE polymer as stabilizer is smaller than those synthesized with PSE polymer, and hence the specific surface area is much higher. FTIR and TGA results confirm the presence of the polymers in the obtained C-S-H composites particles. XRD results indicate that the presence of the polymers reduces the crystallinity of C-S-H due to the absence of the d002 peak at 2θ of 7°. The calorimetry results show that the main hydration peak of cement is dramatically increased by the addition of the C-S-H-polymer composites. It is interestingly found that the acceleration effect of the C-S-H-polymer composites is linearly proportional to the total surface area of the nanoparticles introduced into the cement pastes. At the same time, it is found that the secondary hydration peak, usually known as the sulfate-depletion peak, is greatly advanced by addition of the C-S-H nano-particles in comparison with the blank cement paste. The acceleration effect of the nano-C-S-H is further verified in a pure C₃S system.     

早强型聚羧酸系减水剂对基准水泥早期水化的影响研究

探究早强型聚羧酸系减水剂(ES-PCE)对水泥水化的作用机制,有助于ES-PCE的研发设计与推广应用。本文通过对水泥水化进程、溶解速率、水化产物生长、凝结时间与抗压强度进行表征,分析了ES-PCE与普通聚羧酸系减水剂(PCE)对基准水泥早期水化的影响机理。结果表明:PCE与ES-PCE均会降低水泥悬浮液的溶解速率;PCE的掺入延缓了水泥水化的诱导期与加速期,降低了水化放热量;而ES-PCE仅略微延迟了水泥水化的诱导期,但缩短了加速期,水化放热量基本不变。与基准水泥相比,ES-PCE分别提早了水泥初凝时间10 min和终凝时间85 min。ES-PCE的掺入提高了水泥早期和后期强度,掺0.2%(质量分数)ES-PCE的水泥7 d抗压强度较基准组提高了14%,而同掺量的PCE强度提高仅为前者的一半。PCE与ES-PCE的掺入释放了水泥颗粒团状絮凝结构中的水分,有利于水泥水化,但二者对水化的影响截然相反;PCE分子结构中大量的羧基络合了溶液中的Ca²⁺,抑制了水泥颗粒表面晶核的形成,起到了一定的缓凝作用;然而,ES-PCE分子结构中羧基含量较低,Ca²⁺的络合作用较弱,缓凝效果并不明显,在体系中有效水分增多的情况下,反而促进水泥的水化,起到了早强效果。水灰比为0.4的水泥砂浆中,ES-PCE的掺量适宜控制在0.3%以下,在保证减水率的同时,对水泥早期和后期强度均起到一定的增强作用。     

纳米C-S-H对矿粉-水泥体系水化的影响

C-S-H是通用硅酸盐水泥主要的水化产物,对水泥基材料的性能起着十分重要的作用,但水泥水化产物复杂,难以从水化产物中分离出纯净的C-S-H并研究其对水泥基材料的影响。故本文通过双分解法制备了纳米C-S-H(NC)颗粒,并将其掺入矿粉-水泥体系中,通过无接触式电阻率测定仪、X射线衍射仪、差热分析仪(DSC-TG)、扫描电镜、压汞测试仪(MIP)等探究了NC对矿粉-水泥体系水化的影响。研究发现,在1%~4%(质量分数)掺量范围内,掺入NC可缩短基体的凝结时间,并为水泥早期水化提供更多的活性位点,加速水化产物的形成和沉淀,促进水化产物之间的搭接,从而降低了基体孔隙率并使基体早期强度和水化浆体电阻率均有所提升。     

Influence of activator type on hydration kinetics, hydrate assemblage and microstructural development of alkali activated blast-furnace slags

The hydration of two slags with different Al₂O₃ contents activated with sodium hydroxide and hydrous sodium metasilicate (commonly named water glass) is studied using a multi-method approach. In all systems, C-S-H incorporating aluminium and a hydrotalcite-like phase with Mg/Al ratio ~ 2 are the main hydration products. The C-S-H gels present in NaOH activated pastes are more crystalline and contain less water; a calcium silicate hydrate (C-S-H) and a sodium rich C-N-S-H with a similar Ca content are observed at longer hydration times. The activation using NaOH results in high early strength, but strength at 7 days and longer is lower than for the sodium metasilicate systems. The drastic difference in C-S-H structure leads to a coarser capillary porosity and to lower compressive strength for the NaOH activated than for the sodium metasilicate activated slags at the same degree of slag reaction.     

C-S-H及C-S-H脱水相对水泥石结构改性的研究

以C-S-H及C-S-H脱水相作水泥水化物沉淀中心的品种。从理论上阐明了它们是具有较大介电常数、较小物理化学不均匀系数、高分散度的晶种物质,故具有优先吸附的界面效应及优先沉淀的结晶中心作用,可缓和原始矿物表面的高浓度的屏蔽效应及界面的近程析晶,使水化物分布均匀、结构致密,从而提高水泥石强度。C-S-H及C-S-H脱水相两者中,尤以后者作用更显著。     

Approach by zeta-potential measurement on the surface change of hydrating C3S

The adsorption of Ca²⁺ on C₃S surface and the formation of C-S-H in the induction period of C₃S hydration were investigated by measuring zeta-potential, heat evolution change and by analyzing dissolved ions. Within 20 minutes, the dissolution of Ca²⁺ and silicate ions and the adsorption of Ca²⁺ on the surface of C₃S were alternately repeated. In the induction period (20 50 minutes), Ca²⁺ was adsorbed fairly strongly on C₃S surface giving positive zeta-potentials and the dissolution stopped for a time. In the hydration between 60 and 140 minutes, the C-S-H gel proceeded to crystallize and Ca²⁺ began to dissolve again, giving negative zeta-potentials by Si-O⁻. After 140 minutes, the second evolution was caused by the crystallization of C-S-H and Ca(OH)₂.     

The influence of an ion-exchange resin on the kinetics of hydration of tricalcium silicate

The addition of a finely-ground ion-exchange resin makes it possible to modify the hydration kinetics of C₃S pastes. Analyses of the liquid phase in pastes and more dilute suspensions show that the resin exchanges calcium ions for sodium ions very rapidly during the early stage of hydration and therefore the concentration of silica in solution increases. The resin impacts the hydration of C₃S by other mechanisms which depends on the resin quantity added. For a high resin quantity, the induction period is very short, but the longer-term hydration is enhanced compared to a reference sample without resin. We hypothesize that the surface of the resin can provide sites for the nucleation and growth of C-S-H hydrates and/or portlandite far away from the surface of the C₃S grains. This consequently increases the quantity of hydrates that can precipitate before a continuous hydrate layer forms over the surfaces of C₃S particles.     

The composition of the C-S-H phases in portland cement pastes

The composition of the calcium silicate hydrate (C-S-H) present in Portland cement pastes from eight days to five years old, and in concrete samples ten years old, has been determined by electron probe micro-analysis. The dependence of C-S-H composition on water/cement ratios has also been studied. When the cement is only partially hydrated inner and outer hydrate layers are seen around alite grains. These hydrates have different chemical compositions. With progressive hydration it becomes impossible to distinguish the inner from outer hydrates without a reference alite grain. At this stage two distinct C-S-H compositions can still be found by microanalysis. After further hydration a single CSH composition predominates. The calcium content of C-S-H varies significantly with water/cement ratio and there is new evidence to suggest that in the C-S-H structure Mg replaces Ca, and that Al, S and Fe replace Si.     

Insights into early hydration of Portland limestone cement from infrared spectroscopy and isothermal calorimetry

Isothermal calorimetry and diffuse reflectance infrared DR-FTIR spectroscopy are combined to correlate evolutions of spectroscopic signatures with rates of chemical reactions as reflected in the rate of heat emitted during the first 38 h of cement hydration. Portland limestone cement mortar is employed and the analysis is repeated for two different mixing procedures. Intensive blender mixing with quartz sand is found to cause activation of the cement resulting in a faster hydration process. At early stages of hydration, two types of C-S-H are formed. The spectral intensity of the earlier C-S-H is found to saturate, while that of the later form continues to acquire intensity throughout the 38 h of the experiment. Evidences are presented which support the interpretation that the two forms differ mainly in morphology and water content. Simultaneously with the saturation of the early C-S-H, a transient species is observed with DR-FTIR. This species correlates with the observed thermogram fine-structure.     

水泥–矿渣复合胶凝材料中矿渣的水化特性

通过对不同矿渣掺量时水泥–矿渣复合胶凝材料中矿渣的反应程度、硬化浆体中Ca（OH）2含量以及水化硅酸钙（C–S–H）凝胶的Ca/Si比（Ca和Si的摩尔比）的测定,研究复合胶凝材料体系中矿渣的水化特性。结果表明：在水泥–矿渣复合胶凝材料中,矿渣掺量越大,矿渣反应程度越低,但矿渣掺量≤70%时,对矿渣的反应程度影响不大。高温养护可提高早期矿渣的反应程度,但阻碍其后期的进一步水化。矿渣早期水化生成外部水化产物时消耗一定的Ca（OH）2,使硬化浆体中Ca（OH）2含量降低,矿渣水化吸收Ca（OH）2中的Ca2＋,使生成的C–S–H凝胶的Ca/Si比降低较少;在水化后期,矿渣生成内部水化产物不再消耗较多的Ca（OH）2,使C–S–H凝胶的Ca/Si比降低相对较多,硬化浆体中Ca（OH）2含量有增加的趋势,保证硬化浆体的长期稳定性。     

Early Hydration of Tricalcium Silicate

The hydration of tricalcium silicate (C₃S) in the preacceleration stages was studied. The C₃S particles carry a positive charge during the early stages of hydration. Following a rapid hydrolysis of C₃S, calcium ions adsorbed on the Si-rich surface of C₃S particles, greatly reducing their further dissolution, thus initiating the induction period. The [Ca²⁺] and [OH^-] continue to increase at lower rates and, because Ca(OH)₂ crystal growth is inhibited by silicate ions, become supersaturated with respect to Ca(OH)₂. When the supersaturation reaches a value of ∼1.5 to 2.0 times the saturation concentration, nuclei are formed, and rapid growth of Ca(OH)₂ and C-S-H is initiated. These products act as sinks for the ions in solution, thus enhancing the further dissolution of C₃S.     

减水剂对硫铝酸盐水泥早期水化影响

研究了聚羧酸系高效减水剂(PCE)和萘系减水剂(FDN)对硫铝酸盐水泥净浆工作性能及力学性能影响,通过XRD和SEM检测手段对水化产物进行表征.结果表明:两种减水剂对硫铝酸盐水泥净浆流动度的影响存在饱和点;相比于FDN型减水剂,PCE型减水剂对硫铝酸盐水泥净浆具有更好的减水效率及分散能力.PCE型减水剂阻碍硫铝酸盐水泥净浆早期水化,并降低硫铝酸盐水泥净浆1 d抗压强度;FDN型减水剂能够加速硫铝酸盐水泥净浆早期水化,缩短初凝和终凝时间,提高硫铝酸盐水泥净浆1d抗压强度.两种减水剂对硫铝酸盐水泥净浆3d后抗压强度及水化产物种类均没有影响.     

粉煤灰对水泥中重金属存在形式的影响

本文对添加不同含量的粉煤灰后，熟料水化过程中重金属元素（Cr、Mn、Cu、Pb、Zn）存在形式及其浸出毒性进行了实验和探讨。随着粉煤灰掺入量由0%提升至10%，水化产物形貌中微细孔增多，重金属元素在C-S-H中富集程度增加，熟料重金属元素浸出毒性呈现不同程度下降趋势，最大下降幅度达到56.1%，主要因为微细孔对重金属有较好的吸附作用，且重金属元素在水化产物周围的富集程度增加，有助于重金属离子以较为稳定的形态固化在水化产物中。     

Thermodynamics of Calcium Silicate Hydrates and Their Solutions

The solution that surrounds hydrating cement particles contains dissolved species which are important in the overall process. A method, based on the Gibbs-Duhem equation for a three-component system, has been developed for computing the composition of one phase from values for its equilibrium solubility in a second phase. The method has been used to compute the CaO:SiO₂ ratio for two types of calcium silicate hydrate (C-S-H) gel, one of which is thought to form from hydrating tricalcium silicate (Ca₃SiO₅), and the other by precipitation from appropriate solutions. The results agree well with measured values reported in the literature. They have also been used to help define the probable composition of the C-S-H layer which forms on tricalcium silicate surfaces during the early stages of hydration when the reaction is slow. A chemical potential phase diagram is constructed from which thermodynamic quantities can be computed directly. The free energies of formation have been estimated for two types of C-S-H formed from CaO, SiO₂, and H₂O, These results provide insight into the structure and composition of C-S-H, which is the most abundant product in portland cement systems.     

铁铝酸钙的早期水化

研究了掺有少量异组份的C_6AF_2、C_4AF和C_6A_2F的水化活性,早期水化热及c(?)H_2和(或)CH存在条件下的早期水化特性,讨论了石膏的缓凝机理。结果表明,掺有异组份的C_6A_2F具有高的水化活性及快凝快硬性能;石膏延缓水化的作用主要取决于铁相矿物的水化活性及AFt包裹层的状况。