复合型外加剂对铬铁渣基复合材料性能的影响

研究了不同种类早强剂、减水剂等功能外加剂对铬铁渣基复合材料性能的影响。通过单因素实验考察了不同掺量的Na Cl(NC)、Na2SO4(NS)、Na F(NF)和Al2(SO4)3(AS)等4种无机早强剂对铬铁渣基复合材料性能的影响,利用正交试验考察4种早强剂与木钙(CL)减水剂的复配对复合材料性能及结构的影响,得出复合型外加剂的最佳方案及组成,即NC为0.6%,NF为0.6%,NS为1.2%,AS为0.7%,CL为0.25%。采用XRD和SEM等测试方法分析复合材料水化产物物相组成和微观形貌。研究表明,复合型外加剂加速并促进了铬铁渣基复合材料水化进程,降低孔隙率,提高复合材料的密实度。复合型外加剂具有减水和早强叠加效应,改善流动性的同时提高复合材料的强度,其3,28 d抗压强度可达37.44和66.29 MPa,分别提高了46.6%和18.4%。将无机早强剂与减水剂进行复合设计,既能发挥无机早强剂的良好早强效果,又能弥补早强剂后期强度的不足。     

化学活化剂对铬铁渣水泥复合材料力学性能及水化的影响

以工业废弃物铬铁渣替代不同比例的水泥,并添加不同含量的KCl作为化学活化剂,成功制备了铬铁渣水泥复合材料。分析了铬铁渣掺量及KCl添加量对铬铁渣水泥复合材料抗压强度的影响,并利用傅里叶红外光谱、扫描电子显微镜、热重-差热分析等方法对不同水泥复合材料的样品进行了测试。结果表明,10%(质量分数)铬铁渣掺杂具有较好的抗压强度,且符合Cr~(6+)排放标准;0.6%(质量分数)的KCl加入到10%(质量分数)铬铁渣含量的水泥复合材料中,抗压强度最高,养护7,28和90 d后抗压强度分别为46.13,67.45和78.98 MPa;化学活化剂KCl的加入加速了钙矾石和C-S-H凝胶的形成,有利于提高水泥复合材料的致密性,同时化学活化剂中的氯离子可与水泥复合材料中粉煤灰提供的活性Al_2O_3反应生成水铝钙石,促进了熟料的水合作用,提高了水泥复合材料的早期强度和耐久性。     

蒸养条件下锂渣复合水泥的水化产物与力学性能

利用电感耦合等离子体发射光谱(ICP)、X射线衍射分析(XRD)、扫描电子显微镜与能谱分析(SEM-EDS)及同步热分析(TG-DTG)等手段研究了掺20%锂渣复合水泥在80℃蒸养7 h、7 d和标养28 d条件下的水化产物与力学性能。结果表明:锂渣中SiO_2和Al_2O_3大部分存在于锂辉石中,而少量存在于玻璃体中,且锂渣中存在少量的碳酸盐。与纯水泥不同,锂渣复合水泥在以上三种养护条件下形成的C-S-H凝胶均主要为网状;此外,蒸养7 d时还有水化硫铝酸钙(AFt)和立方体CaCO_3生成,但无水化石榴石形成;蒸养28 d时,还有球形等大颗粒状C-S-H凝胶和立方体CaCO_3生成。蒸养可以促进锂渣和水泥的反应,尤其是锂辉石与水泥水化产物氢氧化钙的反应。在蒸养7 h和7 d条件下,锂渣复合水泥胶砂的抗折强度、抗压强度均明显高于纯水泥胶砂的抗折强度、抗压强度。     

矿物外加剂对丁苯聚合物/水泥复合胶凝材料凝结硬化过程的影响及机制

为了比较沸石、纳米二氧化硅和稻壳灰这3种矿物外加剂对丁苯聚合物/水泥复合胶凝材料凝结硬化过程作用的差异,分别采用这3种矿物外加剂为调凝材料,并从凝结时间、早期强度、水化进程以及水化产物等角度比较3种矿物外加剂对丁苯聚合物/水泥复合胶凝材料的影响。结果表明,3种矿物外加剂都能促进复合胶凝材料的凝结硬化,大幅缩短凝结时间,提高早期强度。但3种矿物外加剂的调凝效果互不相同,调凝机理也有差异:沸石对AFt的生成有较大的促进作用,它不仅能促进C3A的水化,自身也能与Ca(OH)_2反应生成AFt和CSH凝胶;而纳米二氧化硅和稻壳灰对C3S水化的促进作用较强,自身也会与Ca(OH)_2反应生成CSH凝胶。     

化学外加剂对混凝土气孔结构及水化的影响

通过化学外加剂来调节混凝土内部的气孔结构,研究调控组分H对掺有引气剂混凝土气孔结构、性能的影响规律,并利用X射线衍射(XRD)及热重-差示扫描量热(TG-DSC)分析方法,研究了化学外加剂对水泥浆体水化产物及水化进程的影响。研究表明,H掺量为0.2‰时,混凝土的综合性能达到最佳;当掺加调控组分混凝土(KH2)总孔隙率与基准混凝土(K)相近时,增加10~200μm范围孔径的孔隙率,减少200~1600μm范围孔径的孔隙率,使平均孔径及气泡间距系数减小,抗压强度提高;化学外加剂掺加到水泥浆体中,并没有新的晶相生成,并且对水泥浆体水化进程没有明显影响。     

纳米氧化石墨烯增强增韧水泥基复合材料的微观结构及作用机理

通过氧化反应和超声波分散作用制备了不同含氧量氧化石墨烯(GO)纳米分散液,研究了GO氧含量、用量和水化时间对水泥基复合材料微观结构和力学性能的影响。研究结果表明GO能够调控水泥水化产物的形状,促使水泥水化反应形成规整的花状晶体,使得水泥基复合材料的强度特别是拉伸强度和抗折强度显著提高。研究结果证实了GO在水泥复合材料水化过程中起到模板作用,能够调控水泥水化产物的微观结构及提高水泥基复合材料的韧性,同时提出了GO调控水泥基复合材料微观结构的作用机理。本文结果提供了一种可显著增强增韧水泥基复合材料的新方法,具有潜在的应用前景。     

三乙醇胺对锰渣-水泥复合体系早期水化过程的影响

将锰渣与基准水泥等比例混合后在三乙醇胺的激发下制成复合体系,在分析复合体系力学强度的基础上测定复合体系早期水化过程中的Ca(OH)2剩余量,并采用红外光谱分析法、X射线衍射分析法对该体系早期水化过程进行追踪测定.结果表明,三乙醇胺对体系的激发效果明显,三乙醇胺参与了复合体系的水化过程,促进了水化反应程度,加快了锰渣中活性矿物与Ca(OH)2的二次水化,体系中的水化产物增多,有利于提高体系的早期强度.     

速凝剂对低水胶比浆体早期水化与微观结构的影响

低水胶比、高胶凝材料掺量的超高性能混凝土(UHPC)在常温养护条件下易产生凝结硬化不及时的问题。为促进UHPC在隧道初支、工程结构快速修复中的推广应用,拟采用有碱速凝剂(NA)和无碱速凝剂(AS)提升低水胶比浆体的早期凝结硬化速率。本工作通过水化热、水化溶出离子浓度、凝结时间和抗压强度试验研究速凝剂作用下低水胶比浆体的早期水化行为及凝结硬化规律,采用X射线衍射、SEM形貌观察和EDS能谱等手段对水化产物物相组成及微观结构演变规律进行了分析。结果表明,速凝剂的掺入加快了低水胶比复合胶凝材料浆体的早期水化速率,同时也促进了浆体的凝结硬化;NA对UHPC的促凝效果优于AS,其中NA-2%的1 d抗压强度为53.3 MPa, 28 d强度比为94.9%,而AS-4%的1 d抗压强度为38.9 MPa, 28 d强度比为92.3%;速凝剂促使低水胶比浆体快速生成大量水化产物,进而提高了浆体早期微观结构的致密性,且水化产物物相组成受速凝剂类型的影响较为显著。     

钢渣粉性能优化及制备无熟料混凝土的试验研究

为提高固体废弃物综合利用率,通过钢渣分段除铁优化试验和钢渣粉对无熟料混凝土抗压强度影响试验,研究以钢渣-矿渣-脱硫石膏作为胶凝材料制备无熟料全固废混凝土。结果表明,经分段磁选可获得金属铁含量低于0.5%的高性能钢渣粉;当钢渣粉比表面积为640m~2/kg,m(钢渣)∶m(矿渣)=1∶2.5时,无熟料混凝土同时获得较优的3d和28d强度。XRD、TG-DSC、IR和FE-SEM分析表明,在脱硫石膏的激发作用下钢渣和矿渣可以相互促进水化,水化产物以AFt(钙矾石)和C-S-H(水化硅酸钙)凝胶为主。早期钢渣水化促进矿渣的解聚并结合脱硫石膏生成AFt网状结构,随着水化反应的进行胶凝体系生成的C-S-H凝胶充填于AFt网络中使硬化浆体结构致密从而保证强度的增长。     

水泥石的结构、组成与干缩性能的关系

通过干缩测定、IR分析、TG-DSC综合热分析、孔结构测定(MIP法)等方法研究了水泥石的结构、组成与干缩性能的关系.水泥石的结构、组成(孔结构、水化产物的组成和数量、C-S-H的表面性能及化学结构)的改变通过采用矿物掺合料等量取代水泥、干燥前养护温度改变(20℃和60℃)来实现.结果表明,可逆收缩取决于水化产物的数量与C-S-H凝胶的表面性能与化学结构,随压汞法测得的小于30nm的孔体积增加而线性增加;不可逆收缩则与C-S-H凝胶的化学结构及其表面性能有关,C-S-H凝胶的聚合度增加,表面积下降,不可逆收缩减小;总干缩中部分不可逆收缩是由C-S-H的硅酸盐聚合度增加而造成的.     

水化硅酸钙晶种对CaO-SiO2-H2O蒸压体系强度的影响及其机理分析

选取石灰与无定形二氧化硅为原料,利用水热合成法在不同热工条件下制备了水化硅酸钙晶种,研究水化硅酸钙晶种对硅酸盐蒸压制品强度的影响。通过化学分析法探讨了不同蒸压时间下水化硅酸钙晶种对粉煤灰反应程度的影响;利用X射线衍射(XRD)、电子扫描电镜(SEM-EDS)和压汞法(MIP)分析了晶种对不同蒸压时间下CaO-SiO_2-H_2O体系水化产物种类及形貌的影响。研究结果表明:采用钙硅物质的量比为1.0、水热合成温度低于150℃时制备的水化硅酸钙晶种提高CaO-SiO_2-H_2O蒸压体系强度最明显,水化硅酸钙晶种的掺入促进了粉煤灰中SiO_2快速溶出以及水石榴石的分解,提高了水化产物含量;水化硅酸钙晶种的加入可以细化孔结构,使孔结构分布均匀,增加50nm以下的无害孔及少害孔数量,减少大于200nm的多害孔数量。     

碳酸化钢渣和矿渣作硅酸盐水泥混合材水化性能研究

通过对钢渣碳酸化前后的硅酸盐相提取及水化放热性能和将碳酸化钢渣和矿渣作为混合材的硅酸盐水泥的胶砂强度和水化产物种类的测定,以及对它们微观形貌的观察,研究了碳酸化钢渣对胶凝体系水化性能的影响.结果表明,碳酸化使钢渣中硅酸盐相的含量由47.06％下降至14.38％;碳酸化促进了钢渣的早期水化,抑制其后期水化;在配比相同的条件下,碳酸化钢渣-矿渣-硅酸盐熟料体系试样的3、28d抗压强度较未碳酸化钢渣-矿渣-硅酸盐熟料体系试样的高;碳酸化生成的CaCO3促进了熟料的水化;碳酸化钢渣促进了胶凝体系中AFt的生成,且生成水合碳铝酸钙.     

Modification of steel slag powder by mineral admixture and chemical activators to utilize in cement-based materials

Modification of steel slag powder by mineral admixture and chemical activators to utilize in cement-based materials was studied in this work. The results showed that for cement pastes with steel slag alone, the normal consistency water requirement and compressive strength were decreased significantly. Both of the initial setting time and final setting time were also retarded than that of the control sample. When a compound admixture of ground granulated blast furnace slag (GGBFS) -steel slag powder added the compressive strength was evidently improved. Modification of steel slag powder by “Gypsum-type” and “Sodium-type” chemical activators were further studied. Cement paste with the modified compound admixture by 1.5 % calcium sulfate hemihydrate or sodium sulfate, its 28 days compressive strengths could reach to 75.4 and 76.2 MPa, respectively. X-ray diffraction (XRD) patterns showed that the main hydration products mainly included Ca(OH)₂ and ettringite. It indicated that proper mineral admixture and chemical activators had a positive effect regarding early hydration of steel slag powder, and enhanced forming calcium silicate hydrate(C–S–H) gel and ettringite. This work contributes to understanding of how to sustainably manage wastes and byproduct materials and has the potential to provide several important environmental and economic benefits.     

Synthesis of nanoparticles from slag and their enhancement effect on hydration properties of CaO/CaSO4-activated slag binder

Developing a low-cost and eco-friendly alternative to cement is of great significance for reducing the CO₂ emissions. CaO/CaSO₄-activated slag binder may only be served as a promising cementitious material when the severe defect in the early strength is overcame. In this study, gel-like nanoparticles with an average size of ～ 328 nm were prepared from the slag through dissolution at room temperature and reprecipitation at 50 °C. Subsequently, synthetic nanoparticles (SNPs) were added as a supplementary additive to enhance the strength of CaO/CaSO₄-activated slag binder. The effects of SNPs on the strength development, hydration kinetics, hydration products, and microstructure of the slag binders were investigated. The results indicated that the addition of moderate SNPs shortened the duration of induction period and improved the reaction rate in the acceleration period of the slag binders. As a result, large amounts of calcium aluminosilicate hydrate (C-A-S-H) gel was generated at early hydration ages. Meanwhile, SNPs increased the polymerization degree of this gel through the nucleation effect. Gel products’ well-filled the pore spaces between slag particles and yielded a compact microstructure, consequently enhancing the binder strength. The sample with adding 1.5 wt% SNPs exhibited the optimum strengths of 7.78 and 39.86 MPa after 1 and 28 days.     

Simulation of a temperature rise in concrete incorporating fly ash or slag

Granulated slag from metal industries and fly ash from the combustion of coal are among the industrial by-products and have been widely used as mineral admixtures in normal and high strength concrete. Due to the reaction between calcium hydroxide and fly ash or slag, compared with Portland cement, the hydration of concrete containing fly ash or slag is much more complex. In this paper, by considering the producing of calcium hydroxide in cement hydration and the consumption of it in the reaction of mineral admixtures, a numerical model is proposed to simulate the hydration of concrete containing fly ash or slag. The heat evolution rate of fly ash or slag blended concrete is determined from the contribution of both cement hydration and the reaction of mineral admixtures. Furthermore, a temperature rise in blended concrete is evaluated based on the degree of hydration of cement and mineral admixtures. The proposed model is verified with experimental data on the concrete with different water-to-cement ratios and mineral admixtures substitution ratios.     

Measuring adhesion between steel and early-hydrated Portland cement using particle probe scanning force microscopy

Particle probe scanning force microscopy was used to measure adhesion between steel and early-hydrated cement in the study. Particle probes, created by attaching steel microspheres to microcantilevers, were successfully used to collect adhesive forces between steel and early-hydrated Portland cement in air and in saturated lime water. Mixed Gaussian models were applied to predict phase distributions in the cement paste, i.e., low density calcium silicate hydrate, high density calcium silicate hydrate, calcium hydroxide, other hydrated products and the unreacted components. Consistent correlations were achieved for volume fractions between areas with different adhesion measurements and predictions from the hydration model. Results showed that low density calcium silicate hydrate, high density calcium silicate hydrate and other hydrated products exhibit intermediate adhesion to steel microspheres. Calcium hydroxide exhibits the smallest adhesion, while the unreacted components exhibits the largest adhesion among all groups.     

The nature of the hydration products in hardened cement pastes

An understanding of the performance of portland cement-based materials requires knowledge at the microstructural level. Developments in the instrumentation of several techniques have led to improved understanding of the composition, morphology, and spatial distribution of the various products of cement hydration. In particular, our understanding of the nature of the nearly amorphous calcium silicate hydrate (C–S–H) phases – which are the principal binding phases in all portland cement-based systems – has been advanced by developments in solid-state NMR spectroscopy and analytical TEM. This paper presents an overview of the nature of the hydration products formed in hardened portland cement-based systems. It starts with the most straightforward cementitious calcium silicate systems, C₃S and β-C₂S, and then considers ordinary portland cement and blends of portland cement with silica fume, ground granulated iron blast-furnace slag, and finally alkali hydroxide-activated slag cements.     

Alkali activation of reactive silicas in cements: in situ 29Si MAS NMR studies of the kinetics of silicate polymerization

In the highly alkaline environment of the cement paste of a concrete, a source of silica can potentially react in two ways. In the pozzolanic reaction, it can combine with free lime to generate additional calcium silicate hydrate binding phase. Alternatively, reaction with alkali to form a gel can occur; this gel may swell and degrade the concrete. ²⁹Si magic angle spinning (MAS) and cross-polarization (CP) MAS nuclear magnetic resonance (NMR) studies have been performed to determine the silicate connectivity in some model cement systems; ²⁹Si enrichment was utilized to enable a series of spectra to be acquired in situ from a single sample.The hydrate from pozzolanic reaction of lime with silica was similar to the hydrate formed around silica in blended pozzolanic cements, with a relatively high crystallinity and long silicate chains. In the absence of lime, silica reacted with an alkaline solution to produce a gel having a high degree of cross linking, and a range of silicate mobilities. Tricalcium silicate hydration was found to be accelerated significantly by high levels of alkali (KOH) in solution; the hydrate formed had shorter silicate chains and was more crystalline than that produced by reaction in pure water. Hydration in alkali solution of a model blended cement, comprising a mixture of tricalcium silicate and silica, gave rise to two products, a long chain calcium silicate hydrate (C-S-H) and an alkali silicate of low rigidity. The alkali silicate phase gradually polymerized; at later ages it underwent a phase change, although no crystalline phase appeared to be formed. Silicate exchange took place between the C-S-H and the alkali silicate phase at a slow rate.     

Synthesis and heavy metal immobilization behaviors of slag based geopolymer

In this paper, two aspects of studies are carried out: (1) synthesis of geopolymer by using slag and metakaolin; (2) immobilization behaviors of slag based geopolymer in a presence of Pb and Cu ions. As for the synthesis of slag based geopolymer, four different slag content (10%, 30%, 50%, 70%) and three types of curing regimes (standard curing, steam curing and autoclave curing) are investigated to obtain the optimum synthesis condition based on the compressive and flexural strength. The testing results showed that geopolymer mortar containing 50% slag that is synthesized at steam curing (80 degrees C for 8h), exhibits higher mechanical strengths. The compressive and flexural strengths of slag based geopolymer mortar are 75.2 MPa and 10.1 MPa, respectively. Additionally, Infrared (IR), X-ray diffraction (XRD) and scanning electron microscopy (SEM) techniques are used to characterize the microstructure of the slag based geopolymer paste. IR spectra show that the absorptive band at 1086 cm(-1) shifts to lower wave number around 1007 cm(-1), and some six-coordinated Als transforms into four-coordination during the synthesis of slag based geopolymer paste. The resulting slag based geopolymeric products are X-ray amorphous materials. SEM observation shows that it is possible to have geopolymeric gel and calcium silicate hydrate (C-S-H) gel forming simultaneously within slag based geopolymer paste. As for immobilization of heavy metals, the leaching tests are employed to investigate the immobilization behaviors of the slag based geopolymer mortar synthesized under the above optimum condition. The leaching tests show that slag based geopolymer mortar can effectively immobilize Cu and Pb heavy metal ions, and the immobilization efficiency reach 98.5% greater when heavy metals are incorporated in the slag geopolymeric matrix in the range of 0.1-0.3%. The Pb exhibits better immobilization efficiency than the Cu in the case of large dosages of heavy metals.