Investigation of hydraulic activity of ground granulated blast furnace slag in concrete

Ground granulated blast furnace slag (GGBFS), a by-product of the steel manufacturing industry, being used as an effective partial cement replacement material, has already been proven to improve several performance characteristics of concrete. The reactivity of GGBFS has been found to depend on the properties of slag, which vary with the source of slag, type of raw material used, method and the rate of cooling. The present work aims at bringing out a novel relationship between the Hydraulic Index (HI) of slag at 7 and 28 days (HI7 and HI28) and the influencing properties of slag, namely, glass content, fineness and chemical composition by employing multiple regression analysis on 37 slag samples from various sources. HI7 and HI28, thus obtained, have been mapped onto a Slag Activity Index (SAI) plot, giving an indication of the ranges of strength of slag.     

Activation of blast furnace slag by a new method

Blast furnace slag is used as supplementary cementing material for the production of blended cement and slag cement. Its latently hydraulic properties can be activated by several methods. Most applications employ the use of high pH values in the pore solution (> 13.0) to accelerate the corrosion of the glass network of the slag.It is shown in this work that activation is also possible by lowering the pH to a range between 11.8 and 12.2 by the addition of calcium hydroxide and soluble calcium salts. Among the salts investigated in this study are calcium chloride, calcium bromide, calcium nitrate, calcium formate, and calcium acetate. Other salts can be used alternatively as long as they are able to increase the calcium ion concentration and thus reduce the pH in the pore solution via the calcium hydroxide equilibrium. Complex formation of organic anions with calcium ions in the pore solution is a serious handicap when using organic calcium salts.This concept was tested on a particular slag improving its early compressive strength. It was possible to increase the strength of mortar bars produced from the pure slag from 3 MPa to 25 MPa after seven days by adding calcium hydroxide, calcium carbonate and calcium acetate. The early strength of slag cement containing 80% slag was increased from 6 to 16 MPa after two days by adding calcium chloride. The final strength was increased from 36 to 53 MPa after 28 days (water/cement-ratio = 0.40, 20 °C).Analytical data is included to demonstrate that application of the aforementioned concept is able to increase heat liberation and degree of slag consumption.     

利用矿热炉渣、矿渣、精炼渣制备复合水泥

为缓解矿渣等高活性混合材资源的紧张,通过对矿热炉渣、矿渣、精炼渣三种渣按照不同比例复掺进行了试验。试验表明,在加入激发剂后,当矿热炉渣掺量为25%、矿渣为5%、精炼渣为5%时,可配制达到PC42.5水泥;当矿热炉渣掺量为30%、矿渣为15%、精炼渣为5%时,仍可配制合格的PC32.5水泥。     

Stabilization of electric arc furnace dust by the use of cementitious materials: Ionic competition and long-term leachability

Ionic competition in stabilization of major heavy metals from electric arc furnace dust (EAFD) was investigated. The cementitious materials tested (ground granulated blast furnace slag (GGBFS) and ordinary Portland cement (OPC)) were put in contact with solutions made of various combinations of Cr(VI), Pb(II), Zn(II), Ni(II) and Mo(VI) ions. The presence of Ni, Zn or Mo did not influence the Cr fixation by GGBFS and OPC. The ionic competition phenomenon between Cr and Pb was observed for GGBFS in particular.Long-term leaching tests with OPC-EAFD and GGBFS-EAFD showed that OPC is more effective in fixing Cr at 7 days (4.7 mg/L in solution) than GGBFS (79.4 mg/L in solution). GGBFS becomes effective with time and offers a better performance from 56 to 365 days (under 1 mg/L in solution) than OPC (until 11 mg/L in solution). GGBFS and OPC decreased Zn, Pb and Ni concentrations in leaching solutions under 2.5 mg/L.     

Sulfur speciation in granulated blast furnace slag: An X-ray absorption spectroscopic investigation

Sulfur speciation in a granulated blast furnace slag (GGBFS) was analyzed by X-ray absorption near edge structure spectroscopy (XANES) before and after activation by saturated calcium hydroxide and five normal sodium hydroxide solutions. The solution to GGBFS ratio was 0.4.XANES showed that sulfur in GGBFS existed mostly as sulfides (frozen in calcium polyhedra) with a minor amount as sulfate. A slowly-cooled blast furnace slag, in contrast, had most of the sulfide transformed to sulfate. After activation of GGBFS, more sulfate formed and crystalline sulfide phases became more apparent. More slag reacted at lower pH than at higher pH.     

利用钢渣研制复合硅酸盐水泥的正交试验研究

通过正交试验进行了利用钢渣配制复合硅酸盐水泥的初步研究。研究结果表明,将钢渣单独粉磨后与矿渣微粉复合掺入硅酸盐水泥,再适当地辅以掺加石膏和激发剂,可获得性能良好的具有较高强度的复合硅酸盐水泥。     

利用锰渣、矿渣、石灰石制备复合水泥

针对目前矿渣等高活性混合材资源的紧张,实验进行了锰渣、石灰石部分取代矿渣制备复合水泥的试验研究。研究表明,当石灰石粉掺量固定为10%时,相同水泥比例下,随着锰渣和矿渣比例的增加,胶砂试块3d强度增加,28d强度有所下降;当加入复合激发剂后复合混合材总掺量为60%,锰渣和矿渣质量比为4:1时,仍能配制合格的P.C32.5标号水泥。     

Composition and microstructure of 20-year-old ordinary Portland cement-ground granulated blast-furnace slag blends containing 0 to 100% slag

The morphology of outer-product (Op) C-S-H in 20-year-old slag-cement pastes appeared in most blends to be finer than at younger ages. The Ca/Si and Ca/(Si + Al) ratios of the Op C-S-H decreased with increasing slag content, and the Al/Si ratio increased. The Ca/Si ratio of C-S-H in the slag-containing pastes was lower at 20 years than at 14 months and the amount of Ca(OH)₂ was reduced indicating that additional slag must have reacted. The mean aluminosilicate chain length of the C-S-H was very long in all the samples and would be expected to have increased with age. The TEM-EDX and NMR data are consistent with nanostructural models for C-S-H. The Mg/Al ratio of the Mg-Al layered double hydroxide phase (LDH) was lower at 20 years than at 14 months in all cases except for the neat slag paste; aluminium hydroxide-based structure might be interstratified with those of the Mg-Al LDH.     

Tensile and fiber dispersion performance of ECC (engineered cementitious composites) produced with ground granulated blast furnace slag

An engineered cementitious composite (ECC) produced with ground granulated blast furnace slag was developed for the purpose of achieving moderately high composite strength while maintaining high ductility, represented by strain-hardening behavior in uniaxial tension. In the material development, single fiber pullout tests and matrix fracture tests were performed, followed by micromechanical analyses to properly select the range of mixture proportion. Subsequent direct tensile tests were employed to assess the strain-hardening behavior of the composite, which exhibited high ductility and strength with the addition of slag. High ductility is most likely due to enhanced workability and fiber dispersion performance which is attributed to the oxidized grain surface of slag, as verified by fiber dispersion tests. These results suggest that, within the limited slag dosage employed in the present study, the contribution of slag to fiber dispersion outweighs the side-effect of decreased potential for saturated multiple cracking, including a slight increase in matrix fracture toughness and fiber/matrix bond strength.     

粒化高炉矿渣的水化机理探讨

以上海梅山钢铁公司的矿渣为研究对象,探讨粒化高炉矿渣在无激发剂存在的条件下的水化机理,并建立矿渣水化反应过程的化学模型。为矿渣的大规模、无害化、资源化和高附加值利用奠定理论基础。研究表明:在没有化学激发剂存在的条件下,梅山矿渣的水化产物是水化硅酸钙C2SH(C)、水化硅酸钙2CaO·SiO·(2￣4)HO和钙铝黄长石22Ca2Al(Al,Si)2O7。初期的水化过程是矿渣中的Ca2 等网络改变体阳离子与水中的H之间的置换,随着这种置换反应的进 行,溶液中的pH值不断升高,当pH高到一定程度时,矿渣颗粒表面上的HSiO4的溶解度将提高,溶解了的各种形态4的硅酸离子和溶液中的Ca2 、OH反应生成水化硅酸钙凝胶。     

The evolution of strength and crystalline phases for alkali-activated ground blast furnace slag and fly ash-based geopolymers

The increase in strength and evolution of crystalline phases in inorganic polymer cement, made by the alkali activation of slag, Class C and Class F fly ashes, was followed using compressive strength test and synchrotron X-ray diffraction. In order to increase the crystallinity of the product the reactions were carried out at 80 °C. We found that hydrotalcite formed in both the alkali-activated slag cements and the fly ash-based geopolymers. Hydroxycancrinite, one member of the ABC-6 family of zeolites, was found only in the fly ash geopolymers. Assuming that the predominantly amorphous geopolymer formed under ambient conditions relates to the crystalline phases found when the mixture is cured at high temperature, we propose that the structure of this zeolitic precursor formed in Na-based high alkaline environment can be regarded as a disordered form of the basic building unit of the ABC-6 group of zeolites which includes poly-types such as hydroxycancrinite, hydroxysodalite and chabazite-Na.     

Investigation of stabilization/solidification for treatment of electric arc furnace dust: Dynamic leaching of monolithic specimens

Diffusion-controlled leaching of heavy metals (Cr, Ni, Pb and Zn) from electric arc furnace dust treated with ground granulated blast furnace slag (GGBFS) and with ordinary Portland cement (OPC) was evaluated. Monolithic specimens were evaluated under dynamic leaching conditions for 84 days with periodic leachant renewal. The influence of leaching time, nature of the leachant, binder type and the water/solid ratio of the monoliths were investigated. Results obtained showed both binders can immobilize heavy metals in the monoliths under dynamic leaching conditions, with cumulative quantity of leached metal under 0.138 mg (Cr). Alkaline leachant increased metal release from specimens and reducing the water/solid ratio of the monolith allowed for a decrease in the cumulative mass of metals leached. Chemical and mineralogical characterizations indicated that the metals were evenly distributed throughout the specimens for both binders. Decalcification was observed on the OPC monolith border following leaching. This decrease in Ca corresponded to an altered zone (20 μm), identified by scanning electron microscopy. The GGBFS sample did not show an altered zone.     

含钛高炉渣的碳化产物对水泥砂浆强度及电阻率的影响

以攀枝花钢铁公司生产的高钛型高炉渣的碳化产物(碳化渣)取代标准砂为集料制备了水泥砂浆。采用X射线衍射仪(XRD)和扫描电子显微镜(SEM)对高钛型碳化渣进行了成分、物相和形貌表征;测试了不同碳化渣含量下水泥砂浆的抗压强度和电阻率,探讨了不同碳化渣取代量对水泥砂浆电阻率的影响机制。研究结果表明,含有碳化渣的水泥砂浆的强度满足建筑水泥砂浆的要求;在潮湿状态下,碳化渣的引入无法降低28 d龄期水泥砂浆的电阻率;在干燥状态下,当碳化渣的取代量达到60%以上时,水泥砂浆的电阻率可低于标准水泥砂浆,且最低可下降87.5%。高钛型碳化渣可作为导电集料的候选材料用于制备面向建筑加热采暖用的水泥基复合导电材料。     

Effect of components fineness on strength of blast furnace slag cement

The strength development of 1:1 mixes of clinker and blast furnace slag with varying fineness of components from 3000 to 6000 cm²/g has been studied. Overall results indicate that in manufacturing blast furnace slag cement (BFSC), it is not only the fineness of the clinker-slag mix but also of the individual components which govern the choice of the mix composition for a desired strength.     

Utilization of fly ash and ground granulated blast furnace slag as an alternative silica source in reactive powder concrete

Reactive powder concrete (RPC) is an ultra high strength cement-based material. Cement and silica fume (SF) content of RPC are generally rather high compared to the conventional concrete. The aim of this study is to decrease the cement and SF content of RPC using with fly ash (FA) and/or ground granulated blast furnace slag (GGBFS). The effect of these mineral admixtures on compressive strength of RPC has been investigated under autoclave curing. In the first stage, the effect of autoclave time and SF content on compressive strength was determined. In the second stage, SF was gradually decreased and cement was replaced with FA and/or GGBFS at different proportions. The microstructure was investigated by scanning electron microscope (SEM). Test results indicate that, the utilization of FA and/or GGBFS in RPC is possible without significant mechanical performance loss. SEM micrographs revealed the tobermorite having different morphology.     

Evaluation of the degree of Cr ions immobilization by different binders

Disposal of industrial solid wastes can cause environmental risks due to the mobility of toxic elements. Stabilization/solidification (s/s) is an effective tool in the treatment of various wastes; however, there is a lack of chemical fixation on the concentrations of Cr. Thus, Cr, in particular Cr⁶⁺, remains free in the leachate. Some phases of the blast furnace slag seem to be able to exert a solubility control on chromium. This study evaluates the effect of various binders on the fixation of Cr ions. Static leaching tests were conducted at two different water-solid ratios as a means to distinguish elements that have solubility controls. The results show that Cr content decreases very quickly to obtain values near 0.03 ppm soon after the contact between the contaminated solution and the different binders. The sample containing only the slag was the most effective. Cr was evenly distributed in the C-S-H as detected by scanning electron microscope (SEM).     

钢渣作水泥膨胀剂的初步研究

文章介绍了国内外膨胀的发展状况和钢渣利用情况,提出把钢渣掺入水泥中作膨胀的设想并进行了一系列实验。结果表明,用钢渣用膨胀剂,膨胀龄期较长,膨胀状况良好。水泥抗压强度随钢渣掺量的增加而有所降低,水泥安全性合格。     

利用超细粉煤灰及钢渣配制用于道路的复合硅酸盐水泥的试验研究

通过大量试验在水泥熟料中复合掺入超细粉煤灰及磨细钢渣粉,配制了用于公路路面水泥混凝土工程的复合硅酸盐水泥,重点改善道路水泥的抗折强度、耐磨性能以及收缩抗裂性能。结果表明,随着超细粉煤灰及磨细钢渣粉的掺入,所配制的水泥胶砂强度及耐磨性均满足425号道路硅酸盐水泥要求,与基准水泥相比,规定龄期的收缩变形均显著降低,圆环法抗裂试验结果也表明水泥抗裂性能得到大幅度增强。     

粒化高炉矿渣的微观结构和物相分析

以梅山矿渣为研究载体,运用现代分析手段,研究了粒化高炉矿渣玻璃体的矿物组成和微观结构。研究结果表明:梅山矿渣玻璃体中潜在矿相为钙铝黄长石、少量的镁蔷薇辉石,不存在通常认为的β-C2S;玻璃体中的硅铝骨架并不是处于网状结构中,而是处于双四面体岛状结构中;核磁分析证实梅山矿渣中29Si处于Q1的环境中;该矿渣玻璃体中铝的配位数是4。     

磷渣硅酸盐水泥物理性能及其改善途径初探

以多种磷渣样品为研究对象,协同多家试验单位共同探讨了水泥强度检验方法采用ISO法后,磷渣水泥的物理性能及其改善途径。研究发现,磷渣掺量由20%增至60%时,水泥抗折和抗压强度均大幅下降,凝结时间随磷渣掺量增加而显著延长。磷渣与矿渣等混合材复掺,可在一定程度上改善水泥性能;而通过提高水泥细度以及在磷渣中掺入少量钙质和硅铝质材料,可明显提高磷渣水泥强度(约10MPa),大大缩短凝结时间(约4h),改善磷渣水泥物理性能。