Effect of Steel Slag and Granulated Blast-furnace Slag on the Mechanical Strength and Pore Structure of Cement Composites

Reuse of solid industrial wastes is an effective approach to develop low-carbon construction materials. This paper examines how two materials, steel slag（ST） and granulated blast-furnace slag（SL） impact the mechanical performance and pore structure of cement-based systems. Analysis was done on the variations of the porosity, pore size, and pore volume distribution with the curing age and replacement content, and the fractal dimensions of pore surfaces. The results suggested that systems with both supplementary materials had lower early strengths than pure cement, but could generally surpass pure cement paste after 90 d; higher SL content was particularly helpful for boosting the late strengths. The addition of ST increased the porosities and mean pore sizes at each age, and both increased with ST content; SL was helpful for decreasing the system＇s late porosity（especially harmless pores below 20 nm）; The lowest porosity and mean pore size were obtained with 20% SL. Both systems had notably fractal characteristics on pore surfaces, with ST systems showing the highest dimensions at 10% ST, and SL systems at 20% SL. Compressive strength displayed a significant linear increase with fractal dimension.

Influence of Carbonation on Fatigue of Concrete with High Volume of Ground Granulated Blast-furnace Slag

The effect of carbonation on fatigue performance of ground granulated blast-furnace slag concrete was investigated. Based on the static compression tests of carbonated GGBS-concrete, the correlation between carbonation depth and compressive strength was analyzed and an equation between carbonation depth and compressive strength was put forward. Meanwhile, fatigue S-N curves of various carbonation depths were fitted, and the infl uence of carbonation on fatigue life and strength was studied. Carbonation has a dual effect on the fatigue behavior of GGBS-concrete. A fatigue equation based on the depth of carbonation was established. Also, the probabilistic distribution of fatigue life of carbonated concrete at a given stress level was modeled by the two-parameter Weibull distribution.

Dredged marine soil stabilization using magnesia cement augmented with biochar/slag

Dredged marine soils(DMS)have poor engineering properties,which limit their usage in construction projects.This research examines the application of reactive magnesia(rMgO)containing supplementary cementitious materials(SCMs)to stabilize DMS under ambient and carbon dioxide(CO_(2))curing conditions.Several proprietary experimental tests were conducted to investigate the stabilized DMS.Furthermore,the carbonation-induced mineralogical,thermal,and microstructural properties change of the samples were explored.The findings show that the compressive strength of the stabilized DMS fulfilled the 7-d requirement(0.7-2.1 MPa)for pavement and building foundations.Replacing rMgO with SCMs such as biochar or ground granulated blast-furnace slag(GGBS)altered the engineering properties and particle packing of the stabilized soils,thus influencing their performances.Biochar increased the porosity of the samples,facilitating higher CO_(2) uptake and improved ductility,while GGBS decreased porosity and increased the dry density of the samples,resulting in higher strength.The addition of SCMs also enhanced the water retention capacity and modified the pH of the samples.Microstructural analysis revealed that the hydrated magnesium carbonates precipitated in the carbonated samples provided better cementation effects than brucite formed during rMgO hydration.Moreover,incorporating SCMs reduced the overall global warming potential and energy demand of the rMgO-based systems.The biochar mixes demonstrated lower toxicity and energy consumption.Ultimately,the rMgO and biochar blend can serve as an environmentally friendly additive for soft soil stabilization and permanent fixation of significant amounts of CO_(2) in soils through mineral carbonation,potentially reducing environmental pollution while meeting urbanization needs.

Volume and Surface Nucleation of Crystals in Glass Based on Blast-Furnace Slag

Using differential thermal analysis, X-ray phase analysis, electron microscopy, and optical microscopy, the nucleation of crystals in glass obtained by blending metallurgical slag with silicon dioxide has been studied. The type of crystallization (homogeneous or heterogeneous, volume or surface) is revealed for each of nine compositions of synthesized glass. It is shown that the first crystalline phase in a volume crystallizing glass is perovskite (CaO·TiO2);in this phase a nucleation of the main phase occurs: melilite (solid solution of gehlenite 2CaO·Al2O3·SiO2 in akermanite 2CaO·MgO·2SiO2). The fundamental characteristics of homogeneous (for a catalizing phase, perovskite) and heterogeneous (for a catalyzed phase, melilite) of crystallization are determined: the steady state nucleation rate Ist, time of unsteady state nucleation τ, crystal growth rate U, and activation energy of frictional flow. The temperature dependences of Ist, τ, and U are obtained. The kinetics of the crystallization of glass is studied and the rates of the surface crystal growth are determined in the glass of nine compositions. The influence of grinding the particles of the original glass on the sequence of deposition of the crystalline phases was studied. Practical recommendations are presented for the use of blast-furnace slag as a raw material for the synthesis of glass and their further utilization.

Dry Mix Slag—High-Calcium Fly Ash Binder. Part Two: Durability

This work investigates durability of cement-free mortars with a binder comprised of ground granulated blast furnace slag (GGBFS) activated by high-calcium fly ash (HCFA) and sodium carbonate (Na2CO3): the soundness, sulfate resistance, alkali-silica reactivity and efflorescence factors are considered. Results of tests show that such mortars are resistant to alkali-silica expansion. Mortars are also sulfate-resistant when the amount of HCFA in the complex binder is within a limit of 10 wt%. The fineness of fly ash determines its’ ability to activate GGBFS hydration, and influence soundness of the binder, early strength development, sulfate resistance and efflorescence behavior. The present article is a continuation of authors’ work, previously published in MSA, Vol. 14, 240-254.

Dry Mix Slag—High-Calcium Fly Ash Binder. Part One: Hydration and Mechanical Properties

High-calcium fly ash (HCFA)—a residue of high-temperature coal combustion at thermal power plants, in combination with sodium carbonate presents an effective hardening activator of ground granulated blast-furnace slag (GGBFS). Substitution of 10% - 30% of GGBFS by HCFA and premixing of 1% - 3% Na2CO3 to this dry binary binder was discovered to give mortar compression strength of 10 - 30 to 30 - 45 MPa at 7 and 28 days when moist cured at ambient temperature. High-calcium fly ash produced from low-temperature combustion of fuel, like in circulating fluidized bed technology, reacts with water readily and is itself a good hardening activator for GGBFS, so introduction of Na2CO3 into such mix has no noticeable effect on the mortar strength. However, low-temperature HCFA has higher water demand, and the strength of mortar is compromised by this factor. As of today, our research is still ongoing, and we expect to publish more data on different aspects of durability of proposed GGBFS-HCFA binder later.

Tests on Alkali-Activated Slag Foamed Concrete with Various Water-Binder Ratios and Substitution Levels of Fly Ash

To provide basic data for the reasonable mixing design of the alkali-activated (AA) foamed concrete as a thermal insulation material for a floor heating system, 9 concrete mixes with a targeted dry density less than 400 kg/m3 were tested. Ground granulated blast-furnace slag (GGBS) as a source material was activated by the following two types of alkali activators: 10% Ca(OH)2 and 4% Mg(NO3)2, and 2.5% Ca(OH)2 and 6.5% Na2SiO3. The main test parameters were water-to-binder (W/B) ratio and the substitution level (RFA) of fly ash (FA) for GGBS. Test results revealed that the dry density of AA GGBS foamed concrete was independent of the W/B ratio an RFA, whereas the compressive strength increased with the decrease in W/B ratio and with the increase in RFA up to 15%, beyond which it decreased. With the increase in the W/B ratio, the amount of macro capillaries and artificial air pores increased, which resulted in the decrease of compressive strength. The magnitude of the environmental loads of the AA GGBS foamed concrete is independent of the W/B ratio and RFA. The largest reduction percentage was found in the photochemical oxidation potential, being more than 99%. The reduction percentage was 87% - 93% for the global warming potential, 81% - 84% for abiotic depletion, 79% - 84% for acidification potential, 77% - 85% for eutrophication potential, and 73% - 83% for human toxicity potential. Ultimately, this study proved that the developed AA GGBS foamed concrete has a considerable promise as a sustainable construction material for nonstructural element.

Effect of ground granulated blast-furnace slag(GGBFS) and silica fume(SF) on chloride migration through concrete subjected to repeated loading

The effect of ground granulated blast-furnace slag(GGBFS) and silica fume(SF) on the chloride migration through concrete subjected to repeated loading was examined.Portland cement was replaced by 20%,30%,40% GGBFS and 5%,10% SF,respectively.Five times repeated loadings were applied to specimens,the maximum loadings were 40% and 80% of the axial cylinder compressive strength(f′c),respectively.Chloride migration through concretes was evaluated using the rapid chloride migration test and the chloride concentration in the anode chamber was measured.The results indicate that the transport number of chloride through concrete containing 20% and 30% GGBFS replacements and 5% and 10% SF replacements is lower than that of the control concrete,but 40% GGBFS replacement increases the transport number of chloride.Five loadings at 40% f′cor 80% f′c increase the transport number of chloride for all mixes investigated in this study.5% SF replacement has a very close effect on the chloride permeability of concrete with 20% GGBFS when concrete is subjected to 40% f′cor 80% f′c.

Crystallization behavior of blast-furnace slag by single hot thermocouple technique

The crystallization behavior of blast-furnace slag under isothermal and continuous-cooling conditions was studied using the single hot thermocouple technique.The crystallization phases were obtained using FactSage software and X-ray diffractometry.The crystallization kinetic parameters were calculated by combining these results with the Johnson-Mehl—Avrami model.Under isothermal conditions,the shortest crystallization incubation time was 24 and 18 s when the temperatures were 1300 and 1150℃,and the corresponding critical cooling rates were 4.5 and 14.3℃/s,respectively.At 1270℃,the slag was difficult to crystallize and the fiber-forming rate improved.When the continuous-cooling rate was 6.5℃/s,the slag solidified into a glassy state.The main crystallization phases,gehlenite,akermanite,anorthite,and melangite,were most easily precipitated.The growth factors of melangite and anorthite were approximately 1.63 and 1.68,respectively,which indicated that the crystals nucleated on the surface and grew in two dimensions.

相分离法处理攀钢高炉渣新工艺基础研究

提出采用相分离法处理攀钢高炉渣新工艺。作为本研究内容的第一部分 ,考察了熔渣分离过程的基本规律。经热力学分析和实验测定 ,在高温下攀钢高炉渣与Na2 CO3反应的主要产物为硅和钛的含钠复合氧化物。只要条件适当 ,可以实现大部分硅和钛与炉渣中其它组分相互分离。在本实验条件下 ,炉渣粒度和体系温度对反应影响比较显著 ,在满足化学计量配比前提下 ,配碱比对反应的影响不很明显。

马钢冶炼含钛矿炉渣性能的研究

通过对马钢第一、第二铁厂高炉现场炉渣及试验室配制渣样的性能测试与矿相分析 ,得出含钛矿炉渣的合理渣系结构 ,并建立了含钛炉渣成分与其性能之间的数学模型。

KOH亚熔盐法制备钛酸钾晶须和二氧化钛

研究了以高钛渣为原料、采用KOH亚熔盐法制备钛酸钾晶须和二氧化钛的新方法,探讨了反应温度、初始KOH浓度、反应时间和碱矿比等因素对钛酸钾晶须形貌的影响.实验结果表明,反应温度、反应时间和碱矿比对钛酸钾晶须的形貌影响较为显著,并得到长度约20～25μm、长径比约为15～20的钛酸钾晶须.钛酸钾在pH=10～12间水解并煅烧,制备了八钛酸钾晶须;在pH=1～3间水解并煅烧,制备了二氧化钛晶须.

含钛高炉渣制备甲醛吸附剂的研究

鉴于高炉渣中含有具有良好光催化降解作用的TiO2,且来源廉价广泛,因此研究如何高效合理地利用含钛高炉渣便成为必然。采用分析纯盐酸,在室温条件下对含钛高炉渣进行不同时间的酸浸处理,并进行比表面积、SEM扫描电镜、EDS能谱及甲醛吸附性能的测试。结果表明:酸浸处理后吸附剂表面为多孔结构,吸附剂比表面积由4.56 m2/g增大到105.35 m2/g,可用作甲醛的吸附剂;随酸浸时间的延长,吸附剂中Ti的含量由15.33%增加到最高31.39%,折算为TiO2的含量为39.6%,即酸浸处理可使含钛高炉渣中的TiO2富集。其中,酸浸时间为5 h的样品获得比表面积105.35 m2/g、TiO2含量34.7%,甲醛吸附能力达0.36 mg/g,是市场销售活性炭吸附能力(0.12 mg/g)的3倍。

用高炉钛渣冶炼钛硅合金的研究

介绍了用直流电热法从攀钢高炉钛渣中冶炼钛硅合金的工艺。研究了电硅热法冶炼钛硅合金时渣中ＴｉＯ２的还原贫化规律和直流电对钛硅合金冶炼的作用，用直流电硅热法可生产含Ｔｉ２０％左右的钛硅合金，钛回收率小于６０％．开发了直流电硅铝热法生产钛硅合金工艺，采用直流电硅铝热法可生产含Ｔｉ＞３０％、Ｓｉ＜３５％的钛硅合金，钛回收率大于８０％，铁硅合金可部分取代钛铁用于炼钢，还原残渣可用于制水泥。

高钛渣氧化过程的动力学

用热重法研究了高钛渣在空气中的等温和非等温氧化动力学。实验结果表明 ,高钛渣氧化动力学可用缩核模型来描述。利用等温动力学模型公式确定等温氧化初期为化学反应控制 ,后期为扩散控制 ,计算得到相应的表观活化能分别为 19.6 2 ,30 .0 5kJ/mol;通过非等温动力学模型公式确定高钛渣的非等温氧化阶段Ⅰ为界面化学反应控制 ,阶段Ⅱ为界面化学反应和扩散综合控制 ,阶段Ⅲ为扩散控制 。

含钛高炉渣光催化降解糠醛废水

利用含钛高炉渣作为光催化材料光催化降解糠醛废水,采用静态试验的方法研究了粉末含钛高炉渣光催化降解糠醛废水的部分影响因素。在糠醛废水溶液浓度一定的条件下,存在一个最佳投放量为0.7g,降解率为63%,并且催化剂粒径越小催化效果越好,粒径为2μm时,降解率为36%。废水温度30℃时,处理效率最高,达到22%。在酸性条件下,催化剂催化效果稳定。因此含钛高炉渣作为光催化材料对糠醛废水有降解作用。

电炉熔炼钛精矿的热力学讨论

对攀枝花钢铁研究院电炉熔炼钛精矿的有关反应进行热力学分析,认为在电炉熔炼过程中钛精矿中游离的FeO和Fe2O3首先被还原,然后钛精矿中的主要成分FeTiO3按下列顺序逐步被还原:FeO·TiO2→Fe+TiO2→Fe+Ti3O5→Fe+Ti2O3→Fe+TiO;MgO、CaO和Al2O3等杂质在电炉还原熔炼钛精矿的温度(2000K左右)下不可能被还原,从而进入钛渣中;电炉熔炼得到钛渣主要物相为黑钛石,玻璃体硅酸盐相.

铈掺杂改性高炉渣降解模拟染料废水的应用研究

以含钛高炉渣为催化载体,采用浸渍法制备了Ce4+掺杂的负载型催化剂Fe2O3-CeO2-TiO2/γ-A12O3,通过其在CWPO工艺中对模拟染料废水的处理效果来研究催化剂的催化活性,确定了催化剂的最佳制备工艺,并通过XRF、XRD、BET、SEM等手段解释了催化剂的催化机理。研究结果表明:当Ce4+掺杂量为1.2wt%、350℃焙烧2h时,催化剂Fe2O3-CeO2-TiO2/γ-A12O3具有最大的催化活性,这归因于Ce4+掺杂后,催化剂中的活性组分TiO2颗粒得到细化。

钛渣埋弧炉的设计

根据研究和实践,提出了相应的冶炼高钛渣电炉的设计特点和参数。对于钛渣埋弧电炉这种工艺复杂,能耗大,非线性的系统,采用合理的设计参数,优化的设备结构,降低了企业生产的劳动强度,减少设备的热停工时间,提高了埋弧电炉的经济效益,使埋弧电炉高效节电运行。

水冷烟道在钛渣炉中的应用

对钛渣冶炼过程中的烟气特点进行了分析,介绍了钛渣电炉在设计生产过程中烟道出现的问题,针对出现的问题,分析原因并进行结构上的优化和改进,将原有烟道改为水冷形式,改造后经过运行测试,运转正常,效果良好。