Much is unknown about the reaction processes responsible for the formation and polycondensation of geopolymers and other alkali activated materials. In this work, isothermal calorimeter and in-situ ...XRD were adopted to study the heat and mineral evolution of NaOH activated fly ash, metakaolin and ground granulated blast furnace slag. Both activator concentration and temperature have profound influences on duration of exothermal geopolymerization peaks. NaOH activated fly ash is more temperature dependable, with much higher activation energy than metakaolin and slag. The dissolution of source precursor is rapid and the formation of new phases can be detected by the end of the initial dissolution period. The in-situ XRD measurement together with the PONKCS analysis method promotes quantitative estimation of amorphous evolution during alkali activation.
The schematic diagram of experimental apparatus for tire powder pyrolysis by utilization of waste of BF slag.
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•Waste tire pyrolysis was conducted using BF slag as heat carrier in ...rotary reactor.•Pyrolysis of tire with BF slag improves derived oil and gas yields, upgrade oil quality.•Decrease feedstock size can improve heat and mass transfer during pyrolysis.
In this study, a novel “waste energy recycling” strategy is presented, i.e., the sensible heat of blast-furnace (BF) slag is utilized for the production of fuel oil and combustible gas from the pyrolysis of waste tire. The effects of various operating parameters including the slag temperature, the mass ratio of BF slag to tire (B/T) and feedstock size on yields and characteristics of pyrolysis products were systematically studied. The results showed that the presence of BF slag greatly improved the production of derived-oil and increased the contents of H2 and CO in pyrolysis gases. This can be explained by the catalytic activity of BF slag and the CaO-MgO complex in BF slag can prevent the formation of stable chemical structures in hydrocarbons, speed up the degradation of hydrocarbons, weaken CC and CH bonds and make them dissociate more easily, and thereby decrease the activation energy of degradation reactions. Increasing BF slag temperature and B/T ratio, and decreasing feedstock (including both BF slag and tire powder) size favored the heat and mass transfer during pyrolysis process and therefore afforded more liquid and gaseous products. In addition, it was observed that the presence of BF slag decreased viscosity, density, H and O content and increased C content, C/H ratio and calorific value of derived-oil relative to pyrolysis oil derived from solely tire powder, thereby resulting in upgradation of oil quality.
•GGBFS was added in fly ash geopolymer concrete (GPC) to enable ambient curing.•Strength increased with the increase of GGBFS and reduction of activating liquid.•Heat-cured and ambient-cured GPC were ...compared with water-cured OPC concrete.•Tensile strengths given by codes are similar for ambient-cured GPC and OPC concrete.•The predictions are more conservative for heat-cured GPC than for ambient-cured GPC.
Inclusion of ground granulated blast-furnace slag (GGBFS) with class F fly-ash can have a significant effect on the setting and strength development of geopolymer binders when cured in ambient temperature. This paper evaluates the effect of different proportions of GGBFS and activator content on the workability and strength properties of fly ash based geopolymer concrete. In this study, GGBFS was added as 0%, 10% and 20% of the total binder with variable activator content (40% and 35%) and sodium silicate to sodium hydroxide ratio (1.5–2.5). Significant increase in strength and some decrease in the workability were observed in geopolymer concretes with higher GGBFS and lower sodium silicate to sodium hydroxide ratio in the mixtures. Similar to OPC concrete, development of tensile strength correlated well with the compressive strength of ambient-cured geopolymer concrete. The predictions of tensile strength from compressive strength of ambient-cured geopolymer concrete using the ACI 318 and AS 3600 codes tend to be similar to that for OPC concrete. The predictions are more conservative for heat-cured geopolymer concrete than for ambient-cured geopolymer concrete.
•Fly ash geopolymer mixtures were designed adding GGBFS up to 30% of total binder.•Test specimens were cured in ambient temperature (20–23°C) instead of heat curing.•GGBFS enhanced early strength ...development at ambient condition.•Workability and setting time reduced with increase of GGBFS and decrease of alkaline liquid.
Most of the previous works on fly ash-based geopolymers were on the properties of concrete hardened by heat curing, which is considered as a limitation for cast in situ applications at low ambient temperatures. This study aimed to achieve fly ash-based geopolymers suitable for curing without elevated heat. The results show that fly ash based geopolymer concrete for curing in ambient condition can be proportioned for desirable workability, setting time, and compressive strength using ground granulated blast-furnace slag (GGBFS) as a small part of the binder. Inclusion of GGBFS with Class F fly ash helped achieve setting time and compressive strength comparable to those of ordinary Portland cement (OPC).
•The 3D physical model of a Russian blast furnace includes the tuyere and raceway.•Effect of injection condition on the combustion of natural gas and coal is studied.•Suggestions are provided for ...efficient combustion of coal and natural gas.
Natural gas (NG) can replace part of pulverized coal (PC) in the blast furnace (BF) injection as the clean and high-calorific hydrogen-rich energy, which can reduce environmental pollution and energy consumption in molten iron production. In this work, the method of numerical simulation is used to first compare and analyze the differences of NG and PC mixed injection and only PCI on the thermal state, gas composition and PC burnout in the tuyere and raceway of a Russian BF. The research results show that when NG and PC are injected, the temperature near the wall of the tuyere is higher, but the average temperature in the raceway is lower. Then we further clarify the influences of injection parameters on the transmission and combustion performances of PC under the condition of mixed injection of NG and PC. It can be concluded that with the diameter of the NG lance increases, the oxygen consumed by NG combustion in the tuyere increases, resulting in a decrease in the burnout of PC. The change of the NG lance position has relatively less apparent effect on transmission and combustion within the tuyere and raceway of the BF. In addition, as the NG injection (NGI) rate increases from 47 m3/t to 67 m3/t, the oxygen consumption of NG in the tuyere and raceway increases, causing the decrease of PC burnout from 70.11% to 68.31%, the reduction of the CO content but the increase of the H2 content in the primary gas, which can effectively reduce CO2 emissions.
In this study the hydration of quaternary Portland cements containing blast-furnace slag, type V fly ash and limestone and the relationship between the types and contents of supplementary ...cementitious materials and the hydrate assemblage were investigated at ages of up to 182days using X-ray diffraction and thermogravimetric analysis. In addition thermodynamic modeling was used to calculate the total volume of hydrates. Two blast-furnace slag contents of 20 and 30wt.% were studied in blends containing fly ash and/or limestone at a cement replacement of 50wt.%. In all cases the experiments showed the presence of C–S–H, portlandite and ettringite. In samples without limestone, monosulfate was formed; in the presence of limestone monocarbonate was present instead. The addition of 5wt.% of limestone resulted in a higher compressive strength after 28days than observed for cements with lower or higher limestone content. Overall the presence of fly ash exerts little influence on the hydrate assemblage. The strength development reveals that amounts of up to 30wt.% fly ash can be used in quaternary cements without significant loss in compressive strength.
3D printing is a novel technology that has been introduced to construction industry and has been found to have numerous potentials including high speed fabrication of customized building elements ...without formworks and low material waste. Despite such superiority, to ensure the extrudability of materials and their coherent adhesion, most commonly, a higher content of the Portland cement (PC) with other chemical admixtures are used in 3D printed concrete (3DPC) mixes. This common practice, however, can result in augmentation of greenhouse gas emissions and also increase in the costs associated with 3D printing. To avoid this, and provide favorable printability properties, supplementary cementitious materials (SCMs) have gradually become a key ingredient of 3DPC. Utilizing SCMs, previous studies have found the critical effects of SCMs on operational aspects of 3D printers and their controls on a variety of functional parameters. To closely evaluate such parameters, the present study provides a review of the effect of SCMs on 3DPC with and without alkaline activator, focusing on manufacturing techniques, rheological properties, mechanical properties, bond strength between printed layers, effect of curing regime, and shrinkage behavior. The main challenges and future research direction of 3DPC are also presented. Based on the presented review, it is found that coal fly ash, silica fume, blast furnace slag and metakaolin are the main SCMs that are commonly used to enhance pumpability, printability, and buildability of 3DPC, as well as addressing environmental issues associated with the larger use of PC in 3DPC.
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•A higher binder content is typically used in 3DCP, causing an increased environmental impact of 3DCP.•Using recycled materials without mix optimization cannot address environmental impact of 3DCP.•Depending on chemical composition of recycled materials, time gap and shrinkage of 3DPGC can be adjusted.•SCMs can adjust rheology and printability of mixes, causing improvement of 3DCP properties.
This research focuses on the synthesis and characterization of geopolymers based on French pozzolan (P) by adding two types of blast-furnace slags with different chemical compositions (L1 and L2). ...The slags amount varied between 0% and 50%. Sodium silicate (Na2SiO3) and sodium hydroxide (NaOH) were used as the alkaline activator. The physicomechanical properties of the synthesized geopolymer cements were evaluated. Complementary studies using X-ray diffractometry (XRD), infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDX) were also performed. The results found proved that adding the two slags to the pozzolan led to considerable improvement in the geopolymers' physicomechanical properties. In comparison, the L1 slag addition, more magnesian than L2, favored the formation of more quantity of amorphous phase and also the mineral phase of hydrotalcite-type, which justifies the high geopolymers’ physicomechanical characteristics based on L1 slag (series 1) compared with those synthesized from L2 slag (series 2) obtained at 28 days of curing.
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•Geopolymers from volcanic pozzolan (P) and two blast-furnace slags (L1 and L2) were prepared.•Mechanical properties of pozzolan-based geopolymers increased with the increase of blast-furnace slags added.•The 50% L1 slag addition, which is more magnesian than L2 slag, resulted in high compressive strength of 105 MPa.•The synthesized geopolymers are ecological and mechanically efficient to replace traditional building materials.
Blast furnaces are the most crucial equipment in ironmaking processes. Stable operation of the blast furnace is a prerequisite for personnel safety and production efficiency. Therefore, early ...detection of abnormalities in blast furnaces is an important task for ironmaking processes. However, owing to the large fluctuations in the quality of raw materials, dynamic operating conditions, as well as the impact of the hot blast stoves switches, the measurements of blast furnace show severe nonstationary characteristics. All these factors make monitoring the blast furnace a challenging task. In this article, a nonstationary process monitoring method called consistent trend feature analysis (CTFA) is proposed, which can extract the trend-related features and discard perturbations in process data. The directions and amplitudes of the extracted trends are used for abnormality detection, and a local-learning-based method is proposed for determining a time-varying control limit. The detection performance of the proposed method is analyzed, with a sufficient condition and a necessary condition for the detectability given. The effectiveness of the proposed method is validated by the practical data collected from a large-scale blast furnace located in Liuzhou, China.
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