The “filler effect”, due to the physical presence of mineral additions in cement, is mainly known to accelerate the hydration of the clinker component. Previously, this was attributed to the surface ...of the filler providing nucleation sites for C‐S‐H as there is a clear dependence on the surface provided by the filler particles. Our results reveal that the increase in nucleation is quite low compared to the area provided. Based on the isothermal calorimetry experiments and SEM images, we demonstrate that the most important parameter is the interparticle distance. We propose that this is mainly the result of the shearing conditions rather than extra surface available for C‐S‐H as formerly assumed. Quantitatively slag and fly ash behave very similarly to quartz. Limestone, on the other hand, seems also to stimulate C‐S‐H nucleation giving it a higher efficiency in accelerating clinker hydration.
Aiming at the melt splashing behavior in the smelting process of an oxygen-enriched side-blowing furnace, the volume of fluid model and the realizable k−ε turbulence model are coupled and simulated. ...The effects of different operating parameters (injection velocity, immersion depth, liquid level) on splash height are explored, and the simulation results are verified by water model experiments. The results show that the bubbles with residual kinetic energy escape to the slag surface and cause slag splashing. The slag splashing height gradually increases with the increase in injection velocity, and the time-averaged splashing height reaches 1.01 m when the injection speed is 160 m/s. Increasing the immersion depth of the lance, and the slag splashing height gradually decreases. When the immersion depth is 0.12 m, the time-averaged splashing height is 0.85 m. Increasing the liquid level is beneficial to reduce the splash height, when the liquid level is 2.7 m, the splash height reduces to 0.77 m. With the increase in the liquid level, the slag splashing height gradually decreases, and the time-averaged splashing height is 0.77 m when the initial liquid level is 2.7 m.
This paper assesses the feasibility of geopolymers (GPs) for use as lightweight foamed concrete, a crucial step towards reducing the carbon footprint and conserving natural resources. A powder ...activator (i.e., sodium metasilicate) less harmful to the environment was used to activate the fly ash-based GPs, while the limestone aggregates were gradually replaced by up to 100 % waste slag materials to conserve natural resources. Polypropylene fibers were incorporated at high dosage rates of 1 % or 2 %, by volume, to reduce the concrete density and improve its durability properties. Tested properties include flow, density, water absorption, porosity, thermal conductivity, mechanical strengths, drying shrinkage, and resistance to sulfate attack, freeze/thaw cycles, and elevated temperature. Results showed that the concrete mechanical properties improved when the limestone aggregate was replaced by slag materials, but the density and thermal conductivity were slightly curtailed at higher addition rates. The use of polypropylene fibers proved efficient to improve the resistance to freeze/thaw cycles, drying shrinkage, and expansion due to sulphate attack. Such data can help sustain the green building industry development by reducing the carbon footprint and conserving natural resources in foamed concrete applications.
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•Slag aggregate decreased the water absorption and increased the coefficient of thermal conductivity.•Thermal conductivity coefficient of geopolymer foam concretes varies between 0.326 and 0.599 W/m.K.•Slag aggregate and polypropylene fiber significantly reduced drying shrinkage and sulfate expansion.•Thanks to the slag aggregate, a more than 2 MPa compressive strength was obtained after 900 °C.
Reusing and recycling waste materials in the construction industry can provide a significant contribution in terms of environmental and economical aspects. This article reports a material case study ...on the combined use of three industrial by-products (metallurgical slags), namely copper slag (CS), stainless steel slag (SS) and ground granulated blast furnace slag (GGBFS) as solid precursors to produce binary blend alkali activated materials (AAMs). A total of seven binary AAMs mixtures with different ratios (0%, 25%, 50%, and 75%) of CS and SS as partial replacement of GGBFS were activated by a combination of sodium hydroxide and sodium silicate as an alkali solution. The behaviour of the mixtures is reported in terms of flow spread and flow curve, compressive and flexural tensile strengths, mercury intrusion porosimetry (MIP) and water absorption by submerging. The flow spread and dynamic yield stress of the mixtures increased and decreased by partially replacing GGBFS with CS or SS, respectively, leading to better workability properties of the fresh mixture. The use of CS or SS up to 50% reduced the compressive and flexural tensile strengths of the specimens between 30‐42% and 14‐46%, respectively. Despite this drop in strength, the 28 days compressive strength of the studied mixtures was always higher than 50 MPa. The capillary porosity of the specimens increased with higher contents of CS or SS. Water absorption results of the specimens appeared highly influenced by the applied drying temperature in the test method. Overall, partial replacement of GGBFS by CS or SS, targeting binary precursor systems, is promising for replacement levels up to 50%.
•The workability of the AAMs improved by the addition of CS or SS•Comparable strength properties compared to the AAMs with pure GGBFS can be obtained using 50% CS or SS•Compressive strength development of the studied AAMs up to one year, is similar to that expressed in EC2 for PC based materials•The capillary pores of the AAMs increased as higher contents of GGBFS is replaced•Water absorption testing protocols used for PC based materials appeared less suited for the studied AAMs
Recycled materials in the building industry represent an attractive alternative to the consumption of natural resources. The paper shows results obtained by adding electric arc furnace slag (EAFs) as ...partial replacement of natural aggregates in concrete production. EAFs determines a significant increase in the compressive strength of concrete while it does not seem to affect the bending strength and drying shrinkage of cement mixtures. The concrete durability was approached by a careful chemical analysis and microstructural investigation of EAFs. The tendency to deteriorate seems negligible due to a low presence of amorphous and expansive compounds leading to an increase in volume. Moreover, the metals released, compared with the national legislation requirements, meet environmental standards.
•Calcium leached from multiple calcium containing phases.•Sulfur co-leached alongside calcium.•Si, Mn and Ca containing precipitates formed in the leachates.•Calcium extraction efficiency ...35–40%.•Calcium enrichment on outermost zone of reacted Ca2SiO4 particles.
Accelerated carbonation of alkaline wastes such as steelmaking slag offers the potential to combine waste valorisation with climate change mitigation by utilising carbon dioxide (CO2). One method of achieving this is through an indirect carbonation process to produce a marketable precipitated calcium carbonate (PCC), using ammonium salts to selectively extract calcium from steelmaking slag. Two unaddressed design parameters for a slag based plant differing from that of a traditional PCC plant are the effect of mineralogy on extraction efficiency when using a multicomponent, heterogeneous feed such as slag and the challenges raised by the resulting leachate chemistry. This paper presents petrographic textural observations on the effect of calcium leaching via ammonium chloride on individual grains of dicalcium silicate in three different widely unutilised steelmaking slags. These observations are then interpreted in conjunction with measured changes in solution leachate chemistry. The results indicate that although silica enriched regions form at the reaction front, the reaction continues into the core of the particle due to fracture propagation caused by volume reduction as calcium is extracted. Co-leaching of sulfur alongside calcium and the formation of precipitate in the leachate highlights potential engineering challenges when the process is scaled up due to fouling of process equipment. The main mineral phases in all untreated slags were found to be calcium silicates, predominantly dicalcium silicate (Ca2SiO4). This was followed by a complex mixture of calcium/magnesium-wustite (CaFeMnMg)O type phases and srebrodolskite (Ca2Fe2O5(Ti, V)). Results indicate that calcium silicate is the more reactive component of BOS slag, while lime bound as (CaFeMnMg)O is most reactive in HMD and SS slags. Selectivity of the ammonium chloride solvent was high at 95–97% and efficiency of calcium extraction ranged between 25% and 39%.
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•Coal slag potentially used as Si source for the preparation of Li4SiO4 adsorbents.•LAS exhibits the close saturated CO2 adsorption capacity at 650 °C in 1 h.•LAS doped 10 wt% ...activated CS presents 76.43% higher than that without doping.•Si in ACS reacts with Li2CO promotes the transformation of Li+ and CO2.
SiO32- was separated from coal slag (CS), one of the largest annual solid waste emissions, by an alkali extraction method and converted into SiO2 by the reaction with HAc. The prepared SiO2 was mixed with LiAc by an immersion method and calcinated to form Li4SiO4 adsorbents (LAS). The LAS prepared exhibited the close saturated CO2 adsorption capacity of 367 mg/g at 650 °C in 1 h. The influences of calcination temperature, calcination time, and heating rate on the CO2 adsorption capacity of the LAS were systemically investigated and the preparation conditions were optimized. To improve the cyclic stability of the LAS, 10 wt% activated CS (ACS) was doped into LAS. The ACS doping significantly improves the cyclic stability of LAS with the CO2 adsorption capacity 76.43 % higher than that without doping in 20 cycles. Further investigation suggests that the Si in ACS can react with Li2CO3 to form Li4SiO4 and Li2SiO3, which promotes the transformation of Li+ and CO2. In all, our work has provided a new approach to the preparation of Li4SiO4-based adsorbents from CS waste.
The current study explores the effectiveness of an iron slag nanopowder (ISNP), which prepared from local iron steel industry, against gamma/neutron shielding. The structural and physical ...characteristics were experimentally determined. The crystal structure, morphology and elemental composition of the ISNP were studied using X-ray diffraction, scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX). On the other hand, a comprehensive experimental and theoretical study on the γ-ray shielding effectiveness of the ISNP was performed. In which, the experimental results have been validated by comparison with theoretical data which obtained by using the WinXcom program. This paper uses the well-known mathematical relationships to derive many shielding and dosimetry parameters such as effective atomic number and, effective electron density, for photon interaction and photon energy absorption as well as the γ-ray kerma coefficient from the mass attenuation coefficient. The exposure and energy absorption buildup factors have been also calculated. Furthermore, the shielding effectiveness against thermal and fast neutrons has been tested in terms of total macroscopic cross-sections. The results have revealed that the produced ISNP, with crystallite size of 24.5 nm, exhibits good shielding characteristics. Finally, based on this preliminary study, we can have concluded that the iron slag nanoparticles can be suitably used as an effective and safe (lead - free) component for radiation shielding.
•Iron slag nanopowder from local industry was prepared via mechanical milling technique.•The specimen was characterized for structural, physical and radiation shielding properties.•γ-ray attenuation and dosimetry parameters have been determined experimentally and theoretically.•Total macroscopic cross-sections for fast and thermal neutrons were calculated.•This preliminary study provides a framework for future experiments.
•The effect of P2O5 incorporated in slag on the hydration characteristics of cement-slag system.•The migration of phosphorus ions into cement matrix.•The P/Si atomic ratio of the C-S-H gel phase.
...This paper presents the influence of P2O5 incorporated in slag on the hydration characteristics of cement-slag system. It was found that the gradual addition of phosphorus oxide in slag did not change overall mineralogy of the hydration products. Except hydration retardation in the dormant stage, chemically bound water and portlandite contents, hydration degree of slag, and pore structure at all investigated ages were similar among cement-slag pastes with different P2O5 percentages. Furthermore, significantly higher amount of monosulfate was observed as the P2O5 content in slag increased. In addition, a higher Al/Si atomic ratio was measured in the C-S(A)-H gel phase formed in the cement matrix. However, similar Ca/Si atomic ratio of C-S(A)-H gel phase and Mg/Al atomic ratio of hydrotalcite-like phase were determined in all slag pastes, irrespective of the addition of P2O5. In contrast to magnesium ion which was retained within the original slag boundary, phosphorus ions could migrate into cement matrix. Therefore, P/Si atomic ratio of the C-S-H gel phase increased with the increasing phosphorus oxide content in slag, reaching up to ∼0.08.
