The development of self-compacting concretes with electric arc furnace slags is a novelty in the field of materials and the production of high-performance concretes with these characteristics is a ...further achievement. To obtain these high-strength, low-permeability concretes, steel slag aggregates and cupola slag powder are used. To prove the effectiveness of these concretes, they are compared with control concretes that use diabase aggregates, fly ash, and limestone supplementary cementitious materials (SCMs, also called fillers) and intermediate mix proportions. The high density SCMs give the fresh concrete self-compacting thixotropy using high-density aggregates with no segregation. Moreover, the temporal evolution of the mechanical properties of mortars and concretes shows pozzolanic reactions for the cupola slag. The fulfillment of the demands in terms of stability, flowability, and mechanical properties required for this type of concrete, and the savings of natural resources derived from the valorization of waste, make these sustainable concretes a viable option for countless applications in civil engineering.
Normally, recycled fine aggregate (RFA) is an unwanted by-product of construction demolished waste crushing, with high contaminant content. The presence of RFA is highly restricted in ordinary ...Portland cement (OPC) concrete production because of the poor durability and mechanical performance. This paper presents a study of the effect of RFA on the mechanical and durability of alkali activated slag concrete (AASC). Results indicated that RFA can be used as fine aggregate in AASC with superior early age compressive strength compared to river sand in AASC. It is caused by the presence of non-hydrated cement paste attached to the RFA with alkali activate property, which is equivalent to increase the quantity of alkali activator, and accelerate the hydration of ground granulated blast furnace slag (GGBFS) especially in the early age. In later age, the mechanical properties of AASC incorporating RFA are slightly lower than conventional AASC due to the larger porosity in the concrete.
The effects on composite cements of the aluminium content of slag, plus that of additional sulfate, have been investigated. Samples containing cement or composites with 40% replacement by one of 2 ...different slags, differing in aluminium contents, were prepared. A further blended sample was prepared with additional anhydrite replacing 3% w/w of binder. Slag blended mortars showed comparable strengths to the neat cement system at later ages. Adding slag changed the hydration kinetics of the clinker phases. The addition of sulfate had no effect on slag reactivity but increased that of alite. Slags richer in aluminium resulted in greater incorporation of aluminium into C-S-H and encouraged the presence of hemicarboaluminate over monocarboaluminate. The Ca/Si ratios of the C-S-H formed were comparable between the two blends, being marginally lower than that of the neat system. The addition of anhydrite resulted in the adsorption of sulfate onto the C-S-H, plus stabilisation of ettringite.
The effect of phosphogypsum (PG) on the hydration and retardation mechanism of phosphogypsum-based excess-sulfate slag cement (PESC) was mainly investigated. Based on the natural characteristics of ...PG, such as low pH value and the presence of soluble phosphorus impurities, the content of PG passing the 4.75 mm standard sieve was used as a variable to study the retardation mechanism of PG on PESC. It can be inferred from the heat flow and cumulative heat flow that the induction period is significantly prolonged with the content of PG, which is also reflected in the increase of the setting time of PESC. In the early period of hydration, as the content of PG increases, the soluble phosphorus concentration increases, and the pH value decreases. The changes in soluble phosphorus concentration and pH value affect the microstructure and amount of hydrates. Combined with experimental results, it has been demonstrated that the delay in the hydration of PESC by PG content is mainly due to: the excessive dissolution of Ca2+ and SO42- promotes the recrystallization of dihydrate gypsum; the dissolution of soluble phosphorus reduces the pH value in the pore solution and forms precipitates of calcium phosphate and hydroxyapatite; in the initial reaction period, a large amount of ettringite and C-S-H gel precipitate to form a protective film; the decrease in pH value leads to a decrease in carbonization resistance, and CO2 in the air is more likely to attack the PESC paste, react with alkaline substances in PESC, or degrade hydrated C-S-H and ettringite. The above factors all lead to a decrease in exchangeable ions during the hydration, thereby prolonging the setting of PESC.
•Using phosphogypsum-based excess-sulfate cement (PESC) for the preparation of super retarding materials.•PESC can achieve initial setting for 86 hours and final setting for 134 hours without additional retarders, and its 28d-compressive strength is 24.9 MPa.•The retardation mechanisms of phosphogypsum in PESC has been explored.•The microstructure and amount development of hydrates in PESC were analyzed.
In this study, Ti-bearing blast furnace slag (TBS) and ferrochromium slag (FS) were co-utilized to prepare augite-based glass-ceramics. The synergistic effects of TBS and FS on the crystallization ...characteristics, glass matrix evolution, and physical properties of the glass-ceramics were investigated. The results showed that the glass-ceramics prepared from TBS exhibited insufficient crystallization ability owing to the Ti4+ entering the glass network and inhibiting the formation of a gehlenite-like Ca-rich phase. With the introduction of FS, Cr2O3 disturbed the cation distribution in the glass network, reduced the activation energy of crystallization, transformed the crystallization mode and effectively increased the crystallization capacity. Moreover, the addition of FS resulted in the grain refinement of the augite phase, which improved the physical properties. With the addition of 36.89 wt% TBS and 27.67 wt% FS, the obtained glass-ceramics exhibited outstanding physical properties including a bulk density of 3.14 g/cm3, a bending strength of 173.5 MPa, and 727.3 Hv hardness.
Chloride ions penetrated reinforced concrete structures. Corrosion of reinforcing bars occurs because of cracks due to corrosion expansion, which is a problem of chloride damage deteriorating ...structures' performance. Blast furnace slag (from now on referred to as "BFS") is the inevitable by-product of steel product manufacturing as sustainable materials. BFS is more effective in preventing corrosion of reinforcing bars in concrete due to the denser cured and its high ability to immobilize chloride ions. Thus, the influence of BFS on the durability of mortar using BFS powder with different basicity was studied by using "Standard on Test Methods for Chloride Ion Diffusion Coefficients in Concrete" by electrophoresis (Draft) (JSCE-G571-2003)" and the total chloride ion amount was measured following JIS R 5202. The result confirmed that the immobilization performance could be greatly improved by increasing the basicity. It was remarkable in the case of air curing, a curing method for available precast products.
•CS was use as source of aluminosilicate for development of ACM.•The mixes were activated using alkali content of 5% and 7% by weight of binder.•Addition of mineral admixtures in alkali-activated CS ...improves its performance.•MK was found to be more effective than FA.
The paper presents results of an investigation conducted to study the feasibility of use of Copper Slag (CS) as aluminosilicate material for developing Alkali-activated Cementitious Material (ACM). The effect of addition of mineral admixtures such as Fly Ash (FA) and Metakaolin (MK) on the performance of alkali-activated CS was also investigated. In addition to a control mix which was prepared using 100% CS; two other mixes were also prepared by replacing CS with 30% FA and 30% MK respectively. These mixes were activated using alkali content of 5% and 7% by weight of binder. Sodium hydroxide and sodium silicate were used as alkali-activators. Compressive strength tests were performed on alkali-activated cement mixes at different curing ages. The pore-size distribution, mineralogy and microstructure of selected alkali-activated cement mixes were determined using Mercury Intrusion Porosimetry (MIP), X-ray Diffraction (XRD) and Scanning Electron Microscopy (SEM) with Energy Dispersive X-ray Spectroscopy (EDS). Test results indicate that CS has great potential as aluminosilicate material for developing ACM. Further, the addition of mineral admixtures in alkali-activated CS cement improves its performance; however, the addition of MK was found to be more effective than FA in terms of compressive strength and microstructure development.
Reactions Between Liquid CaO-SiO2 Slags and Graphite Substrates White, Jesse F.; Lee, Jaewoo; Hessling, Oscar ...
Metallurgical and materials transactions. B, Process metallurgy and materials processing science,
02/2017, Volume:
48, Issue:
1
Journal Article
Peer reviewed
Open access
In this study, the spreading and infiltration behavior of liquid slag in contact with different grades of graphite was investigated. The wetting and infiltration of slag into graphite were found to ...be highly material dependent. The reduction of silica by carbon is a characteristic of the system, and it generates gaseous products as evidenced by the observation of bubble formation. The higher the temperature and silica activity of the slag is, the greater the slag infiltration and the faster the rate of spreading. Silicon infiltrated into the graphite substrates much deeper than the oxide phases, indicating gas-phase transport of SiO(g) into the graphite pores. Fundamentally, in this system where the liquid and substrate are reacting, the driving force for spreading is the movement of the system toward a lower total Gibbs energy. Reduction of silica in the slag near the interface may eventually lead to the formation of a solid, CaO-rich layer, slowing down or stopping the reduction reaction.
The viscous flow of CaO–SiO2–Al2O3–MgO–TiO2–Cr2O3 slag (CaO/SiO2 = 1.1, Cr2O3 = 0.5 mass%) were investigated to promote understanding of the effect of TiO2 addition on the viscous behavior of ...chromium-containing vanadium-titanium blast furnace slag. The viscosity of the slag was measured using a rotating crucible viscometer. Raman spectroscopy analysis was performed to correlate the viscosity to slag structure. The viscosity of slag was found to significantly decrease with increasing TiO2 content at a fixed basicity. It is because the Ti4+ continuously detached from the network structure, the content of Ti2O64- decreased, and the content of TiO44- tetrahedral monomer increased, which made the slag structure simplified. Consequently, the polymerization degree of the slag decreases with increasing TiO2 content. The variation in slag structure is consistent with the change in measured viscosity.
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