•The effects of limestone powder (LS) depends on its particle size and content.•Using LS to replace fine aggregate improves the properties of concrete.•Using LS to replace cement reduces the ...properties of the concrete.
Limestone powder (LS) is one of the mineral materials in concrete due to its wide availability and low cost. This paper discusses effects of LS on the workability, setting time, shrinkage, mechanical properties and durability of concrete. Such effects are mainly influenced by many factors, including the particle size and content of LS, the polymorph of calcium carbonate and synergetic effect between LS and alumina-rich supplementary cementitious materials (SCMs). In general, incorporating LS, as cement paste replacement or in the form of fine aggregate, improves the properties of concrete. Whereas, when LS is incorporated into concrete to replace cement, effects of LS on the properties of concrete depend on its particle size and content. In the end, some further research needs are also suggested.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
•A sustainable ECC was developed using LC3 cement and PP fiber.•The strain capacity of LC3-ECC (6%) is substantially higher than that of PP-ECC in the literature.•LC3-ECC retains strength enhancement ...and no ductility loss after self-healing subsequent to 2% tensile straining.•LC3-ECC reduces 61% of material cost, 45% of energy consumption, and 48% of carbon emission compared to M45-ECC.
While the ultrahigh tensile ductility and superior durability of Engineered Cementitious Composites (ECC) have been demonstrated, the relatively high energy and carbon intensity, as well as high material cost present potential impediments to broader ECC applications. The objective of this research is to develop a more sustainable and cost-effective ECC. The ordinary Portland cement (OPC) and the commonly used PVA fiber in conventional ECC were replaced by limestone calcined clay cement (LC3) and polypropylene (PP) fiber, respectively. The ECC compressive strength, tensile stress-strain relationship, and microcrack self-healing behavior were studied at three water to binder ratios (0.3, 0.2, 0.16). The novel LC3-PP-ECC showed a tensile strain capacity of greater than 6% and an intrinsically tight crack width below 82 μm when loaded to 1% tensile strain. Further, the LC3-PP-ECC demonstrated efficient recovery of the composite tensile ductility and ultimate tensile strength through self-healing. Compared to typical ECC made with OPC and PVA fiber, the material cost, embodied energy and carbon footprint of LC3-PP-ECC are reduced by 61%, 45%, and 48%, respectively. The superior mechanical properties and durability combined with the low environmental impact and cost for material production promote LC3-PP-ECC as a sustainable material for structural and non-structural applications.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Halloysite is a kind of 1:1 clay mineral having a special nanosized tubular morphology and pore structure. In this work, nanosized tubular halloysite calcined at 750 °C (Hal750) and limestone (LS) ...were used to partially replace the ordinary Portland cement (OPC) for the preparation of limestone calcined clay cement (LC3). The mechanical properties and microstructure of LC3 were studied. The results revealed that the obtained LC3 had higher early compressive strengths on 3 and 7 days than did plain OPC. LC3 with a replacement ratio of 22.5% (containing 15.0% Hal750 and 7.5% LS) resulted in maximum compressive strength of 46.38 MPa, being 9.4% higher than OPC's after 28 days of curing. Further, LC3 featured a compact microstructure and smaller critical pore size than OPC, which is mainly because more additional C-(A)-S-H, hemicarboaluminate (Hc), and monocarboaluminate (Mc) were formed in LC3 system, thus contributing to the matrix densification and strength development. However, when the replacement ratio exceeded 37.5%, the insufficient portlandite (CH) limited the pozzolanic reaction with Hal750, leaving excess Hal750 in the LC3 that led to their inhomogeneous microstructure, and thus weakened the mechanical properties. These results show that halloysite is a promising material for the preparation of LC3 whose properties are sensitive to the replacement ratio used.
•Calcined halloysite is feasible to prepare limestone calcined clay cement (LC3).•The compressive strength of LC3 is sensitive to the replacement ratio by Hal750 and LS.•LC3 prepared from calcined halloysite features a higher compressive strength than OPC.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Darcy‐scale multiphase flow in geological formations is significantly influenced by the wettability of the fluid‐solid system. So far it has not been understood how wettability impacts the pore‐scale ...flow regimes within rocks, which were in most cases regarded as an alteration from the base case of strongly water‐wet conditions by adjustment of contact angles. In this study, we directly image the pore‐scale flow regime in a carbonate altered to a mixed‐wet condition by aging with crude oil to represent the natural configuration in an oil reservoir with fast synchrotron‐based X‐ray computed tomography. We find that the pore‐scale flow regime is dominated by ganglion dynamics in which the pore space is intermittently filled with oil and brine. The frequency and size of these fluctuations are greater than in water‐wet rock such that their impact on the overall flow and relative permeability cannot be neglected in modeling approaches.
Plain Language Summary
In geological systems, in particular in oil reservoirs, the wetting condition of rock, the preference of a fluid to be in contact with a surface in the presence of another fluid, has a significant impact on multiphase flow. Often a simplified picture based on static, wettability‐dependent fluid configurations is used as a basis for modeling where the fluids are assumed to flow through the porous rock within definite connected pathways. Our research, which is based on a time series of 3‐D images obtained during multiphase flow showing the pore‐scale fluid configurations of the brine and oil, demonstrates that this picture is too simplistic. In reality the flow paths change. In systems in which one phase is strongly wetting those changes are fast, small, and rare. However, oil reservoirs are mostly mixed‐wet as surface active components contained in crude oil alter the rock surface. In such mixed‐wet situations, we observe that the movement is slower (minutes instead of seconds), is more frequent, and involves larger fluid volumes. This indicates a different flow regime that cannot be estimated from an extrapolation from strongly wetting rock. This has consequences for the way how multiphase flow in mixed‐wet rock is described in models.
Key Points
Ganglion dynamics in mixed‐wet systems is observed
Oil‐filling events are more frequent and of larger size in mixed‐wet systems and depend on the aging state/wettability of the rock surface
This behavior may impact the overall relative permeability and must be considered in pore‐scale flow simulations
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
•First report of usefully precise Pb–Pb ages of Upper Vindhyan carbonates.•Pb–Pb ages are much older than previously thought.•Results provide direct and independent support to indirectly inferred ...ages.
Age of the upper sedimentary units (Rewa and Bhander Groups) of the largest Proterozoic Vindhyan Basin in central India has so far been considered to be close to 650Ma (late Neoproterozoic) based on collective proxy dates in the absence of direct isotopic dates. A drastic upward revision of this age by more than 300Ma has very recently been proposed from the similarity of the paleomagnetic directions in these units with those of the 1070Ma old Majhgawan kimberlite intrusion into their basal parts, and the presence of detrital zircons not younger than 1020Ma. We report now Pb–Pb isochron ages of 908±72Ma, 866±180Ma and 1073±210Ma for the three distinct carbonate horizons, Bhander-, Balwan- and Lakheri Limestones, respectively as independent and direct evidence on the age of the Upper Vindhyan succession. The consistency of the three ages close to 900Ma provides a strong support for the proposed shift on the timing and duration of sedimentation in the Upper Vindhyan sequence.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
The review summarises literature to examine the transition from portland limestone cement system to composite ternary binder systems involving limestone. Interest in limestone addition as an ideal ...component in multicomponent binder systems has surged as evident from the large volume of literature published in the recent past. A ternary blended system, with co-substitution of limestone, has the potential to complement the reaction of the supplementary cementitious materials (SCMs). The direct addition of limestone powder helps to attain higher substitution levels of portland cement clinker, improve early age properties, and supplement SCM's reactivity. However, the dilution of hydrates could hamper the long-term benefits. In this review, the interaction of fine limestone is classified and elaborated under two broad umbrellas: physical and chemical interactions. The physical interactions can manifest in three ways, namely, filler action, shearing action and improved packing, which alters reaction rate and extent at early ages. The chemical interactions also modify the reaction kinetics and phase assemblage due to nucleation of C-S-H on calcite surfaces, preservation of the ettringite phase and formation of carboaluminates. Two different forms of carboaluminate hydrates — hemicarboaluminate and mono-carboaluminate can be present in the hydrate matrix depending on the balance between carbonate ions and aluminates in the pore solution. Several factors such as replacement level, particle size, choice of SCM, its reactivity and reactive aluminates content, sulphate levels, curing temperature, and duration of curing can control the carboaluminate formation, reaction degree of SCMs and chemical interaction from limestone additions.
A combination of physical and chemical effects makes fine limestone a potential material for co-substitution with aluminosilicate based SCMs, mainly fly ash, slag, and calcined clay. In this review, the factors affecting limestone-SCM composites are summarised based on a detailed literature survey. The effects of SCM-limestone cement composites on hydration kinetics, reaction chemistry, the reactivity of SCMs, the stability of hydrated phases, and contribution to the physical structure development and macroscopic properties by evaluating hydration and mechanical properties are discussed. The importance of AFm (Al2O3–Fe2O3-mono) phases in various deterioration mechanisms in concrete and their influence on performance characteristics in different exposure environment is critically appraised.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
We investigated high-resolution stratigraphic distribution of selected major and trace elements and gamma-ray spectra of fourteen Devonian/Carboniferous (D/C) boundary sections of Europe located in ...the late Palaeozoic Laurussia and Gondwana. The aim was to trace the geochemical signature of a marked forced and normal regressive interval which was associated with rapid progradation of siliciclastics into the marine carbonate systems (Rhenish Massif) and a prominent hiatus in shallow-water ramp settings (Namur–Dinant Basin). This interval represents the late Devonian Hangenberg event (HBE) sensu lato (middle praesulcata conodont zone) as defined by previous authors. This regressive interval (FSST to LST) correlates with thin shale layers (HBE shale) sandwiched between monotonous nodular calcilutite/calcisiltite successions at five pelagic sections of Moravia, Carnic Alps, Montagne Noire, and Pyrenees. In all sections with continuous D/C sedimentation (i.e., except those of the Namur–Dinant Basin), the HBE s.l. interval is accompanied by elevated percentages of detrital proxies (Al, K, Rb, Zr) and changes in their ratios (Zr/Rb, K/Al, Rb/K) which are normally interpreted as indicators of increased siliciclastic input, provenance, and grain size. Zr/Rb and other proxies are traceable even without apparent lithological evidence and can, therefore, facilitate stratigraphic correlation. Paleoredox and productivity proxies (U/Th and Ni/Rb enrichment factors) only rarely show elevated values in the Hangenberg black shale interval, indicating that the associated water dysoxia/anoxia was a local rather than global phenomenon. Global correlations based on the HBE black shales should therefore be dropped in favor of the HBE s.l. interval. Moreover, analysis of sedimentation rates in the upper expansa to kockeli zone interval using the published radiometric ages suggests that the HBE s.l. was a time of significant increase in the rate of siliciclastic supply into the ocean, even in the most distal pelagic sections. Consequently, the previous interpretation of the HBE black shale as a condensed succession deposited during rapid sea-level rise seems unlikely. We interpret the HBE s.l. (i.e., including the HBE black shale) as a marine record of glacioeustatic sea-level drop and increased aeolian transport in connection with late Devonian climatic cooling and glaciation. The set of geochemical markers related to the late Devonian sea-level fluctuation can be used for super-regional to global correlations from platform to basin settings. Moreover, they can facilitate current efforts to determine a new D/C boundary definition.
•Hangenberg events sensu lato recorded rapid detrital influx into marine realms.•Element proxies are perfect tools for neritic to pelagic correlation near D/C boundary.•Hangenberg black shales do not record basin starvation during peak sea level rise.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
In 3D concrete printing (3DCP), it is necessary to meet contradicting rheological requirements: high fluidity during pumping and extrusion, and high stability and viscosity at rest to build the ...layered structure. In this paper, the impact of the hydroxypropyl methylcellulose (HPMC)-based viscosity-modifying admixture (VMA) on the 3D printability and mechanical performance of a limestone and calcined clay based cementitious material is investigated. A combination of VMA and superplasticizer was used for that purpose. In this case, controlling the competitive effects between VMA and superplasticizer becomes critical. The main strategy for 3D printing in this study was to add an optimal dosage of VMA in the solid suspension that was already mixed with water and superplasticizer. A lab-scale 3DCP setup was developed and demonstrated as well. A series of tests was performed to characterize the effects of VMA on flowability, extrudability, open time, buildability, green strength, hydration, compressive strength, and air void content and distribution. Experiments performed in this study showed that the mixture containing 0.24% (of the binder mass) of VMA exhibited satisfactory 3D printability and optimal mechanical performance. Finally, the results, limitations, and perspectives of the current research were discussed.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Tar, among the most difficult contaminants to be removed, is the major technical barrier for the development and application of advanced biomass gasification technology. Catalytic cracking of tar, ...with the advantages of energy recovery from tar, quality increase of product gas and no secondary pollution, has become the main focus currently for tar removal. Among various types of catalysts, CaO based catalysts, including the naturally available calcined limestone/dolomite, the single-/multi-metal active components (Ni, Fe, Mg, etc.) and CaO composite catalysts, and the synthetic CaO based catalysts, have been demonstrated to be effective and economically viable for tar removal. Meanwhile, CaO is also being used in some novel CaO-looping gasification processes as a CO2 absorbent in recent years. Therefore, the CaO derived from different precursors, the in-situ and ex-situ applications of CaO catalysts and the tar removal under different operation conditions have been studied in this review. The tar cracking mechanism over CaO catalysts has been summarized. The single-/multi-metal doped CaO based catalysts for tar removal are also discussed. The use of CaO catalysts in some novel gasification processes and their tar removal efficiency have been also investigated. Finally, the main drawbacks and future perspectives of CaO based catalysts are discussed.
•The detailed mechanism of tar cracking over CaO surface was summarized.•In-/ex-situ use of CaO from different precursors at varied conditions were studied.•Introduction of other metals to form single-/multi-metal doped CaO catalysts was studied.•Tar removal efficiency of CaO catalysts in novel gasification process was clarified.•The main drawbacks and future perspectives of CaO based catalysts were given.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ
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