Influence of RAP aggregates on strength, durability and porosity of cement mortar

Deterioration of mortars exposed to sulfate attack under electrical field

Effect of nanosilica on sulfate resistance of cement mortar under partial immersion

The magnesium and sodium sulfate attacks on Portland cement paste in the presence of applied electric fields were studied, and the mineralogical alterations were investigated by both experiments and thermodynamic modeling. When an electric current flows out of the cement paste, the electric migration of ions induced sulfate ingress and decalcification. Compared with the specimen exposed to Na2SO4, that exposed to MgSO4 for 28 d proceeded to a later degradation stage, which is characterized by the decomposition of ettringite, portlandite, and AFm phases, and the formation of CaSO4. Thermodynamic modeling indicates a neutralization process induced by the electric migration of OH−, which is potentially responsible for the decomposition of ettringite. When an electric current flows into the cement paste, the Mg2+ and Na+ showed different migration behavior. Mg2+ was incorporated to form brucite and M-S-H–like products in a shallow area (~100 μm) on the surface of the specimen, whilst a part of the Na+ could be bonded to form Na-rich silica gel with the other part penetrating through the specimen. By coupling the pore solution chemistry obtained from thermodynamic modeling with the Nernst-Planck equation, the migration behaviors of the ionic species (SO42-, Mg2+, and Na+) were analyzed.

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Understanding the sulfate attack of Portland cement–based materials exposed to applied electric fields: Mineralogical alteration and migration behavior of ionic species

Using durable materials is a sustainable solution for extending the lifetime of constructions. The use of crystalline admixtures makes cementitious materials more durable. They plug pores, capillary tracts and microcracks, blocking the entrance of water due to the formation of crystals that prevent the penetration of liquids. The literature has covered the performance of these admixtures on concrete, but studies on mortars are still scarce. The aim of this study is to investigate the effect of an aggressive environment (sulphuric acid solution—3 wt%) on mortars produced with different percentages of a crystalline admixture (1%, 1.5% and 2% by weight of cement content). Physical and mechanical properties were studied after immersing the mortars in a H2SO4 solution for 90 days. It was found that, after a 90-day sulphuric acid exposure, mortars with the crystalline admixture showed greater compressive strength than the control mortar, besides exhibiting lower mass loss. However, the crystalline admixture did not produce any significant effect on the capillary water absorption coefficient. In a nonaggressive environment, and in the short term, the crystalline admixture did not have a significant effect on the compressive strength, the capillary water absorption coefficient or the ultrasonic pulse velocity.

/pdf/influence-of-crystalline-admixtures-on-the-short-term-8oxuwsd76y.pdf

Influence of Crystalline Admixtures on the Short-Term Behaviour of Mortars Exposed to Sulphuric Acid

Accelerated sulfate attack on mortars using electrical pulse

The invention discloses a hardening accelerator which is composed of the following components in parts by mass: 45-65 parts of Al2(SO4)3, 5-25 parts of triethanolamine, 5-15 parts of sodium fluoride and 10-20 parts of HCOOH. The invention further discloses inorganic heat-insulation mortar based on the hardening accelerator. The mortar is composed of the following components in parts by mass: 60-90 parts of ordinary silicate cement, 10-30 parts of fly ash, 0-10 parts of ash calcium powder, 1-6 parts of dispersible latex powder, 0.1-1 part of cellulose ether, 0-1 part of polypropylene fibers, 0.5-5 parts of the hardening accelerator, 50-80 parts of vitrified micro-beads and 110-160 parts of water. Furthermore, 5%-30% of foams in volume percent are also introduced into the mortar. According to the inorganic heat-insulation mortar disclosed by the invention, the self-made hardening accelerator is added so that the setting and hardening time is short; and continuous mechanical spraying can be used for constructing and the construction efficiency is greatly improved.

Hardening accelerator, inorganic heat-insulation mortar based on hardening accelerator and methods for preparing and spraying inorganic heat-insulation mortar

Ether-Induced Phase Transition toward Stabilized Layered Structure of MoS2 with Extraordinary Sodium Storage Performance

The rapid progress of lithium‐ion batteries (LIBs) and sodium‐ion batteries (SIBs) have extensively promoted the rechargeable battery technology in the fields of electric vehicles and grid scale energy storage systems. With recent highly effective nitrogen doping strategy in terms of improving the overall electrochemical performance in various sorts of battery systems, the bulk N doping/substitution lays on the core innovations toward structural manipulation toward higher ionic conductivity, elevated reversible working plateau, etc. However, the key scientific and practical issues such as the phase formation process, phase transition kinetics, valence change and anionic/cationic physical/chemical behaviors still leave open questions in the direction of their real applications in the next‐generation battery technology. In light of this, a timely and in‐depth perspective is provided on the development of the bulk N doping/substitution strategy of these high‐performance electrodes of LIBs/SIBs adapting nitrogen as anionic center/dopant. Both the variations of phase and structural constitutions, alkali ion storage mechanism, electrochemical change, and the alkali ion kinetics, which are the key scientific parts for the future explorations of these novel and promising electrodes are highlighted. The most urgent and critical commercial obstacles or challenges towards cost‐efficiency synthetic approach without excessive environmental pollutions are also outlined. With the participation of nitrogen in bulk crystals , the overall specific energy density of next‐generation alkali ion batteries will be reasonably promoted and accelerated in the near future.

Nitrogen as An Anionic Center/Dopant for Next‐Generation High‐Performance Lithium/Sodium‐Ion Battery Electrodes: Key Scientific Issues, Challenges and Perspectives

Fe‐Mn based layered oxides are recognized as promising cathode materials for sodium‐ion batteries (SIBs) with high capacities and earth‐abundant ingredients. However, their real‐world applications are still constrained by fast capacity decay accompanied with the requirements of deeper insights into the principles behind. Herein, taking O3‐NaxFe1/2Mn1/2O2 as a classic sample, the capacity fading mechanism of Fe‐Mn based layered oxides is comprehensively investigated through combined techniques. For the first time, it is revealed that Fe migration is merely triggered after the oxidation of ≈0.3 mol Fe3+ based on solid proofs from ex situ X‐ray absorption spectroscopy and Mössbauer spectroscopy, which implies the crucial role of the accumulated structural distortion induced by Jahn–Teller active Fe4+. O3‐P3 phase transition during cycling is obviously constrained along with Fe migration as evidenced by in situ/ex situ X‐ray diffraction, well interpreting the intensified polarization and the resulting large capacity loss. More importantly, within the desodiation depth (≈80% of sodium extraction) where Fe migration is almost absent, the capacity fading is dominantly rooted in the Fe4+ activated and Mn‐dissolution aggravated surface passivation as confirmed by mass/X‐ray spectroscopies and electrochemical analysis. These renewed understandings of the fast capacity decay in Fe‐Mn based layered oxides offer clearer clues for designing desirable cathodes for SIBs.

Limin Zhou

Papers

Accelerated sulfate attack on mortars using electrical pulse

Hardening accelerator, inorganic heat-insulation mortar based on hardening accelerator and methods for preparing and spraying inorganic heat-insulation mortar

Ether-Induced Phase Transition toward Stabilized Layered Structure of MoS2 with Extraordinary Sodium Storage Performance

Nitrogen as An Anionic Center/Dopant for Next‐Generation High‐Performance Lithium/Sodium‐Ion Battery Electrodes: Key Scientific Issues, Challenges and Perspectives

Origin of Fast Capacity Decay in Fe‐Mn Based Sodium Layered Oxides