Regulating the Expansion Characteristics of Cementitious Materials Using Blended MgO-Type Expansive Agent

To promote the application of MgO-type expansive agents (MEAs), the expansion stresses produced by compacted MEAs with different activities cured in water at 40 °C were measured using a self-designed expansion stress test apparatus. Based on these, different MEAs were divided into the early-type MgO expansive agent and the late-type MgO expansive agent classifications according to the stress curves of compacted MEAs. The two types of MEAs were blended with each other at different ratios and added into cement pastes. Results indicated that the expansion of the cement pastes added with blended MEAs lasted from the beginning to 200 days later, and the expansion characteristics can be regulated by adjusting the blending ratio of MEAs and the choice of types of MEAs. The results suggest that the expansion of MEAs can be improved by using blended MEAs in practical applications.

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New Approach for the Determination of Radiological Parameters on Hardened Cement Pastes with Coal Fly Ash

Materials ◽

10.3390/ma14030475 ◽

2021 ◽

Vol 14 (3) ◽

pp. 475

Author(s):

Ana María Moreno de los Reyes ◽

José Antonio Suárez-Navarro ◽

Maria del Mar Alonso ◽

Catalina Gascó ◽

Isabel Sobrados ◽

...

Keyword(s):

Fly Ash ◽

Activity Concentration ◽

Gamma Ray ◽

Coal Fly Ash ◽

Cementitious Materials ◽

New Method ◽

Supplementary Cementitious Materials ◽

Hardened Cement ◽

Cement Pastes ◽

Activity Concentrations

Supplementary cementitious materials (SCMs) in industrial waste and by-products are routinely used to mitigate the adverse environmental effects of, and lower the energy consumption associated with, ordinary Portland cement (OPC) manufacture. Many such SCMs, such as type F coal fly ash (FA), are naturally occurring radioactive materials (NORMs). 226Ra, 232Th and 40K radionuclide activity concentration, information needed to determine what is known as the gamma-ray activity concentration index (ACI), is normally collected from ground cement samples. The present study aims to validate a new method for calculating the ACI from measurements made on unground 5 cm cubic specimens. Mechanical, mineralogical and radiological characterisation of 28-day OPC + FA pastes (bearing up to 30 wt % FA) were characterised to determine their mechanical, mineralogical and radiological properties. The activity concentrations found for 226Ra, 212Pb, 232Th and 40K in hardened, intact 5 cm cubic specimens were also statistically equal to the theoretically calculated values and to the same materials when ground to a powder. These findings consequently validated the new method. The possibility of determining the activity concentrations needed to establish the ACI for cement-based materials on unground samples introduces a new field of radiological research on actual cement, mortar and concrete materials.

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Giant planets around AF and M stars

Proceedings of the International Astronomical Union ◽

10.1017/s1743921313007898 ◽

2013 ◽

Vol 8 (S299) ◽

pp. 64-65

Author(s):

Julien Rameau ◽

Gaël Chauvin ◽

Anne-Marie Lagrange ◽

Philippe Delorme ◽

Justine Lannier

Keyword(s):

Giant Planets ◽

Early Type ◽

Late Type ◽

M Dwarfs ◽

Low Mass Stars ◽

Planetary Mass ◽

Nearby Stars ◽

Low Mass ◽

M Stars ◽

The One

AbstractWe present the results of two three-year surveys of young and nearby stars to search for wide orbit giant planets. On the one hand, we focus on early-type and massive, namely β Pictoris analogs. On the other hand, we observe late type and very low mass stars, i.e., M dwarfs. We report individual detections of new planetary mass objects. According to our deep detection performances, we derive the observed frequency of giant planets between these two classes of parent stars. We find frequency between 6 to 12% but we are not able to assess a/no correlation with the host-mass.

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Investigation of C-S-H in ternary cement pastes containing nanosilica and highly-reactive supplementary cementitious materials (SCMs): Microstructure and strength

Construction and Building Materials ◽

10.1016/j.conbuildmat.2018.10.235 ◽

2019 ◽

Vol 198 ◽

pp. 445-455 ◽

Cited By ~ 11

Author(s):

Daniel da Silva Andrade ◽

João Henrique da Silva Rêgo ◽

Paulo Cesar Morais ◽

Anne Neiry de Mendonça Lopes ◽

Moisés Frías Rojas

Keyword(s):

Cementitious Materials ◽

Supplementary Cementitious Materials ◽

Cement Pastes

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Mechanically activated mine tailings for use as supplementary cementitious materials

RILEM Technical Letters ◽

10.21809/rilemtechlett.2021.143 ◽

2021 ◽

Vol 6 ◽

pp. 61-69

Author(s):

Sivakumar Ramanathan ◽

Priyadarshini Perumal ◽

Mirja Illikainen ◽

Prannoy Suraneni

Keyword(s):

Mine Tailings ◽

Isothermal Calorimetry ◽

Cementitious Materials ◽

Supplementary Cementitious Materials ◽

Strong Correlations ◽

Negative Effects ◽

Cement Pastes ◽

Amorphous Content ◽

Milling Duration ◽

Median Particle

Two mine tailings are evaluated for their potential as supplementary cementitious materials. The mine tailings were milled using two different methods – ball milling for 30 minutes and disc milling for durations ranging from 1 to 15 minutes. The modified R3 test was carried out on the mine tailings to quantify their reactivity. The reactivity of the disc milled tailings is greater than those of the ball milled tailings. Strong correlations are obtained between milling duration, median particle size, amorphous content, dissolved aluminum and silicon, and reactivity of the mine tailings. The milling energy results in an increase in the fineness and the amorphous content, which do not appreciably increase beyond a disc milling duration of 8 minutes. The reactivity increases significantly beyond a certain threshold fineness and amorphous content. Cementitious pastes were prepared at 30% supplementary cementitious materials replacement level at a water-to-cementitious materials ratio of 0.40. No negative effects of the mine tailings were observed at early ages in cement pastes based on isothermal calorimetry and thermogravimetric analysis, demonstrating the potential for these materials to be used as supplementary cementitious materials.

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Shrinkage and Mechanical Properties of Self-Compacting SFRC With Calcium-Sulfoaluminate Expansive Agent

Materials ◽

10.3390/ma13030588 ◽

2020 ◽

Vol 13 (3) ◽

pp. 588 ◽

Cited By ~ 4

Author(s):

Changyong Li ◽

Pengran Shang ◽

Fenglan Li ◽

Meng Feng ◽

Shunbo Zhao

Keyword(s):

Mechanical Properties ◽

Steel Fiber ◽

Volume Fraction ◽

Cementitious Materials ◽

Fiber Reinforced Concrete ◽

Steel Fibers ◽

Steel Fiber Reinforced Concrete ◽

Volume Stability ◽

Calcium Sulfoaluminate ◽

Expansive Agent

With the premise of ensuring workability on a fresh mixture, the volume stability of hardened self-compacting steel fiber reinforced concrete (SFRC) becomes an issue due to the content of cementitious materials increased with the volume fraction of steel fiber. By using the expansive agent to reduce the shrinkage deformation of self-compacting SFRC, the strength reduction of hardened self-compacting SFRC is another issue. To solve these issues, this paper performed an experimental investigation on the workability, shrinkage, and mechanical properties of self-compacting SFRC compared to the self-compacting concrete (SCC) with or without an expansive agent. The calcium-sulfoaluminate expansive agent with content optimized to be 10% mass of binders and the steel fiber with a varying volume fraction from 0.4% to 1.2% were selected as the main parameters. The mix proportion of self-compacting SFRC with expansive agent was designed by the direct absolute volume method, of which the steel fibers are considered to be the distributed coarse aggregates. Results showed that rational high filling and passing ability of fresh self-compacting SFRC was ensured by increasing the binder to coarse-aggregate ratio and the sand ratio in the mix proportions; the autogenous and drying shrinkages of hardened self-compacting SFRC reduced by 22.2% to 3.2% and by 18.5% to 7.3% compared to those of the SCC without expansive agent at a curing age of 180 d, although the expansion effect of expansive agent decreased with the increasing volume fraction of steel fiber; the mechanical properties, including the compressive strength, the splitting tensile strength, and the modulus of elasticity increased with the incorporation of an expansive agent and steel fibers, which met the design requirements.

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Characterization of Titanium Nanotube Reinforced Cementitious Composites: Mechanical Properties, Microstructure, and Hydration

Materials ◽

10.3390/ma12101617 ◽

2019 ◽

Vol 12 (10) ◽

pp. 1617 ◽

Cited By ~ 3

Author(s):

Hyeonseok Jee ◽

Jaeyeon Park ◽

Erfan Zalnezhad ◽

Keunhong Jeong ◽

Seung Min Woo ◽

...

Keyword(s):

Mechanical Properties ◽

Cement Paste ◽

Cementitious Materials ◽

Cement Clinker ◽

Early Age ◽

Potential Candidate ◽

Hydration Kinetics ◽

Cement Pastes ◽

Viable Solution ◽

First Time

In recent years, nano-reinforcing technologies for cementitious materials have attracted considerable interest as a viable solution for compensating the poor cracking resistance of these materials. In this study, for the first time, titanium nanotubes (TNTs) were incorporated in cement pastes and their effect on the mechanical properties, microstructure, and early-age hydration kinetics was investigated. Experimental results showed that both compressive (~12%) and flexural strength (~23%) were enhanced with the addition of 0.5 wt.% of TNTs relative to plain cement paste at 28 days of curing. Moreover, it was found that, while TNTs accelerated the hydration kinetics of the pure cement clinker phase (C3S) in the early age of the reaction (within 24 h), there was no significant effect from adding TNTs on the hydration of ordinary Portland cement. TNTs appeared to compress the microstructure by filling the cement paste pore of sizes ranging from 10 to 100 nm. Furthermore, it could be clearly observed that the TNTs bridged the microcracks of cement paste. These results suggested that TNTs could be a great potential candidate since nano-reinforcing agents complement the shortcomings of cementitious materials.

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Additive Manufacturing of Cementitious Materials by Selective Paste Intrusion: Numerical Modeling of the Flow Using a 2D Axisymmetric Phase Field Method

Materials ◽

10.3390/ma13215024 ◽

2020 ◽

Vol 13 (21) ◽

pp. 5024

Author(s):

Alexandre Pierre ◽

Daniel Weger ◽

Arnaud Perrot ◽

Dirk Lowke

Keyword(s):

Numerical Modeling ◽

3D Printing ◽

Cement Paste ◽

Phase Field ◽

Numerical Approach ◽

Cementitious Materials ◽

Field Method ◽

Phase Field Method ◽

Shape Accuracy ◽

Cement Pastes

The 3D printing of concrete has now entered a new era and a transformation of the construction sector is expected to reshape fabrication with concrete. This work focuses on the selective paste intrusion method, which consists of bonding dry particles of aggregate with a cement paste. This innovative technique could lead to the production of very precise component for specific applications. The main obstacle to tackle in order to reach a high shape accuracy of high mechanical performances of 3D printing elements by selectively activating the material is the control of the distribution of the cement paste through the particle bed. With the aim to better understand the path followed by the solution as it penetrates a cut-section of the granular packing, two-dimensional numerical modeling is carried out using Comsol software. A phase-field method combined with a continuous visco-plastic model has been used to study the influence of the average grain diameter, the contact angle, and the rheological properties of cement pastes on the penetration depth. We compare the numerical modeling results to existing experimental results from 3D experiments and a one-dimensional analytical model. We then highlight that the proposed numerical approach is reliable to predict the final penetration of the cement pastes.

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Supernova Rates

International Astronomical Union Colloquium ◽

10.1017/s0252921100007855 ◽

1996 ◽

Vol 145 ◽

pp. 1-9 ◽

Cited By ~ 1

Author(s):

Sidney Van Den Bergh

Keyword(s):

Luminosity Function ◽

Historical Data ◽

Starburst Galaxies ◽

Early Type ◽

Late Type ◽

Interstellar Absorption ◽

Blue Galaxies ◽

S0 Galaxies ◽

Intermediate Redshifts ◽

Parent Galaxy

Extragalactic supernova rates are reviewed. The main uncertainties in calculated rates are due to (1) the influence of the (still poorly known) luminosity function of supernova of a given type on “control times”, to (2) uncertain corrections for possible inclination - dependent bias in supernova discovery probabilities, and (3) interstellar absorption. The total supernova rate in late-type galaxies is found to be ∼ 2(H0/75)2 supernovae (SNe) per century per 1010LB(ʘ) This is consistent with the rate of 3 SNe per century that is derived from the historical data on Galactic supernovae. It is, however, a source of some concern that none of the three Galactic SNe expected to have occurred during the last century was actually observed!The expansion velocities of SNe Ia are found to correlate strongly with parent galaxy Hubble type. This relation is in the sense that low expansion velocities are only observed for those SNe Ia that occur in early-type galaxies. This suggests that V(exp) correlates with the ages of SNe Ia progenitors. It is speculated that the progenitors of a few SNe Ia with high V(exp) values in E and S0 galaxies were formed during recent starbursts.SNe Ia rates appear to be enhanced in post-starburst galaxies. It is suggested that supernova rates might be quite high in the recently discovered population of faint blue galaxies at intermediate redshifts.

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