scholarly journals Effect of Mixing Light-Burned MgO with Different Activity on the Expansion of Cement Paste

Crystals ◽  
2021 ◽  
Vol 11 (11) ◽  
pp. 1360
Author(s):  
Yang Wang ◽  
Caoning Zhang ◽  
Lingling Xu
Keyword(s):  
High Activity ◽  
Cement Paste ◽  
Temperature Drop ◽  
Curing Temperature ◽  
Mass Concrete ◽  
Early Hydration ◽  
Expansion Behavior ◽  
Hydration Model ◽  
Strength And Durability ◽  
Low Activity

In mass concrete, shrinkage resulting from temperature drop and drying leads to cracking, which can seriously affect the strength and durability of cement-based materials. Fortunately, expansion agents can deter or prevent these effects, especially MgO expansion agents (MEAs). In this study, the effects of four MEAs of different activity on the expansion properties, strength, and hydration of cement paste were explored. The different expansion phenomena between the high activity and low activity MgO was especially explained by the hydration model and dynamic theory. The results indicate that when the other conditions were the same, higher curing temperature and dosage could improve the expansion to some extent. Moreover, the hydration of high activity MgO and the expansion behavior occurred mainly in the early hydration stage, while the hydration of low activity MgO and the expansion behavior had a high contribution rate in the later stage, and the final expansion of cement mixed with low activity MgO was larger.

Numerical Simulation of Autogenous Shrinkage in High-Performance Cement Paste Based on a Multi-Component Hydration Model

2008 ◽  
Vol 385-387 ◽  
pp. 629-632
Author(s):  
Seung Min Lim ◽  
Han Seung Lee ◽  
Xiao Yong Wang
Keyword(s):  
Numerical Simulation ◽  
Cement Paste ◽  
High Performance ◽  
High Performance Concrete ◽  
Autogenous Shrinkage ◽  
Curing Temperature ◽  
Hydration Process ◽  
Material System ◽  
Water Mixture ◽  
Hydration Model

Autogenous shrinkage is the term for the bulk deformation of a closed, isothermal, cement-based material system not subjected to external forces. It is associated with the internal volume reduction of cement/water mixture in the course of the hydration process. However, addition of blended components to cement, especially such as fly ash or silica fume, for the high-performance concrete will lead to a densification of the microstructure. The autogenous shrinkage deformation will increase and the following autogenous shrinkage crack will do harm to durability of concrete structure. In this paper, numerical simulation is suggested to predict autogenous shrinkage of high performance cement paste. The simulation is originated from a multicomponent hydration model. The numerical program considers the influence of water to cement ratio, curing temperature, particle size distribution, cement mineral components on hydration process and autogenous shrinkage. The prediction result agrees well with experiment result.

Separation of Heparin into Subtractions by DEAE-Cellulose Chromatography

1979 ◽  
Vol 42 (05) ◽  
pp. 1452-1459 ◽  
Author(s):  
Robert H Yue ◽  
Toby Starr ◽  
Menard M Gertler
Keyword(s):  
High Activity ◽  
Uronic Acid ◽  
Deae Cellulose ◽  
Exchange Chromatography ◽  
Net Charge ◽  
Uronic Acid Content ◽  
Successful Separation ◽  
Salt Gradient ◽  
Structure And Activity ◽  
Low Activity

SummaryCommercial porcine heparin can be separated into three distinct subtractions by using DEAE-cellulose chromatography and a stepped salt gradient. Gram quantities of heparin can be fractionated by this technique. All three heparin subtractions can accelerate the inhibition of thrombin by antithrombin III with different efficiency. The specific activities of the high activity heparin, intermediate activity heparin and low activity heparin are 228 units/mg, 142 units/mg and 95 units/mg, respectively. Both the uronic acid content and the quantity of N-SO4 for all three heparin subfractions have been evaluated. The high activity heparin has the lowest uronic acid and N-SO4 content. The successful separation of commercial heparin into three distinct subfractions by means of ion-exchange chromatography suggests that the net charge on these three heparin components will serve as a model system in the elucidation of the structure and activity relationship to the biological function of heparin.

scholarly journals Effect of Calcium Nitrate on the Properties of Portland–Limestone Cement-Based Concrete Cured at Low Temperature

Materials ◽  
2021 ◽  
Vol 14 (7) ◽  
pp. 1611
Author(s):  
Gintautas Skripkiūnas ◽  
Asta Kičaitė ◽  
Harald Justnes ◽  
Ina Pundienė
Keyword(s):  
Compressive Strength ◽  
Cement Paste ◽  
Setting Time ◽  
Calcium Nitrate ◽  
Curing Temperature ◽  
Hardened Concrete ◽  
Cement Pastes ◽  
Initial Setting Time ◽  
Initial Setting ◽  
Early Strength

The effect of calcium nitrate (CN) dosages from 0 to 3% (of cement mass) on the properties of fresh cement paste rheology and hardening processes and on the strength of hardened concrete with two types of limestone-blended composite cements (CEM II A-LL 42.5 R and 42.5 N) at different initial (two-day) curing temperatures (−10 °C to +20 °C) is presented. The rheology results showed that a CN dosage up to 1.5% works as a plasticizing admixture, while higher amounts demonstrate the effect of increasing viscosity. At higher CN content, the viscosity growth in normal early strength (N type) cement pastes is much slower than in high early strength (R type) cement pastes. For both cement-type pastes, shortening the initial and final setting times is more effective when using 3% at +5 °C and 0 °C. At these temperatures, the use of 3% CN reduces the initial setting time for high early strength paste by 7.4 and 5.4 times and for normal early strength cement paste by 3.5 and 3.4 times when compared to a CN-free cement paste. The most efficient use of CN is achieved at −5 °C for compressive strength enlargement; a 1% CN dosage ensures the compressive strength of samples at a −5 °C initial curing temperature, with high early strength cement exceeding 3.5 MPa but being less than the required 3.5 MPa in samples with normal early strength cement.

scholarly journals Physical Activity Trajectories and Associated Changes in Physical Performance in Older Men: The MrOS Study

2020 ◽  
Vol 75 (10) ◽  
pp. 1967-1973
Author(s):  
Deepika R Laddu ◽  
Neeta Parimi ◽  
Katie L Stone ◽  
Jodi Lapidus ◽  
Andrew R Hoffman ◽  
...  
Keyword(s):  
Physical Activity ◽  
Grip Strength ◽  
High Activity ◽  
Physical Performance ◽  
Gait Speed ◽  
Functional Independence ◽  
Performance Measure ◽  
Least Square ◽  
Activity Group ◽  
Low Activity

Abstract Background Physical activity (PA) is important to maintaining functional independence. It is not clear how patterns of change in late-life PA are associated with contemporaneous changes in physical performance measures. Methods Self-reported PA, gait speed, grip strength, timed chair stand, and leg power were assessed in 3,865 men aged ≥ 65 years at baseline (2000–2002) and Year 7 (2007–2009). Group-based trajectory modeling, using up to four PA measures over this period, identified PA trajectories. Multivariate linear regression models (adjusted least square mean [95% confidence interval {CI}]) described associations between-PA trajectories and concurrent changes in performance. Results Three discrete PA patterns were identified, all with declining PA. Linear declines in each performance measure (baseline to Year 7) were observed across all three PA groups, but there was some variability in the rate of decline. Multivariate models assessing the graded response by PA trajectory showed a trend where the high-activity group had the smallest declines in performance while the low-activity group had the largest (p-for trend < .03). Changes in the high-activity group were the following: gait speed (−0.10 m/s [−0.12, −0.08]), grip strength (−3.79 kg [−4.35, −3.23]), and chair stands (−0.38 [−0.50, −0.25]), whereas changes in the low-activity group were the following: gait speed (−0.16 [−0.17, −0.14]), grip strength (−4.83 kg [−5.10, −4.55]), and chair stands (−0.53 [−0.59, −0.46]). Between-group differences in leg power trajectories across PA patterns were not significant. Conclusions Declines in functional performance were higher among those with lower PA trajectories, providing further evidence for the interrelationship between changes in PA and performance during old age.

scholarly journals Relationship between the intention–behavior gap and self-efficacy for physical activity during childhood

2018 ◽  
Vol 23 (1) ◽  
pp. 79-86 ◽  
Author(s):  
Tsunenori Isa ◽  
Yuya Ueda ◽  
Ryo Nakamura ◽  
Shogo Misu ◽  
Rei Ono
Keyword(s):  
Physical Activity ◽  
High Activity ◽  
Self Efficacy ◽  
Self Report ◽  
Physically Active ◽  
Education Interventions ◽  
Relationship Of ◽  
The Relationship ◽  
Low Activity ◽  
Actual Participation

This study investigated the relationship of a gap between the intent to be physically active and actual participation in physical activity (‘intention–behavior gap’) and self-efficacy for physical activity during childhood. A self-report questionnaire was used to collect information from 946 children from the fourth and sixth grades in Japan on self-efficacy, intention, and physical activity. Children with an intention–behavior gap (high intent–low activity or low intent–high activity) had higher self-efficacy scores than those with low intent and low activity (27.66 or 27.65 vs. 21.69; p < .001). They had lower self-efficacy scores than those with high intent and high activity (27.66 or 27.65 vs. 30.56; p < .001). Children with an intention–behavior gap had lower self-efficacy for physical activity than those who intended to be and were physically active. Such children may benefit from education interventions that focus on improving self-efficacy.

scholarly journals Activity Profiles of Soccer Players During the 2010 World Cup

2013 ◽  
Vol 38 ◽  
pp. 201-211 ◽  
Author(s):  
Filipe Manuel Clemente ◽  
Micael Santos Couceiro ◽  
Fernando Manuel Lourenço Martins ◽  
Monika Ognyanova Ivanova ◽  
Rui Mendes
Keyword(s):  
High Activity ◽  
Soccer Players ◽  
Activity Time ◽  
Activity Profile ◽  
World Cup ◽  
Physical Demands ◽  
Fifa World Cup ◽  
Medium Activity ◽  
The Mean ◽  
Low Activity

Abstract The main objective of this study was to analyse the distance covered and the activity profile that players presented at the FIFA World Cup in 2010. Complementarily, the distance covered by each team within the same competition was analysed. For the purposes of this study 443 players were analysed, of which 35 were goalkeepers, 84 were external defenders, 77 were central defenders, 182 were midfielders, and 65 were forwards. Afterwards, a thorough analysis was performed on 16 teams that reached the group stage, 8 teams that achieved the round of 16, 4 teams that reached the quarter-finals, and 4 teams that qualified for the semi-finals and finals. A comparison of the mean distance covered per minute among the playing positions showed statistically significant differences (F(4,438) = 559.283; p < 0.001; 2 = 0.836; Power = 1.00). A comparison of the activity time among tactical positions also resulted in statistically significant differences, specifically, low activity (F(4,183.371) = 1476.844; p < 0.001; 2 = 0.742; Power = 1.00), medium activity (F(4,183.370) = 1408.106; p < 0.001; 2 = 0.731; Power = 1.00), and high activity (F(4,182.861) = 1152.508; p < 0.001; 2 = 0.703; Power = 1.00). Comparing the mean distance covered by teams, differences that are not statistically significant were observed (F(3,9.651) = 4.337; p < 0.035; 2 = 0.206; Power = 0.541). In conclusion, the tactical positions of the players and their specific tasks influence the activity profile and physical demands during a match.

scholarly journals The role of graphene/graphene oxide in cement hydration

2021 ◽  
Vol 10 (1) ◽  
pp. 768-778
Author(s):  
Shaoqiang Meng ◽  
Xiaowei Ouyang ◽  
Jiyang Fu ◽  
Yanfei Niu ◽  
Yuwei Ma
Keyword(s):  
Graphene Oxide ◽  
Cement Paste ◽  
Cement Hydration ◽  
Isothermal Calorimetry ◽  
High Mobility ◽  
Nucleation And Growth ◽  
Early Hydration ◽  
Mobility Of Ions ◽  
Cement Surface

Abstract Graphene (G) and graphene oxide (GO) have been shown to significantly improve the mechanical properties of cement-based materials. In this study, the effect of the G/GO on cement hydration was investigated. First, the zeta potential of G/GO in simulated solutions was tested, and the interaction between G/GO’s surface and Ca2+ was explored. Subsequently, scanning electron microscopy was used to observe the morphology of C–S–H nucleation and growth on the cement surface in the cement paste containing G/GO. Furthermore, XRD and TGA analyses were carried out on the hydration products of the sample. At last, isothermal calorimetry was applied to investigate the influence of G/GO on the early hydration of cement. The results showed that the addition of G/GO significantly accelerates C–S–H nucleation and growth on the cement surface. It is indicated that the high mobility ions derived by G/GO in the cement paste dominate the reason for the accelerated hydration of cement. The presence of G, especially GO, facilitates the mobility of ions, especially Ca2+, thus enhances the interaction between the cement surface and the ions. This strong interaction promotes the C–S–H nucleation and growth, and therefore, the hydration of the cement.

scholarly journals Hydration study of mechanically activated mixtures of Portland cement and fly ash

2007 ◽  
Vol 72 (6) ◽  
pp. 591-604 ◽  
Author(s):  
Gordana Stefanovic ◽  
Ljubica Cojbasic ◽  
Zivko Sekulic ◽  
Srdjan Matijasevic
Keyword(s):  
Compressive Strength ◽  
Fly Ash ◽  
Portland Cement ◽  
Mechanical Activation ◽  
Early Period ◽  
Negative Effects ◽  
Early Hydration ◽  
Cement Pastes ◽  
Dta And Tg ◽  
Low Activity

Fly ash (FA) can be used in cement mixtures with certain limitations. The problem of the mentioned mixtures lies in the insufficient activity of the particles of FA in the reactions which are important for the establishment of the mechanical characteristics of cement. This is particularly true for the hydration reactions. As a result of this, cement pastes formed by mixing ash and clinker have worse characteristics compared to those of pure Portland cement (PC), especially in the early period of setting. As is well known, FA can be a good solution for the neutralization of the negative effects generated due to the creation of free Ca(OH)2 during the hydration of PC, provided that the problems with the low activity of FAare overcome. For the experiments in this study, a mixture of Portland cement and fly ash was used, the content of ash in the mixture being 30 % and 50 %. Mechanical activation was performed in a vibrating ring mill. The goal of this study was to demonstrate, through experimental results, that during the mechanical activation of a PC and FA mixture, the components in the mixture which mostly affect the direction, rate and range of hydration reactions occurring in the mixture had been activated. The values of the compressive strength of the activated and non-activated mixtures and the changes of their specific surface area proved that during the grinding process, the mixture PC+FA had been mechanically activated. The highest increase of compressive strength was achieved in the early period of setting, which indicates an improvement in the early hydration of the mixture. XRD, DTA and TG analyses showed that the alite (C3S) and belite (C2S) from the PC and a part of the fly ash were activated. .

Sign in / Sign up

Export Citation Format

Share Document