Development of shrinkage resistant microfibre-reinforced cement-based composites

2012 ◽  
Vol 2 (2) ◽  
Author(s):  
P. Hamedanimojarrad ◽  
G. Adam ◽  
A. Ray ◽  
P. Thomas ◽  
K. Vessalas
Keyword(s):  
Drying Shrinkage ◽  
Shrinkage Strain ◽  
Crack Size ◽  
Moisture Loss ◽  
The Novel ◽  
Total Shrinkage ◽  
Low Concentrations ◽  
Reinforced Cement ◽  
Short And Long Term

AbstractDifferent shrinkage types may cause serious durability dilemma on restrained concrete parts due to crack formation and propagation. Several classes of fibres are used by concrete industry in order to reduce crack size and crack number. In previous studies, most of these fibre types were found to be effective in reducing the number and sizes of the cracks, but not in shrinkage strain reduction. This study deals with the influence of a newly introduced type of polyethylene fibre on drying shrinkage reduction. The novel fibre is a polyethylene microfibre in a new geometry, which is proved to reduce the amount of total shrinkage in mortars. This special hydrophobic polyethylene microfibre also reduces moisture loss of mortar samples. The experimental results on short and long-term drying shrinkage as well as on several other properties are reported. The hydrophobic polyethylene microfibre showed promising improvement in shrinkage reduction even at very low concentrations (0.1% of cement weight).

Influence of Basalt Fiber on Performance of Cement Mortar

2010 ◽  
Vol 426-427 ◽  
pp. 93-96 ◽  
Author(s):  
Chao Hua Jiang ◽  
T.J. McCarthy ◽  
D. Chen ◽  
Q.Q. Dong
Keyword(s):  
Basalt Fiber ◽  
Drying Shrinkage ◽  
Early Hydration ◽  
Remarkable Effect ◽  
Bond Performance ◽  
Four Point Bending ◽  
Initial Work ◽  
Reinforced Cement ◽  
Mortar Matrix

This paper presents initial work with the application of basalt fiber (BF) in the field of reinforced cement composites. Effect of BF on mortar drying shrinkage, mechanical prosperities and bond performance were studied. The results showed that adding of BF reduced markedly dry shrinkage of mortar especially at early ages. BF mortar had a greater compressive and flexural strength at early hydration period，but had a little less strength at the age of 28-days than mortar without fiber. Four point bending tests shows that addition of BF increased effectively toughness of mortar specimen at 28-days at the same loading, but had not a remarkable effect on fracture strength. A good bond was observed between BF and mortar matrix interface zone by SEM in early ages and there was debonding phenomenon between BF and mortar matrix in the long-term ages.

scholarly journals The coronavirus in the MENA region: Enhancing turbulence or mitigating conflicts?

European View ◽  
2020 ◽  
Vol 19 (2) ◽  
pp. 206-211
Author(s):  
Magnus Norell
Keyword(s):  
Middle East ◽  
The Novel ◽  
Crisis Preparedness ◽  
Mena Region ◽  
Existing Problems ◽  
Regional Conflicts ◽  
Current Trends ◽  
Short And Long Term ◽  
Novel Coronavirus

The novel coronavirus (COVID-19) pandemic has affected the countries in the Middle East and North Africa (MENA) region in different ways, and the varying political structures, economic conditions and civil-crisis preparedness of the states in this region have resulted in it being handled in a variety of ways too. Even if it is difficult to assess how the crisis has affected the MENA region in more detail due to the region’s general volatility and ongoing conflicts in Libya and Syria, current trends have so far not shown a diminution in regional conflicts. Nor have the pandemic’s consequences in the Middle East lessened Europe’s problems with the region. Thus the article argues that COVID-19 has not really led to a decrease in the conflicts and wars plaguing the MENA region, and that, therefore, the effects for Europe—both short- and long-term—will still be felt, as existing problems will continue to affect Europe.

scholarly journals Preservation of Avian Cells at Sub-zero Temperatures

1979 ◽  
Vol 32 (5) ◽  
pp. 475 ◽  
Author(s):  
N Ratnamohan ◽  
PB Spradbrow
Keyword(s):  
Dimethyl Sulfoxide ◽  
Cryoprotective Agent ◽  
Cryoprotective Agents ◽  
Long Term Storage ◽  
Low Concentrations ◽  
Short And Long Term ◽  
Term Storage

The cryoprotective agents dimethyl sulfoxide (DMSO), glycerol, polyvinylpyrrolidone (PVP) and dextran were evaluated for their ability to protect avian cells during storage at sub-zero temperatures. DMSO was the most effective cryoprotective agent for the short- and long-term storage of avian cells and glycerol was also effective when used at low concentrations. PVP and dextran did not protect avian cells during storage in our experiments. Primary chicken cells and avian cells at higher passage levels were successfully recovered after storage with DMSO for periods ranging from 4 to 12 months.

scholarly journals Short- and Long-Term Biological Variation in Cardiac Troponin I Measured with a High-Sensitivity Assay: Implications for Clinical Practice

2009 ◽  
Vol 55 (1) ◽  
pp. 52-58 ◽  
Author(s):  
Alan H B Wu ◽  
Quynh Anh Lu ◽  
John Todd ◽  
Joachim Moecks ◽  
Frank Wians
Keyword(s):  
Detection Limit ◽  
Cardiac Troponin ◽  
Troponin I ◽  
High Sensitivity ◽  
Population Based ◽  
Biological Variation ◽  
Cardiac Troponin I ◽  
Low Concentrations ◽  
Short And Long Term

Abstract Background: The improved detection limit and precision in new-generation commercial assays for cardiac troponin I (cTnI) have lowered the 99th-percentile cutoff value, yielding higher frequencies of positive test results. Because serial testing is important in interpreting low concentrations, we evaluated the biological variation of cTnI in both the short (hours) and long (weeks) terms and determined reference change values (RCVs) and the index of individuality (II) for cTnI. Methods: To assess short- and long-term variation, we collected blood from 12 healthy volunteers hourly for 4 h and from 17 healthy individuals once every other week for 8 weeks, measured cTnI with a high-sensitivity assay (detection limit, 0.2 ng/L), and computed analytical, intraindividual, interindividual, and total CVs (CVA, CVI, CVG, and CVT, respectively; CVT = CVA + CVI + CVG) as well as the II. Because of the slight right-skewness of the data, RCVs were calculated with a lognormal approach. Results: Within-day CVA, CVI, and CVG values were 8.3%, 9.7%, and 57%, respectively; the corresponding between-day values were 15%, 14%, and 63%. Within- and between-day IIs were 0.21 and 0.39, respectively. Lognormal within-day RCVs were 46% and −32%, respectively; the corresponding between-day values were 81% and −45%. Conclusions: The low II indicates that population-based reference intervals are less useful for interpreting cTnI values than following serial changes in values in individual patients. This criterion is particularly important for interpreting results from patients who show cTnI increases at low concentrations measured with very high-sensitivity assays, from patients presenting with chest pain (short term), and for evaluating drugs for cardiotoxicity (long term).

scholarly journals Experimental Study on the Shrinkage Behavior and Mechanical Properties of AAM Mortar Mixed with CSA Expansive Additive

Materials ◽  
2019 ◽  
Vol 12 (20) ◽  
pp. 3312 ◽  
Author(s):  
Sung Choi ◽  
Gum-Sung Ryu ◽  
Kyeong-Taek Koh ◽  
Gi-Hong An ◽  
Hyeong-Yeol Kim
Keyword(s):  
Modulus Of Elasticity ◽  
Compensation Effect ◽  
Autogenous Shrinkage ◽  
Drying Shrinkage ◽  
Shrinkage Stress ◽  
Calcium Sulfoaluminate ◽  
Total Shrinkage ◽  
Expansive Additive ◽  
Shrinkage Compensation

In this study, a calcium sulfoaluminate-based expansive additive (0%, 2.5%, 5.0%, and 7.5% by the mass of the binder) was added to compensate for the shrinkage of alkali-activated material (AAM) mortar. Modulus of elasticity curves based on the ACI 209 model were derived for the AAM mortar mixed with the additive by measuring the compressive strength and modulus of elasticity. Moreover, autogenous shrinkage and total shrinkage were measured for 150 days, and drying shrinkage was calculated by excluding autogenous shrinkage from total shrinkage. For the autogenous and drying shrinkage of AAM mortar, shrinkage curves by age were obtained by deriving material constants using the exponential function model. Finally, shrinkage stress was calculated using the modulus of elasticity of the AAM mortar and the curves obtained using the shrinkage model. The results showed that the calcium sulfoaluminate-based expansive additive had an excellent compensation effect on the drying shrinkage of AAM mortar, but the effect was observed only at early ages when the modulus of elasticity was low. From a long-term perspective, the shrinkage compensation effect was low when the modulus of elasticity was high, and thus, shrinkage stress could not be reduced.

scholarly journals Case Study on Early Age Shrinkage of Cement-based Composites

2015 ◽  
Vol 2 ◽  
pp. 79
Author(s):  
Andina Sprince ◽  
Leonids Pakrastinsh
Keyword(s):  
High Performance ◽  
Autogenous Shrinkage ◽  
Drying Shrinkage ◽  
Cement Composite ◽  
Early Age ◽  
Thin Walls ◽  
Reinforced Cement ◽  
Pva Fiber

The aim of this paper was to study the behaviour of new high-performance fibre-reinforced cement composite materials (FRCC) that are reinforced with polyvinyl alcohol (PVA) fibres. The shrinkage deformations at early age, the compressive strength and modulus of elasticity of the new compositions had been determined. Test results shows that the addition of PVA fiber 1.10% and 0.55% by weight of the cement has negligible influence on concrete drying shrinkage, however, it is affect the concrete plastic and autogenous shrinkage. The results of the experiments permitted the prediction of long-term deformations of the concrete. Wider use of this material permit the construction of sustainable next generation structures with thin walls and large spans that cannot be built using the traditional concrete.

Finite Element Modeling of Drying Shrinkage in Concrete Blending with Mineral Admixtures

2011 ◽  
Vol 368-373 ◽  
pp. 1588-1594
Author(s):  
Tie Cheng Wang ◽  
Quan Min Peng
Keyword(s):  
Critical Factor ◽  
Drying Shrinkage ◽  
Moisture Diffusion ◽  
Shrinkage Strain ◽  
Mineral Admixtures ◽  
Granulated Blast Furnace Slag ◽  
Moisture Field ◽  
Adopted Model ◽  
Long Term Behavior

Drying shrinkage is a critical factor influencing the long-term behavior of concrete. In this paper, related parameters for calculating moisture field are discussed based on the theory of nonlinear moisture diffusion. Numerical simulation of shrinkage tests of concrete blending with fly ash and ground granulated blast furnace slag is conducted by ANSYS, considering the solution analogy between moisture field and temperature field. The calculated shrinkage strains are in good agreement with experimental results and the adopted model and finite elements method can be used to predict the time-dependent moisture field and shrinkage strain field in the real structure.

scholarly journals Modelling of Coupled Shrinkage and Creep in Multiphase Formulations for Hardening Concrete

Materials ◽  
2019 ◽  
Vol 12 (11) ◽  
pp. 1745
Author(s):  
Peter Gamnitzer ◽  
Andreas Brugger ◽  
Martin Drexel ◽  
Günter Hofstetter
Keyword(s):  
Viscous Flow ◽  
Effective Stress ◽  
Drying Shrinkage ◽  
Shrinkage Strain ◽  
Viscoelastic Creep ◽  
Limit Value ◽  
Shrinkage And Creep ◽  
Mechanical Models ◽  
Term Response

The durability and serviceability of concrete structures is influenced by both the early-age behavior of concrete as well as its long-term response in terms of shrinkage and creep. Hygro-thermo-chemo-mechanical models, as they are used in the present publication, offer the possibility to consistently model the behavior of concrete from the first hours to several years. However, shortcomings of the formulation based on effective stress, which is usually employed in such multiphase models, were identified. As a remedy, two alternative formulations with a different coupling of shrinkage and creep are proposed in the present publication. Both assume viscous flow creep to be driven by total stress instead of effective stress, while viscoelastic creep is driven either by total or effective stress. Therefore, in contrast to the formulation based on effective stress, they predict a limit value for shrinkage as observed in long-term drying shrinkage tests. Shrinkage parameters for the new formulations are calibrated based on drying shrinkage data obtained from thin slices. The calibration process is straightforward for the new formulations since they decouple shrinkage and viscous flow creep. The different formulations are compared using results from shrinkage tests on sealed and unsealed cylindrical specimens. Shrinkage strain predictions are significantly improved by the new formulations.

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