817 research outputs found
Can superabsorbent polymers mitigate shrinkage in cementitious materials blended with supplementary cementitious mateirals?
Get PDFA promising way to mitigate autogenous shrinkage in cementitious materials with a low
water-to-binder ratio is internal curing by the use of superabsorbent polymers. Superabsorbent
polymers are able to absorb multiple times their weight in water and can be applied as an
internal water reservoir to induce internal curing and mitigation of self-desiccation. Their
purposefulness has been demonstrated in Portland cement pastes with and without silica
fume. Nowadays, fly ash and blast-furnace slag containing binders are also frequently used in
the construction industry. The results on autogenous shrinkage in materials blended with fly
ash or blast-furnace slag remain scarce, especially after one week of age. This paper focuses
on the autogenous shrinkage by performing manual and automated shrinkage measurements
up to one month of age. Without superabsorbent polymers, autogenous shrinkage was reduced
in cement pastes with the supplementary cementitious materials versus Portland cement
pastes. At later ages, the rate of autogenous shrinkage is higher due to the pozzolanic activity
of the supplementary cementitious materials. Internal curing by means of superabsorbent
polymers is successful, independent of this long-term higher rate of shrinkage in mixtures
with supplementary cementitious materials. Superabsorbent polymers proved to be successful
in mitigating self-desiccation
Healcon: self-healing concrete to create durable and sustainable concrete structures
Get PDFWithin the theme ‘Self-healing materials for prolonged lifetime’ (NMP.2012.2.1-3) of the Seventh Framework Programme, self-healing concrete is an important topic. The project HEALCON, which deals with self-healing concrete to create durable and sustainable concrete structures, is funded by EU-FP7 and started in January 2013. The coordinator of the project is Prof. Nele De Belie (UGent) and the consortium partners are UGent, Avecom, TU Delft, Acciona, TUM, TTI, VTT, COWI, DTI, CEINNMAT, Devan and Fescon.
Adequate perpetuation of the road, tunnel and bridge network, is crucial to preserving European cohesion and business operations; and around 70% of this infrastructure is made of concrete. In order to garantuee liquid tightness of concrete structures, and enhance durability of elements prone to bending cracks, smart concrete with selfhealing properties will be designed.
Thanks to the existing expertise of the consortium in the field of self-healing concrete at a lab-scale, a thoughtful selection of promising techniques is possible.
- For early age cracks, a non-elastic repair material can be proposed, such as calcium carbonate precipitated by bacteria, or new cement hydrates of which the formation is stimulated by the presence of hydrogels.
- For moving cracks under dynamic load, an elastic polymeric healing agent is suggested.
Different healing agents and encapsulation techniques are tested and scaled up. Self-healing efficiency is evaluated in lab-scale tests using purposefully adapted monitoring techniques, and optimized with the help of suitable computer models.
Finally the efficiency is validated in a large scale lab test and implemented in an actual concrete structure. Life-cycle cost analysis will show the impact of the selfhealing technologies on economy, society and environment compared to traditional construction methods
Een monument voor het land : overheidsstatistiek in België, 1795-1870
Get PDFIn A monument to the country. Official statistics in Belgium, 1795-1870, Nele Bracke unravels why and how the Belgian state and its predecessors organized and developed an official statistical apparatus in order to collect numerical information. The study captures the underlying objectives and structures, as well as the methods to compile statistics. Nele Bracke investigates the meaning and significance of government statistics in the 19th-century State and society. In Belgium, early social scientists established an internationally renowned ‘statistical system’ designed to collect information about the country, the people and the society. This ‘statistical system’ was built around the ‘Commission centrale de Statistique’ (statistical committee) and the production of demographic, economic and agricultural censuses. In the first part of the book, the author analyzes the institutional history of the ‘Commission centrale de Statistique’ and its predecessors. In the second part of the book, she studies the censuses
Comparison of reaction degrees of slag and fly ash obtained by thermogravimetry and selective dissolution
Get PDFThe evolution of the reaction degree of supplementary cementitious materials (SCM) with
time is an important aspect regarding the design and use of blended cements. However, this
quantification is complex due to the multiple actions of SCM in the cementitious system, such
as the filler effect, the consumption of CH and the formation of secondary calcium silicate
hydrates. In this sense, different methods for the estimation of the reaction degree may be
recommended for each type of SCM. Some of them are indirect methods that quantify
hydration products and compute a reaction degree on that basis, e.g. thermogravimetric
analysis, and others are direct methods that measure the amount of unreacted SCM, e.g.
selective dissolution. In this paper, thermogravimetric analysis and selective dissolution are
applied to estimate the reaction degree of cement pastes admixed with 40% slag or 30% fly
ash. Curing periods ranged from 1 till 90 days. Results from both methods are compared and
some comments on practicalities for their application are made. Although not enough
evidence could be collected for any of the applied methods to be considered as a reference
method, the simultaneous application of these two techniques offers increased reliability than
when only one method is applied
Chloride penetration in concrete under compression or splitting tensile load representing 60-65 per cent of the ultimate load
Get PDFA critical loading ratio is reached at 50% of concrete ultimate load. Beyond this point the
presence of micro cracks exerts a big influence on the chloride transport. For compression the
strain distribution in the sample developed micro-cracking system that is more or less
homogeneously distributed in the sample. Therefore it is expected the same chloride profile
regardless of the position. When combined splitting tensile load and chloride attack are acting
on concrete, the main micro-crack system is located on the loading plane. This contributes to
regular and alike shaped chloride profiles if they are taken from planes that are kept parallel to
the splitting one. Prismatic samples (100 x 100 x 400 mm) made of OPC binder were exposed
to a 3% by weight sodium chloride solution while maintaining a loading ratio equal to 60 %
of the maximum capacity. Cubic samples (side = 150 mm) made of OPC and 50% BFS had
similar chemical exposure while applying a permanent splitting tensile load corresponding to
65 % of their breaking capacity. After the exposure, ground layers were obtained from the
samples to determine the total chloride ingress into the concrete by means of potentiometric
titration and the effect of the load on the chloride ingress was assessed
Een monument voor het land. Overheidsstatistiek in België, 1795-1870
Get PDFIn A monument to the country. Official statistics in Belgium, 1795-1870, Nele Bracke unravels why and how the Belgian state and its predecessors organized and developed an official statistical apparatus in order to collect numerical information. The study captures the underlying objectives and structures, as well as the methods to compile statistics. Nele Bracke investigates the meaning and significance of government statistics in the 19th-century State and society. In Belgium, early social scientists established an internationally renowned ‘statistical system’ designed to collect information about the country, the people and the society. This ‘statistical system’ was built around the ‘Commission centrale de Statistique’ (statistical committee) and the production of demographic, economic and agricultural censuses. In the first part of the book, the author analyzes the institutional history of the ‘Commission centrale de Statistique’ and its predecessors. In the second part of the book, she studies the censuses
Een monument voor het land. Overheidsstatistiek in België, 1795-1870
Get PDFIn A monument to the country. Official statistics in Belgium, 1795-1870, Nele Bracke unravels why and how the Belgian state and its predecessors organized and developed an official statistical apparatus in order to collect numerical information. The study captures the underlying objectives and structures, as well as the methods to compile statistics. Nele Bracke investigates the meaning and significance of government statistics in the 19th-century State and society. In Belgium, early social scientists established an internationally renowned ‘statistical system’ designed to collect information about the country, the people and the society. This ‘statistical system’ was built around the ‘Commission centrale de Statistique’ (statistical committee) and the production of demographic, economic and agricultural censuses. In the first part of the book, the author analyzes the institutional history of the ‘Commission centrale de Statistique’ and its predecessors. In the second part of the book, she studies the censuses
Particle size distribution and specific surface area of SCM's compared through experimental techniques
Get PDFSupplementary cementitious materials (SCMs) are mainly used to produce a green concrete.
To reach that goal effectively, it is highly important to adequately characterize the SCMs. It is
well known that particle size distribution (PSD) and fineness of SCMs have a great influence
on concrete properties. Traditionally, cement fineness has been assessed by the specific
surface area (SSA) through the Blaine method (BM). However, the BM has the simplification
of considering ideal spherical shape particles. The BET theory has also been used to calculate
SSA, however, also some assumptions may lead to inaccuracy in the calculations. Both PSD
and SSA can be evaluated through Laser Diffractometry (LD), but this technique also
considers ideal spherical particles as a simplification. Regardless of the mentioned drawbacks,
these techniques provide useful information to characterize SCMs provided that the
limitations are considered. In this paper, Ground Granulated Blast Furnace Slag (GGBFS),
Natural Pozzolan (NP) and Limestone Powder (LP) are tested using the BM, LD, and nitrogen
adsorption. Particle texture and shape are assessed through petrography and scanning electron
microscope (SEM). Results from BM, BET and LD are compared, analysing the possible
effects of particle shape and texture
Influence of particle size distribution of slag, limestone and fly ash on early hydration of cement assessed by isothermal calorimetry
Get PDFSupplementary cementitious materials (SCMs) enhance early hydration of cement through the
provision of nucleation sites for the precipitation of hydration products. This effect contrasts
with the dilution effect of the mineral addition to the cementitious system. In fact, the net
effect on heat release during the first hours of hydration is the reduction of peak intensity.
Then, only when the specific heat is evaluated in terms of cement weight the actual effect of
the admixture on hydration may be assessed. In this sense, a clear difference may be expected
in accordance with the replacement ratio and fineness of the SCM. Increased specific surface
favors nucleation and it therefore enhances hydration. In this paper, cement pastes admixed
with slag, limestone and fly ash in three different fineness levels and three replacing ratios
were investigated through isothermal calorimetry. The filler effect of each SCM was in
relation with the fineness and replacing ratio, with higher impact on the aluminate reaction
than on the silicate reaction of cement
Evidence for a role of nitric oxide in iron homeostasis in plants
No full textNitric oxide (NO), once regarded as a poisonous air pollutant, is now understood as a regulatory molecule essential for several biological functions in plants. In this review, we summarize NO generation in different plant organs and cellular compartments, and also discuss the role of NO in iron (Fe) homeostasis, particularly in Fe-deficient plants. Fe is one of the most limiting essential nutrient elements for plants. Plants often exhibit Fe deficiency symptoms despite sufficient tissue Fe concentrations. NO appears to not only up-regulate Fe uptake mechanisms but also makes Fe more bioavailable for metabolic functions. NO forms complexes with Fe, which can then be delivered into target cells/tissues. NO generated in plants can alleviate oxidative stress by regulating antioxidant defense processes, probably by improving functional Fe status and by inducing post-translational modifications in the enzymes/proteins involved in antioxidant defense responses. It is hypothesized that NO acts in cooperation with transcription factors such as bHLHs, FIT, and IRO to regulate the expression of enzymes and proteins essential for Fe homeostasis. However, further investigations are needed to disentangle the interaction of NO with intracellular target molecules that leads to enhanced internal Fe availability in plants.RKT is grateful to Department of Science and Technology-Science and Engineering Research Board (DST-SERB) New Delhi, for a Teachers Associateship for Research Excellence (TAR/2019/000064).Tewari, RK (corresponding author), Univ Lucknow, Dept Bot, Lucknow 226007, Uttar Pradesh, India.
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