Crack-free concrete / Noemi Nagy in EUROPEAN COATINGS JOURNAL (ECJ), N° 11 (11/2013)  

[article]  inEUROPEAN COATINGS JOURNAL (ECJ) > N° 11 (11/2013) . - p. 10-14 Titre : Crack-free concrete : Shrinkage-compensating concrete for the European construction industry Type de document : texte imprimé Auteurs : Noemi Nagy, Auteur ; Gabriele Fortunati, Auteur ; Akihiro Hori, Auteur Année de publication : 2013 Article en page(s) : p. 10-14 Note générale : Supplément "Construction chemicals" - Bibliogr. Langues : Anglais (eng) Catégories : Béton sans retrait Contraintes (mécanique) Matériaux -- Fissuration Matériaux cimentaires -- Détérioration Matériaux cimentaires -- Séchage Traction (mécanique) Index. décimale : 620.13 Matériaux de construction : pierre, ciment, béton, liants de Résumé : Shrinkage upon drying is an inherent property of concrete. Therefore concrete structures are prone to undergo considerable shrinkage within a few months, and they usually crack to relieve the tensile stress induced under restraint. Shrinkage-compensating concrete (SCC) eliminates unsightly shrinkage cracks, thereby improves durability, serviceability and reduces maintenance cost. Note de contenu : - Causes of shrinkage cracking - Areas of application - Figure 1 : Length change characteristics of Portland Cement and shrinkage-compensating concrete - Figure 2 : Restrained expansion under water, ASTM C878 - Figure 3 : Long term length change - Figure 4 : Compressive strength evolution - Figure 5 : Fresh concrete properties, drop table flow test - Figure 6 : Trial field application - Figure 7 : Curled joint edges, floor profile ; contraction joints at the peaks 6 m apart from each other, at 3, 9, 15 , 21, 27 and 33 m on the diagram En ligne : https://drive.google.com/file/d/12gxdCfW-0BYEShARiZN-t3gAcmxG0ovd/view?usp=drive [...] Format de la ressource électronique : Pdf Permalink : https://e-campus.itech.fr/pmb/opac_css/index.php?lvl=notice_display&id=19737 [article]

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Experimental study of the effect of curing mode on concreting in hot weather / Nassima Bakir in REVUE DES COMPOSITES ET DES MATERIAUX AVANCES, Vol. 31, N° 4 (08/2021)  

[article]  inREVUE DES COMPOSITES ET DES MATERIAUX AVANCES > Vol. 31, N° 4 (08/2021) . - p. 243-248 Titre : Experimental study of the effect of curing mode on concreting in hot weather Type de document : texte imprimé Auteurs : Nassima Bakir, Auteur Année de publication : 2021 Article en page(s) : p. 243-248 Note générale : Bibliogr. Langues : Français (fre) Catégories : Humidité Matériaux -- Effets du climat Matériaux cimentaires -- Propriétés mécaniques Matériaux cimentaires -- Séchage Polyéthylène Polymérisation Température Index. décimale : 668.9 Polymères Résumé : Most developing countries have hot climate, ordinary jobsites characterized by reduced of human resources, equipment and infrastructures. The objective of this article is to make an experimental study of the influence of the hot climate such as that of Algeria, on the different properties of concrete in the fresh state, such as excessive water evaporation from the concrete surface, increased demand for water, increased slump loss corresponding to additional water on job-site, higher plastic shrinkage cracking and difficulty in controlling air content. At the hardened state, we could mention a reduction of strength at 28 days, decreased durability resulting from cracking at long-term period. To show the problems linked to concreting under these conditions and to present the appropriate solutions concrete or mortar can withstand the conditions in which it is implemented. Thus, negative effects caused principally by hot weather concreting motivated the choice of the such study. The research experimental work conditions in which the cementitious matrix was kept concerned two different environments, namely hot and dry climate conditions (t = 40°, h = 0%) alike the climate of the region of M'sila., and that of a medium with a hot and humid environment (t = 40°, h = 100%). The output of the investigation demonstrated the crucial role of the cure method in hot regions. The comparison of results for a reference concrete kept in air without any curing measures with two curing types simulating hot weather environment of the region M’sila was undertaken. These obtained outcome results were discussed based on the influence of climatic conditions to conclude procedures for hot weather concreting and suitable cure methods. Note de contenu : - MATERIALS - EQUIPMENT AND PROCEDURES : Equipment - Procedures - Tests carried out - RESULTS AND DISCUSSION : Influence of curing methods on compressive and tensile strength Influence of storage conditions on compressive and tensile strength - Influence of curing and climatic storage conditions on the absorption of the mortar - Table 1 : Chemical composition of the cement used - Table 2 : Mineralogical composition of the cement used - Table 3 : Storage conditions of the test pieces DOI : https://doi.org/10.18280/rcma.310408 En ligne : https://www.iieta.org/download/file/fid/60233 Format de la ressource électronique : Pdf Permalink : https://e-campus.itech.fr/pmb/opac_css/index.php?lvl=notice_display&id=37675 [article]

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No magic number / R. A. Nixon in JOURNAL OF PROTECTIVE COATINGS & LININGS (JPCL), Vol. 35, N° 9 (09-10/2018)

[article]  inJOURNAL OF PROTECTIVE COATINGS & LININGS (JPCL) > Vol. 35, N° 9 (09-10/2018) . - p. 24-31 Titre : No magic number : coating concrete after 28 days Type de document : texte imprimé Auteurs : R. A. Nixon, Auteur Année de publication : 2018 Article en page(s) : p. 24-31 Note générale : Bibliogr. Langues : Américain (ame) Catégories : Matériaux cimentaires -- Revêtements:Matériaux cimentaires -- Peinture Matériaux cimentaires -- Séchage Rétrécissement (matériaux) Index. décimale : 667.9 Revêtements et enduits Résumé : Historically, the coating industry has prescribed 28 days of cure time for concrete before coating application. The 28-day threshold was based on conventionally specified strength gain values such as a minimum of 5,000 psi compressive strength at 28 days. The logic behind the adoption of the 28-day rule was twofold. Firstly, the majority of minimum specified strength gain is empirically reached within the first 28 days. Therefore, if the compressive strength has mostly been achieved, then most of the tensile stress that forms cracks will have developed. This assumes that most of the shrinkage of the cement paste has largely occurred but ignores the all-important water-to-cementitious-materials ratio and the paste-to-aggregate ratio. These are the major contributors to shrinkage along with temperature and timing of excess moisture loss from the concrete. Coincidently, these factors are both inextricably tied to the water content in the mix design, which leads us to point number two. Typically, it is believed that all of the excess water not necessary for cement hydration has left the concrete after 28 days. Therefore, the detrimental effects from the exit of moisture from the concrete on coating cure or coating adhesion have been eliminated. This assumes that excess moisture leaving the concrete after 28 days will not inhibit a coating's curing mechanisms. This also ignores the material principles at work in cement hydration. The problem with the magic 28-day number is that there is just as much empirical evidence that 28 days isn't necessary, as there is for its requirement or a longer cure time prior to coating. This article will discuss the many factors affecting the timing for concrete shrinkage (and related cracking) as well as the rate of loss of excess moisture - factors that are not reliant on 28 days of concrete cure time. In addition, case histories will be presented evidencing sucessful coating application on concrete well before 28 days of cure time versus coating problems experienced well beyong 28 days of concrete cure. Further, we will examine mix design and material-related parameters that should be followed when scheldule needs for coating concrete prior to 28 days of cure are essential. Note de contenu : - The basics - Drying shrinkage and excess water in concrete substrates - Real-world experience - Fig. 1 : Concrete shrinkage increases with the water-to-cement for a given aggregate content - Fig. 2 : This graph shows the typical effect of water content on drying shrinkage - Fig. 3 : Reflective cracking which appeared approximately one month after a floor coating system was installed in a pharmaceutical plant - Fig. 4 : No reflective cracking and no moisture-related problems have been observed since this floor coating was installed in a building at a wastewater treatment plant after two years in service - Fig. 5 : Blisters formed in the coating on concrete walls in a wastewater treatment plant only two months after installation Permalink : https://e-campus.itech.fr/pmb/opac_css/index.php?lvl=notice_display&id=31893 [article]

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