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1.
Potential reduction of concrete deterioration through controlled DEF in hydrated concrete
Samo Lubej, Milan Radosavljević, 2013, izvirni znanstveni članek

Opis: Delayed ettringite formation (DEF) is a chemical reaction with proven damaging effects on hydrated concrete. Ettringite crystals can cause cracks and their widening due to pressure on cracked walls caused by the positive volume difference in the reaction. Concrete may show improvements in strength at early ages but further growth of cracks causes widening and spreading through the concrete structure. In this study, finely dispersed crystallization nuclei achieved by adding air-entraining agent (AEA) and short vibration of specimens is presented as the main prerequisite for reducing DEF-induced deterioration of hydrated concrete. The study presents the method and mechanism for obtaining the required nucleation. Controlling long-term DEF by providing AEA-induced crystallisation nuclei, prevented excessive and rapid initial strength improvements, and resulted in a slight increase of compressive strength of fine grained concrete with only marginally lower density.
Ključne besede: delayed ettringite formation, aerated concrete, strength improvement
Objavljeno v DKUM: 10.07.2015; Ogledov: 1514; Prenosov: 31
URL Povezava na celotno besedilo

2.
Influence of delayed ettringite formation on the mechanical properties of aerated concrete
Samo Lubej, Andrej Ivanič, Rebeka Rudolf, Ivan Anžel, 2012, izvirni znanstveni članek

Opis: Delayed ettringite formation (DEF) is a chemical reaction with proven damaging effects on the mechanical properties of a hydrated concrete. Ettringite crystals can cause cracks and their widening due to the pressure on the crack walls caused by a positive volume difference in the reaction. Concrete may show improvements in strength at early stages, but a further growth of the cracks causes widening and spreading of these cracks through the concrete structure. In a hydrated concrete, crystals of ettringite can also cause a disintegration of the concrete. In this paper we investigate the potential to utilise a positive volume difference in DEF in order to improve the mechanical properties of a hydrated fine-grained concrete. Finely dispersed crystallization nuclei, achieved by adding an air-entraining agent (AEA) and a short vibration of specimens, is presented as the main prerequisite for such improvements. The control of the expansion and mechanical properties were performed on the concrete samples with and without AEA by inducing DEF. For a microstructure examination of the fine-grained concrete an optical microscope and a scanning electron microscope were used. We found that controlled DEF, which is guaranteed by adding AEA and with the formation of the uniformly dispersed air bubbles, which are the crystallization sites for ettringite crystals, improves the mechanical properties. The specimens with induced DEF were measured and found to have a 6% increase in the compressive strength.
Ključne besede: ettringite, concrete, aerated concrete, microstructure, mechanical properties
Objavljeno v DKUM: 10.07.2015; Ogledov: 1396; Prenosov: 115
.pdf Celotno besedilo (426,54 KB)
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