Influence of delayed ettringite formation on the mechanical properties of aerated concrete

Samo Lubej (Author), Andrej Ivanič (Author), Rebeka Rudolf (Author), Ivan Anžel (Author)

Abstract

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.

Keywords

ettringite;concrete;aerated concrete;microstructure;mechanical properties;

Data

Language:	English
Year of publishing:	2012
Typology:	1.01 - Original Scientific Article
Organization:	UM FS - Faculty of Mechanical Engineering
Publisher:	Inštitut za kovinske materiale in tehnologije Ljubljana
UDC:	666.9
COBISS:	16490518
ISSN:	1580-2949
Views:	878
Downloads:	80
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Other data

Secondary language:	Slovenian
Secondary title:	Vpliv zakasnele tvorbe etringita na mehanske lastnosti aeriranih betonov
Secondary abstract:	Zakasnela tvorba etringita (DEF) je kemična reakcija z dokazano škodljivim učinkom na mehanske lastnosti hidratiziranega betona. Kristali etringita lahko zaradi pozitivne prostorninske razlike med reaktanti in produkti povzročijo nastanek razpok, rast kristalov etringita na stenah razpok pa povzroči njihovo širjenje. Pri mladih betonih rast kristalov etringita poveča trdnost, v hidratiziranem betonu pa nastanek in napredovanje razpok, kar lahko povzroči tudi razpad betona. V tem članku predstavljamo idejo, kako bi lahko pozitivne volumenske spremembe, ki so posledica DEF v hidratiziranem, drobno zrnatem betonu izkoristili za izboljšanje mehanskih lastnosti. Pogoj za izboljšanje le-teh je zagotovljen z uporabo dodatka aeranta (AEA), s katerim v hidratiziranem betonu zagotovimo enakomerno razpršene zračne mehurčke, ki so nukleacijska jedra. Zgostitev betona smo izvedli z vibriranjem, ki lahko trajale kratek čas. V raziskavi smo prikazali način in postopek izdelave betona z enakomerno razpršenimi nukleacijskimi jedri iz zračnih mehurčkov. Kontrolo nabrekanja in mehanskih lastnosti smo opravili pri vzorcih betona z dodanim aerantom in brez njega z induciranjem zakasnele tvorbe etringita. Za raziskave mikrostrukture vzorcev drobnozrnatega betona smo uporabili optični in elektronski vrstični mikroskop. Ugotovili smo, da lahko z nadzorovano zakasnelo tvorbo etringita, ki je zagotovljena z dodanim aerantom in nastankom enakomerno razpršenih zračnih mehurčkov, ki so nukleacijska mesta za kristalizacijo etringita, izboljšamo mehanske lastnosti. Pri vzorcih z inducirano zakasnelo tvorbo etringita smo izmerili 6-odstotno večjo tlačno trnost.
Secondary keywords:	etringit;beton;aerirani beton;mikrostruktura;mehanske lastnosti;
URN:	URN:NBN:SI
Type (COBISS):	Scientific work
Pages:	str. 573-579
Volume:	ǂLetn. ǂ46
Issue:	ǂšt. ǂ6
Chronology:	nov.-dec. 2012
Keywords (UDC):	applied sciences;medicine;technology;uporabne znanosti;medicina;tehnika;building (construction) trade;building materials;building practice and procedure;gradbeništvo;gradbeni materiali;gradbene obrti in dela;building materials;building components;gradiva;gradbeni [konstrukcijski] deli;applied sciences;medicine;technology;uporabne znanosti;medicina;tehnika;engineering;technology in general;inženirstvo;tehnologija na splošno;materials testing;commercial materials;power stations;economics of energy;preiskava materiala;blagoznanstvo;energetske centrale;energetika;
ID:	1439225