RD108-The Effect of Secondary Ettringite Formation on the Durability of Concrete-A Literature Analysis

Portland Cement Association Research and Development Bulletin RDlOST by Robert L. Day KEYWORDS: accelerated testing, alkali-aggregate reaction, alkalis, calcium aluminates, calcium hydroxide, carboaluminates, carbonation, cement, cement chemistry, chlorides, chloroaluminates, cracking, delayed ettringite formation, Duggan Test, durability, ettringite, expansion, gypsum, heat treatment, hydration, ions in solution, microcracking, monosulphoaluminate, pH, pore solution, porosity, precast concrete, precuring period, preferred orientation, secondary ettringite formation, strength, sulfates, sulfate/aluminate ratio, swelling pressure, tempera- ture, testing, thaumasite, railroad ties, transition zone. ABSTRACT: The report comprises a review and analysis of the available literature pertaining to the causes, effects and prevention ofsecondary (delayed) ettringite in concrete. Over 300publications have been examined. Case studies of damage in concrete possibly caused by secondary ettringite formation are examined first. Fundamental research on secondary ettringite formation, its chemistry, and deposition mechanisms is then reviewed. Key investigations on the topic are analyzed in detail. Next, the potential importance of (a)method of heat-curing and (b)the chemistry of cement is outlined. In the final chapter, a rapid test for evaluation of potential secondary ettringite susceptibility (the “Duggan” test) is evaluated. The analysis indicates that there appears to be a potential for a secondary ettringite formation problem in North America; it is highly probable that secondary ettringite formation can lead to significant deterioration of heat-treated concrete. However, it is unlikely that secondary ettringite formation is, or will be, the sole mechanism responsible for premature deterioration. The critical factors that determine extent of damage due to secondary ettringite formation are(a) duration of delay period before heating the concrete;(b) severity of the heating and/or cooling regime; and (c)the S03/A120~ ratio ofthe cement. There isno evidence that non heat-treated concrete is susceptible to this phenomenon. Further research and improvements to the Duggan test may result in the development ofa useful standard test method to assess the long-term dimensional stability and durability ofconcrete. REFERENCE: Day, R.L.,TheE~ecto~SecondwyEttringite Fonmfion on theDurabi~ityof Concrete: A Literature Analysis, Research and Development Bulletin RD108T,Portland Cement Association, Skokie, Illinois, U.S.A. 1992. MOTS CLI%: alcali, aluminate de calcium, bi%onpr6fabriqu6, carboaluminate, carbonatation, ciment, chimie du ciment, chlorures, chloroaluminates, dormant de chemin de fer, durability, essai, essai acc416r4 essai Duggan, ettringite, expansion, fissuration, formation retardde d’ettringite, formation secondaire d’ettringite, gypse, hydratation, hydroxyde de calcium, ions en solution, microfissuration, monosulfoaluminate, orientation pr4f4rentielle, PH, pc%iodeavant cure, porositd, pression de gonflement, rapport sulfate/aluminate, rdaction alcali-granulat, rkisistance, solution de pore, sulfate, temp&ature, thaumasite, traitement h la chaleur, zone de transition. Rl%UME: Le rapport consiste en une revue et une analyse de la littt%ature disponible en ce qui a trait aux causes, aux effets et 21la pn%ention de la formation secondaire (retard6e) d’ettringite clans le bdton. Plus de 300publications ont dtd examin~es. Des &udes de cas sur des b6tons endommagds, possiblement Acause de la formation secondaire d’ettringite, ont dtdexamindesenpremier. Larecherche fondamentalesurla formation retardde d’ettringite, sa chimie et ses mdcanismes de deposition est ensuite passde en revue. Les investigations d’importance sur le sujet sent analysdes en d&ail. Puis, l’importance potentielle de (a)la m&hode de cure iila chaleur et (b) la chimie du ciment est ddcrite. Dans le dernier chapitre, un essai accdldrdpour 6valuer le potentiel de formation retardde d’ettringite (1’essai “Duggan”) est dvalud. L’analyse indique qu’il est possible qu’il y ait des probl$mes de formation secondaire d’ettringite en Am6rique du Nerd. 11est tri% probable que la formation secondaire d’ettringite produise une d&6rioration importance du b6ton traitd Ala chaleur. Cependant, il est tr&speu probable que la formation secondaire d’ettringite, soit ou devienne, le seul mdcanisme responsible de d&6rioration pr6matur6e. Les facteurs critiques qui d&erminent l’ampleur des dommages dus ?ila formation secondaire d’ettringite sent (a) le ddlai avant chauffage du b&on, (b)la st%%itddu rdgime de chauffage ou de refroissement et (c)le rapport SO~/AlzO~du ciment. 11n’y a aucun indite ~l’effet que le b6ton non chauff6 soit susceptible ?Ice ph~nomhe. Dautres recherches et des ameliorations ~ I’essaiDugganpourraient mener iil’elaboration d’un essainormalisd utile pour determiner lastabilitd dimensionnelle Along terme et la durability du bdton. R~FfiRENCE: Day, R.L., TheEject ofSecondary Ettringite Formation on the Durability of Concrete: A literature Analysis, Research and Development Bulletin RD108T, Portland Cement Association [L’effet de la formation secondaire d’ettringite sur la durability! du btiton une analyse bibliographique. Bulletin de Recherche et D4veloppement RD108T,Association du Ciment Portland], Skokie, Illinois, U.S.A. 1992. Cover Illustrations: Ettringite (white needle-like crystals) in concrete exposed to phenolphthalien stain; atmospheric steam- curing cycle; and precast structure under construction. PCA R&D Serial No. 1929 PCA Research and Development Bulletin RD108T The Effect of Secondary Ettringite Formation on the Durability of Concrete: A Literature Analysis by Robert L. Day Professor of Civil Engineering Civil Engineering De artment The University oPCal a 2500 Universit Drive%x Calgary, Alberta, CanaJa T2N 1N4 ISBN 0-89312-1 69-X 42Portland Cement Association 1992 Page i Summary of Major Conclusions A review and analysis was performed of available literature pertaining to the causes, effects and prevention of secondary, or delayedl, ettringite in concrete. Over 300 publications were examined The principal findings from this project are: Given current Cement-prduction and concrete-construction practices there appears to be a potential for a secondary ettringite formation problem in North America. It is highly probable that secondary ettringite formation can lead to significant deterioration of heat- treated cxmcrete.The extent of the potential problem cannot be predicted with accuracy, but it is likely to involve a small fraction of the pre-cast concrete cast in North America. There is no evidence that secondary ettringite formation has been a principal cause of deterioration in non heat-treated concrete. There is some suggestion that formation of ettringite after initial deterioration by other means can accelerate the deterioration process. Massive formations of ettringite observed in huge cracks and pores appear, for the most part, to be innocuous. The critical factors that determine extent of damage due to secondary ettringite formation (all other factors being equal) are (a) duration of delay period prior to heating; (b) severity of the heating &Jor cooling r6gime; (c) the S03/A1203 ratio of the cement. Use of cements with an WA ratio greater than about 0.7 or an ~/A ratio greater than about 2.0 may result in concrete which+under particular curing and exposure conditions, is susceptible to secondary ettringite formation and subsequent deterioration. Good quality laboratory research confirms that secondary ettringite formation can pro- duce expansion and cracking of concrete made with certain North American commercial cements. In North America it is not unusual to find Type 30 cements with S03 contents in the range 3.5 to 4.0% — which could be as high as 4.5Y0.It is not unusual to find alumina contents of 5% or more and C3A contents of 9% or more. Calculation of the ~/A or ~/A ratios for such cements places them in the maximum expansion ranges determined by He- inz and Ludwig and by Gillott. Rapid heating and/or cooling and/or an inadequate delay period can result in microcracks — predominantly at the aggregate-paste or steel-paste interface. These cracks can act as nucleation sites for the later formation of ettringite. ‘Ihe aggregate-paste and steel-paste interface is a weak zone in the concrete that is high in both calcium hydroxide and ettringite contents. The ready availability of sulphates near the cracked interface provides pessimum conditions for secondary ettringite formation. The transition zone appears to be of higher quality when the interface involves limestone aggregate. This suggests that, all other factors being equal, concrete made with limestone aggregate may be less susceptible to secondary ettringite damage. Saturated, or almost saturated, concrete or concrete subjected to frequent wetting/drying cycles is essential to the formation of secondary ettringite and concrete darnage. Early excessive heat treatments at tem~ratures above approximately 70”C results in sub- stantial amounts of sulphates being bound in an unusual form. These sulphates can be 1 see Section 1.3for an explanationof the terminology“secondaryetlringite” Page ii slowly released back into solution at later ages. This slow release process provides a sup- ply of sulphate ions for secondary ettringite formation. The effect of secondary ettringite formation is substantially reduced by inclusion of an adequate air-entrainment void system in the concrete. Where potential

Load more