Class phpc concrete is used for prestressed concrete when strengths in excess of 41 mpa are specified and should always be used for specified concrete strengths greater than 69 mpa. If concrete is exposed to water for a long period of time, the primary ettringite will dissolve and recrystallize in voids. Heat evolution during the acceleration and deceleration phases was reduced and the exotherm arising from renewed ettringite formation was delayed and diminished in the presence of bi 2 o 3. The experimental program described in this paper confirms the. Def is expansion and cracking of concrete associated with the delayed formation of the mineral ettringite a hydrated calcium sulfoaluminate which is a normal product of early cement hydration. Recommendations for preventing disorders due to delayed ettringite. Significance of delayed ettringite formation and damage mechanisms the primary ettringite formation in the initial stage of the hydration is seen as a positive effect because it read more. In this paper, the effect of fly ash on delayed ettringite formation of heatcured cementbased mortars was investigated. Delayed ettringite formation processes and problems. The degradation of concrete structures caused by delayed ettringite formation def is a problem that affects many concrete structures worldwide 1. Some cases have unfortunately been catalogued in france, and are significant. Smaller but distinct ettringite deposits on oppo site sides of a sand grain. Droplets formation and merging in twophase flow microfluidics.
The primary ettringite a hydrous calcium trisulphoaluminate is a normal reaction product formed from the reaction of c 3a and c 4af with gypsum during the plastic stage of the hydration of portland cement. Scribd is the worlds largest social reading and publishing site. Expansion results from formation of ettringite crystals of submicrometre size in the paste. Preventing alkalisilica reaction and delayed ettringite. There have been far fewer documented cases of def than of asr, and prior to this project, there were no published cases in which def was the sole culprit in causing deterioration in an actual field structure. Delayed ettringite formation how is delayed ettringite. Properties of concrete, first published in 1963, has been internationally acclaimed as the definitive work of reference on the subject for both the professional and the student engineer the fifth edition has been updated to reflect advances in concrete technology over the past decade without losing sight of the original aim. For a pavement that is experiencing accelerated deterioration due to delayed ettringite formation, and that is near a minimum service level condition i. To fulfil the aim of this study, a portion of cement was replaced by class ffly ash, with three. His research was geared toward improving code predictions of prestress loss and shear strength. The article presents a summary of the legal case entitled lone star industries, inc. Delayed ettringite formation delayed ettringite formation is a less common, but potentially more damaging, cause of distress than asr. Techniques for producing droplets can be either passive or active, the latter meaning that external fields are activated at the time and onchip location where. Generally high dosage of ettringite amount contributes to dimentional stability.
The two main chemicals attacks to concrete are attributed to alkaliaggregate reaction aar and the action of sulphates, among which stands out the delayed ettringite formation def delayed ettringite formation. It also occurs as weathering crusts on larnite in the hatrurim formation of israel. The international concrete abstracts portal is an aci led collaboration with leading technical organizations from within the international concrete industry and offers the most comprehensive collection of published concrete abstracts. Asr and delayed ettringite formation def, both concrete internal distress mechanisms. Delayed ettringite formation request pdf researchgate. Impact of the conditions of ettringite formation on ternary systems ettringite hydration products in ternary systems have a strong effect on setting time. A hydraulic cement composition is disclosed which utilizes as part of an expansive component novel coated particles of high alumina cement. Secondary ettringite formation sef is nondestructive. The expansive sulphate internal reaction due to delayed ettringite formation def can damage concrete structures severely. Pdf this version is fully searchable, and interactive. Def is a result of high early temperatures above 70 o c 80 o c in the concrete which prevents the normal formation of ettringite.
However, ettringite, found in this benign state as large. Delayed ettringite formation has been a significant problem in many countries. Delayed ettringite formation def is a possible autogenous expansive reaction of concrete. Pdf delayed ettringite formation in fly ash concrete. Investigations have now also been carried out into this formation of new phases, known as late ettringite formation, which takes place under normal ambient. Risk analysis of the delayed ettringite formation in pile. Over the last decade, a number of reinforced concrete bent caps within houston, texas have exhibited premature concrete damage cracking, spalling and a loss of material strength due to alkalisilica reaction asr andor delayed ettringite formation def. Delayed ettringite formation an overview sciencedirect topics. Droplet formation can be considered as the first step in the microfluidic life cycle. Damage due to the delayed ettringite formation allegedly occurs when material is exposed to temperatures higher than 70c 3,4. Distributed damage in concrete is associated with microcracking due to delayed ettringite formation def, alkali silicate reaction or freeze thaw ft cycles. Investigation of reinforced concrete damage due to cryogenic liquefied natural gas lng exposure university of texas at. Delayed ettringite formation in concrete imx technologies.
Risk of delayed ettringite formation in concrete heated at. It occurs associated with portlandite, afwillite and. Introduction delayed ettringite formation def may be defined as the formation of ettringite in a cementitious material by a process that begins after hardening is substantially complete and in which none of the sulfate comes from outside the cement paste. Delayed ettringite formation def is a cause of disorders capable of damaging concrete structures quite severely. Delayed ettringite formation rocesses and problems 209 fig. After several months or years, ettringite can form again if a new source of sulfate becomes available in the pore solution of the paste, viz. Damage in conjunction with ettringite formation in hardened concrete was first identified in heattreated. In the hydration of the portland cement sample examined by skibsted et al. It is important to differentiate between early ettringite and delayed ettringite formation as this can have an impact on precast concrete beam manufacture. Lehmann, for an occurrence near the ettringer bellerberg volcano, ettringen, rheinlandpfalz, germany. Sulfate resistance of nanosilica contained portland cement. The aim of this study is to assess the coupling effects between some of the main parameters of this. Ettringite crystals in air voids and cracks are typically 2 to 4 micrometers in crosssection and 20 to 30 micrometers long.
The particles have a core of substantially unhydrated high alumina cement and an outer layer of hydration products of the core, which outer layer delays the reaction of the particles with other materials in the composition. Lone star manufactured approximately 500,000 railroad ties using a combination of crushedrock aggregate, type iii moderate highalkali cement, and manual steam curing. Impact of bi2o3 and zro2 radiopacifiers on the early. Strategies for prevention of delayed ettringite formation in large. Delayed ettringite formation aci concrete code issues. Delayed ettringite formation delayed ettringite formation def is a special case of internal sulfate attack.
A possible metric for quantifying this type of damage by ultrasonic ndt is the q factor, which is the ratio of. The effect of natural pozzolan on delayed ettringite formation of the. Claims that slow release of sulfate from the clinker can have a similar effect in concrete not thus heated are unsupported. Delayed ettringite formation delayed ettringite formation gpfuan civilenvironmental op 9 mar 01 10.
Delayed ettringite formation archives civildigital. Delayed ettringite formation def is expansion and cracking of concrete associated with the delayed formation of the mineral ettringite which is a normal product of early cement hydration. Ettringite and monosulfate are also thought to occur in minute crystals closely intermixed with and occupying space within individual inner product or hydrated phenograin csh deposits in ordinary. Deschenes also extensively studied the structural implications of alkalisilica reaction asr and delayed ettringite formation def, both concrete internal distress mechanisms. It can affect materials that have experienced temperatures higher than about 65 c at early age. Many different techniques have been developed to obtain fine control over the size distributions and shape of droplets. Delayed ettringite formation is a relatively rare and controversial phenomenon in concrete deterioration, strongly related to the practice of heat curing. Reduction of concrete deterioration by ettringite using. Server core free download as powerpoint presentation. 2r96, use of fly ash in concrete, aci manual of concrete practice, part 1. This reaction ends as soon as the sulfate concentration, needed for forming the ettringite, decreases below the limit. It occurs in concrete which has been cured at elevated temperatures, for example, where steam curing has been used. Qin, relationship between delayed ettringite formation and delayed expansion in massive shrinkagecompensating concrete, cement and concrete composites, vol.
If both ettringite formation and concrete deterioration are simultaneously reduced, then the case. This pathology is due to the formation of expansive ettringite inside the. However, quantitative evidence of def risk for concrete submitted to similar heating when mature is still scarce. Delayed ettringite formation def is an internal sulfate attack caused by. Preventing asrdef in new concrete center for transportation. Combining with the utilization of waste, an new idea of using the.
Many researchers have concluded that secondary or delayed ettringite is responsible for. Effect of curing conditions and concrete mix design on the. Delayed ettnngite formation def is an endogenous reaction which can cause deterioration. Influence of mineral additions in the inhibition of delayed ettringite. Impact of the conditions of ettringite formation on. It occurs within metamorphically altered limestone adjacent to igneous intrusive rocks or within xenoliths. Ettringite formation in hardened concrete and resulting.
Delayed ettringite because primary ettringite is unstable above 160f, it wont form if curing. Request pdf delayed ettringite formation delayed ettringite formation def can. Ettringite formation and the performance of concrete portland. The latter is caused by the delayed formation of ettringite in a cementitious material and occurs in particular because of a significant heating of the concrete. Delayed ettringite formation def can damage concrete that has. Pdf delayed ettringite formation fami fami academia. Mpa cement fact sheet 3 delayed etttringite formation in. Clicking on an entry in the table of contents will take. Appendix eproposed revisions to the aashto lrfd bridge. In this sample, the mean chain length mcl of the csh gel rose from 2. The effect of the partial cement substitution with fly ash. Experimental pore scale analysis and mechanical modeling of. Factors affecting durability of concrete aggregate. Lessons learned from structures damaged by delayed.
At this stage the concentrations of calcium and sulfate ions in a pore fluid fall to low levels so that continued hydration of the cement takes place in a solution principally of alkali. In turn, the durability of concrete structures can often be affected by chemical attacks, endangering its performance and safety. Alkalisilica reaction and delayed ettringite formation. Alkalisilica reaction asr and delayed ettringite formation def, or combinations of the two, have been found to be the main causes of these problems. Secondary ettringite this is present in hardened, moist concrete.
Early c3a hydration in the presence of different kinds of. Procedures for quantifying the potential degree of future def development in concrete, using accelerated hydration and dta determination of any additional ettringite developed. Under conditions of extreme deterioration, and repeated wetting and drying, ettringite crystals can appear to completely fill voids or cracks. Examples of sulfate attack include ettringite formation, delayed ettringite. Concrete deterioration concerns include, but are not limited to, alkalisilica reactions, delayed ettringite formation, carbonation, longitudinal cracking around corroded reinforcing steel, and laminar cracking at the location of the steel reinforcement. Increases in the mean silicate chain length and the extent of aluminum substitution. Microsoft excel 2007introduction free download as word doc. Many studies have shown the effect of different parameters on the expansion induced by delayed ettringite formation def, but there is not yet a general agreement on their relative effects due to discrepancies on experimental results generally attributed to different experimental conditions. Ettringite formation and the performance of concrete. The conditions of development of delayed ettringite formation def in concrete when submitted to excessive heating during hydration and setting have deserved recent research efforts and tend to be better understood.
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