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. The aft phase ettringite forms rapidly in cements containing natural pozzolanas 197 or fly ash. Ettringite is a calcium aluminum sulfate mineral characterized by high water content, estimated as 32 water molecules per formula unit. In terms of workability of cement based materials, ettringite formation is of major importance. Synthetic, phase pure ettringite has been exposed to a moist co2 atmosphere at 68 and 88% relative humidity rh both at 2125 degrees c and at 40 degrees c. The cement slurry is placed between the casing and the drilled formation for adequate zonal isolation for the lifetime of the well 1. Ettringite formation and sulfate attack on concrete synopsis. This pathology in the chemistry of cement and concrete has been well recognized as delayed ettringite formation def.
Cement on the go portland cement, concrete, and heat of hydration fig. Secondary ettringite is not detrimental to concrete performance. Chemistry of calcium nitrilotrismethylenetriphosphonate. Reasons for the apparent newness of the phenomenon, and. Trbs national cooperative highway research program nchrp webonly document 145. The influence of the neat pregrinding duration on the reaction conversion is a subject of current research. The milestone paper on this subject comes from yamada and hanehara 2001. Ettringite has wide technical application in the ceramic and paper industry. Its hydration leads to the formation of ettringite c6as3h32, iron hydroxide and. The hydration products were investigated using xray diffraction, fourier transform infrared and scanning electron microscopy. Research and development bulletin rdlost by robert l. Perspective overview of delayed ettringite formation and. The hydration of the rapid set cement causes the formation of ettringite crystals in a slightly expansive process. This is because the surface of the columnar parts in ettringite is surrounded by structural water molecules that can interact with oh groups of strongly polar solvent molecules to form hydrogen bonds that can directly exfoliate selenate ettringite and convert to.
It is a shorthand way of writing the chemical formula of oxides of calcium, silicon, and various metals. The mortars steamcured at a temperature 90c exhibit a significant expansion caused by the delayed ettringite. Heat accelerated curing alkali load reactive aggregate moisture cement so 4. The ettringite superplasticizer interaction and its impact on the ettringite distribution in cement suspensions by f. Effect of curing temperature and cement chemistry on the potential for concrete expansion due to def article pdf available in pci journal 491 september 2004 with 514 reads how we measure. Glossary of some terms used in cement, concrete and in the. Well completion michel michaux erik nelson benoit vidick saint etienne, france faced with the concrete skyline. Effect of calcium sulfate on the formation of ettringite. Specifically, some fine aggregates will yield vastly different expansions. Effect of ettringite morphology on the properties of expanding cement systems.
Ettringite formation and the performance of concrete portland. Ettringite is also known as c ement bacillus, which is the name of a naturally occurring mineral of the same composition and structure. Other important variations in portland cement chemistry often escape notice in considerations of permeation capacity. If you missed out on chemistry at school, or it just seems a long time ago, the following short notes might be useful. Final cement strength is pro vided mainly by the amorphous csh gel created by the cement s hydrating sili cate components. Cement chemistry role of superplasticiser in construction industry role of corrosion. Synthesis, crystal chemistry and stability of ettringite, a material with potential applications in hazardous waste immobilization volume 245 gregory j. Preventing alkalisilica reaction and delayed ettringite. Ettringite solubility and geochemistry of the ca oh al so. Cement chemistry cement hydration reaction of cement with water exothermic. The formation of ettringite in the fresh, plastic concrete is the mechanism that controls stiffening. Ettringite formation and sulfate attack on concrete by m. Thermal stability of ettringite exposed to atmosphere.
The effect of 5% magnesium sulfate solution on the formation of secondary ettringite was examined for different time intervals, 3, 7, 28, 60 and 90 days. Damage of concrete due to sulfate attack is one of a serious problem for the durability of concrete structures. A peculiarity of cement chemistry is that very small differences in analytical cao contents mark major differences in the relative proportions of the calcium silicate components c 3 s and. The extent of the potential problem cannot be predicted with. Chemistry of ettringite and thaumasite recommended practice. In addition, the effects of nonreactive aggregates in this test were found to be dramatic in some cases. Ettringite solubility and geochemistry of the ca oh al so h. From a cement chemistry perspective, there are three causes for the reduced shrinkage of rapid set cement. Pdf effect of curing temperature and cement chemistry on. Recommended practice for stabilization of sulfaterich subgrade soils examines the nature of minerals ettringite and thaumasite, and explores the mechanism of their formation in soils stabilized with lime, cement, or fly ash. Pdf kinetic model to predict cement susceptibility to delayed. Vibrational spectroscopy of functional group chemistry and arsenate coordination in ettringite satish c.
Chemistry of ettringite and thaumasite recommended. Water cement grains csh ettringite hydration of the aluminate components, cra and gaf, with and without gypsum. This compound is however responsible for the longterm strength of portland cement concrete. Micromechanical modelling of sulphate corrosion in. Ettringiterelated dimensional stability of co2cured. The mineral compound ettringite ca 3 aloh 6 2 so 4 3 26h 2 o occurs rarely in nature, but is common for cementbased materials. The decomposition behavior of ettringite, ca6al2so43oh1226h2o, at different temperatures was studied by means of isothermal xrd experiments, in which the evolution of the solid is monitored as a function of time. The ettringite superplasticizer interaction and its. Nearly all the so 4 2gets combined to form ettringite in an ordinary portland cement. Cement chemist notation ccn was developed to simplify the formulas cement chemists use on a daily basis.
Influence of grout and cement on groundwater composition. Research and development bulletin rdlost americas cement. It is highly probable that secondary ettringite formation can lead to significant deterioration of heattreated cxmcrete. The preparation of synthetic ettringite is described in this paper. One of these is through the ionic composition of the aqueous phase and in particular through the amount of soluble sulfates. It is a shorthand way of writing the chemical formula of oxides of. Physically, the ettringite was carbonated in the form of powders and pellets, pressed to similar to 80% theoretical density. The model was derived based on kinetics theory applied to cement chemistry and.
This work reports the first observation of resonances from two distinct al sites in octahedral. Delayed ettringite formation def is a possible autogenous expansive reaction of concrete. The ettringite superplasticizer interaction and its impact. Subsequently, if the concrete is exposed to substantial amounts of water for months or years, ettringite reforms, leading to destructive expan sive forces that crack the concrete members. This glossary of terms used in cement, concrete cement analysis is available for free download. Ettringite is formed in hydrated portland cement system as a result of the reaction of calcium aluminate with calcium sulfate, both present in portland cement. Portlandite, csh, and presumably also ettringite, thus successively. Cement used in construction is characterized as hydraulic or nonhydraulic. Kinetics and mechanism of the carbonation of ettringite.
It can affect materials that have experienced temperatures higher than about 65 c at early age. Spry, and hyomin lee many researchers have concluded that secondary or delayed ettringite is responsible for serious premature deterioration of concrete highways. If there is still c 3 a left after this reaction, it can combine with ettringite to form monosulphate or af m phase which has a stoichiometry of c 4 a s h 1218. Chemical structures of organic crystallization inhibitors used in study. Introduction the problem of durability of concrete with cement as binding material comes more and more to the fore with the increased use of concrete, with the changed production and utilization. Ai 2 o 3 perspective 10 aspire summer 2018 overview of delayed ettringite formation and.
Glossary of some terms used in cement, concrete and in the analysis of cementitious materials notes. However, not necessarily any ettringite related expansion is related to sulfate attack. Micromechanical modelling of sulphate corrosion in concrete. The present paper reports a new method for converting ettringite and thaumasite in nonexpansible and insoluble phases, for its application in the restoration of concrete artefacts subjected to. The mechanism of the formation and transformation of ettringite. Further work showed a miscibility gap in the solid solution barnett et al. In cement chemistry hydration is understood to be the reaction of a nonhydrated cement or one of its constituents with water, associated with both chemical and physicomechanical changes of the system, in particular with setting and hardening. The formation of ettringite and the expansion associated with it were studied on paste made from portland cement, two albearing compounds such as calcium aluminate cement and calcium sulphoaluminate cement, and calcium sulfate with different reactivities anhydrite.
Delayed ettringite formation delayed ettringite formation is a less common, but potentially more damaging, cause of distress than asr. Does a high amount of unhydrated portland cement ensure. The experiments were performed at 40, 50, 55, and 60 c for a natural ettringite specimen. Aspects of attack of ordinary portland cement by chloride, sulphate and. Delayed ettringite formation in concrete imx technologies. Igor cigrovski 1 1 faculty of civil engineering, university of zagreb, croatia.
Cement grains csh ettringite hydration of the aluminate components, cra and gaf, with and without. Logan1 1school of natural resources, kottman hall, the ohio state university, columbus, ohio 43210, usa. The fast initial afm formation observed before ettringite. Although it is generally assumed that a solid solution series between ettringite and thaumasite exists, both species have different space groups and a possible discontinuity was identified, characterised by a gap in the adimension of the solidsolution phases barnett et al. The gypsum promotes formation of ettringite around the aluminate. The exposure of cement to high concentration of sulphate anions for a prolonged time period can lead to the formation of secondary ettringite and thaumasite. Delayed ettringite formation a concern for precast concrete. In concrete chemistry ettringite is a hexacalcium aluminate trisulfate hydrate, of general formula. Kamalibernard, in leas chemistry of cement and concrete fifth edition, 2019. Precastprestressed concrete institute, manual for quality control for plants and. Portland cement, concrete, volume 18number 2 and heat of. Ettringite formed by dissolution and recrystallization in void spaces and cracks is often referred to as secondary ettringite. Michael john mccarthy, thomas daniel dyer, in leas chemistry of cement and concrete fifth edition, 2019.
Ettringite ca6aloh62so4326h2o is the first hydration product formed during portland cement hydration. If timed and proportioned properly, the ettringite will run out of sulfates at about seven days from cement finishing and form into smaller monosulfates thus causing the concrete to contract to its original size. Pdf the use of chemical admixtures to prevent delayed. Delayed ettringite formation in concrete jochen stark, katrin bollmann bauhausuniversity weimar germany 1. Minor amounts of secondary ettringite are often encountered in air voids of hardened concretes, regardless of the type of cement used. Apr 30, 2019 here, we report on a first mechanochemical synthesis of ettringite, an important cement hydrate phase. Ettringite is a primary constituent of hydration of portland cement concrete. A singlecrystal neutron diffraction study of ettringite, ca 6 al 2 so 4 3 oh 12 27h 2 o, american mineralogist, 104, 7378. Effect of calcium sulfate on the formation of ettringite in. Its formation plays an important role in the control of setting. Processes in connection with the ettringite formation in concrete are belong to the partly unsolved problems. Resolution of the two aluminum sites in ettringite by 27al.
Alkalisilica reaction asr and delayed ettringite formation def, or combinations of the two, have been found to be the main causes of these problems. The garnets only take up space and do not in any way contribute to the strength of the cement paste. Early c3a hydration in the presence of different kinds of. Reduction of concrete deterioration by ettringite using. The term premature concrete deterioration pcd has been adopted to refer to problems associated with asr and def because it is often difficult to distinguish between them. Pdf cement chemistry download full pdf book download.
Most of the sulfate in the cement is normally consumed to form ettringite at early ages. Jun 10, 2015 the decomposition behavior of ettringite, ca6al2so43oh1226h2o, at different temperatures was studied by means of isothermal xrd experiments, in which the evolution of the solid is monitored as a function of time. Preventing alkalisilica reaction and delayed ettringite formation in new concrete. A singlecrystal neutron diffraction study of ettringite, ca 6 al 2 so 4 3 oh 12 27h 2 o g. Synthesis, crystal chemistry and stability of ettringite, a.
His early work laid the foundations of our understanding of the structure at the nanometre level of csh, the principal product formed when cement is mixed with water, and the one mainly reponsible for its hardening. The experimental data were used to construct a temperaturetransformationtime. Since 1948, his main research interest has been the chemistry of cement. Calcium sulfoaluminate csa cement is a sulfatebased binder whose highperformance hydraulic behavior depends on the rapid formation of ettringite, when grinded clinker is hydrated in presence of gypsum. Aug 28, 2009 calcium sulfoaluminate csa cement is a sulfatebased binder whose highperformance hydraulic behavior depends on the rapid formation of ettringite, when grinded clinker is hydrated in presence of gypsum. Pdf the effect of the ph of the reaction solution on the. Chemistry of ettringite and thaumasite ettringite is a hydrous calcium aluminosulfate mineral that precipitates under alkaline high ph conditions in soil and concrete systems with high sulfate activity 4, 11, 14. Cement in the most general sense of the word, a cement is a binder, a substance that sets and hardens independently, and can bind other materials together.
Chemical composition of characteristic cement clinker. It is a product of the reaction between sulfate and calcium aluminate. The book deals more specifically with the chemistry of portland cement manufacture and the nature of the resulting product, the processes that occur when this product is mixed with water, the nature of the hardened material, the chemistry of other types of hydraulic cement, and chemical and microstructural aspects of concrete, including. Pdf effect of ettringite morphology on the properties of expanding. The sulfate in ettringite can be replaced by carbonate or, probably, partly replaced by two hydroxyl ions, although in practice neither of these is often observed. Recently in texas, there has been significant damage of field structures resulting from concrete durability problems. In mortar i, with standard content of so3, ettringite was formed in small quantities, mainly in the air cavities, and did not influence the expansion. This cement contains 32 45% al 2 o 3, about 15% iron oxides, and 5% sio 2, with the remainder composed of cao. Not all cement components can be expressed by the oxide formulae and shorthand notation chlorides, fluorides etc expressed using normal chemical formulae mineral names are commonly used for raw materials calcite, quartz and for some cement hydration products ettringite, portlandite etc. The formation of ettringite or cement bacillus has been recognized as the cause of excessive expansion, cracking and even complete disintegration of concrete subjected to intensive sulfate attack.
The formed ettringite can be assigned to pdf 00037147628 pdf 2 2016. Investigations on cement expansion associated with ettringite formationj. This cement is produced by sintering a mixture of aluminous typically bauxite and calcareous components, and grinding to a fine powder. Reduction of concrete deterioration by ettringite using crystal growth inhibition techniques by robert d. Disappearance of all reactant reflections after 30 min of the neat pregrinding indicates the amorphization process. He is also the recipient of several awards for his contributions to the fundamental knowledge of superplasticizers and their use in concrete. Some very basic chemistry will help a lot with understanding how cement is made and how it works. The hydration process and formation of ettringite in the binders with different content of. As the ettringite and glue form together, the overall crystal structure of the concrete builds up and thus expands. Modeling for cement materials exposed to external sulfate attack or. The primary phase present is calcium aluminate, or ca. We hope you find it useful please do distribute it freely to any colleagues who may also benefit from it.
In a concrete made from cement containing only clinker and gypsum, ettringite forms early after the cement and water are mixed, but it is gradually replaced by monosulfate. Quantum chemistry studies on the strength performance of ettringitej. The ferrite undergoes two progressive reactions with the gypsum. Given current cement prduction and concreteconstruction practices there appears to be a potential for a secondary ettringite formation problem in north america. It is an expansive compound, and is bigger in volume is of smaller density than its forming chemicals. Manufacture, chemical composition, heat of hydration. Vibrational spectroscopy of functional group chemistry and. Cement chemistry can affect the dispersion efficiency of superplasticizers in various ways. Optimization of the so3 content of an algerian portland cement.
336 349 247 884 1326 932 1428 612 1006 662 1431 1090 1039 350 267 962 1558 446 1430 981 7 900 1285 1375 152 1169 89 986 455 859 375 61 1251 724 599 383 728 1288 231 536 361