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. Preventing alkalisilica reaction and delayed ettringite formation in new concrete. Chemistry of calcium nitrilotrismethylenetriphosphonate. Ettringite or cement bacillus has advantages and disadvantages, depending on the circumstances and conditions in which it forms. Research and development bulletin rdlost americas cement. Recently in texas, there has been significant damage of field structures resulting from concrete durability problems. It is an expansive compound, and is bigger in volume is of smaller density than its forming chemicals. Kinetics and mechanism of the carbonation of ettringite. Does a high amount of unhydrated portland cement ensure. Damage in conjunction with ettringite formation in hardened concrete was first identified in heattreated, precast concrete elements which, during use, had been exposed to openair weathering with frequent wetting. Pdf the use of chemical admixtures to prevent delayed. Resolution of the two aluminum sites in ettringite by 27al. Vibrational spectroscopy of functional group chemistry and arsenate coordination in ettringite satish c. Vibrational spectroscopy of functional group chemistry and.
This work reports the first observation of resonances from two distinct al sites in octahedral. 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. Ettringite formation and sulfate attack on concrete by m. 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. Water cement grains csh ettringite hydration of the aluminate components, cra and gaf, with and without gypsum.
Cement on the go portland cement, concrete, and heat of hydration fig. 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. Secondary ettringite is not detrimental to concrete performance. Michael john mccarthy, thomas daniel dyer, in leas chemistry of cement and concrete fifth edition, 2019. Modeling for cement materials exposed to external sulfate attack or. Pdf cement chemistry download full pdf book download. Its formation plays an important role in the control of setting.
Delayed ettringite formation delayed ettringite formation is a less common, but potentially more damaging, cause of distress than asr. Since 1948, his main research interest has been the chemistry of cement. The aft phase ettringite forms rapidly in cements containing natural pozzolanas 197 or fly ash. Ettringite formation and the performance of concrete.
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. Optimization of the so3 content of an algerian portland cement. Reduction of concrete deterioration by ettringite using. Portland cement, concrete, volume 18number 2 and heat of. This compound is however responsible for the longterm strength of portland cement concrete. Apr 30, 2019 here, we report on a first mechanochemical synthesis of ettringite, an important cement hydrate phase. Cement chemist notation ccn was developed to simplify the formulas cement chemists use on a daily basis. Nearly all the so 4 2gets combined to form ettringite in an ordinary portland cement. 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. Early c3a hydration in the presence of different kinds of.
It is a shorthand way of writing the chemical formula of oxides of calcium, silicon, and various metals. 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. The ferrite undergoes two progressive reactions with the gypsum. The garnets only take up space and do not in any way contribute to the strength of the cement paste.
Ettringite formation and the performance of concrete portland. Disappearance of all reactant reflections after 30 min of the neat pregrinding indicates the amorphization process. Aspects of attack of ordinary portland cement by chloride, sulphate and. Chemical composition of characteristic cement clinker.
Cement grains csh ettringite hydration of the aluminate components, cra and gaf, with and without. A singlecrystal neutron diffraction study of ettringite, ca 6 al 2 so 4 3 oh 12 27h 2 o, american mineralogist, 104, 7378. 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. Cement chemistry can affect the dispersion efficiency of superplasticizers in various ways. The hydration process and formation of ettringite in the binders with different content of. Igor cigrovski 1 1 faculty of civil engineering, university of zagreb, croatia. Cement chemistry cement hydration reaction of cement with water exothermic. Pdf effect of curing temperature and cement chemistry on. The ettringite superplasticizer interaction and its impact. Pdf kinetic model to predict cement susceptibility to delayed. The formation of ettringite in the fresh, plastic concrete is the mechanism that controls stiffening. Logan1 1school of natural resources, kottman hall, the ohio state university, columbus, ohio 43210, usa.
Chemistry of ettringite and thaumasite recommended. Precastprestressed concrete institute, manual for quality control for plants and. 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. Processes in connection with the ettringite formation in concrete are belong to the partly unsolved problems. This cement is produced by sintering a mixture of aluminous typically bauxite and calcareous components, and grinding to a fine powder. Further work showed a miscibility gap in the solid solution barnett et al. Effect of ettringite morphology on the properties of expanding cement systems. Kamalibernard, in leas chemistry of cement and concrete fifth edition, 2019. It is highly probable that secondary ettringite formation can lead to significant deterioration of heattreated cxmcrete.
Influence of grout and cement on groundwater composition. 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. Micromechanical modelling of sulphate corrosion in. The formed ettringite can be assigned to pdf 00037147628 pdf 2 2016. Ettringite is also known as c ement bacillus, which is the name of a naturally occurring mineral of the same composition and structure. 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. As the ettringite and glue form together, the overall crystal structure of the concrete builds up and thus expands. Effect of calcium sulfate on the formation of ettringite in. Delayed ettringite formation def is a possible autogenous expansive reaction of concrete. 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. The experiments were performed at 40, 50, 55, and 60 c for a natural ettringite specimen. Ettringite formed by dissolution and recrystallization in void spaces and cracks is often referred to as secondary ettringite. The extent of the potential problem cannot be predicted with.
It can affect materials that have experienced temperatures higher than about 65 c at early age. The hydration products were investigated using xray diffraction, fourier transform infrared and scanning electron microscopy. If you missed out on chemistry at school, or it just seems a long time ago, the following short notes might be useful. 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. Ettringite is a calcium aluminum sulfate mineral characterized by high water content, estimated as 32 water molecules per formula unit. 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. Synthesis, crystal chemistry and stability of ettringite, a. Ettringite solubility and geochemistry of the ca oh al so. Other important variations in portland cement chemistry often escape notice in considerations of permeation capacity. Most of the sulfate in the cement is normally consumed to form ettringite at early ages. Research and development bulletin rdlost by robert l. Spry, and hyomin lee many researchers have concluded that secondary or delayed ettringite is responsible for serious premature deterioration of concrete highways. Reasons for the apparent newness of the phenomenon, and.
Glossary of some terms used in cement, concrete and in the analysis of cementitious materials notes. 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. This cement contains 32 45% al 2 o 3, about 15% iron oxides, and 5% sio 2, with the remainder composed of cao. Quantum chemistry studies on the strength performance of ettringitej. 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 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. 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. Given current cement prduction and concreteconstruction practices there appears to be a potential for a secondary ettringite formation problem in north america.
Ettringite ca6aloh62so4326h2o is the first hydration product formed during portland cement hydration. Minor amounts of secondary ettringite are often encountered in air voids of hardened concretes, regardless of the type of cement used. This glossary of terms used in cement, concrete cement analysis is available for free download. The fast initial afm formation observed before ettringite. The preparation of synthetic ettringite is described in this paper. Ai 2 o 3 perspective 10 aspire summer 2018 overview of delayed ettringite formation and. Ettringite is a primary constituent of hydration of portland cement concrete.
Alkalisilica reaction asr and delayed ettringite formation def, or combinations of the two, have been found to be the main causes of these problems. In concrete chemistry ettringite is a hexacalcium aluminate trisulfate hydrate, of general formula. One of these is through the ionic composition of the aqueous phase and in particular through the amount of soluble sulfates. Manufacture, chemical composition, heat of hydration. Chemical structures of organic crystallization inhibitors used in study. It is a shorthand way of writing the chemical formula of oxides of. 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. Specifically, some fine aggregates will yield vastly different expansions. Heat accelerated curing alkali load reactive aggregate moisture cement so 4. Thermal stability of ettringite exposed to atmosphere.
Pdf effect of ettringite morphology on the properties of expanding. 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. Final cement strength is pro vided mainly by the amorphous csh gel created by the cement s hydrating sili cate components. Investigations on cement expansion associated with ettringite formationj. The ettringite superplasticizer interaction and its impact on the ettringite distribution in cement suspensions by f.
Some very basic chemistry will help a lot with understanding how cement is made and how it works. Portlandite, csh, and presumably also ettringite, thus successively. Chemistry of ettringite and thaumasite recommended practice. The hydration of the rapid set cement causes the formation of ettringite crystals in a slightly expansive process. In terms of workability of cement based materials, ettringite formation is of major importance. In addition, the effects of nonreactive aggregates in this test were found to be dramatic in some cases. Physically, the ettringite was carbonated in the form of powders and pellets, pressed to similar to 80% theoretical density. We hope you find it useful please do distribute it freely to any colleagues who may also benefit from it. The mortars steamcured at a temperature 90c exhibit a significant expansion caused by the delayed ettringite. The primary phase present is calcium aluminate, or ca. However, not necessarily any ettringite related expansion is related to sulfate attack. Damage of concrete due to sulfate attack is one of a serious problem for the durability of concrete structures.
The milestone paper on this subject comes from yamada and hanehara 2001. The influence of the neat pregrinding duration on the reaction conversion is a subject of current research. 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. 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. Alkalisilica reaction and delayed ettringite formation. 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. Ettringite has wide technical application in the ceramic and paper industry. 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. 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. Well completion michel michaux erik nelson benoit vidick saint etienne, france faced with the concrete skyline. Delayed ettringite formation in concrete jochen stark, katrin bollmann bauhausuniversity weimar germany 1. Pdf the effect of the ph of the reaction solution on the.
Ettringite formation and sulfate attack on concrete synopsis. Cement chemistry role of superplasticiser in construction industry role of corrosion. Reduction of concrete deterioration by ettringite using crystal growth inhibition techniques by robert d. Preventing alkalisilica reaction and delayed ettringite.
Ettringite solubility and geochemistry of the ca oh al so h. He is also the recipient of several awards for his contributions to the fundamental knowledge of superplasticizers and their use in concrete. A singlecrystal neutron diffraction study of ettringite, ca 6 al 2 so 4 3 oh 12 27h 2 o g. Effect of calcium sulfate on the formation of ettringite. It is a product of the reaction between sulfate and calcium aluminate. Delayed ettringite formation in concrete imx technologies. The model was derived based on kinetics theory applied to cement chemistry and. This pathology in the chemistry of cement and concrete has been well recognized as delayed ettringite formation def. The experimental data were used to construct a temperaturetransformationtime. 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. Ettringiterelated dimensional stability of co2cured. 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.
Synthesis, crystal chemistry and stability of ettringite, a material with potential applications in hazardous waste immobilization volume 245 gregory j. The cement slurry is placed between the casing and the drilled formation for adequate zonal isolation for the lifetime of the well 1. Its hydration leads to the formation of ettringite c6as3h32, iron hydroxide and. The ettringite superplasticizer interaction and its. Micromechanical modelling of sulphate corrosion in concrete. Trbs national cooperative highway research program nchrp webonly document 145. Cement used in construction is characterized as hydraulic or nonhydraulic. The mechanism of the formation and transformation of ettringite. Perspective overview of delayed ettringite formation and. Delayed ettringite formation a concern for precast concrete. 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. 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. The gypsum promotes formation of ettringite around the aluminate.
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. 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. Glossary of some terms used in cement, concrete and in the. 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.