Influence of the storage conditions on the dimensional changes of heat-cured mortars

Karen Scrivener
2001
Journal paper

Some cementitious materials cured at elevated temperature may expand on subsequent exposure to moisture. Concern has been expressed as to the relevance of small laboratory specimens to field concretes, in particular due to the potential leaching of ions into the storage solution. The work presented here aims at investigating this effect. Mortars cured at elevated temperature in identical fashion were subsequently stored at 90-100% relative humidity (RH) and in water, a LiOH solution, and KOH solutions of various concentrations. The largest and most rapid expansion occurred with mortars immersed in water. The samples stored at 90-100% RH expanded more slowly. Expansion was even slower when subsequent storage was in LiOH or KOH solutions. The same samples were studied by scanning electron microscopy (SEM) and X-ray diffraction (XRD). These techniques indicated that ettringite had formed over time in all samples, with little apparent relation to the degree of expansion. The composition of the C-S-H gel changed over time, differently for the different storage conditions. © 2001 Elsevier Science Ltd.

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Karen Scrivener
2001
Journal paper

Abstract

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https://infoscience.epfl.ch/record/166420?ln=en

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Concrete

Concrete is a composite material composed of aggregate bonded together with a fluid cement that cures over time. Concrete is the second-most-used substance in the world after water, and is the most w

Cement

A cement is a binder, a chemical substance used for construction that sets, hardens, and adheres to other materials to bind them together. Cement is seldom used on its own, but rather to bind sand

Scanning electron microscope

A scanning electron microscope (SEM) is a type of electron microscope that produces images of a sample by scanning the surface with a focused beam of electrons. The electrons interact with atoms

The origin of early age expansions induced in cementitious materials containing shrinkage reducing admixtures

Patrick Juilland, Barbara Lothenbach, Karen Scrivener

Studies on the early-age shrinkage behavior of cement pastes, mortars, and concretes containing shrinkage reducing admixtures (SRAs) have indicated these mixtures frequently exhibit an expansion shortly after setting. While the magnitude of the expansion has been noted to be a function of the chemistry of the cement and the admixture dosage: the cause of the expansion is not clearly understood. This investigation uses measurements of autogenous deformation, X-ray diffraction, pore solution analysis, thermogravimetry, and scanning electron microscopy to study the early-age properties and describe the mechanism of the expansion in OPC pastes made with and without SRA. The composition of the pore solution indicates that the presence of the SRA increases the portlandite oversaturation level in solution which can result in higher crystallization stresses which could lead to an expansion. This observation is supported by deformation calculations for the systems examined. (C) 2010 Elsevier Ltd. All rights reserved.

2011

Physical and microstructural aspects of iron sulfide degradation in concrete

Emmanuel Gallucci, Karen Scrivener

The microstructural aspects of iron sulfide degradation in dam concrete were investigated by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) in both dam concrete samples and laboratory concrete. The results show that iron sulfide inclusions with a diameter of a few micrometers in the aggregates are reactive and appear to generate expansion first in the aggregates and consequently in the cement paste. The expansion from the iron sulfides is a consequence of the increase in volume of the reaction products formed. The types of iron sulfide present in the aggregate, mainly pyrrhotite (FeS) and pyrite (FeS2), show similar reaction behavior in the aggregates. The released sulfate can lead to a secondary ettringite formation in the concrete matrix, but the degradation associated with this appears to be minor. The reaction of the iron sulfides was found to be very slow even when laboratory samples were exposed to elevated temperatures. (C) 2010 Elsevier Ltd. All rights reserved.

2011

Characterization of interfacial transition zone in concrete prepared with carbonated modeled recycled concrete aggregates

Karen Scrivener

Treatment by accelerated carbonation has been widely studied to enhance the quality of recycled concrete aggregates (RCA) and hence the performance of new concrete produced with the RCA. This is often ascribed to the densification of RCA. This study investigated the influence of carbonation treatment of modeled RCA on the interface between the carbonated RCA and new cement mortar/paste using frictional (shear) and tensile bond tests, microhardness, X-ray diffraction (XRD), thermal analysis (TGA), and scanning electron microscope (SEM). It was found that carbonation treatment resulted in massive calcite precipitating on the surface of RCA, which further reacted with the aluminate species of the new cement to form the monocarbonate (Mc), and served as nucleation sites for the grow of C-S-H on the surface of RCA. These led to local densification around the surface of the carbonated RCA, resulting in a slight reduction of the porosity at the innermost part of ITZ and improved microhardness of ITZ. Moreover, the chemical bonds provided a superior adhesion of the carbonated RCA with the new cement pastes. This improved the bond strengths between the carbonated RCA and the new cement mortar.

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