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Cement
About: Cement is a research topic. Over the lifetime, 68440 publications have been published within this topic receiving 829356 citations.
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TL;DR: In this article, a simple mathematical model for the evolution of concrete carbonation in time, applicable under constant relative humidity higher than 50%, is presented, based on fundamental principles of chemical reaction engineering, and uses as parameters the ambient concentration of CO2, molar concentratrations of the carbonatable constituents, Ca(OH)2 and CSH, in the concrete volume, and the effective diffusivity of CO 2 in carbonated concrete.
Abstract: The paper describes the physicochemical processes of concrete carbonation and presents a simple mathematical model for the evolution of carbonation in time, applicable under constant relative humidity higher than 50%. The model is based on fundamental principles of chemical reaction engineering, and uses as parameters the ambient concentration of CO2, the molar concentratrations of the carbonatable constituents, Ca(OH)2 and CSH, in the concrete volume, and the effective diffusivity of CO2 in carbonated concrete. The latter is given by an empirical function of the porosity of hardened cement paste and of relative humidity, derived from laboratory diffusion tests. The validity of the model for OPC or pozzolanic cement concretes and mortars is demonstrated by comparison of its predictions with accelerated carbonation test results obtained in an environment of controlled CO2 concentration, humidity and temperature. The mathematical model is extended to cover the case of carbonation of the coating-concrete system, for concrete coated with a cement-lime mortar finish, applied either almost immediately after the end of concrete curing or with a delay of a certain time. Parametric studies are performed to show how the evolution of carbonation depth with time is affected by cement and concrete composition (water/cement or aggregate/cement ratio, percentage OPC or aggregate replacement by a pozzolan), environmental factors (relative humidity, ambient concentration of CO2), the presence and the time of application of a lime-cement mortar coating and its composition (water/cement, aggregate/cement and lime/cement ratios of the mortar, percentage OPC or aggregate replacement by a pozzolan).
168 citations
TL;DR: The incorporation of SBR improved the chloride penetration resistance along with the general ionic permeability of the mortar, while increasing its ionic transport resistance and decreasing its electric capacitance as mentioned in this paper.
168 citations
TL;DR: In this article, the authors show that the lower compacted density of fly ash relative to conventional earthfill recommends its use when a fill or embankment must be constructed over soft, compressible ground.
Abstract: The lower compacted density of fly ash relative to conventional earthfill recommends its use when a fill or embankment must be constructed over soft, compressible ground. Field evidence to date indicates that compressibility or settlement of compacted fly ash fills is not significant. Long-term field settlements cannot be predicted satisfactorily on the basis of short-term laboratory tests because fly ash exhibits age-hardening or pozzolanic properties. Low-level additions of lime to the fly ash before compaction accentuate this behavior. Frost susceptibility likewise is not as serious a problem in compacted fly ash as might be presumed from its grain size distribution. Gradation alone does not suffice as a criterion of frost susceptibility; pozollanic properties also play an important role. Undesirable frost heave in compacted fly ash can be reduced to tolerable levels by addition of lime or cement.
168 citations
TL;DR: In this paper, a broad experimental study has been performed, from the end of mixing up to 2 years, on a set of plain cement pastes prepared with the same type I ordinary portland cement (OPC) and various water-to-cement ratios (W/C), and cured at various constant temperatures.
168 citations
TL;DR: Les mesures sont faites pendant le durcissement du ciment apres 1, 14 ou 25 fours d'hydratation; on etudie l'influence de la frequence as discussed by the authors.
Abstract: Les mesures sont faites pendant le durcissement du ciment apres 1, 14 ou 25 fours d'hydratation; on etudie l'influence de la frequence
168 citations