Search results for "Building"
showing 10 items of 1985 documents
Quantitative Determination of Calcium Hydroxide by using Near Infrared Spectroscopy
2018
Calcium hydroxide (CH) is a by-product from hydration reaction of cement along with calcium silicate hydrate (C-S-H) gel. It helps to protect the steel reinforcements in concrete structures from corrosion process due to carbonation. The presence of calcium hydroxide provides a basic environment (pH˃10) that induces the formation of passive oxide film and keeps steel structures from corrosion. The detection and quantification of calcium hydroxide in concrete structures are important to understand the nature and state of the steel structures in concretes. In this research work, the variation of calcium hydroxide to calcium silicate ratios in cement were measured by using near-infrared spectro…
Studies on mechanism and physico-chemical parameters at the origin of the cement setting II. Physico-chemical parameters determining the coagulation …
1996
The physico-chemical parameters determining the coagulation of cements grains previously identified as the first fundamental process of cement setting have been investigated in diluted suspensions using an adapted granulometric method. The analysis of the influence of the ionic concentration in solution on the coagulation reveals that calcium concentration is the parameter which determines the particle interactions. There exists a minimum critical concentration of calcium ions in solution which is required to occur the coagulation of cement particles and a dispersive effect appears for very high concentrations. The results are discussed in relation with DLVO theory and specific interactions.
Does phosphorus affect the industrial Portland cement reactivity?
2018
Abstract The effect of phosphorous on the mineralogy and reactivity of Portland cement has been investigated through an industrial clinkers series. The samples were collected from the same Tunisian cement plant and classified according to the content of P2O5 from 0.5% to 1.1%. All samples were manufactured at the same thermal and cooling conditions as well as possible. The specimens were characterized by X-ray fluorescence spectrometry and optical microscopy techniques and their mineralogy was determined by X-ray powder diffraction coupled to the Rietveld analysis. The cements reactivity prepared from the clinkers was followed by means of isothermalcalorimetry. The compressive strength of t…
Pumice powder as filler of self-compacting concrete
2015
Abstract An experimental study on the rheological and mechanical properties of self-compacting concrete with pumice powder used as filler additive is presented. Self-compacting concrete (SCC) shows its peculiar characteristics in the fresh state and many researches have been developed with reference to its rheological characteristics paying attention to the techniques of self-compacting properties assessment. One of the most important aspect in concrete mix-design is the type and the amount of fillers with respect to water and cement: this amount has great influence not only on self-compacting properties (fluidity, segregation, etc.), but also on the mechanical properties of the mixture. Vo…
Dynamic mode rheology of cement and tricalcium silicate pastes from mixing to setting
2001
Dynamic mode rheometry was used to study the evolution of the structure of cement and pure tricalcium silicate pastes from mixing up to setting and even after setting, together with the nature of the forces responsible for the mechanical properties of the pastes. A special mixer-type tool was used to study rheology during the very first minutes following the end of mixing, which are out of reach with classical tools. Both kinds of pastes have the same behavior. It was found that the main evolution of the structure of the pastes occurs during the very first minutes following the end of mixing, while there is no change in interparticular forces up to setting and even a few hours later. Settin…
Effect of content and particle size distribution of high-calcium fly ash on the rheological properties of cement pastes
1997
Abstract The Theological properties of high-calcium fly ash cement pastes were investigated. An increase both in yield value and plastic viscosity with fly ash content was found. It was also observed that the pastes became more fluid with the higher fly ash fineness. A more important relation was shown between the fine fractions (
Hydration of cementitious materials, present and future
2011
This paper is a keynote presentation from the 13th International Congress on the Chemistry of Cement. It discusses the underlying principles of hydration and recent evidence for the mechanisms governing this process in both Portland cements and other cementitious materials. Given the overriding imperative to improve the sustainability of cementitious materials, routes to reducing CO2 emissions are discussed and the impact of supplementary materials on hydration considered. (C) 2011 Elsevier Ltd. All rights reserved.
SHORT-TERM PROCESSES OF RADIONUCLIDE IMMOBILIZATION IN CEMENT - A CHEMICAL APPROACH
1992
Abstract The ions released in solution by the constituents of cement (principally silicate, aluminate, OH and Ca ions) can combine with the anions and cations from nuclear wastes present in the mixing water to give very insoluble compounds that can fix these ions in the concrete matrix. In order to understand some of the particular physico-chemical processes involved in cement hydration in the presence of analogue elements, tricalcium silicate (C 3 S) was used instead of cement, which is too complex a mixture. It was found that the salt of a chemical analogue, a lanthanide salt, showed some accelerating effects when present in dilute amounts but resulted in large accelerating effects on QS …
Retention of alkali ions by hydrated low-pH cements: Mechanism and Na+/K+ selectivity
2013
Low-pH cements, also referred to as low-alkalinity cements, can be designed by replacing significant amounts of Portland cement by pozzolanic materials. Their pore solution is characterized by a pH near 11, and an alkali concentration much lower than that of Portland cement. This work investigates the retention of sodium and potassium by a hydrated low-pH cement comprising 60% Portland cement and 40% silica fume. It is shown that sorption of potassium is higher than that of sodium and mainly results from counterion charge balancing of the C-S-H negative surface charge. To explain the greater retention of potassium compared to sodium, it is postulated that potassium, unlike sodium, may enter…
Modification of the rate of formation and surface area of ettringite by polycarboxylate ether superplasticizers during early C3A–CaSO4 hydration
2015
Abstract Early C3A–CaSO4 hydration was studied in the presence of various amounts of two polycarboxylate ether superplasticizers differing in their grafting degree. Hydration and surface area developments were investigated by in-situ NMR relaxometry coupled with BET and DSC during the first 2 h after mixing. This study enables a quantitative comparison of the amount and the specific surface area of the ettringite precipitated along the C3A–CaSO4 hydration with or without PCE. The main effect of PCE is to strongly increase ettringite specific area for a variable period. These effects are clearly dependent on the PCE charge and dosage and are reduced when using delayed addition. In this conte…