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Home > Publications > International Concrete Abstracts Portal
The International Concrete Abstracts Portal is an ACI led collaboration with leading technical organizations from within the international concrete industry and offers the most comprehensive collection of published concrete abstracts.
Showing 1-5 of 38 Abstracts search results
Document:
SP302-10
Date:
June 1, 2015
Author(s):
S. Mantellato; Q. Mehmeti; L. Ceni; M. Palacios; and R.J. Flatt
Publication:
Symposium Papers
Volume:
302
Abstract:
One of the essential problems of superplasticized concrete is the loss of fluidity over time. To limit this problem one must improve the compatibility of superplasticizers and cement. This is not a trivial task as cement contains phases with different responses to superplasticizers in the first hours of hydration. In the present work, the role of the polymer structure on the flow loss over time on superplasticized cement pastes has been studied. For this, we have correlated the impact of different molecular structures on the adsorption degree and ionic solution composition with the rheological properties of fresh cement pastes. The results revealed a high excess of aluminium in the aqueous solution. This could be due to aluminum complexation by the polymer or a poisoning of ettringite growth complemented by a stabilization of nano-sized ettringite particles. In addition, except for one of the studied polymers, the flow loss seems to decrease abruptly when the concentration of carboxylate ions in solution drops below a critical value (0.7-1.2 µeq/g).
DOI:
10.14359/51688090
SP302-11
L. Reiter; M. Palacios; T. Wangler; and R.J. Flatt
The ability to control the setting of cement can be of use in various applications such as slip forming, oil well cements, or in normal applications due to variable conditions and time constraints. Typically cement setting is controlled via set retarders or set accelerators, but rarely are the two used in combination. The combination of the two, however, can lead to increased flexibility in construction methods. In this work, we present a system in which the dormant period of cement is extended with sucrose, and then drastically reduced by adding calcium hydroxide, a phase that preferentially adsorbs sucrose. We demonstrate that increasing doses of calcium hydroxide decrease the dormant period of sucrose-retarded cement, up to a complete cancellation of retardation, which is reached at the plateau of the sucrose-calcium hydroxide adsorption isotherm.
10.14359/51688091
SP302-06
Lucia Ferrari and Pascal Boustingorry
Cementitious suspensions all feature common flow characteristics when their flow curve is observed. When plotted as shear stress vs shear rate a minimum in stress is observed towards low shear rates which may be related to the hydration of cement. When plotted as apparent viscosity versus shear rate a minimum often appears towards high shear rates, beyond which the suspension enters a shear-thickening regime the origin of which remains unclear. In between these two limits of shear rate, the expected shear-thinning behaviour takes place, where apparent viscosity may be linked to a shear-rate-dependent degree of suspension flocculation. The present paper aims at shedding some light onto the origins of those features in the context of mix design and superplasticizer technology.
10.14359/51688086
SP302-07
Karen Luke and Adrian Torres
Superplasticizers are often used in conjunction with other additives and this can produce either an adverse or synergistic effect on rheology and setting properties of cementitious systems. These effects can be enhanced when temperatures are increased due to environmental changes or induced temperature as in hydrothermal curing. This research focuses on the compatibilities of different types of superplasticizer either sulfonated naphthalene or polycarboxylate based in combination with a lignosulphonate or hydroxycarboxylic acid type retarder. Rheological measurements were made using a rotational viscometer at temperatures from 25°C (77°F) to 120°C (248°F) under pressure, and plastic viscosity and yield point determined based on the Bingham Plastic model though in almost all cases it was noted that the Power Law or more so the Herschel-Buckley model gives a better fit. Zeta potential was used to characterize particle surface interactions to understand synergy of additive combinations. Setting properties, investigated using conduction calorimetry, were observed to be dominated by retarder response.
10.14359/51688087
SP302-08
Shinji Tamaki; Kazuhide Saito; Kazuhisa Okada; Daiki Atarashi; and Etsuo Sakai
Several studies have been pursued in Japan on developing concrete using high volume blast-furnace slag cement for reducing CO2 emissions arising from calcination of cement. However, when using high volume blast-furnace slag cement, various problems are encountered, such as decreased fluidity retention ability caused by the reduction of admixture dosage and decreased strength enhancement. In this paper, the authors focus on the adsorption properties of polycarboxylate ether superplasticizers and the properties of hardened concrete that incorporates a component of high volume blast-furnace slag cement, and discuss the development of a new type of superplasticizer through molecular design and optimization of the admixture composition. The admixture improved the fluidity and properties of hardened concrete using slag cement containing more than 60% blast-furnace slag.
10.14359/51688088
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