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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 40 Abstracts search results
September 1, 2003
Y Nakajima, T. Goto, and K. Yamada
The performance of 3-naphthalene sulfonate superplasticizer (PNS) is known to be affected by various cement characteristics e.g. the kind of calcium sulfate, the amount of alkali sulfates and free lime, and the phase composition of the clinker especially the amount of C3A. In this study, the affecting mechanisms of these characteristics are explained by a unified model. In the model proposed, the fluidity is assumed to be determined by the adsorbed amount of PNS per unit surface area of hydrates (Ad/Hy) only. Ad/Hy is affected by the S042- concentration in the solution phase of the cement paste if PNS and So42- are in Langmuir type competitive adsorption equilibrium. Of course, the surface area of hydrates also influences fluidity by changing the Ad/Hy ratio. There has been an unsolved problem for the working mechanism of PNS, which is the quantitative discrimination between the absorption into initial hydrates and adsorption onto hydrates. The only PNS adsorbed on hydrates is expected to work as a dispersant. This problem can be avoided by using the proposed model. This model can also take into account the effect of S042 concentration just after mixing affecting the absorption behavior of PNS during initial hydration. This model predicts the performance of PNS only, by two parameters, S042concentration and surface area of hydrates. Based on the model, all cement characteristics relating the So42- concentration and surface area of hydrates are understood to be quite important for the performance of PNS. The well-known cement characteristics mentioned above can be attributed to changes in S042- concentration and surface area of hydrates.
P. Mounanga, A. Loukili, and A. Khelidj
Three superplasticizers (SP) have been studied in this research: the first is based on modified polycarboxylic ether and is used to improve the workability of concrete and to obtain high mechanical characteristics at early age; the second, which contains naphthalene sulphonate, is used to reduce drastically mixing water in concrete and improve mechanical strength at early age; the third SP investigated is melamine-based and is used to improve the workability of concrete creating electrostatic repulsion between cement grains. The intention of the present investigation was to provide more information about the role of these SP in concrete at early age. The apparent activation, initial and final set times by Vicat needle, chemical and autogenous shrinkage were measured for cement pastes having a water/cement ratio of 0.25. The apparent activation energy has been determined by the "setting times method" at different temperatures: 10, 20, 30 and 40 °C. The volumetric autogenous shrinkage was measured at the same temperatures immediately after setting. The experimental results show that the apparent energy activation is slightly modified by the presence of SP. Also, the evolution of chemical shrinkage shows clearly that the SP acts on the hydration kinetic of cement. The effect of a particular SP on autogenous shrinkage at different temperatures can be correctly predicted by means of the maturity concept.
H. Kikukawa and T. lisaka
An equation was formulated for estimating the plastic viscosity of cement paste containing an air-entraining admixture, which is a commonly used chemical admixture for concrete. Air-entraining admixtures slightly increase the plastic viscosity of neat cement paste. The viscosity equation was derived by incorporating this effect, to minimize the difference between the estimation and measurement. The ratio of the plastic viscosity estimated from the proposed viscosity equation to the measured plastic viscosity was found to be approximately 1, the anticipated value. Viscosity equations for mortar and concrete also formulated based on an existing viscosity equation were found to be valid even when the plastic viscosity of the matrix changed.
A. A. Jeknavorian, L. Jardine, C. C. Ou, H. Koyata, and K. Folliard
With the increased use of polycarboxylated-based comb-type polymers as highrange water reducers, more frequent opportunities exist to uncover unexpected interactions with the various materials used in cementitious mixtures. In this paper, attention is drawn to the increased dose-slump response of polycarboxylate-based comb-type superplasticizers versus naphthalene sulfonate formaldehyde condensates (NSFC) when swellable clays are present in certain aggregate sources. In the expanded state, these clays have been found to adsorb polycarboxylate-based superplasticizers, rendering this class of dispersants less effective in providing slump increase or water reduction. This effect is apparently not observed with NSFC. Among the approaches identified to mitigate the adsorption effects of expandable clay materials, a class of sacrificial agents has been found effective in restoring the expected dose-response of polycarboxylate superplasticizers. A model for the interaction of polycarboxylate comb-type polymers with an expandable clay as well as the lab performance of a clay modifying agent will be discussed.
J. Ambroise and J. Pera
A new type of high-performance concrete was developed, based on calcium sulfoaluminate cement. It was designed to reach the following requirements: - high workability: slump higher than 200 mm for at least 50 minutes, - high-early strength: 40 MPa, 6 hours after its preparation, and higher than 55 MPa, after 24 hours. Different polycarboxylate-based superplasticizers and accelerators (lithium carbonate, calcium hydroxide, and normal portland cement) were studied. When the mixture does not contain any accelerator, no strength is recorded after 6 hours. The best accelerating mixture is that containing both lithium carbonate and normal portland cement. The cementitious material is composed of 80% calcium sulfoaluminate cement and 20% normal portland cement. The dosage of lithium carbonate is 0.005% by mass of cementitious material. For a cementitious material content of 600 kg/m3 and W/CM = 0.37, the following performances were obtained: - working time: 65 minutes, - compressive strength: 48 MPa after 6 hours, 57 MPa after 24 hours, and 81 MPa after 60 days.
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