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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
T. Sugamata, T. Sugiyama, and A. Ohta
Recently, ultra high-strength concrete with a specified concrete strength of 100 N/mm2 or more is being applied in Japan. The use of ultra high-strength concrete in the lower stories of high-rise buildings allows the architects to reduce the sectional area of support columns and thus increase floor areas. Other advantages are the suppression of cracking caused by earthquakes, and the increased durability of the concrete structure. In Japan, these ultra high-strength concretes are placed to congested reinforcement point. So, they are required to have high deformability and low viscosity. To produce this kind of concrete having an Fc of 100 N/nun2 or more, the water-cement ratio must be below 25%. Conventional BNS-based high-range water-reducing agents cannot impart high deformability and low viscosity until placement is finished to concrete with low water-cement ratio. Conventional polycarboxylate-based high-range waterreducing agents make the fresh concrete very deformable; however, the viscosity of the concrete increases, resulting in high loads when pumping and subsequent poor placing ability. It is clear that a new high-range water-reducing agent that imparts high deformability and low viscosity to the concrete is needed. A newly developed high-range water-reducing agent (SPN) imparts high deformability and low viscosity to the concrete until placement is finished. The authors compared the viscosity reducing effects of SPN and conventional polycarboxylatebased high-range water-reducing agent in concrete.
The paper summarizes the results on flowing and cohesive superplasticized mixtures studied and placed in the 1970's and 1980's with properties very close to those of Self-Compacting Concretes (SCCs) presently considered to be the most advanced cementitious material. Case histories (from Hong Kong, New York, and Trieste, Italy) concerning placing of superplasticized self-levelling concrete without any vibration at all, published in the 1980's, are re-examined to compare them with the present SCCs. In particular, the paper deals with the ingredients of these mixtures (superplasticizer, cement, fly ash, ground limestone, silica fume, etc.) by examining their specific role in determining the main properties of these concretes, such as fluidity, on the one hand, and resistance to segregation, on the other. Some interesting new materials, such as ground fly ash or powder from recycled aggregates, appear to be very promising for manufacturing SCC in agreement with the requirements needed for sustainable progress.
K. Tsukada, M. Ishimori, and M. Kinoshita
Three new polycarboxylate-based liquid superplasticizers (SPI-3) and powder superplasticizers (PSPI-3), which are made from SPI-3, are synthesized and evaluated. SP3, which has two different lengths of polyoxyethylene chains in one polymer molecule, showed high cement dispersing capability, good fluidity retention and short setting time. PSP3, which is made from SP3, showed low moisture absorption and excellent antiblocking property. The results show the following properties of PSP3, compared to those of general powder type superplasticizers such as Naphthalene-based powder superplasticizer (NS) and Melamine-based powder superplasticizer (MS). 1) Necessary dosage to obtain equal fluidity is about a tenth. 2) Fluidity retention is better. 3) Setting time is shorter. 4) Compressive strength of mortar is higher. 5) PSP3 is non-formalin type superplasticizer.
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.
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.
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