International Concrete Abstracts Portal

A super workable concrete is defined as the concrete which has excellent deformability, high resistance to segregation, and can be filled into heavily reinforced areas without applying vibration. High deformability and high resistance to segregation are important properties of super workable concrete. Since these properties are essentially opposite in nature, they have a tendency to be sensitive to quality fluctuations of materials incomparison to conventional concrete when manufactured at ready mixed concrete plants. For improvement of manufacturing and handling, the authors developed the super workable concrete using ,8 - 1,3-Gluca.n(Curd1a.n) viscosity agent. which i s produced by afermentation process as a The purpose of this study is to investigate the properties of p -1, 3-Glucan which gives a super workable concrete and the mechanism by which it produces such effects. The results confirm that ,8 -1, 3-Glucan exists in the form of independent swollen particles, calcium complex gel which have negative electric charge on their surface. They also indicate that ,4? -1,3-Glucan has the ability to increase the viscosity of cement slurry. Thus, p -1, 3-Glucan gives an effect to increase plastic viscosity without changing yield value of a mortar, which was obtained by wet-screening a concrete.

In the past decade, many efforts have been undertaken to develop highly-workable concrete which consolidates under its own weight without any vibration, specially in Japan. The admixtures used in such concrete are mainly composed of high water reducing superplasticizers, fine limestone dust and viscosity agents to maintain not only high flowability but high segregation resistance of the concrete. The water to cement ratio is generally lower than 0.55. A new admixture is proposed in the present study. It is a mixture of a super-plasticizer and an accelerator with plasticizing properties which also acts as a viscosity agent. The compsition o f the self-levelling concrete is as follows. The total amount of fine materials (cement + fly ash or cement + ground limestone) is 370 kg/m3, while the cement content (normal portland cement CEMI 52.5) is 260 kg/m3. The water to cement ratio is 0.73. The mechanical performancess of the hardened concrete is better than those of a usual French building concrete. The compressive strengths at 16 hrs, 7 days, and 28 days are 8, 30, and 35 MPa, respectively. The unrestrained drying shrinkage reaches 600 to 700 pm/m, at 90 days as predicted from the 28 day results.

Very little has been known about the relationship between the specific properties of particles and the viscosity of suspensions containing them, although it seems very important for the reliable design of quality in the actual use. After the introduction of new rheological theory by Hattori and Izumi (HI theory) based on the DLVO theory and on the structural viscosity theory, it became possible to estimate the time-dependent viscosity of suspension either agitated or unagitated by the calculation. Based on the HI theory, the time-dependent viscosity of unagitated cement paste,-for which the completely dispersed state was assumed as the initial condition, was calculated and results of calculations for the estimation of viscosity increase of cement pastes are presented by the curves showing effects of various properties of cement powders and the condition of use.

Reactive powder mortar (RPM) mixtures cured at room temperature with different portland cement, silica fume and steel fibers were manufactured. The influence of the super-plasticizer type on the RPM performance - in terms of w/c and compressive strength was studied. The acrylic polymer (AP) admixture performed better than the naphthalene (SNF) or melamine (SMF) based super-plasticizers in regard to lower water-cement ratio and higher compressive strength at ages after 3 days. The l-day compressive strength of the RPM with the AP admixture was much lower than that of the corresponding mixtures with SNF or SMF when a C3 A-free portland cement with a low specific surface area was used. This was due to a strong retarding effect of the early hydration when this cement was used in combination with some silica fume types. With other portland cements, the retarding in the early hydration caused by AP did not occur and therefore the l-day compressive strength was quite high. The 28-day compressive strength of RPM specimens, cured at room temperature, were strongly dependent on the type of cement, silica fume and superplasticizer. However, the highest values obtained in this investigation (160-l 80 Mpa) were lower than those reported by the inventors of RPM (170- 230 Mpa).

Betanaphthalene sulfonate condensate (NS) and melamine sulfonate condensate (MS) polymers based superplasticizers have been extensively used in the Precast Industry. Continuos need for improving the performance of concrete has led to the development of products with a higher water reduction and thus higher early strength, typical of melamine based super-plasticizers, but without the drawback of workability loss sometimes encountered with this kind of super-plasticizers. The chemistry of the new product described in this article has been specifically designed to achieve high early and long term strength maintaining the workability typical of NS products at dosages in the range commonly used with melamines. The superior performance obtained with this new product makes it a good alternative to melamine based super-plasticizers when used in precast applications. The paper reports the effect of the new p-naphthalene sulfonate based super-plasticizer on water reduction, air content and compressive strength in concrete prepared with different types and brands of cement conforming to the new EN 197-1 standards. The results show that significant improvements in terms of water reduction and strength development can be achieved with this new NS based product, especially when used with CEM I type cements.