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In the absence of admixtures, the workability of calcium aluminate cement (CAC) concretes is similar to that of Portland cement concrete. However, the classic types of superplasticisers for Portland cement concrete, lignosulphonates and polynaphthalene sulphonates, have only a modest effect on the workability of concrete made from calcium aluminate cements. Consequently, the placement of CAC concretes at water to cement ratios below about 0.4 can be difficult and necessitates the use of a high cement content (1, 2) . In contrast, a ‘new generation’ superplasticisers (poly carboxylate polyox) has been found to be highly effective in improving the rheology of calcium aluminate cement concrete. If used alone they can also severely retard the setting time, but this effect can be overcome if they are used in combination with other admixtures. This paper discusses the effect of superplasticisers on the flow and setting time of CAC mortars.

Depending on the nature of the materials used, the characteristics of both fresh and hardened concrete can be systematically altered with concrete admixtures. Special investigations were carried out on different polymers used as superplasticizers to determine the mode of action. The emphasis of the investigations was on the adsorption behaviour of the polymers on different cements phases and their influence on the rheological properties of mortar. The adsorption behaviour was investigated by High Performance Liquid Chromatography and the rheological properties were determined in standard mortar mixtures by the flow table spread measurement and by using the Viskomat NT to determine the flow characteristics. Additionally pore solutions were analized Based on these results some interesting correlations co used to explain the mode of action of superplasticizers.

Lignosulfonate has a long history as plasticizers in concrete. This paper reports an investigation of the effect of ultrafiltration of lignosulphonate on rheological properties of concrete with two different modified lignosulfonates. It is shown how the modification also changes the adsorption of the lignosulfonate on the cement and the effect this has on the properties of the fresh concrete. The workability of the concrete is different for the lignosulfonates tested, however, true differences in workability are only observed by the applied rheological approach. The rheological measurements reveal differences in terms of plastic viscosity. Modifications of the lignosulfonate change the performance of the lignosulfonate as a plasticizing admixture. Increased molecular weight and purity of the lignosulfonate increase the plasticizing effect and also improve the ability of the lignosulfonate to reduce the viscosity of the concrete. The viscosity reduction is for a high molecular weight lignosulfonate efficient even at very low dosages. Increasing the molecular weight and purity of the lignosulfonate also reduce the concrete set retardation. High molecular weight lignosulfonate is because of the viscosity and yield value reduction an effective material for formulation of a plasticizing admixture.

This Symposium Publication includes 37 papers selected from the conference that took place in Nice, France, in October 2000. Topics include effects of superplasticizers, interaction of admixtures with calcium aluminate cements, lignosulfates, admixtures for improving resistance to chemical attack, effects of admixtures on concrete shrinkage, and many more. Note: The individual papers are also available as .pdf downloads.. Please click on the following link to view the papers available, or call 248.848.3800 to order. SP195

Chemical admixtures play a central role in modern concrete materials and technologies. In conjunction with mineral additives such as silica fume, chemical admixtures have enabled major improvements in many of the properties of concrete, particularly, compressive strength and durability. Chemical admixtures have also assisted in developing new concrete technologies, for example, concrete pumping and self-leveling, underwater concreting and shotcreting. Chemical admixtures have further promoted the use of secondary industrial materials (blast furnace slag and fly ash) in cementitious systems, contributing to resource conservation and environmental sustainability. In the continuing quest for more cost-efficient and environmentally acceptable materials and technologies, it may thus be expected that chemical admixtures will continue to play an important role in future generations of concrete. Probing into the future, how will concrete chemical admixtures evolve in the coming decades? What trends can be anticipated in future developments and use of these admixtures ? What will be the driving influences for these developments? This paper addresses some of the issues that are considered relevant driving forces to promote changes in the use of currently available chemical admixtures, or in the development of new admixtures. The trends already apparent in cementitious materials and concrete applications provide a reasonable basis for proposing probable trends in the evolution of concrete admixtures into the 2 lSt Century.