Superplasticizers are key components to enhance greatly the workability of concrete. A new carboxylic acid-based copolymer was synthesized and evaluated as a superplasticizer. This copolymer was prepared from methacrylic acid and 2-acrylamido-2-methylpropane sulfonic acid through free radical polymerization. The test results on cement pastes indicate that this copolymer could uniformly disperse the cement particles and improve the fluidity of the system. Compared to the commercially available naphthalene-based superplasticizer, the polymer requires less amount to achieve the same mini-slump value, and provides longer slump retention time. Thus the synthesized resin has a potential to become a superplasticizer. Finally, the workability and compressive strength of concrete with this new admixture were also tested, and compared with that of the commercial superplasticizers.

Polycarboxylate-based superplasticizers (air-entraining and high-range water-reducing agents) contain a polycarboxylate-based dispersant (PAS and a dispersion retainer. The PA adsorbs to the surface of the binding material particles. Due to steric effects, the particles are well dispersed, resulting in a high level of water reduction and high fluidity (l),(Z). It is considered that in the study of the dispersion effects of superplasticizers, it is important to understand the adsorption properties of the PA. We focused on the molecular size and adsorbed number of PA molecules. Based on the chemical structure and molecular weight of the PA, we calculated its molecular size and determined that the maximum length of the extended trunk polymer was 20 nm and that of the side chain was 7 nm. Considering the effective volume based on thermodynamics, one PA molecule is adsorbed to every 400 nm2 of particle surface. However, according to calculations based on the actual measurement of specific surface area and adsorption amounts, one PA molecule is adsorbed to every 100 nm2 of the particle surface. It is suggested that PA molecules shrink and are adsorbed on the surface of binding materials more densely than expected.

The time dependence of the interaction between hydrating cement particles and a poly-naphthalene sulfonate (PNS) superplasticizer has been investigated using rapid response calorimetry and other physico-chemical approaches. The study focuses on the processes which occur during the first instants following the immersion of the cement particles into the solution, in the presence, or absence, of the PNS superplasticizer. Specifically, the investigation aims to elucidate the dominant phenomena in the coupled processes taking place in the water/cement/sulfate/PNS system, and the consequences of these phenomena on 1- the reaction rates and products and 2- the cement-superplasticizer compatibility The systems discussed here are cement pastes at W/C=3 containing cements having highly different alkali sulfate contents and a normal PNS super-plasticizer. The kinetics of the initial reactions (O-30 min.) are monitored by fast response adiabatic calorimetry; the superplasticizer adsorption, and variations in the ionic composition of the interstitial solution, are also determined at short time intervals during the same period. The evolution of the hydrate phases as a function of time is monitored through XRD analyis.

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

A newly developed ‘polyether-based super-plasticizer’ was found to be much more suitable for self-compacting concrete than the conventional ones because of several advantages, such as high dispersability with minimal setting retardation while maintaining segregation resistance. Polyether-based superplasticizers’ features long ethylene oxide (EO) graft chains which give high dispersability by their steric repulsion, and short main chain with smaller amount of carboxyl group which leads to high early-strength. Furthermore, segregation resistance is improved by using this new superplasticizer with higher content of EO. This new superplasticizer has made possible the self-compacting concrete applications resulting in manpower savings, and improvement of quality and productivity.