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.

Several superplasticizers were synthesised by an esterification reaction using commercial polymethacrylic acid and polyethylene oxide chains to produce comb-type polymers. These superplasticizers, with same main chain length, but different ester ratios were evaluated in self-compacting concrete (SCC) using cement with a high C3A and soluble alkali content. There is a strong relationship between the initial efficiency (flow value) and the carboxylic ester ratio of the polymeric material. In order to further understand this relationship, preliminary adsorption isotherms using a basic calcium carbonate suspension medium in the presence of these polymers, with and without an addition of sodium sulphate were investigated. The results show clearly that the level of adsorption in a basic calcium carbonate suspension medium decreases when the concentration of sodium sulphate increases, and strongly decreases when the comb-type polymers ester ratio increases. The results tend to show an effect of ionic strength and not an effect of ions influence.

A new slump-loss-controlling agent was found that could control the slump retention time for more than 90 minutes with minimal setting retardation. This slumploss-controlling agent was based on the polyether-grafted polymer in which the specific monomers were co-polymerized. Although this agent did show weak initial dispersing ability of cement particles just after the addition to cement slurry, it was decomposed in the alkaline condition of the cement slurry and gradually enhanced its dispersing ability, which made long retention of dispersability possible. Utilizing the technology of long polyether-grafted chains, which was previously reported to be very effective to disperse cement particles by steric repulsion, high dispersing retention ability with lower dosage and minimal setting retardation could be achieved. This slump-loss-controlling agent has already been used successfully worldwide. This technology will bring various possibilities and merits in concrete construction field such as shortening the construction period.

Concrete technology has evolved considerably lately with the use of New Generation Superplasticizers (NGS). Both laboratory and job site results show some interesting results in combining NGS and Plasticizers. One example is the combination of polycarboxylate derivatives and plasticizers-with set retardation secondary effectseveral examples have been reported where these combinations are more efficient for keeping the fluidity level as a function of time than the NGS alone. Another example of particular interest is the combination of a PolyOxyEthylene DiPhosphonate (POEDP) with a Plasticizer. Some results have shown that the Plasticizer improves somehow the reactivity of the POEDP Considering that Trisulfoaluminate forms at the early stage of the hydration of cement and that this reaction has a significant influence on the rheological properties of the paste the influence of POEPD and plasticizer combinations on the synthesis of Ettringite was analyzed. Rheological and adsorption measurements have been performed on paste of ettringite produced by mixing calcium hydroxide and aluminium sulphate (i) alone, (ii) in the presence of POEDP, and (iii) in the presence of POEDP and Gluconate.

The old concept for optimum sulfate content in portland cement developed by Lerch in 1946 was further applied to study and explain cement admixture interactions related to the soluble sulfate content in systems with portland cement, mineral and chemical admixtures. It was shown that Lerch's criteria for optimum sulfate in portland cement based on isothermal calorimetry is applicable also for studies of modem systems with multiple binders and admixtures. Indirect evidence on the cause of some cement-admixture interactions was provided by means of testing for the effect of additional soluble sulfate added to the cement prior to testing.