Triethanolamine (TEA) and Triisopropanolamine (TIPA) are used in small amounts as grinding aids in the cement grinding process. TIPA is particularly known to enhance mechanical strength of mortars at 7 and 28 days while TEA does not. A mechanism based on the formation of a soluble TIPA-iron hydroxide complex which could increase the degree of hydration of the cement and so could improve the mechanical properties, has been proposed for the TIPA. The aim of this work is to explain why addition of TIPA or TEA which have close molecular structure lead to different results on the mechanical properties of mortars. The physico-chemical evolution of a cement's hydration was first followed by coupling isothermal calorimetry and ionic concentrations measurements. Then, mechanical compressive tests were carried out on mortars (limestone aggregate). Tetracalcium aluminoferrite (C4AF) hydration is modified in presence of both additive because of the formation of a soluble complex between trialkanolamine and iron III. An adsorption of TEA on the Portlandite surface is significant during the silicate phase hydration, while TIPA does not adsorb. In the case of TEA, the molecule affinity for the Portlandite surface is stronger than that of the formation of the soluble complex. These results could explain differences obtained on mechanical compressive tests of mortars characterising by an increase of the mechanical strength in presence of TIPA.

SP-217 This Symposium Publication includes 39 papers selected from the conference that took place in Berlin, Germany, in October 2003. Topics include cold-weather concreting, durability, polycarboxylate and polycondensate, self-compacting concrete and much more.

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.

The effect of N,N'-dimethylaminoethanol on the corrosion of steel due to carbonation as well as due to chloride ingress is experimentally investigated in this paper. Mortar mixtures were prepared with Portland and blended cements and were exposed in a curing room with a 10%C02 content and 50%-60% relative humidity. Specimens remained in the above mentioned chamber for five weeks. Results available until at that age indicate that carbonation of all mixtures is significantly decreased if N,N'-dimethylaminoethanol is added in the mixure. Significant protection was also offered in the case of the presence of chlorides. In the latter case the inhibiting behavior of N,N'dimethylaminoethanol based corrosion inhibitor against reinforcement corrosion was evaluated by steel reinforcement specimens immersion in artificial concrete pore solution containing corrosion inhibitor and varying amounts of Cl- ions added as NaCl. The corrosion current density, corrosion rate and breakdown potential were determined by electrochemical methods (Linear and cyclic polarization).

A detailed investigation on the concrete specimens made with different chemical admixtures was carried out after 10 years of exposure in the marine splash environment. Chemical admixtures include air-entraining admixture (vinsol), water-reducing admixture (lingosulfonate group), various high-range water-reducing and air-entraining admixtures (naphthalene, melamine, polycarboxyl and amino-sulfonate group), and drying shrinkage reducing admixture (glycol ether plus amino alcohol derivatives). The specimens were tested for carbonation depths, chloride ingress, oxygen permeability, electrochemical and physical evaluations of corrosion of steel bars in concrete, porosity and mineralogy of the mortar portion, and SEM (Scanning Electron Microscopy) investigation of steel-concrete interface. Naphthalene group of high-range water-reducing and air-entraining chemical admixture shows relatively better performance with respect to the strength development and chloride ion ingress in concrete. The use of shrinkage reducing admixture shows no harmful effect after 10 years of exposure. The specially adopted method of casting concrete used in this study causes a formation of good steel-concrete interface that prevents the initiation of corrosion even for water soluble chloride concentration around 1.5% of cement mass.