The interaction mechanism between polycarboxylate-type superplasticizer (PCP) and cement hydration is not fully understood and incompatibilities between concrete and additive are sometimes observed. In some cases, the fluidity tends to increase ("over-fluidification") few minutes after mixing. This is a problem because the over-fluidification leds to bleeding of the concrete which could be critical on job site. Our study consisted first in highlighting the phenomenon of "over-fluidification" by slump flow tests on mortar. Next, the time evolution of the rheological behaviour of cement pastes in the presence of PCP was analysed thanks to a rheometry protocol in order to quantify the phenomenon. Later on, a parametric study was undertaken using this methodology. The operating conditions such as temperature and mixing process were studied as well as the effect of PCP structural parameters and the chemical characteristics of cement. In order to understand the origin of the phenomenon, adsorption measurements of PCP on cement particles were performed in the same conditions as those in the rheological measurements. Indeed, the phenomenon of "over-fluidification" could be related to the rate of the initial adsorption and the adsorption kinetics, both of which depend on the parameters of the process, the PCP structure and the cement reactivity.

Dynamic and static stability of self-consolidating concrete (SCC) affect the production, transport, and overall performance of the concrete. Viscosity- modifying admixtures (VMAs) are often incorporated to enhance the stability of SCC, especially in the case of cast-in place concrete. The influence of a new type of polysaccharide, diutan gum, on key characteristics of SCC targeted for the construction and repair of concrete infrastructure is examined. The investigation compares the performance of SCC made with diutan gum and different types of high-range water reducing admixtures (HRWRAs), including polynaphtalene sulphonate (PNS)-based and two polycarboxylate polymer (PCP)-based HRWRAs. The effect of admixture combination on workability, rheology, stability, and setting time was investigated. The robustness of optimized VMAHRWRA system and key durability parameters of the concrete were also determined. Test results indicate that the use of diutan gum increases the plastic viscosity and yield stress of SCC. Regardless of the VMA and HRWRA combination, the use of diutan gum can significantly decrease segregation and bleeding, and lead to greater homogeneity of the concrete during the dormant period of cement hydration. The performance of SCC made with diutan gum depends on the type of PCP in use. Out of two PCP-based HRWRA, one system resulted in lower HRWRA demand, increase in viscosity with the increase in VMA content, and greater stability. The use of PCP and diutan gum is shown to lead to adequate robustness where the SCC can tolerate small changes in sand moisture content without significant effect on SCC properties. SCC made with medium dosage of diutan gum and PCP is shown to develop adequate air-void system and excellent frost durability and resistance to de-icing salt scaling.

One-pack hybrid admixture (HSP) combining high fluidity, viscosity-reducing property, and shrinkage-reducing capability for high strength concrete with a target strength of 60 to 150 MPa was developed and examined. HSP showed high fluidity and viscosity-reducing performance, as well as excellent autogenous shrinkage-reducing effect to achieve a reduction in the autogenous shrinkage of 21 to 44% with respect to that of concrete containing a conventional high-range water-reducing admixture. HSP was therefore found to be a simple and effective solution to shrinkage problems for a wide range of high strength concretes.

Pure C3A hydrates under formation of layered phases (e.g. C4AH19 and C2AH8) which quickly convert to the cubic phase C3AH6. In presence of polycarboxylate (PC) superplasticizers during C3A hydration, intercalation of the PC molecule into the layered calcium aluminum hydrate occurs. The resulting organo mineral phases Ca-Al-PC-LDHs are very stable. They were characterized by powder XRD, elemental analysis, IR spectroscopy and TEM microscopy. XRD patterns show that with increasing side chain length (nEO) of PC, the distance (basal spacing) between the [Ca2Al(OH)6]+ layers increases. PCs with side chain lengths up to 45 ethylene oxide (EO) units intercalate well whereas a PC with 111 EO units no longer intercalates. Calculations indicate that the PC side chains mostly are compressed or tilted to fit in between the inorganic layers.

The influence of silane-based hydrophobic agents, added to concrete as chemical admixtures, on the corrosion resistance of galvanized steel reinforcement embedded in concrete was studied. Sound or deliberately pre- cracked concrete specimens, with 0.5 or 1 mm wide crack, were manufactured with w/c of 0.45 and 0.75, both in the presence and in the absence of a silane admixture. The specimens were exposed to wet-dry cycles in a 10% NaCl aqueous solution. The results, in terms of electrochemical measurements, as well as visual and metallographic observations carried out on the galvanized steel reinforcement removed from the specimens, showed that the hydrophobic concrete is able to protect galvanized steel reinforcement from corrosion even in the presence of cracks in the concrete cover, especially when a high w/c is used.