Étude de l'influence de l’ajout initial et d’un ajout retardé d'adjuvants sur le comportement des matériaux cimentaires

Abstract

Concrete is preferred as material for construction mainly because, it is one of the cheapest material available and can also be produced by using locally available materials. However, the factual acceptance emanates from the fact that it is regularly evolving to fit the diverse and needs of the increasingly developed and industrial contours of the world today. There are several modifications adopted to produce materials of higher capability. One such modification to produce high strength capabilities of concrete is incorporation of admixtures. It mainly increases the mechanical and durability characteristics of concrete. However, these also lead to undesired side effects. One such effect is delaying of hydration. Cement hydration involves complex mechanism with coupled reaction from multi-components. Addition of these admixtures creates interferences with mineral phases reactions which implicates to the mechanisms which remain unclear. These can affect the efficacy of cement hydration. So additional research experiments are required in the field of dosages and additional time of admixtures. In this present investigation, influences of dosages and addition time are studied on different admixtures such as superplasticizer, viscosity modifying admixture, C-S-H seeds, nanoclay and accelerators. For all these, three percentages of admixtures are individually incorporated for initial and delayed addition. Moreover, the present study considered hydration analysis and quantification of elements and mechanical characteristics. For hydration characteristic, we consider calorimetry. For quantification of elements and mechanical characteristic, we consider ICP-OES and compressive strength. Addition time effects following different percentages of admixtures are the primarily studied on this investigation. Results show that delay addition induces higher hydration activity with higher concentrations of ions compared to initial addition. These lead to a better hydration. With C S-H seeds, the compressive strength slightly decreases with the increasing in percentages of this admixture while with delayed addition, strength is not impacted. Moreover, we observed a delaying time and intensity of heat flow for delayed addition of C-S-H particles. With addition of viscosity modifying admixture and nanoclay, we have not observed any variations in pore solution composition with the increase in dosages and the total heat flow as well as compressive strength decrease. We observed, an increase in total heat flow for delayed addition for all admixtures. Nevertheless, the compressive strength at 28 days decreases with delayed addition of superplasticizer and viscosity modifying admixture. Interestingly, for nanoclay the compressive strength increases with delayed addition. In summary, effect of addition time is dependant of admixture type and conclusions differ on characteristic desired. Moreover, admixtures modified cement particles surface with impacting their hydration which may vary among different admixtures and types of cement. Consequently, these results and observations are not generalizable and imply some systematic research in addition time of admixture to improve the use of chemical admixtures.

Date	9 Jul 2020
Original language	French
Awarding Institution	École de technologie supérieure
Supervisor	Claudiane Ouellet-Plamondon (Supervisor)