The aim of the present work is to evaluate the effect of nano-silica (NS) on the hydration, the rheology and the strength development of cement pastes. The advance of chemical reactions is monitored by mean of isothermal calorimetry and thermogravimetric analysis: adding nano-silica particles speeds up the hydration of the cement paste but alter its workability. Indeed, the effect of the nano-silica particles on the hydration kinetics can be modelled by accounting for its high specific surface and a flocculation model based on the DLVO theory is proposed so as to investigate the stability of nano-silica suspensions in the fresh cement paste. As a consequence, the dosage of nano-silica can be optimized to promote the early age strength. Lastly, a ternary blend incorporating fly ash can be designed so as to provide an early age strength similar to that of the cement while lowering the induced CO 2 emissions.
PCEs are well known to improve the initial fluidity of CSA. However, their dispersion efficiency drops quickly over time. This issue can be solved by incorporating retarders. In this context, this paper deals with the influence of citric acid, used as a retarder, PCE and their combination on the hydration and workability of CSA. Isothermal calorimetry, XRD and TG analysis were used to describe the hydration process, while workability was characterized with the mini-cone test. Adsorption behavior was investigated using total organic carbon analyzer coupled with ion chromatography. Results show that the introduction of citric acid retained the dispersion efficiency of PCE over time. However, the initial dispersion efficiency of PCE was decreased by citric acid as the latter tend to adsorb first on the surface of cement grains, inhibiting the adsorption of PCE. A dispersion model was proposed to describe the acting mechanism of these admixtures on CSA.
The aim of this work was to investigate the effect of polycarboxylate type superplasticizers (PCE), and three different retarders (citric acid, tartaric acid, potassium gluconate) and their combination on hydration process and rheological properties of CSA at early age. The hydration process was described through isothermal calorimetry, while the rheological properties were characterized through yield stress of cement pastes determined by rheometry. The results show that gluconate is the most powerful retarder, followed by tartaric acid, then citric acid. PCE strongly improves the fluidity of the pastes but a rapid loss of workability is noticed. On the contrary, retarders slightly decrease the yield stress of the pastes but slowdown the loss of fluidity. The combination of the both admixtures allows to maintain high fluidity for longer time. However, for citric acid, and even more for tartaric acid, a rheological instability, characterized by a decrease followed by an increase in the yield stress over time, is noticed. Potassium gluconate seems to be the best retarder to combine with PCE since no instability and longer maintenance of workability were observed. An optimum dosage, leading to the best initial fluidity to the pastes, was also determined for the three retarders. The rheological results are related to the delay induced by the retarder on the hydration products formation for the first hours of hydration and to competitive adsorption between retarder and PCE.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.