Cette étude a été menée afin d’identifier les paramètres qui permettent de contrôler la réaction de géopolymérisation et les propriétés d’usage des matériaux finaux. Différentes sources aluminosilicates et solutions alcalines ont donc été sélectionnées afin d’évaluer leur réactivité. Ensuite, une étude de faisabilité des matériaux consolidés a été initiée pour identifier les zones d’existence des matériaux géopolymères dans le diagramme ternaire Si/Al/M/O. L’évolution des échantillons au cours de la formation a été suivie par analyses thermiques (ATD-ATG), pour quantifier l’énergie nécessaire à la formation des oligomères, et par spectroscopies infrarouge et résonance magnétique nucléaire afin de déterminer la nature des réseaux formés et le taux de la réaction. Une forte corrélation a été mise en évidence entre la réactivité des précurseurs, la structure locale et poreuse et les propriétés mécaniques. Ces données ont été exploitées pour valoriser d’une part une argile tunisienne de faible réactivité et d’autre part pour recycler un déchet géopolymère dans des nouvelles formulations. / This study was undertaken to identify the parameters that control the geopolymerization reaction and the working properties of the final materials. To do this, various aluminosilicate sources and alkaline solutions have been studied to exacerbate their reactivity. Then a feasibility study of the consolidated materials was conducted to identify the geopolymer existence domain in Si-Al-M / O ternary diagram. The evolution of samples during formation was monitored by thermal analysis (DTA-TGA), to quantify the required energy for oligomer formation, and infrared and nuclear magnetic resonance spectroscopies to determine the nature of formed networks and the reaction rate. A strong correlation was evidenced between the precursors reactivity, the local and porous structure and the mechanical properties. The obtained results have been exploited to use poorly reactive Tunisian clay as alternative aluminosilicate source and also to reuse geopolymer waste in new formulations.

This thesis reports on the research outcome of corrosion mechanism and corrosion rate of mild steel in different environments (saline, alkaline solutions and concrete media) using potentiodynamic polarization technique. The study also included the effect of corrosion on bond strength between reinforcing steel and concrete using pull-out test. Corrosion of mild steel and 316L stainless steel with different surface conditions in 1, 3 and 5% saline (NaCl + Distilled water) was investigated. Specimens ground with 200 and 600 grit silicon carbide grinding paper as well as 1μm surface finish (polished with 1μm diamond paste) were tested. In case of mild steel specimens, reduction in surface roughness caused increase in corrosion rate, while in 316L stainless steel corrosion rate decreased as the surface roughness improved. Metallographic examination of corroded specimens confirmed breakdown of passive region due to pitting corrosion. Corrosion of mild steel was also investigated in alkaline solution (saturated calcium hydroxide, pH =12.5) contaminated with 1, 3 and 5% saline. A series of corrosion experiments were also conducted to examine the efficiency of various concentrations of calcium nitrite (CN) on corrosion behaviour of both as-received and polished mild steel in alkaline solution containing 3% saline after 1 hour and 28 days of exposure. Corrosion rate was higher for the as-received than polished mild steel surface under the same testing conditions in NaCl alkaline solution with and without nitrites due to the effect of surface roughness. Morphology investigation of mild steel specimens in alkaline solution ii containing chlorides and nitrites showed localized pits even at nitrite concentration equal to chloride concentration. Corrosion of steel bars embedded in concrete having compressive strengths of 20, 30 and 46MPa was also investigated. The effect of 2 and 4% CN by weight of cement on corrosion behaviour of steel bar in low and high concrete strengths specimens were also studied. All reinforced concrete specimens were immersed in 3% saline solution for three different periods of 1, 7 and 15 days. In order to accelerate the chemical reactions, an external current of 0.4A was applied. Corrosion rate was measured by retrieving electrochemical information from polarization tests. Pull-out tests of reinforced concrete specimens were then conducted to assess the corroded steel/concrete bond characteristics. Experimental results showed that corrosion rate of steel bars and bond strength were dependent on concrete strength, amount of CN and acceleration corrosion period. As concrete strength increased from 20 to 46MPa, corrosion rate of embedded steel decreased. First day of corrosion acceleration showed a slight increase in steel/concrete bond strength, whereas severe corrosion due to 7 and 15 days corrosion acceleration significantly reduced steel/concrete bond strength. Addition of only 2% CN did not give corrosion protection for steel reinforcement in concrete with 20MPa strength at long time of exposure. However, the combination of good quality concrete and addition of CN appear to be a desirable approach to reduce the effect of chloride induced corrosion of steel reinforcement. At less time of exposure, specimens without CN showed higher bond strength in both concrete mixes than those with CN. After 7 days of corrosion acceleration, the higher concentration of CN gave higher bond strength in both concrete mixes. The same trend was observed at 15 days of corrosion acceleration except for the specimen with 20MPa compressive strength and 2% CN which recorded the highest deterioration in bond strength.

This thesis reports on the research outcome of corrosion mechanism and corrosion rate of mild steel in different environments (saline, alkaline solutions and concrete media) using potentiodynamic polarization technique. The study also included the effect of corrosion on bond strength between reinforcing steel and concrete using pull-out test. Corrosion of mild steel and 316L stainless steel with different surface conditions in 1, 3 and 5% saline (NaCl + Distilled water) was investigated. Specimens ground with 200 and 600 grit silicon carbide grinding paper as well as 1¿m surface finish (polished with 1¿m diamond paste) were tested. In case of mild steel specimens, reduction in surface roughness caused increase in corrosion rate, while in 316L stainless steel corrosion rate decreased as the surface roughness improved. Metallographic examination of corroded specimens confirmed breakdown of passive region due to pitting corrosion. Corrosion of mild steel was also investigated in alkaline solution (saturated calcium hydroxide, pH =12.5) contaminated with 1, 3 and 5% saline. A series of corrosion experiments were also conducted to examine the efficiency of various concentrations of calcium nitrite (CN) on corrosion behaviour of both as-received and polished mild steel in alkaline solution containing 3% saline after 1 hour and 28 days of exposure. Corrosion rate was higher for the as-received than polished mild steel surface under the same testing conditions in NaCl alkaline solution with and without nitrites due to the effect of surface roughness. Morphology investigation of mild steel specimens in alkaline solution ii containing chlorides and nitrites showed localized pits even at nitrite concentration equal to chloride concentration. Corrosion of steel bars embedded in concrete having compressive strengths of 20, 30 and 46MPa was also investigated. The effect of 2 and 4% CN by weight of cement on corrosion behaviour of steel bar in low and high concrete strengths specimens were also studied. All reinforced concrete specimens were immersed in 3% saline solution for three different periods of 1, 7 and 15 days. In order to accelerate the chemical reactions, an external current of 0.4A was applied. Corrosion rate was measured by retrieving electrochemical information from polarization tests. Pull-out tests of reinforced concrete specimens were then conducted to assess the corroded steel/concrete bond characteristics. Experimental results showed that corrosion rate of steel bars and bond strength were dependent on concrete strength, amount of CN and acceleration corrosion period. As concrete strength increased from 20 to 46MPa, corrosion rate of embedded steel decreased. First day of corrosion acceleration showed a slight increase in steel/concrete bond strength, whereas severe corrosion due to 7 and 15 days corrosion acceleration significantly reduced steel/concrete bond strength. Addition of only 2% CN did not give corrosion protection for steel reinforcement in concrete with 20MPa strength at long time of exposure. However, the combination of good quality concrete and addition of CN appear to be a desirable approach to reduce the effect of chloride induced corrosion of steel reinforcement. At less time of exposure, specimens without CN showed higher bond strength in both concrete mixes than those with CN. After 7 days of corrosion acceleration, the higher concentration of CN gave higher bond strength in both concrete mixes. The same trend was observed at 15 days of corrosion acceleration except for the specimen with 20MPa compressive strength and 2% CN which recorded the highest deterioration in bond strength.

Hyaluronic acid is commonly used in dermatological fillers in the form of gels. It is established how these gels' firmness is affected by the amount of cross linker and hyaluronic acid respectively. However, the effect of hydroxide ions in solution is rather unknown. This thesis examines how the alkalinity of the solvent affects the intrinsic viscosity of 3 MDa hyaluronic acid by using the method of Ubbelohde capillary viscometry. Sodium hydroxide solutions between 2 and 10 wt% were prepared to study the variation in intrinsic viscosity at concentrations relevant for cross linking (1<wt%). From these respective solutions, four solutions of different mass concentrations of hyaluronic acid were made. The flow time of respective samples were measured between two points in the capillary viscometer in a controlled temperature of 25 °C with an SI Viscoclock to ensure a high accuracy.From the resulting flow times, the intrinsic viscosity was calculated. The intrinsic viscosity varied between 0,55 and 0,70. The relation between intrinsic viscosity and hydroxide ion concentration had a correlation coefficient r < 0,001. No trend could be ensured as the confidence interval for the intrinsic viscosity at the different concentrations was too large.