ياسر رشيدي

The primary objective of this thesis is to investigate the hybrid effect of halloysite nanotubes (HNTs) and biopolymers on the mechanical properties and durability of cement mortar exposed to chloride ions. To this end, three different biopolymer treatments—casein (C), guar gum (GG), and xanthan gum (XG)—were employed to prepare colloidal dispersions of HNTs in an alkaline cementitious environment. The eva‎luation of the dispersion and time-dependent stability of untreated HNTs in alkaline cement solutions revealed rapid agglomeration and sedimentation. However, XG-treated HNTs demonstrated superior stability compared to those treated with GG and C. Additionally, XG-treated HNTs exhibited a well-dispersed state in suspensions at a pH of 13, with an average particle size of approximately 20 nm, whereas untreated HNTs displayed particle sizes ranging from 200 nm to 7000 nm. Subsequently, the hybrid effect of HNTs and biopolymers on the microstructural and macroscopic properties of cement mortar was examined. Microstructural analyses revealed that incorporating XG-treated HNTs into cement mortar reduced the calcium hydroxide (CH) content through pozzolanic reactions, accelerated cement hydration, and promoted the formation of additional gel structures. Moreover, the modification with HNT-XG shifted the pore size distribution toward smaller diameters and enhanced the microstructural morphology. Macroscopic test results indicated that cement mortar containing HNT-XG achieved the greatest improvements in mechanical properties, permeability, and durability under chloride ion exposure compared to other mixtures studied. After 90 days, the HNT-XG mixture demonstrated increases of 29.4%, 37.1%, and 35.3% in compressive strength, ultrasonic pulse velocity (UPV), and electrical resistivity, respectively. Furthermore, reductions of 23.4%, 15.8%, and 30.1% were observed in total porosity, initial water absorption, and the capillary water absorption rate, respectively. Significant decreases of 41.9% and 28.4% were also recorded in electrical conductivity and the chloride ion migration coefficient. Finally, the presence of XG-treated HNTs in the cementitious system enhanced resistance to the initiation of steel reinforcement corrosion. The corrosion rate of the 90-day HNT-XG reinforced mortar was reduced by 43.4% compared to the control sample.

نانولوله هاي هالوسيت , زيست پليمرها , پخش شدگي , ملات سيماني , خواص ريز ساختار , خواص كلان ساختار

Halloysite nanotubes , Biopolymers , Dispersion , Cement mortar , Microstructure propertices , Macrostructure properties

Yaser Rashidi

Dr. Asghar Habibnejad Korayem