Chloride Permeability and Microstructure of Portland Cement Mortars Incorporating Nanomaterials

Chloride permeability of concrete has-been recognized as a critical intrinsic property affecting the durability of reinforced concrete. An experimental study was done, designed to examine the chloride permeability and microstructure of portland cement mortar with nanomaterials admixed at 1% by weight of cement. The electromigration test showed that, for cement mortars of the same mix design, the incorporation of nanoparticles (Fe-2 O-3, Al2O3, TiO2, and SiO2) and nanoclays (montmorillonite) improved the chloride penetration resistance of the mortar, as indicated by the reduced apparent diffusion coefficients of chloride anion. The nanomaterials also reduced the general ionic permeability of the mortar, as indicated by the reduced electric charge passing through. Such improvements were especially significant when using nano-SiO2 and nanoclays. The electrochemical impedance spectroscopy test indicated that incorporation of nanomaterials in cement mortar significantly increased its ionic transport resistance and decreased its electric capacitance, and again such effects were especially significant when using nano-SiO2 and nanoclays. The field emission, scanning electron microscopy test revealed that the admixing of nanomaterials not only led to denser cement mortar but also changed the morphology of cement hydration products. Mechanisms are proposed to explain the physicochemical changes induced by the nanomaterials and the specific surface area of nanomaterials is demonstrated as one of the key-factors. Considering the low cost of nanoclays, their use in concrete to reduce chloride permeability and to improve other properties of concrete is promising.