International Concrete Abstracts Portal

The influence of silane-based hydrophobic products - used as concrete chemical admixtures - on the corrosion of steel rebars was studied. Reinforced concrete specimens with and without a silane admixture were exposed to seawater or to aqueous solutions of de-icing salts containing chlorides. Sound and uncracked or deliberately pre-cracked concrete specimens were manufactured and cured before the exposure to aggressive environments. In the pre-cracked specimens the concrete crack tip was in contact with the steel reinforcement. The results - in terms of corrosion electrochemical potential, short circuit electric current and visual corrosion observed on the steel reinforcement - were compared with those obtained on the corresponding uncracked specimens. In uncracked specimens any corrosion process was completely blocked independently of the water to cement ratio and concrete cover provided that hydrophobized concrete was used. This effect was due to lack of water penetration, and then of the chloride ingress, through the pores of the hyrophobized cement matrix. In uncracked specimens without the silane admixture, there was corrosion risk when high water to cement ratio and/or thin concrete cover were adopted. On the other hand, corrosion of steel rebars was surprisingly more severe in cracked specimens manufactured by hydrophobized concrete rather than in the corresponding reference concrete specimens without the hydrophobic admixture. These results can be interpreted by admitting that oxygen diffusion -which is needed to feed the corrosion process - can occur directly as a gaseous phase through the open concrete voids in hydrophobized concrete, whereas in concrete without silane oxygen can diffuse much more slowly only through the water filled concrete voids.

Galvanized steel and corrosion inhibitors added to concrete are considered methods to protect reinforcement from corrosion. In present paper the simultaneous and separated use of both methods are considered. Concrete specimens have been made for the study. For depassivation the spray salt chamber was used. The results show that if NO2 is used the resistance of galvanized steel to chloride attack is improved. Bare steel embedded in concrete with NO2 - resists well chloride attack.

A technology to impart high fluidity to concrete with an extremely low W/C range of about 0.2 is required, in order to place ultra high- strength concrete with a compressive strength of over 100 MPa. For this purpose, the authers have developed a methacrylic water- soluble polymer as a superplasticizer (SSP) that imparts adequate workability and excellent cement dispersing capability to concrete mixtures with low W/C. Also, the high cement content of ultra high- strength concrete containing normal portland cement leads to high concrete temperature due to heat of hydration, posing problems of thermal cracking and low long- term strength. In this study, the authers used a low- heat, belite- rich portland cement recently developed in Japan, together with powder silica fume to produce ultra high- strength concrete containing the SSP with a low water- binder ratio of approximately 0.2. As a result, the belite-rich portland cement was foud to reduce the adiabatic temperature rise without causing set retardation when compared with normal portland cement. In addition, the concrete showed high fluidity as well as a high long- term compressive strength of over 150 MPa. These results suggest that the SSP is highly compatible with low- heat cement and is very effective in producing high-performance concrete when used in combination with this type of binder.

Seven different polymer latexes, characterised by different resistance to alkaline hydrolysis, were used to produce polymer-modified cement mortars. The following polymers were tested : styrene-butadiene copolymer, vinyl acetate-vinyl versatate copolymer, vinyl acetate-vinyl versatates terpolymer, vinyl acetate-ethylene copolymer, vinyl acetate-vinyl propionate copolymer, vinyl acetate-dibutyl maleate copolymer and vinyl acetate homopolymer. Measurements of compressive strength, dynamic modulus of elasticity, water absorption and bond-strength to a concrete substrate were carried out on the polymer-modified mortars in comparison to a reference mixture without polymers. Infrared and XRD analytical techniques were used to investigate the alkaline hydrolysis of the polymers and cement hydration, respectively. The results indicate that polymers with higher resistance to hydrolysis performed better in terms of higher bond strength to the concrete substrate and lower water absorption of the corresponding mortars.

Recently comb-like macromolecules which have a graft chain made of polyethylene oxide are attracting attention as superplasticizers and put to practical use in the field of flowing and high strength concrete. Comparing ordinary AE water reducing agents, these admktures have a higher water reducing ratio, smaller change of slump with the time and less set retarding property. The properties of solid spheres dispersed in solvent is explained by the magnitude of the inter-particle potential energy. We discuss the total potential energy of alite stabii by adsorbed superplasticizer containing polyethylene oxide graft chains. The interparticle potential energy was mainly controlled by steric hindrance effect of adsorbed macromolecule and van der Waals interaction of .