International Concrete Abstracts Portal

Because of the shortage of aggregate, the reinforced concrete -containing sea sand and/or sea water can probably be used for marine structures. These marine structures may experience corrosion problems due to salt attack that can result in early deterioration. Therefore, such structures should be protected against corrosion damage induced by chloride ion to extend the service life. This study was focused on a basic counter-plan against concrete corrosion related to marine infrastructures, especially the evaluation of effects of various corrosion inhibitors with different cover thicknesses. Several electrochemical/corrosion test techniques, i.e. half -cell potential, linear & cyclic polarization behaviors & autopsy inspection, were included. Based on this long-term(7 years) study, it was concluded that a chloride ion accelerated reinforcement corrosion seriously, however, a increase of cover thickness and adoption of some inhibitors could provide positive effects against the chloride-induced corrosion. In addition, it was recognized that the electrochemical corrosion tests generally agreed with those of visual autopsy examinations in these long-term experiments.

One of ways to improve the durability of the reinforced concretete structures is sealing with various coating materials on the surface of the concrete that represses the penetration of moisture, chloride ions and carbon dioxide gases which may cause the reduction of durability. Up to now epoxy and urethane-based coating materials are widely used for coating. However, these amterials have the characteristics of poor crack bridging, large thermal expansion and vulnerable color by ultraviolet rays. Also their coating effect depends on application methods that it is dubious of maintaing long-term durability so the development of new alternative coating materials is in demand.Test were performed on an aluminum oxide-isocyanate-based material for coating in order to improve the weather resistance, adhexiveness to concrete surface, resistance of chloride penetration and carbonation by forming the aluminum oxide coating on the surface. Aluminum oxide-isocyanate-baced coating material is compared with other coating materials, and shows higher color retention against ultraviolet rays and resistance of chloride penetration and carbonation and protection of reinforcing steel against corrosion.

Fiber reinforced polymer composite (FRPC) wraps are increasingly being used for rehabilitation and strengthening of concrete structures This paper presents the results of an experimental study on the tensile performance of cement-based specimens wrapped with FRPC sheets subjected to wet-dry and freeze-thaw cycles. The tensile strength values were evaluated using the ASCERA hydraulic tensile tester. This simple testing technique provides a uniform stress distribution throughout the specimen, thus minimizing eccentricity and gripping effects, which can be of a significant source of error. Cement-based specimens were wrapped with three different types of FRP tow sheets: two carbon and one glass. Test variables included the type of fiber (Cl, C5, and GE) and the environmental exposure conditions. The specimens were conditioned in three different environments, as follows: a) room temperature (23C), b) 300 wet-dry cycles using salt water and c) 300 freeze/thaw cycles. At the end of each exposure, ultimate strength and load-extension behavior were obtained and then compared to the performance of unconditioned samples. Results show that specimens wrapped with carbon fiber reinforced polymer (CFRP) experienced no reduction in strength due to exposure, whereas specimens with glass fiber reinforced polymer (GFRP) experienced a significant reduction in strength. Fractography was used to identify the failure initiating flaw and failure mode for the fractured tensile specimens.

This contribution deals with the development of slurries for the restoration of brickwork buildings in Northern Germany. Various slurries on the basis of two binders with a high sulphate resistance with an admixture of solid glass globules respectively were developed, one slurry on the basis of lime the other on the basis of cement. Their aggregate is of fine quartz sands and various additives were used. The slurries were developed to restore historical terracotta. Beside the workability and the water retention capacity of the slurries, technological pa-rameters such as dynamic modulus of elasticity, compressive strength, bending and bond strength and hygrical parameters such as water absorption, water desorptions and water vapour diffusion were investigated. Further important characteristics were the resistance to freezing and thawing, the scuff resistance and the efflorescence behaviour. Some of the slurries were successfully applied to the terracotta surfaces.

In China, ancient concrete was excavated in which a hydraulic type of cement resembling modern cement was supposed to have been used. This paper gives first, detailed characterization on the raw stone of this ancient cement both from chemical and mineralogical point of view. Also, an attempt has been made to reproduce the ancient cementitious material by burning the raw stone. The change in the hydration products and mechanical properties of hardened specimen were pursued during a hydration test, and the results can be summarized as follows. l The raw stone bears a striking resemblance in chemical composition to the modern ordinary Portland cement (as recalculated in the de-carbonated form). l Small crystal size silicious species such as quartz, clay, mica and feldspar were well dispersed in the texture of the raw stone. l B -Ca,SiO, was observed in the burned stone at 1000°C. l An increase in hydration products( CSH and Ca(OH) 2 ) were observed with progress of hydration. l The hydrated paste specimen showed a compressive strength of 10 MPa at 28 days with a w/c of 0.60.