Toyoaki Miyagawa

Application of Desalination to Concrete Admixing Fly Ash or Blast-Farnace Slag

This paper mainly describes corrosion behavior of the steel bars in concrete specimens using fly ash or blast-furnace slag, deteriorated by chloride attack, carbonation of concrete, or complex of both mechanisms. Furthermore, chloride removal effect due to applying desalination to such deteriorated specimens is investigated. Results obtained from this study can be summarized as follows: (1) Carbonation depth of concrete using fly ash or blast-furnace slag was larger than that of normal concrete and the larger replacement rate of them became, the more carbonation depth of concrete increased. (2) As the result of measurement of Cl- content in concrete before desalination, in the case of carbonated specimens, soluble chloride percentage to total chloride near the exposed surface was increased with the influence of carbonation of concrete. (3) Chloride removal percentage due to applying desalination to non-carbonated specimens was 15-30% as a whole cover concrete. On the other hand, in the case of carbonated specimens, Cl- ion near the exposed surface was decreased by desalination and chloride removal percentage reached 50-80%.

Study on realkalization with electrolyte containing lithium ion

This study tried the application of electrochemical realkalization using Li3BO3 solution as the electrolyte, compaired with the case of usual Na2CO3 solution. The results obtained from this study are shown as follows: (1) The rate of concrete expansion by alkali-silica reaction (ASR) after realkalization using Li3BO3 solution was smaller than the case of Na2CO3 solution. (2) The realkalization effect obtained just after treatment was enough even when Li3BO3 solution was applied like as the case of Na2CO3 solution. (3) The pH value of cover concrete at 1 year after finishing realkalization using Li3BO3 maintained the same level as the case of Na2CO3 solution. Further more, the pH value obtained by realkalization using Li3BO3 solution maintained acceptable level under the accelerated condition of carbonation for 30 days.

Water Permeability of High Slag Content Concrete

The purpose of this study was to determine the water permeability of high slag content concrete (HSCC) incorporating large amounts of ground granulated blast-furnace slag (GGBS) of high fineness. The main variables are the replacement level of slag, the fineness of slag and the type of chemical admixtures. The slag content in cement ranged from 0 to 95% by weight of total cementitious materials and the fineness of slag ranged from 404 to 1200 m squared/kg. Within the range of this study, the following results were obtained: 1. The coefficient of water permeability of high slag content (HSC) concrete increased as the content of ground granulated blast-furnace slag (GGBS) was increased. However the water tightness of HSC concretes could be improved by utilizing high fineness slag within the range of 122 m squared/kg, and was further improved by utilizing an air entraining and high range water reducing (AEHW) admixture. 2. Both the total porosity and mean diameter of pores increased by raising the slag content, but decreased as the fineness of slag increased. The water permeability of HSC concretes was closely related to the porosity, with the diameter over the certain threshold value, rather than to the mean diameter of pores.

INFLUENCE OF DESALINATION ON BEHAVIOR OF PRESTRESSING STEEL

Desalination is the electrochemical method aiming to remove chlorides from reinforced concrete structures. Until now, it has been applied only to reinforced concrete structures and not to prestressed concrete structures. In this study, desalination was applied to chloride contaminated concrete specimens with pretensioned prestressing steel bars. As a result of the slow strain rate tensile test of prestressing bars after applying desalination, significant influence of treatment on the elastic behavior and plastic behavior until the tensile strength point was not shown but the influence of hydrogen embrittlement due to treatment was impacted on the fracture strength and the contraction rate of fractured sections. As a result of absorbed hydrogen measurement of prestressing steel bars from treated specimens, the release peak of diffusible hydrogen was found. Furthermore, as a result of keeping treated specimens for 1 month, the first peak of diffusible hydrogen (around 470 K) and the change of the fracture behavior due to hydrogen embrittlement disappeared.