International Concrete Abstracts Portal

Electro-migration and diffusion of ions in electrolyte solution are theoretically described by the Nemst-Plank equation. Also, electro-migration and diffusion of ion can be related by using the Einstein’s equation in dilute solution. In concrete, however, the relationship between electro-migration and diffusion is still unclear, for the influence of the concentrations in pore solution is unknown. Previous work of the authors has shown that it is possible to assess the diffusion coefficients of chloride ion in an ordinary Portland cement mortar through conduction tests by following the Nemst-Plank equation, Debye-Huckel theory and electro-neutrality. This paper evaluates the adaptability of this method to mortars made of several binders, such as ordinaly Portland cement, high-early strength Portland cement, sulfate-resistant Portland cement, low-heat Portland cement, Portland blast-furnace slag cement, ordinary Portland cement with fly ash, ordinary Portland cement with silica fume. In these cases, the concentrations of calcium, sodium, potassium, chloride, and hydroxide ions are different from that of the ordinary Portland cement case. Thus, the adaptability of this method is confirmed in mortar made of a wide range of binders.

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.

Recently, various electrochemical rehabilitation methods, such as desalination, re- alkalization and electro-deposition, have been developed in order to recover deteriorated concrete due to chloride ion or carbonation, and to improve the durability of reinforced concrete structures. However, there is not sufficient information about the influence of these methods on hydration reaction of cement matrix. From this point of view, the authors studied about desalination; relationship between cumulative current and removal of chloride ion, and influence of desalination treatment on hydration reaction of cement matrix with the aid of solid-state 29Si-NMR spectroscopy. The results show that the amount of chloride removed and the charge efficiency depend on the initial chloride content and cumulative current. From 29Si-NMR analysis of specimens which were stored for 4 years after desalination treatment under condition of 20°C and 60%R.H., the ratio of higher-condensed silicates varied depending on the cumulative current during desalination. It became obvious that desalination process influences hydration re cement silicates. action of

A laboratory test and a case history of deteriorated reinforced concrete slab repair are presented. Since several structural problems have been reported for reinforced concrete slabs, it is necessary to establish repair techniques for such slabs. Many structural problems of reinforced concrete slabs derive from a decline in rigidity with age. Although several techniques have been developed, their effectiveness has not been ascertained, especially over the long term. A laboratory test was conducted to ascertain the effectiveness of repair techniques. Based on the test results, the overlay repair technique was applied to actual slabs. In the case history, short and long-term performances of the repaired slabs were measured for more than 2000 days. Changes in the rigidity and natural frequency of the slabs were examined. The material properties and adhesive strength of old and new concrete were also examined. Although the static and dynamic performances of the repaired slabs improved remarkably, their performances gradually decreased with age. It is important to allow a reasonable margin of error for repairing deteriorated slabs.

Three repair mortars were compared in terms of chloride attack preventive capability to propose an appropriate repair method applicable to the damaged concrete structure by chloride-induced corrosion. The repair methods were the cover replacement method and the surface coating method. The ability of these two methods to prevent corrosion were compared in terms of corrosion area and mass loss after 10 years’ outdoor exposure. It was proven that the cover replacement method extending over the backside of reinforcing steel using SBR polymer cement mortar with a corrosion inhibitor was effective while the surface coating method was applicable when the amount of chloride in concrete structures was excessive.