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The durability of reinforced concrete structures has been acquiring an increasing degree of emphasis in research activities. The development of concrete mixtures with regard to different attacks imposed on concrete structures by climatic influences plays a decisive role in this context. Under certain conditions, the performance of these concretes can be increased by using pozzolanic additions, such as fly ash or blast-furnace slag, as cementitious components. This publication intends to summarise the influence of these cementitious components on important processes contributing to chloride-induced corrosion. Diffusion and corrosion cells were used to examine the diffusion resistance and corrosion rate of mortars and concretes containing up to 60 mass.% of fly ash and up to 75 mass.% of blast-furnace slag in relation to the total content of cementitious binders. The results of pore structure investigations were also employed in order to clarify the influence of these cementitious components on ion transport in the microstructure of the concrete.

This paper presents extensive long-term data on chloride penetration into unprotected and protected members of a reinforced concrete structure exposed to an aggressive salt-laden environment. The test results up to 11 years of exposure show that chlorides penetrate very rapidly into the concrete from an early stage, and this penetration increases with time. There was a visible peaking of chloride concentration in the vicinity of the location of the reinforcing bars. Structural members protected with the acrylic rubber coating showed an almost total absence of penetration of chlorides throughout the exposure period, and the coating maintains long-term durability of RC structures under marine environment. The accumulated chloride ions in concrete become important for the durability of reinforced concrete and these have been calculated from the distributions of chlorides in relation to the exposure period. Analytical evaluation shows that the accumulated chlorides are expressed by a model represented by an equation with coefficients,where the coefficients are closely related to environmental conditions and characteristics of concrete.

The relationships between the autogenous shrinkage, and the hydration reaction of cement and the structural change of hardened cement paste have been investigated by hermetically curing the cement pastes of normal portland cement, type B - blast furnace slag cement and 10% silica-fume blended cement prepared at W/C of 0.5 and 0.25 and continuously measuring the humidity changes and the shrinkage strains of hardened cement pastes to obtain the basic data for elucidating the mechanism of autogenous shrinkage. Although there was a time lag between the autogenous shrinkage and the humidity change of hardened cement paste, no autogenous shrinkage took place in the cement paste prepared at W/C of 0.5 showing no humidity reduction. The autogenous shrinkage observed in the cement paste prepared at W/C of 0.25, therefore, is considered to be caused by the self dessication at a relative humidity (RH) from 100 to 80%. The autogenous shrinkage occured mainly during a period from 8 hours to 4 days and slightly increased after that. It is considered that the autogenous shrinkage takes place because the free water contained in pores particularly in fine gel pores formed by producing a large quantity of C-S-H is consumed by the hydration reaction and the humidity in the hardened cement paste is reduced. The autogenous shrinkage of type B - blast furnace slag cement paste was approximately 1,800~ which was about 1.8 times that of normal portland cement paste. Since type B - blast furnace slag cement paste produces more C-S-H than normal portland cement paste, thereby causing remarkable autogenous shrinkage. The autogenous shrinkage of 10% silica-fume blended cement paste is about 1,000u almost same as that of normal portland cement paste, since the pozzolanic reaction is suppressed in its paste prepared at W/C of 0.25 up to 4 days.

In 1997, CANMET in association with the American Concrete Institute and several other organizations in Australia sponsored the Fourth International Conference on the subject. The conference was held in Sydney, Australia. More than 120 papers from 30 countries were received and peer reviewed in accordance with the policies of the American Concrete Institute; 81 were accepted for publication. The accepted papers deal with all aspects of durability of concrete, including chloride and sulphate attack, freezing and thawing cycling, alkali-aggregate reactions, cathodic protection, and the role of supplementary cementing materials to enhance durability of fiber-reinforced concrete and performance of repaired concrete structures. Note: The individual papers are also available as .pdf downloads.. Please click on the following link to view the papers available, or call 248.848.3800 to order. SP170

An analytical expression for estimation of the depth of concrete carbonation is derived by considering that carbonation is controlled by dif-fusion of CO2 in concrete. The depth of concrete carbonation with time is given simply iii terms of the diffusion coefficient of CO2 iii concrete: con-centrat ion of ambient CO2, a n d concent rat ion of carbonat able CaO in the hydration products of cement iii concrete. The diffusion coefficient of CO2 in concrete, which is a function of the volume of empty pores iii concrete, is described and suitably modified. The given expression provides a good explanation for the relationship be-tween the depth of carbonation and the internal microstructure of concrete. The estimated results are compared with some available experimental data and the results of carbonation of a 39-year-old concrete bridge. The expression shows good reliability.