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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.

This paper presents results from a major long-term study on chloride induced steel corrosion in concrete. Specifically, data on concrete resistivity and estimated corrosion rates of steel in concrete have been measured and compared. The performance of 50 reinforced concrete slabs made with a range of portland and blended cement binders was evaluated. A high C3A cement, a low C3A cement, a blended fly ash cement and a blended blast furnace slag cement were used. All reinforced concrete slabs were exposed to high chloride conditions by partial immersion in simulated sea water conditions. Reinforcement was cleaned and weighed prior to embedment into the concrete slabs. Periodic non-destructive measurements of concrete performance included half cell potential monitoring, concrete resistivity and electrochemical measurements of rates of corrosion of steel in concrete using potentiodynamic anodic procedures. In addition, individual slabs were broken for reinforcement recovery at predetermined times during the study and measurements made of the area of corrosion and the weight loss of steel through corrosion. As opposed to the initiation-propagation model frequently cited in the literature, three distinct segments were apparent when the estimated corrosion current data were plotted against the concrete resistivity over a period of five years for reinforced concrete slabs considered in this study. The first stage was described as the Quiescent Stage, during which it was found that resistivity increased with time and estimated corrosion current values were low. Upon reaching a maximum resistivity value, a second stage of corrosion took place. This stage was described as the Active Stage, during which resistivity values decreased and estimated corrosion current values increased. After this, a third or Breakaway Stage of corrosion was reached, during which resistivity values decreased at a lower rate while estimated corrosion currents increased significantly. The findings for each of the above stages were consistent with the exposure conditions applied to the slab, in that, after chlorides had reached the steel and caused depassivation, the concrete resistivity decreased while the steel corrosion rate increased. Using the above information, it was found that the time taken to reach the maximum resistivity value could be used as a criterion for corrosion onset as, after this time, steel corrosion rates in concrete could be expected to increase.

High Performance Concrete (HPC) has been developed primarily for its strength having a compressive strength in excess of 70 MPa, approximately double the strength of conventional concrete. The porosity of this type of concrete, especially when silica fume is added to the mix, much lower than conventional mixes. It is, therefore, assumed that high performance concrete provides significantly better protection against corrosion of reinforcing steel than conventional concrete, but this has not yet been substantiated. A field exposure program is underway with cast-in-place and pre-cast samples, containing embedded reinforcing steel probes exposed to pulp & paper industry effluent at two locations on Vancouver Island, B.C., Canada. The cast-in-place samples were loaded in three-point bending prior to exposure to initiate cracks in the location of the corrosion probes. Probes were also embedded in uncracked areas of the beams. One lower quality concrete, one industrial standard concrete, one HPC and one HPC containing silica fume were included in the test matrix. Parallel laboratory corrosion studies are being conducted on cast-in-place specimens exposed to a simulated effluent. The initial results of the field exposure showing the difference in corrosion protection of reinforcing steel in the four different types of concrete subjected to accelerated curing and conventionally cured are presented. Laboratory results investigating the effect of cracking on the corrosion protection provided by the four types of concrete are also presented. The reinforcing steel corrosion was evaluated using linear polarization resistance (LPR) and the more recently developed electrochemical noise measurement technology. The suitability of these techniques to measure and monitor the corrosion of reinforcing steel in concrete is also discussed.

In this report, freezing and thawing test, carbonation test and length change test were carried out, determine the effects of differences in cement kind and curing methods on the durability of super-workable concrete, focusing mainly on placing during cold weather. Normal portland cement and three kinds of low heat type cement were used. A w/c of 50% was used for the normal portland cement, and a ratio of between 3O~35% for the low heat type cement. The curing methods of the specimens are standard curing, atmospheric curing, site sealed curing, site water curing and heat curing. During freezing and thawing test and accelerated carbonation tests, it was found that when heat curing is employed to prevent initial frost damage, if due consideration is not given to the temperature and wetness conditions of the curing concrete, there are cases where durability may be worsened instead of improved. With regard to the measurement of length change by the test methods adopted in current standards, there is a distinct possibility that the measurement values are not only due to drying shrinkage, but are also strongly influenced by autogeneous shrinkage of the concrete