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The background to a major study into the corrosion characteristics of steel reinforcement within portland and blended cement concretes is presented. The objectives of this work included an investigation into relationships between chloride-ion concentration and the onset and rate of steel corrosion in concrete. Corrosion activity of steel reinforcement within concrete specimens was measured using procedures including half-cell potential, resistivity, and potentiodynamic anodic polarization. A total of four binder types that included a slag-blended cement and a fly ash-blended cement were used. Chlorides were introduced into the concrete specimens subsequent to casting and curing by partial immersion into salt solutions. The development of a procedure to electrochemically measure the corrosion rate of steel in concrete slab specimens partially immersed in chloride solutions is described. Some of the data obtained using this procedure are discussed in relation to measured half-cell potentials for slab specimens. Based on information available to date, assessments were made regarding the relative marine durability performance of the various binder types considered. Obtained half-cell potential data were analyzed with respect to the time taken to reach -350 mV (versus Cu/CuSO 4), a value where there is a 95 percent probability of corrosion activity as defined by ASTM C 876. Using statistically based procedures, it was found that concrete water-binder ratio was the major influence on the time taken for half-cell potentials to reach -350 mV. The binder type also had a significant influence on the time taken for potentials to reach -350 mV. Considering concretes cast at equal water-binder ratios, half-cell potentials for reinforcement with slag-blended cement concretes took longer to reach -350 mV when compared with other binders tested.

Cubes and slab specimens prepared from three concrete mixtures containing three types of fly ash (FA), Classes F, C, and F/C, and a control portland cement concrete (PC) were cast and moist cured for either 7 or 28 days. Following 14 days of air drying, the cubes were immersed for 21 days in, and the slabs ponded for 12 months with, 15 percent NaCL solution. Chloride-ion distribution profiles were determined at four depth intervals. For all four concretes, the chloride ion permeability decreased when the length of moist curing was increased from 7 to 28 days. However, after 12 months of testing, the two mixes containing FA Class F and F/C exhibited such low chloride-ion contents at depths below 25 mm that the length of moist curing had little influence on chloride-ion reduction in contrast to that found for PC concrete, and to a lesser degree, concrete containing FA Class F. Use of all thre FA materials resulted in remarkable improvement in concrete impermeability when compared with PC concrete.

It is well known that reduction of free lime in reinforced concrete by air carbon dioxide neutralization and calcium carbonate formation makes steel reinforcement more susceptible to corrosion, since the reduction of pH eliminates the passivity conditions and can promote iron corrosion. On the other hand, the addition of pozzolan also causes a reduction of free lime by producing calcium silicate and calcium aluminate hydrates. It may therefore seem that fly ash addition, which improves many aspects of concrete durability, can specifically reduce the iron protection from corrosion promoted by reduction of pH. Concretes containing different amounts of ordinary portland cement and fly ash were produced. Fly ash (an additional 20 percent by weight of cement), was used either to replace cement or as an additional ingredient without any cement reduction. Plain and reinforced specimens were manufactured. All the specimens were kept in a carbon dioxide enriched (30 percent by volume) room to accelerate the carbonation process. The carbonation depth on plain concrete specimens and electrochemical measurements on reinforced specimens were carried out. The results indicated that fly ash addition reduces the carbonation rate when used without cement reduction, whereas it accelerates the process when used to replace cement. The electrochemical measurements of electric potential and polarization resistance are not significantly affected by the presence of fly ash, especially when added without cement reduction. The visual observation of iron reinforcement indicated that fly ash addition does not substantially modify the corrosive aspects, even when it replaces cement.

Sulfate damage in concrete is a result of the reaction between C 3A in portland cement, which produces the hydration of calcium silicates and water soluble sulfates. The damage is reduced or overcome by replacing some of the cement with low-lime fly ash. High-lime fly ashes usually contain some free lime, anhydrite, iron oxide, and C 3A contents of PC-fa mortars and their sulfate expansions determined according to ASTM C 452 showed that, beside the sulfate resistance factor R, free CaO/Fe 2O 3 and C 3A + free alumina/free CaO ratios of the PC-fa mixes containing high fly ashes can be used to determine their sulfate susceptibility.

The resistance of fly ash concrete to sulfate attack is dependent on both its chemical and physical characteristics. The chemistry and mineralogy of both fly ash and cement influence the sulfate resistance of hydration products, while the permeability of concrete influences the rate of ingress of sulfate ions. Researchers are studying the interdependence of the chemical and physical characteristics of fly ash concrete, as they affect sulfate resistance. Both ASTM Type I and II cements have been partially replaced by both ASTM Class F and C fly ashes. Cement replacement levels of 25 and 35 volume percent have been studied. Fly ashes have been added as mineral admixtures at the concrete mixing stage and interground with the cement constituents, as in blended cement production. Concrete specimens have been monitored for linear expansions and mass changes while immersed in 10-percent sodium sulfate solution. This paper reports on the sulfate resistance of fly ash/Type II cement concrete mixtures after 450 days of sulfate exposure. Data from 57 concrete mixtures are included, 28 of which utilized fly ash/ cement intergrinding procedures.