International Concrete Abstracts Portal

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

In most concrete markets these days, there are several varieties of pozzolans and ground slag available for use in regular and high-performance concretes. Each one has its strong points when blended with portland cement in concrete and, properly used, will provide concrete of enhanced durability. Recently, concrete containing more than one such material has become common, even to the point of being available as ternarv or quaternarv blend. This paper reviews the data available on durability of concrete produced from‘ multiple blends and discusses some of the potential benefits to specifiers and users.

Choosing the optimum cementing material system is a key question when designing a concrete structure to last for a long time in a chloride environment. There is a lack of reliable comparative information on the short and long term performance of cementing material blends, incorporating materials such as silica fume, fly ash and slag. In this contribution, various cementing material blends are examined for their potential ability to resist chloride ion penetration. A range of mixtures was tested to assist designers in material selection for concrete in a chloride environment. Silica fume, blast furnace slag, Class C and F fly ash were examined at 0.30 and 0.40 water to cementing materials ratios (w/cm) for mortars and concrete. Ternary blends of normal portland cement/slag/silica fume and normal portland cement/slag/fly ash were also tested. The diffusion coefficients were determined by chloride migration using a D.C. potential gradient, and by chloride pending/profile grinding. Silica fume was found to be essential to obtain low diffusion coefficients particularly at an early age. Some additional reduction in diffusion coefficient is obtained with ternary blends of silica fume plus slag or silica fume plus Class F fly ash.

The resistance to chloride penetration is one of the prime parameters in specifying concrete in marine applications and in a quality assurance scheme during construction. The aim of this research was to compare alternative accelerated laboratory test procedures for the assessment of chloride penetration into concrete containing supplementary cementitious materials. Three binder systems, a normal portland cement (PC), one with 30% fly ash and a third with 50% slag, were investigated under three curing conditions, 7 days water curing, air curing, and 12 hours 65 C water curing. Chlorides penetration was measured by static ponding (5% NaCl solution) and cyclic ponding (2%, 5% and 15% NaCl solutions with 12 hour wetting and drying cycles). The effect of the age at start of testing and the test duration were also investigated. The water absorption was tested by measuring weight gain, and the results were compared with that of the chloride penetration tests. It was found that the cyclic ponding test with 15% NaCl solution resulted in accelerated chloride penetration and a clearer chloride penetration front compared to the use of 2% and 5% NaCl solutions. Good correlation was found between the results from cyclic chloride ponding and static ponding. While the chloride penetration depth was found not vary significantly with test age from 7 to 56 days for all the three mixes, the increase of chloride penetration with the test duration from 3 to 14 days was much pronounced for the PC mix than the fly ash and slag mixes. The chloride penetration was highest in the air cured specimens and the lowest in the water cured specimens for all the three mixes, and the slag concrete had the lowest chloride penetration within the three mixes under each of the three curing conditions. It was also found that water absorption correlated poorly with chloride penetration.

Electrochemical tests on mortar electrodes in alkaline chloride solutions were carried out to determine the critical chloride content depending on the mortar composition (type of cement, cement content, water-cement ratio and concrete additions). Sodium chloride, with varying chloride concentrations (between c(NaC1) = 14 and 508 mmol*L-1), was used to initiate corrosion. Depassivation times of the mortar electrodes as well as corresponding total and free chloride contents were determined. By means of macrocell corrosion tests without polarisation and at a constant concentration of the test-solution of c(NaC1) = 282 mmol*L-1, the diffusion process of the chloride and the chloride binding (dependent on the age of the test amples) were investigated in order to obtain reference values for the depassivation time of the steel. Potentiostatic tests with constant polarisation at USHE = +500 mV in alkaline chloride solutions of different concentrations were carried out for 11 different mortar mixtures to determine the critical corrosion-initiating chloride content. A linear relation between corrosion-initiating free and total chloride content was found. A minimum critical chloride content of 0.25 wt.-% relative to cement was determined.