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SP192 In 2000, CANMET, in association with ACI, the Japan Concrete Institute, and several other organizations in Spain and Canada, sponsored a fifth international conference held on June 4-9, 2000, in Barcelona, Spain. More than 120 papers from 35 countries were received and peer reviewed in accordance with the policies of the American Concrete Institute; 73 were accepted for publication. The accepted papers deal with all aspects of concrete durability. In addition, several sessions dealing with sulfate attack, superplasticizers and supplementary cementing materials, and near surface testing for the durability of concrete were organized. In addition to the papers that have been published in the refereed proceedings, more than 30 papers were presented at the conference.

Durability of reinforced concrete structures (RCS) seems to be poor when compared with those of ancient un-reinforced structures. When ordinary durability (service life of 40-50 years) is needed, the poor behavior of RCS stems from human negligence in adopting the well consolidated and available experiential knowledge. However, for long-term durability requirements (service life of 100 years and more) the inherent vulnerability of the steel-concrete system must be taken into account. The inherent vulnerability of RCS substantially depend on the following "weak points" of concrete: (I) Low tensile strength (ii) High modulus of elasticity (iii) Microcracking caused by restrained thermal and drying shrinkage or service loading. This paper critically examines some possible future scenarios to achieve long-term-durability in RCS, including: a) Improvement in the corrosion behavior of the metallic reinforcement through the use of corrosion inhibitors, protection of the reinforcement with a coating, chance in the composition of reinforcing bars, or cathodic protection. b) Use of non metallic reinforcement. c) Increase in the tensile strength and/or ductility of concrete mixtures based on rubber-like polymer additions. d) Surface coatings for concrete protection.

Since 1990 the Anode-Ladder-System has been used world-wide to monitor the corrosion risk of new concrete structures. This sensor-system is an embedded macrocell system indicating the depth of the critical chloride content initiating corrosion of the reinforcement. Subsequently the time-to-corrosion of the reinforcement can be determined continuously, enabling the owners of buildings to initiate preventive protection measures before damage like cracks and spalling occur. However, this system can only be installed before placement of the concrete. Therefore a new sensor system has been developed to monitor the corrosion risk for the reinforcement also in existing or repaired structures. This new Expansion-Ring-System consists of 6 anode rings separated by sealing rings and a cathode bar, which are installed in small holes drilled into the concrete and connected by a special expansion mechanism. Actually it is in the stage of final testing in laboratories and pilot projects.

The development of a curing time estimator is described: it is based upon an existing model of the microstructure and porosity gradients in the cover concrete that correlates well with relevant hydration and pore structure measurements. The same model also yields capillary porosities that correlate with measurements of compressive strength and water absorption rate. The objective is to provide a single method to estimate curing times for CEM I and CEM II (portland and portland/fly ash) concretes in a wide range of climatic conditions and achieve a consistent, well-defined measure of cover concrete performance. New hydration and pore structure measurements are briefly reviewed in relation to the existing model of microstructure and porosity in cover concrete. Recent developments regarding European standards for curing and concrete durability are considered. A criterion of capillary porosity in the matrix of cover concrete is used to unify the durability-related effects of curing period, cement type, water/binder and climatic conditions. The initial input to the estimator is the cement type to be employed. The nest input is a maximum water/binder, as necessary to ensure durability under the expected exposure conditions; this automatically sets a target capillary porosity in the cover concrete, based upon recent curing period recommendations from European standards committees. Subsequent inputs define the climatic conditions in terms of exposure capillary porosities in the cover concrete for a wide range of curing periods so that a period can be chosen without exceeding the target porosity. Capillary porosities for reduced water/binders, 95and 90% of the input value, are also tabulated to illustrate the reductions in curing period that are possible with these higher concrete qualities. Examples are given to illustrate the effect of each of the eight inputs; water/binder, exposure relative humidity and cement type are the most influential. It is evident that in many cases control of cover concrete performance via curing options is limited relative to the control offered via small changes in the concrete mix proportions of alternative cements.

This study points out the close relationship between several quality indicators of recycled aggregate and the performance of recycled aggregate concrete. Regarding the diversity in quality and composition of the recycled concrete products, three laboratory produced air-entrained-concretes with low, medium and high water-cement ratios and a non-air-entrained concrete with medium W/C were processed for recycling. Recycled aggregate concretes were produced with a water/cement of .55, and tested after 28 days of moist curing. Results of the capillary water immersion and permeable porosity tests indicate that structure and amount of adhered mortar as well as the recovery percent of original coarse aggregate and other physical properties of recycled coarse aggregate, especially the inclusion of recycled fine aggregate into the system are the mean reasons creating important differences in the permeable pore system and captivity of recycled aggregate concretes. Relatively low pore content of the non-air-entrained type adhered mortar compared with the air-entrained ones influences the concrete porosity in the same way. The volume of permeable pores in concrete produced with non-air entrained type of recycled aggregate seems to be reduced. Although entrained air pores of the adhered mortar increase the total volume of the permeable voids, they play a role of interrupting the capillaries. The findings of this research indicate that all possible variations in recycled aggregate properties must be taken into account to be able to design durable recycled aggregate concretes.