International Concrete Abstracts Portal

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.

The effect of a range of curing regimes on the resistance to chloride penetration of concretes has been studied. Concretes with two binder systems namely normal portland cement (NPC) and a 30% fly ash blend (FA) were subjected to four different curings. They include 1-day sealed, 7-day sealed, 7-day wet and a simulated steam curing. Subsequent to each curing regime, the samples of grade 40 concretes were air cured I standard laboratory conditions until the age of 28-day before exposure to 15 cycles and 100 cycles of immersion in 3% NaCl solution and drying. Resistance to chloride ion penetration was evaluated by examining both the chloride profile and diffusion coefficient (calculated by Fick's second law). Thus the role of curing in governing the resistance of concrete to chloride ion penetration was established. NPC concrete was found to be more sensitive to the type of cuing than the fly ash concrete. NPC concrete subjected to 1-day and 7-day sealed curing resulted in lower chloride penetration resistance than the 7-day wet curing. However, the fly ash concrete showed remarkable tolerance to the lack of moist curing giving very similar performance in both 1-day and 7-day sealed curing as the 7-day wet curing. Steam curing resulted in poorer resistance t chloride penetration for both concretes. For each type of curing, the fly ash concretes gave significantly better resistance to chloride penetration than the NPC concrete (of similar grade). Effect of curing on sorptivity and volume of permeable voids (Vpv) of concretes of grades 20, 40 and 50 were also studied. Both sorptivity and Vpv were found to be influenced by the type of curing for both binders. Vpv was found to show correlation to the long-term chloride penetration resistance of the concrete. No such correlation was found for sorptivity values.

Reinforced-concrete slabs were cast and tested for durability for a period of fifteen months. The slabs were partially immersed in a 2.0% chloride ion solution. Three types of concrete were tested. These were normal-weight medium strength (NWMS), lightweight high-strength (LWHS), and normal-weight high strength (NWHS) concrete. The main tests consisted of measurement of corrosion potential, corrosion current and chloride ion penetration. It has been found that the values of corrosion potential and current were substantially different in the three different types tested. Extremely low values of corrosion current were detected in high strength concrete slabs whether made of lightweight or normal-weight concrete. Large amount of cementitious materials and very low ratio of water to cementitious materials are believed to strongly contribute to produce very low corrosion current. However, LWHS slabs were extremely low. The paper presents the results and discusses likely explanation of these observations.

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.