International Concrete Abstracts Portal

"A collection of 24 papers form an international panel of experts on topics ranging from fundamental laboratory studies of concrete durability to case histories of concrete rehabilitation. The volume is arranged in three parts. Part 1: covers the more fundamental aspects and laboratory investigations. Topics include freeze-thaw resistance, durability of high strength concrete, corrosion of reinforcing steel, air voids in concrete, and effects of high range water-reducers. Part 2: covers field studies where concrete is exposed to natural conditions. Topics include carbonation of concrete, deicer scaling resistance of roller compacted concrete pavements, performance in marine environments, and microbiologically-induced deterioration. Part 3: covers case histories of the performance and rehabilitation of concrete structures in severe service environments. The types of structures include cooling tower shells, precast prestressed concrete conveyor bridge, heavy duty dock, elevated road way, and a masonry structure under corrosive exposure." 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. SP122

The air or oxygen permeability of concrete is usually measured by means of techniques that utilize mechanical driving forces. Thus, air or oxygen is forced to pass through a piece of concrete using different mechanical pressures. The flow of gas so measured is used as an indication of concrete permeability and sometimes is also used to predict the durability of concrete reinforcements based on the relationship between anodic corrosion rate and amount of oxygen, which may be reduced in the cathodic areas. However, this extrapolation may lead to erroneous conclusions, because a dry concrete allows a higher amount of oxygen to pass through it than a wet one, although the corrosion rate should be much lower in dry than in wet concrete. In this paper, comparisons between flow of oxygen measured in paste, mortar, and concrete specimens held at different relative humidities using electrochemical driving forces (polarization at about -750 mV SCE), and corrosion rates (measured by means of polarization resistance) are presented to discuss the inherent relationships. The results show that the oxygen permeability is only dependent on the amount of electrolyte inside the pores, but the corrosion rate is also dependent on the concrete resistivity, which is fixed by the amount of pore water content.

A study was made of three commercially available "second-generation" high-range water-reducing admixtures (HRWR) using cement of high and moderate C3 A content and having a cement content of 545k lb/yd3 (323 kg/m3) and a water-cement ratio (w/c) of 0.50. Second-generation HRWR were used to reduce cement and water contents by 15 to 16 percent. Hardened concrete specimens were prepared and tested for freeze-thaw resistance, resistance to deicer scaling, permeability to chloride ions, drying shrinkage, and compressive strength development. In addition, the air-void systems of concretes containing second-generation HRWR and air-entraining admixtures were analyzed by linear transverse. Similar tests were performedon flowing concretes, where cement and water contents were maintained constant and second-generation HRWR were added to increase initial slump levels to 7 to 9 in. (75 to 225 mm). Results indicate that caution must be exercised when using these admixtures to reduce cement contents in concretes subjected to deicing chemicals, as performance may be adversely affected, especially in high-slump "flowing" concretes. Additionally, drying shrinkage may be moderately increased in these concretes.

The relative durability of air-entrained concrete with and without boiled linseed oil coating was evaluated using the rapid freeze-thaw method of ASTM C 666, Procedure A, by measuring the reduction in dynamic modulus and weight loss of the test prisms. Surface scaling was also monitored visually. The richness of the mix was varied by using cement factors of 267 kg/m3 (450 lb/yd3) and 300 kg/m3 (506 lb/yd3). Freeze-thaw durability was reduced in some test prisms of the richer mix through the addition of a chloride-based setting and strength accelerator. Curing prior to freeze-thaw cycling was varied in the lean mix. Prisms were either water-cured for 2 weeks prior to coating with linseed oil before testing, or were coated with linseed oil after removal from molds at 24 hr and then cured under ambient low humidity before freeze-thaw testing at 2 weeks. Uncoated specimens that were water-cured for 2 weeks prior to freeze-thaw cycling served as the control. The use of undiluted linseed oil proved to be superior to using a 50 percent Varsol-50 percent boiled linseed oil mixture, contrary to what was expected. Mixes proved to be quite durable except for the mix in the third series, in which the chloride-based accelerator reduced the freeze-thaw resistance below acceptable limits. The use of a linseed oil coating provided some, though insufficient, improvement in the durability of this mix.

Samples from nine air-entrained concrete mixes made with and without a superplasticizer were examined under a scanning electron microscope to determine the size distribution of the voids in the 0.5 to 50 æm range. Concurrently, samples of the same mixes were examined under a binocular microscope to determine the size distribution of the voids in the 10 to 1000 æm range. The voids observed under the electron microscope were separated into two categories: air voids (spherical in shape or nearly so) and large capillary pores (irregularly shaped). The results show that, in mixes, the amount of capillary pores with diameters ranging from 0.5 to 50 æm is relatively important (the number of these voids generally represents approximately half the total number of entrained air voids). The role of these pores in the frost resistance of concrete is believed to be strongly dependent on their degree of saturation at the time of freezing. The number of air voids smaller than 10 æm in diameter, however, was found to represent less than 10 percent of the total number of entrained air voids. These small air voids are thus expected to have little influence on frost durability. The results also indicate that the distribution of the ir-void diameters is influenced by the nature of the air-entraining agent but not by the use of a superplasticizer. The distribution of air-void diameters was found to be approximately the same for all mixes, irrespective of the value of the spacing factor.