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

Long service life of concrete depends on correct choice and use of materials. Problems such as ASR (alkali silica reaction) and the prospect of sulfate attack and corrosion need early and proper identification and attention. Resistant materials must be selected and properly used to insure control of these adverse conditions. Low alkali cement or sulfate-resisting cement must be used as appropriate in these situations. Other requirements often overlooked are those essential to prevent or minimize thermal cracking of massive structural concrete, as in power plants, bridge piers, foundation elements, and thick linings of large tunnels. The ordinary concrete in municipal use, especially in new subdivisions, is often short of durability and exhibits much cracking, due to failure to follow the most fundamental rules of good practice, especially freezing weather protection, enough cement, control of slump, ample provision of joints, and curing. Sidewalks and driveways are too often disfigured and disappointing. Curing is often neglected. Specifications for the work must cite the requirements in complete detail and be followed explicitly when the work is done.

Twenty-seven high-performance concrete mixes (with 28-day strengths in the 80 to 100 MPa range) were prepared to evaluate the deicer salt scaling resistance of such concretes after various periods of curing. Three water-cement ratios (0:30, 0:26, and 0:23) were used, and for each water-cement ratio a minimum of three mixes were made with different air-void systems: one with a spacing factor of approximately 200 æ, one with a slightly higher value, and one without any air entrainment. Canadian Type 30 cement with an addition of 6 percent silica fume was used for all mixes. The coarse aggregate was a 14 mm minimum size, crushed, very dense, dolomitic limestone. The curing period varied between 1 and 28 days. A total of 54 specimens (2 for each test condition) were submitted to 150 daily cycles in accordance with ASTM Standard C 672, using sodium chloride as a deicer. Weight loss was measured to evaluate the deterioration of the concrete surfaces. The scaling resistance was found to be extremely good in all cases, irrespective of the length of curing, water-cement ratio, or spacing factor value, weight losses after 150 cycles being always lower than 0.50 kg/mý. No correlation was found between the scaling resistance and the spacing factor or the length of curing. Loss of mass was generally concentrated around a few aggregate particles. These results indicate clearly that it is possible to prepare high-performance concretes with very good deicer salt scaling resistance without using any air entrainment.

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.