International Concrete Abstracts Portal

Paper acquaints those interested in concrete durability with the scope and duration of a new long-term field and laboratory testing program which began in 1989 and will continue through 2004. It has been commissioned by the Reinforced Concrete Research Council (RCRC) of the American Society of Civil Engineers, and is designed to compare the effects of warm and cold seawater environments on the durability of reinforced and prestressed concrete elements made using concrete materials and additives which have become available over the past 15 years. It is a follow-up study to those conducted by the U.S. Army Corps of Engineers, and guided by the RCRC, during the period 1950 through 1976.

Reinforced concrete masonry structures can be effectively used in corrosive environments provided that the design is based upon a rational assessment of the exposure condition. An investigation of wall that had 6000 g of muriatic acid and 11,000 g of sodium hypochlorite stored along its exterior face indicated accelerated deterioration of the wall due to inadequate design and no protection afforded to the wall when the building's usage was changed from general warehouse to chemical storage. Poor construction practices also contributed to the distressed condition. The investigation utilized electrical, visual, and chemical means of assessing the structures's condition. The primary tool was a copper-copper sulfate (Cu-CuSO4) half cell conforming to ASTM C 876. The resulting equipotential contour map provided valuable information regarding the wall's corrosion potential. Visual observations of exposed, corroded reinforcing steel confirmed the half-cell readings. Chemical analysis of block, mortar, and grout samples extracted from the wall revealed high but inconsistent water-soluble chloride ion contents.

The service conditions for concrete construction in the coastal areas of the Arabian Gulf are considered to be those of one of the most aggressive environments in the world. Deterioration of hardened cement paste due to salt attack is one of the leading reasons for poor performance of concrete structures in this region. Calcium, magnesium, sodium salts of sulfates, chlorides, and carbonates extensively contaminate the ground, groundwater, and the aggregates. In such an environment, structures built with concrete which can be rated as good in temperate climatic conditions can hardly last for a decade or two. Field and laboratory studies are in progress at King Fahd University of Petroleum and Minerals at Dhahran, Saudi Arabia, to formulate preventive measures. As a part of this endeavor, the performance of in-service concrete structures is monitored. This paper details the investigations carried out to evaluate the performance of these concrete structures. Data developed in this investigation show that the aggressive service environment is the major cause for concrete deterioration, as such appropriate mix design techniques and construction practices are to be adopted for the production of a very dense and impermeable concrete.

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.