The paper provides guidelines for the development of concrete mixtures that will function in an aggressive environment. Performance will be based upon durability and not high strength. In few cases will strength greater than 5000 psi (34.4 MPa) be of structural value. Some concrete has performed well in severe environments for more than 100 years while some newer concretes exposed to similar environments have deteriorated prematurely. Attention to basic concrete technology during the early years contributed to long-term durability. in the authors' opinions, emphasis on strength without regard to special needs for durability contributed to the current performance problems. Graphical means are suggested whereby the need for high performance concrete for durability can be identified by project type and environment. The requirements for various durability requirements are listed and summarized in a cross reference table that can aid in translating qualitative measures into quantitative terms.

We developed an enhanced flowable concrete using both a binary low-heat cement and coarse aggregate of 40 mm maximum size, usable in large-scale mass concrete structures (this concrete is provided with a high flowability and an excellent resistance to segregation, and is able to be placed densely without compaction). We verified that its fundamental performance surpasses that of existing types of concrete. Further, we also verified that it possesses superior workability when compared with conventional concrete. Next, we established production, quality control, and construction methods for super-workable concrete through experiments at a large scale construction site, and utilized it in a large-scale structure. We were able to verify the following results: superior workability of the concrete because it can be spread and compacted easily; effective control over thermal cracking because concrete temperature rose very little. Furthermore, the hardened concrete is confirmed, from the core samples, to be very compact and has excellent strength. 161-493

Theodore Roosevelt Dam is a rubble-masonry dam, located on the Salt River, 76 miles northeast of Phoenix, AZ. The dam will be modified by adding a mass concrete gravity section to the downstream face of the dam. Over 350,000 yd 3 of mass concrete will be placed. A high-performance mass concrete mixture was developed that met conflicting low heat and strength development requirements. The mixture needed to meet thermal requirements of no more than 45 F total adiabatic temperature rise in 20 days, and less than 5 F adiabatic temperature rise after 20 days. In contract, the mixture needed to meet early-age compressive strength requirements of 1000 psi between 3 and 7 days and have sufficient paste to insure bond between the new concrete and the original masonry structure. The Bureau of Reclamation developed a concrete mixture with a 4-in. maximum-sized-aggregate (MSA), containing 270 lb of cementitious material per pubic yard that met design requirements. The cementitious material consisted of 80 percent cement and 20 percent fly ash. A low-heat, Type II cement was used, with a heat of hydration of 65 calories per gram at 7 days. The fly ash is an ASTM class F ash. The concrete has a water-to-cementitious materials ration of 0.53. The mixture is very workable, and reaches a compressive strength of 1100 lb/in.¦ in 7 days. It has a total adiabatic temperature rise of 43.4 F, with only 2 F temperature rise after 20 days.

Three types of High Performance Concrete (HPC) for highway applications were investigated: Very Early Strength (VES), High Early Strength (HES) and Very High Strength (VHS). Two of the objectives of the research were to measure the chloride permeability of these concretes and explore an alternate method using AC impedance. Many of the concretes had coulomb values of 4000 and higher, placing them in the "high permeability" category as specified by AASHTO T 277 - Rapid Chloride Permeability Test (RCPT). Coulomb values were also found to decrease with concrete age and with increased silica fume content. Coulomb values were found not to vary significantly with dosage of calcium nitrite used as accelerator, up to 6 gal/yd 3 (29.7 l/m 3). The AC impedance test results (ohms) were found to correlate well with the RCPT results (coulombs) and were sufficiently accurate to place the concretes in the proper chloride permeability category. The advantages of the AC impedance test are that it is faster and less expensive than the RCPT and it avoids the potential heating problem sometimes encountered in the RCPT. AC impedance was found to increase with concrete age and with increased silica fume content and decrease with increased calcium nitrite dosage.

The cable-stayed bridge which is being built across the Elorn river near Brest (western France) will have the world's longest span (400 m, or 437 yd) in this range of full concrete bridge. Besides a normal-strength concrete (C 35/6,500 psi), a lightweight concrete (LC 32/4,600 psi) is extensively used in the deck, in order to minimize the effect of dead load on the overall stability. But the most significant part of the loads to be carried by the bridge is due to the wind, with a maximum accounted speed (in the design) of 210 km/h (130 mph). Furthermore, the bridge is located about 3 km (2 miles) from the sea; thus, the wind will carry a large amount of chlorides. This is why the term serve environment seems to be appropriate for the Elorn bridge. Two grades of high-strength concrete--namely C60/ psi and C80/ psi--are used in the towers. For the first time in France--and perhaps in the world--a strength of 80 MPa (11,600 psi cylinder strength) has been used in the design of a bridge. Details on the concrete mix proportions, producing facilities, placing techniques and testing of samples are given in this paper. A special emphasis is put on the thermal curing aspects. As the thickness of the towers walls is 1.10 m (3.5 ft), the temperature can reach more than 80 C in the pylons. The effect of heat of hydration on the long-term strength and modulus was investigated. Also, finite-element calculations were performed, in order to predict the stresses induced by thermal gradients, and to choose the most appropriate curing (thermal insulation, time of form removal, and so on).