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In Japan, a new super-workable concrete, which has higher flowability and filling capacity, has attracted attention as being effective in rationalization of concrete execution. It can be applied for simplifying placing work while securing high quality of reinforced concrete structures. Especially in case of heavily reinforced structures, it is highly applicable because of its excellent filling capacity or lower consolidation effort. For several years, the authors have studied improvements of workability of some special concretes, such as anti-washout underwater concrete, expansive grouting concrete for inverted placement, and ultra high-strength in-site concrete, and have consequently succeeded in developing super-workable concrete, suitable for rapid placing or perfect filling without consolidation. The authors also have established a new evaluating method for segregation resistance of mortar and aggregate, that is useful to design mix proportion, or keep high quality of super-workable concrete in site. Recently, opportunities to apply super-workable concrete to several actual structures with difficult construction conditions have arisen. One is the LNG (liquefied nitrogen gas) in-ground storage tank, which has much complicated reinforcement at the junction of base mat and side wall, another is a tall, thin reinforced concrete wall, which must be placed from upper point, 6 to 8 m in height. This paper describes the basic properties of super-workable concrete, the new method of quality control, and a summary of applications to reinforced concrete structures mentioned.

On April 13, 1992, the engineer of the Merchandise Mart, one of Chicago's downtown buildings, reported flooding of the building basement. A few hours later flooding was found to be related to an eddy observed at the Chicago River. The flooding was occurring through a system of service tunnels built at the beginning of the century and abandoned in the late 1940s. The failure of the tunnel was caused by wood pilings installed at the end of 1991 to protect the bridge abutment in the Chicago River. The flooding of these tunnels affected more than 100 downtown Chicago businesses, which had to be evacuated for several weeks. The repair of the tunnel was conducted in two stages using high-performance concrete (HPC). First, an interim plug was placed using a high-performance, underwater concrete. The severe environment caused by the current in the tunnel required concrete to be highly fluid, have anti-washout properties, set quickly, and gain strength rapidly Second, a permanent plug was placed using HPC concrete designed to reduce heat of hydration and minimize potential for thermal cracking. Actual temperature of the permanent plug was monitored by thermocouples and compared to a computer-generated model. The use of this system to predict performance of special concretes allowed the concrete supplier to start a new generation of high-performance concretes.

To insure the tightness function of nuclear reactor containments, a special high-performance concrete (HPC) having a high silica fume content (30 kg/m 3) and a low cement content (270 kg/m 3) has been developed. The aim of this concrete formulation, which has a 28-day compressive strength of about 75 MPa and very good workability, is both to control the risk of cracking of the concrete in the structure and to reduce creep. This paper describes the feedback from experience acquired in the construction of the first HPC containment built in Civaux, France. The advantages and the difficulties encountered and overcome in the use of this material are presented, together with the results of tightness tests of the structure. The industrial mastery now achieved of this special HPC formulation also made it possible to take the performance of this concrete into account in the engineering of the work. This led to a new containment design, presented in this paper, combining HPC and very strong prestressing using 55 T 15 cables. This new design substantially improves the safety of nuclear reactors for severe accidents (core melting and hydrogen deflagration): the structure is guaranteed gas-tight up to an internal pressure of about 1 MPa.

Concrete is an essential component of the seal system planned for geologic repository under development for disposal of defense-generated radioactive wastes in the U.S. Performance requirements for concrete at this facility are unique: mass-concrete seals will be placed underground in a region where all the groundwaters are rich in chloride, and some also are highly concentrated in magnesium and sulfate ions. Sodium chloride in brines presents less of a problem than do other ions. In experiments simulating the worst-case of brine composition and availability, the nature and extent of deleterious chemical reactions were determined for materials being considered for use in mass concrete for a repository. Chemical degradation of cement pastes related to this concrete included loss of calcium and precipitation of magnesium compounds, and formation of other sulfate- and chloride-bearing phases. Calcium was lost first from calcium hydroxide and then from C-S-H. Strength loss is attributed principally to loss of these phases, and not to substitution of magnesium for calcium in hydration products.

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.