International Concrete Abstracts Portal

SP-153 In 1995, CANMET, in association with ACI, U.S.A. Electric Power Research Institute, Canadian Electrical Association, and several other organizations in Canada and the United States, sponsered the Fifth International Conference on fly ash, ferrous and nonferrous slags, and silica fume was held. The two volume proceedings of the Fifth CANMET/ACI Conference contains 62 papers from 23 countries.

Canada Centre for Mineral and Energy Technology (CANMET) has an ongoing project dealing with the role of supplementary cementing materials in concrete technology. As a part of this program, a new type of concrete known as high-volume fly ash concrete has been developed. In this type of concrete, the water and cement (ASTM Type I) contents are kept very low, about 115 and 155 g/m 3, respectively, and the proportion of low-calcium fly ash in the total cementitious materials content is about 56 percent. This type of concrete has excellent mechanical properties and durability characteristics. In spite of very good properties shown by the high-volume fly ash concrete, one concern about the use of this type of concrete is its performance at early ages due to its low cement content and the slow reaction process of fly ash. This can be an obstacle for the use of this type of concrete when compressive strengths over 10 MPa at one day are needed or when proper curing cannot be provided for a long period of time. One way to improve the early-age properties of this type of concrete is to use ASTM Type III portland cement. Therefore, a study was undertaken to develop engineering data base on the high- volume fly ash concrete using ASTM Type III cement. Concrete mixtures were made using ASTM Type III portland cement from a source in the U. S. A. and three low-calcium fly ashes also from source in the U. S. A. A reference mixture (without fly ash) was also made for comparison purposes. The use of ASTM Type III cement instead of Type I cement noticeably improved the early-age strength properties of the high-volume fly ash concrete incorporating the fly ashes investigated in this study; this was done without having any detrimental effect on long-term properties of the concrete. The one- day compressive strengths were about 5 to 8 MPa higher than those of the high- volume fly ash concrete made with the same fly ash and Type I cement. The use of Type III cement also shortened slightly the setting time of the high-volume fly ash concrete. Durability characteristics and drying shrinkage of high- volume fly ash concrete made with ASTM Type III cement were no different than those for the concrete made with Type I cement.

The purpose of this study was to examine the mechanical and durability properties of high-volume fly ash concretes for structural applications. Four concrete mixtures were prepared with the amount of fly ash, from Italian source, varying from 0 to 50 percent by weight of total cementitious materials. A large number of concrete specimens were cast and tested to determine the compressive, flexural, and splitting tensile strengths, modulus of elasticity, fracture parameters, concrete-steel bond properties, drying shrinkage, and durability properties. The results of this study showed that high-volume fly ash concrete has considerable potential in a wide variety of structural applications.

Concrete placed in contact with a sulfate environment can severely degrade due to formation of expansive compounds such as ettringite. The use of low-calcium fly ashes in concrete have been successful in mitigating these expansions. However, some high-calcium ashes have the potential to cause increased expansion of the concrete, leading to accelerated deterioration. This research focuses on producing cements interground with Class C fly ash, which can be used to produce sulfate-resistant concrete. ASTM Type I and Type II cements were blended with a sulfate-susceptible Class C ash in amounts from 0 to 70 percent fly ash. Concrete was produced using a standard Texas Highway Department 306 kg/m 3 mixture and the various interground and unblended cements. Specimens were soaked and monitored monthly for 3-1/2 years in a 10 percent sodium sulfate solution to accelerate sulfate attack. Results indicate that certain specimens made with interground cements having fly ash contents between 25 and 70 percent, and additional blended gypsum, achieved lower expansion than control specimens made with Type II, Type V, or 0 percent C 3A cements alone. This was true for fly ash/cement blends using both Type I and Type II cements. Compressive strengths of the fly ash blends, through 365 days, attained levels generally comparable to, or better than, the controls.

In the present research project, fly ash was mechanically processed to 1 to 5 micron particle size. Mortars and concretes were made from these processed fly ashes. In this paper, the results of the micronized fly ash are compared to the results gained with air classified fly ash, silica fume, and blends. It was found that using ground fly ashes, very fluid mixtures can be produced with excellent strength and durability properties. Because of the growing interest in ultra-fine supplementary cementing materials (SCM's) for high-performance concrete, there is a need to find ways to micronize fly ashes in an economical way.