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In October, 1994, CANMET in association with the American Concrete Institute sponsored a fourth conference on the superplasticizers and chemical admixtures in Montreal. The objective of this conference was to bring to the attention of the concrete community the new developments in chemical admixtures since the last conference in 1989. A total of 25 papers were accepted for publication in this special proceedings from the conference. If you are involved with superplasticizers and chemical admixtures, this special publication is a must. 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. SP148

High-performance concretes (HPC) typically have low w/c to achieve the desired levels of strength and durability. As a result, HPC have a tendency to be stiff and lose their workability rather quickly. Often, high-range water-reducing admixtures (HRWRA) are used to improve the workability of HPC. Care must be exercised when using any admixture, or combination of admixtures, to insure that there are no detrimental side effects that might shorten the life of the concrete. Research has shown that, although retempering concrete with an HRWRA will generally improve workability and maintain the strength of low-w/c concretes, it may also reduce freeze-thaw resistance. Therefore, an experimental study was

The key to casting high-strength concrete with compressive strength of more than 100 MPa into complicated reinforced structures is to give the concrete high fluidity as well as to improve strength. The authors developed an acrylic copolymer-based new superplasticizer that can improve fluidity of concrete with water-binder ratio of around 0.20. Paper presents results of a series of studies conducted to determine the properties of fresh and hardened high-strength concrete using the newly developed superplasticizer. The effect of the new superplasticizer was examined with varying water-binder ratio, type of cement, and temperature compared with conventional superplasticizers. The new superplasticizer needed a much lower dosage than conventional superplasticizers to attain a certain slump (250 mm) for a water-binder ratio of around 0.20, and it significantly reduced concrete viscosity. Sufficient workability was kept for 2 hr without much delay in setting time, while conventional superplasticizers showed large slump loss and excessive delay in setting time. Results of strength development, drying shrinkage, and freeze-thaw resistance did not show any harmful effect. Field studies were conducted on application of the high-strength concrete to a prestressed concrete bridge with design strength of 100 MPa using the new superplasticizer. Workability and strength development of concrete were tested and resulted in sufficient quality.

High-strength concrete with air-entraining high-range water-reducing admixture, 0.35 water-cement ratio, 148 kg/m 3 unit water content, and about 60 MPa compressive strength, was produced, and the admixture content and sand percentage were varied. The consistency property was measured by the slump test, and the compaction property and segregation resistance were determined by the flow time through an inverted slump cone. An appropriate mixture that balanced these properties relative to the admixture content and sand percentage was determined from the test. The appropriate mixture can be consolidated by using a shorter vibrating time and lower frequency than in the case of ordinary concrete.

The impact of superplasticizers and water-soluble polymers, i.e., rheological modifiers, on the rheology and performance of cement-based systems has been investigated. Combinations of water-soluble polymers and superplasticizers can be used to formulate grouts, mortars, and concretes with properties tailored for specific applications. Cement-based systems studied ranged from highly fluid injection grouts to cohesive, flowable concretes suitable for underwater construction and repair applications. Paper demonstrates how the rheology and performance characteristics of cement-based systems can be manipulated using superplasticizers and rheological modifiers. Specifically, the performance properties of a high-molecular-weight polysaccharide produced to fermentation are compared and contrasted with cellulose derivatives. Combinations of water-soluble polymers and superplasticizers can be formulated to produce a continuum of properties ranging from highly fluid, nonseparating grouts to low-slump concretes with enhanced workability and water retention. Choice of the proper combination of superplasticizer and water-soluble polymer is determined by the functional demands of each application.