From this survey and the literature search conducted, the three most important factors that must be controlled to obtain good high-performance concrete are: the selection and control of the ingredient materials, the batching sequence, mixing efficiency of the equipment and the curing method. It was seen that the mix design needs carefully planned trial batches to determine the compatibility of the materials, such as cement and chemical admixtures, to avoid segregation, and to achieve a desired workability and compliance with specification requirements: workability, which includes finishability, and curing.
The workability is usually determined by a slump test, but this test does not measure a very important rheological parameter, the plastic viscosity. The plastic viscosity of the mortar forming the skin of the concrete determines the stickiness and the finishability. Also, the plastic viscosity of the cement paste or mortar influences the segregation of the mix, by preventing aggregates from settling.
The concrete plastic viscosity is a major parameter governing the concrete flowability and pumpability [6]. After the concrete is placed into the forms, the plastic viscosity controls the ease of placement. Therefore, there is a need for a new simple test to be used in the field to measure the plastic viscosity in conjunction with yield stress.
The prediction of the concrete workability from the mix design as well as the prediction of the effect of vibration on segregation is necessary. Further research is needed to obtain a complete prediction model that includes the influence of vibration.
Curing, which includes moisture and temperature control, must be optimized to avoid cracks. Further research is needed to be able to establish guidelines for curing of concrete depending of mix composition and ambient conditions.
The authors would like to thank all the persons that took the time to return our surveys. Also, a special appreciation goes to François de Larrard, guest research at NIST from Laboratoire Central des Ponts et Chaussées (France) for his invaluable suggestions and comments.