Hydraulic concrete – Placing – Rheology and maturity of concretes

Concrete, a component used in a wide range of construction applications, must satisfy a number of safety, durability and aesthetic requirements. To meet these requirements in the hardened state, it is clear that it must first exhibit robust rheological characteristics in the fresh state and, more specifically, at the moment of final placement in the formwork.

As the real construction material is reinforced concrete (rebar and/or fibers), concrete must protect these rebars, and this function can only be fulfilled once the notion of minimum rebar cover has been taken into account. Nor should it be forgotten that the material must be protected from drying out immediately after casting, and again immediately after demolding. In some cases, the concrete surface is treated or coated: these operations must be carefully studied beforehand to adapt the substrate.

Once the objectives to be achieved have been defined, the conditions of implementation must be set out in a set of specifications covering all phases of construction:

• formwork and reinforcement ;

• transport and pouring of concrete (by gravity, pumping or spraying);

• concrete clamping method (vibration, self-placing) ;

• concreting adaptations related to the ambient conditions expected during the construction period;

• the possible need to pour deep foundation elements, to pour in large masses, or in water;

• and, of course, the various prescribed surface treatments.

In this first part, the reader will find the basics needed to design and prepare the worksite in terms of the rheology of fresh concrete, on the one hand, and the measures to be planned (and implemented) in order to know the mechanical characteristics of the concrete, enabling work to be carried out on young concrete, such as the tensioning of prestressing reinforcement or, more simply, form stripping.

Chapter 5 contains a glossary of the main technical terms used in this article.