Report rep031 : Advanced Testing of Cement-Based Materials during Setting and Hardening - Final Report of RILEM TC 185-ATC

Concrete changes continuously its phase or state. After mixing the constituents which are cement, water, aggregates, additives and admixtures it is a rather viscous suspension. Depending on the type of concrete it is vibrated in the mould and consolidates or it is self-compacting and consolidates under the action of gravity. The consolidation phase lasts during the so-called dormant period when the binder constituents react only for a very small amount with water and the concrete behaves as a thixotropic fluid. The fresh concrete is setting after about one hour. The state changes from a fluid to a material with low strength and stiffness. After a few hours the concrete is not workable anymore. It becomes stiff and converts to a solid material when it hardens. Of course, the mentioned phase changes depend on the type of cement. For a gunite cement the periods are in the order of minutes, for a slow hardening cement it may be several hours, and with the addition of admixtures one can delay the phase changes by a retarder or can them speed up by an accelerator.

The phase changes are extremely important for the construction process, they determine the construction speed, the time of shutter removal, the time of partial prestressing, and the time of lifting prefabricated elements. In mass-concrete structures the heat of hydration is an important issue and, together with it, the degree of hydration which determines in turn all mechanical and physical properties of early-age or hardening concrete.

The transient stages from fresh concrete via hardening concrete to hardened concrete have got more and more attention the last years. The RILEM workshop “Testing during concrete construction” which was held in 1990 was the first one addressing the testing issues. The extensive knowledge of RILEM members has been brought together in the Technical Committee 185-ATC “Advanced testing of cement based materials during setting and hardening”. The committee was proposed in 1998 and approved by RILEM in 1999. The first committee meeting took place in April 2000 and five working meetings followed until March 2004. It was decided to work on a state-of-the-art report which was finished in 2005.

Contents

Chapter 1

Chapter 2

Chapter 3

Chapter 4 - Mechanical Wave propagation

Chapter 5

Chapter 6

Chapter 7

Chapter 8