Concrete, fresh: initial setting time and activation energy during setting (NT BUILD 476)

Abstract

SCOPE

This NORDTEST method specifies a method for the determination of the initial setting of fresh concrete by measuring the heat development of the concrete during the first hours. A method of determination of the activation energy during the setting period is also specified. The setting of concrete normally refers to the start of the growth of strength which is determined for concrete according to NT BUILD 197. The initial setting period is normally finished within eight hours after mixing. The time for the initial setting of concrete is the age at which 12.5 kJ heat is liberated per kg cement according to Clause 6.3. This age corresponds with the age at which the penetration resistance, as defined in NT BUILD 197, reaches 3.5 MPa.

FIELD OF APPLICATION

Since the setting of concrete is a gradual process, any definition of time of setting must necessarily be arbitrary. In this test method, the time required for the concrete to liberate a specified amount of heat is used to define the time of initial setting. This test method can be used to determine the effects of variables, such as brand, type and content of cementitious material, water content, and admixtures, upon the time of initial setting of concrete. This test method may also be used to determine compliance with specified time of setting requirements. The setting time of the concrete is a function of the curing temperature. It is necessary to know the activation energy of the setting period, in order to estimate the setting time for temperatures different from +20 °C by calculating the maturity. The activation energy during the setting period is different from the activation energy of the remaining hardening period.