Actions during hardening 91
of early-age thermal cracking, even when the element might not seem very
massive.
The water/cement ratio does not seem to influence significantly the heat
production rate during hardening. However, as a higher water/cement ratio
will lead to a higher ultimate degree of hydration, the total cumulated heat
will be higher as well. Nevertheless, thermal stresses are governed more
by the heat production rate during hardening and less by the total cumulated heat after a long time. It should be repeated, however, that a higher
water/cement ratio will lead to lower strength values, and thus possibly to
a higher cracking risk.
The nature of the aggregates can influence the evolving temperature fields
during hardening by influencing the thermal properties of the concrete.
The aggregate size, which can be quite large in very massive structures, can
influence the paste volume of the concrete and thus the required cement
content (see also Section 1.4.3 in Chapter 1).
Plasticizers can reduce the water/cement ratio and thus increase the
concrete strength, possibly reducing the early-age thermal cracking risk.
However, a lower water/cement ratio will lead to a higher autogenous
shrinkage and a higher cement content might also be needed to maintain
sufficient workability. This can make the situation very complex in the case
of high strength concrete with a very low water/cement ratio.
4.4.2.2 Geometrical parameters
The massivity of the concrete element is a very important parameter for
the study of early-age thermal cracking. The massivity of an element is
typically defined as the ratio of volume to surface. However, comparing different shapes or geometries, the massivity does not seem to enable
quantitative comparisons. A more accurate parameter combining size
and shape seems to be the equivalent thickness (De Schutter and Taerwe
1996b). The higher the equivalent thickness, the higher the risk of earlyage thermal cracking.
4.4.2.3 Atmospheric parameters
At higher environmental temperature, the hydration process of the concrete
will typically proceed faster. This will lead to an accelerated production of
the heat of hydration and to higher temperature gradients in the hardening element. However, the influence of the environmental temperature also
depends on the size of the element, the presence of the formwork, the casting temperature of the fresh concrete … and thus should be verified in view
of all these parameters.
of early-age thermal cracking, even when the element might not seem very
massive.
The water/cement ratio does not seem to influence significantly the heat
production rate during hardening. However, as a higher water/cement ratio
will lead to a higher ultimate degree of hydration, the total cumulated heat
will be higher as well. Nevertheless, thermal stresses are governed more
by the heat production rate during hardening and less by the total cumulated heat after a long time. It should be repeated, however, that a higher
water/cement ratio will lead to lower strength values, and thus possibly to
a higher cracking risk.
The nature of the aggregates can influence the evolving temperature fields
during hardening by influencing the thermal properties of the concrete.
The aggregate size, which can be quite large in very massive structures, can
influence the paste volume of the concrete and thus the required cement
content (see also Section 1.4.3 in Chapter 1).
Plasticizers can reduce the water/cement ratio and thus increase the
concrete strength, possibly reducing the early-age thermal cracking risk.
However, a lower water/cement ratio will lead to a higher autogenous
shrinkage and a higher cement content might also be needed to maintain
sufficient workability. This can make the situation very complex in the case
of high strength concrete with a very low water/cement ratio.
4.4.2.2 Geometrical parameters
The massivity of the concrete element is a very important parameter for
the study of early-age thermal cracking. The massivity of an element is
typically defined as the ratio of volume to surface. However, comparing different shapes or geometries, the massivity does not seem to enable
quantitative comparisons. A more accurate parameter combining size
and shape seems to be the equivalent thickness (De Schutter and Taerwe
1996b). The higher the equivalent thickness, the higher the risk of earlyage thermal cracking.
4.4.2.3 Atmospheric parameters
At higher environmental temperature, the hydration process of the concrete
will typically proceed faster. This will lead to an accelerated production of
the heat of hydration and to higher temperature gradients in the hardening element. However, the influence of the environmental temperature also
depends on the size of the element, the presence of the formwork, the casting temperature of the fresh concrete … and thus should be verified in view
of all these parameters.