Actions during hardening 93
• Retarders are only helpful in controlling the early-age crack risk
when they lead to a slowing down of the entire hydration process.
Many commercially available retarders only influence the dormant
period, delaying the setting time. However, after the dormant period,
the hydration reaction follows the same rates as without a delayed setting. In this case, the retarder will not be helpful to decrease the risk
of early-age thermal cracking.
• Reinforcement will not significantly influence the thermal field in
hardening of massive concrete elements. The resulting thermal stresses
will also not be influenced significantly. On the other hand, reinforcement can be helpful in reducing crack width and crack spacing in case
early-age thermal cracking is occurring.
• Cooling measures can reduce the risk of early-age thermal cracking.
Two types of cooling measures can be considered: cooling of the constituent materials before mixing and casting, or incorporating cooling
pipes in the concrete element in order to evacuate (part of) the heat of
hydration during hardening.
• An appropriate choice of formwork type (insulating or not), in combination with an appropriate demoulding strategy can also be helpful in avoiding early-age thermal cracking. This should, however, be
studied case by case.
For a more detailed study of practical measures to avoid early-age thermal cracking in massive hardening concrete elements, reference is made to
the literature (De Schutter 1996).
4.4.4 example
For the construction of a harbour dock in Antwerp, Belgium, a new type
of non-reinforced massive concrete quay wall has been designed. While for
previous docks reinforced L-shaped walls have typically been constructed,
the new type of quay wall (Figure 4.14) has a so-called J-shape, a total height
of about 30 meters, a maximum thickness of about 20 meters, and contains
no reinforcement at all. The self-weight of the quay wall is sufficient to
withstand the ground pressure and the shape makes sure that compressive
as well as tensile stresses within the concrete remain below acceptable levels. The volume of the quay wall is about 300 m³/m. The unique combination of geological conditions and the possibility to build the quay wall in
open-cut, enabled the construction of the J-shaped type of quay wall on
this specific location in Antwerp (De Schutter and Vuylsteke 2004).
Due to the massivity of this quay wall, a major issue however is the problem of early-age thermal cracking. An important aspect herewith is the
casting procedure. It was studied whether casting in several layers would
reduce the risk of early-age thermal cracking. Finite element simulations
• Retarders are only helpful in controlling the early-age crack risk
when they lead to a slowing down of the entire hydration process.
Many commercially available retarders only influence the dormant
period, delaying the setting time. However, after the dormant period,
the hydration reaction follows the same rates as without a delayed setting. In this case, the retarder will not be helpful to decrease the risk
of early-age thermal cracking.
• Reinforcement will not significantly influence the thermal field in
hardening of massive concrete elements. The resulting thermal stresses
will also not be influenced significantly. On the other hand, reinforcement can be helpful in reducing crack width and crack spacing in case
early-age thermal cracking is occurring.
• Cooling measures can reduce the risk of early-age thermal cracking.
Two types of cooling measures can be considered: cooling of the constituent materials before mixing and casting, or incorporating cooling
pipes in the concrete element in order to evacuate (part of) the heat of
hydration during hardening.
• An appropriate choice of formwork type (insulating or not), in combination with an appropriate demoulding strategy can also be helpful in avoiding early-age thermal cracking. This should, however, be
studied case by case.
For a more detailed study of practical measures to avoid early-age thermal cracking in massive hardening concrete elements, reference is made to
the literature (De Schutter 1996).
4.4.4 example
For the construction of a harbour dock in Antwerp, Belgium, a new type
of non-reinforced massive concrete quay wall has been designed. While for
previous docks reinforced L-shaped walls have typically been constructed,
the new type of quay wall (Figure 4.14) has a so-called J-shape, a total height
of about 30 meters, a maximum thickness of about 20 meters, and contains
no reinforcement at all. The self-weight of the quay wall is sufficient to
withstand the ground pressure and the shape makes sure that compressive
as well as tensile stresses within the concrete remain below acceptable levels. The volume of the quay wall is about 300 m³/m. The unique combination of geological conditions and the possibility to build the quay wall in
open-cut, enabled the construction of the J-shaped type of quay wall on
this specific location in Antwerp (De Schutter and Vuylsteke 2004).
Due to the massivity of this quay wall, a major issue however is the problem of early-age thermal cracking. An important aspect herewith is the
casting procedure. It was studied whether casting in several layers would
reduce the risk of early-age thermal cracking. Finite element simulations