69
Chapter 4
Actions during hardening
DOI: 10.1201/b12914-4
4.1 IntroductIon
One of the major difficulties with concrete as a construction material is the
volume instability as a function of time. Due to several phenomena, often
occurring simultaneously, the dimensions of a concrete element evolve in
time even without external mechanical loading. When the resulting deformations are restrained, cracking and damage can occur in the structural
concrete element. Especially during the hardening process, the cracking
risk can be quite high, because in this stage the young concrete already
has a relatively high stiffness and still a relatively low strength (see also
Chapter 1).
As a consequence of the hydration process, water is chemically bound.
The hydration products have a smaller volume than the reacting products,
which is called chemical shrinkage. Furthermore, the consumption of water
leads to some internal drying, especially in the case of binders with a low
water/cement ratio. Consequently, a volume reduction is noticed, called
autogenous shrinkage. Further details are given in Section 4.2 of this
chapter.
As soon as the hardening concrete element is exposed to external drying, water is typically exchanged from the material to the environment, as
the environment normally is dryer than the hardening concrete. The loss
of water also gives rise to a volume reduction of the concrete, called drying shrinkage. In wet environment, the concrete element can show expansion instead of shrinkage. Further details are given in Section 3 of this
chapter. In addition to drying shrinkage, concrete also shows carbonation
shrinkage (Neville and Brooks 2010). Carbonation shrinkage can lead to
damage in autoclaved aerated concrete as explained in Section 5.2.3 of
Chapter 5.
Another effect of the hydration process is the exothermal production of
hydration heat. This heat energy will cause a temperature increase of the
concrete element. In a typical situation, the core of the element will show
a higher temperature than the surface of the element, leading to thermal
Chapter 4
Actions during hardening
DOI: 10.1201/b12914-4
4.1 IntroductIon
One of the major difficulties with concrete as a construction material is the
volume instability as a function of time. Due to several phenomena, often
occurring simultaneously, the dimensions of a concrete element evolve in
time even without external mechanical loading. When the resulting deformations are restrained, cracking and damage can occur in the structural
concrete element. Especially during the hardening process, the cracking
risk can be quite high, because in this stage the young concrete already
has a relatively high stiffness and still a relatively low strength (see also
Chapter 1).
As a consequence of the hydration process, water is chemically bound.
The hydration products have a smaller volume than the reacting products,
which is called chemical shrinkage. Furthermore, the consumption of water
leads to some internal drying, especially in the case of binders with a low
water/cement ratio. Consequently, a volume reduction is noticed, called
autogenous shrinkage. Further details are given in Section 4.2 of this
chapter.
As soon as the hardening concrete element is exposed to external drying, water is typically exchanged from the material to the environment, as
the environment normally is dryer than the hardening concrete. The loss
of water also gives rise to a volume reduction of the concrete, called drying shrinkage. In wet environment, the concrete element can show expansion instead of shrinkage. Further details are given in Section 3 of this
chapter. In addition to drying shrinkage, concrete also shows carbonation
shrinkage (Neville and Brooks 2010). Carbonation shrinkage can lead to
damage in autoclaved aerated concrete as explained in Section 5.2.3 of
Chapter 5.
Another effect of the hydration process is the exothermal production of
hydration heat. This heat energy will cause a temperature increase of the
concrete element. In a typical situation, the core of the element will show
a higher temperature than the surface of the element, leading to thermal