Mass Concrete – Essential Concreting Practices

Mass Concrete – Essential Concreting Practices
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Mass Concrete

Mass concrete refer to very thick structure (> 80mm). These structures often have large volume, which generally means that large volumes of concrete have to be installed in a short time. This requires extremely goof planning and efficient processes.

Mass concrete is used for:

  • Foundations for large loads
  • Foundations for buoyancy control
  • Massive walls (e.g radiation protection)

These massive structures create the main following problems:

  • High temperature differences between internal and external concrete layers during setting and hardening.
  • Very concrete maximum concrete temperatures
  • As a result of curing from the outside to inside, big differences in the humidity occur and therefore shrinkage is forced.
  • Secondary consolidation (setting) of the concrete and therefore cracking over the top reinforcement layers and also settlement under the reinforcement bars.

Risks:

All these problems can causes cracks and cement matrix defects:

So called “skin or surface cracks” can occur if the external/internal temperature difference is more than 150C or outer layers can contract due to their drying out. Skin cracks are generally only a few centimeters deep and can close again later.

Measures to be taken:

  • Low cement content and cements with low heat development
  • Largest possible maximum aggregate sized (e.g 0-50 mm instead of 0-32 mm)
  • If necessary, cool aggregates to obtain a lower initial fresh concrete temperature
  • Place the concrete in layers (layer thickness <80 cm)
  • Retard the bottom layers to ensure that the whole section can be re-compacted after placing the top layer.
  • Use curing with thermal insulation methods
  • Ensure correct design and distribution of joints and concreting sections, to facilitate heat dissipation and accommodate temperature fluctuations



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