Mass Concrete

[jteahan]

Is there an industry-accepted definition of what constitutes a "mass concrete" pour? Can a designer require a mass concrete mix design without telling the contractor which pours are mass concrete pours? Or should a contractor be expected to know which pours are mass concrete pours based on dimensions, etc.?

 

[RiBeneke]

I have encountered the term 'mass concrete' being used to mean 2 different things.

1) Meaning unreinforced concrete not subject to significant bending loads. For example a 'mass concrete' unreinforced strip footing under a brick wall.

2) Meaning a large volume concrete pour, reinforced or unreinforced, in which temperature control becomes an issue. Normally temp issues start to become significant if distance from the centre of the cast to the nearest surface exceeds about 600 mm (2 ft). Temp control requirement is also very dependant on mix design, large aggregate size, accelerators, pozzolans, ingredient temp, ambient temp, permissible surface cracking, amount and distribution of reinforcement, formwork etc.

The designer should understand these issues and deal with them. The contractor should know that they exist, but would not normally be expected to provide a solution without input from the design engineer.

 

[Zambo]

According to ACI116R mass concrete is defined as "any volume of concrete with dimensions large enough to require that measures be taken to cope with generation of heat from hydration of the cement and attendant volume change to minimise cracking".

Because this definition doesn't provide a specific measure many agencies have developed their own definitions of mass concrete such as; any concrete element having a least dimension greater than 0.9m.

I would suggest that a contractor should at least be aware of potential problems and approach the designer to discuss any precautions which may need to be taken.

Zambo