Question

What causes thermal cracking of concrete in early day of concreting? Name 4 methods that can be used to control it and give reasons in details.   

Answer 1

Thermal cracking in early days of concreting is a major issue and prevention is very necessary.This is caused mainly by hydration process.Hydration is nothing but mixture of water and cement.In hydration process high amount of temperature is produced.Temparature differnces between concrete structure and that of sorroundings vary in a significant amount.Due to this thermal stresses are produced.As a result volume of concrete changes significantly.Cooler portion contracts more than the warmer portion.Due to this thermal deformation,cracks are appeared in concrete in early days of concreting process.

4 methods that can be used to control thermal cracking of concrete as follows-

a. Cooling pipes can be installed between the reinforcement bars and cold water can be pumped through it.Which will help to prevent the temperature rise in the concrete due to thermal expansion and eventually development of cracks can be prevented.

b.Low heat hydration cement can be used.It is like the ordinary portland cement.It composed of low percent of tricalcium silicate and higher percentage of dicalcium silicate.It produces very low amount of heat of hydration during the early setting and hardening period of concrete.As a result thermal stress production is prevented and concrete becomes safe from thermal cracks.

c.Thermally insulated formwork can be used to prevent thermal cracking.They are generally made of polystyrene foam,polyurethane foam,cement bonded wooden fibre etc.These give the required thermal protection to the concrete and help to prevent concrete cracks by controlling the temperature differences between the concrete and the sorroundings.

d.Use of fly ash is also effective in reducing thermal cracks.Fly ash can be used with ordinary portland cement.Fly ash is a pozzolan,containing aluminious and silicious materials.Fly ash slowers the hydration process than normal.As a result, heat evolution due to hydration process decreases and thus help in prevention of development of thermal cracks.