Why is concrete poured in layers

Stratified pouring basically is to be aimed at large volume concrete character, prevent cement hydration heat concentration, too big, produce temperature crack. Layered pouring can reduce the hydration heat peak, easy to heat dissipation, vibration in place.

Reasons for layered pouring:

1) Concrete when pouring a vibration process, and vibration is to ensure the density of the concrete, the general existing vibration equipment amplitude is limited, too thick beyond the working range of the vibrator, easy to produce empty drum phenomenon. If a pouring is too thick, the air in the concrete is not easy to discharge in vibration, vibration time is too long and will cause concrete segregation that is, mud stone separation, affect the strength of concrete.

2) Cement in mass concrete in the hydration process to release a certain amount of heat, and mass concrete structure section is thick, the surface coefficient is relatively small, so the heat generated by cement is not easy to disperse in the structure. In this way, the hydration heat inside the concrete can not be sent out in time, and even accumulate higher and higher, so that the temperature difference between inside and outside increases. The cement hydration heat released by concrete per unit time is related to the amount of cement per unit volume of concrete and cement varieties, and increases with the age of concrete. Layered casting and timely heat dissipation are beneficial to reduce temperature crack of mass concrete.