10.6 : 混凝土收缩

The loss of water or chemical reactions reduces the concrete's volume, a process known as shrinkage. 

Practically, shrinkage in concrete is measured as linear strain even though shrinkage contributes to volumetric strain, which is three times the linear strain.

In its plastic state, concrete loses water due to evaporation from its surface or water absorption by the dry underlying layers, leading to a volume contraction in the concrete, known as plastic shrinkage.

The higher the rate of evaporation, the more plastic shrinkage. This evaporation rate is influenced by the concrete's temperature, the surrounding air's temperature, relative humidity, and wind speed.

Moreover, concrete mixes with higher cement content exhibit more plastic shrinkage than those with lower cement content.

As the cement hydrates, the internal pores within the cement paste begin to dry out, developing capillary tension within these pores, resulting in compressive forces on the hydration products.

As a result, a uniform reduction in the concrete's volume occurs, known as autogenous shrinkage.

Lastly, high-performance concrete exhibits greater autogenous shrinkage compared to normal concrete due to its low water-to-cement ratio.