1.Most of the concrete built by modern workers and civilians has the properties of large-volume concrete, and attention should be paid to volume stability (hydration heat and shrinkage). Concrete (including concrete with different admixtures) generally exhibits micro-expansion deformation in water and generally shrinkage deformation in air.

2.The higher the amount of cement, the higher the water consumption, the greater the amount of cement slurry, the greater the slump and the greater the shrinkage. Avoid pouring concrete in the rain. In case of light rain, rain protection measures (especially for the blanking part) should be taken and the water-cement ratio should be adjusted.

3.The larger the water-cement ratio, the larger the shrinkage. The water-ash of high-strength concrete is relatively small, which is beneficial to the later drying. However, due to the cement slurry or cementitious materials and the effect of high-efficiency water reducer, it is better than the medium-low strength concrete. The shrinkage is large, and the tension-to-pressure ratio decreases as the strength increases. Low water to cement ratio is detrimental to early plastic shrinkage.

4.The larger the exposed surface, the smaller the enclosed area and the larger the shrinkage. Represented by the reciprocal of the hydraulic radius r = L / F, see the second chapter of the book "Engineering Structure Crack Control".

5.The shrinkage of slag cement is larger than that of ordinary cement, the shrinkage of fly ash cement and bauxite cement is smaller, and the shrinkage of fast hard cement is larger; the hydration heat of slag cement and fly ash cement is lower than that of ordinary cement, so cement type should be selected according to thickness . Major projects should be carried out with hydration heat and shrinkage tests.

6.The shrinkage of aggregates in sandstone has increased dramatically. The larger the mud content in the coarse and fine aggregates, the larger the shrinkage and the lower the tensile strength, which should be strictly limited.

7.The earlier and longer the early curing time (7-14 days), the smaller the contraction. Moisturizing and curing to avoid severe drying can effectively reduce the shrinkage stress. Pay attention to vibrating, especially at the junction of beam and slab (or wallboard), but do not over-vibrate to prevent segregation and massive bleeding. Spraying the floor immediately after pouring, secondary calendering, covering the plastic film, and strengthening the moist curing is very beneficial for controlling cracks.

8.The greater the environmental humidity, the smaller the shrinkage, the higher the ambient temperature, the drier, the greater the shrinkage.

9.The coarser the aggregate size, the smaller the shrinkage, the finer the aggregate size, the higher the sand ratio and the larger the shrinkage.

10.The higher the activity of the cement, the finer the particles, the larger the specific surface area and the greater the shrinkage. (Admixture particle size affects the same properties)

11.The greater the reinforcement ratio, the smaller the shrinkage, but the excessive reinforcement will increase the tensile stress of the concrete. The reinforcement should be fine and dense, and should not be thick and thin. Note that in the area of shrinkage stress concentration, the structural reinforcement is strengthened. The prestressed structure reinforces the non-prestressed reinforcement.

12.The greater the wind speed, the greater the contraction. Pay attention to the cast-in-place concrete in the high air to avoid direct sunlight on the newly poured concrete surface during the hot season.

13.Improper selection of admixtures and admixtures significantly increases shrinkage; selection is appropriate to reduce shrinkage, especially early contraction.

14.The higher the environment and concrete temperature, the greater the shrinkage. The longer the stoppage exposure time, the greater the contraction.

15.Shrinkage and environmental cooling occur simultaneously, which is more unfavorable for engineering.

16.Backfill the soil as soon as possible, the soil is the best curing medium for concrete. Closing the house and decoration as early as possible is beneficial to reducing the contraction.

17.The amount of bleeding is large, the surface water content is too high, and the early surface shrinkage is increased, but the early dewatering of the concrete surface should be avoided to increase the shrinkage.

        18.For medium and low-strength grade cements with less dosage, concrete with lower water ash and less slump, most of the shrinkage completion time is about one year. The concrete with a large amount of cement and a high strength grade is about 2 years. The final                 shrinkage of concrete is about 20 years old. The handling and repair of minor shrinkage cracks is not a “quality accident”.