The causes of concrete structure cracking are very complex, which may be caused by design, material and construction. The top ten reasons related to materials include:
1、 Poor cement stability
1）Free calcium oxide or free magnesium oxide are crystal particles fired at high temperature. The curing is very slow. The curing is carried out only after the cement is hardened, causing the solid phase volume expansion of the surrounding cement stone and cracking of the cement stone.

2）When the amount of gypsum is too much, after the cement hardens, it will continue to react with solid hydrated calcium aluminate to form high sulfur hydrated calcium sulphoaluminate, with a volume increase of about 1.5 times, which will also cause the cracking of cement paste.

6、 Poor aggregate quality
1）The high content of mica in aggregate weakens the bonding force between cement and aggregate and reduces the strength of concrete.
2）Too much organic matter and light matter in aggregate will delay the hardening process of cement and reduce the strength of concrete, especially the early strength.
3）Sulfide in aggregate can react chemically with tricalcium aluminate in cement, with volume expansion of 2.5 times, resulting in cracking.
7、 Alkali aggregate reaction
The basic aggregate such as opal, andesite, Xuan Wuyan, diabase and phyllite may react with alkali strong cement to form alkali silica gel with expansive capacity, which will cause the expansion and failure of concrete and produce cracks.
8、 Excessive water cement ratio and slump
1）Water cement ratio and slump will directly affect the strength of concrete. In order to meet the pumping conditions, the pumped concrete has large slump and good fluidity, which is easy to produce the phenomenon of less local coarse aggregate and more mortar. At this time, when the concrete is dehydrated and dried, it will produce surface cracks.

2）Some concrete has bad phenomena such as segregation and bleeding, resulting in uneven distribution of various components of concrete, great difference in hydration reaction, and easy to produce cracks.

9、 Influence of admixtures
1）The poor adaptability of admixture and cement will increase the shrinkage of concrete in varying degrees.
2）Improper selection of admixtures (such as expansion agents), expiration, or misuse of counterfeit products are also prone to cracks.
10、 Mineral admixture
The higher the fineness of mineral admixture, the greater the shrinkage of concrete; The greater the content, the greater the shrinkage. Generally, commercial (pumped) concrete contains a large amount of fly ash (15% ~ 30%), and the concrete shrinkage is large. Therefore, the project using commercial (pumped) concrete is easy to crack. At the same time, the early strength of concrete is poor, which is not enough to resist the early internal tensile stress and prone to cracks.