Mixing expansive agent into commercial concrete can limit the expansion and compensate the shrinkage of commercial concrete, which is beneficial to improve the impermeability and crack resistance of commercial concrete. The compactness, strength and durability of commercial concrete mixed with expansive agent are also improved under multi-directional constraints. Nevertheless, there are still different opinions on the application of expansive agent in commercial concrete. The reasons are as follows: the commercial concrete mixed with expansive agent often can not produce the expected expansion, and the commercial concrete structure still appears deformation and cracking in the middle and late stage or even early stage. In addition, the durability of commercial concrete mixed with expansive agent, especially the carbonation resistance and corrosion resistance of steel bars, has also attracted much attention. In view of the above problems, this paper mainly studies the alkalinity change, carbonation resistance and corrosion resistance of commercial concrete mixed with UEA expansive agent. The effects of temperature, humidity, water-binder ratio, types and contents of mineral admixtures on the ultimate expansion of commercial concrete with expansive agent were studied. The effects of temperature and humidity on the stability of ettringite are discussed, and the reasons and conditions for delaying the formation of ettringite are analyzed.

The research results show that:

① With the increase of ①UEA content, the alkalinity of commercial concrete decreased slightly, but the range was very small. When the content reaches 20% of the cement content, the pH value of commercial concrete system is still above 12.0.

(2) With the increase of expansive agent content, the carbonation resistance and steel corrosion resistance of commercial concrete decrease, which is obvious for commercial concrete with water-binder ratio greater than 0.4; When the water-binder ratio is lower than 0.4, the expansive agent has little effect on the carbonation resistance of commercial concrete and the protection of steel bars.

③ Temperature and humidity have an important influence on the efficiency of expansive agent. When the humidity is saturated and the temperature is lower than 70℃, with the increase of temperature, the early expansion efficiency of the expansion agent increases, and the middle and late expansion efficiency decreases slightly. When the temperature exceeds 80℃, the expansion efficiency of expansive agent decreases greatly with the increase of temperature, which is mainly related to the stability of ettringite.

(4) Mineral admixtures have certain influence on the expansion performance of the expansion agent, among which fly ash has little influence, and the addition of ground slag and silica fume will weaken the expansion effect of the expansion agent.

⑤ The expansion behavior of commercial concrete mixed with expansive agent is affected by water-binder ratio, and the expansion effect of expansive agent in commercial concrete with low water-binder ratio is relatively low.