Concrete false setting refers to an abnormal early curing or premature hardening of cement. After leaving the machine, the initial setting is achieved in a short time, and plasticity appears again after re-stirring. This phenomenon is called false setting of concrete.
There are many factors that cause abnormal condensation of concrete, such as concrete water reducer, cement, air-entraining agent, ambient temperature and wind force, etc., which may lead to abnormal condensation of concrete. As far as the current situation of concrete engineering construction quality is concerned, the incompatibility of natural environment temperature, water reducing agent and cement is one of the important reasons for abnormal condensation of concrete and even concrete engineering accidents.
1. The main reason for the false setting of concrete：
(1) The ambient temperature is too high, and the concrete loses water too early in strong winds. If the maintenance is not in place and the concrete surface is not covered for a long time, it will lose water and harden soon. The concrete on the next layer is still relatively soft and does not cause condensation.
(2) The adsorption of cement, admixtures, sand and gravel aggregates to concrete admixtures will suddenly increase with time and ambient temperature conditions, and the slump will be quickly lost.
(3) Too high cement temperature is also an important reason for false setting.
2. Specific solutions：
(1) In summer, it is best not to use cement with too high temperature to mix concrete in commercial concrete mixing plants.
(2) In summer, use cool underground water (with ice if necessary) to mix the concrete.
(3) The concrete must be maintained, and the concrete should not lose water or be exposed to cold too early.
(4) Before construction, it is necessary to do a good job in the applicability test of cement and concrete water reducing agent, observe the loss of fluidity when mixing concrete, and investigate the setting time of concrete at room temperature.
(5) The concrete mix ratio should be moderate
(6) Abnormal concrete should be analyzed according to the specific situation, and the abnormal parts should be disposed of as soon as possible to reduce the risk of construction quality.
