Requirements for Concrete Additives for Fine Stone Concrete Pump Delivery
To improve the pumpability of concrete, it is necessary to increase the amount of cement, use a larger water-cement ratio and sand ratio, and use a stricter aggregate gradation, which means an increase in cost or a decrease in quality. A more economical and effective way is to use admixtures to improve the pumpability of concrete. There are many types of additives, among which the admixtures that can improve the pumpability of concrete include air-entraining agents, water-reducing agents, retarders and pumping agents. The water reducing agent can change the cohesive structure of the cement slurry to the dispersive structure, thereby improving the fluidity. If the fluidity of freshly mixed concrete is kept unchanged, the use of water reducing agent can greatly reduce the amount of water used for mixing, thereby improving the stability of concrete and increasing its strength and compactness. If the strength of the concrete is kept constant, the amount of cement can be saved. Commonly used water reducing agents are lignosulfonate and naphthalenesulfonate formaldehyde condensate, such as calcium lignosulfonate, NNO, Jianyi, MF, FDN and so on. Air-entraining agent can make concrete produce many fine air bubbles, improve the cohesion and water retention of concrete, improve fluidity, and also improve the frost resistance and impermeability of concrete, but it affects the strength of concrete. Commonly used air-entraining agents are rosin soap, sodium alkyl sulfonate, sodium fatty alcohol sulfate and aluminum powder air-entraining agents. Retarders can delay the setting and hardening process of concrete, and sometimes also act as water reducers. The role of the retarder is to prolong the transport time of concrete, especially when pumping is very important in high temperature seasons. Commonly used retarders are molasses, calcium lignosulfonate, tartaric acid, citric acid, boric acid, etc. Pumping agent is a kind of lubricant, like other admixtures, it can significantly improve its fluidity without changing the mixing ratio of concrete, that is, it can expand the design range of concrete mixing ratio. There are three types of commonly used pumping agents: turbid water type, air-entraining plastic, chemical type and non-gas-assisted plasticizing type, and there are many specific varieties. In order to improve the pumpability of concrete, and to obtain comprehensive effects such as improving the quality of concrete or saving cement, one or several admixtures are used. For the use effect, dosage and adding method of various admixtures, please refer to relevant regulations.