Air entrainment was found out by chance from the mid-1930s.[two] At that time, cement manufacturers had been employing a grinding assist to enhance the entire process of grinding cement. This grinding assist was a combination of assorted chemicals, like salts of wood resin, which have been additional for the cement https://amorphousboronpowder04704.birderswiki.com/1477626/polycarboxylic_ether_based_superplasticizers_an_overview