Air entrainment was identified by chance within the mid-1930s.[2] At that time, cement manufacturers were being using a grinding help to reinforce the whole process of grinding cement. This grinding aid was a mixture of various chemicals, which include salts of wood resin, which were being added on the cement https://3dfilament61581.weblogco.com/35517608/the-2-minute-rule-for-concrete-mould-release-oil