Bakelite

Bakelite is a fast-setting phenol resin, which after being released in liquid form will quickly harden. Similar to very quickly drying, extremely hard concrete, Bakelite is deployed inside of NERV HQ in the event that an Evangelion loses control and needs to be quickly restrained. Also, part of NERV HQ's defensive system includes the capacity to flood presumably most or possibly all access corridors with Bakelite, as a means of cutting off enemy approach.