m.f NAJJAR - Civil engineering Department, AL-Fateh University, Libya,
h.s ABDELGADER - Civil engineering Department, AL-Fateh University, Libya,

The pouring of underwater concrete is considered as challenge for engineers even during the design or during implementation and supervision, due to the fact that many precautions must be taken for the success of casting process.The most important precaution is to protect the fresh concrete during the casting process from the water until thecompletion of the pouring of concrete and the concrete harden, so as to avoid the risk of washout of cement past andsegregation of aggregates. Concrete can be placed underwater successfully though good design of concrete mix, andthrough choosing the most suitable method for placing of concrete underwater. There are wide ranges of methods forunderwater concreting including traditional methods such as tremie method and pumping method, there are also somenew and non common methods such as grouted aggregate which is known as two-stage concrete method. Two-stageconcrete is considered as one of modern techniques in the concreting industry. The two-stage concrete or pre-placedaggregate method, as the name implies, consists of filling form with aggregate and then injecting grout to fill thevoids through pumping tubes extended to the bottom of the form. The main objective of the research is to present astudy for the capability of preparation and execution of pouring the concrete underwater by using two-stage concretemethod.

Underwater concrete, Two stage concrete, Grout, Coarse aggregate.