Bi-layer diaphragm walls: Evolution of concrete-to-concrete bond strength at early ages

An innovative structural element typology is proposed, referred to as a bi-layer diaphragm wall. Its two layers are poured and sprayed, respectively, in two phases; the first layer is a standard reinforced-concrete diaphragm wall, while the second consists of a layer of sprayed concrete with steel fibers, which performs a dual waterproofing and structural role. Through an experimental campaign, our research aims to study the evolution of bond strength between the two concretes at early ages. Three preparation techniques were studied: milled surfaces, milled and epoxy-bonded surfaces, and saturated milled surfaces. The results reveal that the shear strength of milled surfaces follows a typical maturity law, regardless of the milling direction. In contrast, a wide range of results is evident for in situ epoxy-bonded surface preparations.