Ottimizzazione del calcestruzzo ad alta resistenza meccanica con superfluidificante per la diga delle Tre Gole in Cina

A series of tests and analyses were conducted to optimize the mix-composition of the high-compressive strength (40-45 MPa) and erosion-resistant concrete for the Three-Gorge Dam construction. The main challenge was to choose the best binder content in this type of concrete which often, for its hydration heat, is characterized by severe shrinkage and susceptibility to cracking. In the end, a retarding superplasticizer, based on a carboxylated acrylic ester (CAE) copolymer, emerged as the best superplasticizers thanks to its high water-reduction and low slump lost. In-situ monitoring on the spillways of the 3-Gorge Dam has shown that, in addition to the high workability and better compatibility with the available binder, the CAE-based superplasticizer in the C40 (40 MPa at 28 days) and C45 (45 MPa at 28 days) concretes can help to reduce the hydration-heat-induced temperature rise of about 6°C, vis-à-vis that of sulfonate naphthalene (SN) based superplasticizer. The practical significance of this improvement is to give the contractor additional means to limit the differential thermal strain below the concrete's permissible strain level, and then to allow the contractor to suppress thermal cracking by as much as 83 %. From the viewpoint of cost effectiveness, the use of the carboxylated polyacrylate superplasticizer can help the contractor to save significantly from temperature control and placing process during casting, without necessarily increasing the unit cost of the concrete.