Abstract

A numerical model that accounts for the hydration and aging phenomena during the early ages of concrete curing is presented in a format suitable for a finite element implementation. Assuming the percolation of water through the hydrates already formed as the dominant mechanism of cement hydration, the model adopts an internal variable called hydration degree, whose evolution law is easily calibrated and allows an accurate prediction of the hydration heat production. Compressive strength evolution is related to the aging degree, a concept that accounts for the influences of the hydration and curing temperature on the final mechanical properties of concrete. The model capabilities are illustrated by means of a wide set of experimental tests involving ordinary and high performance concretes, and through the simulation of the concrete curing on a viaduct deck of the Öresund Link.

Abstract

Abstract

The main objectives of this research work are to find new ways of reducing costs in the manufacture of composite materials, automate processes and improve energy efficiency by looking for alternatives to the use of autoclave, always meeting the quality requirements. For this, an out of autoclave curing process is studied through an innovative system of automatic and fast curing of composite parts for the aeronautic, automotive and construction sectors. The process allows the curing of prepregs of various materials and geometries. The process includes the provision of temperature by heating plate with electric resistances, pressure and vacuum adjustable through an air compressor, and cooling through circuit through mechanized plates. The main innovative feature of this system is the pressure supply with compressed air to the piece by means of a moldable and reusable silicone membrane, which allows to extend the field of study to complex elements saving the current limitation of hot plates presses, and without the need to place countermold. CFRP cured parts are manufactured in this new system, then their properties are compared with autoclave cured parts and similar properties are obtained, and auxiliary materials are considerably reduced. It can be concluded that this system improves energy efficiency, reduces costs and optimizes times.

Abstract

In the present work the influence of the graphene type (GNP) and the different crosslinking agent ratios in the curing of graphene-epoxy dispersions and in the glass transition temperature (Tg) of the formed nanocomposite is studied. The epoxy resin type DGEBA (LY) has been crosslinked with an aromatic polyamine (XB). Two types of graphene have been used: one non-functionalized (GNPn) and another functionalized with amino groups  (GNPNH2). In the two systems, 5 compositions with different XB / LY ratios have been studied and, the content of graphene has been varied (6 and 10% by weight). The curing reaction has been studied by Differential Scanning Calorimetry. It has been observed that the presence of graphene accelerates the curing reaction and that the enthalpy of reaction depends on stoichiometry and graphene content. It has also been found that the variation of the Tg of the material with the stoichiometry, depends on the curing protocol.