It is estimated that within Europe the value of all structures (infrastructure and built environment) represent a value of approximately 50% of the national wealth of most countries. Approximately 50% of the expenditures in the construction industry are spent on repair, maintenance and remediation of existing structures. In the future these expenses will probably increase even more. A large proportion of these expenses are due to problems related to lacking durability of concrete structures. Thus, to reduce these expenses it is required to make designs for the service life of concrete structures, in which the service life is explicitly specified.
The durability of a concrete structure is influenced by a number of chemical and physical processes, which develop over time. These processes change the performance of the concrete over time, e.g. reduction of the bearing capacity or changing the aesthetic appearance. The most common of these processes are: frost attack, reinforcement corrosion, alkali-aggregate reactions, and sulphate attack.
Frost attack is a physical deterioration of concrete and it is normally divided into two classes, depending on the type of damage, internal freezing damaging the bulk concrete and scaling of the surface. When assessing damages caused by frost attack a division is made between freezing with fresh water (normally internal damage) and freezing with water containing salt present (normally scaling of surface). The damages caused by frost attacks are usually seen as scaling of the surface, where in some cases the aggregates particles are exposed and may come loose, or as cracking of the concrete. The presence and intensity of frost attack depend on the exposure environment, moisture and temperature conditions, the execution during construction and the concrete composition. The aim of this thesis is to estimate the effects of the temperature variation over the Cemetitious Materials.
This research work is divided in two parts: The Thermodynamic and Mechanical Properties of Cementitious Materials under Freezing and Thawing Actions. In the first part based on thermodynamic theories in case of freezing, the ice radius was computed. The capillary and gel porosity were computed by DuCom program and finally the ice quantity was made. The result of the analysis was compared by experimental results done by Powers and Brownyard.
In both cases for lower water cement ratios the ice quantity is almost the same, but in the case of higher water cement ratios, the Powers model supra-estimate the ice quantity. In the present model, the ice quantity is constant after -250C, fact that was confirmed by experimental data; the elastic modulus presents the same values in case of -250C and -400C, which means the ice is already formed at -25C0 and the damage quantifications for different limit temperatures are the same.
In the second part a complete experimental investigation regarding temperature variation effect was made. The main purpose of the experiment was the elastic modulus investigation and the influence of water cement ratio, minimum temperature, temperature change rate over the specimenfs stiffness. Mortar concrete with water cement ratios W/C-100%, 55% and 35% was analyzed. The limit temperature was -100C, -250C, -400C and for each case different temperature change rates were used. The experiment reveals the behavior of mortars in different conditions.
Both aspects: The Thermodynamic and Mechanical Properties of Cementitious Materials under Freezing and Thawing Actions are interconnected and a common approach tried to offer a general view of the freezing phenomena.