Corneliu Bob
University Politehnica of Timisoara, Romania
Title: About the deterioration of concrete structures due to the shrinkage and temperature variation
Biography
Biography: Corneliu Bob
Abstract
The concrete shrinkage
A negative characteristic of using concrete as building material it is due to its volume instability during time passing: there is the concrete property to shrink and crack during its drying process.
There are two stages of concrete shrinkage:
- Plastic shrinkage and cracking due to cement composition and /or environmental conditions during casting (rapid early drying) of concrete; it is developed after the concrete was made (30 minutes to 6 hours.).An original explanation concerning plastic shrinkage and false setting is presented. The types of damages are: diagonal cracks in roads and slabs, random cracks in reinforced slabs, cracks over reinforcement in slabs.
- Long term drying shrinkage which produced cracks due to the water release from fresh concrete into the environment; it is measured starting 24 hours, since the concrete was made and cast, to months. Cracking are produced in thin slabs and in walls due to inefficient joints and insufficient curing. Few case studies are to be presented: large platforms, bridge pillars, a slab of multi storey frame structure.
Temperature variation on concrete structures
As well as the concrete shrinkage, the temperature variation will induce into building elements the volume instability which will create internal stress. An interesting case of a reinforced concrete basin under temperature variation is to be presented. For basins, made of prefabricated elements, the deteriorations were not relevant, but for a basin erected with monolith connections, very sensitive damages (cracks and large deformations) were observed due to temperature variation.
Other types of concrete cracks are produced by: plastic settlement; early thermal contraction; construction, formwork and sub-grade movements, etc.
The concrete cracks of structures represents a real problem for owners and engineers due to diminishes of strength, stiffness and durability of constructions (see Fig.). In such cases the rehabilitation or demolition of structure elements, represent the necessary solutions