Substrate pre-treatment technology
The first step in any concrete structure repair intervention is the pretreatment of the surface. This technological step includes any intervention on the surface or crosssection of the structure prior to any other technological step.
Depending on the extent of the damage and the nature of the repair, this step can usually be divided into 3 stages:
Pre-treatment of the surface has primarily the following goals:
• Creation of load-bearing cohesive surfaces for the application and proper anchoring of fixing materials, insulating, fastening layers, or protective sealants.
• Modification of the cross-sections, creation of pass-throughs and dimensional adaptation of the structure to the intended use.
• Prevention of further degradation of the structure, which is usually caused by corrosion of the reinforcement.
In short, pretreatment should generally provide a cohesive surface with sufficient tensile strength, sufficiently dry, and reasonably rough. At least up to the following general criteria should be considered when selecting technical means and surface pre-treatment procedures:
• Purpose and nature of the repair
• Contamination with unwanted fragments
• Condition of the structure in terms of statics
• Accessibility of the structure
• Length of shutdown
• Influence or possible influence on healthy (unremoved) concrete
• Occupational safety and state of hygiene
• Impact on the surroundings of the repaired structure (dust, noise, vibration, etc.),
• Price
The price and depth of preparation are closely related to the purpose of the repair, e.g. the thickness of the layers removed. Intervention depth is usually determined by the load-bearing capacity (tensile strength) or contamination depth of the surface.
Anyhow, the limiting factor for the depth of the intervention must, first and foremost, be the load-bearing capacity of the weakened elements, to ensure the static safety of the repaired item. Conversely, the limiting factor is the minimum thickness of the added layer, and for horizontal surfaces, thicker layers of properly anchored concrete may be technologically and economically more beneficial than thin layers of significantly more expensive materials, especially for horizontal surfaces.
The accessibility of the structure or of the areas to be repaired often precludes the use of equipment designed for large horizontal surfaces (milling machines, shot blasting equipment, etc.).
Every effort must be made to minimize the negative impact on the structure and concrete. Installations and technology that cannot be shut down or removed must be minimized in their effects.
It is important to take special care when there is a risk of liquids or vapours igniting. Furthermore, this category of aspects includes the necessary dynamics of the demolition intervention on both the structure itself and its nearby neighbours. Additionally, special concerns related to health and safety must be considered as they may lead to the exclusion of techniques. For example, those techniques that can cause silicosis because of the generation of silica dust must be dismissed. Moreover, not only dust but also noise and vibration are important health and safety aspects to consider – especially when using hammers.
On another note, it is important to keep track of the time schedule for the repair intervention, the time to allow the technology to be shut down and minimize the use of such powerful apparatus so that pretreatment of surfaces can be carried out without unexpected time pressures.
