Concrete repair

One of the most important problems is the repair and reconstruction of concrete structures, the lack of compatibility of repair mortar and concrete. One of the most important factors in selecting suitable repair materials for damaged concrete is the bonding between repair materials and concrete, which ensures that the member is restored and the concrete is integrated and in the restored part is not weak. The following properties are important for compatibility between repair materials and concrete

1 – Alcocity module
2 – Shrinkage (drop)
3. Creep
4. Thermal degradation and …….

The compatibility between the base concrete and the repair concrete is very important in terms of elastic modulus. If this is not taken into account, after refitting the loaded member, due to the different strains created in the repair mortars and the base concrete, Or the repair material is crushed, or it is separated from concrete, which in no case is preserved in the two modes of integration.

Types of repair materials
• 1-Cementation
• 1.1 – Cement mortar with additives such as microsilica, fiber and …
• 2.1. Polymer-modified cementitious materials
• 2-Polymer wells

Important parameters of choice of repair materials
1 – Size and shape of patches repair
2 – The presence of the armature in place
3 – Temperature changes and humidity
4 – Impact loads, continuous and continuous

Mortar repairs with cement base
• Cement mortar as a repair material has advantages such as low cost and similar appearance of concrete cement mortar with concrete. The repair materials with cement base are generally composed of cement in different types and fine aggregates. Cement content is Sand one to two to one to three.

Cement mortar containing additives
It can be used to improve the properties of admixture mortars (such as lubricants, powders, fibers …). It adds that it improves the properties of the mortar in both loose and loose conditions.

A: Improve the properties of the mortar in a loose state –
• Increase efficiency without increasing water
• Swing or initialize the initial time
Decrease or decrease mortar expansion
– Slow drop of slump

B: Improve the properties of rigid mortar –
Reduced permeability
•• -Speed ​​to gain resistance at an early age
• Increase resistance and modulus of elasticity
– Improve the strength of concrete against impact

Concrete and repair mortar containing fibers
Types of fibers used in concrete or mortar repairs are asbestos, linen, glass, polyethylene, polypropylene and ………
Property:
1 – Resistance to wear, weathering, throat, fatigue stress, impact
2. Reduce cracks and prevent cracks from opening
3. Increase relative deformation capacity
4 – High tensile strength

Polymer or latex modified concrete cement mortar
The use of polymers in concrete or mortar has been commonplace since ancient times. Natural polymers, which are the same organic matter in nature, are more stable in the environment under different environmental conditions. The most common type of polymer in concrete and mortar, bitumen It was natural that it was used for sealing.

Polymer Latex Types:
1-polyvinyl acetate
2-Bodynthians
3 – Acrylics

How to mix polymers with concrete or mortar repair
Applicable polymers in concrete are prepared as tiny particles in water (emulsion), which are in the form of a white liquid in milk, which is referred to as liquid or glue or as latex, and in a volume or weight percentage, depending on the mixing pattern to the concrete Is added

How to fix a mortar or concrete made with Portland cement by Latex
Primary reaction: These reactions occur in a conventional mortar during a hydration process. At this stage, the latex particles adhere to the surface of the cement particles inside the concrete.
Secondary reaction: Immediately after the mixing of concrete materials, the cement and polymer particles are distributed uniformly in water and the polymer film network develops in three stages.
Stage 1: The precipitation of a part of the polymer particles on the non-hydrated cement
The second step is the penetration of the polymer particles into the interior of the pores and inside the concrete, which, by hydration and water reduction, brings together polymer particles inside the pores and forms a continuous layer on the surface of the hydrated paste.
Stage III: With further water loss in hydration, polymer particles become more compact and form a film layer.

The effects of polycarbonate on repairs
1 – lubrication and increase the efficiency of concrete or mortar in paste form
2- Treatment with regard to the role of polymer to prevent water loss in the mortar
3. Increase the durability of concrete
4. Decrease permeability
5 – Increased tensile strength, flexural flexure

Epoxy and resin mortar
Of the various types of resin systems, the epoxy resin mortar is most often used in the repair of concrete structures. For small repair surfaces requiring rapid resistance, mortars based on polyester resin and acrylic resins are used. Resin mortar Compared to cement mortars, they have the advantages of fast and fast curing to achieve high resistance. They do not alkaline. The bonding resistance of these materials is high, but it is not cost effective due to its expensive thicknesses of up to 10 mm. .

Repair techniques
The extent of the failures in determining the type of repair method plays an important role, which is summarized in the following categories
Divided into:
1. Hand-tightening (or localized)
2 – sprinkling concrete
3. Redraw

Cracks in concrete buildings and other structures must always be inspected by the responsible Structural Engineer before the concrete repair and protection works begin. The precise nature / reason for the crack, together with its full extent and any structural or other significance must first be determined.
From this structural assessment, which is usually undertaken as part of the Condition Survey and Diagnostic Assessment the most appropriate remedial solution such as resin injection can be specified and incorporated into the schedule of the overall concrete repair and protection works.
Resin Injection to Repair Non–Structural Cracks in Concrete.
If the crack in the reinforced concrete is due to past movement or excessive loading applied to the element or the structure as a whole i.e. during the original construction, work, or the installation of heavy equipment for example; then it may well have no structural significance.
When the structural engineer confirms that it is no longer moving then it may simply be filled with an appropriate repair or surface levelling mortar and overcoated to prevent the ingress of aggressive liquids or gases i.e. with the same protective coating as the rest of the surface. However if it is possible that at least some thermal or other slight movement could occur in the future, causing the crack to open again, then the crack can be structurally re-bonded with a suitable low pressure epoxy injection resin for example, or at least a crack bridging coating should be used. Where the crack has no structural significance but is definitely subject to significant thermal or other movement, then a suitable crack bridging surface coating should always be used or dependent on its size and location, the crack
may be transferred and treated as a movement joint in the surface i.e. formed to the correct size, brought through to the surface and sealed with an elastic joint sealant such as Sikaflex Construction.
European Standard EN1504 Part 9 Principle 1 (Protection Against Ingress) Method 1.2 Surface Coating with Crack Bridging Ability: Method 1.3 Locally Bandaged Cracks; Method 1.4 Filling Cracks; and Method 1.5 Transferring into Joints – Can all apply as appropriate to the structure’s situation and requirements.