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STRUCTURAL REPAIR & STRENGTHENING

Most structural problems can be avoided by proper design and planning; but structural failures have been common for a long time, and sometimes are costly to handle properly.

Corrosion of steel in concrete can be seen to be a significant problem for many reinforced concrete structures if moisture is present. If there is no salt to cause corrosion in the short term, carbonation will affect most structures over the centuries. If the structure cannot be kept dry then there is a range of techniques that can be used depending on the structure, its condition and the cause and extent of the problem.

Like masonry and brick, reinforced concrete structures deteriorate under attack from external elements such as freeze-thaw damage (the expansion of frozen moisture within the structure as it thaws), and erosion. In a composite man-made material such as concrete there are additional mechanisms caused by the greater complexity of its composition. Of particular concern today is the alkali silica reaction in the concrete and the corrosion of the reinforcing steel, both of which are affected by the alkalinity of Portland cement concrete. Portland cement is made by burning constituents which include lime in a kiln and grinding the result to a fine powder. This produces a highly alkaline material which reacts with water and hardens. When it is added to coarse and fine aggregate and mixed with water, the cement combines with the aggregate and hardens to form concrete. The hardening process (hydration reaction) is complex and continues over many months if not years, depending on the amount of water in the mix. There must be excess water for workability and a pore network therefore develops as it dries out. Excess calcium hydroxide and other alkaline hydroxides are present in the pores and a solution of pH 12.0 to 14.0 develops (pH 7.0 is neutral; values below indicate acidity, and alkalinity above). It is this pore network and the solutions it contains that are critical to the durability of the concrete.

If corrosion of steel in concrete is suspected, a deterioration survey must be carried out to identify the cause, mechanism and extent of corrosion. An inadequate investigation can lead to higher costs and inadequate repairs. There are certain tests which are specific to the corrosion assessment of steel in concrete, relying on the electrochemical nature of the corrosion process. These are half-cell potential measurement, resistivity measurement and corrosion rate measurement.

Application – Enlargement of Beam


Application – Pressure Grouting
Permeation grouting is an economical means to remediate existing and potential geological and foundation support problems, without causing major disruption to structures. The pressure grouting process consists of the direct pressure injection of a liquefied grout (micro fine cement) into voids, cracks, fractures, cavities, or even between a bearing media and a structure, foundation or bearing walls. The permeation grouting methods can take the forms of compaction, curtain, chemical, micro fine cement, slurry, or any other permeation application used to install a cement grout or low-mobility material. The pressure method requires that the media gels or solidifies within or around the treated areas: soil, pipes, cracks, fractures, conduits, or holes. The main purposes of the permeation grouting are to improve support, strength, and function of a given media, element. Or substance, i.e., concrete walls, pipes, blocks, gravel, cement columns, or soils. These permeation (cement) techniques have more applications than just sealing and can also be used to lift structures such as: floors, walls, buildings, bridges, columns, highways, parking lot pavement, towers, and more.

Application – Carbon Fiber Lamination
Strengthening of a structure may be necessary if increases in loads, changes in structural articulation or intended use occur, and also, after accidental damages. Depending on the location of structure, access to the repair area, or the time allow for the repair, several materials and technique have to be considered. Carbon Fiber Reinforced Polymer Strip is an external strengthening system that can be used on structural elements comprised of concrete, wood, or steel. This system consists of a pultruded, pre-cured carbon fiber reinforced polymer (CFRP) strip and a high modulus/high strength epoxy gel. The strips are adhered using epoxy gel to structural elements to increase flexural capacity, fatigue resistance and reduce deflection.

Application – M.S. Plating
Describes surface-covering where a metal is deposited on a conductive surface. Plating has been done for hundreds of years, but it is also critical for modern technology. Plating is used to decorate objects, for corrosion inhibition, to improve solder ability, to harden, to improve wear ability, to reduce friction, to improve paint adhesion, to alter conductivity, for radiation shielding, and for other purposes. Jewelry typically uses plating to give a silver or gold finish. Thin-film deposition has plated objects as small as an atom, therefore some plating is nanotechnology.

There are several plating methods, and many variations. In one method, a solid surface is covered with a metal sheet, and then heat and pressure are applied to fuse them (a version of this is Sheffield plate). Other plating techniques include vapor deposition under vacuum and sputter deposition. Recently, plating often refers to using liquids. Metalizing refers to coating metal on non-metallic objects.

Application – Anchoring System
Chemical anchors are ideally suited for high load applications, as the resulting bond is stronger than the base substrate material itself in almost all instances. Additionally as the system is based on chemical adhesion, no pre-loading stress is imparted to the substrate, as it is with expansive mechanical anchors. Therefore chemical anchors are also ideal for fixing close to edges, they can be installed at reduced centers and they are better for close group anchoring.

Application – Epoxy Injection
Epoxy Injection Resin is a system for welding cracks back together. This welding restores the original strength and loading originally designed into the concrete. Epoxy injection restores the structural qualities the concrete design intended. In other words under most conditions it makes the concrete as good as new. It creates an impervious seal to air, water, chemicals, debris, and other contamination. A crack, obviously, is a sign of failure caused by stresses, inadequate design, improper curing, etc. One of the dangers of a structural crack is the effect that it has on the reinforcing bar. The reinforcing represents one of the main structural values of the concrete. Cracks left unprepared allow moisture, road salts and other contaminants to penetrate and attack the rebar. The rebar deteriorates, losing the structural value and losing the entire structure is often the result. Epoxy injection resin has two purposes. First, it effectively seals the crack to prevent the damaging moisture entry. Secondly, it monolithically welds the structure together. The sealing properties of the injection prevent premature deterioration of the reinforcing. This can be of equal, or in some cases greater importance than the structural welding. It would theoretically always be desirable to get this welding effect.