Concrete strengthening

It is thus apparent that care must be taken when selecting materials for the deep patch repair of reinforced concrete members to ensure that the material is structurally compatible with the substrate. 

Conventional techniques for dealing with such situations involve the construction of additional supports, prestressing or the enlargement of structural members. In the latter case this may involve the bonding of new concrete to old. An alternative solution is to use mild steel plates bonded by an adhesive to the external surface of the concrete member in question. These two techniques will now be discussed in turn. 

Unless a portion of the original concrete is removed and replaced with a higher strength material, then a concrete overlay will usually result in an increase in member self weight. Applications at ground level are therefore more common than in suspended beams or slabs, although the use of polymer modified concrete overlays has found some favour in the refurbishment of bridge decks in North America(9). 

Adhesives are often employed to achieve the necessary longitudinal shear connection for full composite action between the fresh and 

Epoxies are preferable to other resin systems in that they can be formulated to bond to moist hardened concrete and yet be able to cure within the wet environment of the fresh concrete. Polyesters do not generally bond reliably under wet conditions. The system must also be selected with due regard to the temperature of application. Resins claimed to have good bonding performance at 20 C may give rather poor bond strengths at the lower cure temperatures prevalent on UK construction sites during much of the year. 

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For repair, the concrete of reservoirs is impregnated with Silor composition to seal the concrete, strengthen it, and increase its chemical stability. Polyester cloth is glued at wall/floor joints using the one-component polyurethane adhesive UTK-M. 

Use of conservative material properties (typically 95 % fractiles are used). In case of civil stmctures, the time-dependent concrete strengthening is normally also neglected. 

R. Ortiepp, S. Ortiepp and M. Curbach, Stress transfer in the bondjointofsubsequentiy appiiedtextiie reinforced concrete strengthening , in M. Di Prisco, R. FeiicettiandG.A. Piizzari (eds) Fibre Reinforced Concrete- BEFiB 2004, Proc. RILEM Symp., PRO 39, RILEM Publications, Bagneux, France, 2004, pp. 1483-1494. 

Concrete Additives. Poly(vinyl acetate) was first used in concrete in the 1940s as a thermoplastic polymer to strengthen the concrete matrix. 

The word "composites" has a modern ring. But using the high strength of fibres to stiffen and strengthen a cheap matrix material is probably older than the wheel. The Processional Way in ancient Babylon, one of the lesser wonders of the ancient world, was made of bitumen reinforced with plaited straw. Straw and horse hair have been used to reinforce mud bricks (improving their fracture toughness) for at least 5000 years. Paper is a composite so is concrete both were known to the Romans. And almost all natural materials which must bear load - wood, bone, muscle - are composites. 

Liquid resin-based systems which, like the chemical surface hardeners, penetrate into the surface of a concrete topping or directly finished slab and protect the acid-susceptible cement matrix from attack and, at the same time, strengthen the surface of the concrete are now being increasingly used. These in-surface seals leave the slip resistance of the concrete floor virtually unchanged but the treated floors are easier to clean and are more durable. 

Two-component epoxy resin water thinned dispersions are now being used as floor sealers. They have good adhesion to concrete as well as good chemical resistance. However, the particle size of the dispersion is comparatively large (approximately 1-1.5 microns) and consequently penetration into good-quality concrete is minimal and an on-surface seal is obtained. However, with porous low-quality concrete substances, considerable binding/strengthening, etc. of the surface can be achieved with water-dispersible epoxy resin-based floor sealer. 

It is important to note material such as those plastics or wood that are weak in either tension or compression will also be basically weak in shear. For example, concrete is weak in shear because of its lack of strength in tension. Reinforced bars in the concrete are incorporated to prevent diagonal tension cracking and strengthen concrete beams. Similar action occurs with RPs using fiber filament structures. 

An option for upgrading blast resistance of an existing building may be to provide additional beams, columns, or walls strengthened with a mortar or concrete pneumatically projected at high velocity onto a surface. The concrete is placed on a cage of reinforcement, which is doweled into elements of the existing stmcture. 

Steel on steel frame, concrete roof, major strengthening to withstand blast... 

Strengthening concrete masonry walls by reinforcing and grouting, or adding shotcrete layer on the outside walls. 

Methods have been studied to inhibit this reversal process. Some have involved the addition of olefins such as limonene, myrcene, and cyclopentadiene to the ends to inhibit the depolymerization. Such stabilized polysulfur has been incorporated into concrete and asphalt mixes to strengthen them. Concrete blocks, posts, and parking tire restrainers containing polysulfur... 

Once it is cured, concrete has several surface characteristics that are problems for bonding or sealing. The concrete surface is extremely alkaline and will destroy any hydrolysis-sensitive materials that are present at the interface. It often has a weak, porous surface layer that must be penetrated or removed before being bonded. Thus, sealers and primers are commonly used to moisture-proof and strengthen the concrete surface prior to bonding. 

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