When damaged concrete has a broad area of faults or cracks, replacement concrete is a way of repair. This type of concrete restoration involves removing damaged concrete from the structural member, preparing the region for repairs, and then using replacement concrete. When the repair area reaches 1 square foot and the depth surpasses 6 inches, and the repair is of substantial continuous area, this approach is applied.
Replacement concrete repairs are also used for:
Holes that go all the way through concrete portions. Except where epoxy-bonded concrete replacement is required or permitted as an alternative to concrete replacement, holes in which no reinforcement is encountered or in which the depth extends 1 inch below or behind the backside of the reinforcing steel and which are larger than 1 square foot and deeper than 4 inches. Larger-than-half-square-foot holes in reinforced concrete that extend beyond the reinforcement The most popular concrete repair material, replacement concrete, will suit the needs of the vast majority of concrete repairs.
Without the use of a bonding agent or Portland cement grout, replacement concrete repairs are done by bonding new concrete to the repair areas. The repair is compatible with the old concrete in terms of thermal expansion and other physical and chemical qualities because the damaged concrete is replaced with high-quality concrete that is very comparable to the surrounding concrete. As a result, the optimum repair method in many circumstances is the use of replacement concrete.
Preparation of Surface for Replacement Concrete:
Preparation should be as follows in order to achieve satisfactory results with the replacement concrete method:
To use replacement concrete, the reinforcement in the reinforced concrete should be exposed for at least 25mm surrounding it. For replacement concrete, the minimum depth of concrete removal should be roughly 25mm, and it should continue until all of the problematic concrete has been removed. If the hole is for a vertical member, the top should be cut with a 1:3 upward slope from the back toward the face where the concrete will be poured. This is necessary to allow concrete vibration without leaving air pockets at the top of the repair. If concrete is being removed from one side of the structure to the other.
Cutting damaged concrete should be done in such a way that no current concrete is destroyed and no concrete is spalls.Before excavating the damaged concrete, the outlines of areas to be repaired should be saw cut as specified to a depth of 1-1/2 inches for repairs on surfaces prone to damaging water action and for other repairs on exposed surfaces.The existing concrete surfaces to which fresh concrete is to be bonded must be clean, rough, and dry on the surface. Prior to placement, any excess material on the joint caused by form fabrication must be eliminated.
Materials for Replacement Concrete:
The water-cement ratio in repair concrete should be the same as in identical new constructions or the existing structure, although it should not exceed 0.47 by weight. To minimise water content and subsequent shrinkage, utilise aggregate with a maximum size of as large as possible and a slump as low as is consistent with appropriate placement and complete vibration. Entrapped air should make up 3 to 5% of the concrete. To reduce shrinkage, the concrete should be laid as cool as possible, preferably at 20 °C or lower. During hot weather, materials should be stored in shaded regions. When combining water, it may be necessary to use ice.Material batching should be done by weight, but batch boxes can be utilised if they are the exact size needed.
For replacement concrete, the slump should be as low as feasible, and it should be less than 75mm.
Starting with an over-sanded mix with a maximum aggregate size of 20mm, a maximum water-cement ratio of 0.47 by weight, 6 percent total air by volume of concrete, and a maximum slump of 100 mm, structural concrete placements should be commenced. This specific mix should be applied to the junction at the bottom of the placement several inches deep. On the construction joints, a mortar layer should not be applied.
Application of Replacement Concrete:
The quality of a repair is determined not only by the use of low-slump concrete, but also by the thoroughness with which the vibration is measured before, during, and after the concrete is deposited. Over-vibration is unlikely to occur. If accessibility allows, immersion-type vibrators should be employed. Pressure should be applied to the fill and the form vibrated immediately after the hole has been entirely filled. This procedure should be repeated every 30 minutes until the concrete has hardened and is no longer responsive to vibrations. Wedging or tightening the bolts protruding through the pressure cap applies pressure.
The replacement of concrete in open-top forms, such as those used to rebuild the tops of walls, piers, parapets, and curbs, is a relatively easy procedure. Only materials that have been proven to produce long-lasting concrete should be utilised. To allow for quick drainage, top surfaces should be slanted. Forms for concrete replacement repairs can normally be removed the day after casting, unless doing so will harm the green concrete, in which case stripping should be delayed for another day or two. Some types of replacement concrete don’t require the use of forms. Replacement of damaged or degraded paving or canal lining slabs, if the slab is replaced to its entire depth, entails processes similar to those necessary for best outcomes during initial construction.
Curing and Protection of Replacement Concrete:
After the forms have been removed or the concrete has set, it is critical that the replacement concrete be cured. There is a risk of full failure of the repaired concrete if the replacement concrete is not properly cured. Water curing is particularly desirable, at least for the first 24 hours, due to the limited volume of most repairs and the tendency of old concrete to absorb moisture from new material. A soil-soaking hose installed beneath a plastic membrane covering the repair area is one of the best techniques of water curing. When using a curing compound, the ideal curing combination is an initial water-curing period of 7 days (never less than 24 hours) followed by a surface-curing period of 7 days (never less than 24 hours).
Given the massive amount of concrete structures that surround us on a daily basis, it’s easy to overlook how concrete allows us to live the lifestyles we do in our ever-changing urban settings. Concrete, like us, need regular maintenance. The tensions and demands of regular life have an impact on it.
Corrosion, structural damage, water infiltration, seismic activity, and a variety of other factors can cause concrete to deteriorate. Sika has developed a comprehensive solution for restoring and rehabilitating concrete structures based on years of study and decades of practical experience. From design to final completion on site, Sika customer guidance and support is second to none. All of this is based on more than a century of research.
Concrete building and infrastructure repair and renovation is an important procedure because it allows us to take a more sustainable approach to construction by extending the life of a project and avoiding destruction and reconstruction. The selection of an appropriate restoration technique based on the core cause of concrete failure can also improve a structure’s overall performance. Sika offers a diverse range of products and solutions to address a variety of concrete repair issues.
Concrete is a common building material in dams for core walls, spillways, stilling basins, control towers, and slope protection because it is economical, durable, and strong. Poor workmanship, construction techniques, and construction materials, on the other hand, may result in flaws that must be repaired later. Flowing water, ice, or other natural factors that cause long-term degradation or damage to concrete structures must be repaired. Failure of a concrete structure due to neglecting to execute routine maintenance and repairs as they arise could result in structural or hydraulic failure. As a result, the dam’s continuing safe operation and use may be jeopardised.
Considerations for Concrete Repair
Major structural issues include floor or wall movement, significant cracking, inappropriate alignments, settlement, joint displacement, and extensive undermining. When concrete replacement solutions are needed to repair deteriorated concrete, it is recommended that an inspection be performed by a registered professional engineer to assess the concrete’s overall condition, determine the extent of any structural damage, and determine the necessary remedial measures. Drainage systems are typically required to relieve high water pressures beneath floors and behind walls. Furthermore, reinforcing steel must be adequately built to withstand tension zones, as well as shear and bending stresses in structural concrete caused by external loading (including the weight of the structure). As a result, any concrete repair procedure’s final product should
Also Check
COARSE AGGREGATES IN HIGH STRENGTH CONCRETE