Concrete Replacement: TECHNOLOGIES, MATERIALS and PREPARATION of the mixture
Asphalt is a favorite choice for many homeowners as it’s durable and cost-effective. Unfortunately, depending on the climate in your area and the frequency of cars and other vehicles that go over it, the asphalt will sustain all sorts of damages over time. That’s why, every now and then, it should be completely removed and replaced with a new one. You can patch it up to a certain point, but after a while, repairing an old asphalt can no longer do the trick. Eventually, your parking lot or the sidewalk in front of your house will start to look ugly. Furthermore, with the complete removal, we will be able to identify and fix any issues in the subgrade, making your new parking lot even better. West Mount Concrete offers a complete removal and replacement (R&R) of the following:
- Residential concrete driveways
- Concrete parking lots
- Concrete slabs
- Concrete sidewalks and patchings
Concrete Replacement: NEW TECHNOLOGIES AND MATERIALS FOR ITS CARRYING OUT
Concrete is a reliable, durable material, but it is also subject to destruction. There are several reasons for premature concrete loss of performance: adverse atmospheric effects, corrosion of fittings, biological factors. The appearance of cracks opens access to the valve water and aggressive gases. In turn, the corroding reinforcement increases in volume and leads to the formation of new cracks. Repair and restoration of surfaces must be carried out in advance, until the destruction has reached a critical point.
The purpose and methods of conducting Concrete Replacement
Repeated repair work carried out without observing the technology and using improperly selected materials not only leads to unproductive material costs, but can also cause even more severe damage to reinforced concrete and concrete structures.
Professionally planned concrete repairs have several goals:
- restore the bearing capacity of the structure;
- protect the fittings from corrosion;
- reinforce concrete element with composite materials.
Concrete Replacement is a multi-stage process involving several stages:
- survey of the structure;
- finding out the causes of destruction;
- repair planning;
- selection of repair technologies and compositions;
- carrying out repairs;
- quality control of its implementation.
Materials for Concrete Replacement should have a number of properties, the most important of which is the ability to compensate for shrinkage of concrete.
Preparatory stage for concrete repair
The key to high-quality repair work is the thorough cleaning of the base from weak concrete. The cleaned surface must be roughened.
It is necessary to inspect the fittings included in the repair area. The metal is completely cleaned of rust and protected against corrosion by special means. These compounds can perform a dual function – along with the protection of the reinforcement from corrosion, they provide an old-new connection for the repair mixture.
The mass is applied at least twice with a brush.
Immediately before using repair mixtures, the concrete surface is moistened and aged until excessive moisture evaporates.
Mixes for concrete repair
As a repair mixture, micro reinforced sulfate-resistant plaster is used. This composition has a number of valuable qualities:
- significant adhesion to the old concrete base;
- water and vapor impermeability;
- high strength characteristics;
- increased resistance to the negative effects of corrosion and aggressive environment.
If the initially applied “old-new” adhesive layer is already dry, then before applying the repair plaster it must be moistened.
For minor damage, a repair mortar is made that has medium ductility. Smoothing is carried out using a metal trowel.
With significant damage, but not exceeding 50 mm, the mixture is applied in several layers. The first layer – hard plastic – “pounces.” After the start of setting of the first layer, a second and then a third layer is applied, which has a medium plastic consistency. After the last operation, the surface is smoothed using a metal trowel or jute rag.
The composition and mechanical properties of repair mixtures are similar to those of concrete. Therefore, when loading, both the old part of the structure and the repair will work the same way.
Layers of the final repair mixture are applied in mutually perpendicular directions. The latter is overwritten by a trowel.
Repair and protection of concrete by injection
The injection method is a promising method for repairing concrete structures. The essence of the operation is the injection into the body of concrete under the pressure of polymer materials. This allows you to fill all cracks and voids that are not visually determined.
After setting and completion of the polymerization process, the injection mortar hardens and fastens the cracks, reinforcing concrete or brickwork. Thanks to the creation of a membrane on several layers of the structure, an excellent waterproofing barrier is ensured, which in the future ensures that water does not leak through the floor or walls.
Before starting repair of waterproofing, all the seams of the foundation with active leaks are opened.
To carry out an injection operation, holes are drilled in concrete at angles determined by the thickness of the masonry or screed. Usually, the angle is 10-450C. To pump polymer materials, it is advisable to use special equipment that introduces the solution into the holes before filling under the required pressure.
If the material is introduced at insufficient pressure, then it will not be able to penetrate all cracks and microcracks. Excess pressure is fraught with expansion of cracks and further destruction of the concrete structure or brickwork.
After injection, the surfaces are treated with repair compounds.
The injection method makes it possible to improve waterproofing without major repairs. In this case, the solution is introduced only at the place where the crack formed. This method is also applicable for waterproofing an air cushion, which has lost its tightness due to corrosion of masonry and brick.
Formulations for injection
For injection of cracks in concrete or masonry, the following compositions are used:
Polyurethane resins seal and fill all types of joints: dry, water-saturated, wet cracks, create a cut-off waterproofing by raising capillary moisture along the walls. Injection with these materials can be carried out using special hoses embedded in the structure prior to its concreting. Hydroactive polyurethane resins are used for structures that work when large amounts of water are supplied under pressure.
For sealing and sealing injection of cracks in concrete and brick walls, acrylate-based resins are used. Using these gels, the building is additionally sealed from the outside by the method of pumping the composition along the soil-structure boundary – the creation of an anti-filter curtain. Acrylate resins elastically seal and fill microcracks in stone and concrete structures.
Epoxy resins are used for hard, bonding and reinforcing filling of dry joints and cracks. Using resin, it is possible to restore not only the external integrity of the surface, but also the normal transfer of internal forces in the concrete structure. Epoxy is injected using pre-installed overhead or internal injectors called packers. The crack between the packers is broken and cracked with epoxy repair compounds.
Epoxy resins can be used to fill cracks with an opening of up to 0.05 mm.
The use of modern repair technologies and materials for Concrete Replacement makes it possible not only to eliminate the consequences of the destruction of the concrete structure, to restore its integrity, but also to improve some of its operational characteristics laid down by the project.
Concrete Replacement at Low Temperatures
A feature of work with cement mortars is a narrow range of operating temperatures (17 … 30 ° C) and humidity requirements (80 … 85%). With a decrease in temperature, the processes of cement hydration (chemical reaction of cement with water with the formation of monolithic concrete) sharply slow down, and at a temperature of + 5 ° C they completely stop. At temperatures below 0 ° C, ice crystals form in the concrete structure, which break the bonds formed in the concrete structure. When the temperature rises above 0 ° C, broken bonds are not restored, which prevents the building from being monolithic. Ideally, for the complete “maturing” of concrete, it is necessary to maintain a temperature of at least 15 ° C throughout the entire volume of the structure or the repaired area for all 28 days.
Applied Concrete Replacement Technology at Low Temperatures
The emergence of new dry mixes with additives and methods of maintaining the optimum temperature in the repaired area made it possible to carry out repair work with high quality.
Requirements for the preparation of repair compounds:
The mixture should be made in a heated room.
Stirring is carried out 25% longer than under normal conditions.
Transportation is carried out in any type of thermos.
Concrete delivery time to the object no more than 45 min. at a temperature of the mixture 20 … 30 ° C.
The temperature of the mixture with stirring is 25 … 35 ° C, which is achieved by adding hot water from (40 … 70 ° C).
The sizes of the fractions are determined by the size of the damage and should not exceed 1.5 mm.
The main stages of work
The scope and list of works for repair at low temperatures is somewhat different from those carried out at optimal temperatures in terms of the composition and scope of the “Work” section:
Investigation of damage, the choice of repair technology, drawing up a technological map and estimates.
Preparation of a damaged surface (removal of weakened and contaminated areas, cleaning of reinforcement from concrete and rust residues).
Preparation and delivery of the mixture.
Concrete Replacement Works:
- heating the damaged surface at a speed of up to 1 ° / s to remove snow or icing and drying;
- applying the repair mixture with a thickness of not more than 20 mm in any way (with a large depth and area of damage, it is necessary to install anchors and additional fittings);
- covering the repair surface with a heat and moisture insulating mat (thermos method) or installing a heater, preferably infrared or electric film type, under the mat.
Control of strength characteristics and temperature regime of cement hydration (methods and timing of control are indicated in the routing).
Final control on samples and reporting.
The volume and composition of the repair stages depends on each specific damage and is determined at the first stage at which the contract is concluded. It is important that steps 2 … 4 are time aligned.
Antifreeze additives have long been known. Without them, construction or repair work with concrete in most areas with harsh environmental conditions is impossible.
According to the principle of action, the additives differ in:
Lowering the freezing point of the liquid, which allows the hydration process to continue at a temperature below 0 ° C.
Increasing the hydration rate due to the formation of their own chemical bonds with cement and the release of additional heat in the repair layer.
Having a complex effect, which consists in accelerating the hydration process, and the reaction products with cement lower the freezing temperature of water.
Additives consist of more than a dozen chemical compounds that are available and cheap to manufacture. In addition to the direct action of additives with modifiers and plasticizers, they can give concrete: plasticity, frost resistance during operation, water-repellent properties, corrosion resistance, additional density due to the filling of pores with solid chemical reaction products.
Additives are added with water in the preparation of “clean” concrete. The amount of additives is calculated based on the actual air temperature. It is important that the volume and composition of additives is limited by the requirement that, at the time the temperature drops below that specified by the manufacturer and the chemical reactions stop, concrete must gain at least 30% of its design strength. After increasing the temperature and freezing of concentrated saline aqueous solutions that do not form crystals, the hydration process resumes.
Antifreeze additives are highly active chemical compounds that must be taken into account when adding them to ready-made mixtures of different manufacturers. For example, anti-frost additives can be added to the Stabilcem injection repair mixture, as it is not designed for temperatures below + 10 ° C, but has good characteristics.
Dry ready mixes with thixotropic properties and reinforced with synthetic fiber are actively promoting on the market. Thixotropy is the property of a material to become fluid under dynamic load (concrete mixer, concrete pump with sprayer, putty knife). When the load disappears, the material becomes denser and does not drain from a vertical surface. Mixtures have a number of excellent qualities: ease of use, adhesion, water resistance, compressive strength and bending, but they cannot be used at temperatures of the main concrete and air below + 5 ° C. It is reasonable to use repair compositions of this type if it is possible to ensure the temperature regime ( heating the base and mixture to a temperature of 25 … 30 ° C, thermal insulation or heating of the repaired area), which seriously limits their scope.
Repair work with concrete at low temperatures is carried out as a last resort, because they are technologically more complex and costly.