There’s no doubt that concrete is an effective building material that is widely used in today’s construction industry. Like any compound, however, its properties change gradually with time due to numerous factors and at some point, it will need to be repaired. Concrete is prone to issues such as cracking and other more complex issues depending on the type of structure and how old it is.
The most cost-efficient and effective method of repairing concrete is by using shotcrete which is concrete that is pneumatically sprayed through a hose at high velocity onto a receiving surface. While shotcrete has many other applications such as swimming pools, slope stabilisation, retaining walls, basement walls, and excavation, today we’ll be focusing on the steps required to ensure the successful repair of a concrete structure.
What type of structures?
Shotcrete is very versatile and can be used on a wide range of concrete structures as a repair method. Despite this, when considering the properties of shotcrete, this process is most effective on vertical surfaces like walls, columns, and pier caps, and horizontal surfaces like beam bottoms, slab soffits, ceilings, and deck overhangs. When these types of structures have integrity issues or when an additional layer of concrete is required to cover reinforcement, shotcrete is typically used because there is little to no forming requirements.
With any shotcreting project, one of the most vital requirements to a successful outcome is surface preparation. The following steps should be taken prior to performing any shotcrete repair project:
- Determine the areas of the concrete which require repair
- Remove any unsound concrete using either a high-pressure water blaster or a chipping hammer. When doing this, avoid damaging any reinforcing bar or substrate concrete
- If you find any reinforcing bar has been damaged, it must be replaced or supplemented. Never place any new reinforcing bar behind or in front of any existing reinforcing bar
- Thoroughly remove any dust or contaminants from the concrete surface and use an abrasive blast or water blast on any exposed reinforcing steel
- Lastly, spray the surface with water and wait until the area has reached a saturated surface-dry (SSD) state
After following the steps above, apply the shotcrete to the required area. Begin by filling the corners with shotcrete first and move the nozzle continuously to cover all reinforcing bar. It’s vital that the shotcrete is applied homogenously and there is no build up in a particular area. If you find there is overspray in a certain area, use a blow pipe to remove it in the same way you would remove rebound found in the corners and on reinforcing steel.
Once the initial layer has been applied, proceed with additional layers after thoroughly preparing the surface of the preceding layer to ensure maximum adhesion. The thickness of each layer is dependent on the project specifications, however this can easily be increased with the appropriate additives. When the final layer of shotcrete has been applied (reaching just passed the desired plane), allow it to harden until the shotcrete can be worked without diminishing the bond. Most commonly, a trowel is used to cut back the material so it’s flush with the surface. Keep in mind that the material should never be overworked so that delamination’s or spalls appear on the surface. Proper curing techniques should then be applied to enhance the physical properties of the shotcrete and to reduce any shrinking.
Using shotcrete to repair existing concrete structures is widely used to ensure the surface of the structure remains intact and weather-resistant. With any shotcreting project, the success is largely dependent on the experience of the shotcrete contractors, so it’s strongly encouraged to use contractors who have plenty of experience in the type of work you wish to complete. If you’re interested in using shotcrete to repair a concrete structure, reach out to the professionals at Evolution Shotcrete by calling 07 5561 8885.