What Is Shotcrete?
- Shotcrete/mortar/spray-concrete is a kind of refined concrete drizzled by gas hose-pipe nozzle at high pressure & velocity on a projectile motion on a prepared wall surface.
- It is strengthened by conventional steel rods, steel mesh or fibres.
- It is often utilised in tunnels, underground walls, retaining walls, drainage systems & swimming pools for interim support.
- For slope protection with wire mesh and in some confined areas wherever prosaic concreting cannot be done.
- It can be sprayed on any type of surface (vertical or overhead).
- The shotcrete method needs less formwork and is more economical and cheap (needs only a small industry to get manufactured).
- It forms a good chemical bonding among a variety of materials.
Shotcrete & Concrete
- Concrete is a building material that comes with an exceeding diversity of choices, together with lightweight, heavyweight, porous, and fibre-reinforced, to suit a range of construction needs.
- It consists of refined rock-dust & water paste that solidifies.
- Shotcrete is a specific style of concrete that can either be dry-mix or wet-mix.
- It has become acclaimed for its unique application technique that is distinctive from prosaic concrete.
How Does the Application of Shotcrete Dissent from Concrete?
- The main distinction between shotcrete and concrete happens during its placement.
- Concrete is applied by employing a mixing truck, which prepares the mixture and pours it onto the ground.
- The fresh concrete is then sprayed.
- Conversely, shotcrete is placed using a cement gun.
- The gun applies the mixture at a high rate, which gives the end product high strength, high sturdiness, and low permeability.
- Sand (Natural/ Crushed)
- Coarse Mixture (Below 10mm)
- Fly ash/ Microsilica
Types of Shotcrete Technology
There are two types of Shotcrete Technology. Which is as follows.
- Dry-Mix Shotcrete
- Wet-Mix Shotcrete
#1. Dry-Mix Shotcrete
It involves inserting the dry ingredients into a gun and then spray them through a hose to the nozzle.
The inner part of the nozzle possesses a water ring which uniformly injects water into the mixture as it is being oozed out from the nozzle and propelled on the wall surface.
The water and the dry mixture are not thoroughly mixed but is completed as the mixture hits the receiving surface. This requires a skilled nozzleman, peculiarly in heavily bolstered sections.
Advantages of Dry-Mix Shotcrete
- The dry mix process is beneficial in repair applications when it is necessary to stop & adjust frequently.
Disadvantages of Dry-Mix Shotcrete
- Dust will be higher as we are using the dry ingredients. It is not applicable where the shotcrete quantity is applied more frequently.
#2. Wet-Mix Shotcrete
In wet-mix shotcrete, ready-mix concrete is used, which is sprayed through delivery paraphernalia such as a concrete pump which propels the mixture through the delivery hose where compressed air and accelerator is added at the nozzle point.
Advantages of Wet-Mix Shotcrete
- Less rebound (shotcrete falls down due to paucity in setting).
- Less dust compared to dry-mix shotcrete.
- Larger volume can be placed in lesser time.
Disadvantages of Wet-Mix Shotcrete
- A highly skilled operator is needed in spraying.
- W/c, pressure and accelerator dosage has to be unambiguous.
Shotcrete wall placement gives the subsequent benefits for quicker installation:
- Set concrete wall thickness and vertical alignment.
- Shotcrete wall at a faster rate than form-and-pour.
- Finish concrete to any specification.
Shotcrete Wall Benefits
- Potentiality to place walls top-down, bottom-up or a full excavation.
- Substantially increase production compared to cast in situ concrete walls.
- ACI shotcrete specifications are readily available.
- Effortlessly incorporate shotcrete as an amendment order during construction.
- High strength, low permeability and high durability.
- Faster concrete set-up reduces labour costs.
- Better bonding to the receiving surface.
- Reduction of forming materials by up to 100%.
- No extra concrete footings required for wall supports.
- Diminished crane time for form setting and concrete pouring.
Properties of Shotcrete
- A small maximum size mixture used and cement content is high.
- It is ought to enhance sturdiness in most cases.
- Whereas typical concrete is consolidated by vibration, shotcrete is consolidated by the impact of a high-velocity jet bashing on the surface.
- This method not only increases the cement content due to rebound but also brings about completely dissimilar air-void systems affecting the sturdiness of shotcrete.
- The application procedures have a greater effect on the in-place properties of shotcrete than the mix proportions.
- Shotcrete specimens usually sawed from test panels of about one-meter square and 75 millimetres dense made by gunning out plywood.
Applications of Shotcrete
- Shotcrete is widely employed in different construction such as skinny overhead vertical or horizontal surface, notably the curved or folded sections, canal, buildings, marine structures, bridges, reservoir, and tunnel lining.
- It is additionally employed in tunnels, canals, reservoirs, swimming pools, water retaining structures, and pre-stressed tanks.
- Shotcrete has successfully been utilised in the stabilisation of rock slopes, underground excavations and temporary protection of freshly excavated rock surfaces.
- It may be a utility for protection against long-term corrosion of pilling, coal bunker, oil tanks, steel building frames, and other structures, renovation of old buildings and fire vandalised structures as well as in encasing steel to form the structure water-resistant.
- These are developed for high-temperature applications, like the refractory lining of kilns, chimneys, furnaces, etc.
- They are also used for waterproofing walls.
Advantages of Shotcrete
- The shotcrete can be applied by a nozzle from a secured haughtiness. It requires no vibration or compaction after placement since it is blown into place under pressure.
- More economical than prosaic concrete and requires less formwork. It is a reasonable thanks to build concrete in curves and serpentine shapes that are arduous or unfeasible with traditional concrete forming, such as those required in tanks, domes, swimming pools, and skate parks.
- Eximious bonding in nature which makes the concrete layers terribly robust.
- Among the benefits, it does not need a tortuous system of forms just like the more amicable poured-in-place concrete, since it is applied as a stiff paste and is solely a one-sided type, or none the last bit if it is applied over compacted soil.
- It can be used with steel reinforcing bars, welded wire reinforcing mesh, fibre reinforcement mixed with the concrete, or with no reinforcement.
- It has identical non-combustible and fire-resistant qualities as concrete that has been formed and poured in a prosaic manner.
- It minimises man-power.
- Helps to manage cement-water ratio.
Disadvantages of Shotcrete
- The primary pitfall of shotcrete compared to slooshed concrete is the bulk of your time that it takes when utilised for Brobdingnagian foundations, structural piers, and other structures with giant cross-sections, in juxtaposition to using prosaic forms for these giant structures.
- Another disadvantage is the dusting drawback.
- Two common issues when applying shotcrete are gravel within the concrete concoction that is too colossal, which hinders with the spraying of the concrete; and ready-mixed concrete that is too wet so that it does not adhere well to vertical and overhead surfaces.
- Production cost is incredibly high.
- Much concrete is squandered in comparison to prosaic concrete.
- High skilled manpower needed to perform the work.
- The procedure is sophisticated to some extent.