Shotcrete Machine: What Is It & How It Works
Another way of applying concrete in different construction site aside from concrete pouring is concrete spraying which is one of the advance way in concrete industry.
The choice of concrete spraying over the conventional way is growing day by day as many have known its benefits.
Concrete spraying is flexible, economical and lesser time consumption during the process. Such advantages of concrete spraying are:
– Concrete can be done with less or no formworks
– Concrete can be applied on higher elevation as the sprayed concrete are made to bear its own weight
– Higher concrete adhesion
– And aside from its elevation, thickness of the concrete is also flexible.
What Is Shotcrete Machine
One way of concrete spraying is by using the shotcrete method. Shotcrete machine is an equipment used for concrete or mortar spraying.
The basic components of a shotcrete machine are the concrete pump, compressor, the control and the remote, the arm or hose and the nozzle.
With this different components, the concrete or mortar is being conveyed by the trapped air to the nozzle and being controlled to be sprayed into any area.
The shotcrete machine can be used in different application or construction jobsite like:
– Tunnel, Underground & Mining Stabilization and Construction
– Slope and Trench Stabilization
– Honeycomb/ Structural Concrete Repair
– Historical Building Restoration
– Sealing Works
What Is The Purpose Of Shotcrete
The purpose of the shotcrete is for the concrete spraying which has greater properties over the conventional method of applying concrete which is concrete pouring.
With the advancement of equipment also comes the advancement of the concrete material.
Since the shotcrete can be used in greater elevation, it needs to carry or bear its own weight given the height. In order for the concrete to stick or adhere during the shotcrete appication, the ratio between the cement and water is usually lower than usual.
With this shotcrete method, the concrete have higher adhesion and bond strength compared to the conventional method thus reduces the need of admixtures.
This is also to avoid sagging during the shotcrete application unlike the concrete pouring which have formworks and scaffold to support the weight or the water-cement ration during the application.
With the lower cement and water ratio, shotcrete can acquire higher compressive strength in a short span of time compared with the conventional method which needs to cure for some time.
Because of the high velocity due to the use of shotcrete, the compaction of the concrete is also carried out which increases the strength of the concrete.
Gaining high compressive strength in a shorter span of time gives you a high output which positively affects your cost and schedule.
How Does It Work
There are two ways of using the shotcrete method, it is for the dry process sprayed concrete and wet process sprayed concrete. Dry process sprayed concrete uses a dry mix of cement and aggregates fed in the spraying nozzle with finely atomised spray of water added to the dry mix to hydrate the cement.
The wet process sprayed concrete uses a mixture of concrete, aggregate and water which go through the nozzle with high pressure of air.
Dry Process of Sprayed Concrete
The dry process of shotcrete is using a predetermined ratio of concrete and aggregate, depending of the strength it should achieve, without mixing it to water.
The dry mixture will be fed into the machine and is pressurized with high velocity airstream that will be conveyed on the hose to the spraying nozzle.
In the spraying nozzle area, the atomized spray arrangement of water is found for the purpose of hydrating the cement mixture.
Just like achieving the right ratio of dry mixture between cement and aggregate, the right amount of water will be sprayed consistently to achieve the right compressive strength.
Wet Process of Sprayed Concrete
The wet process of shotcrete is by using a batch of a mixture of water, cement and aggregates. This mixture can be of readily mixed or are being mixed on site.
The batch of the mixture should be done before feeding in to the machine especially for larger concrete spraying application. The mixture will be then feed, wherein the water-cement ratio be controlled depending on the strength to achieve, and a high velocity air is applied in order for it to pass through the hose to the nozzle.
If being used in a large batch or longer time, admixtures should be on the side to control the hydration of the mixture.
How To Operate A Shotcrete Machine
As discussed, shotcrete machine can be used for dry mix and wet mix.
Dry Process of Sprayed Concrete
- Fed the dry mixture into the open hopper/ barrel of the shotcrete. To avoid clogging, provide liners on the chamber to lessen lumps of dry mixture
- With the control, allow the dry mixture to be blown by the compressed air into the spraying hose nozzle.
- As the dry mixture pass the nozzle, control the separate water nozzle to hydrate the dry mixture with the right amount of water
- In using the shotcrete, the nozzle should be far from the area with at least 0.6 meter to 1 meter.
- The shotcrete operator should maintain the right amount of water to hydrate the dry mixture to achieve the compressive strength.
Wet Process of Sprayed Concrete
- Fed the wet mixture (water, cement and aggregate) into the equipment.
- Control the air velocity to be used in pushing the wet mixture through the hose to the nozzle.
- The nozzle should be at least 0.2 meter to 0.5 meter away from the area where the concrete should be applied.
- The shotcrete operator should be able to use the equipment in a consistent and constant rate with no pulsation to achieve the right compressive strength.
- To adjust the wet mixture especially when used in a long time, admixtures should be readily available whenever to avoid clogging of the nozzle when the mixtures gets dry.
Shotcrete machine is one of the most helpful equipment in the construction jobsite but can be tricky.
The things you need to consider when using a shotcrete is the method which is the dry mix or the wet mix, the right ratio of water, cement and aggregates and most especially is that the shotcrete operator should be well-equipped.
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