Wet Shotcrete Application - Hacettepeyunus.hacettepe.edu.tr/.../pdf/Wet_Shotcrete_Application.pdfIn this presentation, I will cover these topics; a brief introduction to necessity
Introduction General Info About Shotcrete Application of Wet Shotcrete Comparison Demonstration Conclusion Questions
03.01.2012 2 Özgün Can Özgüneş
Presenter
Presentation Notes
In this presentation, I will cover these topics; a brief introduction to necessity of shotcrete, general info and working principle of wet shotcrete, application parameters of wet shotcrete, a brief comparison between dry and wet techniques, then I prepared a little demonstration for you, than I will finish my speech with last closing comments. Then I can take your questions.
Before starting to present, I want to introduce myself, my name is Özgün Can Özgüneş and I’m currently studying Mining Engineering at Hacettepe University. This is my email adress, so anytime, you can ask questions to me via this email.
We excavate rock for:
Tunnels Roads Mining Various jobs
Problem is same: fractured, unstable rock
03.01.2012 4 Özgün Can Özgüneş
Presenter
Presentation Notes
At our present time, we excavate earth rock for many things in order to ease our life. Build underground tunnels for cars, trains,... Trim mountains to pass roads near them,... Opening mines to excavate ores,... And so many other jobs. But all of these works brokes the balance of nature, and this returns us as a very big problem: Fractured and unstable rock,.. Waiting to collapse.
Use support systems: Rock Bolt Wire Mesh Steel Arc
For complete perfectness:
Shotcrete
03.01.2012 5 Özgün Can Özgüneş
Presenter
Presentation Notes
So what can we do? We can use various support systems like rock bolts, wire meshes and steel arcs. Yes, they can provide really great support, but for completing the puzzle, we need one more thing. Shotcrete!
03.01.2012 6 Özgün Can Özgüneş
Presenter
Presentation Notes
This a picture that shows the application of shotcrete.
Fast, easy and cost-effective
Provides support to whole area
Prevents chipping and peeling
Visually looking good
03.01.2012 7 Özgün Can Özgüneş
Presenter
Presentation Notes
Why we need shotcrete? Because it can be applied really fast and easy, this is beneficial for economy. Secondly, Other support systems provides point or small area support, but shotcrete provides support to whole area that applied, and Besides it’s support, it covers the whole area, prevents little particles from dropping. And last, it creates a visually good looking surface, flat and homogenuesly textured.
Dry-mix Shotcrete Wet-mix Shotcrete
03.01.2012 8 Özgün Can Özgüneş
Presenter
Presentation Notes
There are two types of shotcrete, dry-mix and wet-mix. Difference between them is only the mixing place of water and cement. At dry-mix system, dry, powder-like cement feeded to system, accelerated to hose via this compressed air, and at here operator mixes it with water. But at wet-mix system, water and cement are already mixed at bucket, it only pumped to hose and accelerated via compressed air.
03.01.2012 9 Özgün Can Özgüneş
Presenter
Presentation Notes
Rollers forcing mix to move inside hose by pressing on hose.
1. Mixing cement and water
2. Pumping wet-mix to hose
3. Providing compressed air to hose
for accelerating wet-mix
03.01.2012 10 Özgün Can Özgüneş
Presenter
Presentation Notes
Working principle of wet-mix shotcrete system can be briefed as this: 1, 2, 3. And now, we have a video of general shotcrete application.
There are three important working parameter. Number one is water/cement ratio, this is the most important factor, because it affects the strength of final concrete product. Second, pumping speed is determines how much mixed material sent to hose. And last factor, compressed air pressure, determines the speed of shotcrete spray. Also there is an important point, first two parameters can only be set before work starts and cannot be changed by operator at operating time, but the last parameter, is controlled by operator, and can be changed instantly at operating time.
Generally between 0.40 and 0.55
Lower ratio gives better strenght
Higher ratio gives better filling
03.01.2012 13 Özgün Can Özgüneş
Presenter
Presentation Notes
Water/cement ratio of wet-mix shotcrete changes between 0.40 and 0.55, and you choose an optimum value between them. When you decrease that value, your concrete generally tends to be more strength, but can’t fill the surface voids well.
Perpendicular to application surface
Start from bottom and rise slowly
Continuously make swirling motion
03.01.2012 14 Özgün Can Özgüneş
Presenter
Presentation Notes
There are 3 simple rule for making a perfect shotcrete application. First, You need to apply shotcrete to surface as perpendicular as possible. Second, you need to start from bottom, fill there properly and then rise the target. Last, always make small circular motion, in order to obtain homogeneously applied shotcrete.
Rebound Increases
Can’t fill surface well
Can’t get a homogeneous concrete
03.01.2012 15 Özgün Can Özgüneş
Presenter
Presentation Notes
And, what if we don’t? ...............
Occurs from high speed of particles
Increases with low application angle
Greater than 45o Smaller than 45o 03.01.2012 16 Özgün Can Özgüneş
Presenter
Presentation Notes
What is rebound? Rebound is the particles that don’t stick to surface, but just bounce off the surface and go elsewhere. In brief, rebound is lost material, time and money. We accelerate and spray shotcrete at really high speed to surface, so it tends to bounce from surface. Lowest rebound occurs at 90 degree perpendicular application, and rebound level is tolerable to 45 degrees. But after that, we lose great amount of material to rebound. So never apply shotcrete at angles smaller than 45 degrees to surface.
03.01.2012 17 Özgün Can Özgüneş
Presenter
Presentation Notes
This is a special attachment head for easy applying shotcrete at higher places without decreasing the angle too much. Or there is a better option, a robotic arm that can apply shotcrete always perpendicular to surface, no matter how high it is.
Wire Mesh Reinforced
Fibre Reinforced
Silica Fume
03.01.2012 18 Özgün Can Özgüneş
Presenter
Presentation Notes
We generally need to reinforce shotcrete, in order to get maximum strenght out of it. There are three ways; wire mesh reinforcement, fibre reinforcement and silica fume.
03.01.2012 19 Özgün Can Özgüneş
Presenter
Presentation Notes
This is the application of wire mesh. At wire mesh reinforcement; first wire mesh layer applied to surface, then shotcrete is applied.
Steel Fibre Synthetic Fibre
03.01.2012 20 Özgün Can Özgüneş
Presenter
Presentation Notes
Or, at fibre reinforcement, these fibres added to shotcrete mix and sprayed to surface inside shotcrete. Two types are availible; steel and synthetic. Steel ones are more expensive, but gives a little more strenght. Here you can see steel fibres inside shotcrete.
Wire Mesh Fibre
03.01.2012 21 Özgün Can Özgüneş
Presenter
Presentation Notes
Placing wire mesh to surface is time consuming, dangerous and costs more. Also shotcrete can’t completely fulfill voids behind wire mesh. But with fibres, those are not problems anymore.
Also called as Micro Silica
Additive material to cement
Increase compressive strenght to triple by
adding %13 silica fume to cement
Reduces rebound
03.01.2012 22 Özgün Can Özgüneş
Presenter
Presentation Notes
This is not actually a reinforcement, it is actually an additive.
