Cutting the Concrete

You have asked a question that no-one here can answer for you from the information provided.

The floor would have been constructed to provide a certain level of support for loads that will travel across it. The re-enforcement, thickness and grade of concrete used, level of compaction of the underfill material, and so on would all contribute to this strength and capability to supply the service.

Your site engineer/designer should be able to give you direct instruction as to what is expected. Especially so that the new material does not move (sink) under load

By the way, why do you need 300 wide? If this is only for control cable for limit switches a smaller trench should be adequate.

If you do install the cables, I suggest that you put them through a conduit (Large pipe) rather than just bury them. This means that if replacement is necessary you do not need to dig up the roadway again.

So, we will make it smaller. We are planning to put the steel pipe down there to run the cables. Since we don't have large pipe, we intent to use 02x3/4 inch steel pipe. One for motor, one for limit switches.

If you used to that. You can answer it. I am aksing for the simplest action about cutting and returning the concrete floor since I am not civil experts. Why you think it so complex?

Additional information, since this is the main gate area so the maximum load of lorries travels in and out should be <66,138pounds.

I don't know of any manufacturers' names, but I've heard of boring systems that can tunnel under the concrete. This would eliminate the concrete cutting, as well as any worries about disturbing whatever reinforcement.

Any Traffic Signal Contractor should be able to bore under the road to alleviate cutting the road. It is a simple solution. Just needs a push pit on the other side to receive the conduit.

It is much more expensive. No one will use such kind of technology to install two 3/4inch pipes. But, what is push pit?

just a hole to get to the end of the conduit.

You don't have to use a bore machine. I've seen contractors use a jack hammer horizontally many time to drive it. You need to use a different nose on the conduit though. You can't be as accurate as a bore machine but in 12m you should be fine. You also need to start a little deeper. If you do use this method you will need a push pit on the starting end as well since you won't be driving down but just horizontally.

good idea, but do you not have to excavate large holes at either end of the bit you want the pipes to run under to give you access??

Would it not be better NOT to have to dig at all??

Yes, you do have to dig pits on either end when using the jackhammer method.

Once you place cuts into the concrete you are just giving water someplace else to go, freeze and crack the pavement later on. How many times have you seen sawcuts after 5-10 years with no cracks coming off of them?

If there is an expansion joint across the way, then I'd cut parallet to that at the clearance for the pipes to fit, drop them in and backfill with good quality concrete.

If you do this at the expansion joint then there is already the discontinuity in the concrete and the narrow cut means the truck tyres and such are less likely to break it away.

It would be REALLY nice if the expansion joint was in the line of the gates, then a cover strip could be introduced with a W profile to guide the gates and disguise the cut in the concrete below.

Unfortunately, there are not any expansion joints there. To support the weight of the gate. People used the 02 steel rails embed into the concrete (the distance of these two rails would be 600mm). Every 1.5m along the rails, they used a steel bar to weld the 02 rails together.

I will cut the concrete along the center line (150mm) of these 02 rails. With this smaller width, the tunnel would not be impacted by lorries.

Sorry for my poor English. Hope that you don't feel annoyed.

oh, I forget, I need to cut for around about 12m. Is there any possibility of cracking after months of using after concrete (I mean a mix of water, cement, gravels, and sand...)?

When you cut the slab, examine what is there, rebar, thickness etc wise, and just duplicate it--It we are talking about 12" , then adding some re-bar inserts , to the existing slab, may be necessary-The existing slab has already been designed to specs, so just duplicate, with the appropriate tie ins--

when you cut the floor, use a concrete saw and angle your cuts so that you remove a wedge shaped section, with the widest section at the top, with say a 15 degree slope to the wedge. Lay your pipe and if the subsurface is wet enclose the finished pipe in 1.5" flexible plastic tubing to prevent the risk of a flooded conduit. Then, when you refill with the proper mix of concrete you should add a latex bonding additive as well as coat the walls of the wedge with it. That means the new cement will adhere well, and in addition, the wedge shape will prevent 'punch through' of the new section under a point load. No matter how much additive you use, the edge of the joint will never have the strength of the original and if the walls are parallel a fork lift truck might punch the filled spot down if it was not wedge shaped. With the wedge shape it is like a keystone in an arch, and concrete is very good in compression.

Good point. But I am thinking about why not use the plastic pipes only? Because the steel pipes will be rust when the rainy season come. Remember that I put them under the floor and I still don't really know how thick is this slab.

As I noticed, water always stagnates in this area after rain. Yes, I will try to narrow the cutting width and will use PVC pipes for this.

The issue considered as done. Thank you.

I suggest that you call in a contractor that has the ability and experience to complete this task, as I guess you are trying to do this yourself, or organise it.

As the trench you are planning to make (300mm X 300mm) is across a walkway or road way used by vehicles or people then as you are excavating so deep you will need to replace the removed rebar and tie the NEW rebar into the existing reinforcing for the remaining floor.

Not a small job!

However if you can re-route the pipework, maybe overhead (thinking out loud here) it MAY save you time and money.

Another way could be to lay the pipework on the surface and protect it with curved heavy gauge piping, or concrete over it... and by placing it in the gate, you have now made a speed bump!

I will make it much smaller enough to lay three pieces of 3/4inch pipe. Everything is decided and I will approve the method statement this week. Hope it would last for long.

Real simple THAT IS SO.

After you have installed all-- pour fresh Concrete and cure for 2 days at least.

mm

my suggestion is to chip the top surface of the concrete so that 1/3 rd portion of pipe is inside the slab (make sure that slab on either side of pipe also chipped for some extent for bonding of old and new concrete use bonding compound like neto bond and other precaution necessary for proper bonding ) and the pipe is place by providing reinforced fresh concrete on the top such that it acts as humps.along the length.chipping is done for bonding.