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Is concrete corrosive to plastic?

Concrete can eat plastic but not all types of plastic. The alkaline content in concrete will gradually corrode most plastics so that this material disintegrates over a long period of time. There are other types of plastics like PVC and Polyethylene, that are not subject to the corrosive property of concrete.

gizmoplans.com - Can Concrete Eat Plastic? (How About PVC Pipe?) - Gizmo Plans

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I have always wondered whether the concrete can eat away the ubiquitous plastic material found in our concrete buildings and office complexes. I did some research on this subject and found some very interesting answers. Concrete can eat plastic but not all types of plastic. The alkaline content in concrete will gradually corrode most plastics so that this material disintegrates over a long period of time. There are other types of plastics like PVC and Polyethylene, that are not subject to the corrosive property of concrete. Today most of us will probably find life very difficult without the convenience that we are used to – a good, working, and durable plumbing system in our homes and offices. In this article, we will explore, in particular, the relationship between concrete and plastic, as well as how this affects our lives on a daily basis, from plumbing installation activity as well as the construction industry.

Concrete and Plastic – Above Ground

Does concrete corrode and eat plastic? Yes, the alkaline content in concrete will but it is very gradual and this corrosion process happens over a long period of time. There is a very strong co-existing relationship between these two materials. Understanding the relationship between concrete and plastic is crucial for plumbing activity, which in turn is an important part of the construction industry. Most people who spend their lives in the concrete jungles of our cities are surrounded by plastic material in their homes, offices, and malls. You see, we are not talking about the things made of plastic material that is used in homes or offices like plates, glasses, mugs, or tubs. The plastic we are referring to is mostly away from our sight, hidden in the concrete walls of your residential or office building. You will agree with me that there seems to be an inseparable relationship between these two materials. Alkaline chemicals in concrete like calcium hydroxide, sodium hydroxide, and potassium hydroxide can eat into plastic, though according to Bernard Erin, PVC is known to have excellent resistance to these chemicals. In the past, we see that metal pipes were prevalent in plumbing, but this been changing over the 20th and 21st centuries. These metal pipes were prone to quicker corrosion in a shorter lifespan. Also, metal being a good conductor of heat, the pipes made of metal caused the water too frequently freeze up resulting in people not having access to running water during much of the cold winter months. If you lived or worked in a building that was made with concrete you would not look forward to spending winter in your home or office. Homes and buildings have now been fitted with PVC plastic plumbing for a few decades. PVC is used in the manufacture of water pipes and numerous other products.

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It is believed that inserting a barrier between the concrete or concrete slab and the plastic piping during the building construction stage will prevent the concrete from eating away at the plastic piping or plumbing. This ensures the building is free of any leaks that may further develop.

Concrete and Plastic used in Construction

For heating systems at homes or offices, engineers in the construction industry use a plastic pipe called the barrier pipe. This type of pipe prevents an oxidizing agent from getting through it into the water system thus preventing or greatly reducing the possibility of corrosion. A type of material like resin, that is bonded between the inner and the outer layers of the pipe acts as a “barrier”. The pipe material is made from polyethylene or polybutylene. In the construction industry, it is true that the most vital of all activities is laying and constructing the foundation properly. A fairly exact science! If your foundation is right, then your building is good. The opposite situation is probably unimaginable under any circumstances. One trick that the engineers have been successfully using for a few years is the use of slip sheets. You will ask me now what the slip sheet is. Well, it is a sheet of polyethylene plastic, which is typically less than 0.5 inches though it comes in various sizes of thickness. The soil on which you lay the foundation of your building structure can expand and contract as per its water content which typically changes during the curing process of construction. This changing water content in the soil affects the concrete on the soil which ultimately results in cracks on future floor finishes like wood, vinyl, carpeting, and tile. These cracks are the direct consequence of concrete shrinking, as it becomes dry. Construction engineers avoid these cracks by using a process called post-tensioning that involves plastic slip sheets to avoid cracks.

The concrete is compressed in the post-tensioning process. This process helps in preventing any cracking and shrinking that may be caused by soil that expands and contracts by changing water content. How do the engineers post-tension a concrete slab foundation?

Well, in order to do this, they run steel strands in a grid pattern, like a square, through the concrete slab. Understand that plastic sheathing covers each strand of steel before they are run through the slab. This sheathing does two things. 1) it protects the steel from being eaten away by the concrete and

2) it allows the slab to move during the stressing operation

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Each of the steel strands has an anchorage on either end. Every strand, with its anchorage and sheathing, is called a tendon.

Process of post-tensioning:

Stress is applied on the tendons usually along one end; sometimes it can be both ends

The steel stretches, but the anchorage keeps it in place

The concrete is compressed

As a result of this process, the concrete is prevented from developing cracks. Now, let us see how the slip plastic slip sheets are used in this process of post-tensioning. The plastic sheets are either between the bearing surface and the slab or directly underneath the slab. Placed in this way, the sheets work to facilitate smooth movement of the slab, along the ground. The tendons will not have an even and flat surface along which to move without the slip sheets. The tendons must be able to move easily or smoothly along the ground, else the concrete will not be compressed or compacted enough to avoid cracks and shrinkage. The post-tensioning process will be a failure If the construction engineers or the builders fail to install the plastic slip sheets altogether or if they fail to install them correctly. Consequently, the concrete slab will not be compacted enough as it should be and will have a high probability of developing cracks in the future. In construction activity, especially around building a strong foundation, we have seen the importance of a type of plastic that is not “eaten” or corroded by concrete. The sheathing around each steel rod in the grid pattern acts as a barrier between the steel and the concrete and prevents the steel from being corroded.

The Takeaway from Concrete and Plastic

We have discussed two very important situations where concrete does not have the power to eat away at plastic. PVC plastic has plenty of uses in home and office plumbing situations, among others. Barrier pipes are very good at resisting or preventing corrosion by restricting air inflow into the water they carry. Polyethylene or polythene that has very important applications in the construction industry avoid future shrinkages and cracks in the foundations of building projects, wherever they are installed, correctly. Concrete does have strong alkaline chemicals that eat away or corrode plastics but, as we have seen, not all plastic materials are subject to this corrosive property. Interesting conclusion!