Concrete Subgrade Washout: Causes & Fixes
This past week, we looked at a bunch of other photographs from different angles showing the broken concrete paving at an area that isn’t really even used for vehicular traffic. It’s likely that this settlement happened within reason years as the concrete is not even actually very old.
You can tell that the deterioration of the surface of the concrete is not excessive to the point that the internal aggregate is significantly exposed. Generally when the internal aggregate is exposed to the point that you can easily visually discern it from the remainder of the sand and cement in the concrete mixture, the concrete has either been intentionally treated with a surface application intended on exposing the aggregate in the concrete or it has deteriorated with a significant amount of exposure to the elements over time.
When you get closer to the surface of the concrete, it’s apparent, the concrete isn’t actually that old, yet it’s destroyed. Last week, we looked at some of the potential causes for this type of significant collapse of a concrete slab and failure. One of the big issues here, the causes of this failure, is that there isn’t reinforcement in the slab.
This of course is not a primary cause, but it’s a secondary type of line of defense that would be normally found in most types of concrete slabs, yet it’s missing here. Essentially, builders use steel reinforcement. That steel reinforcing is often found in the form of a wire grid or mesh or in the form of deformed reinforcement bar.
Steel reinforcement provides resistance against differential settlement. Here, the root cause is actually related to a type of differential settlement or an overloading in a point load type position. Excessive point loads or defects or damage caused by a significant weight applied in a small area can lead to this type of breakage and deterioration.
When you look at the exposed raw edge of the slab, shown below, you can see, there is no steel reinforcement sticking out of the edge of that slab.
The combination of steel and concrete, used together, particularly with the steel in the middle of a slab such as the one shown below is a strong union. These two elements marry together very well. On its own, steel would be very expensive, to build large structural elements such as roadways and slabs. You couldn’t essentially build a road out of nothing but steel. However, in some cases steel would be very strong. Imagine, a long roadway of maybe a mile in length, built with just a 3-in thick steel plate.
While it would be strong, it would be extremely expensive, near impossible to move, and it would also have significant issues because of movement related to thermal expansion. Concrete, by comparison, doesn’t have those same types of challenges. Concrete can be installed in relatively small batches. Also, steel, like most metals, is a terrific conductor. It conducts energy, whether it be in the form of electricity or thermal energy. Those energies pass through steel very well.
Concrete, by comparison, is more like an insulator. This difference actually helps concrete perform better during typical daily temperature fluctuations. These fluctuations happen around us every day. Not every day is the same. Some days we’ll have high fluctuations and other very small amounts of fluctuation. For example, in the middle of the winter, the morning temperature might start out at 25°, but overnight low might be around the same temperature.
In the middle of the spring or summer, the morning temperature might start out around 40° F but get up to as high as 80 to your 90° F. That range of differences is significant. Using steel, particularly in a very large installation would not work effectively. Especially if it were a monolithic type installation.
Concrete naturally has an incredibly high compressive strength. That’s an inherent characteristic in concrete. Steell, by comparison, has extremely high tensile strength. Concrete generally lacks tensile strength and for this reason the two elements work very well together.
This is a pretty basic precept or understanding in most of construction, but here, for some reason, likely related to cost cutting, they didn’t install any steel reinforcement in the concrete. Of course, saving pennies, when it cost pounds, is a bad idea. It’s very unwise to cut corners, even when it seems to save a potentially large amount of money upfront if it will cost way more in the long run.
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We can help with a variety of historic masonry restoration needs and upkeep, from modest tuckpointing and or repointing to complicated and extensive historic masonry restoration. Infinity Design Solutions is a historic restoration specialist contractor specializing in both historic masonry restoration such as tuckpointing our repointing, and brick repair. If you have questions about the architectural details or facade of your historic building in Washington DC, reach out and say hello and if we can help we’ll be glad to assist you. You can email us or call us on the telephone at the following link: contact us here.