Concrete

Causes of Concrete Deterioration

Concrete has enjoyed a reputation as a “set it and forget it” building material since it became popular in the mid-twentieth century. However, concrete definitely is victim to plenty of external influences. Many of those influences can cause serious degradation. 

Builders today are realizing that existing concrete structures won’t last forever. Many buildings from the 20th century, and even some built in the last few decades, show significant damage. Let’s look at what these signs are, and the causes for concrete deterioration.

General signs of deterioration

Fortunately, concrete, as well as most paving work, wears its heart on its sleeve. It’s easy to see damage to concrete and find it. On the other hand, it’s rare for the damage to be totally hidden. So here’s what you should look for:

  • Cracking: This is the most common type of damage sustained by concrete. Fortunately, cracks are easily visible, and thus easy to treat once spotted. Be aware though, that hairline cracks can become massive over time, as they allow water inside. When that water expands and contracts, you get small cracks becoming bigger and radiating out more fractures.
  • Discoloration: A change in the color of the concrete is not a good sign. If the concrete is changing to a brown/reddish color, it means that there are other chemicals in it. Often the change in color is from corrosion from metals or exposure to other outside chemicals.
  • Erosion/Disintegration: These two (used interchangeably), are denoted by cracks and crumbling. They are often caused by the freeze thaw cycle, or heavy precipitation.

 

Specific signs of degradation

Sometimes very specific elements cause concrete to deteriorate. For example cracks can be caused by a huge variety of things, but the specific cracks that look like scales are caused by an alkali-silica reaction. Here is a list of specific types of damage often sustained by concrete. 

  • Spalling: Spalling is basically when the concrete flakes away. It can be unimportant or extremely serious. Spalling occurs when the concrete is installed poorly in the first place OR when it is under too much structural stress. 
  • Alkali-Silica reaction: This chemical reaction in the concrete causes a scale-like cracking pattern. The concrete swells outward and in doing so the surface cracks like the surface of a desert drying after the rain. Also called concrete cancer, it can read to serious degradation, and might even require demolition after being untreated for some time.
  • Delamination: Caused when the top surface of the concrete (the laminate) separates from the lower levels. It is found by tapping on the concrete, if a hollow sound is made, the concrete is delaminated.
  • Scaling: Scaling occurs when the mortar covering concrete begins to wear away. The mortar is an outside protective layer, so when it goes, the aggregate underneath the surface becomes exposed. 
  • Chemical diffusion: Also called chemical corrosion or penetration, this happens when a chemical is exposed to the concrete and works its way through the layers. This is a common occurrence with solvents and acids. Chemical diffusion causes cracks, divots, and pits. 

 

Causes of the degradation

Now that you know what to look for, let’s take a look at what causes the problems listed above. Looking through the specific causes of concrete degradation will help create some insights on how to avoid them.

Exposure to chemicals

Chemicals exposed to concrete can wreak all sorts of havoc. From erosion to chemical penetration, there are many threats posed by various chemicals to concrete. 

Some of the chemicals might come from routine maintenance:

  • Antifreeze agents put on pavement in the winter. These include liquid chemical compounds and salt.
  • Cleaning agents for concrete.

Many of the chemicals that damage concrete come from tangential outside sources.

  • Vehicles leaking oils/other fluids on pavement.
  • Concrete in industrial buildings becoming exposed to solvents or other agents used in manufacturing, agriculture, etc.
  • Paint or graffiti. 
  • Accidents and spills.
  • Natural solvents. Carbonic acid, acid rain, and other solvents from nature can seep into the ground and damage concrete. This is especially a threat to underground concrete (foundations). Concrete structures at the bases of hills and mountains may have similar exposure.
  • Degradation of the reinforcing steel. When the steel that supports concrete starts rusting or dissolving. 

Weather

Weather – most notably water is probably the number one destroyer of concrete. The freeze-thaw cycle erodes mountains over time. Concrete is not immune. When water freezes, it expands by 9%, according to a Cement.org study (look at page 4).  It’s not hard to imagine water getting into small cracks and freezing to break them open further. The problem is degenerative, once water is in your concrete, it can be impossible to get out.

The freeze thaw cycle also effects the ground. The ground sets differently in the warm months than when it is frozen. This setting can crack and break concrete foundations. Weather damage most often is in the form of cracking and potholes.

Structural stress

When the concrete begins to degrade, or the reinforcing steel begins to degrade, it can not take as much stress. This means that structural concrete may no longer be up to the job it was built for once the deterioration begins. 

Adding new levels to a building, placing heavy machinery, or building with heavy materials may induce too much stress on concrete, and cause serious damage. Stress can show up in many forms, spalling, scaling, and cracking.

Improper installation

Just about all of the problems and signs of bad concrete can be caused by one other thing as well: improper installation. If the concrete is mixed poorly, sets poorly, or installed poorly, a myriad of issues can arise. The rebar can dissolve, cracking can occur, delamination…the list goes on. 

Get your concrete installed right

If you want your asphalt paving, concrete, or cement inspected for issues, don’t hesitate to contact Reliable Paving. We are an experienced paving contractor who can check your concrete for damage, do repairs, and entire new installations. You want your concrete installation to be done right, the first time, so get a service that’s reliable.

Ancient Concrete and New Construction

In modern Italy, a unique question has only been answered in the last several years. Modern concrete constructions built at the seaside have degraded and crumbled after only a few years. The salty sea waves and ocean wind had destroyed creations of modern technology while ancient concrete has lasted thousands of years. Why do our modern buildings collapse while ancient concrete islands can withstand the elements for millennia? 

How the Romans did it

Ingredients

The ancient Romans started building concrete thousands of years ago. They used various ingredients, including some of which are hard to reproduce in modern labs. 

Opus caementicium, or concrete, was used commonly in ancient times. It was made in the same over all method that modern concrete is. It consists of an aggregate and a mortar. The aggregate was made from small rocks, pebbles, and hard pieces, just as it is now. The mortar functioned as the binding agent, keeping everything together as an extremely tough glue. However, a few different construction ingredients and methods keep ancient Roman constructions in good working order while our own fall apart. Opus caementicium used aggregate made from tuff. Tuff is a rock made from volcanic ash, ejected from vents during a volcano’s explosion. There are many types of tuff, but the tuff was not the most important ingredient.  

What really keeps the Roman buildings together is how the binder and aggregate interacts. Gypsum and quicklime were used, as well as pozzolana. Pozzolana is a volcanic ash that is resistant to sea salt – more so than modern concrete. The pozzolana was used in conjunction with the binders to create a cement that strengthened and became more resistant over time. 

Reactions with the outside world

Pozzolana and quicklime benefits from interacting with salt water over time. A rare crystal, tobermorite, formed over time as these three materials were exposed to one another. As seawater washed between the natural cracks in the concrete, it reacted with materials found in the volcanic rock. 

As the seawater flowed in the concrete, it would wash away the volcanic ash. It might seem that washing away part of the ingredients of the concrete would weaken the concrete, but it actually had the opposite effect. As the ash washed away, it allowed new formations. In particular, crystals could form and make interlocking “plates” that strengthen the concrete over time. Phillipsite, naturally found in volcanic rock, and seawater builds up a special type of tobermorite crystals. These crystals are called aluminous tobermorite crystals. Aluminous refers to the element aluminum. Aluminum is a light metal that is known for it’s low weight and tensile strength. These new crystals form over time, filling in tiny fissures and making the building stronger over time. 

Thanks to the unique reactions of the Roman concrete with seawater, it has the reputation of being the strongest, longest lasting concrete.

Other elements of construction also aided Roman buildings. The dome-shaped tops of many Roman buildings and their foundations aided longevity as well. The tops of many Roman structures were made of a less-dense, lighter weight concrete. The foundations were made of denser, harder, tougher concrete. The heavy foundations and light tops kept the buildings in place and stable. This type of construction is especially useful in the earthquake-prone Italian peninsula. 

What we can learn from ancient concrete

After reading the first half of this article, what we have to tell you now might seem like a surprise. Roman concrete has some amazing properties, but it is not actually better over all than modern concrete. There are quite a few reasons why this is true, and we will take a look at them. 

Benefits of Roman concrete

  • It gets stronger over time with reaction to sea water.
  • It is more natural, and has a lower environmental footprint.

Why it’s not quite as good as we think it may be

To most people, the idea of concrete that strengthens over time seems amazing. However, to any paving contractor or mineralogist, the idea of a concrete strengthening with crystals is pretty normal. Crystals form on all kinds of surfaces. The combination of materials that makes up cement makes the appearance of crystals pretty common. 

This article covers the following points, and some of the articles you might find about Roman seawall cement quite well.

There are a few other factors that really do effect how fast deterioration of modern cement occurs.

  • Roman cement did not have reinforcing steel. Rebar, or steel beams in the cement changes the chemical structure. Embedded steel actually corrodes the concrete when exposed to seawater. Modern cement has this steel, and thus is more inclined to degrade. Simply not using rebar extends the life of modern cement.
  • The southern Italian peninsula has a very temperate weather cycle. Unlike many other places where sea cement building might be compared, there is no freeze/thaw cycle. One of the main reasons for the breakdown of cement is water freezing in it’s small pores. 
  • Survivor bias is the idea that old things are better than new things. We believe this, because the old things that last are still there, and we don’t see the old things that no longer exist. This goes for buildings, societies, appliances, and vehicles. 

Looking for the best cement work?

Here at Reliable Paving, we follow the newest and most accurate data regarding cement and asphalt paving. Our over 35 years of experience and 200 plus person team means that no paving job is too big or difficult. We can make our paving ideal for the location and climate of your choice. If you have any questions, or would like a consultation about your paving job, don’t hesitate to contact us today.