Much Has Been Written About Concrete Failure…
When All is Said & Done, Its About Adding the Least Amount of Water & Not Over-Mixing
Have you ever had to deal with bad concrete – cracking, surface erosion to the point of where stones appear and come loose, severe dusting, loosening floor tiles, etc.? Were you ever told that failure was due to the sun, weather, water table, placed on too hot or cold of a day, etc.? Did the concrete installer ever admit to using an inferior batch of concrete and/or over-working the placed material?
Concrete was invented by the Romans in the second century B.C., and, for all intent, its still made the same way today by mixing cement powder, sand, stone, and water – and mixed for a short period of time. If the art of making concrete is virtually the same as in Roman times, why are there Roman concrete structures still standing after more than 2,000 years and many of todays concrete jobs fail soon after installation?
The process of concrete setting and hardening is called curing which is similar to a cake baking in an oven. The difference being that an oven is fueled by gas or electricity and concrete curing gets its heat from the chemical reaction between the cement powder and water.
Both, the cake and concrete mix, get transformed from a slush-mix to a firm state by the addition of heat for a length of time. The curing/baking time is set by nature which provides the guide for the baker or the concrete mason to follow. Severe failure can also be caused by too little heat (winter cold) or too much heat (direct hot sun).
The Romans would mix their concrete by hand, within a few foot steps from the placement site to ensure sufficient handling time (placement, leveling, troweling, etc.) without having to add more water. Once placed, the concrete was covered and left for weeks to cure to maximum strength.
After over 45 years of working with concrete, I feel that my take on the matter has merit.
Perils of adding too much water:
From the moment water is introduced to the dry mix, the wet cement powder generates heat. The Romans would add just enough water to ensure getting the maximum amount of heat from the cement powder. Because the Romans would place the concrete mix in a minimal amount of time, virtually all of the heat went to curing (baking) the concrete to its maximum strength. Today, as more water is added to prevent mix hardening, the heat gets diverted to warming the excessive amount of cold water – heat travels from hot to cold. Because the amount of fuel (cement powder) is not increased, less heat is left to cure the concrete. i.e. An under-baked cake or cookie.
Size of concrete voids:
If the concrete mix contains a maximum amount of dry material and a minimal amount of water, the space water filled when the mix was wet becomes a void when the concrete cures. The result: Less water begets smaller voids and stronger concrete. More water begets larger voids and less actual concrete. More water sets concrete up for curing deficiencies and failure risks.
The concrete professionals need to stop beating-around-the-bush as to why much of todays concrete fails to perform as well as the Romans product. The adage, “When you point one finger at someone or something, you are pointing three fingers at yourself”, fits this problem well. Todays concrete failure problems begin with mixing improprieties linked to the quest of getting a job done quicker, cheaper, and nothing beyond legal requirements. The quality of professional pride and accountability has mutated to verbal grandstanding deflecting the proverbial buck (pointing the finger) into the black hole of greed and irresponsibility.
To help prevent common concrete failures:
1. Dont start adding water to the dry mix until about 10 minutes before the mix is to be placed. And, add only a minimal amount of water.
2. Employ testing practices that are pragmatic and not just a tool for diverting the real blame.
3. Mix, place, and cure concrete with Roman precision.
Accountability fosters pride, craftsmanship, and triumph over unnecessary failure. Demand concrete excellence and you will always fare better.
If you wish to discuss a concrete problem, please feel free to contact me or a Gabriel Concrete Advisor.
Thank you for allowing me into your day.