What is better? - Pavers vs. Concrete

This is a question that I get all the time.

I'll start out with that I install both. Being certified by the ICPI (Interlocking Concrete Pavement Institute) and the NCMA (National Concrete Masonry Association) I feel that I can speek intelligently on this topic.

Just as most things - there are pluses and minuses to both.

And just as most things - poorly installed products will function poorly as well. 

     Pavers in the Unites States are only considered a paver if they meet requirements set forth by the ASTM (American Society of Testing and Materials).  Their web address is http://www.atsm.org/. The current Paver Classification is ASTM C936.

To be a paver it must have the following characteristics:

• An average compressive strength of 8,000 psi or greater

• An average absorption no more than 5%

• Resistance to at least 50 freeze-thaw cycles with average material loss not exceeding 1%

• Conformance to abrasion resistance tests

• A length to thickness ratio of no more that 4:1 (that's right a paver that has a side longer that 4 times it's height is no longer a paver - it's just a slab of concrete) 

• Unsightly pavers can be replaced (I once had a customer spill rusty water on some)

• They can be picked up to allow for a utility line or pipe to be repaired, and then placed back down and no one would ever know the difference

Concrete (this is true of many different types of concrete - stamped, textured, exposed aggragate etc...)

• Concrete is ordered by the contractor usually between 3500 - 4500 psi and a slump of between 3-7, I like 5 or 6 depending on the weather

• Cracking of concrete is a feature not a flaw

• Different batches of concrete may be different colors

• Unless you have samples taken (think large projects and state jobs) quality control is a mixed bag

• placing something as simple as a wire or pipe underneth can require expensive saw cutting and / or jack hammering

Now that you know a little about the two, lets talk about which is better when.

    Poured concrete is great at taking compression loads just not as great at taking tensile loads. For example concrete makes excellent footings for decks - in fact I would say the best. Poured concrete is also great for foundation walls. The walls will surely develop cracks but usually that is acceptable for a basement. And when it is not acceptable such as in a finished basement the walls are covered up anyway. 

    What it is not good at is being poured 4" thick and being driven on. It's not that you can't do it, it's just next to impossible to stop it from developing cracks. Have you ever heard of the saying - "Step on a crack - break your mothers' back". Try walking down a sidewalk and not seeing a crack. 

This is a picture of stamped concrete with a crack in it!

Now what are pavers good at and why?

Pavers are great at taking those loads. They do this because of the way that they interlock in 3 different ways.

1. Horizontal interlock - this is the pavers ability to resist side to side shifting movement, it is created by the pattern of the pavers allong with the tightness of that pattern and at the edges of the project edge restraints. They can be aluminium edge restraints specifically designed for this application set in place with 12" spikes. Edge restraints can also be the concrete foundation that the patio is up against, a curb etc.

2. Vertical interlock - this is the pavers ability to resist moving either up or down. Vertical interlock is primarily achieved by the tightness of the pattern and the quality of the preperation of the sub-base and base materials inder the pavers.

3. Rotational interlock - this is the pavers ability to resist rotating. We've all experienced stepping on a piece of flag stone only to have one side lift up. That is the flag stone rotating. Creating this type of interlock is achieved through the tightness of the pattern and the ratio of the paver height to length. That's why flagstone lifts, no rotational interlock.

Pavers are also good at being low maintanence - just a few cleanings a year with a blower will keep them looking great! And by the way properly installed pavers will not have weeds growing through them. Buy that's a whole blog atricle in itself.

Still don't believe how strong pavers are? Below is a Driveway that we built and drove a 70,000 pound truck on it just 2 days after construction. And we drove it right to edge.

Tri-axle dump truck loaded - 70,000 plus pounds