Crack-Crete: The Big Lie

"Let's do concrete - it's cheaper and stronger!"

I hear this constantly. Concrete is, in the general public's eye, a sturdy product. If it's a sure thing, it's "Concrete Evidence". A concrete jungle is the hard and unforgiving cityscape. "Set In Stone" implies cementitious products, since concrete hardening is known as "Setting Up".

Concrete is ubiquitous with construction built to last. Overpasses, roads, driveways, aprons, curbs, patios, the list goes on. There's a massively disappointing fact which I, and every mason, builder, and contractor knows - We guarantee your concrete will crack.

Yes, that's right. It's a guarantee.

A good pour doesn't show it at first. Usually, the relief joints hide the first cracks as intended. As time wears on, slabs begin to look more fissured, until, in a long enough timeline, the slab is an uneven, hazardous mess. Concrete, the embodiment of all that is hard and durable, is brought to its knees by Father Time. Usually, people get 20-30 years out of a driveway or flatwork before the jackhammers, dump trucks, skid loaders, and mixers descend on the space once again.

Why does concrete crack?

Concrete cracks because it is extremely inflexible. Cementitious products (anything made with Portland Cement) have incredible compressive strength ratings. It's every other measure of strength in which concrete falls flat. Concrete is known to break when exposed to flexing, uneven loads or shock loads. This leaves a laundry list of reasons concrete cracks, one which could warrant its own blog article. But let it be known - concrete flatwork always cracks.

There's the rather innocuous and mostly annoying cracks, such as these, which are part and parcel of concrete being concrete. They're supposed to crack on the expansion joints, but tiny fractures may appear simply because the weather dried it too fast, or a little too much water was in the mix. These are kind of lame, but not really worrisome for longevity.

And there are the more egregious - those cracks which you could lose a coin or a key in, the ones which feel uneven underfoot, caused by base settlement, inadequate installation practices, or simply existing for a very long time.

How is cracking prevented, or at least, delayed?

Most contractors, or at least the good ones, spend most of their time prepping the area on any concrete job. Soil has a tendency to rise or settle depending on water holding capacity or organic material. A smart builder knows this, and will excavate all the soil containing organic matter from the proposed concrete site. Organic matter can decompose and create pockets, which allow concrete to settle and crack. This usually involves removing 4-12 inches of soil, depending on samples and jobs performed in similar areas. This area is compacted with heavy machinery until all the air and water pockets are worked out of it.

Next, the contractor will call a dump truck to deliver the base material - either baserock or engineered soil. Baserock and engineered soils are devoid of organics and made of rock fines and larger aggregates which lock together when compacted, and will not swell or shrink when exposed to water. The base is vibra-plated into place and smoothed until flat. Now the contractor can build his forms out of wood. Wooden forms are almost like a mold, and determine the shape and size of the concrete.

Next step - Reinforcement. Usually, rebar (steel rods lain in a grid) or wire mesh (grid of wire) are used to reinforce concrete. Rebar and mesh act like a skeleton; the backbone of concrete, and keep the concrete held together. However, poor quality rebar or poorly installed rebar can rust, swell, and break concrete, so proper rebar placement is quite important. After a strong, 4000PSI mix has been poured, screeded, floated, fresnoed, troweled, edged, and stripped of forms 24 hours after the pour, the work is over...for now.

"But I just installed my concrete, and I'm terrified it'll break up!"

Maintenance is key! Did you know concrete needs maintenance, just like your lawn, bushes, and garden beds? Concrete often begins cracking due to moisture. Believe it or not, concrete is very pourous. It contains big pockets and voids which fill with water and can break if they freeze or heat up too fast. To remedy this, smart homeowners choose to seal their concrete. It creates a film, which blocks out oils, waters, and grime. The finish looks incredible, but concrete must be re-sealed regularly to stay its strongest and prettiest.

"Wow, that sounds like a lot of long term costs. I'm going to have to break it up and replace it within my lifetime anyways. Is there a more long term option?"

I'm glad you asked, hypothetical customer. History time!

In certain parts of the world, up-front install costs are not nearly as important as longevity. In other parts, big equipment and nice tools simply aren't options. When the Romans built their roads, they didn't have concrete mixers, compactors, skid steers, paving machines, or jackhammers. They did, however, have lime, limestone, sandstone, and a series of limited hand tools and tamps. They slowly, meticulously, paved the roads the best way they knew how, using compacted rocky dirt and crushed-up lime as a base material, and the finest stones they could scrounge up for the surface. Say what you want about the irregular surface, but there's no denying these roads, with their extremely deep 1-2 foot subbase layer, stayed flat, firm, and usable for centuries! The romans knew their masonry.

Countries such as Denmark and Sweden are viewed as role models for virtually every developed/developing country in regards to social programs and healthcare. But we can look to them for paving advice too! Scandinavian architecture is deeply rooted in tradition, and the pedestrian walkways and driveways are no exception. Hundreds of years ago, the first square road cobbles were lain. They're still using those original road cobbles for a litany of flatwork purposes.

The granite planks are a new phenomenon. They look modern and dainty, but the roadbase below is hard as a rock and infinitely repairable. When a paver sinks or gets damaged, one man with a hammer, level, shovel, and wheelbarrow can simply go fix it without creating a mess or noise.

Concrete still has a place. This sidewalk in the city of Copenhagen is paved with inexpensive interlocking concrete pavers. Small pieces of concrete are less likely to crack than big ones. Note the curbing - it's not poured or edged. It's one-meter long pieces of precast masonry, ordered when needed and installed with small crews and simple tools. Since the concrete is not joined together, it can settle, expand, and contract without cracking. And if it does, simply pop the cracked one out and lightly hammer a fresh one in.

Take a look at a sidewalk repair site in China. The repairmen are likely having lunch in the big black truck, but notice the pedestrians still have access. Even with a full crew working full tilt, nobody has to worry about flying debris, ear damage, smoke, silica dust, or heavy equipment. It's simply workers with tamps, wheelbarrows, and shovels.

With great paving comes great opportunities - this neighborhood in China installed braille pavers, so the blind can always find their way.

Notice this paver pattern - large square granite pavers. Much harder and stronger than concrete. I'd reckon the base is at least 12 inches deep. Not a crack, low spot, high spot, or tripping hazard in sight.

And now, let's contrast this with America...

Both built, and maintained, by the lowest bidder. And it shows.

No simple repairs here! It's time to fix the pedestrian hazards by making a pedestrian hazard, only to re-do it every other decade.

The bottom line - pavers, while more expensive and time consuming to install at first, can last hundreds of years and cost less in the long run. Pavers are objectively cooler looking. What if, instead of a big slab of grey, your driveway looked like this one?

What if, instead of a cracked, sad mess, your walkway had this look for hundreds of years?

Of course, trees, accidents, leaks underground, or incorrect base material can, and will, make humps or sunken spots. But unlike concrete, even the most novice DIY'er could pull off a professional looking repair job in an afternoon - provided he or she owns a rubber mallet, a shovel, a bubble level, a hand tamper, and a wheelbarrow. In fact, go look in your garage now. See those tools? You're all set to fix your own driveway for free as long as you own a paver hardscape!

A professionally finished and reinforced concrete slab is tricky to install, and a paver driveway will run tens of thousands, and take even skilled pros weeks.Whether you choose concrete, or an alternative, we can help, from design and consulting, to maintenance, years after we lay the final brick.

707-755-0612.

If I don't respond, I'm probably on my excavator, digging a deep, strong base.