10 Common Questions about Concrete in Edmonton

Whether building a house or pouring a driveway, here are quick questions that will help you better understand concrete.

What is concrete?
Concrete is a mixture of aggregates and paste. Sand, gravel or crushed stone make up the aggregates.  Portland cement and water act as the paste, which binds the aggregates together and makes them stronger.
Portland cement is a generic term for the binding agent in concrete made out of calcium, silicon, aluminum, iron and other ingredients.  It is dark in colour and gives concrete its characteristic gray colour.

Cement and concrete, are they the same thing?
Concrete and cement are not the same things. Cement is an ingredient in concrete that acts as a binding agent. Cement makes up about 15 percent of the concrete mix by volume.  A cement mixer is a term that is misused.  It should be a concrete mixer!

What does it mean to cure concrete?
Curing concrete is a necessary process that increases the strength and durability of the concrete.  Concrete hardens due to the chemical reaction between cement and water over time. The temperature of the concrete must stay within an acceptable range, and the concrete must remain hydrated.

Why does concrete crack?
Concrete Cracks due to a variety of reasons, but the most common is the volume of the concrete shrinks slightly when it dries out.  Concrete contractors put lines or joints in the concrete, so there is a nice strait predictable crack in the concrete. Other factors could be incorrectly mixed concrete mixture or extreme weather shifts.

Why can’t you pour concrete in the winter?
Concrete needs to cure at a temperature above freezing so that it can harden.  The chemical reaction that sets the concrete only works when the temperature is above freezing. With the climate in Alberta during the winter months, pouring concrete is impossible unless you heat the job site with a hoarding and heating area.

What decorative finishes can I add to my concrete?
Concrete Contractors can add colour by adding pigments before or after placing concrete when using white cement instead of gray cement. Colourful aggregates or chemical stains can also alter the colour of the concrete after it is placed.

Exposed aggregate is a popular finish in the newer Edmonton communities. It is when the paste is removed from the top layer of concrete, and the aggregate underneath is exposed.

Sandblasted concrete is smooth and looks like it was polished.

Stamped concrete can add a decorative pattern to the concrete in a variety of designs.

The most common finish, however, is slip-resistant broom overlay.  You will see this pattern on any sidewalk in the city.

What is “28 Day” strength?
When concrete hydrates, it hardens and gains strength. Hydration is a chemical reaction between the cement and the aggregate, which is very fast to begin but slows down over time. Concrete continues to harden over its lifespan, but the process slows down considerably after time. 28-day strength is a measure of the concretes strength after 28 days of curing.

What standards govern concrete quality?
Concrete quality in Canada is governed by the requirements outlined in the CSA A300 compendium of cement standards. The standards are set by the government and must be adhered to for engineering any building.

Why does concrete need to be placed quickly?
Concrete must be placed within 120 minutes of discharge under CSA standard 123 1-09.  The timeframe ensures the concrete is workable during that time, and the concrete can be placed effectively. It becomes more rigid, relatively fast, so time is of the essence!

What is concrete finishing?
Concrete finishing is what your concrete contractor does after the concrete gets placed to give the final appearance. It includes troweling, joints, brushing, colour, and appearance. It is a highly skilled process that makes or breaks the look of the concrete.

Contact Brett at Garden Concrete in Edmonton for any of your concrete needs!