What
is the difference between cement and concrete?
Cement,
more correctly called 'Portland cement' is a grey powder that reacts
chemically with water. When cement is added to water, sand and stones this
mixture is called concrete and this hardens into a rock-like material.
oes concrete sometimes crack?
As
concrete hardens a small amount of shrinkage takes place. Cracks can
develop when this shrinkage is restrained: for example by concrete slabs
sticking to the ground or to adjacent walls. For more information on
cracking please refer to CIP 4 in the 'Concrete in Practice' series.
How
is cement made?
Limestone
is heated in a rotary kiln where it undergoes a chemical change and is
then finely ground into a powder. In most cement plants several other
natural ingredients are added to the limestone to adjust the chemistry,
the most common of these are marl, shale, iron ore and gypsum.
What
does 'curing' of concrete mean?
Concrete
continues to gain strength as long as it is maintained in a moist
condition and very cold temperatures are avoided. 'Curing' is the
maintaining of satisfactory temperature and moisture conditions for the
concrete. There are a number of alternative methods for curing concrete.
For more information on this topic please refer to CIP 11 in the 'Concrete
in Practice' series.
What
ingredients go into concrete?
The
main ingredients of concrete are cement, water, sand and coarse aggregate
(gravel or crushed stone). One or two chemicals are normally added at a
ready-mixed plant to improve the performance of the concrete. The most
common admixtures used are water-reducers that improve the strength and
air-entraining admixtures that make the concrete resistant to cycles of
freezing and thawing. For more information on admixtures please refer to
CIP 15 in the 'Concrete in Practice' series.
What
determines how strong concrete will become?
The
most important factor influencing the strength of concrete is the ratio of
water to cement in the mixture. The lower this ratio is, the stronger will
be the concrete. Therefore the easiest way to increase the strength of
concrete is to use more cement in the mixture; the easiest way to weaken
concrete is to add more water.
What
is 'air-entrained' concrete?
Air-entrained
concrete contains billions of microscopic air bubbles that enable the
concrete to resist the damaging effects of freezing and thawing. This is
achieved by the addition of an air-entraining admixture at the ready-mixed
plant. Air-entrained concrete should be used whenever concrete will
experience freezing so is essential for driveways, patios, footpaths and
roads in cold or temperate climates. Air-entrainment cannot be achieved
when mixing concrete by hand.
Can
it be too hot or too cold to place concrete?
When
concrete is placed in very hot and sunny conditions it tends to dry out.
When completely dry no further strength will be achieved. Similarly when
the temperature approaches freezing the hydration slows to a standstill.
Concrete can be placed under hot and cold conditions provided that
appropriate curing methods are used to protect the concrete from these
adverse effects.
What
kind of joints should be used in concrete paving (such as a driveway)?
The
most common joints used in concrete paving are called 'control joints'.
These are to accommodate the shrinkage that is normal in concrete.
'Isolation joints' may also be required to separate the paving from posts,
drains, or adjacent walls.
What
causes light and dark patches in some concrete?
Discoloration
is a lack of uniformity in the colour or tone of the concrete. There are a
number of different types of discoloration with different causes. The most
common type, known as 'trowel burn' results from placing and finishing
concrete after the hydration has started and the concrete is beginning to
set. For more information on this topic please refer to CIP 23 in the
'Concrete in Practice' series.
How
thick does a concrete driveway need to be?
Throughout
North America it is conventional to form residential driveways with
2"X4" lumber. This results in a pavement thickness of approximately
3.5 inches or 80mm. This thickness is adequate for cars, pick-ups and SUVs. If heavier commercial vehicles will use the driveway more frequently
then a greater thickness of concrete is needed. Next Level Concrete always pours to a depth of 4 inches with 30 MPA concrete in the Edmonton and Calgary area.
How
is the strength of concrete measured?
The
strength of concrete generally refers to its compressive strength. This is
measured by casting cylinders while the concrete is still plastic and
crushing them after 28 days. Most concrete has a specified 28 day strength
between 20 MPa (3000 psi) and 35 MPa (5000 psi). If cylinders are not made
cores can be drilled from the hardened concrete at any age and tested in
the same way.
Who
invented cement and when?
Cement
was used throughout the Roman Empire using limestone as its main
ingredient and volcanic ash when it was available. The cement used
throughout the world today is credited to Joseph Aspdin, a brickmason of
England who patented his process in 1824. He called this product 'Portland
cement' because the concrete produced resembles the natural stone quarried
at Portland, England.
What
is the tallest concrete building in the world?
The
tallest free-standing structure in the world is the CN Tower in Toronto,
Canada. This stands at 554 metres. However it is argued that the CN Tower is not really a building even though it has a restaurant and observation
tower. The tallest building in the world is currently the Taipai 101 tower in Taipei, Taiwan. Completed in 2004, this tower rises to 509
meters, and has 101 floors. Both the CN Tower and Taipei 101 were constructed in concrete.
How
can stains be removed from a concrete driveway?
The
most common stains affecting concrete driveways are oil stains, rust and
tire marks. Almost all stains can be removed from concrete and even the
most severe can be substantially improved.
Contact Us Today for a Free Estimate |
Because concrete is so versatile, preferred for durability, appearance,
low maintenance, and indicates quality construction from the first
glance. A concrete driveway does it all.
Concrete driveways have long been known to give trouble-free service
to homeowners. The reason is simple. Concrete is enduring…many driveways
last for 30 years and longer without major maintenance. Just as with many
high-quality purchases, concrete costs less in the long run.
The existing layer of concrete is broken out and dumped by a machine, usually a Bobcat, with a special bit.. The existing gravel base is reusable so you will save money as opposed to a new concrete driveway..
Surface bleed water must evaporate before proceeding with the final
finishing. Properly specified concrete should allow finishing operations
to begin almost immediately. A concrete broom is used for the final finish.
Before brooming, the surface should be stiff enough to retain marks or grooves
left by the bristles of the broom. A trowel finish is not recommended because
it could leave the surface slippery and unsafe. The rougher broom finish
improves traction. Snap chalk lines to indicate where joints go.
Joints
in concrete pavements control the location and spread of cracks. They can
be hand-tooled or saw cut, and should be made to a depth of no
less than 1 inch for a four inch thick slab. Joints should be spaced
no more than 10 feet apart for a 4 inch slab. Driveways that are wider,
12
feet or more, also require a joint down the center. Panels should
be as square as possible, but in no case, should the long side be more than
1½ times
longer than the shorter side. Jointing should begin as soon as
possible after the finishing operations. If jointing is to be done with
a hand groover,
proceed when the concrete sustains foot pressure with only a ¼ inch indentation.
If sawed, begin within 24 hours.