|Concrete is a construction material that consists of cement (commonly Portland cement) as well as
other cementitous materials such as fly ash and slag cement, aggregate (generally a coarse
aggregate such as gravel, river rock gravel, limestone or granite, plus a fine aggregate such as sand
or manufactured sand and water) and chemical admixtures. There are several types of cement, but for
residential use type "A" is generally used. The other types are for special purpose applications such
as "high early" cement used when a rapid cure MUST be effected for the concrete. And there are
many other types of cement used for special applications for the concrete.
Many people call concrete "cement." This is like calling a cake "flour." Cement to concrete is like
flour to cake. Flour is certainly a requisite ingredient and goes far in making the cake - cake; but flour
is only a part of the formula. Cement is the same way. It is a VITAL ingredient in concrete but it is only
a part of the entire composition of concrete. What is IMPORTANT to know is that cement is like the
"glue" that bonds everything else together. If you want strong concrete that does not crack (if control
joints are spaced correctly), then add more cement or increase the PSI (pounds per square inch of
compressive strength), of the concrete. For residential applications 3000 PSI is the norm.
Concrete solidifies and hardens after mixing and placement due to a chemical process known as
hydration. The water reacts with the cement, which bonds the other components together, eventually
creating a stone-like material. It is used to make pavements, architectural structures, foundations,
motorways/roads, overpasses, parking structures, brick/block walls and footings for gates, fences
and poles. Concrete is the NUMBER ONE material in the world used for building, roads, infastructure,
buildings, dams, and any type of construction requiring strength over time.
Concrete is used more than any other man-made material on the planet.. As of 2010 about eight
billion cubic meters of concrete are made each year, which equals one cubic meter for every person
on Earth. Concrete powers a $40 billion industry in the United States which employs more than two
million workers. More than 65,000 miles of freeways and highways in America are made of this
material not to mention that over 95% of buildings have some concrete in their design or structure.
Concrete is the number one material for foundations for both residential and commercial buildings,
structures, high-rises, bridge supports and anything requiring a solid foundation.
|KNOWLEDGE YOU SHOULD HAVE ABOUT REINFORCEMENT
|THINGS YOU SHOULD KNOW ABOUT CONCRETE
REINFORCEMENT AND CONTROL JOINTS
|GENERAL INFORMATION ABOUT CONCRETE
The vast majority of people in the greater Houston area believe that the amount of steel or rebar you put in the concrete has a direct
correlation to the strength of the concrete. They also believe that if you put a lot of rebar into the concrete it stops it from cracking.
NEITHER OF THESE STATEMENTS ARE TRUE!! THE NUMBER ONE CAUSE OF INDISCRIMINATE CRACKS IN CONCRETE IS
EITHER LACK OF; OR IMPROPERLY PLACED CONTROL JOINTS !!!! When placing a "slab on grade application" like a driveway or
patio, walk, etc. - the ultimate compressive strength of the concrete is based upon how solid the grade is upon which it is placed. IT
IS VERY IMPORTANT TO UNDERSTAND THE CORRELATION BETWEEN THE SUB-GRADE AND CONCRETE STRENGTH! Think
about putting concrete on jello as opposed to putting it on a solid base. That's why on commercial jobs as well as on freeways,
streets and any commercial roadway - the sub-grade is developed extensively PRIOR to placement of the concrete.
What reinforcement does ON A SLAB ON GRADE APPLICATION, is to prevent the expansion of a crack ONCE THE CRACK HAS
DEVELOPED!! This may sound strange, but nonetheless - it is true. One can put 1/2 inch rebar in the concrete or even 5/8 inch but
in the final analysis, the strength is based upon what the concrete is placed on as well as the ultimate strength of the concrete
initially. If the sub-grade is not solid, then one cannot expect the concrete to have a solid foundation and the concrete will mirror
whatever it is placed on. For example, if there is a problem with the sub-grade, expect to see problems with the concrete on top.
Many people experience this when they see the concrete "shift" or fall and or crack indiscriminately.
WWF or wire mesh, has 6 inch centers whereas steel reinforcement can be placed on 12, 14, 16, or 18 inch centers. 18 inch centers
is the most common application of rebar in slab on grade applications such as residential driveways, etc. In the final analysis, wire
mesh does a better job than steel rebar because the 6 inch spacing does a better job of stopping the crack from developing than the
12 to 18 inch spacing on the rebar. Steel reinforcement "does NOT" add to the compressive strength as much as is believed, but
becomes a trade-off against the prevention of crack expansion. That's why one sees so much steel placed in commercial work.
Steel is a requirement for all cities when placing driveway aprons. (the part of the drive from the street to the walk). In the final
analysis - you, the homeowner, dictate what we use for reinforcement. Our mantra is --- what is your peace of mind worth?
|WHAT ABOUT WOOD JOINTS????
Unfortunately 90% of the driveways in the greater Houston area have wood used for control joints. First we must learn the
definition of a control joint. A CONTROL JOINT MEANS THE CONTRACTOR CONTROLS WHERE THE CONCRETE WILL
CRACK - IT'S THAT SIMPLE, BUT ESSENTIAL TO GOOD CONCRETE WORK! Concrete cracks because it never completely
cures. Therefore it retains a water content for over 50 years. The water content causes the concrete to expand and contract
which ultimately causes it to crack. We know that a 4 inch slab with a mass over 120 square feet will crack REGARDLESS of
how much reinforcement is placed into it !! A control joint makes it crack along straight and even lines therefore maintaining
the cosmetic look of the concrete slab. Control joints also act as a conduit for water which is the biggest enemy of concrete.
IN THE HOUSTON AREA WOOD IS USED AS CONTROL JOINTS. ALTHOUGH CONCRETE SPECIALISTS WILL INSTALL
WOOD JOINTS PER THE OWNERS REQUEST - WE DO NOT RECOMMEND WOOD IN CONCRETE!! SINCE CONCRETE
RETAINS WATER FOR SUCH A LONG PERIOD AND IS EXTREMELY CAUSTIC; AND WOOD (EVEN TREATED WOOD) IS
SO POROUS, THE WOOD ROTS OUT QUICKLY AND THE HOMEOWNER IS LEFT WITH A 3/4 (THREE QUARTERS OF AN
INCH), INCH GAP BETWEEN HIS SLABS. WOOD AND CONCRETE ARE ENEMIES. CONCRETE ATTACKS ANYTHING ONE
PLACES INTO IT, THEREFORE WOOD IS AT A SEVERE DISADVANTAGE WHEN PLACED IN CONCRETE. WOOD AND
CONCRETE SHOULD NOT BE USED TOGETHER!!! THE ONLY WAY TO PLACE WOOD IN CONCRETE IS TO CREATE A
PLASTIC BARRIER IN SOME FASHION BETWEEN THE WOOD AND CONCRETE.
WE USE A JOINER AND/OR SAW-CUTTING TO ESTABLISH CONTROL JOINTS. THE JOINER DEPRESSES THE SLAB 3/4
TO 1 INCH AND PERFORMS THE SAME (IF NOT BETTER), FUNCTION AS THE WOOD JOINTS. MOREOVER, YOU STILL
HAVE 3 1/4 INCHES OF CONCRETE BELOW THE JOINT WHICH WILL NEVER ROT AND HELPS PREVENT GRASS FROM
GROWING BETWEEN THE JOINTS. THIS TYPE OF JOINT ALSO ACTS AS A CONDUIT FOR WATER. WHEN POSSIBLE
WATER SHOULD BE KEPT FROM GETTING BELOW THE CONCRETE SURFACE BECAUSE ONCE THE SUB-GRADE IS
COMPROMISED, THERE EXISTS NO SUPPORT FOR THE CONCRETE AND A CRACK OR SETTLING WILL OCCUR.
ONCE WATER GETS BENEATH YOUR CONCRETE MANY THINGS CAN HAPPEN --- ALL OF THEM BAD!!!
BELOW IS AN EXAMPLE OF CORRECTLY SPACED CONTROL JOINTS WITH A PICTURE FRAME BORDER ON THE
PATIO. THE CONTROL JOINTS ARE SAW-CUT SO ONE CAN BARELY SEE THEM, BUT THEY SERVE THE SAME
PURPOSE AS WOOD - ONLY BETTER. THE BLOCKED OUT AREA IS FOR THE INSTALLATION OF A COLUMN TO
SUPPORT THE OVERHANG WHEN THE OWNER ADDS THE PATIO CAP OVERHEAD.
CONTROL JOINTS ARE ESSENTIAL TO GOOD SLAB ON GRADE CONCRETE PLACEMENT!!
|THIS IS ALSO A GOOD EXAMPLE OF CORRECTLY SPACED CONTROL JOINTS. THESE JOINTS WERE
PLACED WITH A JOINER. THERE IS NO WOOD USED AND THE JOINTS SERVE A MUCH BETTER
USAGE BECAUSE THERE IS NO WOOD TO ROT OUT AND CREATE A "GAP" BETWEEN THE
CONCRETE SLABS. AGAIN - THERE IS NO WOOD IN THE CONCRETE DRIVEWAY PICTURED ABOVE.
Curing compound is merely a liquid agent that forms a film over the concrete to prevent the water from escaping too
rapidly. Think of it as a blanket over the concrete. There are many types, but the most common is a latex based water
soluble type because of the cost as well as the effectiveness. Other types are oil based but are prohibited in some states.
Curing compounds are rarely used in Houston, however they are useful in areas adjacent to salt water to prevent rapid
deterioration of the concrete during the initial hydration process. Use of a curing compound is essential in hot climates.
|ABOVE IS AN EXAMPLE OF CORRECTLY PLACED CONTROL JOINTS USING A JOINER.
THERE IS NO WOOD IN THE CONCRETE. A JOINER IS A TOLL THAT DEPRESSES THE
SLAB INTO A 'V' AND DOES THE SAME THING AS THE WOOD - ONLY BETTER!!
|Above is an example of saw-cut joints. We do it in decorative concrete because they do
not take away from the overall look of the decorative finish. You can barely see the joints
as opposed to wood joints which take away from the overall look of the finished product.