Building a Concrete Patio,Houston Patio,Concrete Patio,Pour Concrete,Concrete Patios,Paver,Sugarland

At   Affordable Concrete Contractors of Houston we build more than a
dozen Residential and Commercial stamped concrete patios and stamped
concrete driveways a month, countless square feet of Foundations, Parking
lots and sidewalks.

Over the years we've realized that the old adage' "They don't build 'em like
they used to" couldn't be more true about concrete Patios and Driveways.

About 90% of all the Driveways and Patios we tear out and replace have
wooden joints that rot and increase water intrusion potential, un-reinforced
concrete with about enough steel in the slab to make a nail or two and no
base, piers or compacted granular fill.

The staff here at www.ConcreteForever.com takes our hats off to all those
"They don't build 'em like they used to" concrete contractors because
without all of the shoddy concrete work done 20 years ago we wouldn't
have a job!

Twenty years from now however there isn't going to be a lot of Driveway and
Patio Replacements or Concrete Foundations to repair and you'll see why
after you read our Do it Yourself tutorial on "Building a Concrete Patio"

Sitework:
Establish a bench mark (elevation of slab) and fabricate batter boards at
the corners of the proposed concrete patio. The batter boards should be set
up with a builders level or transit and perimeter lines checked for a minimum
1/8" per ft fall for proper drainage. Install masonry string outlining the
perimeter of the outside edge of the proposed concrete patio.

Excavation:
Excavate approximately 8" below the desired elevation, removing the soil
from the area of the new patio inside the strings, You'll need to bring in 2" of
3/4" gravel and proportion the gravel to provide a average minimum
compacted compressive strength of a 80% compaction of uniform density
and thickness. Then, bring in 2" of a granular sub-base and machine
compact this sub-base to provide a minimum 95% compaction of uniform
density and thickness,to prevent potential sedimentary displacement and
minimizing thermal expansion variables.

Pre Soil Treatment:
After you've leveled off the granular base and reached your design
compaction parameters then you will need to treat the pre soil with
chlorpyrifos prior to installing a .006 mil vapor barrier.

Reinforcement:
Once this is in place then construct a "Central Grid Mat" using #4 steel
rebar every 12" -15" on center each way and "spin-tied" at each crossing.
Place the reinforcement grid on 3" rebar chairs. The rebar must not be any
closer to any surface (bottom, sides or top) more then 3" to alleviate
hydrostatic thermal expansion (ACI 318-02)

Optimizing the Correct Concrete Mix:
Ready mix concrete companies just bring out the concrete that you order
and they don't make any guarantees about anything. You are responsible for
the placing of the concrete and any cracks, settlement or discolorations are
the sole responsibility of the person that signs the delivery ticket.
For this reason it is important to hire an engineer or very experienced and
certified concrete contractor to engineer the concrete mix for your particular
application. In Houston Texas, depending on the humidity and barometric
pressure, the day of the pour we optimize the concrete mix with
variable proportions of tri-calcium silicate, hardeners and bi-calcium
silicates in terms of performance variables, air entraining admixtures and
fiber supplemental reinforcement. The most important property is the
compressive strength. Cement particle-size distribution to strength
development is a determining factor assuming that the depth of the hydrated
layer is independent of particle diameter to quantitatively predict the effects
of particle-size distribution on strength evolution, which is an important
factor influencing compressive strength, with phase compositions becoming
significant at later ages.

You'll need to order 5/8" gravel aggregate with 6 sacks of pure Portland
per cubic yard concrete with a maximum 4" slump. Be sure that no more
than 10% fly ash is present in the mix. Once the concrete arrives on site you
will need to measure the concrete temperature. It is well known that the
chemical reaction of cement with water is exothermic and liberates a
considerable quantity of heat during the curing period. When cement,
water, stone and sand are mixed together, a chemical reaction starts. This
is between the cement paste and water. In this curing process, the volume
of the slab, and the inner pressure/strain exerted on the rebars will change
in a fashion that depends on the composition of the concrete mixture.

The curing process is affected by the water to cement ratio, the curing
temperature, humidity and the type of cement. Hydration is responsible for
the hardening (strength) of the concrete. For concrete, the gain in strength
continues for a long time, and theoretically for an indefinite period of time.
However, the strength of the concrete reaches a peak within 7days. During
this process something else happens. Water in the concrete mixture will
evaporate, resulting in a decrease in the volume of the concrete. The
volume of concrete also decreases due to re-arrangement of finer particles
within the larger ones. The different proportions of cement, water, air
entrainements, admixtures and sand will bring about different temperatures,
pressure and strain variations within the concrete slab as well. The result of
the volume change is strain, also known as shrinkage strain, and this is
responsible for some small cracks that may appear after the curing process
of an improperly optimized concrete mix, also aggrevating the thermal
stresses induced during the curing process may cause cracks within the
slab, thus weakening it.

The maximum optimum temperature of the concrete for this particular
application cannot exceed 40.2 °C. The temperature change measured
within the concrete follows the same trend as the ambient air and surface
temperatures surrounding the slab but with a larger change in the initial
stage and tailing off to the ambient temperature with increasing time. Adjust
air entrainment and tri-calcium silicate admixture proportions according to
the absorption component properties criteria.

The barometric pressure variables and humidity criteria need to be
calibrated into the optimization performance variables table (provided by a
www.concreteforever.com on site project manager) prior to the pour by a
qualified engineer or by a one of the qualified Concreteforever.com
technicians, as this will determine the performance criteria and the optimum
amounts of air entrainment and bi-calcium silicates admixtures required to
optimize the mix according to these variables

Pouring the Concrete:
Fill the forms with the concrete making sure the steel reinforcement grid
stays centrally mobilized, Use an electric concrete vibrator to alleviate
potential voids around the steel grid and against the outer perimeter forms.
Screed the surface of the concrete with an aluminum 2"x4" beam that is
hollow, ( NEVER use a wooden 2x4 as it will flex and unevenly distribute the
concrete leaving an undesirable, untrue and "puddling" surface.

Floating the Concrete:
Once the concrete has been successfully screeded then, tamping the entire
surface with a "jitterbug" or "aggregate seeder" pushing the aggregate
approx 5/8" below the surface, thus optimizing the hydrating layer and
forcing the liquid cementious properties of the concrete mix to the surface
creating an optimum "top-coat". Then, using a minimum 48" magnesium
bullfloat, apportion the concrete evenly with the bull-float while another
simultaneously edges the concrete with an edger with a min 1/2" crown. As
the concrete hydrates the water is lost from the paste by evaporation or
absorption by aggregate, formwork, or subgrade which will further reduce
the reaction. If the internal relative humidity drops below 80%, hydration and
strength gain will stop. The rate of strength gained is directly related to the
amount of moist curing. The Maturity of the hydrating concrete mix is an
essential function of its temperature. Concretes of the same mix at the
same maturity have approximately the same strength, irrespective of the
actual temperatures experienced. A maturity meter is required to evaluate
the changes in temperature generated in the hydrating concrete, then apply
a mathematical formula to the measurements to calculate maturity.
Numerous mathematical formulas have been proposed for calculating
maturity, minimizing thermal stresses induced by the cooling of warm
concrete to cooler temperatures & the atmospheric pressure utilized to
increase the rate of strength development of the hydrating concrete. An
optimum temperature may range from 37.6 degrees celsius to 41.9
degrees celsius and is a compromise of strength gain and ultimate strength.
Now that the optimum temperature has matured the surface is ready to be
floated with either steel trowels, broom, lithochrome colors or stamped to
the desired texture.

article written by D. Hunt

"If you made it way down here then you must be spinning by now from all
the specs.....give us a call and we'll install your upcoming exotic perfect
concrete patio at an affordable price!"

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