Building a Concrete Driveway > Do it yourself > Driveway Specifications

Building a Concrete Driveway > Do it yourself > Driveway Specifications

If your in the market for a new driveway and you live in Houston,Texas or any part of South Texas then you
might want to catch up on the latest engineered specifications criteria for building a reinforced Concrete
Driveway designed specifically for our soil condition parameters in this region of the country.



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While your removing your old driveway, dig down 8" deeper and remove the black soil.
Distribute 6" of crushed concrete, granite or gravel and machine pack the sub base to a
minimum 90% compaction of uniform density and thickness.

Once you;ve compacted your sub-base then distribute clean washed sand a minimum 2"
deep. Mist the sand with water as you machine vibra-plate the sand to a minimum 95%
compaction of soil uniform density and thickness.

Set your forms up for your new driveway 12 ft apart for a single car
driveway and 24 ft apart if you want a two car driveway. The Concrete
needs to be 6" thick to meet national building codes requiring that all
steel reinforcement encased with concrete a minimum 3". (to prevent
hydrostatic expansion deterioration. Where the driveway meets the
street you'll need to make the radius a minimum 48". Incert 18" dowels
#5 rebar rods into the street @ 24" on center with epoxy -
maintain an exposure of 9"

Measure 10' ft back from the street and install an expansion joint as per city municipality
building codes. This section of concrete drive needs to have #4 steel Rebar rods spaced
12" apart each way forming a grid that is placed on 3" chairs. All dowels must be a min 9"
(preferably 12" overlap) Tie these grids into you drilled into the street, (3" below
elevation).

If your neighborhood has a sidewalk running through your driveway then you will need to
match the width (48" and incert you form for your sidewalk closest to your residence level
while the form closest to the street needs to have a 1/8" per ft fall.

Your curb and gutter needs to be formed up to continue across uninhibited. The depth
of the curb and gutter should be 12" deep by 16" wide with cont reinforcement.

At this point your ready to install your #3 steel rods in your driveway spaced 15" apart on
center each way and placed on 3" chairs to maintain the 3" encasement.

Now your ready to order concrete. Call a ready mix company (preferably Metro Concrete
if you live in Houston, they don't "cut" the Portland cement with fly ash like many of the
ready mix companies are beginning to do).

You'll need to order 1" gravel aggregate with 6 sacks of pure Portland per cubic yard
concrete with a maximum 4" slump. 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 structure, thus weakening it.

The maximum optimum temperature of the concrete 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

Now that you've optimized your concrete mix you are ready to pour the cement.
Screeding the cement off must be done with an .o24 min aluminum professional grade
concrete screed 2x4 and NOT a wood 2x4. (wooden 2x4 will flex and bow causing
undesirable surface variations). Plus we will laugh you off the job-site if we catch you!

Float the surface with magnesium floats and texture with a horse hair broom resulting in
a fine textured finish that will be slip free.

If a stamped concrete finish is desired then our SCI certified Stamped Concrete
Technicians should perform all texturing, stamping & concrete mix optimizations.

article written by D. Hunt

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