tech101

A cracked concrete driveway can take thousands of dollars off the value of your home & should be replaced and the costs in the South eastern Usa generally average about $7.55 per sq ft for a 6" thick concrete driveway over a compacted granular stabilized sand base with #3 rebar reinforcement @15" o.c.e.w. or #4 rebar @ 12" o.c.e.w. in the cities right of way (usually the first section of concrete driveway starting at the street) Concrete Removal will add an additional cost of $1.50 - $2.00 to have a dumptruck and bobcat with a hydra hammer attachment come out and lift the concrete out and haul it away (concrete removal rates can be as fast as 250 sq ft per hour!) Permits are usually only required in the City of houston when the Approach or the sidewalk on the cities right of way is to be replaced, permits are relatively a simple process and require a contractor to be bonded, have a copy of the platte plan with the transposed propsed driveway along with detailed concrete driveway specifications. The permit fees usually cost less than $100 in most parts of Metro Houston unless you hire a permit service obtain the permit on your behalf which usually costs between $350-$400 Remove your old concrete driveway and dig down 8" deeper and remove the top soil. Distribute 6" of crushed concrete, granite or gravel and machine pack the sub base to a minimum 95% compaction of uniform density and thickness. Once you;ve compacted your sub-base then distribute clean washed stabilizede sand a minimum 3" 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". Insert 18" dowels & use #5 rebar rods into the street @ 24" on center with epoxy -maintain an exposure of 9" or embeddment 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 insert 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 one that doesn'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 7 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 rebar 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