Quality Driveway Construction
The following are recommendations for creating a quality driveway installation.
1. Planning and Preparation
* Concrete must be cast on a prepared subgrade that is uniform in soil composition and compaction.
* For drainage, the grade must be sloped a minimum of 1/8th inch per foot from all existing structures
* Stake formwork securely providing a minimum slab depth of 4 inches.
* Dampen the subgrade and formwork prior to placement (particularly during summer construction).
2. Mix Design Recommendations
The mix design recommended for driveway construction must meet the following requirements:
* Compressive strength: 4000 psi minimum @ 28 days (refer to local code requirements)
* Air Content: 6.5 +/- 1.5%
* Aggregates: coarse aggregates meeting MDOT 6AA (ASTM C33, 4S) classification
* Slump: 4 +/- 1 inch
3. Placing and Finishing Guidelines
To construct a durable wearing surface, the sequence for placing and finishing is as follows:
* Screeding or strike-off
* Floating, followed by a waiting period for the water sheen (bleed water) to dissipate
* Edging and jointing
* Brooming (to provide a non-slip surface)
* Do not finish the surface while bleed water is present.
* Do not 'bless" the surface with water to facilitate finishing.
* Do not steel trowel the surface…wood/magnesium floats are recommended.
* Steel trowelling can entrap bleedwater resulting in a non-durable surface
* Discharge from the mixer must be completed within 90 minutes of batching of concrete.
* Prolonged mixing or delayed placement will adversely affect the quality of the concrete with regards to air content and compressive strength.
* Control joints must be spaced at intervals not exceeding 10 feet with a minimum depth of cut equal to ¼ the slab thickness. A centerline control joint is required for driveways greater than 12 feet in width.
* Where new construction abuts existing structures (i.e. garage floors, brick veneer walls, fence posts, etc.) an isolation joint extending the full depth of the concrete slab is required.
4. Curing Requirements
* Following placement, the driveway must be cured to attain the strength and durability potential of the concrete.
* From mid-April to mid-September, cure the concrete incorporating one of the following methods:
* Apply a membrane curing compound according to the manufacturer's instructions.
* 7 day continuous water soaking
* Saturated burlap with polyethylene cover (secured in place)
* From mid-September to mid-April, employ a waterproof cover (i.e. insulating blankets) maintaining the curing temperature above 55°F for a minimum of 7 days.
* Cold weather concreting practices must be observed for concrete placed after November 1st.
5. Homeowner Care
* Do not drive on the 'new' concrete for at least 7 days.
* Do not allow water to drain beneath the slab ….. settlement cracks may develop.
* Do not allow snow and ice to accumulate the first winter ….. keep the driveway shoveled off.
* Do not apply deicing chemicals for snow and ice removal the first winter. As an alternative, sand can be used for traction.
* WARNING: Never use deicers containing ammonium sulfate or ammonium nitrate (i.e. fertilizers). Such products are known to aggressively attack concrete.
* Michigan is classified as a severe weathering region. Therefore, a sealer must be applied approximately 30 days following placement provided that the surface is dry and ambient temperatures are above 55°F.
* Contact your local Ready Mix producer (or building supply store) to purchase a concrete sealer.
* Follow the manufacturer's instructions for sealer application.
* Re-application of the sealer is generally required every 2 years.
This information used by permission of the Michigan Concrete Association
www.miconcrete.org
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Showing posts with label paw paw lawton. Show all posts
Friday, January 30, 2009
Cold Weather Concrete Tips
Cold Weather Concrete
Residential Concreting:"The COLD Facts"
With the arrival of fall and cooler temperatures, the placement of residential flatwork can continue, provided that the principles of "Cold Weather Concreting" are followed. By definition (ACI 306), cold weather conditions exist when "…for more than 3 consecutive days, the average daily temperature is less than 40°F AND the air temperature is not greater than 50°F for more than one-half of any 24 hr. period."
ACCELERATED EARLY STRENGTH GAIN
To overcome delayed strength and initial set development associated with cold weather conditions, one or a combination of the following mix adjustments are recommended:
* Substituting Type I with Type III cement
* Addition of calcium chloride admixtures
* Addition of non-chloride accelerators
* Increasing the Type I cement content by 100-200 lbs.
PLACEMENT GUIDELINES
* Do not place concrete on a frozen subgrade; upon thawing, uneven settlement and cracking are likely to occur.
* The minimum concrete temperature, as placed and maintained, must exceed 55°F. . . however, caution should be exercised with concrete temperatures above 75°F.
* Appropriate curing and cold weather protection must be incorporated to prevent the concrete from freezing.
CURING AND COLD WEATHER PROTECTION
To develop the strength, durability and permeability potential of the concrete, curing and protection during cold weather conditions are essential. The following guidelines are recommended upon placement:
* The curing period must extend a minimum of 7 days (maintaining the 55°F temperature).
* Do not seal freshly placed concrete. Sealing retains water in the concrete thereby keeping it saturated during freeze/thaw conditions.
* Cold weather protection is best provided through insulating blankets or loose straw (minimum 12 inches deep) sandwiched between a waterproof cover e.g. polyethylene.
MIX DESIGN RECOMMENDATIONS
A minimum specified compressive strength of 4000 psi at 28 days is required for exterior flatwork exposed to cyclic freezing and thawing. The slump, as placed, should not exceed 5 inches with the exception of those mixes incorporating mid or high range plasticizers. The recommended air content is 6.5 ±1.5%.
OWNER CARE - FIRST WINTER
* Deicing salts must not be applied…for traction, sand is recommended.
* Do not allow snow and ice to accumulate…this maintains the concrete in a saturated condition during freeze-thaw conditions.
This information used by permission of the Michigan Concrete Association www.miconcrete.org
Residential Concreting:"The COLD Facts"
With the arrival of fall and cooler temperatures, the placement of residential flatwork can continue, provided that the principles of "Cold Weather Concreting" are followed. By definition (ACI 306), cold weather conditions exist when "…for more than 3 consecutive days, the average daily temperature is less than 40°F AND the air temperature is not greater than 50°F for more than one-half of any 24 hr. period."
ACCELERATED EARLY STRENGTH GAIN
To overcome delayed strength and initial set development associated with cold weather conditions, one or a combination of the following mix adjustments are recommended:
* Substituting Type I with Type III cement
* Addition of calcium chloride admixtures
* Addition of non-chloride accelerators
* Increasing the Type I cement content by 100-200 lbs.
PLACEMENT GUIDELINES
* Do not place concrete on a frozen subgrade; upon thawing, uneven settlement and cracking are likely to occur.
* The minimum concrete temperature, as placed and maintained, must exceed 55°F. . . however, caution should be exercised with concrete temperatures above 75°F.
* Appropriate curing and cold weather protection must be incorporated to prevent the concrete from freezing.
CURING AND COLD WEATHER PROTECTION
To develop the strength, durability and permeability potential of the concrete, curing and protection during cold weather conditions are essential. The following guidelines are recommended upon placement:
* The curing period must extend a minimum of 7 days (maintaining the 55°F temperature).
* Do not seal freshly placed concrete. Sealing retains water in the concrete thereby keeping it saturated during freeze/thaw conditions.
* Cold weather protection is best provided through insulating blankets or loose straw (minimum 12 inches deep) sandwiched between a waterproof cover e.g. polyethylene.
MIX DESIGN RECOMMENDATIONS
A minimum specified compressive strength of 4000 psi at 28 days is required for exterior flatwork exposed to cyclic freezing and thawing. The slump, as placed, should not exceed 5 inches with the exception of those mixes incorporating mid or high range plasticizers. The recommended air content is 6.5 ±1.5%.
OWNER CARE - FIRST WINTER
* Deicing salts must not be applied…for traction, sand is recommended.
* Do not allow snow and ice to accumulate…this maintains the concrete in a saturated condition during freeze-thaw conditions.
This information used by permission of the Michigan Concrete Association www.miconcrete.org
Hot Weather Concrete Practices
SUCCESSFUL HOT WEATHER CONCRETING
Throughout summer, difficulties in mixing, placing and curing concrete often arise. High ambient/concrete temperatures, low relative humidity, and moderately high wind velocities contribute to rapid evaporation of moisture from the surface and accelerated set characteristics (hydration). By reviewing the guidelines presented in this bulletin, you will recognize and be prepared for hot weather conditions.
RECOGNIZING HOT WEATHER
The evaporation chart located below can determine when precautions need to be exercised during hot weather conditions. Any combination of air temperature, relative humidity, concrete temperature, and wind velocity that results in an evaporation rate exceeding 0.10 lbs/ft2/hr will increase the probability of plastic shrinkage crack development and related finishing concerns. Precautions to minimize the rate of surface evaporation are recommended at this point. When the evaporation rate exceeds 0.20 lbs/ft2/hr, the recommended precautions become mandatory.
PLASTIC SHRINKAGE CRACKING
Plastic shrinkage cracks are defined as a network of discontinuous cracks that appear on the surface of a freshly cast concrete slab during or shortly after finishing. The cracks typically form parallel to each other at intervals up to 3 feet apart, penetrating the surface to a depth of 1-2 inches. Plastic shrinkage cracks develop when the rate of evaporation exceeds the rate of bleedwater migration to the surface. During placement, concrete is unable to withstand the tensile force resulting from the rapid evaporation of surface moisture (and associated linear shrinkage) eventually leading to plastic shrinkage crack formation.
CURING
Immediately following placement, cure the concrete with one of the noted techniques: membrane curing compound application, continuous seven day soaking, wet burlap/polyethylene cover, curing paper.
RECOMMENDED CONSTRUCTION PRACTICES
To minimize the potential for plastic shrinkage crack development and related finishing concerns, the following recommendations are listed for planning your next hot-weather related construction project:
1. Prior to placement, dampen forms and subgrade materials.
2. Consult your ready mix supplier for hot weather mix design alternatives.
3. Schedule prompt transport, placement, and finishing of concrete. Whenever possible, schedule early morning placements.
4. Erect temporary windbreaks to reduce wind velocity over the concrete surface.
5. Erect temporary sunshades to reduce concrete surface temperatures.
6. To minimize surface evaporation, incorporate fog misting or evaporation retarders. Continue fog misting until curing is initiated. Evaporation retarders (usually polymers) can be spray applied following screeding with little or no affect on finishing or adhesion of membrane curing compounds.
7. Incorporate synthetic fibers (polypropylene) to resist shrinkage cracking.
Figure. 1 - Effect of concrete and air temperatures, relative humidity, and wind velocity on the rate of evaporation of surface moisture from concrete. This chart provides a graphic method of estimating the loss of surface moisture for various weather conditions. To use the chart follow the four steps outlined above. If the rate of evaporation approaches 0.2 lb/ft2/hr (1kg/m2/hr), precautions against plastic shrinkage cracking are necessary (Lerch 1957).
This information used by permission of the Michigan Concrete Association www.miconcrete.org
Throughout summer, difficulties in mixing, placing and curing concrete often arise. High ambient/concrete temperatures, low relative humidity, and moderately high wind velocities contribute to rapid evaporation of moisture from the surface and accelerated set characteristics (hydration). By reviewing the guidelines presented in this bulletin, you will recognize and be prepared for hot weather conditions.
RECOGNIZING HOT WEATHER
The evaporation chart located below can determine when precautions need to be exercised during hot weather conditions. Any combination of air temperature, relative humidity, concrete temperature, and wind velocity that results in an evaporation rate exceeding 0.10 lbs/ft2/hr will increase the probability of plastic shrinkage crack development and related finishing concerns. Precautions to minimize the rate of surface evaporation are recommended at this point. When the evaporation rate exceeds 0.20 lbs/ft2/hr, the recommended precautions become mandatory.
PLASTIC SHRINKAGE CRACKING
Plastic shrinkage cracks are defined as a network of discontinuous cracks that appear on the surface of a freshly cast concrete slab during or shortly after finishing. The cracks typically form parallel to each other at intervals up to 3 feet apart, penetrating the surface to a depth of 1-2 inches. Plastic shrinkage cracks develop when the rate of evaporation exceeds the rate of bleedwater migration to the surface. During placement, concrete is unable to withstand the tensile force resulting from the rapid evaporation of surface moisture (and associated linear shrinkage) eventually leading to plastic shrinkage crack formation.
CURING
Immediately following placement, cure the concrete with one of the noted techniques: membrane curing compound application, continuous seven day soaking, wet burlap/polyethylene cover, curing paper.
RECOMMENDED CONSTRUCTION PRACTICES
To minimize the potential for plastic shrinkage crack development and related finishing concerns, the following recommendations are listed for planning your next hot-weather related construction project:
1. Prior to placement, dampen forms and subgrade materials.
2. Consult your ready mix supplier for hot weather mix design alternatives.
3. Schedule prompt transport, placement, and finishing of concrete. Whenever possible, schedule early morning placements.
4. Erect temporary windbreaks to reduce wind velocity over the concrete surface.
5. Erect temporary sunshades to reduce concrete surface temperatures.
6. To minimize surface evaporation, incorporate fog misting or evaporation retarders. Continue fog misting until curing is initiated. Evaporation retarders (usually polymers) can be spray applied following screeding with little or no affect on finishing or adhesion of membrane curing compounds.
7. Incorporate synthetic fibers (polypropylene) to resist shrinkage cracking.
Figure. 1 - Effect of concrete and air temperatures, relative humidity, and wind velocity on the rate of evaporation of surface moisture from concrete. This chart provides a graphic method of estimating the loss of surface moisture for various weather conditions. To use the chart follow the four steps outlined above. If the rate of evaporation approaches 0.2 lb/ft2/hr (1kg/m2/hr), precautions against plastic shrinkage cracking are necessary (Lerch 1957).
This information used by permission of the Michigan Concrete Association www.miconcrete.org
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