Homeowner Care of Concrete
Although concrete is one of the most durable construction products, it endures the harshest elements of our climate. Other wearing surfaces such as carpets and wood floors often have protective products applied (i.e. stain resistors and sealers) to extend their service life and durability while facilitating easier maintenance. To provide the same protection to your concrete driveway, it is recommended that it be treated with a protective sealer. By following the guidelines outlined in this brochure, your driveway will be durable and serviceable for many years to come.
Curing
Prior to applying a protective sealer, your driveway must be cured to attain the strength and durability potential of the concrete. Curing maintains the concrete at satisfactory moisture and temperature conditions to allow hydration to continue. Curing should commence following placement and extend a minimum of 7 days.
Any one of the following methods can be used:
* Spray on curing compound (according ASTM C309).
* Polyethylene cover.
* Seven day continuous water cure.
* Saturated burlap with polyethylene cover.
Of the methods mentioned, the spray on curing compound provides the most cost effective approach towards curing particularly during summer concrete construction.
Sealing
Once your driveway is cured and given an opportunity to air dry (approximately 1 month), it is now ready to be sealed. A protective sealer minimizes moisture and deicing salt penetration into the surface of the concrete. Concrete surfaces must be sealed when ambient temperatures are favorable and certainly before the onset of winter. Depending on the type of sealer, regular maintenance may be required. Contact you local ready mix producer for sealing products available in you area.
Care and Maintenance
Although concrete is an extremely durable product, the following care and maintenance guidelines will add to the value of your investment:
1. Do not apply deicing chemicals for snow and ice removal during the first winter. To provide traction, sand is recommended.
2. Never apply deicers containing ammonium sulphate or ammonium nitrate. These products may be packaged and sold as deicers, but aggressively attack and deteriorate concrete surfaces.
3. For stain removal, do not use harsh acids. Use a product specifically designed for the stain in question and for use on concrete.
4. Keep concrete clean of snow and ice at all times.
This information used by permission of the Michigan Concrete Association
www.miconcrete.org
Showing posts with label tips. Show all posts
Showing posts with label tips. 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
Concrete Parking Lot Construction Tips
Concrete Parking Area Construction
Suggested Specifications
General
Concrete parking lot pavements should be plain un-reinforced concrete built in accordance with the specifications.
Pavement Thickness
Slab depth for parking lots should be as shown on the plans.
Recommended parking area slab depths, based on use, are as follows:
* Light Use: 4" concrete - Parking for passenger cars, light trucks and occasional use by heavier trucks.
* Medium Use: 5" concrete - Driveways and parking areas for light to medium trucks plus occasional use by heavier trucks.
* Heavy Use: 6" or thicker concrete - Driveways and parking areas for heavier commercial and industrial trucks. (Pavements for heavy industrial trucks should be designed on an individual basis.)
Concrete Quality
In general, concrete should be mixed and delivered according to the requirements of ASTM C94, "Standard Specifications for Ready Mixed Concrete". Concrete specifications are as follows:
* Minimum compressive strength of 4000 psi at 28 days.
* Air content of 6½ ± 1½%
* Maximum five (5) inch slump. When mixes containing high range water reducers (superplasticizers) or combination of type A and type E admixtures (flowing concrete) are used, the slump as placed should not exceed eight (8) inches.
* Aggregates meeting ASTM C33 for severe exposure conditions.
Subgrade Preparation
The subgrade under all pavement should be brought to the required lines and grades and compacted to a uniform density. Any pockets of soft material that cannot be compacted should be removed and replaced with suitable material. Ready mixed concrete trucks and other equipment can operate on the prepared subgrade providing the subgrade is kept smooth and compacted prior to placing concrete. At the time of concrete placement, the subgrade should be in a moist, but not muddy condition. Adding granular sub-base material is not required. More information on subgrade preparation.
Concrete Placing, Finishing and Texturing
A uniform thickness of concrete (according to the design) should be placed on the prepared subgrade, adequately consolidated, and struck off to the proper elevation. All concrete should be placed continuously to prevent the formation of "cold joints". Wherever placement operations stop, a bulkhead will be installed to form a straight joint. Concrete should not be placed on a frozen subgrade. The sequence of finishing operations should be as follows: strike off and consolidation, floating (if necessary), edging, and texturing.
No finishing operations should be performed when there is excess moisture or bleed water on the surface. In general, adding water to the surface of the concrete to assist in finishing operations is not recommended.
Check the pavement surface with a ten foot straight edge.
A uniformly textured surface should be provided.
Curbs
Curbs should be constructed at the location shown on the plans. Curb and gutter can be constructed separately from the slab, or the curb may be cast integrally with the slab. The curbs should be textured to match the pavements.
Curing
Immediately after texturing, cover the surface with a white pigmented curing compound complying with ASTM Specification C309 (at the rate of one gallon per 200 square feet) or by 7-day coverage with white polyethylene or waterproof paper.
Mid-April to mid-September: Use a sprayed on curing compound applied according to the manufacturers recommendations. Mid-September to mid-April: Use waterproof covers and maintain curing for at least 7 days at temperatures above 40°F. If concrete sealers are to be used, allow a 30 day air drying period before applying the sealer.
Joints
The pavement should be jointed to control cracking. The joint lay out, compatible with the contractors paving method and equipment, must be submitted to the architect or engineer for approval prior to construction.
Longitudinal and transverse spacing should be at regular intervals. Individual spacing may vary slightly to meet catch basin and manhole castings. (The suggested transverse joint spacing is: 10 feet for 4" slabs, 12 feet for 5" slabs, and 15 feet for slabs 6". The suggested longitudinal joint spacing is 12 feet.)
Contraction joints may be made by sawing, tooling, or installing an approved insert to a minimum depth of 25% of the slab thickness. Sawed joints shall be cut as soon as possible without ravelling the concrete.
Joints should be continuous across the slab and must extend completely through the curb.
Install full depth expansion (isolation) joints, ½" thick, to isolate fixed objects abutting or within the paved area. These fixed objects include existing pavements, sidewalks, castings and structures.
Joints do not require sealing.
Opening to Traffic
Pavement under construction should be protected with barricades and all traffic (with the exception of joint sawing equipment) for seven (7) days.
Pavement Protection
The contractor is responsible for concrete placed during rain or cold weather and any concrete damaged by rain or low temperature should be removed and replaced at the contractor's expense.
When concrete is placed late in the year the contractor should submit a plan of his procedures for protection to the architect or engineer for approval prior to construction.
This information used by permission of the Michigan Concrete Association www.miconcrete.org
Suggested Specifications
General
Concrete parking lot pavements should be plain un-reinforced concrete built in accordance with the specifications.
Pavement Thickness
Slab depth for parking lots should be as shown on the plans.
Recommended parking area slab depths, based on use, are as follows:
* Light Use: 4" concrete - Parking for passenger cars, light trucks and occasional use by heavier trucks.
* Medium Use: 5" concrete - Driveways and parking areas for light to medium trucks plus occasional use by heavier trucks.
* Heavy Use: 6" or thicker concrete - Driveways and parking areas for heavier commercial and industrial trucks. (Pavements for heavy industrial trucks should be designed on an individual basis.)
Concrete Quality
In general, concrete should be mixed and delivered according to the requirements of ASTM C94, "Standard Specifications for Ready Mixed Concrete". Concrete specifications are as follows:
* Minimum compressive strength of 4000 psi at 28 days.
* Air content of 6½ ± 1½%
* Maximum five (5) inch slump. When mixes containing high range water reducers (superplasticizers) or combination of type A and type E admixtures (flowing concrete) are used, the slump as placed should not exceed eight (8) inches.
* Aggregates meeting ASTM C33 for severe exposure conditions.
Subgrade Preparation
The subgrade under all pavement should be brought to the required lines and grades and compacted to a uniform density. Any pockets of soft material that cannot be compacted should be removed and replaced with suitable material. Ready mixed concrete trucks and other equipment can operate on the prepared subgrade providing the subgrade is kept smooth and compacted prior to placing concrete. At the time of concrete placement, the subgrade should be in a moist, but not muddy condition. Adding granular sub-base material is not required. More information on subgrade preparation.
Concrete Placing, Finishing and Texturing
A uniform thickness of concrete (according to the design) should be placed on the prepared subgrade, adequately consolidated, and struck off to the proper elevation. All concrete should be placed continuously to prevent the formation of "cold joints". Wherever placement operations stop, a bulkhead will be installed to form a straight joint. Concrete should not be placed on a frozen subgrade. The sequence of finishing operations should be as follows: strike off and consolidation, floating (if necessary), edging, and texturing.
No finishing operations should be performed when there is excess moisture or bleed water on the surface. In general, adding water to the surface of the concrete to assist in finishing operations is not recommended.
Check the pavement surface with a ten foot straight edge.
A uniformly textured surface should be provided.
Curbs
Curbs should be constructed at the location shown on the plans. Curb and gutter can be constructed separately from the slab, or the curb may be cast integrally with the slab. The curbs should be textured to match the pavements.
Curing
Immediately after texturing, cover the surface with a white pigmented curing compound complying with ASTM Specification C309 (at the rate of one gallon per 200 square feet) or by 7-day coverage with white polyethylene or waterproof paper.
Mid-April to mid-September: Use a sprayed on curing compound applied according to the manufacturers recommendations. Mid-September to mid-April: Use waterproof covers and maintain curing for at least 7 days at temperatures above 40°F. If concrete sealers are to be used, allow a 30 day air drying period before applying the sealer.
Joints
The pavement should be jointed to control cracking. The joint lay out, compatible with the contractors paving method and equipment, must be submitted to the architect or engineer for approval prior to construction.
Longitudinal and transverse spacing should be at regular intervals. Individual spacing may vary slightly to meet catch basin and manhole castings. (The suggested transverse joint spacing is: 10 feet for 4" slabs, 12 feet for 5" slabs, and 15 feet for slabs 6". The suggested longitudinal joint spacing is 12 feet.)
Contraction joints may be made by sawing, tooling, or installing an approved insert to a minimum depth of 25% of the slab thickness. Sawed joints shall be cut as soon as possible without ravelling the concrete.
Joints should be continuous across the slab and must extend completely through the curb.
Install full depth expansion (isolation) joints, ½" thick, to isolate fixed objects abutting or within the paved area. These fixed objects include existing pavements, sidewalks, castings and structures.
Joints do not require sealing.
Opening to Traffic
Pavement under construction should be protected with barricades and all traffic (with the exception of joint sawing equipment) for seven (7) days.
Pavement Protection
The contractor is responsible for concrete placed during rain or cold weather and any concrete damaged by rain or low temperature should be removed and replaced at the contractor's expense.
When concrete is placed late in the year the contractor should submit a plan of his procedures for protection to the architect or engineer for approval prior to construction.
This information used by permission of the Michigan Concrete Association www.miconcrete.org
Subscribe to:
Posts (Atom)