520PERVIOUS CONCRETE PAVEMENT SYSTEM

520.1DESCRIPTION—This work is the construction of plant-mixed pervious concrete pavement on a prepared

surface designed to allow the infiltration of storm water into the subsoil. The pervious concrete surface layer is a horizontal plane that is permeable to water and air. The second layer of the storm water system is an open graded, angular stone layer used for temporary storm water detention.

520.2MATERIAL—

1.a For use in Concrete. AASHTO No. 8, Type A

1.b For use in Detention Basin. Either AASHTO No. 3 as the primary detention coarse aggregate topped with AASHTO No. 57 as a choker and leveling course; or AASHTO No. 57 only, as designed and specified.

2.a For use in Concrete. Fine Aggregate, Type A

2.b For use in Detention Basin. Fine Aggregate, Type A or Type B

Design the mixture to have a plastic unit weight between 115 pounds to 130 pounds and water cement ratio of 0.36 ± 0.04. Adjust the mix water, if necessary, during production if the mixture has a dull or dry appearance to produce a wet metallic sheen without causing the paste to flow from the aggregate. Additional mix water may be added at the project, if necessary, to achieve this condition provided the plastic unit weight is within 5 pounds per cubic foot of the target design unit weight. If reactive aggregates are used in the mixture, remediate for Alkali-Silica Reaction as specified in Section 704.1(g). Furnish the proposed mix design identifying all mixture components and weights or dosage amounts to the DME/DMM at least 3 weeks before the scheduled start of producing the mixture for the project. Include the target in-situ void content and 28-day unit weight values on the mix design form.

Representative at the start of the project. Do not begin production until receiving approval of the QC Plan.

curing period according to ACI 306.1.

added in 5F increments to provide time for placing and finishing the pervious concrete before initial set.

520.3CONSTRUCTION—

finishing operations to be used in production and construct at the project site on a prepared subgrade and base using the material and construction requirements used in production. Each section must have an area of at least 225 square feet. Perform infiltration on both test sections according to ASTM C1701. The average of both infiltration values must exceed 200 inches per hour. Submit the following information for each test section to the Representative:

• Test Section Thickness - Section 501.3(s). Thickness cannot be more than 1/4-inch less than the design thickness.

• Void Content - ASTM C1754. Void structure of 20% ± 5%

• Hardened Density - ASTM C1754 (The average hardened densities of the two test sections will be the hardened density used as the basis of acceptance for the remainder of the project with a tolerance of ± 5 pounds per cubic foot and not to exceed 130 pounds per cubic foot.

Test sections may, with approval, be incorporated into the project.

using either a form-riding paving machine, roller screed, vibrating screed, or an asphalt paver. The final surface finish may be applied with steel finishing equipment, or a motorized pan finisher provided the surface voids are not sealed.

not use pneumatic tire rollers.

subgrade to be left as permeable as possible. If erosion of subgrade has caused accumulation of fine materials or surface ponding or both, remove the accumulated material using light equipment and scarify the underlying soil to a minimum depth of 6 inches using a spring tooth rake or equivalent and a light tractor. Avoid driving concrete mixers or other equipment through the installation area. Correct and repair damaged or compacted areas to the satisfaction of the R epresentative. Notify the Representative upon completion of subgrade work for final inspection and acceptance before proceeding with basin and choker course installation.

bottom of the detention base with a minimum of 2 inches of fine aggregate to prevent soils from migrating into the storm water storage area. Wrap basin sides with a non-woven geotextile fabric. Install detention basin coarse aggregate in 8 inch maximum lifts. Compact the course as specified in Section 360.3. Install aggregates to grades as indicated. Place the specified depth(s) of coarse aggregate on top of the fine aggregate and roll as specified in Section 5 20.3(b)1. Remove temporary sediment control materials when the site is fully stabilized.

elevations. Apply form-release agent to all formed faces in contact with the concrete immediately before placement. Undamaged vertical faces of previously placed concrete may be used for subsequent placement.

minimum of 70 to 100 revolutions of the drum. Unless otherwise approved, place pervious concrete within 90 minutes after final introduction of any mix water.

concrete placements o the material is saturated but without standing water. Deposit the concrete either directly from the transporting equipment or by conveyor onto the subgrade. Do not place pervious concrete on frozen material. Deposit concrete between forms to an approximate uniform height. Spread the concrete using mechanized equipment or hand tools without segregation. Where trucks or buses may access the concrete, utilize a paver equipped with compaction tampers. For other areas, a roller screed or vibrating screed may be used.

roller to eliminate seams. Do not allow rollers to bridge previously placed and cured concrete for 7 days or before the Representative is satisfied the concrete has achieved sufficient strength to prevent damage. Steel troweling may be used provided the surface voids remain open and the average density requirement and permeability values are met.

with polyethylene sheeting. Thoroughly secure the curing sheet at all exterior edges and interior laps to prevent removal from wind. Maintain curing for a minimum of 7 days.

concrete immediately upon f inal finishing to approximately 1/4 slab thickness using a pervious concrete cross rolling tool or saw cut after the concrete has achieved sufficient compressive strength to prevent aggregate from being dislodged. If joints are saw cut, remove fines produced from the operation by vacuum to avoid clogging. If curing is interrupted, control the operations o the polyethylene sheeting and curing is reinstituted within 60 minutes of the initial removal.

any time during the 24-hour period following concrete placement or if rain is forecasted to occur before final finishing and curing. I f a rainfall event occurs, immediately stop production, form a construction joint , and apply the polyethylene sheeting. With approval , a construction joint may be saw cut before resuming placement. Pervious concrete subjected to rainfall will be evaluated after curing for loss of mortar at the surface and repaired or removed and replaced at the discretion of the Representative.

5,000 square feet according to PTM No. 1. Transport the cores to the LTS for testing, indicating the required concrete thickness, density, and void content from the test sections.

2.a Project core lengths tested by LTS will be considered acceptable if meeting the following:

• Average core length: 3/8-inch + 3/4-inch

• Length of any individual -1/2-inch

2.b Oven dry density. ASTM C1754

2.c Core void content. Acceptance will be ± 5% of the average voids in the cores of the accepted test section.

10,000 square feet of pervious concrete placed according to ASTM C1701. Remove and replace pervious concrete not meeting or exceeding a minimum average infiltration rate of 200 inches per hour. Document the average infiltration value from testing for use in future maintenance activities.

at least 7 days during which the ambient temperature has exceeded 55F during any time of the day.

520.4MEASUREMENT AND PAYMENT—Square Foot