Interlocking concrete pavements (ICP) are flexible pavements. Flexible pavements are designed to spread loads imposed on a small area of the pavement surface through a base layer (or series of layers or sub-bases) to a large enough area of the soil sub-grade that the soil sub-grade can support the load without rutting.
A 1,000 lb. wheel with a footprint of 40 sq. in. exerts a load on the pavement surface of 3,600 lbs./sq. ft. With proper design and construction, a flexible pavement can expand the footprint to 8 sq. ft. on the soil sub-grade, thus reducing the load on the subgrade to only 125 lbs./sq. ft. In a flexible pavement, the pavement surface and base have the ability to move slightly or flex under load then recover when the load is removed. The unique aspect of interlocking concrete pavements is that the pavers interlock to help spread the imposed loads. There are three kinds of interlock: vertical, rotational and horizontal.
VERTICAL INTERLOCK
This is achieved by the shear transfer of loads to surrounding units through the sand joints. This shear transfer also prevents one paver from
in the moving vertically in relationship to its neighbour(s).
ROTATIONAL INTERLOCK
This is achieved through use of the proper paver thickness in relationship to load and use and by a perimeter edge restraint. A slight crown constructed into the pavement will increase rotational interlock and the load bearing capacity of the pavement.
HORIZONTAL INTERLOCK
This is achieved through the use of laying patterns that minimize the length of uninterrupted joint lines and disperse forces from braking, turning and accelerating vehicles. Certain geometrically interlocking paver shapes enhance horizontal interlock.
The components of an ICP are:
- Subgrade• Geotextile (if needed) • Sub-base (if needed) • Base • Bedding Sand • Edge Restraint
- InterlockingConcrete Pavers • Joint Sand
CONSTRUCTING THE ICP
UTILITY LOCATION
Before beginning any phase of the construction process, make sure that all underground utilities,services and structures have been located and clearly marked on the ground surface in all areas involved in the construction process including access lanes. In many areas, a single number such as Miss Utilities may be called.
Items to be located are:
- Electrical• Sanitary sewer • Gas • Septic tank • Water supply
- Telephone• Storm sewer • Cable TV • Drain field • Irrigation piping
SITE ACCESS
Before any demolition, delivery or construction equipment is allowed on site, make sure that there are no hazardous conditions such as overhead electric lines in the way. Plan all activities so that no damage will occur to existing pavements, structures, trees, shrubbery, gardens or other site amenities.
LAYOUT
Identify the area to be excavated and mark it on the ground with spray paint. Make sure the area to be excavated is at least 12 in. wider on all outside edges than the size of the pavement. Place grade stakes with string lines just outside the area to be excavated, making sure that the excavation is at least 12 in. wider than the edge of pavement. Mark the elevations on the stakes so that the depth of excavation can be checked as it progresses. Use nylon mason’s line and set it at the finished elevation of the pavement. Measure all excavations and base thickness from these lines. Set the initial elevations and check them at the beginning of each day with a builder’s level. The stakes can be moved at night by mischievous persons.
String lines set at final or finished elevations should be sloped. All lines (and final elevations of the pavement) should slope away from the house or building. The minimum recommended slope is 1.5 percent or a drop of 3/16 in. for every foot of pavement. Many pavements are sloped at 2 percent or 1/4 in. per every foot of pavement as this will better facilitate drainage. The maximum slope for comfortable walking is 7 degrees or about 12 percent. A builder’s level should be used to establish elevations using marks on stakes set around the area to be paved.
EXCAVATION/SUB-GRAD
- Base must be 12 in. wider than pavement on all sides.
- Useproper base material.
- Placeand compact base in layers.
- Fullycompact.
EDGE RESTRAINT
Edge restraints must be installed on that part of the pavement edge which is not restrained by an existing structure such as a building, concrete curb or concrete slab. Edge restraints are typically placed before installing the bedding sand and pavers. Some edge restraints can be installed after placement of the pavers and before compaction. Trowelled concrete edge restraint is installed after the pavers have been placed. Be sure that any area where bedding or joint sand can escape through or under the edge restraint is lined with a strip of Geotextile. Loss of sand will cause eventual settlement of the pavers. Back fill outside of edge restraint as soon as possible to prevent sand from escaping under the edge restraint.
SAND SETTING BED
Loose screed the washed concrete sand to an uniform thickness of 25 mm (1 in.) over the compacted base course. In no case should the sand be greater than 40 mm (1-1/2 in.) thick.
PAVERS
In most ICP projects, the pavers, regardless of paver shape, are laid in patterns where two sets of joints run perpendicular to each other. Radii or curves are cut into the pavement after the field pavers have been laid but not compacted. Straight joint lines not only make the finished pavement look clean and sharp but make installation much easier. If pavers shaped to geometrically interlock with each other are not laid in straight lines, they will not fit together. To keep joint lines straight, parallel string lines or chalk lines snapped on the sand setting bed should be used. The lines should be spaced five to ten feet apart with the spacing equal to the laying modulus of the paver shape being installed. This can be determined by laying a course of pavers in the proper pattern with 3mm ( 1/8 in.) joints and measuring the distance between at the desired line separation distance.
Procedure:
- Snapa string line on the screeded sand in the centre of the area(s) to be placed.
- Theline should be perpendicular to the laying face.
- Placepavers in the given laying pattern on both sides of the line.
If additional lines are snapped, they should be parallel to each other. Check this by measuring the distances at the opposite ends of each line. They should be equal.
- Ifthey are not parallel, they can be erased and snapped again.
Parallel string lines are also used to pave around openings in the pavement such as manholes or swimming pools.
Procedure:
- Pullperpendicular string or snap chalk lines on all four sides of the opening.
- Laypavers on one side, then the other.
Count the courses needed to surround the openings on each side. They should be equal in number on both sides.
- Thenfill around the remaining side of the opening.
- Cutpavers to fit and fill against the edge restraint around the opening.
CUTTING PAVERS
Pavers may be cut with any one of three basic pieces of equipment. They are:
- Mechanicalor guillotine splitter
- Masonrysaw
- Handheld cut-off saw
