Click Here to download (PDF) the National Standards for Raising and Leveling Concrete, as developed by the Concrete Repair Association. These specifications have been adopted by numerous municipalities, county governments, and State Departments of Transportation throughout the United States.
Concrete Replacement Specifics (check locations for availability)
CRC Concrete Raising Corporation provides concrete removal and replacement services for concrete areas that cannot be repaired by way of concrete raising due to the concrete’s lack of structural integrity.
CRC will usually prescribe the following, unless the concrete is irregular in terms of thickness and/or design, or other specifications are required:
Mix Design: CRC uses a “straight” 6-bag mix design (3,000-to-4,000 psi rating) unless otherwise stated or specified. In comparison, some contractors utilize a “Modified” design that allows for a 5-bag mix and the use of fly ash or another supplement.
“Low-Chert Aggregate”: will slightly increase the cost of materials, CRC uses “Low-Chert” to minimize the potential for “Chert-pops” or “Pop-outs”. “Chert-pops” are created when porous aggregates (a physical property of chert, a silicate with sharp edges) hold moisture, which has a tendency to freeze and expand (especially in Wisconsin winters), creating enough pressure to literally “pop-out” of the concrete. “Low-Chert” is generally 95-to-88 percent chert-free and is available through CRC’s Ready-Mix suppliers.
Wire mesh: is used unless otherwise specified by the customer, as CRC prefers the ability of the mesh to reinforce the concrete. The wire mesh is placed in a grid pattern, and is designed to add tensile strength to the concrete. Although wire mesh does not prevent cracking, it does hold the concrete together to reduce/eliminate cracks from widening and assists in preventing the concrete from settling (trip hazards, ponding water, etc.)
Wire mesh is different from Fibermesh®, an additive that is used to reduce the amount of concrete cracking as a result of plastic shrinkage. Fibermesh® will increase the tensile strength of the concrete.
Additionally, CRC will commonly use steel reinforcement rods when placing (or replacing) concrete adjacent to building foundations and/or garage floors to reduce the likelihood of settlement and thus pitch at/near structural areas.
Suitable Base or Subgrade: Industry standards call for a two-to-four-inch (2-4”) minimum base of crushed rock or gravel at the location of concrete pour/placement. It is important that all organic materials are removed from the area prior to the placement of the rock/gravel and that the area be compacted properly to avoid future settlement and/or non-uniform support.
General Guidelines (Texture, Pitch, Control Joints): The Americans with Disabilities Act (ADA) Guidelines specify a surface texture and pitch to reduce slip-and-fall liability and hazardous walking environments. Most applications simply incorporate a broom-finish texture and a pitch of one-inch per four-feet (to facilitate proper water drainage).
Control Joints are strategically placed by contractors such as CRC to allow for natural expansion and contraction of the concrete. Placement of the control joints varies by location (i.e. driveway control joints will be further apart than service walk control joints). These joints are designed to create low-resistance areas for hidden cracking to occur. It is the objective of each contractor to have cracks take place at the control joints so that they are not readily seen when cracking occurs.
New concrete should be sealed after allowing for a standard cure time of fourteen to thirty (14-30) days to reduce the amount of water absorption. Water that penetrates and expands due to freezing damages concrete – that is, water expands approximately nine percent (9%) when it freezes, which produces enough force to break the concrete bonds and cause the concrete to “Flake”, “Pit”, “Spall”, and/or “Crack”. Not to mention the deteriorating effects moisture has on any metallic reinforcements used within the concrete for structural stability and strength. Sealing concrete, after it is clean and dry, will reduce the likelihood of water absorption, especially if a penetrating sealant (such as siloxane) is used.
Reducing the absorption will also lessen some of the damaging effects of deicing salts, which melt the ice/snow initially, but allow for refreezing of moisture when the temperature drops and the deicing salt is diluted.
Additional information, including but not limited to: actual concrete specifications, permits, costs, form placement and removal, re-landscaping (if needed), barricades, actual use of area, and warranties, will be provided by the CRC location providing the service of concrete replacement.
In need of assistance in developing specifications for a slab raising or “mud jacking” project?
