The following are suggested specifications for slipform curbing. Specifications were attained after interviewing DOT officials, contractors, slipform machine company representatives and engineers who have been working in similar climates to that of Maine in already proven areas.
Concrete for slipform curbing will meet the same requirements for concrete curb under 502.05. This includes a minimum compressive strength of 4000 psi.
Section 609.09-Method of Measurement
Concrete slipform curb will be measured by the meter or linear foot.
Section 609.10-Basis of Payment
Pay Item Pay Unit
Curb Type 6 meter [linear foot]
Concrete may be placed with an approved slipform machine that will produce a finished product according to the design specified in the plans and will meet the same standards set for cast-in-place curbing. For cold weather slipforming, the outside temperature must be at least 36°F (2.2°C) and rising. The curb shall be placed on a firm, uniform bearing surface, shall conform to the section profile specified in the plans and shall match the appropriate grade. Proper curing shall be insured through the use of a curing compound spray that meets ASTM specifications. Expansion joints will be provided at ends of curve radii or wherever the curb meets rigid structures such as building foundations or fire hydrants. Contraction joints will be placed at 10 foot (3 m) intervals using sawing methods, which cut 1-3″ into the concrete. Joints shall be constructed perpendicular to the subgrade and match other joints in roadways, sidewalks or other structures when applicable.
Same as Section 609.05 (b)
Slipform curbing must be adequately protected after placement. The concrete shall be allowed to cure for at least 72 hours. During cold weather conditions, when temperatures drop below the required temperature of 36°F (2.2°C) after placement, curbing shall be protected by concrete blankets or a combination of plastic sheeting and straw. After any placement of slipform curbing, regardless of weather conditions, the placed curbing shall be adequately protected by traffic control devices and flagging as necessary.