What are the curing requirements for structural concrete on highway works?

"(ii) (12/14) Accelerated curing. Elevated-temperature curing as described below may be used only for concrete made with Portland cement (CEM I) or sulfate-resisting Portland cements (CEM I-SR 0 or CEM I-SR 3). (a) The formwork may be generally heated to no more than 20°C prior to the placing of concrete. (b) Once placing is complete the concrete shall be left for 4 hours without additional heating. The concrete temperature can then be raised at a maximum rate of 10°C per ½hour. (c) The concrete temperature shall at no time exceed 70°C. (d) The rate of subsequent cooling shall not exceed the rate of heating. (e) Cubes shall be manufactured and cured under identical conditions to those to which the concrete is subjected. The use of accelerated curing methods for concrete containing other types of cement or any admixture shall not be used." [1] "6 (12/14) When concrete is placed at air temperatures below 2°C, the following requirements shall be met: (i) The aggregates and water used in the mix shall be free from snow, ice and frost. (ii) The surface temperature of the concrete at the time of placing shall be at least 5°C. Where the concrete is made using CEM I or a CEM II/A cement, the concrete temperature shall not be more than 30°C. Where the concrete is made using a CEM II/B or a CEM III cement, or equivalent combination, the concrete temperature shall not be more than 35°C. (iii) The surface temperature of the concrete shall be maintained at not less than 5°C until the concrete reaches a strength of 5 N/mm² as determined by tests on cubes that were cured under identical conditions to the structural concrete. (iv) Before placing concrete, the formwork, reinforcement, prestressing steel and any surface with which the fresh concrete will be in contact shall be free from snow, ice and frost. (v) Cement shall not be allowed to come into contact with water at a temperature greater than 60°C." [1] "There shall be no excess water on the top surface on completion of compaction. Slipforming shall be performed with appropriate equipment using methods to ensure that the requirements of this Specification are met." [2] "(12/14) Curing of Concrete 5 (i) (03/20) General. Curing Class 3 in accordance with Clause 8.5 of BS EN 13670 shall be used unless otherwise specified in contract specific Appendix 17/4. Additional special curing requirements may be given in contract specific Appendix 17/4. Immediately after compaction and thereafter for the duration of applied curing, except where elevated temperature curing is used, concrete shall be protected against harmful effects of weather, including rain, rapid temperature changes, frost, and from drying out. The method of curing shall provide a suitable environment for the concrete to mature and prevent loss of moisture harmful to the quality of the concrete." [2] "Where the Contractor proposes to use a curing liquid, compound or membrane on surfaces on which a waterproofing system is to be laid, it shall be completely removable. The Contractor shall keep records of all curing liquids, compounds and membranes and the areas of subsequent removal; such records shall be subsequently supplied to the Overseeing Organisation in accordance with the requirements of CG 302." [2]

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