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<br />002436 <br /> <br />Durango Pumoing Plant - Stage I <br /> <br />Use of combustion heaters will not be permitted during the first 24 hours of <br />curing unless unformed concrete surfaces are sealed from the resulting carbon <br />dioxide-rich environment. <br /> <br />8. Gradually discontinue the protection against cold temperatures such that the drop <br />in temperature of any portion of the concrete will not exceed: <br /> <br />a. Sections less than 36 inches: 5 degrees F per hour and 40 degrees F in 24 <br />hours for sections less than 36 inches <br /> <br />7. <br /> <br />I, <br /> <br />b. Section greater than 36 inches: 5 degrees F per hour and 20 degrees Fin <br />24 hours for sections greater than 36 inches. <br /> <br />9. When precipitation or freezing weather appears imminent, immediately make <br />ready at the placement site all materials which may be required for protection of <br />concrete. Do not place concrete until adequate provisions for protection against <br />weather, both during and following the placement, are made. <br /> <br />10. Keep concrete curing membranes intact, and other curing materials and processes <br />maintained as necessary to ensure continuous curing for the minimum specified <br />curing time. <br /> <br />G. Curing <br /> <br />I. Furnish all materials and perform all work required for curing concrete. Cure <br />concrete surfaces by the applicable method specified in tables 03300C - Formed <br />Surfaces and 03300D - Unformed surfaces. <br /> <br />2. Treat all concrete surfaces as specified to prevent loss of moisture from the <br />concrete until the required curing period has elapsed or until immediately prior to <br />placement of other concrete or backfill against those surfaces. <br /> <br />3. Allow only sufficient time to prepare construction joint surfaces and to bring them <br />to a surface-dry condition between discontinuance of curing and placement of <br />adjacent concrete. <br /> <br />4. As soon as unformed concrete surfaces have been finished, as specified, and have <br />attained a dull appearance free from bleed water and moist sheen, treat as <br />specified herein. <br /> <br />5. Remove forms within 24 hours after the concrete has hardened sufficiently to <br />prevent structural collapse or other damage by careful form removal. <br /> <br />6. Repair, where required, all minor surface imperfections irnmediately after form <br />removal in accordance with USBR M-47. <br /> <br />7. Complete minor surface repair within 2 hours after form removal and <br />immediately follow with the initiation of curing by the applicable method. <br /> <br />8. Keep concrete surfaces continuously moist after form removal until initiation of <br />cunng. <br /> <br />9. The Contracting Officer will test or require approved manufacturer's certification <br />of all curing compound prior to use. Acceptance under the clause entitled <br /> <br />Cast-in-Place Concrete <br />03300 - 32 <br />