1 of 18  Construction of Giresun Wastewater Treatment Plant  Tender Dossier Volume 3 Employer’s Requirements  Section 06: Concrete and Steel Works  Vibration shall not be applied directly or through the reinforcement to sections or layers of concrete  which have hardened to the degree that the concrete flows in the formwork over distances so great as  to cause segregation.  Every care shall be taken to see that reinforcement and fittings attached to the shuttering are not dis- turbed and that no damage is caused to concrete that has already set or to the internal face of the shut- tering by using immersion type vibrators. In areas of congested reinforcement, it may be necessary to  use small diameter pokers and the Contractor shall supply suitable sizes of pokers for each part of the  work. Vibration of concrete by hammering the shuttering with hand tools shall not be permitted.  When placing concrete against horizontal or inclined elements of waterstops, they shall be lifted and  the concrete placed and compacted to a level slightly higher than the underside of the waterstop before  releasing the waterstop to ensure complete compaction of the concrete around the waterstop.  The duration of vibration shall be limited to that required to produce satisfactory compaction without  causing segregation. Vibration shall not be continued after water or excess grout has appeared on the  surface.  Concrete shall not be disturbed after compaction and placing in its final position. Concrete that has  partially set before final placing shall not be used and shall be removed from the site.  Where concrete is to be placed against or on top of previously executed work, the surface of the old  concrete shall be thoroughly wire brushed, hacked and cleaned with water and air under pressure to  expose the surface of the aggregate and to remove all laitance.  Placing Concrete on Previously Executed Work  Special care shall be taken to ensure that the new concrete is thoroughly compacted and rammed  against the old.  Concrete shall be protected from damage by climatic conditions (direct sunlight, rain, snow or frost),  running water or mechanical damage during curing. All methods to be used for curing and protection  of freshly placed concrete shall be subject to the prior approval of the Engineer.  Protection and Curing of Concrete  The maximum and minimum ambient temperatures and humidity shall be measured and recorded each  day by the Contractor. The records shall be made available for the Engineer's inspection.  As finishing proceeds, all exposed surfaces shall be covered with a wet hessian sheet followed by a  reflective polythene sheet. These shall be securely fastened around the edges and supported in order  not to damage the finished concrete surface. As soon as practicable, the hessian and polythene shall be  lowered into close contact with the concrete and securely weighted or fastened down to prevent wind  blowing underneath. The hessian sheet shall be maintained in a moist condition at all times and shall  be inspected at intervals not exceeding 6 hours. Concrete shall be kept moist on exposed surfaces for a  period of not less than 10 days or as approved by the Engineer.  Alternative methods of protecting and curing concrete may be approved by the Engineer. In any case,  liquid curing membranes shall not be used on exposed surfaces or where laitance is to be removed and  aggregate exposed to provide satisfactory bond for placing further concrete or mortar screeds. Liquid  curing membranes shall not be used where mortar, resin mortar or joint sealant is to be applied.  Sufficient methods to afford full protection to a concrete pour shall be available at the place of work  prior to the commencement of concreting.  6_Vol3_d4.3_Section 6 Concrete and steel works_en_GIR_rev6.docx 