1 of 18  Construction of Giresun Wastewater Treatment Plant  Tender Dossier Volume 3 Employer’s Requirements  Section 06: Concrete and Steel Works  Concrete Placed in Water  Concrete shall not be placed under water without the written approval of the Engineer. The Contractor  shall submit his detailed proposals of the plant and method for underwater concreting.  The method of placing concrete under water shall be such as to keep as much as possible of the con- crete being placed out of direct contact with the water so as to avoid any rapid movement or agitation  of exposed surfaces. The work shall, where possible, be carried out in one operation. Where this is  impracticable, laitance, washed out aggregate or foreign matter which may have accumulated on the  previously placed concrete shall be completely removed prior to additional concrete being placed. This  concrete shall then be placed directly on the cleaned surface. Tremie pipes shall be smooth bored, wa- tertight and fitted with quick release joints and have an adequate cross-section for the size of aggregate  to be used. Bottom opening skips shall be straight sided, perfectly smooth and fitted with externally  operated bottom opening double doors and overlapping canvas flaps. Toggle bags shall be used only  for small pours and for depositing small discrete quantities of concrete. Bagged concrete shall not be  used for permanent work.  During and after concreting underwater, pumping or dewatering operations in the immediate vicinity  shall be suspended until the Engineer permits them to be continued.  The Contractor shall take great care during hot weather to prevent the cracking or crazing of concrete.  The Contractor shall arrange for concrete to be placed in the early morning or late evening as directed  by the Engineer.  Concreting in Hot Weather  The Contractor shall pay particular attention to the requirements specified herein for curing.  Formwork shall be shaded from direct exposure to the sun both prior to placing of the concrete and  during its setting. The Contractor shall take appropriate measures to ensure that reinforcement in the  section to be concreted is maintained at the lowest temperature practicable.  Cold weather is defined as the situation existing at the Works, where either or both of the following  conditions existing:  Concreting in Cold Weather  The temperatures of ambient air, concrete at various levels and intervals not exceeding 5 m and cool- ing water where applicable shall be measured by means of thermocouples and recorded Where necessary, the Contractor shall design, install and operate a cooling system by which cooling  water is pumped through a piping system in order to decrease the heat of hydration during concreting.  The proposal for such a cooling system shall be submitted to the Engineer for his approval well in ad- vance of the concreting operations.  Concrete at placing shall have a temperature of not more than 32°C. If necessary, the Contractor shall  cool the aggregates and mixing water by methods approved by the Engineer.  Under no circumstances may concrete be placed in contact with frozen ground or formwork, or in con- tact with ice, snow or frost on the ground or on formwork or reinforcement. Concrete shall not be  made with frozen materials.   The mean daily air temperature over three or more successive days has dropped below 5°C.   The air temperature at the time considered is below 2°C  6_Vol3_d4.3_Section 6 Concrete and steel works_en_GIR_rev6.docx 