The construction should avoid rainstorm, high temperature and low temperature as much as possible. If the construction must be carried out, special measures must be taken.
1. Construction measures in rainstorm season
The general layout of the site shall take into account the drainage measures such as production and living temporary facilities, construction sites, and foundations; make preparations for drainage and flood prevention at the construction site, strengthen the management of drainage facilities, and often dredge drainage ditches to prevent blockages; during site planning and construction, overall consideration should be given to site drainage, and drainage ditches should be set up on both sides of the road; road maintenance should be done to ensure smooth transportation; strengthen the storage and storage of construction materials, set up drainage ditches around the warehouse and clear them, and configure sufficient rain-proof materials to meet the rain-proof requirements of construction materials and rain-proof construction in rainy days, and prevent items from being damaged by rain and water; equipped with a sufficient amount of drainage equipment to meet the drainage needs of the site, the reservoir area or the cable channel when necessary.
2. Construction measures in high temperature season
In the high temperature season, the concrete pouring temperature shall not be higher than 28 ℃. Reasonably layer and block, use thin layer pouring, and try to use low temperature period or night pouring; try to use low hydration heat cement, optimize the concrete mix ratio, mix high-quality composite admixtures, fly ash, etc., reduce the amount of cement per unit volume of concrete, and add an appropriate amount of expansion agent.
3. Winter construction measures
Earthworks. Construction of foundation earthworks should be avoided as far as possible in winter. If construction is required in winter, a detailed construction plan, reasonable construction plan and practical technical measures should be formulated, and at the same time, construction management should be organized to strive to complete the construction in a short time. The roads on the construction site should be kept clear, and necessary anti-skid measures (such as covering the road with straw bags) should be added to the transport vehicles and driving roads. When excavating the side of adjacent buildings, measures should be taken to protect the foundation soil of old buildings from freezing damage. During construction, try to dig and fill as quickly as possible to prevent the foundation from freezing. Drainage measures should be taken in the foundation pit groove to prevent the accumulation of water, resulting in the formation of landslides due to multiple freeze-thaw cycles in the lower part of the soil wall. Necessary thermal insulation measures should be taken at the bottom of the excavated foundation pit, such as retaining foot mud or laying straw bales. Before backfilling with earthwork, the ice, snow and thermal insulation materials at the bottom of the foundation pit should be cleaned up.
Reinforcement works. When the steel bar is cold drawn at negative temperature, the controlled stress method or the controlled cold drawing rate method can be used. For the cold drawing of hot-rolled steel bars that cannot be distinguished from batches, the method of controlling the cold drawing rate should not be adopted. When cold-drawing steel bars using controlled stress method under negative temperature conditions, since the elongation decreases with the decrease of temperature, if the control stress remains unchanged, the elongation will be insufficient, and the strength of the steel bar will not meet the design requirements, so the control stress of cold drawing at negative temperature should be higher than normal temperature. Cold-drawing control stress maximum cold-drawing rate: Welding of steel bars under negative temperature can adopt welding methods such as flash butt welding, arc welding (bar, lap, groove welding) and electroslag pressure welding. Welding steel bars should be arranged indoors as much as possible. If welding must be done outdoors, the ambient temperature should not be too low. In snowy weather, there should also be certain shielding measures, welding uncooled joints, and it is strictly forbidden to encounter ice and snow.
Concrete works. Portland cement or ordinary Portland cement should be used for concrete construction in winter. If necessary, antifreeze should be added (determined according to the temperature). In order to reduce freezing damage, the water consumption in the mixing ratio should be reduced to a minimum. The formwork and insulation layer should be removed after the concrete has cooled to 5℃. When the temperature difference between the concrete and the outside world is greater than 20℃, the surface of the concrete after the formwork has been removed should be temporarily covered to allow it to cool slowly. Uncooled concrete is highly brittle, so the structure must not be subjected to shock or dynamic loads before cooling.
Masonry works. The cement should be made of ordinary Portland cement, the grade is 325R, and the cement should not be damp and agglomerated. Ordinary bricks, hollow bricks, small concrete hollow blocks, and aerated concrete blocks should be cleaned of surface dirt, ice and snow before masonry. Bricks and blocks that have been frozen after being flooded should not be used. Lime paste and other measures should be taken to keep warm and antifreeze. If it is frozen, it should be thawed before it can be used. The sand should be medium sand, and the mud content should meet the requirements of the specification. The sand should not contain ice cubes and frozen blocks with a diameter greater than 1cm. The consistency of masonry mortar is different from that of normal temperature construction, and the consistency of mortar should be improved by preferentially using admixtures. Under the condition of negative temperature, the consistency of mortar can be 1~3cm larger than normal temperature, but not more than 12cm to ensure the adhesion between mortar and brick.
Decorative works. When the temperature is right, grab the exterior decoration first. After the minimum temperature is lower than 0 ℃, if it is necessary to decorate, the scaffold should be hung with double-layer straw curtains to block the wind, and the mortar should be mixed with water mixed with salt. When the temperature is 0~-3℃ (referring to the expected minimum temperature within three days), add 2% (by weight of water). The construction of the coating project in winter should be carried out under heating conditions, and the indoor temperature should be kept balanced and should not change suddenly. The indoor relative humidity is not more than 80% to prevent condensation. When brushing oil-based paint, the ambient temperature should not be lower than +5 ℃, and when brushing water-based paint, it should not be lower than +3℃, and the temperature should be controlled in combination with the temperature specified in the product manual.
Ground Engineering. For the indoor ground leveling layer, the door and window passage openings should be covered and insulated during surface layer construction to ensure that the construction is carried out under the condition that the indoor temperature is above 5 ℃. When the temperature of the outdoor part is expected to be around 0℃ for three days, the cement mortar should be mixed with 1%~2% salt water solution, and there should be reliable antifreeze and heat preservation measures.
Roofing works. The winter construction of the roofing project should be carried out in a windless and sunny weather, making full use of the sunshine conditions to increase the temperature of the surface layer, and a movable windshield device should be installed on the windward side. Before the construction of each layer of the roof, the snow, ice, snow and sundries on the base layer should be cleaned up, and the materials used should not contain ice and snow blocks.
Winter construction of steel structure works. During the construction of steel structures, in addition to compiling the construction organization design, the welders who have obtained qualified welding qualifications should also be trained in the welding process under negative temperature. After passing the examination, they can participate in the construction of steel structures under negative temperature. When welding electrodes and seams for structural welding at different negative temperatures, on the premise of satisfying the design strength, low-hydrogen electrodes with lower yield strength and better impact toughness should be selected., the important structure can use high toughness ultra-low hydrogen electrode.
Steel structure installation. Prepare the installation process flow chart; when the components are transported, the ice and snow on the transport box should be removed, and attention should be paid to non-slip pads; the appearance of the components should be checked and corrected; equipment used for installation and operation under negative temperature should be debugged before the equipment is used, and if necessary, it will be tested at low temperature and repaired in time if any problems are found. The lifting ring used for installation at negative temperature must be made of steel with good toughness to prevent brittle fracture at low temperature.
Completion acceptance information. Submit the following completion materials for the supervisor to carry out the completion acceptance of various concrete projects: the quality inspection and acceptance report of the concealed works and their parts of each concrete project building; defect repair and quality accident handling report of each concrete engineering building; other completion materials as instructed by the supervisor.
