A, concrete construction in winter:
1, selection of cement varieties:
According to the principle that portland cement and ordinary portland cement are preferred in winter construction, and the strength grade is not lower than 42.5, "Chaohu" brand 42.5 portland cement is selected.
2, concrete preparation and mixing:
(1) In winter, aggregates piled in the open air may contain ice, snow and frozen blocks. Before concrete mixing, the ice, snow and frozen blocks should be removed first.
(2) Strengthen the temperature control of mixing concrete materials, so that the outlet temperature of concrete mixture is not lower than 65438+/-00℃ to meet the needs of concrete mixing and synthesis temperature.
Before mixing, test the temperature of raw materials. When the temperature of raw materials can't meet the needs, first consider heating and stirring water with a boiler. Rinse the agitator with hot water before feeding. The feeding sequence is aggregate, water, stirring, and then adding cement. The stirring time is 50% longer than normal temperature.
3, concrete transportation and pouring:
(1) Due to the low temperature, the heat loss of concrete is large. In order to prevent the concrete from being affected by freezing damage after pouring and meet the requirement that the temperature of concrete entering the mold is not lower than 5℃, the transportation time should be shortened as much as possible. For the construction of small and medium-sized bridges and small structures that are far away, five concrete trucks should be used for transportation to ensure the continuous operation of concrete pouring and shorten the pouring time.
(2) Before concrete pouring, remove the snow, ice and dirt on the formwork and steel bar.
(3) When constructing joint concrete in winter, it should be heated before pouring new concrete, so that the joint surface temperature can reach above 5℃. Cover it with a double straw bag after watering.
(4) The temperature of prestressed concrete hole grouting should be above 5℃.
⑤ During the construction of cast-in-place pile concrete in winter, antifreeze and antifreeze shall not be mixed.
6. Avoid low temperature construction in concrete construction, and try not to pour concrete at night.
4, concrete curing:
(1) The poured concrete shall be cured by steam heating method, greenhouse method or heat storage method according to the actual situation.
(2) Small and medium-sized bridges and small structures after concrete pouring shall be maintained by heat storage method. After the concrete is solidified, cover the second layer of hay curtain first, then cover the surface with a layer of watercolor strip cloth, and support itself by the hydration heat generated by the concrete's own reaction, without sprinkling water for maintenance. At the same time, assign special personnel to observe the temperature, especially the parts that are easy to cool, and make records. If the measured temperature is lower than 10℃, the greenhouse method is adopted for health preservation.
(3) Cast-in-situ continuous box girder concrete is cast on the ramp bridge bracket of Maya Interchange. After the concrete is finally set, it shall be cured by steam method, and the curing shed shall be tightly insulated. The box girder from the rubber plate to the top plate is all wrapped with new colored strips to prevent the wind from blowing into the curing shed and prevent the concrete from shrinking and deforming due to the large temperature difference between inside and outside, and it is arranged in the inner box. Two warm pipes, and hold people on duty to check the temperature in the steam shed, so that the concrete temperature rises and falls evenly. During steam curing, the heating rate is 10- 15℃/h, the constant temperature is about 60℃, the maximum temperature does not exceed 80℃, and the cooling rate is 15-20℃/h until it is higher than the outside temperature10-20℃/h. When curing concrete, the corrugated pipe should be strictly protected, and it is forbidden to drop water and other sundries into the channel, and prevent the corrugated pipe from rusting. At the same time, assign a special person to be on duty 24 hours a day, observe the temperature on time, and record the temperature measurement in winter concrete construction.
Second, the masonry construction in winter:
L, winter construction, block should be kept clean, assign personnel to clear the blocks and ice cubes and frozen blocks in the sand in time. Blocks frozen after soaking cannot be used. The temperature of masonry mortar should be kept above 0℃, and the temperature difference between mortar and stone surface should not exceed 20℃.
2. Due to the large temperature difference before and after winter construction, the materials for mixing mortar should be heated first, and the highest temperature of water should not exceed 80℃ and the highest temperature of sand should not exceed 40℃, so the temperature of mixing mortar should not be lower than 20℃. Mortar should be used as it is mixed, and the mixing time is longer than that at room temperature 1 times. Masonry should be covered with film first, and then covered with two layers of grass curtain. When the temperature is below 5℃, it is not allowed to spray water for curing. At the same time, early strength agent can be added to concrete to accelerate the hardening speed of mortar and shorten the heat preservation time.
Third, strengthen the quality inspection of concrete and masonry engineering.
In winter concrete construction, in addition to strengthening the control of the construction process, we should also do a good job in protecting the finished products. In addition to the construction according to the specification requirements, the temperature and ambient temperature during concrete pouring should also be checked, and the following inspection work should be done specifically:
L, control the water consumption and heating temperature of concrete;
2, adopt the correct curing method, control the curing time, hold people check and record in the concrete engineering construction temperature inspection record;
3. The temperature of aggregate and water entering the mixer, and the temperature of concrete mixture when it is discharged from the machine and poured shall be checked 4 times per shift by special personnel, and recorded;
4. For concrete entities covered with thin film straw bags for health preservation, especially when the temperature is the lowest, check them four times day and night. For entities adopting steam heating for health preservation, check 1 time every hour when heating up and cooling down, 1 time every two hours when maintaining constant temperature, and check the indoor and outdoor ambient temperature four times day and night, and make records;
5, check the concrete temperature, should be carried out in accordance with the following provisions:
(1) The layout of temperature measuring holes shall be plotted and numbered.
(2) The thermometer should be isolated from the outside temperature and kept in the thermometer hole for not less than 3 minutes.
(3) The position of the thermometer hole should be set in a place where it is easy to cool down when the heat storage method is used for keeping in good health, and in a different position far away from the heat source when the steam method is used for keeping in good health.
(4) In winter concrete construction, in addition to standard curing specimens, specimens with the same number and structural conditions should also be prepared. For the concrete structure cured by steam heating method, in addition to making standards, specimens cured to 28d under the same conditions as the concrete structure should be made at the same time to test the strength of 28d after steam curing, and do a good job of concrete quality evaluation in winter construction.
During the winter construction of masonry, the following inspections should be paid attention to and recorded in the construction records.
(1) Assign special personnel to check the outdoor temperature, the temperature in the straw curtain and the temperature of mortar, and check it regularly day and night for 4 times every day.
(2) When the masonry is constructed in winter, the mortar strength should be tested on the specimens cured for 28d under standard curing conditions, and the number of specimen making groups should not be less than that of the specimens constructed at room temperature. For each masonry unit, the specimen should be cured at the same time with the masonry under the same conditions, so as to check the actual growth of mortar and make a good strength evaluation.
Four, actively get in touch with the local meteorological department, do a good job of meteorological observation, so that when the temperature drops, you can take preventive measures.