Summer has the characteristics of high temperature, precipitation, precipitation, dry fast. Therefore, the summer concrete project construction is divided into: from raw materials into the factory, mix ratio design and control, concrete factory control, concrete construction control and other stages, is a system engineering. Concrete in the delivery and use process is affected by various factors, easy to appear fast condensation, dry shrinkage and other adverse conditions, if the construction, maintenance process does not take effective measures, may cause quality problems.
1.Concrete raw materials into the plant control
The quality control of raw materials in summer construction focuses on the use temperature of cement, the performance of admixtures and the control of mud content of sand and stone. Under normal circumstances, the storage temperature of cement is 40 ~ 60 ° C, and the temperature in summer is above 25 ° C. Under such a temperature, the cooling speed of cement becomes slower, and the problem of false coagulation of concrete or slump loss of concrete is easy to occur during the use of hot cement. Therefore, increasing the inventory of cement will relatively extend the cooling time of cement, so as to ensure the stability of cement performance and the stability of concrete performance. In addition, the characteristics of high temperature in summer easily lead to a large slump loss of concrete, the conventional reason for this situation is that the mud content of sand and stone is large, resulting in the adsorption of water and admixtures; Second, the plastic retaining ability of concrete admixture is poor; The third is to catch up with the construction period in the process of engineering construction, in order to chase the short setting time of concrete, resulting in insufficient admixture retarding components.
The above situation should be paid more attention in the process of mass concrete construction, and a series of concrete cooling measures should be carried out if necessary, which is not described here.
2.Mix ratio design and control
Summer concrete mix design, according to the performance of raw materials, considering the high temperature in summer caused by the characteristics of fast hydration of cementitious materials, make full use of this performance, adjust the proportion of cementitious materials in the concrete mix ratio, moderate increase the amount of additives, so as to control the hydration speed of concrete (hydration heat calculation), It can also achieve the effect of increasing the durability of concrete, and the production cost of concrete will be reduced, and the construction performance of concrete will be improved. In addition, effective measures and means should be established in the production process of concrete to ensure that the mix ratio of concrete is strictly implemented.
3.Factory control of concrete
Before the concrete leaves the factory, the factory inspection should be carried out to visually measure the slump of the concrete, estimate the transportation time and slump loss of the concrete, and ensure the slump of the concrete into the machine. In the process of factory inspection, when it is found that the concrete slump and workability are abnormal, the concrete should be prohibited from leaving the factory, and the adjustment should be made after analyzing the reasons. If the problem is caused by non-accidental reasons, it is necessary to carry out a unified and comprehensive inspection on all the concrete production process.
In addition, the transport of concrete should also be controlled. Due to the possible problems of transport vehicles, traffic control, slow construction speed and other reasons, it is easy to cause the concrete transportation time to increase; Therefore, the configuration of 5 to 10㎏ concrete admixtures in each transport vehicle (can be packed in buckets) can effectively improve such a situation.
4. The construction control of concrete is the key to ensure the quality of concrete engineering
4.1Preparation before construction
4.1.1Before concrete pouring, check the thickness of foundation, formwork and its protective layer, and the location and size of embedded parts, etc., confirm the error, and rectify the abnormality
4.1.2Formwork and steel bars shall not be stained with debris, dirt, formwork shall not have cracks, and formwork in contact with concrete shall be coated with lubricant or padded film material.
4.1.3For the foundation and formwork in contact with the concrete, water should be sprayed to moisten the surface before construction to reduce the surface temperature, but the formwork should be prevented from storing water.
4.1.4The concrete was poured at night as much as possible.
4.2The pouring sequence is reasonable
4.2.1It is not allowed to pour the slurry of the moistening pipe into the column, wall, beam and other parts.
4.2.2When pouring walls, columns and other higher components, the height of a pouring is not separated by concrete, generally not more than 500mm per layer, and the upper layer is poured after ramming, and attention should be paid to vibration in place so that the concrete is full of end corners.
4.2.3When the floor, beam, wall and column are poured together, the wall and column are poured first, and after the concrete is settled, the beam and floor are poured again.
4.2.4When the floor and beam are poured together, the beam is poured first and then the floor is poured.
4.2.5When pouring, it is necessary to prevent the movement and deformation of steel bars, formwork, positioning steel bars, etc.
4.2.6When pouring concrete in layers, it is necessary to pay attention to the integration of the upper and lower layers of concrete, and the upper layer of concrete should be poured before the initial setting of the next layer of concrete. When pouring the upper layer of concrete, the vibrator must be inserted into the next layer of concrete about 5cm in order to form a whole.
4.2.7In order to prevent the segregation of concrete, when the free fall height of concrete from the height of more than 2 meters, a string tube or chute should be set to ensure that the segregation phenomenon does not occur when the concrete falls.
4.2.8Control the pouring speed of concrete, ensure the continuity of concrete pouring, and prevent construction cold joint.
4.3Reasonable vibration
4.3.1When the temperature of concrete rises, in order to facilitate construction, the general slump is required to be larger, resulting in the increase of concrete shrinkage, strength is greatly reduced. If the method of increasing the amount of cement is used to supplement the water consumption requirements, the setting time and early hydration heat have a greater impact on the concrete, and the cracks caused by excessive shrinkage will be more. Therefore, the slump should be reduced as much as possible under the premise of meeting the construction requirements.
4.3.2For concrete with high fluidity, overvibration will distribute cement slurry, mortar and coarse aggregate from the upper layer to the lower layer, and its shrinkage ratio is 3:2:1. Therefore, cement slurry on the surface of concrete is easy to produce shrinkage deformation cracks under the constraint of the lower layer mortar and stones. Therefore, in the concrete pouring process, dispersed fabric should be used, and then the concrete is basically flat with an iron rake, and then the plum vibration, the point between the vibrator inserted should be about 400mm apart, the vibration time should not exceed 15s, and the coarse aggregate can be evenly distributed on all levels of the concrete as a benchmark.
4.3.3When pouring concrete, such as high temperature, sun exposure, wind weather, pouring should be immediately covered with plastic film to avoid the occurrence of concrete surface hardening. If induration occurs, secondary vibration can be performed. Sunshade and windproof measures should be taken when necessary.
4.3.4In the event of heavy rain in summer, the concrete that has been poured is covered with film.
4.4Rational wiping
4.4.1After the concrete is vibrated and flattened for the first time, the concrete mix will naturally sink under the action of its own gravity until the initial setting. When the concrete first sets, the surface will appear uneven, and even shrinkage deformation cracks will appear.
4.4.2The appearance of incompactness and plastic shrinkage deformation cracks on the concrete surface accelerates the speed of water loss on the concrete surface and intensifies the cracks, especially in the weather environment of high wind and high temperature, this situation is easy to occur, so it is necessary to carry out the second or third rubbing pressure before the final solidification of the concrete to eliminate the plastic shrinkage deformation cracks that have appeared.
4.4.3Do not water the surface treatment, if you really need to use a sprayer limited spray.
4.5curing membrane to keep wet
4.5.1In summer, if the maintenance is not timely, the strength will not only be reduced, but some joints will develop to the depth until they run through. Therefore, moisturizing curing is the fundamental measure to prevent the plastic shrinkage deformation of concrete cracks, so that the tensile strength of concrete can be generated early to resist the subsequent tensile stress, and better prevent the generation of concrete cracks.
4.5.2After the completion of the surface treatment operation, maintenance is carried out in a timely manner, so that with the cover, when the concrete surface is not floating, can be gently pressed by the finger, you can begin to cover and sprinkle water moisturizing maintenance, and continuous watering maintenance after the final setting, must ensure that the concrete surface is fully moist, and not less than 7 days, and the anti-seepage anti-crack agent shall not be less than 14 days.
4.5.3After the concrete of the slab members is poured and pressed, it is covered with plastic film to prevent the evaporation of surface water. When the concrete is hardened to the point that it can be used, the plastic film is removed, the sack or straw curtain is laid on it, and the water is poured thoroughly. When conditions permit, the water storage is nearly adequate for maintenance.
4.5.4The column with large section should be wrapped in wet gunny bag with water spray maintenance, or wrapped in plastic film with self-maintenance.
4.5.5After the wall concrete is poured, and the concrete reaches a certain strength (1 to 3 days), the formwork on both sides should be loosened in time if necessary, about 3 to 5mm from the seam, the shower pipe should be set up on the top of the wall, spray maintenance, and the covering such as sacks or straw curtains should be hung on both sides of the wall after the removal of the formwork, to avoid the direct exposure of the sun to the wall, the basement wall should be backfilled as soon as possible.
4.6Solid template, timely loading
4.6.1sed by cracks, the formwork support must be strong.
4.6.2Before the strength of the concrete does not reach 1.2MPa, it is not allowed to step on the young concrete, support the mold and load.
4.6.3The concrete must reach the specified strength when demolishing the mold. Premature demolishing and bearing will lead to quality problems such as tearing and cracking of the concrete surface
5.END
“Quality is life, safety is more important than Mount Tai”, improve the ideological understanding of summer concrete construction, make preventive preparations in advance, formulate the corresponding control details, increase the control of each link, and timely rectification when anomalies are found, will be able to effectively improve the overall quality of the project.
Post time: Jul-23-2023