The better the maintenance, the less likely the concrete structural members are to crack; the impact on concrete carbonation: the better the maintenance, the slower the carbonation speed and the shallower the carbonation depth. This paper is especially recommended to the construction workers, to study, understand and implement it in depth, so as to contribute to the quality of concrete engineering.
4.2 New technology of concrete early maintenance
(1) Maintenance of cast-in-place concrete slabs: It is best to adopt a new technology of rubbing the surface of the slab and covering it with a plastic film, that is, after the concrete is poured for a section, first use a vibrator to vibrate the concrete, and then find the slab surface and use a wooden washboard After rubbing for a short period, roll the plastic roll from front to back on the thatch. The beginning and end of the roll of film should be pressed with a wooden washboard to make it stick to the concrete to prevent it from being blown up by strong winds. Do not lift all the plastic film when setting out the wires. You can use a paper knife to cut off the parts that are in the way of the wires. Although this is a bit troublesome, it saves a lot of maintenance water and man-hours in the future, which is quite cost-effective.
(2) Concrete column maintenance: It is best to wrap the column surface with plastic film after the column is removed from the formwork, sprinkle water before wrapping, and then wrap the column surface tightly so that the water inside does not evaporate and achieve a good condition. self-care effect.
(3) Conservation of concrete shear walls: Apply qualified concrete curing fluid immediately after the shear walls are demolished, especially in winter construction. In addition to construction in winter, it is also possible to use the method of assigning a special person to sprinkle water for maintenance. Sprinkle water once an hour, and set up two people to take turns on duty. When using the method of brushing the curing liquid, it must be possible to form an impermeable film on the surface of the concrete member after the curing liquid is brushed. If it fails once, it can be brushed again. If a waterproof film cannot be formed, it proves that the curing solution is unqualified and must not be used.
(4) Concrete pavement (ground) maintenance: After the indentation of the pavement is completed, immediately cover the plastic film. At the beginning, it should be pressed with soil or sand, and then it should be covered, and then the side and tail of the upwind direction should be pressed. After the thatching is completed in this way, one side of the plastic film can be slightly lifted the next day and then filled with water, and the film should be covered. From then on, as long as the film is not blown by the strong wind, everything will be fine. If there is a place blown by strong wind, it should be watered quickly and covered with thatch again. Such a continuation shall not be less than 14 days.
4.3 Guarantee measures for concrete maintenance (implemented by the competent construction department)
(1) Improve the maintenance awareness of the supervisors, so that each site supervisor pays as much attention to the supervision and maintenance as the supervision of the construction of steel bars. If the concrete curing is not in place, the next process is not allowed. If the concrete strength is caused by excessive carbonation depth when the structure rebounds, the on-site supervisor should also be held accountable.
(2) Determine the limit value of the carbonation depth within one year: if the newly poured concrete can meet the specification requirements in the early maintenance, within one year: the carbonation depth of concrete with C40 and above is not greater than 1.5 mm, and the standard maintenance (standard maintenance 28 days later transfer to outdoor natural curing) is not greater than 1mm; the carbonation depth of C30 and C35 concrete is not greater than 2.5mm, and the standard culture is not greater than 1.5mm; the carbonation depth of C20 and C25 concrete is not greater than 4mm, and the standard culture is not greater than 2.5mm. It is suggested that when the country amends the relevant specifications or regulations of concrete, the limit value of the carbonation depth of concrete within one year shall be stipulated. When the structural rebound is accepted, if the carbonation depth of the concrete exceeds the limit, it can prove that the early maintenance of the concrete is poor, and the construction and supervisors must be held accountable. Reduce the phenomenon that the demand side and the supply side shuffle each other and argue with each other due to unqualified structural strength.
4.4 Measures to ensure that the structural concrete meets the design requirements
(1) Considering the unreasonable human factors at the construction site and the fact that it is difficult to ensure that the construction personnel can maintain the concrete well in the near future, it is necessary to increase the surplus coefficient of the production mix ratio. The compressive strength of the concrete produced after 28 days of standard curing should be Greater than 1.2 times the design strength. In fact, the compressive strength of ready-mixed concrete after 28 days of standard curing only accounts for about 70% of its final strength, and the concrete after 28 days still has a strength margin of about 30%. The surplus number will be reduced to nothing. Since the ready-mixed concrete is a semi-finished product when it is delivered to the buyer, the other half needs the active cooperation of the buyer to make qualified finished concrete. Reasonable vibration and maintenance are important links for making qualified concrete. Because the supply side cannot control the demand side, it is necessary for the construction administrative department and the supervision company to strengthen the supervision of the construction unit, so that it can be constructed according to the specifications, so that the ready-mixed concrete can be developed in a durable, environmentally friendly and green direction.
(2) Construction personnel are prohibited from adding water to the concrete mixture, and using admixtures to adjust the slump of the mixture. Due to the long waiting time after the concrete is transported to the construction site, the loss of concrete slump is large, which makes it difficult to pour, and the construction personnel unreasonably request to increase the slump, even if the delivery slump of the concrete mixture meets the requirements of the buyer, Pumpers and pourers also add water to the pump bucket, they only care about good pumping and easy operation, and never have the future strength and durability of concrete in mind.
In order to prevent construction workers from adding water to the mixture at will, concrete production enterprises should change their concepts and look for problems from their own services: if the concrete we deliver to the construction site can be easily pumped and poured without excessive collapse; if Our transport trucks waited too long at the construction site in special circumstances, resulting in a small slump of the mixture, and our driver can actively add an appropriate amount of admixture to the mixing drum to increase the slump of the mixture. Slump, can the builder still add water to the concrete mix? Therefore, don't just blame the construction workers for adding water to the mixture, but instead, the concrete production company does not need the construction personnel to add water to the concrete mixture. This requires our concrete production enterprises to increase the training of transport truck drivers, so that every driver can learn to add admixtures to the concrete mixture reasonably and moderately to increase the slump of the mixture.
