Are You Getting All Your Curing Right?

The application of commercial concrete has greatly improved the quality of construction projects, and promoted the development of commercial concrete industry, but the problem of early cracking of concrete structure caused by the lack of timely maintenance of commercial concrete is difficult to eradicate, has become a hotspot of complaints about the quality of construction projects, but also the focus of quality supervision.

After the concrete is poured into shape, watering should be carried out in a timely manner to cover the moisture conservation to meet the concrete surface to maintain a certain moist state. At the same time, in order to prevent the rapid and rapid evaporation of water, the surface should also be covered with plastic film, sacks or straw sacks and other covering materials, but only to do these points or not enough.

The maintenance of concrete, one of the purposes is to ensure that the concrete moisture in a certain period of time, resulting in concrete cracks is complex, multifaceted reasons, but the lack of experience in the construction of commercial concrete and maintenance is not timely is one of the main reasons for cracks in commercial concrete.

After pouring concrete, the reason for the gradual hardening of the concrete can be gradually set, mainly because of the hydration of cement, and hydration needs appropriate temperature and humidity conditions, so in order to ensure that the concrete has appropriate conditions for hardening, so that its strength continues to grow, the concrete must be maintained.

The essence of maintenance – watering maintenance, maintaining appropriate humidity, to ensure that the cement hydration reaction.

The secret of curing – time control.

A concrete curing program selection and development

  1. Determination of conservation time

(1). Determination of the onset of conservation

China’s concrete structure engineering construction specifications stipulate that concrete should be timely moisturizing maintenance after pouring; concrete quality control standards stipulate that for concrete pouring surface, especially plane structure, it is appropriate to use plastic film covering moisturizing while pouring forming; concrete structure engineering construction quality acceptance specifications stipulate that concrete should be covered and moisturizing maintenance within 12h after pouring, and most of the current construction also follow this rule, that is, about 12h after pouring start moisturizing maintenance.

To be more specific, after the concrete pouring is completed, water should be poured before and after the initial setting to curing, but do not cause man-made damage to the concrete surface as a limit.

(2). Determination of the duration of curing time

Are You Getting All Your Curing Right

  1. Choice of conservation methods

Concrete curing program should be based on site conditions, environmental temperature and humidity, structural parts, components or products, raw materials and the performance requirements of concrete and other factors to develop, curing program, the choice of curing methods generally use water spraying curing, water storage curing, cover moisture curing, brush curing agent curing, winter heat storage curing and other methods. During construction, when developing the curing program, it often occurs that only a single curing method is used throughout the construction process, and for the sake of convenience, water spray curing is mostly used. In order to ensure the realization of concrete performance, according to the different parts of the structure should be a reasonable choice of curing methods.

(1). Foundation for the exposed surface of the bulk concrete should be used to cover the curing method. Foundation for the exposed surface of large volume concrete using water curing method is more convenient, but the actual construction is difficult to meet the number of sprinkler maintenance, easy to cause interruption of night curing, for large volume concrete, to control the interior of the concrete and surface and surface temperature difference between the outside world that is to maintain the appropriate temperature gradient inside and outside the concrete, uninterrupted 24h maintenance is essential.

According to past construction experience, in the process of large volume concrete curing using forced or uneven cooling cooling measures not only relatively high cost, poor management of large volume concrete is easy to produce penetration cracks, such methods in housing construction projects are less used, and sprinkler maintenance easy to pit water, unfavorable backfill. Therefore, the foundation of the exposed surface of large volume concrete to cover the maintenance is appropriate.

(2). Concrete structure construction specifications: the basement floor and superstructure of the first floor of the column, wall concrete with mold curing after the end of water can be used to continue to curing, if necessary, can also be used to cover the curing or spraying curing agent curing way to continue to curing; according to the test, the different curing effect of seepage in turn: water curing > grass bag cover watering > coating curing agent > natural curing, so for the basement floor using water curing is the most reasonable program.

(3). Other parts of the column, wall concrete can be used for sprinkler maintenance; If necessary, can also be used to cover the maintenance or spraying curing agent maintenance; But the column system of the main load-bearing structure should be used as far as possible to cover the plastic sheeting method; Shear wall structure is best used to paint the curing agent method.

(4). plane structure, it is appropriate to use plastic film covering moisture while pouring forming; but for the bathroom floor, roof plane, in order to achieve the best anti-seepage effect, where possible, it is appropriate to use water storage maintenance. Construction of common problems is easy to ignore the floor slab bottom surface of the maintenance, floor slab bottom mold removal, part of the construction workers because the surface layer has been done maintenance, and the bottom layer can not be sprinkled with water or cover maintenance, painting curing agent and increase the cost, so in the maintenance program, often intentionally or unintentionally omitted on the floor slab bottom mold after removal of the maintenance, and the requirements of the exposed surface of concrete should be cured, shall not omit any part, so the floor slab bottom mold Should be sprayed over after removal

Dense curing agent for maintenance.

  1. Determination of conservation temperature

Thermal insulation measures should be taken during concrete maintenance to prevent drastic changes in the surface temperature of concrete due to environmental factors (such as exposure to the sun, sudden drop in temperature, etc.). During the maintenance period, the temperature difference between the core of the concrete and the surface, and between the surface and the environment should not exceed 20 ℃. Before the construction of large volume concrete, a strict curing program should be developed to control the temperature difference between inside and outside the concrete to meet the design requirements.

After demolition of concrete in winter and hot season, if there is a sudden change in the weather, appropriate thermal insulation (cold season) thermal insulation (summer) measures should be taken to prevent excessive temperature stress on concrete.

Minimum periods for wet curing of different concrete

Note: The curing time for bulk concrete should not be less than 28d.

  1. Control of conservation humidity

The shrinkage of concrete in addition to the cold shrinkage caused by the temperature drop, that is, temperature drop contraction, there is the effect of cement hydration, the relative humidity of concrete with the progress of cement hydration and decrease, thus causing the reduction of concrete volume caused by self-drying, leading to the early age of concrete shrinkage of their own, concrete shrinkage by environmental relative humidity significantly, 70% of the concrete curing humidity of 90% of the concrete curing humidity of the concrete, the concrete is not only the relative humidity of the environment. The dry shrinkage at each of the measured ages was large, and the dry shrinkage rate at the 3-d age was 8.3 times greater than that at the 3-d age. The lower the relative humidity of the environment, the greater the dry shrinkage value, and the development rule of the dry shrinkage value with the age of the early development of fast, later development of slow and gradually stable.Are You Getting All Your Curing Right

Summary

(1). When formulating concrete curing program, multiple curing methods should be selected and formulated for comprehensive curing according to the site conditions, ambient temperature and humidity, structural parts, components or products, raw materials and requirements on concrete properties.

(2). The starting time for curing is appropriate after the concrete is poured, before and after the initial setting on the watering curing.

(3). The duration of curing time to the time specified in the specification for the shortest time, vertical concrete structure to increase the curing time, combined with the composition of concrete and concrete ratio, ambient temperature and humidity, curing methods, wind, wind speed and many other factors to consider.

(4). Whether to stop sprinkling maintenance is determined by the day of the lowest temperature below 5 ℃. The temperature difference between the interior and surface of the concrete and between the surface and the outside world will be considered according to the curing measures, methods and many other factors.

(5). Concrete shrinkage is significantly influenced by the relative humidity of the environment, and effective curing is only effective when plastic film is adhered to the exposed surface of concrete and condensation water is maintained.