Curing and release of Architectural concrete.

CHAPTER I. Cured.

Once the concrete has been placed and compacted, it must be cured, especially at an early age, to avoid moisture loss due to surface evaporation. In addition, temperature control of the concrete must be carried out.

Like all the previous procedures, the consistency in the concrete stage will allow us to obtain architectural concrete surfaces with a uniform appearance.

There are four fundamental requirements for successful curing, the importance of which varies depending on the volume, surface area, and concrete exposure to be cured.

Duration: All precautions must be maintained until the cement has sufficiently hydrated.

Temperature: A reasonably uniform temperature must be maintained throughout the section during curing.

Moisture: Premature evaporation of moisture from the concrete must be prevented.

Protection: Concrete must be protected from mechanical damage.

Curing is one of the most essential parts of all these methods, so great care must be taken when selecting the correct method; For flat horizontal surfaces, where a perfect appearance is generally desired, the use of spray or standing water should be avoided because the uniformity of the colour is materially affected.

Plastic membranes and waterproof paper should not be used to cure coloured floors because they cause uneven moisture distribution over the concrete surface, as they retain moisture very effectively, resulting in a stained surface due to improper migration and distribution of soluble materials in concrete.

Poorly cured concrete begins its life with a defect that can be fatal. Instead of being filled with hydrated cement, water-filled voids will remain void after the water has evaporated from the mix.

Surface concrete is weak, porous, and more prone to damage from wear, steel corrosion, chemicals, and freezing and thawing.

Curing prevents early loss of moisture and controls the temperature of the concrete.

Types of curing.

To maintain the moisture content in the concrete, the following two categories can be arranged:

Continuous application of water to replenish the amount lost.

The procedure to replace the evaporated water is limited fundamentally to the irrigation of the exposed surfaces. When watering, precautions must be taken so that it does not erode the faces, and it must be frequent at the beginning of curing to become sporadic as the concrete hardens.

Replenishing lost water includes completely covering slabs and floors with water, using hoses with holes, and applying saturated materials as covers. These covering materials may include fabrics, straw, earth and sand.

Prevention of excessive moisture loss.

Curing compounds are used to prevent excessive moisture loss. These include the use of reinforced waterproof paper and polyethylene sheets, which are periodically moistened for a period of time, depending on the aggressiveness of the weather.

Curing methods and periods must be consistent with producing a uniform colour. These should be tested on a cast-in-place model to determine any adverse effects.

Standard curing procedures are formwork curing, membrane curing, moist curing, and hot weather curing.

Cured in the formwork.

Almost all the beams, columns and lower parts of the slabs receive the curing leaving them in their formwork. To avoid stains caused by the type of formwork material, a liquid sealant is applied to the formwork according to the manufacturer's instructions. If ACI recommendations are followed, colour variations due to rapid surface drying and rapid temperature changes will be minimized.

The faster the formwork is removed, the lighter colour will be achieved on the surface.

Moist curing

Extreme care must be taken to ensure that the selected wet coating does not discolour the concrete surface. For example, the use of plastic sheeting can help cover complex-shaped elements, but colour differences may be observed between the areas where the plastic sheet is in contact with the concrete and the areas where it is not in touch.

Membrane cured

Liquid curing membrane compounds can cause discolouration and staining and prevent adhesion of permanent repairs or coatings that may be required. For the use of these membranes, the effects that their compounds can cause on the finished surface must be taken into account. Therefore, this curing type must be evaluated for the base model used in the construction.

Cured in hot weather

In hot weather, the time that elapses between the casting of the architectural concrete and the start of curing, it is crucial to prevent variations in colour and shrinkage cracks due to irregular drying.

Curing in the concrete should be started as soon as possible, before the completion of the concrete pour, to avoid defects in the concrete.

For this type of climate, curing with water is preferable. Effective methods include the use of moist polyethylene-covered tissues or continuous water spray. For large areas of slab, curing compounds are more practical. The white-pigmented components help keep the concrete's temperature low by reflecting sunlight and reducing heat absorption.

Cured in cold weather

Water curing should be avoided if the temperature is below freezing, as this can cause hazards as water leaves artificial heat sources and freezes. In addition, water-cured concrete is prone to saturation when cold protection is removed. This action makes it more vulnerable to damage caused by freezing.

It is best to seal the water in the mix with curing compounds, plastic sheeting or waterproof paper in cold climates. Then, as hydration occurs, internal spaces that are filled with water are partially emptied to prevent frost damage.

Cured in coloured concrete

The curing of the coloured concrete must be done with the materials recommended by the manufacturers of the colouring agent or additives. Curing waxes of the same colour or a harmonious colour with the colour of the concrete mass is widely used for horizontal surfaces such as slabs and floors. This wax is applied by spray or roller to the flat surface of the fresh concrete.

For the curing of coloured concrete, any method that can stain the concrete, such as damp earth, straw or coloured damp cloth, must be ruled out. This is because even using typical concrete curing compounds can result in poor appearance.

Running water or sprinklers are not a good alternative because they can stain the concrete or cause efflorescence. Waterproof plastic sheeting and paper can cause a blotchy appearance due to uneven moisture distribution on the surface.

Unmold

The demolding operation is particularly critical in the case of architectural concrete, not only to avoid normal surface scratches but also to prevent damage to surface designs. Before removing the formwork, the concrete must have acquired sufficient strength to be self-supporting and resist mechanical damage during the striking process. If the adhesion between the face of the form and the concrete is more excellent than the cohesion within the concrete at the surfaces, spalling can occur, and the corners can be damaged.

The forms must be removed without causing damage to the concrete. Leverage against the concrete surface must be prohibited during the removal of the forms. In addition, it is prudent to provide corner and edge protection after removing the formwork to prevent damage from other activities.

In the case of white or coloured concrete, surface forms must be removed at the end of a similar time interval to avoid colour changes.

Rojas

Architecture and Engineering