Work is poured on concrete
In small concrete paving projects, with the help of a strong shovel or rake, level the wet concrete surface approximately, then re-trowel the concrete with a smooth edge board to achieve the correct level. Troweling causes the air bubbles trapped in the concrete body to be removed and at the same time immerses the coarse aggregates in the concrete and at the same time brings a sufficient amount of fine-grained stone materials to the surface, which makes the concrete surface smoother.
Rod vibrators can also be used to remove more unwanted air bubbles, thus ensuring that coarse aggregates do not sink into the concrete, although this is more important in the performance of aerated concrete than plain concrete. .
In larger projects, by preparing vibrating beams and impact rollers drawn on the concrete surface
They remove trapped air bubbles and level the entire surface in one step. Usually three or four times passing the ingot is enough to obtain an acceptable finished surface with an accuracy of -10 6-10 mm. Excess concrete accumulated in front of the ingot must be removed.
Concrete polishing is a relatively polished surface with a few trowels on wet concrete, but in large and important paving projects, if you want a smoother surface you should use a steel (floating) trowel. This works best when the concrete begins to harden, leaving less of an impact trowel. Hand trowels are also suitable for smaller surfaces, provided that a completely uniform finish is not necessary. Larger trowels are used for larger surfaces, and a motor trowel should be used if a perfectly polished finish is desired.
Judging the exact time to start polishing, whether by hand or with a motor trowel, is a skill in itself, and is gained after years of experience; If done too soon, the effects will never go away, and if it is too late, the concrete will not be rubbleable for a precise finish. Concrete with a perfectly polished surface can be somewhat slippery, especially when the concrete is outdoors and outdoors. Wet or icy conditions. It is recommended that in the flooring of the yard, as soon as the surface is polished by a trowel, a light brush is drawn perpendicular to it in order to provide sufficient friction when the concrete hardens. For this purpose, it is appropriate to use a soft hair brush that has the ability to create grooves to a depth of 1 mm.
On roads with low and light traffic load, such as a private road to the house, parking lot and the like, the concrete is left to harden after polishing and is done gradually by keeping the surface moist. The site is usually inspected after 10-12 hours for immediate repairs if needed. This method is satisfactory in small work but in larger slabs, especially where the final strength is critical, in the early stages of concrete curing. More precision is needed to meet the design objectives.
The two determining parameters that should be controlled in the first 24-72 hours of concrete curing are:
1. Drying by evaporation
2. Temperature fluctuation
The easiest way to prevent the concrete from drying out quickly is to keep it moist. There are different ways to achieve this goal, but the most common methods are as follows:
Keep it moisturized well – it is difficult to apply in practice and may weaken the surface.
Plastic Sheet Cover – Cheap and effective, but can trap water vapor between the slab and the cover.
Spraying a plastic membrane – is relatively expensive, but is becoming more common. This membrane can be removed after a few days.
Temperature control is important only when the ambient temperature is less than 4˚C. Temperatures above 20˚C cause premature drying of the concrete, and can be controlled as above, or can be achieved by providing shade. Found.
In winter, freshly poured concrete can be covered with sacking, straw, mat, straw or polystyrene to protect the slab from the cold overnight. Concreting is usually not done in adverse weather conditions, when the ambient temperature is below 4˚C, except in minor cases. In these cases, the surrounding space should be kept warm so that the ambient temperature exceeds the limit value of 4˚C.
Operation time of concrete pavement
Concrete strength usually reaches design strength after 28 days. Although this is true, it does not mean that the sign can not be used during this period. In most cases, the movement of any device on the concrete slab should be completely avoided in the first 48 hours. After that, you can walk on the slab with caution, but we are not allowed to drive heavy vehicles or low-speed vehicles for up to 5 days after concreting. In heavy uses such as highways, airport runways, ports or commercial areas, we are not allowed for 10 days due to vehicle traffic on the concrete.
In concrete slabs, the molds can be removed after 24 hours, although they usually stay in place for up to 3 days unless we want to visit the edges of the slab. Care must be taken when tapping the formwork to avoid damaging the concrete as the concrete is still fresh.