How to pour concrete: mix preparation, laying, features

At what temperature can you work with concrete? What is better to make formwork? Is it possible to rearrange it, filling the monolith in small sections? In what cases is enough spudding, and when is necessary vibrolaying? Let's try to answer these and some other questions.

Preparation of the mixture

Начнем с подготовки бетона. В общем-то, требования к бетонным смесям различного назначения изложены во многих нормативных документах; в нашем случае источником информации послужит СНиП 3.03.01-87 «Несущие и ограждающие конструкции».

So what are the requirements of building regulations?

• Fillers should be applied fractionated and washed.. A mixture of rubble and sand for concrete in its original form when mixing is not used.

Explanation: Concrete brands imply a well-defined percentage of sand and coarse aggregate. Dosing fill different types, supplied as a mixture, is impossible.

• Components are dosed by weight.. However, dosing by volume of additives (plasticizers, etc.), administered in the form of aqueous solutions, is allowed.
• The exact ratio of components is selected for each batch of cement and aggregate based on the results of the inspection. (granulometry, strength tests, cement quality control).
• For aggregate with the size of the largest grain up to 40 mm, two fractions are enough (rubble and sand). With a larger size of a larger fraction in concrete, you need to enter another one, a smaller size (sand, crushed stone fraction 20 mm, crushed stone fraction 40 mm).
• For slabs, the size of the aggregate should not exceed half its thickness. For an arbitrary reinforced concrete structure - 2/3 of the smallest distance between reinforcement elements.

What is the composition of various grades of concrete? Where do they apply?

Laying: general recommendations

How to pour concrete? SNiP 3.03.01-87 contains recommendations in this area.

Concrete mixes keep within a timbering horizontal layers of an identical thickness; direction of laying should be the same in all layers. In this case, the next layer is laid before the previous one is set.

Is it possible to pour concrete parts, with long breaks?

Yes, but with certain reservations:

1. The strength of the previously laid array should reach a value of at least 1.5 MPa.
2. The location of working joints (joints between previously laid and fresh concrete) is strictly regulated. In particular, they can be parallel to the smaller of the slices of the floor slab, located at the level of the top of the foundation or the bottom of the beam when concreting the columns.

Important: before resuming work, the inclined or horizontal surface of the working seam must be cleared of debris, dust, washed with water and dried. The same requirement is relevant for rocky foundations under the monolith.

The upper level of the mixture should be 5-7 cm below the edges of the formwork.

When vibrating, the vibrator should not rest on the reinforcement, embedded parts or formwork elements. Immersion vibrator is immersed by 5-10 cm in the previously laid layer; it should be rearranged in increments of no more than one and a half radii of the device.

After setting, it is necessary to prevent sharp fluctuations in the moisture content of the concrete: the embedded structure is protected from precipitation and direct sunlight.

Useful tips

So, pour concrete. General principles are clear; However, at different stages of the work we will inevitably encounter a number of minor technical problems.

Temperature

The optimum temperature for curing strength with a concrete monolith is +15 - +25 C. Is it possible to pour concrete at 5 or 45 degrees?

And what about negative temperatures?

• At temperatures slightly above zero, the curing rate decreases slightly; however, the final strength of the monolith does not suffer. Moreover, under the condition of minimal thermal insulation of the formwork and the surface of the monolith (for example, if you cover them with a warm tarp), you can also work at -5 ° C. Self-heating of the cement during hydration will not allow water to crystallize.
• At high temperatures, acceleration will accelerate; the cost of accelerated ripening of the monolith is its uneven drying and the appearance of cracks. The problem is solved: the surface of hardening concrete is watered a couple of times a day with water or covered with a wet sacking.

• At temperatures significantly below zero, concretes with antifreeze additives are used to reduce the crystallization temperature of water. As an option - the formwork is heated by a heating cable or heat guns.

Formwork

Most often, with independent construction, it is constructed with its own hands from the improvised material. Two typical problems of improvised formwork are deformation of boards or plywood when moistened and the laboriousness of cleaning from the set solution. What to do?

A simple instruction will help to solve both problems in one fell swoop: before pouring, the formwork is laid with thick polyethylene strips laid with overlap. At the same time, the film will prevent leakage of the cement jelly, accompanied by a drop in the final structural strength.

Compaction

Is it necessary to compact the concrete? When enough sticking, and when you need a vibrator?

Tightening the soil

How to pour concrete floors on a dirt base?

How to insulate such a floor?

1. The soil, shot to the desired level and leveled to the horizon, is filled up with 10-15 centimeters of sand. Sand is poured with plenty of water for maximum shrinkage.
2. The layer of rubble of the same thickness is leveled and rammed.
3. On rubble the waterproofing - a polyethylene film is spread.
4. Выкладывается бетонная подушка - 10 см бетона марки M100.
5. On the concrete which has gained durability the heater is laid out - a dense (not lower than C-35) foam or extruded polystyrene foam. Thickness - 40-150 mm, depending on the climatic zone.
6. Another layer of polyethylene is laid out; on it, on supports with a height of 1.5-3 cm, the reinforcing mesh is expanded.
7. Finally, we fill the floor with concrete by 8-10 cm, level the screed over the beacons, and after gaining strength, we apply a clean finish.

Conclusion

Of course, in the framework of a small article, we were able to touch upon not all the subtleties of concrete work. A number of additional materials to the attention of the reader will offer a video in this article. Successes!