Stonehenge in England, the Peruvian citadel in Machu Picchu, the pyramids of the pharaohs in Egypt - all these great works of ancient architecture serve as evidence that natural stone is one of the oldest and at the same time durable building materials in human history. But it is very difficult to work with it, it is difficult to transport and extremely time-consuming to process and install.
How good it would be to have a similar material in the form of batter, giving it an arbitrary shape, which, after solidification, would acquire the properties of a stone. Such an amazing "liquid stone" exists, and we call it concrete. It is a composite material that includes three main elements.
Three simple ingredients for the perfect building material
- Cement (common name for silicates and calcium aluminates) - takes up 10-15% of the total volume of the solution.
- Water - 15-20%.
- Coarse grain mixand fine aggregates (sand, gravel, large pieces of crushed rock, recycled glass, etc.) - typically 60-75%.
Speaking of concrete as a composite material, you need to understand that its ingredients, so unlike the final product, acquire high strength and durability not just as a result of the drying of the mortar, but due to a chemical reaction. When water is added, cement hydrate crystals begin to grow, forming a crystal lattice and tightly holding sand and gravel together. It is because of this that after pouring the concrete has to be moistened for several days, and obtaining a good result is possible only if a number of technological requirements are observed.
Two stages of "growing up" of concrete
Due to the fact that this building material is "born" in a liquid state, concrete pour molds can be given almost any desired configuration, after which, as a result of hydration, setting occurs, and then the concrete hardening stage.
- Setting is perhaps the most important and fairly short-lived process, starting about two hours after the solution solidifies and ending an hour after that (at 20ºC). This period is very dependent on the pouring temperature of the concrete and, for example, at 0ºC it can take up to 20 hours, while in hot weather the setting time, on the contrary, is significantly reduced.
- Hardening is a non-linear process that proceeds most dynamically at the first stage, when the concrete, approximately withinmonths, gaining most of its strength, while its final hardening occurs only after a few years.
Everyone has flaws, but the iron rod inside will solve any problems
It is immediately worthwhile to understand that it is better to pour concrete prepared by an industrial method, purchasing it from a trusted manufacturer that guarantees its compliance with the declared brand. This is the only way to obtain a material that meets the requirements predetermined by the customer, reflected in the concrete passport (density, filler fraction, frost resistance, water resistance, mix mobility).
One of the main characteristics that determined the widespread use of concrete is its ability to withstand significant physical compressive loads. Density is responsible for this indicator, which is determined by the ratio of the mass of the material to the volume occupied. In heavy grades of mortar with a filler of natural stone of various fractions (crushed stone, pebbles or gravel), the weight of one cube of pouring concrete is from 1.8 to 2.5 tons. Materials of this type are used in the construction of structures that experience significant loads (supports, ceilings, foundations, etc.). For lightweight concrete used for the construction and insulation of walls, floors and lightweight ceilings, perlite, expanded clay and all kinds of foamed polymers serve as fillers. The density of such a solution varies from 0.6 to 1.8 t/m3.
Unfortunately, the big disadvantage of concrete is that when stretched, it can withstand loads about 10 times less than whencompression, and is easily destroyed even with slight bending. This problem is solved by pouring concrete around twisted steel rods (reinforcement) fastened to each other in the form of a lattice.
After hardening, a new composite material is obtained - reinforced concrete, in which concrete provides compressive strength, while steel resists bending and stretching. Other materials are sometimes used for reinforcement, including various types of plastics, but steel will warp in heat and cold at about the same rate as concrete, which means the material will not collapse from the inside.
Fundamentals of reinforced concrete longevity
It is clear that due to a number of objective reasons it is not expedient or possible to order a solution from professional suppliers. Moreover, observing the technical conditions, even pouring concrete with your own hands, you can get a good result.
The foundation of a house is its foundation and a guarantee of the trouble-free functioning of everything that it is designed to support. There is a great variety of ways to lay it: from block and pile - to the creation of a tape monolithic-reinforced belt. However, with all the richness of choice, in all these cases it will be concrete, or rather, reinforced concrete. In the case of individual development, the most common is the last of the listed options. At the same time, the foundation is poured with concrete in a continuous layer around the entire perimeter of the future building, on top of the reinforcingframe.
All work on the construction of the foundation can be divided into three stages.
- Preparatory - site planning, installation of reinforcement and installation of formwork.
- Concrete pouring work - mixing, pouring, laying mortar and maintaining concrete.
- Final - formwork dismantling, visual inspection and elimination of minor defects.
Foundation: looking for answers to a lot of questions
The overall dimensions of the foundation, in addition to its obvious parameter - length, depend on many initial conditions: bearing load (type of wall material, number of storeys, presence of a basement), soil type, terrain, groundwater level, depth of soil freezing, height snow cover and more.
If we talk about the minimum dimensions, then the depth of the foundation should be at least half a meter, the removal above the ground should be from 30 cm, and the width should be at least one and a half times the masonry size of the wall material.
Formwork: the story of how form determines content
The formwork consists of a shield part and a stop. When forming it, it must be taken into account that concrete at the first stage is a fluid solution that fills all the free space. Therefore, to obtain a good result, the shield surface should be as even as possible, not contain cracks and differences in height, and to maintain an ideal vertical, it is recommended to use a building level or plumb line. At home, formwork panels are made from pine boards with a cross section of 20-25 mm, sewnbetween each other with a plank of the same material, as well as plywood, chipboard or metal sheets.
At the same time, it is extremely important not to forget about one more property of the concrete mortar, namely, its high specific gravity, because the thickness of the panel formwork elements and the stop (usually wooden) should compensate for the pressure of the concrete mass. In addition, it is advisable to lubricate the working surface of the shields with grease or cover with a polyethylene sleeve, which will ensure the perfect smoothness of the foundation, prevent the mortar from flowing into the cracks of the formwork and simplify its subsequent dismantling.
The rebar frame should guarantee inextricable strapping over the entire surface of the future foundation, as a rule, one cubic meter of concrete, depending on the diameter, accounts for 70 to 120 kg of reinforcing bars.
The secret of making concrete potion
At the next stage, the actual preparation of the mixture for pouring concrete begins. Since we are talking about private construction, we will use classic ten-liter buckets as a measuring unit. The brand of concrete depends on the ratio of its constituent materials, and M300 is most often used for the foundation. Such a solution corresponds to the following proportions: for 1 bucket of Portland cement grade 400, there are 2 buckets of sand and 4 - crushed stone. The amount of water strongly depends on the moisture content of the sand and is calculated experimentally during the first batch. Then all the ingredients are thoroughly mixed in a large container or concrete mixer. The finished mortar should have a uniform viscous consistency, not flow out through the joints of the formwork, and at the same time fill all voids well.
Concrete placement order
It is necessary to lay the concrete mixture in horizontal uniform layers, about 20 cm high, distributing the mortar over the entire width of the formwork and avoiding gaps. This is a very time-consuming and dynamic process, since in order to achieve an ideal solidity of the foundation, the next layer of concrete must be applied before the previous batch has set. At the same time, during pouring (in the absence of a deep vibrator), the mortar must be constantly stirred and pierced with an iron bar or scrap to fill all voids and deaerate the concrete in order to obtain a uniform strength of the foundation.
The he althy "childhood" of concrete determines its long life
Immediately after the completion of the pouring, the stage of care for the concrete mixture begins, which, depending on weather conditions, takes from three to five days. First of all, this concerns periodic (every 2-4 hours) moistening of the concrete surface. The higher the temperature, the more often it needs to be done, but if the work is carried out in the cool season and the temperature ranges from 0 to + 5ºC, then watering is not done at all, protecting fresh concrete from direct sunlight and temperature changes with moistened sand or sawdust. It is also necessary for the first two or three days to prevent walking on the flooded surface and protect it from other mechanical damage. The strength of concrete increases most rapidly in the first days, and after a week and a halfis about 70% of the declared brand indicators (28 days).
Now you can carefully remove the formwork and evaluate the result. If shells and corner chips are found, the surface of the foundation is rubbed with a solution based on sand and cement, and excess sagging is removed with a trowel.
Concrete, as always, on top
All the advantages of concrete have found their application in the construction of floors. This is primarily strength, evenness, moisture resistance and durability, and the relatively high thermal conductivity, combined with the active use of underfloor heating systems today, has gradually migrated from the shortcomings to one of the priorities for using this type of material.
At the same time, the technology of pouring concrete into the floor is even simpler than the strip foundation described above. The key point here is the high-quality preparation of the surface to be coated, which implies the presence of a solid base, the creation of a hydro-barrier and thermal insulation for the future floor. In fact, the role of the formwork in this case is played by the platform itself and the walls of the room, and with a standard coating thickness of 6 to 8 cm, the whole process will not take much time. In addition, for such work, light concretes or fine-grained fillers with a lower grade compared to those used in the foundation are often used. Masonry wire mesh is used as reinforcement, and the main difficulty lies in the ideal setting of guide beacons, which can serve as trimmings of an ordinary pipe. Due to significantthe size of the open surface, special attention should be paid to the care of the concrete screed after its laying, which is similar to the measures above.
With strict observance of rather simple conditions of the technological process, concrete structures are able to perform the functions assigned to them for many years, delighting not only you, but also your grandchildren with their reliability.
