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Reinforced concrete walls: how they are realized and with which technologies

Posted with permission from Kwik Stamped Concrete: North America’s best stamped concrete company

Reinforced concrete (ca) combines and completes two important building materials: concrete (concrete) and steel . The concrete has a good resistance to compression but not to traction while the steel has an excellent resistance to traction. This fundamental collaboration is possible thanks to the property of adherence of the bars and to the comparable coefficient of thermal expansion of the two materials.

Generally, the ca consists of concrete and steel bars, suitably shaped and interconnected, which are drowned in it, especially in areas where it is necessary to deal with traction efforts.

Wall in concrete: how it is made
The process that leads to the realization of the concrete is long. The chemical reaction that transforms the mixture of aggregates, cement and water into a solid and compression-resistant material is divided into two parts: the setting and hardening . The first phase is the grip, which lasts about 24 hours, in which the material acquires a solid consistency but not yet mechanical characteristics. With the second phase, that is the hardening (which occurs in about 28 days) the material assumes its mechanical characteristics.

Since the concrete needs time to take its own shape and its mechanical characteristics, it is necessary to prepare formworks,a casing in which the steel bars are drowned. When the concrete casting is carried out in the fluid state, the formworks “contain” it until the end of the setting process and after the hardening process starts.

The formworks must consist of two panels, connected together by means of special spacers, at a distance equal to the thickness of the wall to be built. The panels must be vertical (check the plumb line) and must not be deformed under the weight of the concrete casting.

After casting the concrete, the formwork must be left for about 48/72 hours (depending on the season, ventilation and other factors), or until the casting has obtained a mechanical resistancesuch as to ensure the absorption of the stresses to which the structure is subjected immediately after the disarmament. At this point the formwork loses its function and can be removed because the structure is now capable of self-bearing.

Construction of reinforced concrete walls: formworks
Until a little while ago the only way to build a concrete wall was through wooden formworks, inside which were already prepared the irons and the brackets of the wire mesh, to hold the concrete at the time of the casting.

In fact, wood has always been a material that is easy to work with and to shape, light to maneuver on site and breathable. However it has the disadvantage of not being able to be used for more than two or four times as it impregnates and loses its transpiring power.

Beginning in the mid-twentieth century, new formwork systems began to be developed with the aim of industrializing the site and increasing production efficiency. Alsoformwork materials have increased, in fact today it is possible to realize with metal panels, panels based on expanded polystyrene or elements in fiber-reinforced or compensated materials.

The formworks can be reused or already conceived from the principle as non-reusable. One speaks of a “formwork to lose”, when the structure remains incorporated in the work even after the hardening of the concrete. This typology has undergone numerous improvements by integrating more functions such as thermo-acoustic insulation or finishing.

Recycled materials in construction? Six concrete cases

Last June 2017 the Report of the Recycle Observatory was published, promoted by Legambiente, whose objective is to tell and investigate the changes deriving from the use of recycled materials also in the building sector, under the pressure of Directive 2008/98 / EC, implemented at national level, which foresees that in 2020 a target of 70% of the recycling of construction and demolition waste will be achieved.

“Today it is possible to respond to these problems, as demonstrated by the many countries where the amount of materials extracted with a strong push to reuse aggregate and aggregate waste from recycling has been reducing for years, as well as with rules to protect the landscape and asset management. In Italy today there are about 2,500 quarries from aggregates (more than 4,700 in all) and at least 14,000 abandoned, of which more than half are former sand and gravel quarries.

Changing this situation, opening up a green economy that is creating research, innovation and jobs throughout Europe, is in the interest of the Italian business system.

Yet, alongside these great opportunities, the problems that the application encounters are relevant. In fact,

the processes are proceeding too slowly and the companies that in recent years have invested in research and development on materials and aggregates from recycling are faced with often insurmountable regulatory barriers ».

The advantages of investing in the Green Economy in buildings
1) European experiences show an increase in both employment and entrepreneurial activities, evidenced by the creation of specialized supply chains.

2) There is a noticeable reduction in the extraction from quarry: « reaching 70% of recycled material recovery would generate over 23 million tons of materials that would allow to stop the production of at least 100 sand and gravel quarries for a year » .

3) Reduction of greenhouse gas emissions: «increasing the amount of tires recovered and used up to double it by 2020, it would be possible to resurface 26,000 km of roads. The energy savings achieved, considering that more materials derived from oil would not be used, would be over 400,000 MWh. That is the consumption in more than two years of a city like Reggio Emilia, with a cut in CO 2 emissions of 225,000 t ».