A brief history of Concrete
Spain began to use reinforced concrete more than twenty years behind the Nordic countries. In 1890, reinforced concrete structures of a certain size and complexity were already being built in Europe. The first recorded work in reinforced concrete is a simple deposit discovered in Puigverd (Lleida), executed by the military engineer Francesc Macià with a patent from Monier. The Puigverd warehouse in Lleida, generally considered the first Spanish reinforced concrete construction, was completed in December 1893 and is still in service. And it was in the year 1898, when a self-taught French engineer, architect and builder named François Hennebique invented a construction system with reinforced concrete, which allowed the rapid spread of this material in Europe at the beginning of the 20th century. And it was he who began the construction of the first two buildings in Spain with a reinforced concrete structure. They were two specific works, with projects imported from France, but necessary to definitively introduce this new material. At the same time, in Paris, most of the pavilions for the Universal Exposition of 1900 were being built with reinforced concrete. It was at the turn of the century when reinforced concrete constructions had already reached technical maturity in Europe. Despite the late incorporation, it can be seen from the works carried out that, in a short period of time, between 1901 and 1906, Spain reached the same technical and constructive level as the rest of the pioneering countries in the use of reinforced concrete. . The improvement and introduction of a constructive technique is not a followed process, since there are many elements that intervene. Patents were very important in the early development of reinforced concrete as they provided a certain guarantee that the product worked. It must be understood that the first reinforced concrete structures were not calculated as it is done today. They were bought as such and built, so the chances of collapse were minimal since the exact same structure was repeated. The patents sold structural systems whose operation was corroborated by the empirical experience and expertise of their inventor. These patents on reinforced concrete registered in Spain between 1884 and 1906 were a solid foundation that provided Spanish technicians and companies with constructive skills in the use of reinforced concrete. In this article, I analyse the study of the introduction process of reinforced concrete in Spain from a technical and playful perspective, from its introduction through patents to its rapid development and use between 1901 and 1906.
But first things first…what is concrete?
Concrete is a construction material made from cement, sand, gravel or ground stones, and together with steel, it is one of the most used in architecture and engineering works worldwide. One of its main characteristics is its high malleability since it allows a great variety of forms, its great stability, its durability, low cost and fast drying.
How is concrete made?
Concrete is manufactured in a concrete plant from the raw material that composes it: aggregate (sand and gravel), cement and water (it can also include other components such as additives, reinforcing fibres, etc.). These components, which are previously stored in the concrete plant, are dosed in the appropriate proportions, to be mixed in the case of mixing plants or directly unloaded into a truck mixer in the case of dosing plants.
The proportion of the concrete components is crucial to obtain the type of concrete required. The more water you add to it, the more manageable it will be, but it will also be less resistant.
The process requires that first of all, you have to mix the dry materials, that is, the cement, the sand and the gravel until everything has been homogenized. A good indication that this has occurred is when the mix takes on the greyish colour of cement. This indicates that the aggregates are ready to receive the water that is added little by little, and to mix progressively, assessing the consistency that the concrete acquires.
What are the general types of concrete that exist?
An immense variety of types of concrete has been created according to its use, properties, aesthetics, use that is going to be given to it in construction or due to the durability required of the material:
• Mass concrete: it is used to fill large volumes. The main property of this use is the ability of the material to support large vertical and symmetrical loads. When used in this way, it is necessary to irrigate the material to cool it down and thus avoid its cracking effects. This occurs due to thermal shock between the internal part of the concrete that is heated by the cement hydration process and the external part that usually cools more quickly. It is also necessary to take into account the climatic temperatures that are going to be concreted, trying to avoid the central hours of the day in the summer season.
• Structural concrete: According to the specifications indicated in the current Structural Concrete Instruction EHE-08, it is the concrete required in any type of reinforced or mass concrete structures, and used both in buildings and in civil works.
Its main applications are pillars, beams, walls, slabs, and screeds, it is usually used in any type of civil works or building, and its main characteristic is that it seeks to extend its durability and support the loads applied to it.
• Light concrete: also called cellular, it is a variety that seeks to reduce density and improve thermal and acoustic insulation. In addition, it is often used to regularize uneven floors, lighten structures or rehabilitate roofs in poor condition. It is a white material used in construction. It is obtained by means of a mixture of water, lime, silica sand and cement, to which an expanding agent is incorporated in the final phase of kneading. This reacts generating air bubbles inside the mass. This product was invented and patented by J.A. Ericsson in 1924. Ericsson was a Swedish architect who was looking for a material that had the advantages of wood in construction and eliminated its disadvantages: its need for maintenance, fragility, and combustibility. It was at the beginning of the 1960s, as a result of the growth experienced by the construction sector, when buildings began to require a greater insulation capacity to use in roofs and slabs in contact with the ground that was light and acted as a thermal insulator.
• Reinforced concrete: consists of joining concrete with steel to provide greater resistance to the structure. It is one of the most used in the construction of tunnels, bridges, buildings, roads, etc. Reinforced concrete works very well because two materials are joined: concrete and steel. This interaction between both materials allows the structural element to resist stresses both in traction and compression very well. An important problem with mass concrete (concrete without steel reinforcement) is that it behaves very badly when bone tension loads are applied to it, as in a beam, since it does not have tendons that constrain it, mass concrete would fail. Inserting reinforcement along the length of the beam gives you the strength of steel to cover that weak point. There are several synonymous names that describe l The union of these two construction materials: Reinforced concrete or reinforced concrete.
• Prestressed concrete: It tries to further improve tensile reinforced concrete, so it is built industrially with steel, subjecting it to compression actions before putting it into use. This type of concrete offers greater support to the structures, reducing the incidence of fissures and cracks and reducing the amount of steel that has to be introduced into the structure. It was patented in the year 1920, this concrete prestressing technique was designed to compensate for the tensile forces exerted on the concrete when it enters structural load. And it achieves this by introducing steel reinforcement in tension prior to the pouring of the concrete. In other words, prior to the pouring of the concrete, the bars, wires or steel cables are placed, which are tensioned before pouring the concrete. In this way, the mixture solidifies on the already-stressed reinforcements. Likewise, we can find another technique for manufacturing prestressed concrete, this is called post-stressing. In it, the metallic reinforcements are tensed once the concrete has already set and solidified, this is through the use of active reinforcements mounted on pods. This provides greater structural strength, as well as resistance to tensile forces.
• Polished concrete: Also called polished concrete, it is actually a decorative finish, it is not a purely said coating. This product is mainly used in exterior spaces of parking lots, shopping centres or sports fields and, sometimes, in some interiors. Polished cement is a finish made by dusting a cementitious mortar with aggregates and then buffing the floor to a shine with a rotary grinder. This technique of polishing the pavement is called trowelling. Polished cement is designed to cover large surfaces where the most important thing is the functionality of the pavement rather than its aesthetics. This is because polished cement is identified by its great stability and resistance, two elements that make it ideal for covering those industrial surfaces that are exposed to high traffic and weight. In fact, they are widely used for loading and unloading areas, since polished concrete paving does not break as easily as other types of finishes. In addition, polished cement pavements resist tire rolling very well. That is why we see this type of finish very frequently in car parks and car parks. Another of the qualities of polished cement floors is that their smooth and shiny surface prevents the accumulation of dust and dirt. A finish that also favours the feeling of spaciousness.
All the properties of concrete
Special types of concrete and their properties
With the passage of time, different types of concrete have been perfected to adapt to the needs of the market. Scientific and technical advances have made it possible to improve its resistance and prolong its useful life, which means that we can see concrete structures built in the fifties that are still in use without any indication of damage.
As we know, concrete has two states of the form: when it is freshly mixed and when it has set, that is, when it has hardened. The fresh state is the fresh mix of concrete components, which can still be cast into any shape. While the cured state is when the concrete has hardened and cannot be moulded without causing irreversible fractures. Fresh concrete is heterogeneous and is composed of solids, liquids and gases in equal proportion when well mixed. Its main properties are its consistency, docility, homogeneity and specific mass.
The consistency of concrete: It is the ability of fresh concrete to deform. It is mainly measured by the drop in centimetres in the Abrams cone test. This is; a conical vessel is filled with mixed concrete, turned upside down and placed on the ground. The collapse that the cone produces due to its own weight is measured in centimetres and this is the consistency of the concrete.
The consistency of the concrete is directly related to its dosage since the coherence of the different components depends on it, especially the volume of water within the mixture. Hence, we can say that the density, mechanical resistance, waterproofing, and even the surface finish of the concrete will depend on the consistency.
Docility: Very similar to the consistency of concrete. It is equivalent to the workability of fresh concrete. It is its ability to be placed at its destination with the means of compaction available. It is mainly measured by the drop in centimetres in the Abrams cone test.
Homogeneity: It is the quality of distribution throughout the mass of all the components of the concrete in the same proportions. The quality of homogeneity is opposed by the defect of segregation or settling. It is measured by the specific mass of portions of fresh concrete separated from each other. Specific mass: It is the relationship between the mass of fresh concrete and the occupied volume. It can be measured with compacted or uncompacted concrete. The density of freshly compacted concrete is a measure of the degree of effectiveness of the compaction method used. It is measured in kg/m3
Open time: It is the period of time that elapses between the mixing of the concrete and the beginning of the setting. It is a very important property because it is where the concrete can be handled without diminishing its characteristics. Sometimes the carriers add water to the dough to prolong this time but it drastically reduces the resistance of the same.
Properties of hardened concrete: The character of hardened concrete is acquired by the concrete from the end of the setting. Hardened concrete is made up of the aggregate, the hardened cement paste (which includes the water that has reacted with the cement compounds) and the open or closed pore networks resulting from the evaporation of excess water, occluded air (natural or caused for an additive). The properties of hardened concrete are Density: It is the ratio of the mass of the concrete and the volume occupied. For well-compacted concrete with normal aggregates, it ranges between 2,300-2,500 kg/m3. In the case of using light aggregates, the density ranges between 1000-1300 kg/m3. And if heavy aggregates are used, the density ranges between 3000-3500 kg/m3.
Compactness: It is the quality of having the maximum density that the materials used allow. The main characteristic of highly compact concrete is the best protection against the access of harmful substances to the reinforcement.
Permeability: Very similar to compactness and is the degree to which concrete is accessible to liquids or gases. The factor that most influence this property is the relationship between the amount of added water and cement in the concrete (w/c). The greater this ratio, the greater the permeability and therefore the more exposed the concrete is to potential attacks.
Resistance: Hardened concrete presents resistance to compression, traction and wear actions. Its main characteristic is its resistance to compression, which makes it the important material that it is. It is measured in Mpa (Megapascals) and can reach up to 50 Mpa in normal concrete and 100 Mpa in high-strength concrete. The tensile strength is much smaller if steel reinforcement is not used, but it is of great importance in certain applications. Wear resistance, of great interest in pavements, is achieved by using very resistant aggregates and very low water-cement ratios.
Hardness: It is the property that concrete has as a finish and that changes over time due to the phenomenon of carbonation. One method of measuring it is with the rebound rate provided by the Smichtd sclerometer using the Moh unit. A block of hardened polished concrete is a relatively hard material since its hardness varies between 6 and 7 Mohs.
Shrinkage: It is the phenomenon of concrete shrinkage due to the progressive evaporation of absorbed water that forms menisci on the periphery of the cement paste, and capillary water. In addition, in hardened concrete water is present in different states. We must take into account that after the setting of the concrete, which occurs in the first hours of life, generally between 2 and 10 hours, the concrete continues its setting process that can last for 28 days and goes between the plastic state and the state solid. Hydraulic shrinkage before setting is often referred to as the shrinkage that can occur before the solid state is reached, that is, hydraulic shrinkage before the end of the setting. Or, hydraulic shrinkage after setting when the concrete or concrete is in a solid state (without the physical-chemical processes having finished) and the post-setting stage begins. That is why it is important to spray the concrete with water during its curing stage to dissipate the heat and prevent it from cracking.
What are its advantages?
Concrete is one of the most used materials in Spanish construction because it is considered one of the most advantageous on the market in its price-quality factor:
• It is easily accessible thanks to its components that are abundant in nature and easy to extract.
• Reduces the risks of permeability.
• It is quick to adapt according to its structural purposes.
• It has very long durability, thanks to the quality of its properties.
• It is ductile and malleable.
• It is resistant to heat and, therefore, to deformation or collapse.
• It has high resistance to compression, bending, cutting and traction when reinforced with steel, making it a very safe material.
• Requires almost zero maintenance.
Is concrete sustainable?
A significant part of structures worldwide is made of concrete. Its use is increasingly linked to sustainability decisions, as it is a 100% recyclable material, contributes to the energy efficiency of buildings, reduces CO2 emissions and the temperature in urban environments, etc. These are some of its characteristics:
• Respect for the environment: concrete has the ability to absorb carbon from the atmosphere and reduce the amount of CO2 in the air. This is called the CO2 sink effect, which makes it a star resource in terms of sustainability.
• Contribution to global energy efficiency: concrete has the quality of being a thermal insulator, which allows energy consumption to be reduced as a result of temperature peaks, minimizing the energy cost of buildings, as well as collaborating in the reduction of greenhouse gases involved in energy production.
• High resistance: concrete gives buildings and bridges a lot of strength against fire or natural phenomena such as earthquakes, improving the service of the structures and their level of social security.
• Guarantee of quality of life for citizens: concrete has the quality of providing high durability to infrastructures, allowing their preservation with little maintenance costs.