Since ancient times, construction materials that can be called concrete have been used. Roman concrete was made from volcanic ash (pozzolana) and hydrated lime. Roman concrete was superior to other concrete recipes (for example, those consisting solely of sand and lime, usually called mortar)[2]​ used by other cultures. Apart from volcanic ash, brick dust could also be used to make conventional Roman concrete. In addition to conventional Roman concrete, the Romans also invented another mixture, from volcanic ash and clay.[3]​ But be careful: a mixture of lime, sand and water is a mortar, while a mixture of lime, sand, water and gravel is already lime concrete.

Some types of concrete used to make sculptures and planters are called artificial stone, cast stone, reconstituted stone or composite stone.[4]​ There is no single, precise formula that differentiates artificial stone from other construction materials where the binder is lime. This is because the term predates modern chemical science and has been attested since at least the 1790s.

In the century and later, the term artificial stone referred to various products, including numerous concretes where the binder was cement (a treated mixture of limestone and clay).[4]​ The English word cement, in addition to the same meaning of "treated mixture of limestone and clay" that it has in Spanish, means "anything that joins",[5]​ so that it can be said in English lime-cemented concretes, concretes where the binder is lime, called "lime concrete".

Foam concrete (foam concrete or foamed cement) is a cement-based material that incorporates stable air bubbles to create a lightweight and highly insulating product. Unlike air-entrained concrete, which introduces small air bubbles through an additive during mixing, foam concrete replaces coarse aggregates with these air bubbles, resulting in a significant difference in density: it varies from 400 to 1,600 kg/m, while air-entrained concrete maintains its density at about 2,000 kg/m.

Foam concrete is produced by mixing cement or fly ash, sand, water and an aerated synthetic foam, which provides stability to the air bubbles. It offers excellent thermal and acoustic insulation properties, making it suitable for applications such as insulating or filling gaps and trenches. Its lightweight nature also makes it easier to handle and transport compared to traditional concrete. Foam concrete can be easily molded into different shapes and sizes. Logically, it has less compressive strength than conventional concrete.

Vacuum concrete, made by using water vapor that produces a vacuum inside a concrete mixer to release air bubbles within the concrete, is being investigated. The idea is that the steam displaces the air normally over the concrete. When the steam condenses into water, it will create a low pressure on the concrete which will draw air out of it. This makes the concrete stronger due to less air in the mix. One disadvantage is that the mixture must be made in an airtight container.

The final strength of the concrete increases by approximately 25%. Vacuum concrete hardens very quickly, so forms can be removed only 30 minutes after pouring the mixture into them, even in columns 20 feet (6 meters) high. This is of considerable economic interest, especially in a precast factory, since the formwork can be reused at frequent intervals. The bond strength (of its components) of vacuum concrete is approximately 20% higher than that of normal concrete.

The surface of the vacuum concrete is completely free of pitting and the top layer, to a depth of 1/16 inch (1.6 millimeters), is highly abrasion resistant. These characteristics are of special importance in the construction of concrete structures that will be in contact with water flowing at high speed. It adheres well to old concrete and can therefore be used for renewing road slabs and other repair work.

Reinforced concrete is concrete poured into a formwork where there is a reinforcement of corrugated steel bars. Once solidified, the formwork is removed, and the bars remain within the concrete matrix, giving the assembly resistance to both compression and traction, making it very suitable for building in areas hit by earthquakes (anti-seismic construction) and has no maintenance costs.[6]​.

Asphalt concrete is a mixture of 2 types of aggregates and asphalt instead of cement. It doesn't carry water. As asphalt is solid at room temperature, it has to be heated to a temperature between 150 and 160 °C to make the mixture.[7]​.

This type of concrete is capable of developing high strength within hours of being poured (normal concrete takes 28 days to reach its maximum strength). This feature has advantages such as the possibility of removing the formwork early (also, depending on the applications, the formwork can be dispensed with and simply tamp the hot mixture after pouring it) and to advance the construction process very quickly, leaving the repaired road surfaces fully operational in just a few hours. Maximum strength and durability may vary from standard concrete, depending on composition details.

Normal concrete, once poured, needs to be compacted, usually with a vibrator, to remove air bubbles and excess water. The usual thing is to use electric vibrators. It can also be done with non-power tools. If this is not done, the resistance is lower and defects may appear. Concrete defects in Japan were found to be mainly due to the high water-cement ratio used to increase workability. Poor compaction was primarily due to the need for rapid construction in the 1960s and 1970s. Hajime Okamura foresaw the need for concrete that was highly workable and did not depend on mechanical force for compaction. During the 1980s, Okamura and his doctoral student Kazamasa Ozawa at the University of Tokyo developed self-compacting concrete (SCC), which was cohesive but fluid and took the shape of formwork without the need for mechanical compaction. In the United States, SCC is known as self-consolidating concrete.

The SCC is characterized by the following:

SCC can save up to 50% in labor cost due to 80% faster pouring and less formwork wear.

In 2005, self-compacting concretes accounted for 10 to 15% of concrete sales in some European countries. In the US precast concrete industry, SCC accounts for more than 75% of concrete production. 38 departments of transportation in the US accept the use of SCC for highway and bridge projects.

This emerging technology is made possible by the use of polycarboxylate plasticizers, instead of the older naphthalene-based polymers, and viscosity modifiers to prevent aggregates from segregating.

It is specially designed for radiation containment.[8]​.

Aerated concrete produced by adding an air-entraining agent to concrete (or a lightweight aggregate, such as expanded clay aggregate or cork and vermiculite granules) is sometimes called aerated concrete, lightweight aerated concrete, variable density concrete, lightweight or ultralight concrete,[9]​ which should not be confused with autoclaved aerated concrete, which is not self-nailing, but is treated in an autoclave, an apparatus for produce high pressures and temperatures. It is manufactured off-site using a completely different method.

In the 1977 work A Language of Patterns: Cities, Buildings and Construction, architect Christopher Alexander wrote in pattern 209 about "Good Materials":.

«Regular concrete is too dense. It is heavy and difficult to work with. After setting you cannot cut it or nail it. And its surface is ugly, cold and feels hard unless it is covered with expensive finishes that do not integrate the structure.

And yet, somehow concrete is a fascinating material. It is fluid, strong and relatively cheap. It is available in almost all parts of the world. A professor at the University of California, P. Kumar Mehta, has just found a way to convert rice husk waste into Portland cement. [...] Is there any way to bring together all these good qualities of concrete and also have a light material, easy to work with, with a pleasant finish? There is. It is possible to use a wide range of ultralight concretes with density and compressive strength very similar to those of wood. They are easy to work with, you can nail them with normal nails, they can be sawed, drilled, repaired easily.[...]

We believe that ultralight concrete is one of the fundamental mass materials of the future.

The density of a material is normally measured in kilograms per cubic meter of that material (kg/m³). That of regular concrete is around 2400 kg/m³. That of an ultralight concrete can reach 300 kg/m³,[9]​ although at this density it would not serve as a structural element (it would not support a load, it would break) and would function only as a filler or insulator. The less dense a concrete is, the less pressure it resists[9]​ and the more thermal and acoustic insulation it provides.[9]​ This is because it replaces coarse aggregates (stones, which conduct heat and sound well) with air or a light material such as clay, cork granules or vermiculite. There are numerous products that use a foaming agent similar to shaving cream to mix air bubbles with the concrete.

Applications of cellular concrete include:

Cyclopean concrete is the construction technique of adding smaller or larger stones while pouring normal concrete.[10]​.

Roller-compacted concrete, sometimes called rolled concrete, is a rigid, low-cement concrete that is installed using techniques borrowed from earthmoving and paving work. The concrete is placed on the surface to be covered and compacted there using large, heavy rollers normally used in earthmoving (rollers). The concrete mix reaches a high density and cures over time forming a strong monolithic block. Roller-compacted concrete is normally used for concrete pavements, but it has also been used to build concrete dams, since it allows for faster construction, and therefore, lower cost (the time during which the structure does not produce economic returns is shorter because it is still being built).[11]​.

Air-entrained concrete is a type of concrete that intentionally incorporates small air bubbles (10 to 500 micrometers in diameter) by adding an air-entraining agent during the mixing process. These air bubbles improve the workability of the concrete during placement and improve its durability when hardening, particularly in regions prone to freeze-thaw cycles. Unlike cellular concrete, which is lightweight and created by introducing stable air bubbles using a foaming agent, air-entrained concrete maintains its density (air is made up of 6–12% by volume). Other advantages that can be cited are: greater resistance to cracking and surface damage, greater durability against fire damage and general resistance. Additionally, air voids in air-entrained concrete act as internal cushioning, absorbing impact energy and increasing resistance to physical forces.

High-strength concrete or ultra-resistant concrete[12]​ has a compressive strength greater than 40 MPa (6,000 psi). In the UK, BS EN 206-1 defines high strength concrete as concrete with a compressive strength class greater than C50/60. High-strength concrete is made by reducing the water-cement (W/C) ratio to 0.35 or less. Silica fume is often added to prevent the formation of free calcium hydroxide crystals in the cement matrix, which could reduce the strength of the cement-aggregate bond.

The low water/cement ratios and the use of silica fume make this concrete mixtures significantly less workable, which can be a problem in applications where dense corrugated steel reinforcement is necessary. To compensate for this lower workability, superplasticizers are commonly added to high-strength mixes. Aggregates must be carefully selected for high-strength mixes, as weaker aggregates may not withstand high loads and cause failure (the crack that brings down the structure) to begin in the aggregate, rather than in the matrix or in an air bubble (the result of improper compaction of the concrete), as typically occurs in normal concrete.

In some high-strength concrete applications, the design criterion is not ultimate compressive strength, but elastic modulus.

Contenido

El hormigón de alto rendimiento (HPC por sus siglas en inglés) es un término relativamente nuevo para el hormigón que cumple un conjunto de estándares superiores a los de las aplicaciones más comunes, no solo en lo tocante a la resistencia. Si bien todo hormigón de alta resistencia también es de alto rendimiento, no todo hormigón de alto rendimiento es de alta resistencia. Algunos ejemplos de dichos estándares utilizados actualmente en relación con HPC son:.

El HPC es un hormigón que desarrolla una resistencia superior a 50 megapascales (7251,9 psi) a los 28, 56 o 90 días. Estas resistencias generalmente requieren agregados de roca dura bien calibrados (es decir, no vale cualquier tamaño de piedraː deben encontrarse en un intervalo específico de centímetros), una proporción bastante alta de cemento más cenizas volantes, aditivos reductores de agua y humo de sílice, con un contenido de agua relativamente bajo. Para dispersar adecuadamente el humo de sílice, que generalmente se suministra en formato granular, puede ser necesario mezclar el hormigón durante más tiempo. Las mezclas ricas pueden producir un alto calor de hidratación en colocaciones espesas, lo que se puede moderar utilizando una mayor proporción de cenizas volantes, hasta un 30 % del contenido de cemento. Asimismo, para incrementar la fluidez se puede utilizar polvo de piedra caliza.[13]​.

Ultra-high performance concrete

Ultra-high performance concrete (UHPC) is a new type of concrete being developed by agencies interested in infrastructure protection. UHPC is characterized by being a cement composite material reinforced with steel fiber with compressive strengths greater than 150 MPa and even 250 MPa.[15]​[16]​ UHPC is also characterized by its composition: normally without coarse aggregates, with fine-grained sand, fumed silica, small steel fibers and special high-strength Portland cement mixtures.

Current types of UHPC (Ductal, Taktl, etc.) differ from normal concrete in compression by their hardening upon deformation, followed by sudden brittle failure. Various government agencies and universities around the world are conducting ongoing research into tensile and shear (shear stress) failure of UHPC. Compression, tension and shear are the types of internal stress to which a concrete element can be subjected within a construction.

Micro-reinforced ultra-high performance concrete

This material is the next generation of UHPC. It has a three-dimensional, continuous and multi-layer microsteel mesh. In addition to the high compressive strength, durability, and abrasion resistance of UHPC, microreinforced UHPC is characterized by extreme ductility, energy absorption, and chemical, water, and temperature resistance.[17] It surpasses UHPC in durability, ductility, and strength, because the performance of the discontinuous and dispersed steel fibers in normal UHPC is relatively unpredictable, while microreinforced UHPC, with its ordered mesh, is It is used in explosion-, bomb-, and earthquake-resistant constructions, in structural and architectural overlays, and in complex facades.

The Ducon company was one of the first to develop microreinforced UHPC,[18][19]​ which has been used in the construction of the new World Trade Center (2001-present) "World Trade Center (2001-present)") in New York.[20][21][22]​.

Lime concrete is a mixture of 2 types of aggregates, water and lime "Lime (material)") instead of cement.[23]​ The difference with mortar is that it only contains one type of aggregate, the fine one (sand) and is used as a minor link for larger elements (bricks, window frames, etc.), while with lime concrete large architectural elements can be made, such as walls or vaults.[24]​.

A successful formula was developed in the middle of the century by Dr. John E. Park. Lime has been used since Roman times as both mass foundation concretes and lightweight concretes using a variety of aggregates combined with a wide range of pozzolans (baked materials) that help achieve greater strength and setting speed. Lime concrete was used to build monumental architecture during and after the Roman concrete revolution, as well as in a wide variety of applications such as floors, vaults or domes. Over the past decade, there has been renewed interest in using lime for these applications.

Environmental benefits.

Health benefits.

Rubberized concrete uses pieces of tires as aggregates. In addition to recycling this voluminous waste, it is more resistant than normal concrete, lighter and insulates better.[26]​.

The use of recycled glass as an aggregate in concrete has become common, with large-scale research being carried out at Columbia University in New York. This greatly improves the aesthetic appeal of the concrete. Recent research results have shown that concrete made with recycled glass aggregates has shown better long-term resistance and better thermal insulation, due to the better thermal properties of these aggregates.

Gypsum concrete is a construction material used as a base for floors [27]​ in wood-frame and concrete constructions for fire rating,[27]​ acoustic insulation,[27]​ radiant heating,[28]​ and floor leveling. It is a mixture of gypsum "Gypsum (mineral)"), Portland cement and sand.[27]​ One of its advantages is its lightness. It weighs less than normal concrete and maintains comparable compressive strength and costs. It is also easy to work with and level, allowing for faster installation and greater productivity. The use of gypsum concrete for radiant heated floors became popular in the 1980s with the introduction of cross-linked polyethylene (PEX) tubing, which is not susceptible to concrete corrosion. It should not be confused with lime concrete. Lime is calcium oxide or hydroxide, while gypsum is calcium sulfate.

Stamped concrete has a specific surface finish. After laying a concrete floor, the surface is impregnated with hardeners (they can be pigmented) and a mold is stamped, which can be textured to simulate stone, brick or even wood. After sufficient hardening, the surface is cleaned and its pores are usually sealed (for example with a coat of paint or enamel) to provide protection. The wear resistance of stamped concrete is generally excellent and is therefore found in applications such as parking lots, pavements, walkways, etc.

Ceramic aggregates with a density lower than that of water are used for low-density structural concrete. These aggregates may include expanded clays and shales, preferably with water absorption less than 10%. For structural concrete, exclusively low-density aggregates are used as coarse aggregates, and natural sand as fine aggregates. However, for moderate density concretes, lower percentages are used.[13]​.

Low-density structural concrete may exhibit high compressive and tensile strengths, with still acceptable creep and shrinkage, but will generally be less rigid than conventional mixes.

Its most obvious advantage is low density, but these concretes also have low water permeability, greater thermal insulation and represent less load for floating structures. The resistance to ice abrasion is similar to that of normal concrete.

The disadvantages are that water absorption by aggregates can be relatively high and consolidation of concrete by vibration can cause low-density aggregate to float. This can be avoided by minimizing vibration and using fluid mixtures.[13]​.

geopolymer concrete, green concrete or ecological concrete[29]​ uses geopolymer cement instead of Portland cement. This geopolymeric cement is composed of inorganic aluminosilicate (Al-Si) polymers that can use recycled industrial waste (e.g. fly ash or blast furnace slag) as manufacturing inputs, resulting in up to 80% lower carbon dioxide emissions. Due to its chemical structure, geopolymer concrete, in addition to lower greenhouse emissions, has greater durability than conventional concrete.

It uses lighter aggregates than normal concrete, such as slag, vermiculite, cork, straw and other materials.[10] Cork granules are a waste product from the production of bottle caps from the treated bark of the cork oak. These granules have a density of approximately 300 kg/m, lower than that of most other lightweight aggregates. Using them in the so-called cork concrete is a circular economy activity. Cork granules do not significantly influence cement hydration, but cork powder can.

Using cork instead of aggregates, or in addition to them, changes the characteristics of the product with respect to standard concrete: it reduces thermal conductivity (and therefore insulates better), reduces density and improves energy absorption, which may be appropriate for certain applications. The compressive strength decreases greatlyː a test of cork concrete found that, in the best case, it was 4.3 megapascals, one fifth of that of normal concrete.[30]​.

Normal concrete, conventional concrete, common concrete or standard concrete is that obtained by following the mixing instructions that usually appear on bags of cement, generally using sand and gravel as aggregates and often mixed in improvised containers (or directly without a container, pouring a bag of sand into the ground at the same time as another of cement, making a hole in the pile with the shovel, adding water and gravel and mixing with the same shovel). The ingredients of any particular mixture depend on the nature of the application. Ordinary concrete can generally withstand a pressure between 10 to 40 megapascals (MPa)—1,450 to (5,800 pounds per square inch (psi), an Anglo-Saxon unit of pressure. In less demanding uses, such as binder concrete, it withstands many fewer megapascals than structural concrete.

There are many types of ready-mixed concrete available that include powdered cement mixed with aggregates and that only need water.[31]​ There are also those that, in addition to water, require coarse aggregates.[32]​.

Normally, regular concrete can be made by mixing, for every kilo of Portland cement, 2 kilos of dry sand, 3 kilos of dry gravel and half a liter of water. The sand should be mortar or brick (washed and sifted if possible, with a sieve) and the gravel should be washed if possible. Organic materials (leaves, twigs, etc.) should be removed from sand and gravel to ensure maximum strength.[33]​.

Modular concrete consists of elements made in a factoryː the mixture is poured into a mold or formwork, and when it has hardened, it is removed from the mold and stored, waiting to take the elements, normally by truck, to their final location, where they will be fixed by the method chosen by the architect (cement mortar, adhesive resin, bolts and screws, etc.). Precast concrete are conceptually the same, but while the term "modular concrete" is used for elements that, when assembled, will make up a specific structure (a house, a bridge),[34]​ "precast concrete" is used for other elements (slabs, blocks) that are not intended for a specific configuration.

Concrete for marine habitat is used in artificial reefs. Concrete creates a refuge and a home for marine life.[35]​ These are normally prefabricated elements on land, with organic shapes, which are then placed in a studied way in marine environments.

For its part, percolated concrete consists of first placing the gravel and then pouring over it, or injecting, the cement and sand mortar.[36]​.

El hormigón permeable, utilizado en pavimentos permeables, contiene una red de poros o huecos para permitir que el aire o el agua se muevan a través del hormigón.

Esto permite que el agua se drene naturalmente a través de él y facilita la reposición de aguas subterráneas. Esto no lo hace el hormigón convencional, que además necesita infraestructura de drenaje de aguas superficiales.

Se produce dejando fuera parte o la totalidad del agregado fino (finos, arena). El agregado grueso restante (piedras) se liga con una cantidad relativamente pequeña de cemento Portland. Una vez fraguado, normalmente entre el 15 % y el 25 % del volumen corresponde a huecos, lo que permite que el agua drene a través de él con un caudal del orden de magnitud de 5 gal/ft /min (70 litros/m/minuto).

Facility

Pervious concrete is installed by pouring it into molds, then screeded to level the surface (but not smoothed), and then compacted or tamped into place. Due to the low water content and air permeability, 5 to 15 minutes after tamping, this concrete must be temporarily covered with a 6 mil (0.15 millimeter) polyethylene plastic, or it will dry prematurely and will not hydrate or cure properly. Once the curing process is complete, this plastic is removed and discarded.

Characteristics

Permeable concrete can significantly reduce traffic noise by allowing the air that the vehicle's tires squeeze against the pavement to easily escape. This product cannot currently be used on major US state highways due to the high pressure resistance requirements (pounds per square inch (psi)) set by most states for highways to withstand heavy trucks without cracking. Pervious concrete has been tested up to 4,500 psi.

Polymer concrete or polymer concrete uses polymers instead of cement to bind the aggregate. Polymeric concrete can gain a lot of strength in a short time. Its compressive strength is between 50 and 150 megapascals. It resists corrosion well and, when reinforced, has significantly greater adhesion to the reinforcement than normal concrete. On the other hand, it is susceptible to temperature and humidity.[37]​.

Prestressed concrete or prestressed concrete is reinforced concrete whose reinforcement is subjected to a tensile stress before installing the element in its final destination. It is a type of precast concrete. Sometimes we talk about post-tensioned concrete, in which the reinforcement is tensioned after it is installed.

Shotcrete (from shot, to shoot, and concrete, concrete, also known by the trade name Gunite, from gun, gun or cannon) uses compressed air to shoot concrete onto (or into) a frame or structure. The biggest advantage of the process is that shotcrete can be applied at heights or on vertical surfaces without formwork. It is often used for concrete repairs or placement on bridges, dams, swimming pools and in other applications where formwork is expensive or material handling and installation is difficult.

Shotcrete is frequently used against vertical soil or rock surfaces as it eliminates the need for formwork. It is sometimes used for rock support, especially in tunnels. Shotcrete is also used in cases where water seepage into an environment, due to a high water table or other underground sources, is a problem. This type of concrete is often used as a quick solution for erosion of loose soil types in construction zones.

There are 2 methods of applying shotcrete.

Additives such as accelerators or fiber reinforcements can be used for both methods.

High temperature applications, such as masonry kilns and the like, generally require the use of a refractory cement; If Portland cement-based concretes were used, they could be damaged or destroyed by these high temperatures, but refractory concretes are capable of withstanding them. Materials may include calcium aluminate cements, fireclay, ganister and high aluminum minerals.

Tabby concrete, also known as tabby concrete, is made by burning oyster shells to obtain lime and then mixing it with water, sand, ash and broken oyster shells.

Nanoconcrete contains nanoparticles (its largest dimension is less than 100 micrometers -microns-, μm). They can be made of Portland cement.[38]​ If they are made of silicon dioxide, the workability of the mixture, the resistance to compression and impermeability are improved.[39]​ If they are made of titanium dioxide, they give the finished element the ability to self-clean and eliminate contaminants.[40]​ If they are made of hematite, an iron oxide, with the formula FeO, the element, once loaded, can detect the compression it is undergoing without having to carry a sensor.[41] Other nanoparticles increase the modulus of elasticity or compressive strength.

Las investigaciones en curso sobre mezclas y componentes alternativos han identificado fórmulas que prometen nuevas propiedades y características.

Self-healing flexible concrete

Researchers at the University of Michigan have developed engineered cement composites (ECC), a flexible, fiber-reinforced concrete. It contains many of the ingredients used in normal concrete, but instead of coarse aggregate it includes microscale fibers.[42] The mixture has much lower crack propagation and does not suffer the usual cracking and subsequent loss of strength at high levels of tensile stress. Researchers have been able to push mixtures to a strain greater than 3 percent, beyond the more typical 0.1 percent point at which failure occurs. In addition, the composition of the material promotes self-healing. When cracks appear, excess dry cement in the concrete is exposed. It reacts with water and carbon dioxide to form calcium carbonate and repair the crack.[43][44]​.

Concretes that capture carbon dioxide

Researchers have attempted to fix CO in concrete by developing advanced materials. One way is to use magnesium silicate (talc) as an alternative to calcium. This reduces the temperature required for the production process and decreases the release of carbon dioxide during cement manufacturing. During the hardening phase, additional carbon is sequestered.[45][46][47][48][49] Reducing carbon dioxide emissions, or capturing carbon dioxide from the atmosphere, is of great importance, because this CO produces the greenhouse effect and global warming. Precisely, cement production is one of the industrial processes with the highest emissions, along with steel and aluminum.[50]​.

A related method is mineral carbonation (CM). Produces stable carbonate aggregates from materials containing calcium or magnesium and CO. Stable aggregates can be used for concrete or to produce carbon-neutral building elements, such as precast concrete or bricks.[45]​ [51]​[49]​ The company CarbonCure Technologies uses waste from oil refineries to make its bricks and wet cement mix, offsetting up to 5% of its carbon footprint.[45]​ [49]​ Solidia Technologies bakes its bricks and precast concrete at lower temperatures and cures them with gas, stating that it reduces its carbon emissions by 30%.[45]​ [49]​ Carbonaide") uses carbon dioxide in the curing phase of precast concrete production and has demonstrated savings of up to 40% in cement consumption with its first client.[52]​.

Another calcium-based mineral carbonation method has been inspired by the biomimetics of natural calcium structures. Ginger Krieg Dosier of bioMASON has developed a method to produce bricks without using kilns or releasing a significant amount of carbon. The bricks are grown in molds for four days using a microbiologically induced calcite precipitation process. The bacteria Sporosarcina pasteurii forms calcite from water, calcium and urea, incorporating CO from the urea and releasing ammonia for fertilizer.[45]​ [53]​.

A research team has discovered a way to use a form of microalgae called coccolithophores to mass produce calcium carbonate through photosynthesis at a faster rate than corals. They can survive in warm, cold, salt and fresh water. The technique has the potential to absorb more than it emits. Between 1 and 2 million acres of open ponds could supply enough microalgae to meet U.S. cement consumption. The team claims that the material can be immediately substituted into existing production processes.[54]​.

Living walls resistant to desiccation

Another approach involves the development of bioresponsive lightweight concrete that can be used to create desiccation-resistant living walls. Researchers at the Bartlett School of Architecture are developing materials aimed at promoting the growth of poikilohydric plants such as algae, mosses and lichens (organisms that have no mechanism to prevent desiccation). Once established, the combination of new materials and plants can potentially improve stormwater management and absorb pollutants.[55]​.

Eat smog

Titanium dioxide has been added to concrete mixes to reduce smog (pollution mixed with fog and smoke). When sunlight hits this concrete, titanium dioxide acts as a photocatalyst, breaking down smog and reducing the buildup of bacteria and dirt on the surface. It can also be used to decompose nitrogen dioxides created by industrial processes or by pollution from vehicles with thermal engines.[56]​.

energy generating concrete

Scientists from the University of Aarhus (Denmark) have integrated the bacteria Shewanella oneidensis into concrete, known for its ability to reduce metal ions (removing electrons from them), so that the whole becomes a battery that can store and release electrical energy. Scientists have also developed a microfluidic system to feed these bacteria, so that the behavior is permanent.[57]​.

Since ancient times, construction materials that can be called concrete have been used. Roman concrete was made from volcanic ash (pozzolana) and hydrated lime. Roman concrete was superior to other concrete recipes (for example, those consisting solely of sand and lime, usually called mortar)[2]​ used by other cultures. Apart from volcanic ash, brick dust could also be used to make conventional Roman concrete. In addition to conventional Roman concrete, the Romans also invented another mixture, from volcanic ash and clay.[3]​ But be careful: a mixture of lime, sand and water is a mortar, while a mixture of lime, sand, water and gravel is already lime concrete.

Some types of concrete used to make sculptures and planters are called artificial stone, cast stone, reconstituted stone or composite stone.[4]​ There is no single, precise formula that differentiates artificial stone from other construction materials where the binder is lime. This is because the term predates modern chemical science and has been attested since at least the 1790s.

In the century and later, the term artificial stone referred to various products, including numerous concretes where the binder was cement (a treated mixture of limestone and clay).[4]​ The English word cement, in addition to the same meaning of "treated mixture of limestone and clay" that it has in Spanish, means "anything that joins",[5]​ so that it can be said in English lime-cemented concretes, concretes where the binder is lime, called "lime concrete".

Foam concrete (foam concrete or foamed cement) is a cement-based material that incorporates stable air bubbles to create a lightweight and highly insulating product. Unlike air-entrained concrete, which introduces small air bubbles through an additive during mixing, foam concrete replaces coarse aggregates with these air bubbles, resulting in a significant difference in density: it varies from 400 to 1,600 kg/m, while air-entrained concrete maintains its density at about 2,000 kg/m.

Foam concrete is produced by mixing cement or fly ash, sand, water and an aerated synthetic foam, which provides stability to the air bubbles. It offers excellent thermal and acoustic insulation properties, making it suitable for applications such as insulating or filling gaps and trenches. Its lightweight nature also makes it easier to handle and transport compared to traditional concrete. Foam concrete can be easily molded into different shapes and sizes. Logically, it has less compressive strength than conventional concrete.

Vacuum concrete, made by using water vapor that produces a vacuum inside a concrete mixer to release air bubbles within the concrete, is being investigated. The idea is that the steam displaces the air normally over the concrete. When the steam condenses into water, it will create a low pressure on the concrete which will draw air out of it. This makes the concrete stronger due to less air in the mix. One disadvantage is that the mixture must be made in an airtight container.

The final strength of the concrete increases by approximately 25%. Vacuum concrete hardens very quickly, so forms can be removed only 30 minutes after pouring the mixture into them, even in columns 20 feet (6 meters) high. This is of considerable economic interest, especially in a precast factory, since the formwork can be reused at frequent intervals. The bond strength (of its components) of vacuum concrete is approximately 20% higher than that of normal concrete.

The surface of the vacuum concrete is completely free of pitting and the top layer, to a depth of 1/16 inch (1.6 millimeters), is highly abrasion resistant. These characteristics are of special importance in the construction of concrete structures that will be in contact with water flowing at high speed. It adheres well to old concrete and can therefore be used for renewing road slabs and other repair work.

Reinforced concrete is concrete poured into a formwork where there is a reinforcement of corrugated steel bars. Once solidified, the formwork is removed, and the bars remain within the concrete matrix, giving the assembly resistance to both compression and traction, making it very suitable for building in areas hit by earthquakes (anti-seismic construction) and has no maintenance costs.[6]​.

Asphalt concrete is a mixture of 2 types of aggregates and asphalt instead of cement. It doesn't carry water. As asphalt is solid at room temperature, it has to be heated to a temperature between 150 and 160 °C to make the mixture.[7]​.

This type of concrete is capable of developing high strength within hours of being poured (normal concrete takes 28 days to reach its maximum strength). This feature has advantages such as the possibility of removing the formwork early (also, depending on the applications, the formwork can be dispensed with and simply tamp the hot mixture after pouring it) and to advance the construction process very quickly, leaving the repaired road surfaces fully operational in just a few hours. Maximum strength and durability may vary from standard concrete, depending on composition details.

Normal concrete, once poured, needs to be compacted, usually with a vibrator, to remove air bubbles and excess water. The usual thing is to use electric vibrators. It can also be done with non-power tools. If this is not done, the resistance is lower and defects may appear. Concrete defects in Japan were found to be mainly due to the high water-cement ratio used to increase workability. Poor compaction was primarily due to the need for rapid construction in the 1960s and 1970s. Hajime Okamura foresaw the need for concrete that was highly workable and did not depend on mechanical force for compaction. During the 1980s, Okamura and his doctoral student Kazamasa Ozawa at the University of Tokyo developed self-compacting concrete (SCC), which was cohesive but fluid and took the shape of formwork without the need for mechanical compaction. In the United States, SCC is known as self-consolidating concrete.

The SCC is characterized by the following:

SCC can save up to 50% in labor cost due to 80% faster pouring and less formwork wear.

In 2005, self-compacting concretes accounted for 10 to 15% of concrete sales in some European countries. In the US precast concrete industry, SCC accounts for more than 75% of concrete production. 38 departments of transportation in the US accept the use of SCC for highway and bridge projects.

This emerging technology is made possible by the use of polycarboxylate plasticizers, instead of the older naphthalene-based polymers, and viscosity modifiers to prevent aggregates from segregating.

It is specially designed for radiation containment.[8]​.

Aerated concrete produced by adding an air-entraining agent to concrete (or a lightweight aggregate, such as expanded clay aggregate or cork and vermiculite granules) is sometimes called aerated concrete, lightweight aerated concrete, variable density concrete, lightweight or ultralight concrete,[9]​ which should not be confused with autoclaved aerated concrete, which is not self-nailing, but is treated in an autoclave, an apparatus for produce high pressures and temperatures. It is manufactured off-site using a completely different method.

In the 1977 work A Language of Patterns: Cities, Buildings and Construction, architect Christopher Alexander wrote in pattern 209 about "Good Materials":.

«Regular concrete is too dense. It is heavy and difficult to work with. After setting you cannot cut it or nail it. And its surface is ugly, cold and feels hard unless it is covered with expensive finishes that do not integrate the structure.

And yet, somehow concrete is a fascinating material. It is fluid, strong and relatively cheap. It is available in almost all parts of the world. A professor at the University of California, P. Kumar Mehta, has just found a way to convert rice husk waste into Portland cement. [...] Is there any way to bring together all these good qualities of concrete and also have a light material, easy to work with, with a pleasant finish? There is. It is possible to use a wide range of ultralight concretes with density and compressive strength very similar to those of wood. They are easy to work with, you can nail them with normal nails, they can be sawed, drilled, repaired easily.[...]

We believe that ultralight concrete is one of the fundamental mass materials of the future.

The density of a material is normally measured in kilograms per cubic meter of that material (kg/m³). That of regular concrete is around 2400 kg/m³. That of an ultralight concrete can reach 300 kg/m³,[9]​ although at this density it would not serve as a structural element (it would not support a load, it would break) and would function only as a filler or insulator. The less dense a concrete is, the less pressure it resists[9]​ and the more thermal and acoustic insulation it provides.[9]​ This is because it replaces coarse aggregates (stones, which conduct heat and sound well) with air or a light material such as clay, cork granules or vermiculite. There are numerous products that use a foaming agent similar to shaving cream to mix air bubbles with the concrete.

Applications of cellular concrete include:

Cyclopean concrete is the construction technique of adding smaller or larger stones while pouring normal concrete.[10]​.

Roller-compacted concrete, sometimes called rolled concrete, is a rigid, low-cement concrete that is installed using techniques borrowed from earthmoving and paving work. The concrete is placed on the surface to be covered and compacted there using large, heavy rollers normally used in earthmoving (rollers). The concrete mix reaches a high density and cures over time forming a strong monolithic block. Roller-compacted concrete is normally used for concrete pavements, but it has also been used to build concrete dams, since it allows for faster construction, and therefore, lower cost (the time during which the structure does not produce economic returns is shorter because it is still being built).[11]​.

Air-entrained concrete is a type of concrete that intentionally incorporates small air bubbles (10 to 500 micrometers in diameter) by adding an air-entraining agent during the mixing process. These air bubbles improve the workability of the concrete during placement and improve its durability when hardening, particularly in regions prone to freeze-thaw cycles. Unlike cellular concrete, which is lightweight and created by introducing stable air bubbles using a foaming agent, air-entrained concrete maintains its density (air is made up of 6–12% by volume). Other advantages that can be cited are: greater resistance to cracking and surface damage, greater durability against fire damage and general resistance. Additionally, air voids in air-entrained concrete act as internal cushioning, absorbing impact energy and increasing resistance to physical forces.

High-strength concrete or ultra-resistant concrete[12]​ has a compressive strength greater than 40 MPa (6,000 psi). In the UK, BS EN 206-1 defines high strength concrete as concrete with a compressive strength class greater than C50/60. High-strength concrete is made by reducing the water-cement (W/C) ratio to 0.35 or less. Silica fume is often added to prevent the formation of free calcium hydroxide crystals in the cement matrix, which could reduce the strength of the cement-aggregate bond.

The low water/cement ratios and the use of silica fume make this concrete mixtures significantly less workable, which can be a problem in applications where dense corrugated steel reinforcement is necessary. To compensate for this lower workability, superplasticizers are commonly added to high-strength mixes. Aggregates must be carefully selected for high-strength mixes, as weaker aggregates may not withstand high loads and cause failure (the crack that brings down the structure) to begin in the aggregate, rather than in the matrix or in an air bubble (the result of improper compaction of the concrete), as typically occurs in normal concrete.

In some high-strength concrete applications, the design criterion is not ultimate compressive strength, but elastic modulus.

Contenido

El hormigón de alto rendimiento (HPC por sus siglas en inglés) es un término relativamente nuevo para el hormigón que cumple un conjunto de estándares superiores a los de las aplicaciones más comunes, no solo en lo tocante a la resistencia. Si bien todo hormigón de alta resistencia también es de alto rendimiento, no todo hormigón de alto rendimiento es de alta resistencia. Algunos ejemplos de dichos estándares utilizados actualmente en relación con HPC son:.

El HPC es un hormigón que desarrolla una resistencia superior a 50 megapascales (7251,9 psi) a los 28, 56 o 90 días. Estas resistencias generalmente requieren agregados de roca dura bien calibrados (es decir, no vale cualquier tamaño de piedraː deben encontrarse en un intervalo específico de centímetros), una proporción bastante alta de cemento más cenizas volantes, aditivos reductores de agua y humo de sílice, con un contenido de agua relativamente bajo. Para dispersar adecuadamente el humo de sílice, que generalmente se suministra en formato granular, puede ser necesario mezclar el hormigón durante más tiempo. Las mezclas ricas pueden producir un alto calor de hidratación en colocaciones espesas, lo que se puede moderar utilizando una mayor proporción de cenizas volantes, hasta un 30 % del contenido de cemento. Asimismo, para incrementar la fluidez se puede utilizar polvo de piedra caliza.[13]​.

Ultra-high performance concrete

Ultra-high performance concrete (UHPC) is a new type of concrete being developed by agencies interested in infrastructure protection. UHPC is characterized by being a cement composite material reinforced with steel fiber with compressive strengths greater than 150 MPa and even 250 MPa.[15]​[16]​ UHPC is also characterized by its composition: normally without coarse aggregates, with fine-grained sand, fumed silica, small steel fibers and special high-strength Portland cement mixtures.

Current types of UHPC (Ductal, Taktl, etc.) differ from normal concrete in compression by their hardening upon deformation, followed by sudden brittle failure. Various government agencies and universities around the world are conducting ongoing research into tensile and shear (shear stress) failure of UHPC. Compression, tension and shear are the types of internal stress to which a concrete element can be subjected within a construction.

Micro-reinforced ultra-high performance concrete

This material is the next generation of UHPC. It has a three-dimensional, continuous and multi-layer microsteel mesh. In addition to the high compressive strength, durability, and abrasion resistance of UHPC, microreinforced UHPC is characterized by extreme ductility, energy absorption, and chemical, water, and temperature resistance.[17] It surpasses UHPC in durability, ductility, and strength, because the performance of the discontinuous and dispersed steel fibers in normal UHPC is relatively unpredictable, while microreinforced UHPC, with its ordered mesh, is It is used in explosion-, bomb-, and earthquake-resistant constructions, in structural and architectural overlays, and in complex facades.

The Ducon company was one of the first to develop microreinforced UHPC,[18][19]​ which has been used in the construction of the new World Trade Center (2001-present) "World Trade Center (2001-present)") in New York.[20][21][22]​.

Lime concrete is a mixture of 2 types of aggregates, water and lime "Lime (material)") instead of cement.[23]​ The difference with mortar is that it only contains one type of aggregate, the fine one (sand) and is used as a minor link for larger elements (bricks, window frames, etc.), while with lime concrete large architectural elements can be made, such as walls or vaults.[24]​.

A successful formula was developed in the middle of the century by Dr. John E. Park. Lime has been used since Roman times as both mass foundation concretes and lightweight concretes using a variety of aggregates combined with a wide range of pozzolans (baked materials) that help achieve greater strength and setting speed. Lime concrete was used to build monumental architecture during and after the Roman concrete revolution, as well as in a wide variety of applications such as floors, vaults or domes. Over the past decade, there has been renewed interest in using lime for these applications.

Environmental benefits.

Health benefits.

Rubberized concrete uses pieces of tires as aggregates. In addition to recycling this voluminous waste, it is more resistant than normal concrete, lighter and insulates better.[26]​.

The use of recycled glass as an aggregate in concrete has become common, with large-scale research being carried out at Columbia University in New York. This greatly improves the aesthetic appeal of the concrete. Recent research results have shown that concrete made with recycled glass aggregates has shown better long-term resistance and better thermal insulation, due to the better thermal properties of these aggregates.

Gypsum concrete is a construction material used as a base for floors [27]​ in wood-frame and concrete constructions for fire rating,[27]​ acoustic insulation,[27]​ radiant heating,[28]​ and floor leveling. It is a mixture of gypsum "Gypsum (mineral)"), Portland cement and sand.[27]​ One of its advantages is its lightness. It weighs less than normal concrete and maintains comparable compressive strength and costs. It is also easy to work with and level, allowing for faster installation and greater productivity. The use of gypsum concrete for radiant heated floors became popular in the 1980s with the introduction of cross-linked polyethylene (PEX) tubing, which is not susceptible to concrete corrosion. It should not be confused with lime concrete. Lime is calcium oxide or hydroxide, while gypsum is calcium sulfate.

Stamped concrete has a specific surface finish. After laying a concrete floor, the surface is impregnated with hardeners (they can be pigmented) and a mold is stamped, which can be textured to simulate stone, brick or even wood. After sufficient hardening, the surface is cleaned and its pores are usually sealed (for example with a coat of paint or enamel) to provide protection. The wear resistance of stamped concrete is generally excellent and is therefore found in applications such as parking lots, pavements, walkways, etc.

Ceramic aggregates with a density lower than that of water are used for low-density structural concrete. These aggregates may include expanded clays and shales, preferably with water absorption less than 10%. For structural concrete, exclusively low-density aggregates are used as coarse aggregates, and natural sand as fine aggregates. However, for moderate density concretes, lower percentages are used.[13]​.

Low-density structural concrete may exhibit high compressive and tensile strengths, with still acceptable creep and shrinkage, but will generally be less rigid than conventional mixes.

Its most obvious advantage is low density, but these concretes also have low water permeability, greater thermal insulation and represent less load for floating structures. The resistance to ice abrasion is similar to that of normal concrete.

The disadvantages are that water absorption by aggregates can be relatively high and consolidation of concrete by vibration can cause low-density aggregate to float. This can be avoided by minimizing vibration and using fluid mixtures.[13]​.

geopolymer concrete, green concrete or ecological concrete[29]​ uses geopolymer cement instead of Portland cement. This geopolymeric cement is composed of inorganic aluminosilicate (Al-Si) polymers that can use recycled industrial waste (e.g. fly ash or blast furnace slag) as manufacturing inputs, resulting in up to 80% lower carbon dioxide emissions. Due to its chemical structure, geopolymer concrete, in addition to lower greenhouse emissions, has greater durability than conventional concrete.

It uses lighter aggregates than normal concrete, such as slag, vermiculite, cork, straw and other materials.[10] Cork granules are a waste product from the production of bottle caps from the treated bark of the cork oak. These granules have a density of approximately 300 kg/m, lower than that of most other lightweight aggregates. Using them in the so-called cork concrete is a circular economy activity. Cork granules do not significantly influence cement hydration, but cork powder can.

Using cork instead of aggregates, or in addition to them, changes the characteristics of the product with respect to standard concrete: it reduces thermal conductivity (and therefore insulates better), reduces density and improves energy absorption, which may be appropriate for certain applications. The compressive strength decreases greatlyː a test of cork concrete found that, in the best case, it was 4.3 megapascals, one fifth of that of normal concrete.[30]​.

Normal concrete, conventional concrete, common concrete or standard concrete is that obtained by following the mixing instructions that usually appear on bags of cement, generally using sand and gravel as aggregates and often mixed in improvised containers (or directly without a container, pouring a bag of sand into the ground at the same time as another of cement, making a hole in the pile with the shovel, adding water and gravel and mixing with the same shovel). The ingredients of any particular mixture depend on the nature of the application. Ordinary concrete can generally withstand a pressure between 10 to 40 megapascals (MPa)—1,450 to (5,800 pounds per square inch (psi), an Anglo-Saxon unit of pressure. In less demanding uses, such as binder concrete, it withstands many fewer megapascals than structural concrete.

There are many types of ready-mixed concrete available that include powdered cement mixed with aggregates and that only need water.[31]​ There are also those that, in addition to water, require coarse aggregates.[32]​.

Normally, regular concrete can be made by mixing, for every kilo of Portland cement, 2 kilos of dry sand, 3 kilos of dry gravel and half a liter of water. The sand should be mortar or brick (washed and sifted if possible, with a sieve) and the gravel should be washed if possible. Organic materials (leaves, twigs, etc.) should be removed from sand and gravel to ensure maximum strength.[33]​.

Modular concrete consists of elements made in a factoryː the mixture is poured into a mold or formwork, and when it has hardened, it is removed from the mold and stored, waiting to take the elements, normally by truck, to their final location, where they will be fixed by the method chosen by the architect (cement mortar, adhesive resin, bolts and screws, etc.). Precast concrete are conceptually the same, but while the term "modular concrete" is used for elements that, when assembled, will make up a specific structure (a house, a bridge),[34]​ "precast concrete" is used for other elements (slabs, blocks) that are not intended for a specific configuration.

Concrete for marine habitat is used in artificial reefs. Concrete creates a refuge and a home for marine life.[35]​ These are normally prefabricated elements on land, with organic shapes, which are then placed in a studied way in marine environments.

For its part, percolated concrete consists of first placing the gravel and then pouring over it, or injecting, the cement and sand mortar.[36]​.

El hormigón permeable, utilizado en pavimentos permeables, contiene una red de poros o huecos para permitir que el aire o el agua se muevan a través del hormigón.

Esto permite que el agua se drene naturalmente a través de él y facilita la reposición de aguas subterráneas. Esto no lo hace el hormigón convencional, que además necesita infraestructura de drenaje de aguas superficiales.

Se produce dejando fuera parte o la totalidad del agregado fino (finos, arena). El agregado grueso restante (piedras) se liga con una cantidad relativamente pequeña de cemento Portland. Una vez fraguado, normalmente entre el 15 % y el 25 % del volumen corresponde a huecos, lo que permite que el agua drene a través de él con un caudal del orden de magnitud de 5 gal/ft /min (70 litros/m/minuto).

Facility

Pervious concrete is installed by pouring it into molds, then screeded to level the surface (but not smoothed), and then compacted or tamped into place. Due to the low water content and air permeability, 5 to 15 minutes after tamping, this concrete must be temporarily covered with a 6 mil (0.15 millimeter) polyethylene plastic, or it will dry prematurely and will not hydrate or cure properly. Once the curing process is complete, this plastic is removed and discarded.

Characteristics

Permeable concrete can significantly reduce traffic noise by allowing the air that the vehicle's tires squeeze against the pavement to easily escape. This product cannot currently be used on major US state highways due to the high pressure resistance requirements (pounds per square inch (psi)) set by most states for highways to withstand heavy trucks without cracking. Pervious concrete has been tested up to 4,500 psi.

Polymer concrete or polymer concrete uses polymers instead of cement to bind the aggregate. Polymeric concrete can gain a lot of strength in a short time. Its compressive strength is between 50 and 150 megapascals. It resists corrosion well and, when reinforced, has significantly greater adhesion to the reinforcement than normal concrete. On the other hand, it is susceptible to temperature and humidity.[37]​.

Prestressed concrete or prestressed concrete is reinforced concrete whose reinforcement is subjected to a tensile stress before installing the element in its final destination. It is a type of precast concrete. Sometimes we talk about post-tensioned concrete, in which the reinforcement is tensioned after it is installed.

Shotcrete (from shot, to shoot, and concrete, concrete, also known by the trade name Gunite, from gun, gun or cannon) uses compressed air to shoot concrete onto (or into) a frame or structure. The biggest advantage of the process is that shotcrete can be applied at heights or on vertical surfaces without formwork. It is often used for concrete repairs or placement on bridges, dams, swimming pools and in other applications where formwork is expensive or material handling and installation is difficult.

Shotcrete is frequently used against vertical soil or rock surfaces as it eliminates the need for formwork. It is sometimes used for rock support, especially in tunnels. Shotcrete is also used in cases where water seepage into an environment, due to a high water table or other underground sources, is a problem. This type of concrete is often used as a quick solution for erosion of loose soil types in construction zones.

There are 2 methods of applying shotcrete.

Additives such as accelerators or fiber reinforcements can be used for both methods.

High temperature applications, such as masonry kilns and the like, generally require the use of a refractory cement; If Portland cement-based concretes were used, they could be damaged or destroyed by these high temperatures, but refractory concretes are capable of withstanding them. Materials may include calcium aluminate cements, fireclay, ganister and high aluminum minerals.

Tabby concrete, also known as tabby concrete, is made by burning oyster shells to obtain lime and then mixing it with water, sand, ash and broken oyster shells.

Nanoconcrete contains nanoparticles (its largest dimension is less than 100 micrometers -microns-, μm). They can be made of Portland cement.[38]​ If they are made of silicon dioxide, the workability of the mixture, the resistance to compression and impermeability are improved.[39]​ If they are made of titanium dioxide, they give the finished element the ability to self-clean and eliminate contaminants.[40]​ If they are made of hematite, an iron oxide, with the formula FeO, the element, once loaded, can detect the compression it is undergoing without having to carry a sensor.[41] Other nanoparticles increase the modulus of elasticity or compressive strength.

Las investigaciones en curso sobre mezclas y componentes alternativos han identificado fórmulas que prometen nuevas propiedades y características.

Self-healing flexible concrete

Researchers at the University of Michigan have developed engineered cement composites (ECC), a flexible, fiber-reinforced concrete. It contains many of the ingredients used in normal concrete, but instead of coarse aggregate it includes microscale fibers.[42] The mixture has much lower crack propagation and does not suffer the usual cracking and subsequent loss of strength at high levels of tensile stress. Researchers have been able to push mixtures to a strain greater than 3 percent, beyond the more typical 0.1 percent point at which failure occurs. In addition, the composition of the material promotes self-healing. When cracks appear, excess dry cement in the concrete is exposed. It reacts with water and carbon dioxide to form calcium carbonate and repair the crack.[43][44]​.

Concretes that capture carbon dioxide

Researchers have attempted to fix CO in concrete by developing advanced materials. One way is to use magnesium silicate (talc) as an alternative to calcium. This reduces the temperature required for the production process and decreases the release of carbon dioxide during cement manufacturing. During the hardening phase, additional carbon is sequestered.[45][46][47][48][49] Reducing carbon dioxide emissions, or capturing carbon dioxide from the atmosphere, is of great importance, because this CO produces the greenhouse effect and global warming. Precisely, cement production is one of the industrial processes with the highest emissions, along with steel and aluminum.[50]​.

A related method is mineral carbonation (CM). Produces stable carbonate aggregates from materials containing calcium or magnesium and CO. Stable aggregates can be used for concrete or to produce carbon-neutral building elements, such as precast concrete or bricks.[45]​ [51]​[49]​ The company CarbonCure Technologies uses waste from oil refineries to make its bricks and wet cement mix, offsetting up to 5% of its carbon footprint.[45]​ [49]​ Solidia Technologies bakes its bricks and precast concrete at lower temperatures and cures them with gas, stating that it reduces its carbon emissions by 30%.[45]​ [49]​ Carbonaide") uses carbon dioxide in the curing phase of precast concrete production and has demonstrated savings of up to 40% in cement consumption with its first client.[52]​.

Another calcium-based mineral carbonation method has been inspired by the biomimetics of natural calcium structures. Ginger Krieg Dosier of bioMASON has developed a method to produce bricks without using kilns or releasing a significant amount of carbon. The bricks are grown in molds for four days using a microbiologically induced calcite precipitation process. The bacteria Sporosarcina pasteurii forms calcite from water, calcium and urea, incorporating CO from the urea and releasing ammonia for fertilizer.[45]​ [53]​.

A research team has discovered a way to use a form of microalgae called coccolithophores to mass produce calcium carbonate through photosynthesis at a faster rate than corals. They can survive in warm, cold, salt and fresh water. The technique has the potential to absorb more than it emits. Between 1 and 2 million acres of open ponds could supply enough microalgae to meet U.S. cement consumption. The team claims that the material can be immediately substituted into existing production processes.[54]​.

Living walls resistant to desiccation

Another approach involves the development of bioresponsive lightweight concrete that can be used to create desiccation-resistant living walls. Researchers at the Bartlett School of Architecture are developing materials aimed at promoting the growth of poikilohydric plants such as algae, mosses and lichens (organisms that have no mechanism to prevent desiccation). Once established, the combination of new materials and plants can potentially improve stormwater management and absorb pollutants.[55]​.

Eat smog

Titanium dioxide has been added to concrete mixes to reduce smog (pollution mixed with fog and smoke). When sunlight hits this concrete, titanium dioxide acts as a photocatalyst, breaking down smog and reducing the buildup of bacteria and dirt on the surface. It can also be used to decompose nitrogen dioxides created by industrial processes or by pollution from vehicles with thermal engines.[56]​.

energy generating concrete

Scientists from the University of Aarhus (Denmark) have integrated the bacteria Shewanella oneidensis into concrete, known for its ability to reduce metal ions (removing electrons from them), so that the whole becomes a battery that can store and release electrical energy. Scientists have also developed a microfluidic system to feed these bacteria, so that the behavior is permanent.[57]​.