Use of concrete dates back to 3000BC and was only used for industrial purposes. But as time passes it has become one of the most standard materials used and even plays a major role in the infrastructure sector. This fact itself makes it a potential subject for researchers who are in line to concrete production and development. However present-day research shows that some of the current concrete treatment methods, such as the application of chemicals and polymers in the production of concrete are a source of many health and environmental risks, are effective only in the short-term.
In line with this matter, researchers and engineers aim to further develop concrete and produce a type which possesses better properties. This is mainly for the fact that the existing concrete formula has not only health and environmental hazards but also has several limitations in many aspects like in the terms of its strength, ductility, resistance to strain, durability, water absorption capacity, brittleness, resistance to cracking and self-healing.
Traditional concrete is composed of cement, composed primarily of water and fine and coarse aggregates. While modern concrete, despite maintaining the traditional mixture, has additional components called Admixtures. Admixtures are additives which aids the original mixture and improves its quality, manageability, acceleration and retardation of time, and its pouring capacity.
These admixtures has its unique chemical compounds in which each has a specific function in the final mixture. Such functions are achieved with the use of the following compounds [1] Lignosulfunate and Hydrocarboxilic acids collected from wood and chemical bybroduct for water reduction.
[2] Abietic and pimeric acids Alkyl-aryl sulphonates from wood resins and industrial detergents for air entrainment. [3] Fatty acids from Vegegtable and animal fats for waterproofing. [4] Calcium Chlorate, Calcium formate and Triethanolamine from chemical production by-products for accelaration of both setting and hardening capabilities while reducing chloroaluminate hydrates, which causes softening. And [5] Borates and Magnesium salts obtained from Borax mining and chemical production for the Retardation of the cement in concrete. These additives may be added before or after the mixing process of concrete.
In this case most type of concrete uses Portland Cement, invented by Joseph Aspidin (1824), which is actually burnt ground chalk and clay removed of Carbon dioxide (CO2) better known as Lime or calcium oxide, CaO: from limestone, chalk, shells, shale or calcareous rock ,Silica, SiO2: from sand, old bottles, clay or argillaceous rock, Alumina, Al2O3: from bauxite, recycled aluminum, clay, Iron, Fe2O3: from from clay, iron ore, scrap iron and fly ash, Gypsum, CaSO4.2H20: found together with limestone. Global Concrete Production industry makes about over 37 billion dollars yearly with a production amount of 10 billion tons of concrete.
In relation to this the chemical reaction from the overall production of cement affects the environment with just from the chemical reaction of CaCO3 to yield CaO and Carbon dioxide (CO2) accounted to an amount of 5 % of CO2 annually released in the atmosphere. The additives of silicon and aluminium oxides in the concrete mixture releases heat in the process thus varying amount account to varying levels of heat in which it affects the concrete design itself. In recent happening fly ash was used to partially to replace Portland cement as both a strengthening factor and also an environmentally friendly way to manufacture cement.
Currently concrete is considered to have high versatility as a construction material and is suited for agricultural applications. However the current mixture and composition of concrete shows numerous deficiencies from its permeability and durability. In terms of its mechanical properties concrete is quasi brittle which is one of the three major modes of failure of materials [1] quasi brittle failure, [2] brittle, and [3] ductile failure. Quasi-brittle failure is where concrete exhibits a strain-softening behaviour which undergo very little deformations before failure. Where the Less the deformation is, the lesser will be the warnings.
Concrete also possesses [1] low tensile strength of 1/10th of its compressive strength that’s why reinforcement of fibres and polymers are used, [2] low ability to consume impact energy of only 1-2 % of steel thus needed to be enforced with fibres, [3] low specific strength, [4] has long curing time of 28-30 days due to the reaction of chemicals that leads to the release of heat in the mixture, [5] requires formwork, which is expensive, to support its own weight. [6] Demands strict quality control of labour during mixing, placing, and curing to achieve superior quality and the most common issue of concrete is that [7] it is easily cracked when tensile stress at extreme fibre exceeds the tensile capacity of concrete due to many reason like shrinkage, inadequate water for hydration etc, which is why even the tiniest crack leads to corrosion of reinforcements which then causes degradation of concrete leading to ingress of deleterious substances into concrete, resulting in deterioration of structures.
Although it is not possible to wholly prevent crack formation, various types of techniques are used to aid the crack in performing self -healing. In order to achieve such actions of without producing health and environmental hazards, treatment methods that are environmentally friendly and long-lasting like the process of Bio-mineralization are high in demand.
Bio-mineralization process is a sophisticated process and a widespread phenomenon in nature leading to the formation of a variety of inorganic minerals by living organisms. Thus the idea of having the addition of urease engendering bacteria along with calcium source which ensues to precipitation of calcite, the most thermally stable form of the three forms of calcium carbonate, in concrete allowing smooth transition of reaction with the ureolytic bacteria to achieve self-healing potential of it being long-lasting, rapid, and achieve active crack repair, with the addition of extended service life.
Furthermore, present studies showed that the use of these bacteria-based self-healing approach prevails the other treatment techniques due to the efficient bonding capacity and compatibility with concrete compositions. Thus the development of Bacterial Concrete or simply Bioconcrete .
Bioconcrete is a special type of concrete invented by Microbiology Researcher Henk Jonkers and his team which is specially designed to increase the concrete’s lifespan by increasing the durability of the its structure by attaining self-healing capacity aided by uerolytic bacteria and its precursor.
These co-called urease engendering bacteria are non-pathogenic laboratory cultivated species that can resists alkaline levels and mechanical stress present in concrete mixture. In a crack of a bioconcrete, water is forced into the crack in which bacteria from genus Bacillus, specifically either B.Pseudofirmus, B. Cohnii, B. Filla and B. Pasteurii and B. Subtilis, and reacts with it. Depending on the type of uerolytic bacteria used in the process affects the quality and performance of the bioconcrete, thus having a variety. The bacteria then germinates and generates urea which is then integrated along with the calcium precursor: Calcium lactate (Ca(C3H5O2)2, activating it, letting bacterial germinating spores to produces biominerals through metabolic reaction at 25o C and freshly seal micro cracks by Calcium carbonate (CaCO3), an active ingredient in agricultural lime created when calcium ions in hard water react with carbonate ions to create limescale, precipitation forming a base called Limestone to fill in the crack. This chemical process is known as Microbiologically Induced Calcium Carbonate Precipitation (MICCP)
Given these type of concrete it also has 2 ways of it being applied. [1] Direct application, where the bacteria specie with the calcium lactate are directly added while making the concrete and [2] Encapsulation Light Weight Aggregate method is where part of the coarse aggregates is replaced by light weight aggregate infused with twice the amount of calcium lactate solution and bacterial spores placed inside biodegradable capsules is mixed with clay particles, composed 6% healing agents. Whenever concretes crack, water enters the capsules and being biodegradable the capsules break. Then the bacteria is released to slowly feed on the lactate and forms limestone.
In the construction industry, Concrete is the most widely-used material in the world. Concrete has been used to build stunning infrastructures all around the world. However no matter how well concrete is reinforced and preserved, it will eventually crack. And it being prone to frequent cracking is its’ major flaw as repairs and maintenance are both expensive and intensive and that it affects the most significant attributes of concrete which are its compressive strength and durability. With concrete being used in almost everything, no wonder numerous researchers, scientists and even engineers race to produce stronger and efficient cement. Thus enters the invention of a self-healing concrete infused with bacteria now called as an ingenious creation to become a building material to replace traditional concrete. Bioconcrete possesses the capabilities that is considered to be the shortcomings of concrete. Such capabilities are: [1] Self-healing ability, [2] Decreases permeability of water and other liquids, [3] Splitting Tensile strength is increased, [4] Increased durability, [5] Maintenance cost is lower than concretes’, [6] Compressive Strength is increased, and [7] Concrete Durability is increased through the encapsulation method.
While the concept might of its creation seemed easy and straightforward, developing this self-healing concrete to be of use in major construction projects and the likes would be no easy task. Even its invertors consumed 3 years of research as to how to make a living microorganism survive in a dry stone-like material such as concrete. Thus having them utilize and produce a bacteria that feeds on calcium rather than sugar, which was eliminated for sugar softens and makes concrete weak. And that showed in an experiment which used the Encapsulation method that the bacterial spores would be crushed by smaller holes and that majority of the bacterial spores in the cures cement mixture were less available for less than four months. Currently this type of bioconcrete is being tested in the United Kingdom in a project entitled: Material for Life (M4L) which is piloting three separate concrete-healing technologies for the first time in real-world settings, with a view to incorporating them into a single system that could be used to automatically repair concrete in the built environment. In line with this a number of ongoing studies targets the weak aspects and if deemed successful it could pave a way for the era of low-cost biological buildings.
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