Bio Concrete

 

                                                 BIO CONCRETE

TABLE OF CONTENT

1.   INTODUCTION………………………………….07

2.   METHOD OF USING & ITS MECHANISM.…..14

3.   COMPARISION  WITH  CONVENTIONAL CONCRETE……………………………………….18

4.   MERITS AND DEMERITS……………………….26

5.   SCH IN INDIA…………………………………….29

6.   CONCLUSION…………………………………….33

INTRODUCTION

Concrete: The word concrete is originated from the Latin word “concretus” which means condensed and hardened. The earliest use of cement is dated back to twelve million years ago, while the early use of concrete-like building material is dated back to 6500 BC. However, it wasn’t formed as concrete until later during the Roman Empire.

Concrete is a composite mixture of coarse aggregate, fine aggregate and binding material such as cement, lime etc with water in a definite ratio.

As revolutionary as it was and still is, modern concrete has a short lifespan caused by the formation of cracks shortening the longevity of a particular construction. Many researchers have been attempting to improve concrete in order to get a better longevity among many other things. That’s how the concept of self-healing finds its way to concrete. There are two main areas of research when it comes to developing this kind of concrete; the natural way of hydrates to seal cracks over time, and the artificial way to seal cracks which needs a man-made intervention. The main purpose of such work is to increase concrete’s durability, which will have a huge positive impact on both the environment and economics.

On the other hand, it might also improve the architectural designs by forcing new design methods and hence, change the shape of internal spaces so that it serves many functions and provides flexibility.

Definition of Self-healing

A self-healing material is described as a material that is capable of repairing itself back to the original state. The concept of self-healing concrete (SHC) that happens over time (autogenic) has been noticed for over 20 years. It can be observed in many old structures which have remained standing for long periods of time in spite of the fact that they have limited maintenance. This observation concludes that the cracks heal when moisture interacts with non-hydrated cement clinker in the crack. Nevertheless, in present-day constructions the cement is lowered as a result of modern construction methods. Hence, the amount of available non-hydrated cement is less and therefore, the natural healing effect is reduced.

The principal phases of the natural healing ability are the inflammation and hydration of cement pastes; followed by the precipitation of calcium carbonate (CaCO₃), and lastly the obstruction of flow paths as a result of the deposition of water impurities or the movement of some concrete bits that get detached throughout the cracking process.  Many factors are considered in the natural way of healing, such as; temperature, degree of damage, freeze-thaw cycles, the age of the concrete and the mortar state.

As for the artificial way to repair cracks in concrete, which is man-made self-healing process was first invented in 1994. The main method and first approach was to use a healing agent (adhesive) which is encapsulated inside a micro capsule, once a crack forms, it causes the micro capsules to break, releasing the healing agent, hence healing the crack. The adhesives can be stored in short fiber or in longer tubes (Nishiwakietal 2006, Joseph 2008, Josephetal. 2008) however, more effective mechanisms were later approached by researchers at Cardiff University, the University of Cambridge, the University of Bath, and Korea Institute of Construction. In this article two of the main approaches – that seem promising and distinguished – will be tackled briefly alongside the advantages and disadvantages of using this kind of concrete, which will soon be inevitably used worldwide.

Bacteria-Based Healing Process

Also known as Bio-Concrete; this kind of concrete uses a simple process to close the formed crack. The main mechanism is achieved by making a concrete mixture that contains

(i)         a precursor like calcium lactate (Ca(C3H5O2)2)

(ii)  bacteria planted in micro capsules (or just added to the mixture)that will later germinate.

 Once the water reaches the crack. As soon as the bacteria germinate, they produce limestone (CaCo3) caused by the multiplying bacteria. Dr. Richard Cooper of Bath’s Department of Biology & Biochemistry says that incorporating bacteria in concrete adds a double layer shield in order to prevent corrosion in steel. Not to mention that it employs oxygen present which would then benefit the process of steel corrosion.

The bacteria which are applied in this kind of concrete are Spore-forming and alkali-resistant bacteria. Bacteria from this group are the most suitable as they are spore-forming and can live for more than 200 years in dry conditions. Therefore, using bacteria as a healing mechanism is one of the best mechanisms to produce this kind of concrete because of its sustainable organic properties.

MATERIALS:

1.    Cement :

Ordinary Portland cement of grade 53 available in local market is used in the investigation. The cement used has been tested for various properties as per IS: 4031-1988 and found to be confirming to various specifications of IS: 12269-1987 having specific gravity of 3.0.

2.    Coarse Aggregate :

Crushed granite angular aggregate of size 20 mm nominal size from local source having specific gravity of 2.71 is used as coarse aggregate.

3.  Fine Aggregate :

Natural river sand having specific gravity of 2.60 and confirming to IS-383 zone II is used.

4.  Water :

Locally available portable water confirming to standards specified in IS 456-2000 is used.

5.  Microorganisms :

Any of the following bacteria may be used for the process:

· Bacillus sphaericus

· Bacillus cohnii

· Bacillus halodurans

· Bacillus pseudofirmus

· Bacillus subtilis

METHODOLOGY –

The following steps are involved in the implementation of the project :

• Literature Survey

• Collection of Required RAW materials

• Designing of concrete M20 Grade mix as per IS: 10262-2009

• Culturing of Calcite Depositing Bacteria

• Casting and curing of controlled concrete cubes, beams and

cylinders

• Creating a fault plane for bacterial concrete application

• Application of cultured bacteria for cracked Surface

• Strength and durability tests on healed concrete

• Comparison of strength and durability characteristics of controlled M20 grade concrete and bacteria healed concrete

• Discussions and conclusions to be done on the results obtained.

Method Of Using And Its Mechanism

The method of using microbes in bacterial concrete is known as microbial Induced Calcium Carbonate Precipitation (MICCP) or bio mineralization. Bio miner­alization is a biological precipitation in which organisms create a local micro environment by providing chemi­cal precipitation of mineral phases extracellularly. Some usually occurring metabolic processes including sulfate reduction, photosynthesis and urea hydrolysis end up in giving CaCO3 as there byproduct. Various bacteria can precipitate calcium carbonate in both natural and labo­ratory conditions. Calcium carbonate precipitation is mainly governed by following factors.

·       Calcium concentration.

·       DIC (Dissolved Inorganic Carbon) concentration

·       Nucleation sites.

·       pH Value

The main mechanism behind making a self-healing con­crete is that the bacteria should be able to convert the soluble organic nutrients into insoluble inorganic calcite crystals which seals the cracks. The self-healing agent that is applied to the concrete consists of two components, bacteria which acts as a catalyst and calcium lactate i.e. the mineral precursor which is converted to calcium carbonate minerals. The presence of CO2 and calcium hydroxide within the concretion of calcium carbonate in control concrete as shown in the reaction given below:

               CO₂+ Ca (OH)₂ → CaCO₃+ H₂O

The calcium carbonate is formed due to the presence of limited CO₂ .Calcium hydroxide being soluble in nature dissolves in excess water and comes out from cracks as leaching. In self-healing concrete active metabolic conver­sion of calcium nutrients takes place due to the presence of bacteria.

Ca(C₃H₅O₂)₂+ 7O₂ →CaCO₃+ 5CO₂+ 5H₂O

There are two pathways of calcium precipitation done by microorganisms:

·       It involves Sulphur cycle in which Sulphur reducing bacteria carry out Sulphur reduction in anoxic envi­ronment.

·       It involves nitrogen cycle, explicitly the amino acid oxidative deamination and urea or uric acid degrada­tion using ureolytic bacteria in aerobic environment and in anaerobic conditions nitrate reductions.

One of the most commonly used methods applied for MICCP is hydrolysis of urea through the urease enzyme in an environment in which calcium is in abundance. This method results in the hike in the dissolved carbon (inorganic) concentration and pH. Urease propels the hydrolysis of urea in bacterial environment to ammonia and CO₂, resulting in pH and carbonate concentration increase. 1 mol of urea forms 1 mol of ammonia and 1 mol of carbonate by intracellular hydrolization, which in turn forms additional 1 mol of ammonia and carbonic acid spontaneously as follows:

CO(NH₂)₂ + H₂O →NH₂COOH + NH₃

NH₂COOH +H₂O →NH₃H₂CO₃

A state of equilibrium in is attained to form bicarbonate in water, pH rises due to 1 mol of ammonium and hydrox­ide ions.

H₂CO₃→ 2H⁺ + 2CO₃^2-

NH₃+H₂O → NH₄^- + OH^-

Ca^2- + CO^3- → CaCO₃

Observations depict that in calcium precipitation a key role is being played by surfaces of bacteria due to the involvement of negatively charged ions and neutral pH, the metal ions with positive charge can combine with bacterial surfaces thereby encouraging heterogeneous nucleation. The possible biochemical reaction can be summed up as:

Ca^{2+ +} Cell → Cell-Ca²⁺

Cl^- + HCO^3- + NH₃ → NH₄Cl + CO₃^2-

Comparision Of Conventional And Self Healing Concrete:

·       The test results of bio concrete and conventional con­crete showed an difference. The table and graphs given shows the clear information regarding compressive strength, split tensile strength and flexural strength of M20 conventional concrete and M20 bio concrete using differ­ent types of bacteria.

·       This study helps to understand the how self healing concreteHas high strength and durability than conventional concrete.

·      Comparision of Compressive strengths:

The results of compressive strength of bacterial concrete and conventional concrete are given in Table 1 and Graph 1.

Compressive Strength comparision between Conventional Concrete and Self Healing concrete of subtilis, sphaericus and pasteurii of Bacillus bacterial Family.

Compressive strength comparision graph

       ·      Comparision of Split Tensile strengths:

The results of split tensile strength of bacterial concrete and conventional concrete are given in Table 2 and Graph 2.

Split Tensile Strength comparision between Conventional Concrete and Self Healing concrete of subtilis and sphaericus of Bacillus bacterial Family.

Split tensile strength comparision graph

·      Comparision of Flexural strengths:

The results of flexural strength of bacterial concrete and conventional concrete are given in Table 3 and Graph 3.

Flexural Strength comparision between Conventional Concrete and Self Healing concrete of Pasteurii of Bacillus bacterial Family.

                    Flexural strength comparision graph

Merits and Demerits of Self Healing Concrete:

Merits:

·       The use of bio concrete significantly influences the strength of concrete.

·       It has lower permeability than conventional concrete.

·       It offers great resistance to freeze-thaw attacks.

·       The chances of corrosion in reinforcement are reduced.

·       Remedying of cracks can be done efficiently.

·       Maintenance cost of this concrete is low.

·       Helpful in filling of cracks in concrete.

·       Helpful to reduce leakage of residential building.

·       Helps to reduce permeability in concrete.

·       Helpful to reduce corrosion of reinforced concrete.

·       It increases durability of concrete.

·       Design of bacterial concrete is not mentioned in IS codes or any other codes.

Demerits:

·       Cost of this concrete is comparatively higher than  conventional concrete i.e. about 7-28% more than conventional concrete.

·       The sprouting of bacteria is not suitable in any envi­ronment.

·       The investigations involved in calcite precipitation are costly.

·       It is not suitable for Indian atmospheric condition.

·       It gives better results only if comes in contact with water.

·       Process of activation of bacteria is tedious.

·       It takes more time for working of bacteria in concrete.

Benefits it Can Serve in India

The climate of India is diverse from region to region because of its topography. It observes a wide range of temperature changes from mountains, plains, forests, to beaches.

 Many cities such as New Delhi, Lucknow, Patna, Varanasi etc. observe drastic temperature changes from very warm climate in April to mid-June to very cold cli­mate between November and February. Extreme climates can deteriorate the concrete surfaces and which may ulti­mately result in failure of structure.

 Bio concrete can be used as the best alternative for constructions in extreme climates. As India is a developing country, impressive infrastructure plays an important role so bio concrete can be used in the construction of crack resistant and dura­ble high rise buildings and underground constructions. Apart from this bio concrete can be used for constructing structures meant for irrigation.

Structures constructed in India

In recent months, A professor in the department of civil engineering at the University of British Columbia (UBC) has had his eyes fixed on a road.

That road, though, happens to be more than 12,500 km from Vancouver, where he is based. It’s a demonstration project in a village about 90 km from Bengaluru and uses advanced materials and technology that could help with enhancing rural road connectivity.

The project is the result of research that marries materials science and structural engineering to create self-repairing roads that are cost effective, have greater longevity and are sustainable.

Banthia, who graduated from IIT-Delhi before moving to Canada 34 years ago, undertook the project under the auspices of the Canada-India Research Center of Excellence IC-IMPACTS, where he is scientific director.

In 2014, his team selected Thondebavi village, after a series of interactions with gram panchayat members and the local community. Based at UBC, the center is focused on research collaboration between Canada and India to develop and implement “community-based solutions to the most urgent needs of each nation”.

Construction of the road, which connects Thondebavi to the highway and replaces a dilapidated dirt track, was completed in the late winter of 2015, but the last few months were critical as it had to be monitored for how it lasted through the extreme heat of an Indian summer and the monsoon. Now, it can be claimed a success.

The road’s thickness, at about 100 mm, is about 60% less than that of a typical Indian road, reducing cost and materials. About 60% of the cement is replaced with flyash, thus curbing the usual carbon footprint, especially as cement production releases greenhouse gases. It comes with built-in crack healing, as high strength concrete is supplemented with fibre reinforcement with nano-coating that makes it absorb water and keeps the road hydrated.

These are fibres which have a hydrophilic nano-coating on them. Hydrophilia means they attract water and this water then becomes available for crack healing. Every time you have a crack, you always have unhydrated cement and this water is now giving it the hydration capability, producing further silicates which actually closes the crack in time.”

CONCLUSION

 Concrete is the world’s most durable, reliable and economical construction material with an annual consumption in volume by society only surpassed by water. Currently, no alternatives for concrete exist which can be supplied at a sufficient scale globally. The durability and lifetime of concrete structures depend mainly on their chemical environment, nano- and micro-sized pores in the materials and larger cracks formed with time by physical stress or heavy loadings.

The aim of the project is to develop microbial and chemical additives which can heal concrete structures by filling up the pores and cracks when these are formed in the material. The principal approach will be microbially-induced calcium carbonate precipitation, where bacterial endospores are encapsulated into the concrete. When cracks occur, water will penetrate and induce the endospores to germinate and grow, thereby producing CO2 which in the alkaline, Ca-rich environment of concrete will result in CaCO3 precipitation.

The actual, fully-financed project is a part of a larger project, which also involves a student and a Post Doc associated with the Section for Microbiology at Bioscience and the experimental work will be performed in collaboration with this section. The study will be performed at the Department of civil and structural engineering and it will focus on laboratory-based experiments for detection of pores and cracks in concrete structures using microstructural characterization techniques for probing pores, pore connectivities and cracks in concrete. The chemical environment in these pores and cracks will be explored and approaches to modify the pore-solution chemistry will be developed to create functional conditions for microbially-induced CaCO3 precipitation. In addition, the structural evolution and morphology of the formed calcium carbonate will be characterized to explore its impact on pore and crack connectivities  in the concrete material.

·       Microbial concrete technology has proved to be better than     many conventional technologies because of its eco-friendly nature, self-healing abilities and increase in durability of various building materials.

·       The overall development of strength and durability of Self-healing concrete by using Bacillius subtilis bacteria and polyethylene fibre has investigated and compared with control concrete

·       The more CaCO3 precipitations, the better the self-healing effect will be. The concentrations of bacteria and Ca 2+ will greater the amount of precipitated CaCO3.

·       This process results in the precipitation of substantially higher amounts of calcium carbonate inside the crack to be healed.

·       The reason for this can be explained by the strictly chemical processes in the control and additional biological processes in the Self-healing concrete.

·       Polyethylene fiber can be increased its mechanical properties of the concrete

·       Optimum strength is obtained on self healing concrete specimen. Bacillus subtilis strain can improve the characteristics of cement composites.