ECO BLAC BRICKS An innovative step towards greener India
Report Submitted by-
Arun M
CERTIFICATE
ACKNOWLEDGEMENT
TABLE of CONTENTS
INTRODUCTION For centuries the red clay brick has been, quite literally, the building-block of India. Simple, cheap, and locally available, these bricks are ubiquitous across the country, and continue to be manufactured by the billions using techniques largely unchanged since the time of the British Raj. However, as India’s population booms, the traditional kiln-fired brick is being produced on a scale never seen before, and the boom is having unexpected consequences. A number of environmental drawbacks have arisen, such as topsoil depletion from the harvesting of clay and greenhouse gas emissions due to the massive energy demands of the kilns. Once taken for granted as the nation’s primary building material, many manufacturers and policymakers are now wondering whether the red clay brick can continue to serve rising demand. At the same time, a seemingly unrelated problem is plaguing Indian industry: the country’s 800 paper mills are burning cheap raw materials to generate energy, and together they can produce as much as 80,000 tons of waste ash every day. Much of this ash is unusable and sent to landfills, occupying valuable farmland at great expense to paper mill owners. A team at MIT, including Tata Fellow Michael Laracy and Postdoctoral Associate Thomas Poinot, looked at these problems and spotted an opportunity to solve both at once: Using industrial ash to develop an alternative building material to the red clay brick. The result of their research is the eco-BLAC brick, a low-cost, environmentally-friendly masonry unit, formulated using industrial ash.
FIRED CLAY BRICK RAW MATERIALS Natural clay minerals, including kaolin and shale, make up the main body of brick. Small amounts of manganese, barium, and other additives are blended with the clay to produce different shades, and barium carbonate is used to improve brick's chemical resistance to the elements. Many other additives have been used in brick, including byproducts from papermaking, ammonium compounds, wetting agents, flocculants (which cause particles to form loose clusters) and deflocculate (which disperse such clusters). Some clays require the addition of sand or grog (pre-ground, pre-fired material such as scrap brick). THE MANUFACTURING PROCESS
GRINDING, SIZING, AND COMBINING RAW MATERIALS First, each of the ingredients is conveyed to a separator that removes oversize material. A jaw crusher with horizontal steel plates then squeezes the particles, rendering them still smaller. After the raw materials for each batch of bricks have been selected, a scalping screen is often used to separate the different sizes of material. Material of the correct size is sent to storage silos, and over-sized material goes to a hammer-mill, which pulverizes it with rapidly moving steel hammers. The hammer-mill uses another screen to control the maximum size of particle leaving the mill, and discharge goes to a number of vibrating screens that separate out material of improper size before it is sent on to the next phase of production. EXTRUSION With extrusion, the most common method of brick forming, pulverized material and water are fed into one end of a pug mill, which uses knives on a rotating shaft to cut through and fold together material in a shallow chamber. The blend is then fed into an extruder at the far end of the mill. The extruder usually consists of two chambers. The first removes air from the ground clay with a vacuum, thereby preventing cracking and other defects. The second chamber, a high-pressure cylinder, compacts the material so the auger can extrude it through the die. After it is compressed, the plastic material is forced out of the chamber though a specially shaped die orifice. The cross-section of the extruded column, called the "pug," is formed into the shape of the die. Sections of desired length are cut to size with rotating knives or stiff wires. In molding, soft, wet clay is shaped in a mold, usually a wooden box. The interior of the box is often coated with sand, which provides the desired texture and facilitates removing the formed brick from the mold. Water can also be used to assist release. Pressing, the third type of brick forming, requires a material with low water content.
The material is placed in a die and then compacted with a steel plunger set at a desired pressure. More regular in shape and sharper in outline than brick made with the other two methods, pressed bricks also feature frogs.
CHAMFERING THE BRICK Chamfering machines were developed to produce a furrow in brick for such applications as paving. These machines use rollers to indent the brick as it is being extruded. They are sometimes equipped with wire cutters to do the chamfering and cutting in one step. Such machines can produce as many as 20,000 units per hour. COATING The choice of sand coating, also applied as the brick is extruded, depends on how soft or hard the extruded material is. A continuous, vibrating feeder is used to coat soft material, whereas for textured material the coating may have to be brushed or rolled on. For harder materials a pressure roller or compressed air is used, and, for extremely hard materials, sand blasting is required.
DRYING Before the brick is fired, it must be dried to remove excess moisture. If this moisture is not removed, the water will burn off too quickly during firing, causing cracking. Two types of dryers are used. Tunnel dryers use cars to move the brick through humidity-controlled zones that prevent cracking. They consist of a long chamber through which the ware is slowly pushed. External sources of fan-circulated hot air are forced into the dryer to speed the process. FIRING After drying, the brick is loaded onto cars (usually automatically) and fired to high temperatures in furnaces called kilns. Tunnel kilns have changed in design from high-load, narrow-width kilns to shorter, lower-set wider kilns that can fire more brick. This type of design has also led to high-velocity, long-flame, and low-temperature flame burners, which have improved temperature uniformity and lowered fuel consumption.
BASIC ADVANTAGES OF CLAY FIRED BRICKS Aesthetic Appeal Thermal & Acoustic Insulation Zero Maintenance Cost Fire Resistance Flexible in Application
DISADVANTAGES OF CLAY FIRED BRICKS To make 60 billion bricks, 185 million tons of top soil is needed. Ultimately, near about 7500 hectares of very fertile land is deliberately eroded to meet the demand of clay bricks for construction every year. This devastating act is slowly killing our environment and we will be left with no fertile land for agriculture in near future. Deforestation also occurs in search of soil source for clay brick manufacturing. Burnt clay bricks are manufactured using old outdated technology and no quality testing facilities are available at manufacturing site. Most bricks which are manufactured using outdated technology are inferior in quality with low compressive strength. They are not suitable for multi-storey buildings. Most brick kilns use coal or wood for the firing purpose. This results in production of fly ash and a lot of other pollutants.
ECO-BLAC BRICKS: SUSTAINABLE MASONRY FROM INDUSTRIAL WASTE
For centuries, the clay fired brick has been the most popular building material in India due to its local availability and low cost. However, negative environmental and social impacts surrounding its production have raised concerns about its future use. At the same time, India is experiencing a growth in industry, and a number of industrial wastes are being generated which are often disposed of in harmful ways to the population and the environment. The aim of this research is to solve both problems by recycling industrial waste into masonry construction materials. The primary industrial waste which will be utilized is boiler ash, a byproduct of combustion during energy production at small- and medium-sized factories. Currently, this ash has no application due to its variability in physical and chemical properties, and is landfilled at great expense to both the environment and factory owners. For this reason we see opportunity in creating a robust design which can account for these variabilities by using alkali-activation technology. These low-cost masonry units can be made with reduced energy demands, a smaller carbon footprint, and less natural resource consumption than traditional masonry. This solution is scalable all over India, as there are factories producing boiler ash throughout the country. Current work is being done in Muzaffarnagar, U.P., where the team is partnering with the owner of a paper mill to implement a pilot plant on site.
BOILER ASH Boiler ash is a generic term applied to many types of ash produced by the burning of various materials. They are 4 general types of boiler ash commonly available, each with its own chemical and environmental characteristics: Wood Ash – from boilers where wood (or bark) is used as a heating source. Coal Ash – from coal powered electrical generating power plants, actually two forms, bottom ash and fly ash. Tire Ash – produced from burning shredded tires for fuel in generating plants. Incinerator Ash – produced from burning MSW (Municipal Solid Waste, i.e. Garbage) as a waste disposal method
FLY ASH - Arsenic, cadmium, copper, gallium, lead, antimony, selenium, zinc and other chemicals are commonly found to concentrate in fly ash. Due to the lime slurry used fly ash tends to be very alkaline (toxic). Also studies have found that as little as 8% fly ash by weight mixed with soil can increase the salinity 5-6 times in a short period of time. It has also been found depending on application rates that fly ash suppresses beneficial microbes in the soil and as little as 10% can cause a 50% reduction in microbial activity. COAL ASH is toxic (mutagenic and carcinogenic) and contains many radioactive elements like uranium and thorium along with arsenic and mercury. When used as a soil amendment many species of plants suffer growth problems. Some plants have been found to accumulate toxic amounts of selenium, manganese, aluminum and boron in their tissues. Small amounts of ash when leached have been found toxic to many animal species (fish and others) leading to deformities and death. Toxic material from coal ash has also been found in drinking water from wells.
THE MANUFACTURING PROCESS
The manufacturing process of Eco-BLAC bricks uses boiler ash and alkali-activation technology. This technology uses the boiler ash as an alumino-silicate, combining it with an alkaline activator solution. When combined, the ash dissolves, followed by the construction of a geo-polymer gel, a solid 3D network that gives the bricks strength and durability. This solution reuses industrial waste (70% in the current model) rather than topsoil, and is low-cost and low energy.
THE ALKALI - ACTIVATION PROCESS
Alkaline activation is a chemical process in which a powdery aluminosilicate such as fly ash is mixed with an alkaline activator to produce a paste capable of setting and hardening within a reasonably short period of time. The strength, shrinkage, acid and fire resistance of the resulting material depends on the nature of aluminosilicate used and the activation process variables.
APPLICATIONS FOR ALKALI – ACTIVATED FLY ASH
Concretes made with these materials can be designed to reach compressive strength values of over 40 MPa after short thermal curing times. Concrete made with alkali-activated fly ash performs as well as traditional concrete and even better in some respect, exhibiting less shrinkage and stronger bond between the matrix and reinforcing steel. In addition to its excellent mechanical properties, the activated fly ash is particularly durable and highly resistant to aggressive acids, the aggregate-alkali reaction and fire. This family of materials fixes toxic and hazardous substances very effectively.
Manufacturing process of Eco-Blac Bricks
PERFORMANCE SPECIFICATIONS OF ECO-BLAC BRICKS
The bricks have been subjected to a battery of tests, including compression, durability, and water absorption, with promising results. In terms of strength they are better than the red clay bricks and at a far less cost to the environment.
ADVANTAGES OF USING ECO-BLAC BRICKS
Making use of fly-ash bricks or other alternative building materials could slow down the rate of deforestation. Every year, a vast area of forest is destroyed in search of soil for brick manufacturing. Modern Fly ash bricks are manufactured using high end preprogrammed hydraulic machines. Bricks from these machines are tested for its quality and durability. Compressive strength of Fly-ash Bricks is high and uniform whereas compressive strength of clay bricks is low and uneven. While traditional bricks must be kiln-fired at 1000°C, consuming huge amounts of fuel, the eco-BLAC brick can be cured at ambient temperatures, massively reducing energy requirements. This process also produces no emissions, unlike the traditional kiln technology, which produces carbon dioxide (roughly 76 million tons CO2/ year), carbon monoxide, sulphur dioxide, nitrogen oxides, black carbon, and particulate matter.
In a life-cycle assessment versus the clay-fired brick, the Eco-BLAC brick performed better in all categories, 24% better in human health, 15% better in climate change and 33% better in resources. The human health category focused on the production of respiratory particulate matter, the climate change category focused on production of CO2 and the resources category focused on depletion of non-renewable resources. With the product still in development, researchers hope to reduce the environmental impact even further, using additional wastes in the mix and reducing chemical use.
REFERENCES “Alkaline activation, procedure for transforming fly ash into new materials. Part I : Applications”. (Angel Palomo and Ana FernandezJimenez) tatacenter.mit.edu (“Changing how India builds, one brick at a time ”) “EcoBLAC : Sustainable Masonry from Boiler Ash”. (Hugo Uvegi, Sam Wilson, Piyush Chaunsali, Michael Larcy, Thomas Poinot, John Ochsendorf, Elsa Olivetti)
