GGBS is fast becoming the most sustainable green building material, and it also proves the growing need for use of value-added green products in the Indian construction industry, write Manjunatha L. Ramachandra and Dr. Sandhya R Anvekar.


Manjunatha L. Ramachandra, Research Scholar (PhD), Management, Research and Development Centre, Bharatiyar University.
Dr. Sandhya R Anvekar, Professor, VTU, Bengaluru.

With more than 1.2 billion people, there is a growing demand in India for the basic requirements of housing, infrastructure, workplaces, business premises, etc. The construction industry has a huge demand to provide for these requirements on a continuous basis.
The building industry provides 4.0 to 10 percent of worldwide employment and generates 5.0 to 16 percent of GDP (Gross Domestic Product). But, the built environment accounts for 40 percent of energy consumption, 40 percent of CO₂ emissions, 30 percent of the consumption of natural resources, 30 percent of waste generation, and 20 percent of water consumption.
Ready Mixed Concrete as a product is continuously evolving and moving forward by replacing traditional Site Mixed Concrete (SMC). RMC companies in India are also providing value addition to the construction industry by offering new generation special concrete products that are green through continuous innovation, research and product development.
Due to exponential growing in urbanisation and industrialisation, byproducts from industries are becoming an increasing concern for recycling and waste management. Ground Granulated Blast Furnace Slag (GGBS) is one such by-product from the blast-furnaces of iron and steel industries, which is very useful in the design and development of high-quality cement paste/mortar and concrete.

Introduction
The blast furnace slag is a by-product of the iron manufacturing industry. Iron ore, coke and limestone are fed into the Blast Furnace and the resulting molten slag floats above the molten iron at a temperature of about 1500⁰C to 1600^oC. This molten slag has a composition of about 30-40 percent SiO₂ and about 40 percent CaO₂, which is close to the chemical composition of Portland cement.
After the molten iron is tapped off, the remaining molten slag, which consists of mainly siliceous and aluminous residue (Higgins, 2007) is then water-quenched rapidly, resulting in the formation of a glassy granulate. This glassy granulate is dried and ground to the required size (Hooton, 2000), which is known as Ground Granulated Blast furnace Slag (GGBS).
Concrete is one of the main raw materials used for civil engineering works and one of the best material invented by mankind in the human history which has found its place as the second most consumed material after water. Ready-mixed concrete too is used almost in all the projects in India to save time and achieve quality.
Concrete is a versatile building material. It can be designed and used for most of the structural demands with the necessary aesthetic requirements. It also ranks as one of the sustainable building materials with the use of supplementary cementitious materials, like Fly ash and GGBS.
There is an increased demand for Ready-Mixed Concrete (RMC), special concretes like HSC, HPC, SCC, FRC, temperature controlled concretes, light weight concretes, colour concretes, polished concrete and stamped concrete. Sustainable concrete products like blended concretes and pervious concretes – which are green – are also in great demand.
With the explosive growth and faster phase in construction and new innovations in the designs of buildings, the use of advanced, innovative and decorative concretes, and construction techniques are gaining recognition in India

Importance and Significance of RMC and Special Green Concretes for the Indian Markets
India is the second largest producers of cement in the world. The use of ready-mixed concrete as a product vis-à-vis traditional manual site mixed concrete in the construction sector and infrastructure projects has come a long way ever since the first commercial ready-mixed concrete plant was established in Pune in the year 1992.
RMC has been very popular in developed countries for the last six to seven decades and it is the most popular method of production of concrete. RMC is a better product due to advanced manufacturing technology, involving a higher degree of mechanisation and automation technology. It is technologically superior to the traditional manual site mixed concrete.
The benefits of RMC in terms of quality, speed, life-cycle cost and eco-friendliness are some of the very big advantages compared to Site Mixed Concrete. RMC is a readily available product, and it is replacing traditional site mixed concreting at construction sites across India due to its various advantages.
Cost-wise, it is 15-20 percent costlier than the site mixed concrete due to taxation on the product and manufacturing process. But, the industry is witnessing sweeping changes in the customer mindset, with large numbers of concrete users migrating to the RMC from the traditional manual SMC. Also, reputed RMC companies are offering value-added special concretes and other concrete products to the consumers, which are eco friendly.
 
GGBS – the world’s most sustainable building material
GGBS is a hydraulic binder, like cement which has been known and used for more than 150 years. It improves the quality and durability and performance of concrete, and its production is virtually CO₂-free. Yet, its many advantages in producing sustainable, high-quality concrete remain underappreciated and underused.
The production of GGBS requires little energy as compared with the huge energy needed for the production of Portland cement. The replacement of Portland cement with GGBS will lead to significant reduction of carbon dioxide gas emissions.
Not only is it an environmentally friendly construction material but GGBS concrete has better water impermeability properties as well as improved resistance to corrosion and sulphate attacks. As a result, the service life of a structure is enhanced and the maintenance cost reduced substantially. It can be used to replace as much as 70-80 percent of the Portland cement used in concrete in case of mass concrete applications for reducing temperature differences and to avoid thermal cracking.

Chemical Composition of GGBS
Ground Granulated Blast furnace Slag consist essentially silicates and alumina silicates of calcium. It is a by-product of manufacture of pig iron in blast furnace. Portland cement is a good catalyst for activation of slag because it contains the three main chemical components that activate slag lime, calcium sulphate and alkalis.
The material has glassy structure and is ground to less than 45 microns. The surface area is about 400 to 600 m² / kg Blaine. The rough and angular shaped ground slag in presence of water and an activator, which are commonly sulphates and/or alkalis which are supplied by Ordinary Portland Cement, react chemically with GGBS, hydrates and sets in a manner similar to Portland cement.
Richardson (2006) reported that in the early hydration of GGBS and Portland cement, the Portland cement released alkali metal ions and calcium hydroxides (CH). The slag reacted initially with calcium hydroxide, resulting in the breaking down of the glassy structure of the slag. As hydration continues, more calcium hydroxides would precipitate from the Portland cement and calcium silicate hydrate (CSH) would be produced.
As CSH are developed, they would fill the pores and contribute to strength development and chemical resistance. The additional CSH fills the pores making pore size refined.

Properties of Concrete made with GGBS blend with Ordinary Portland Cement
Plastic Concrete
Water Demand: For concrete made with equal slump, lower water content is required compared to ordinary Portland cement. This will help in reduced capillary pores and, hence, concrete will be of better durability.
Stiffening time: Because GGBS is slower to react with water than OPC, its use in concrete increases the stiffening time of concrete. This will help in more time available for placing the concrete.
Heat of hydration and early age thermal cracking: The rate of heat evolution associated with GGBS is reduced as the proportion of slag is increased. This helps in greater heat dissipation and reduced temperature rise, which will reduce the likelihood of thermal cracks. Lower thermal cracks helps in long-term durability.
Hardened Concrete
Compressive strength and strength development: The rate of hydration reaction of GGBS concrete is temperature dependent. GGBS has higher activation energy than OPC and, therefore, their reaction rate is more sensitive to temperature change.
As the temperature increases, the rate of gain of strength in GGBS blend concrete is greater than OPC concrete. The influence of temperature on strength development is of significance when considering the behaviour of concrete in-situ. In such situations, the rate of strength development and ultimate strength may be appreciably different from that indicated by standard cured cubes.
Tensile Strength and Elastic Modulus: Compared to concrete produced with only OPC, the GGBS blend produced concrete tends to have a slightly higher tensile strength and elastic modulus for a given compressive strength.
Drying Shrinkage: Use of GGBS has very little – if any – influence on the drying shrinkage of concrete.
Creep: For high replacement levels (>70 percent) reduction in creep of as high as 50 percent is possible due to later age strength gain of GGBS blended concrete.
Surface Finish: Generally, GGBS makes it easier to achieve a good surface finish. In addition, the colour of concrete will be lighter than concrete produced with only OPC.
Formwork Pressure: Higher formwork pressure is relevant with the use of GGBS blended concrete when concrete is cast at ambient temperatures as low as <5^oC, else it is not relevant.
Formwork Striking Time: Use of high levels of GGBS blend (>70 percent) in concrete may require the extension of formwork striking time. In practice, however, the actual construction process often requires concrete to be cast one day and vertical formwork next day. In such cases, it is quite likely that minimum striking time will, in any case, be extended and that, therefore, the use of GGBS may not affect the actual construction process.
Curing: For long-term durability, it is beneficial if GGBS blended concrete is cured for longer than concrete produced with only OPC.
Durability: Durability of concrete is related to its permeability or diffusion to liquids and gases and its resistance to penetration by ions such as CL- and SO₃+. Generally speaking, provided concrete is well cured, GGBS blended concrete is likely to be more durable than similar concrete produced with only OPC.
Permeability: In well-cured concrete containing blend of GGBS, the long-term permeability is reduced due to continued hydration beyond 28 days and overall finer pore structure.
Alkali-Silica Reaction: Use of GGBS blend with OPC is one of the ways to reduce the Alkali Aggregate Reaction, when aggregate used in concrete is alkali reactive. Use of blend of GGBS with OPC reduces the total alkali content in cementitious material, thereby deterioration of concrete due to alkali aggregate reaction could be avoided.
Sulphate Resistance: Concrete containing GGBS are acknowledged to have higher resistance to attack from sulphates than those made with only OPC. This is due to overall reduction in C₃A level of concrete and to the inherent reduction in permeability. Provided Al₂O₃ of GGBS is less than 15 percent, then concrete containing about 70 percent of GGBS is considered as comparable to concrete produced with Sulphate Resistant Cement (SRC).
Chloride Ingress: GGBS-blended concrete is significantly more resistant to the ingress of chloride ions in concrete apart from reduced permeability. OPC used with GGBS blend chemically binds the chlorides with slag hydrates effectively reducing the mobility of chlorides, thereby reducing the reinforcement corrosion risk.
Carbonation: The influence of addition of GGBS on carbonation has been the subject of much research and there still appears to be some disagreement as to its effects. The reasons for much of this debate appear to be related to the test procedures and conditions used in the studies and to the basis on which comparisons are made.
Alkalinity: Despite the reduction in Ca(OH)₂ caused by secondary slag hydration reactions, the pH of paste remains at a level which is well in excess of that which would affect the passivity of the reinforcing steel.
Abrasion Resistance: In adequately cured concrete – when comparison is made with equal grade of 100 percent OPC concrete – there is slight advantage in terms of abrasion resistance due to use of GGBS blend in concrete.

Benefits of using GGBS
It is generally known that GGBS can improve the durability of a concrete structure by reducing the water permeability, increasing the corrosion resistance and increasing the sulphate resistance. The improved properties can extend the service life of structures and reduce the overall maintenance costs.
Quality, sustainable concrete: Dried and ground to a fine powder, GGBS can be used to make quality, sustainable concrete. To ensure its activation, GGBS is most often used with normal cement (OPC). It will typically replace 30-70 percent of cement on an equal weight basis.
Reduction in CO₂ emissions: The manufacture of normal cement (OPC) results in the emission of 700 to 930kg of CO₂/t of cement (British Cement Association, 2009) – approximately 50 percent from decarbonation of the limestone raw material (process emissions), 40 percent from fossil fuel consumption, and 10 percent from generating the electricity used in the process. GGBS manufacture typically releases 35kg of CO2/t of GGBS less than 4.0 percent of the carbon footprint of normal cement.
Solar reflectance of GGBS mixed Concrete: Concrete made with GGBS will have a high solar reflectance. Studies in the US have shown increases of 20 percent in reflection of sunlight by concrete with GGBS. This will reduce the “heat island” effect in urban developments, as well as having other beneficial effects (reduced need for artificial lighting at night, safer roads from better visibility). Significantly, the reflected sunlight is not infrared radiation, and so will not be trapped by the greenhouse effect of the earth’s atmosphere.
Concrete with improved Durability: Durability is essential to the long service life of concrete. In practice, concrete will deteriorate over time. The factors driving this deterioration can be internal (e.g., alkali-silica reaction) or due to external aggressive environments (e.g., sulfate attack, or the effects of chlorides on reinforced concrete).
GGBS substantially improves the ability of concrete to resist deterioration from all major threats to long service life. Requiring the use of GGBS is now established best practice where long service lives must be achieved, even in the most aggressive environments. GGBS concrete will even provide better fire resistance.

GGBS in concrete
GGBS can be used in concrete as GGBS or as Portland slag cement (combinations of OPC cement and GGBS allowed under IS 455). There is no technical basis under which to prefer one option or the other once in concrete. The GGBS behaves the same, irrespective of whether or not it was previously mixed with cement. Nevertheless, opinions are divided on the best approach.
Using GGBS has two advantages over Portland slag cement (PSC). The concrete manufacturer can optimise the proportion of GGBS percentage according to the technical/environmental requirements to be met; and, GGBS shipped directly to the RMC plant will have lower embodied CO2 (avoiding energy use in additional transport to/from the cement plant and mixing in a cement plant). For the lowest embodied CO2, GGBS use is to be preferred in all constructions.
Impact of using GGBS in concrete
·  Reduction in the emission of CO₂ from cement production plants.
·  Improved durability.
·  Reduced potential for cracking
·  Reduced permeability
·  Reduced corrosion repairs cost nearly by 5.0 percent of developed nation’s GDP
·  Use of waste or by-products reduces the clinker usage.
·  Increased benefit to cost ratio and Longer service life
GGBS –a sustainable material for Green building construction
Replacing the Portland cement by GGBS helps in reducing CO2 emissions and in conserving non –renewable resources of limestone. Use of GGBS in concrete is recognised by LEED (Leadership in Energy and Environmental Design) and adds points towards its certification.

Usage and promotion of green building products through RMC route
The Indian cement industry is the second largest in the world with an installed capacity of 400 million tonnes and the production for the year 2013-14 was around 270 million tonnes. If we compare cement consumption through RMC in India, ready mix concrete industry used just 2.0 percent in the beginning of the 90s. Presently, though, the commercial RMC alone consumes around 9-10 percent of the total cement production and producing approximately 32-35 million cum of commercial ready-mixed concrete annually.
Captive RMC plants, which are set up at project sites in metros and cities, have been estimated to produce around another 35-38 million cum of site batched concrete annually, which in turn takes the total production of mechanised concrete (production of concrete from RMC batching plants) in India to about 67-73 million cum annually. In developed countries, the cement consumption through RMC route is about 70-75 percent (USA) and 65-70 percent (Europe and Japan).
As a testimony to the growth of RMC industry in India, as per our best knowledge, currently there are more than 1000 to 1100 commercial RMC plants set up and operating in about 98 to 110 cities and towns across India. In total, there are more than 2600-2900 RMC batching plants in operation throughout the length and breadth of the country.

Need for usage and promotion of Green products in the concrete and construction industry
Concrete is widely considered as the backbone of the construction industry, with a current consumption of 1 cubic meter per person, per year (Gartner E, 2009). Ordinary Portland cement (OPC) has been used for around 200 years now as a binder material. However, OPC has high embodied energy of 4.2MJ/kg (Peng J et al, 2014; Huang Li C et al, 2011; Huntzinger DN et al, 2009).
The contribution of OPC is approximately 5.0-7.0 percent of global man made CO2 emissions (Huntzinger DN et al, 2009; Meyer C et al, 2009). High CO2 emissions arising from OPC manufacturing are from calcination of limestone, and high energy consumption during manufacturing (Gartner E et al, 2009).
During the recent past many alternatives to OPC concrete have been proposed to reduce green house gas emissions, which are Blended Cement Concretes, comprising OPC that has been partly substituted by supplementary cementitious materials, as binders for concrete.
According to Flower and Sanjayan, use of blended cements results in reduction of CO2 emissions by 13–22 percent. These estimates vary according to the local conditions at the source of raw materials, binder quantity and amount of OPC replacement, type of manufacturing facilities, climate, energy sources, and transportation distances.

Value added green concrete products using GGBS as mineral Admixture
For any RMC manufacturing industry, designing and producing products which are sustainable is the top most priority today. Most of the concretes and value-added products which are being produced today at RMC plants make use of sustainable raw materials like flyash, GGBS and slag, replacing cement as well as natural river sand. The demand for manufactured sand is also increasing.
Value-added concrete products are different from that of traditional concretes. These concrete products are made by using one or more special additives like Flyash, GGBS, Micro silica, Alccofines, metakaolin, synthetic or steel fibers, EPS Beads, Colour pigments, super plastisizers, PC-based admixtures, etc. These value-added special products enhance durability, workability and setting times while delivering a higher performance mix.
During the recent past, leading commercial RMC companies in India have launched and are supplying many branded and non-branded value-added green concrete products either using GGBS or Fly ash as mineral admixture.

Future of value-added green RMC products in Indian concrete industry
Continuous research work and efforts are going on in the field of concrete technology both in India as well as globally to introduce many newer products to the Indian market. Branded value-added concrete products from commercial RMC companies are available in the markets with various brand names and the details are available on the websites of respective companies.
As the Indian construction market matures, the demands for these special value-added concrete products will grow exponentially, and a day will come very soon when 30-40 percent of the concrete produced by the commercial RMC companies will be special value-added concrete products.
To popularise RMC products, RMC producers should be certified for quality by a third party organisation. Ready Mixed Concrete manufacturers association helps to do this if the producers become members of the organisation.

Conclusions
GGBS blended concrete have been used successfully in concrete for many years in many countries throughout the world. From all the available technical literature, it is inferred that there are potentially many technical benefits to be gained from using the GGBS. Where structures have to be designed for durability requirements in very aggressive environment conditions, GGBS blend mixes are recommended in standards of most developed and developing countries.

RMC industry in southern, western and eastern Indian markets are adopting the use of GGBS in their concrete mixes for giving value addition to their customers in respect of cost effectiveness, sustainability and durability performance due to the availability of the product by many reputed manufacturing companies.
RMC Industry and scope for special value-added green concrete products will, thus, continue to grow in the coming years due to very high infrastructure growth in India and change in consumer and consultants mind set. This will prompt an increasing number of RMC plants to be set up at, preferably in tier II and tier II cities in the coming years. There will, thus, be a migration of concrete users from SMC to RMC due to shortage of skilled manpower and product superiority of RMC.

-----------