Prof. Chandrakant B Shah
Professor Emeritus, Faculty of Technology, CEPT University Life member and Founder of Gujrat chapter of ICI
Dr. Parth Thaker
Assistant Professor, Faculty of Technology, CEPT University
Construction materials consume energy in procurement from sources, transportation to the place of processing, processing and in storage as well. Ordinary Portland Cement (OPC) and stone aggregates are some of the ingredients of concrete. OPC consumes energy in procurement, transportation of its ingredients, processing and in production. Aggregates consume energy in procurement, transportation to the production site of concrete and in processing. Total energy consumed in these processes is termed as Embodied Energy (EE). Reduction of EE of concrete is possible by replacement of OPC by industrial wastes such as Fly Ash, Ground Granular Blast Furnace Slag, and utilization of natural stones as aggregates with due care of natural ecology and landscape.
Concrete is an inexpensive and durable material; therefore, it is the most common and globally used building material. Concrete consumption has increased two folds – relative to steel, over the past 50 years. In the year 2012, Consumption of concrete was estimated to have topped 10 billion cubic meters worldwide, consists of approximately 3.8 Gt cement, 2.0 Gt of water used for concrete making, and 17.5 Gt of aggregates. Concrete manufacturing is a significant source of global carbon dioxide emissions. Concrete production was responsible for approximately 8.6% of all anthropogenic carbon dioxide emissions in the year 2012 .
Concrete is a prime construction material for buildings. Its ingredients are:
(1) Ordinary Portland cement (OPC), 53 Grade as per IS 12269,
(2) Natural or quarried crushed stones as coarse aggregate of 20 mm or 40 mm maximum size (MSA), as per IS 383-2016,
(3) Natural or crushed quarried sand as a fine aggregate as per IS 383-2016,
(4) Water as per IS 456- 2000.
The total energy in ingredients of concrete and that in production, transportation, placement and compaction of concrete in elements of the building is termed as ‘Embodied Energy’ (EE) of concrete.
This study explores the possibility of making ‘Green Concrete’ in the construction of buildings. In the study, “Green Concrete” means concrete having less EE through the utilization of industrial wastes and low resource consuming materials.
Scope of study
Scope of the study includes EE in OPC, coarse and fine aggregates and water as described hereunder. EE up to a place of making concrete in city of Ahmedabad, Gujarat is considered as a case in the study.
EE in concrete
EE in concrete consists of that in its ingredients as described under.
The quantity of water and hence its EE in a cubic meter of concrete is a function of its workability. Workability depends upon properties of aggregates (MSA, shape, and surface texture). The maximum size of aggregates depends upon the size of reinforcement bars, their spacing and cover requirement. Workability of concrete also depends upon means of compaction of concrete. From Table 1, it can be noted that quantity of water per cubic meter of concrete varies from 115 liters with 40 mm MSA smooth rounded spherical aggregates to 225 liters for 20 mm MSA angular rough textured ones. Wet density (kg per cubic meter) of concrete varies inversely with the quantity of water. The quantity of aggregates would be the wet density of the concrete minus quantity of water and OPC.
EE in OPC includes energy used in mining of its ingredients, its transportation, grinding, sieving, and storage in silos at the place of its production. Further EE in OPC includes thermal energy used in rotary kiln as per process, energy in grinding clinkers, sieving and storage of OPC in silos and bagging, packing and transportation to the place of concrete making. EE per kg of OPC varies as per technology of production employed in a plant. The quantity of OPC in a cubic meter of concrete is a function of the quantity of water and w/c ratio and is about 12% to 18% of the quantity of concrete.
EE in coarse aggregates includes energy used in quarrying, crushing, sieving, and transportation to the place ok making concrete depends upon the source(s) of procurement, transportation and processing. Aggregates from natural deposits have less EE than that of crushed quarried aggregates. Maximum size and texture of aggregates affects the EE of a cubic meter of concrete indirectly through the quantity of water for workability. EE per kg of aggregate is low but its mass in concrete is high. EE in fine aggregate includes energy used in dredging, sieving and transportation to the place of making concrete. EE in fine aggregate includes energy used in dredging, sieving and transportation to the place of making concrete.
Measures to make green concrete
1) Replacement of OPC by supplementary cementitious materials
Monocalcium Silicate (CaO. Sio2), a product of hydration of OPC, contributes to strength, and durability of concrete. Calcium hydroxide (Ca (OH)2) another product, leaches out leaving pores in the mass of concrete. By adding a pozzolan material, calcium hydroxide can be converted into monocalcium silicate. The overall result is gain in strength and durability properties of concrete. Fly Ash, a waste from thermal power stations using bituminous coal, satisfying requirements of IS 3812 is a pozzolan material. IS 456-2000 allows 20 percent of a pozzolan material as replacement of OPC.
From the above discussions, it can be inferred that the concrete mix has a wide spectrum. A set of four tables is presented in Table 2 to 5 as an illustration (for 40 mm MSA and four for 20 mm MSA). Workability of 30 to 60 mm slump, w/c ratio of 0.5, the average specific gravity of 2.78 of aggregates and IS Zone II-III sand are assumed in the Tables2 to 5. 0.0 to 30 percent replacement of OPC by fly ash and types and proportions of coarse and fine aggregates are variables in the Tables 2 to 5.
Summary of the illustrations is presented in Table 6. It is observed from the summary that contribution of EE of OPC that of concrete is generally high. Replacement of OPC by fly ash reduces EE of concrete. Using water reducing admixtures, the quantity of OPC and hence its EE can be reduced. Reduction of EE of concrete due to the reduction of the quantity of OPC would be partly offset by the increased quantity of aggregates because of the increased wet density of concrete.
a) % EE of OPC and aggregate is 98% to 99% of total EE of concrete,
b) From the summary, it can be seen that EE varies from 483 KWh in a cubic meter of concrete with 40 mm smooth rounded aggregates to 750 KWh in that with 40 mm MSA crushed aggregates. Corresponding values for 20 mm MSA are 778 KWh and 511 KWh (more than 50% of both in concrete with 40mm and 20mm MSA).
c) EE of concrete reduces with replacements of OPC by fly ash. For 30% replacement of OPC, EE reduces from about 483KWh to 395 KWh in concrete with 40 mm MSA and from 511 KWH to 412 KWh for 20mm mesa. The percentage reduction is about 18%.
1) Di Filippo, James, Jason Karpman, and J. R. DeShazo. “The impacts of policies to reduce CO2 emissions within the concrete supply chain.” Cement and Concrete Composites (2018).
2) Miller, Sabbie A., Arpad Horvath, and Paulo JM Monteiro. “Readily implementable techniques can cut annual CO2 emissions from the production of concrete by over 20%.” Environmental Research Letters 11.7 (2016): 074029.
3) Indian Standard-I.S. “IS 12269-1987: Specifications for 53 Grade Ordinary Portland Cement”, Bureau of Indian Standards, New Delhi, (1987).
4) Indian Standard, I. S. “IS 383, Specification for Coarse and Fine Aggregates from Natural Sources for Concrete”, Bureau of Indian Standards, New Delhi, 2016.
5) Indian Standard, I. S. “456: 2000: Plain and Reinforced Concrete Code of Practice”, Bureau of Indian Standards, New Delhi, (2000).
6) SP23, I. S. “Handbook on concrete mixes.” Bureau of Indian Standards, New Delhi (1982).
7) BIS. “IS 3812: Specification for fly ash for use as pozzolana and admixture.” (2003).
8) Alcorn, Andrew. Embodied energy and CO coefficients for NZ building materials. The Centre, 2003.
Professor C.B.Shah is a Professor Emeritus at Faculty of Technology, CEPT University Ahmedabad. He is B.E.Civil from Gujarat University and M.S. from University of Wisconsin, Madison USA. Professor C.B. Shah was Dean of Faculty of Technology at CEPT University, besides teaching experience of more than 25 years at CEPT University, Professor has professional experience of more than 25 years in design of concrete mixes and testing of concrete structures by NDT and other methods.He has been a contributor to various national and international journals, and magazines through his research papers and articles. He was the chair of the thesis committee and guided undergraduate, master, and doctorate thesis.
Dr.ParthThaker is an assistant professor at Faculty of Technology, CEPT University. Heholds M. Tech in Structural Design from CEPT University and a Ph.D. in ConcreteTechnology from Gujarat Technological University. He has worked in academic positionsat various institutions and pursued professional work such as exhibition buildings,industrial buildings, and schools. He has been a contributor to various national andinternational journals, and magazines through his research papers and articles. He ispresently in charge of the concrete laboratory at CEPT University and is an activemember of the working committee of Indian Concrete Institute (Ahmedabad Chapter).