SUSTAINABILE CONCRETE IN NUCLEAR STRUCTURES
Ranjan Kumar1, Kapilesh Bhargava1, DK Nagori2, K Srinivas2, Ankush Sharma2
1. Bhabha Atomic Research Centre, Mumbai & Homi Bhabha National Institute,
Anushaktinagar, Mumbai, India
2. Bhabha Atomic Research Centre, Mumbai, India
ABSTRACT. Concrete is a global builder and widely used construction material in nuclear
structures all over the world. Since long time, concrete has been serving the power, societal
and commercial needs of the mankind through means of building the nuclear structures e.g.
nuclear power plants, accelerators, radiological laboratories etc. to sustain our progress. The
basic materials that comprise concrete are also global and this makes it second to water only
in volume consumption. Contribution of concrete in developing the living world is immense
and it has unique contribution to how we live both now and in the future. Concrete is having
versatile relevance and potential for further exploitation. In the present day scenario, ensuring
correct, durable and sustainable applications of concrete, and addressing environmental
concern is challenging. Research on sustainable concrete material properties is of great
importance. Use of various constituent materials e.g. chemical admixtures of plasticizer/super
plasticizer category as well as viscosity modifiers and mineral admixtures like fly ash and
silica fume, high performance concrete has resulted into production of sustainable concrete
The present paper summarizes the development of use of sustainable concrete in nuclear
structures in India.
Keywords: Sustainability, Concrete, nuclear structure.
Dr Ranjan Kumar is a Scientific Officer/F in Civil Engineering Division, Bhabha Atomic Research
Centre, Mumbai, India and PG teacher at Homi Bhabha National Institute, Mumbai, India.
Telephone:02225593062 Email Id: ranjancv42@gmail.com.
Dr Kapilesh Bhargava is a Scientific Officer/H, Nuclear Recycle Board, Bhabha Atomic Research
Centre, Mumbai, India and Professor at Homi Bhabha National Institute, Mumbai, India.
Telephone:02225597999 Email Id: kapilesh_66@yahoo.co.uk.
Shri DK Nagori is a Scientific Officer/H and Superintending Engineer in Civil Engineering Division,
Bhabha Atomic Research Centre, Mumbai India. Telephone: 02225596158 Email Id:
dknagori@barc.gov.in.
Shri K Srinivas is a Scientific Officer/H and Chief Engineer in Civil Engineering Division, Bhabha
Atomic Research Centre, Mumbai India. Telephone: 02225595445 Email Id: srinivas@barc.gov.in.
Shri Ankush Sharma is a Scientific Officer/C, Bhabha Atomic Research Centre, Mumbai India.
Telephone: 02225593086 Email Id: ankushs@barc.gov.in.
INTRODUCTION
Concrete is invariably used in nuclear industry. In nuclear industry, the main structure is
nuclear reactor or a group of reactors together with all associated structures, systems and
components necessary for safe generation of electricity. Other nuclear facilities include all
nuclear fuel cycle and associated installations encompassing the activities covering from the
front end to the back end of nuclear fuel cycle processes and also the associated industrial
facilities such as heavy water plants, beryllium extraction plants, zirconium plant, etc.. The
major component of nuclear power plant is containment structure which is made of pre
stressed concrete. The requirement of containment structure is radiological protection, leak
tightness, durability, structural integrity etc. The production of concrete constituents namely
cement and aggregate raise environmental concerns. The cement production releases
greenhouse gases and the contribution of cement industry to global CO2 emission is
approximately 7% [1]. Aggregate is also responsible for loss of habitat, erosion,
sedimentation etc. There is massive consumption of natural resources e.g. water, aggregates
etc. There is waste generation from demolition of concrete structures. Construction and
demolition waste is also among the primary sources of waste [2]. It affects energy use and
environment which is responsible for un-sustainability. There is a need to reduce resource
consumption and carbon footprint. Environmental friendly concrete is need of the day.
Replacement of cement and aggregate with alternative materials will create sustainable
concrete. Aggregate replacement can be done with recycled concrete aggregate, agricultural
and industrial wastes, recycled waste, lightweight aggregate, wastes obtained from
demolition etc. The usage of sustainable concrete solves many problems like cost reduction,
waste disposal, conservation of natural resources and protection of environment etc. The
performance, durability, strength and service life of sustainable concrete need to be evaluated
before their use. Identification of alternative constituents of concrete requires extensive
studies, preparation of trials mixes of concrete and testing. In the present paper, development
and use of sustainable concrete in nuclear industry is highlighted.
CONCRETE IN NUCLEAR STRUCTURES
Concrete is used in nuclear industry because of a number of advantageous properties it has;
mould-ability, easy manufacturing process, usage of mainly locally available ingredients,
relatively less production cost, good strength in compression, good shielding property against
radiation especially gamma radiation, etc.
For nuclear facilities, generally four types of concrete are used namely normal density
concrete, heavy density concrete, high performance concrete and self compacting concrete.
Concrete ingredients are normally cement, mineral admixtures, chemical admixtures, fine
aggregate, coarse aggregate, water and ice.
Normal density concrete is having density in the range of 22 to 26 kN/m3 and range of grade
of concrete is from M25 to M60. This type of concrete is used for structural members of
concrete structures. Temperature of placement is generally specified. Design requirement of
concrete is achieved at site.
Heavy density concrete is having density in the range of 36 to 56 kN/m3. This type of
concrete is used to meet the shielding requirement of nuclear structure. Heavy density
aggregates obtained from haematite, barites, ilmenite etc., steel/lead shots, steel punching etc.
are used to prepare heavy density concrete.
High performance concrete (HPC) is used for specific performance and uniformity
requirements e.g. placement and compaction without segregation, early age strength,
toughness, service life in severe environment, long term mechanical properties etc. HPC is
prepared with addition of acceptable mineral admixtures and suitable ingredients.
Self compacting concrete does not require vibration for compaction and it gets compacted by
self weight of concrete. Proper workability of concrete is maintained. Mix design is done to
ensure the required workability. Various tests on concrete are conducted for ensuring the
desired design parameters.
Design criteria of concrete structures important to nuclear safety are divided into three
categories namely radiological protection, serviceability and structural strength. Additionally,
leak tightness of the liquid-retaining structures is considered [3].
Concrete ingredients
Cement should be from approved brand confirming to relevant Indian Standard. Mineral
admixtures used for production of concrete are silica fume, fly ash, ground granulated blast
furnace slag (GGBS), pozzolanas, rice husk ash etc. Tests are conducted on concrete for
ensuring proper silica content, loss on ignition and specific surface etc. Uniform blending of
mineral admixtures with cement is ensured [4]. Chemical admixtures used for concrete
production are plasticisers, super plasticisers, retarding agent, viscous modifying agent etc.
Two or more admixtures may be used for same concrete after ensuring interaction and
compatibility. Generally, dosages of retarders, plasticizers and super plasticizers shall be
restricted to 0.5, 1.0 and 2.0 percent respectively by mass of cementitious materials [4]. A
higher value of above admixtures may be used based on performance tests relating to
workability, setting time and early age strength. Compatibility of admixture and cement
should be ensured. Fine aggregate and coarse aggregate to be used for nuclear facilities
should confirm to relevant code [5]. Slag and crushed over burnt brick or tile may be used for
plain concrete members [4]. Heavy weight aggregate or light weight aggregate e.g. bloated
clay aggregates and sintered fly ash aggregates may also be used after satisfactory data on the
properties of concrete made by them [4]. Use of fly ash increases workability, durability and
strength of concrete. Silica fume increases strength of concrete.
Fly ash is obtained as a waste product from thermal power stations and industrial plants using
pulverized or crushed or ground coal or lignite as fuel for boilers. The fly ash as a pozzolana
in the manufacture of and for part replacement of cement, as an admixture in concrete, and
products such as fly ash concrete blocks, asbestos cement products, etc, have been used. Use
of fly ash not only saves scarce construction materials but also assist in solving the problem
of disposal of this waste product. The guidelines for extraction, physical and chemical
requirements of fly ash for use as pozzolana for manufacture of cement and for part
replacement of cement in concrete have been provided [6]. Addition of fly ash in concrete
increases the workability and strength.
Silica fume is very fine non-crystalline silicon dioxide. It is a bi-product of the manufacture
of silicon, ferrosilicon from quartz and carbon in electric arc furnace. Silica fume is
expensive as compared to fly ash.
High performance concrete with high compressive strength, low shrinkage and high
durability are required. High performance concrete for containment structure using silica
fume content 7.5 to 10% was established by several trails to meet workability, strength,
shrinkage and durability requirements [7]. Finely divided fly ash and silica fume are used for
high strength concrete.
SUSTAINABLE CONCRETE IN NUCLEAR STRUCTURE
Due to higher safety concern in nuclear structures, workable and durable high strength
concrete is required. Use of chemical admixture such as plasticizer, super plasticizer
increases the workability of concrete. High strength concrete is obtained by using mineral
admixtures e.g. silica fume, fly ash, granulated blast furnace slag etc. replacing cement partly.
Use of chemical and mineral admixtures together can provide high performance concrete
(HPC). HPC is characterized by higher strength, workability and durability. Self compacting
concrete (SCC) is also used in nuclear structure and this concrete is compacted under the
action of self-weight. Performance of concrete in fresh stage is better as compared to normal
concrete. Chemical admixture such as viscosity modifying agent is used in case of SCC.
HPC of grade M60 using silica fume was used for Unit 1 of Kaiga dome [7]. Silica fume is
used in proportion of 5 to 10% of cement or fly ash content is at least 25% or slag content is
at least 50% in a mix [8]. There are two types of fly ash concrete namely low volume fly ash
concrete (LVFAC) and high volume fly ash concrete (HVFAC) where cement replacement
levels are 10-40% and 40-50% respectively. High volume fly ash concrete with 40% to 50%
cement replacement is used with sintered fly ash light weight aggregates for production of
M45 concrete for nuclear power plant structure in Soffolk, UK. This resulted in to huge cost
savings. In many Indian nuclear power plants (NPP), both LVFAC and HVFAC were used
with cement replacement level of 24-40% for safety related structural concrete and 40-50%
for non structural concrete respectively [9]. Self compacting concrete with high volume fly
ash has been used in Indian NPPs. Use of fly ash concrete make the concrete sustainable.
CONCLUDING REMARKS
The paper suggests that concrete for construction of nuclear structures needs to be durable,
achieved following sustainable practices. Different options that may be followed, which fit
within this are considered, including, cement selection, material proportioning and the use of
mineral admixtures are reviewed.
The paper concludes by providing an indication of how both durability and sustainability can
go together simultaneously. Use of various constituent materials e.g. chemical admixtures of
plasticizer/super plasticizer category as well as viscosity modifiers and mineral admixtures
like fly ash and silica fume, high performance concrete has resulted into production of
sustainable concrete. Development of use of sustainable concrete in nuclear structures in
India has been summarized.
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