International Journal of Civil Engineering and Technology (IJCIET)
Volume 8, Issue 10, October 2017, pp. 498–506, Article ID: IJCIET_08_10_051
Available online at http://http://www.iaeme.com/ijciet/issues.asp?JType=IJCIET&VType=8&IType=10
ISSN Print: 0976-6308 and ISSN Online: 0976-6316
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CONTROLLED LOW STRENGTH MATERIAL
(CLSM) AS ROBUST BACKFILL MATERIAL
Anil Jadhav
Nexus Techno Consultants
Pramod Bongirwar
Indian Road Congress
R. R. Raut
Pune Municipal Corporation
D. P. Patil
Pimpri Chinchwad Municipal Corporation
ABSTRACT:
soil or improved soil/ aggregates with predefined gradation (GSB, WMM) are
primitively used for backfill, (both structural / non-structural back fill), pavement
bases, void filling etc., with its inherent limitations of air voids, stiffness, need for
compaction, susceptibility to water penetration, susceptibility of settlement etc.
Controlled low strength material (CLSM) eliminates the drawbacks of soil backfill
providing durability to the supporting structure. CLSM is compulsorily a back fill
material and not a low strength concrete, rather it can be well defined as material
which is designed as concrete with flow ability and strength as per the requirement
and used as backfill to avoid the drawbacks of the soil or murum backfill.
Contrary to the soil, the strength and thus the bearing strength of the fill can be
controlled allowing with scope for future changes. ACI 116R defines CLSM as per the
strength criteria, “CLSM as material that results in a compressive strength of less
than 8.3 Mpa”
CLSM can be designed with varying strength and density, considering the cost and
future needs, low strength CLSM shall be necessary to allow future excavation,
whereas if the there is no scope for future excavation the strength can be at higher
side, further the density of CLSM can be modified as per the cost and material needs.
Properties of CLSM can be enhanced as per the requirement to compensate
particular need like corrosion resistance, Exacavatability, strength flow ability etc.
Material properties such as shrinkage, subsidence and settlement are not
considered as specification performance or requirement properties. These properties
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Anil Jadhav, Pramod Bongirwar, R.R Raut and D.P.Patil
are considered as inherent to CLSM and as such; do not require the establishment of
specification requirement.
Keywords: Clsm, Robust Backfill Material
Cite this Article: Anil Jadhav, Pramod Bongirwar, R. R. Raut and D. P. Patil,
Controlled Low Strength Material (Clsm) As Robust Backfill Material, International
Journal of Civil Engineering and Technology, 8(10), 2017, pp. 498–506
http://www.iaeme.com/IJCIET/issues.asp?JType=IJCIET&VType=8&IType=10
1. INTRODUCTION:
Laying of new utility services is a continuous operation in all urban areas. The road side land
being public land is used for laying the services after taking permission from competent
authority. The depth of services could range from 30 centimeters to few meters in case of
sewer drains or water mains .Normally after making the trench the same material is backfilled
or even if new materials brought the strict control on quality is not maintained for being a
small quantity .Proper compaction in such narrow width also poses serious practical problem.
Sometimes trench width is increased to accommodate available compaction equipment .Due
to inadequate compaction the trench portion get settled, and lead to pot hole formations
leading to public criticism. Besides it requires continuous maintenance.
CLSM therefore proves an ideal material which addresses all these problems .The highly
flow able material fill all voids and uneven side, this gives additional support to moving
vehicles and settlement of trench does not take place hence the damage to road surface. In all
urban areas there is tendency to construct concrete roads .Edge strip of 1 to 1.5 m is left and
either flexible pavement is adopted or paver block is laid .This facilitates convenient laying of
services While laying the new services the entire top surface get disturbed. Improper
compaction leads to distortion to surface and hence car owners do not have tendency to use
this strip and thus there is permanent loss to road width .Solution to this, is a base of CLSM
and also restoration of trench by CLSM only. CLSM therefore can prove an ideal solution for
this typical urban problem
2. LITERATURE REVIEW – APPLICATIONS AND ADVANTAGES:
Flow ability without compaction makes it suitable for tight and restricted areas, compared to
traditional soil or modified soil backfill in various
2.1. Backfills:
The Ease of placing CLSM in restricted places without compaction facilitates the reduction in
trench width or excavation. Traditional methodology of backfilling in layers and compacting
will never provide with the uniformity of density as facilitated by CLSM. CLSM can be
placed in layers, allowing each layer to harden prior to placing the next layer.
2.2. Structural Fills:
CLSM with higher strength can be produced to act as structural fills, in case of BC soil it can
distribute structures load on greater area. CLSM can provide a uniform and level surface for
uneven sub-grades under foundation footings and slabs.
2.3. Utilities Bedding:
CLSM provides an excellent bedding material for pipe, electrical, telephone, and other types
of conduits. The flow able characteristic of the material allows the CLSM to fill voids beneath
the conduit and provide a uniform support.
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Controlled Low Strength Material (Clsm) As Robust Backfill Material
Encasing the entire conduit in CLSM also serves to protect the conduit from future
damage. If the area around the conduit is being excavated at a later date, the obvious material
change in CLSM versus the surrounding soil or conventional granular backfill would be
recognized by the excavating crew, alerting them to the existence of the conduit. Coloring
agents have also been used in mixtures to help identify the presence of CLSM.
2.4. Erosion Control:
Laboratory studies, as well as field performance, have shown that CLSM resists erosion better
than many other fill materials. CLSM can be used in riprap for embankment protection and
in spilling basins below dam spillways, to hold rock pieces in place and resist erosion. CLSM
is used to fill flexible fabric mattresses placed along embankments for erosion protection,
thereby increasing their strength and weight.
In addition to providing an erosion resistance under culverts, CLSM isused to fill voids
under pavements, sidewalks, bridges and other structures where natural soil or non-cohesive
granular fill has eroded away.
2.5. Void filling:
Tunnel shafts and sewers—filling abandoned tunnels and sewers, it is important to use a flow
able mixture. A constant supply of CLSM will help keep the material flowing and make it
flow greater distances.
Basements and underground structures—abandoned basements are often filled in with CLSM
by pumping or conveying the mixture through an open window or doorway.
2.6. CLSM has also been used to fill abandoned underground storage tanks
(USTs).
Nuclear Facilities:
CLSM can also be used in unique applications at nuclear facilities, such as waste stabilization,
encapsulation of Decommissioned pipelines and tanks, encapsulation of waste-disposal sites,
and new landfill construction.
3. RESEARCH SIGNIFICANCE:
With the exponential increase in rehabilitation of utilities and development of new utilities
like, fibre optical line, natural gas lines the linear and cross excavation along road have also
increased, the tradition practice of filling the trench with the same material usually resulted
into summit of loose soil along road or depression along road. Further there was no proper
control of procedure to handle this issue. The present study is taken up to resolve the above
problems by developing a robust material and construction procedure or technology which
would add aesthetic up gradation to city look up avoiding shabby patchwork. The main focus
of the study was to develop concrete with flow ability which will be used as backfill
facilitating its property control competing with the rates of local backfill soil.
CLSM developed had essentially all the materials locally available with which the local
contractors are well versed further the preparation techniques were bit modified for intended
use. The mix design procedure was as per IS10262:2009 using fly ash as main component and
cement as secondary also specially formulated admixture were developed for activating fly
ash to exhibit hydraulic characteristics as adding fly ash may result into increase in initial
setting time. The primary focus was to exhibit early setting with flow ability because of old
city layout which was unfavorable for diversions and proper excavation.
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4. MATERIAL USED:
Conventional CLSM mixtures usually consist of same ingredients as that of normal concrete
Water, Portland cement, fly ash or other similar products, and finer or coarse aggregates or
both. The use of standardized materials is not always necessary provided the new materials
added are inactive in nature , Selection of materials should be based on availability, cost,
specific application, and the necessary characteristics of the mixture, including flowability,
strength, Exacavatability, and density.
Cement: Ordinary Portland Cement (OPC) of grade 53 confirming to IS 11269:2013 with
a specific gravity of 3.12 was used.
Fine Aggregates: Basalt rock chrused to confirm zone II of IS 383:1970 with specific
gravity ranging from 2.8-3.01 was used. Silt Content was not considered since the strength
aspect was not significant. Further it is suggested to use locally available non-reactive
aggregates like over burnt bricks in CLSM as it would be a wise decision to reduce the final
cost of CLSM.
Coarse Aggregates: Locally available, basalt stone aggregates with maximum nominal
size 20mm confirming to IS 383:1970 was used.
Water: Portable water was used to mixing and curing of CLSM
Admixture: Specially formulated admixture was used, the admixture was developed in two
components. The first component was Naphtha based retarder cum workability chemical used
for increasing the initial setting time and exhibiting flow ability like Self Compacting
concrete. The second component consists of accelerator cum activator to start the setting and
strength gain.
4.1. MIX DESIGN:
The proportioning of the ingredients was as per IS10262:2009, with fly ash as the main
ingredient and cement as supplementary material, further the focus of the mix design was to
develop substitute for backfill which matches its rate but consist the advantages of CLSM. So
the density was lowered to 1750 kg per cubic metre which can be advocated to match with the
density of traditional backfill material like murum, GSB etc. The design was formulated for
fine contents to match up with the requirements of Self compacting concrete to yield flow
ability without segregation.
The typical all in aggregate gradation was as below:
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4.2. CONCRETE MIX DESIGN:
Materials
Unit
Weight
Cement
Fly Ash
Micro silica
20 mm
10 mm
R.Sand
C.Sand
Water
Admixture
Kg
Kg
Kg
Kg
Kg
Kg
Kg
Kg
Kg
50
200
0
313
364
0
567
195
1.50
%
M.C.
0.60
0.85
0.05
1.21
W.A
1.28
1.31
1.47
3.65
Correct
0.68
0.46
1.43
2.44
T.Correct
2.13
1.68
0.00
13.85
17.65
1.00cum
50
200
0
311
363
0
554
213
1.50
4.3. RATE ANALYSIS OF CLSM:
Sr.NO.
Description of Material
1
2
3
4
5
6
7
8
9
10
10 MM
Crush Sand
River Sand
20 MM
Cement
Fly Ash
Admixture
Water
Transportation
Operating Cost
TOTAL
GRAND TOTAL
Average
Rate / kg
0.41
0.55
0
0.41
5
1.5
60
0.05
150
300
Design 1
Amount RS.
363
554
0
311
50
200
3
213
1694
148.83
304.7
0
127.51
250
300
180
10.65
150
300
1772
RS 1772
5. LABORATORY TRIAL:
Laboratory trials were conducted to study workability and strength behaviour of CLSM.
Observations of CLSM workability was noted in laboratory for intial flow which was
intentionally kept at 600mm considering the lead time of 30 min. The sole purpose of 1st
component of admixture added was to retard the setting or dropping of slump of CLSM.
Figure 1 Flow observed after 30 min around 580mm average
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After adding second component which necessarily consists of accelerator and fly ash
activator, the slump of 170 mm was noted after 60 min
Figure 2 Slump: 170 mm after 60 min
Final settings of CLSM in casted cubes were around 4 hours in laboratory. Compressive
strength of cubes was noted after 28 days curing as per IS 516:
Sr.no
1
2
3
Cube Size
150x150x150
150x150x150
150x150x150
Strength
3.25
3.10
2.98
Average
3.11 Mpa
5.1. PILOT FIELD TESTS:
CLSM field trails were conducted with the help of Pune Municipal Corporation at Ideal
Colony, Kotrud Pune. The trail was intended for backfill the conduit excavation along the
road.
The Second field trail was conducted with the aid of Pimpri Chinchwad Municipal
Corporation at Dapodi for backfilling the MNGL conduit excavation across the busy PuneMumbai Expressway.
5.2. Kotrud-Pune Trial: (Along the Road) Dated: 06-09-2016
CLSM was produced with mechanized plant (Ready Mix Concrete Plant) of 0.5 cubic
metre per batch capacity and transported through transit mixer with a lead time of about 30
min
The first component was primarily used at mixing point i.e. RMC plant which gave a flow
of about 400-600 mm till 1 hour, again since strength didn’t play a major role in CLSM the
water content can be at higher side to retain the flow ability depending upon the lead time or
distance of point of discharge. The second components which consist of accelerator with
activators were mixed in transit mixer/miller with measured quantity at the point of discharge
10 min before discharge of CLSM with proper mixing. This component enable the CLSM set
early for facilitating human movement, but vehicular movement both light and heavy were
not advised.
Addition of second component reduces the flow ability after 30 minutes, so considering
the distance of discharge point it should be accordingly added.
CLSM was placed in trenches of about 600mm deep, initial flow was good enough to
make the CLSM to flow in all corners and notches on the trench; the trench was filled once
till the surface. The surface was roughed after two hours on initial setting.
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Figure 3 Actual Site Photo after 4 hour.
CLSM was hardened enough to bear the load of human which satisfied the design
considerations of setting within 6 hours and avoided the practical problems of citizen
interference.
6. RESULTS:
The 28-day compressive strength of the CLSM was determined using cube specimen of
150mmX150mmX150mm as per IS 516.The compressive strength developed was 3.43Mpa in
28 days.
Sr.no
Cube Size
Strength
Average
1
2
3
150x150x150
150x150x150
150x150x150
3.25
3.60
3.45
3.43 Mpa
6.1. Dapodi-MNGL line Trail –Pimpri Chinchwad Dated: 15-08-2017
CLSM was produced with mechanized plant (Ready Mix Concrete Plant) of 1.25 cubic metre
per batch capacity and transported through transit mixer with a lead time of about 60 min
Going with the experience, the first component was primarily used at mixing point i.e.
RMC plant which gave a flow of about 550-700 mm, the second component was mixed in
transit mixer/miller with measured quantity at the point of discharge 10 min before discharge
of CLSM with proper mixing.
CLSM was placed in trenches of about 750mm deep, initial flow was good enough to
make the CLSM to flow in all corners and notches on the trench, the trench was filled in
layers to prevent the excess pressure transfer on sides bracing. The surface was roughed after
two hours on initial setting.
A compressive strength result for 28 days using cube moulds of specimen 150x150x150
as per IS 516 was 4.25 Mpa Average.
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7. CONCLUSION:
Based on the lab studies and pilot projects Conducted, the following conclusion can be drawn.
In the view of problems faced due to disadvantages of convention backfill material results
are in favour of CLSM.
The desired engineering properties of CLSM in fresh and hardened state can be altered or
modified depending upon the project requirement gives CLSM upper hand over the
convention soil back fill.
The rate analysis of CLSM further advocates its use compared to the convention backfill
material which will never give the uniformity in density of back fill and involvement of
labour dependency.
REFERENCES:
[1]
[2]
[3]
[4]
[5]
[6]
[7]
ACI Committee 229 (Reapproved 2005) Controlled Low Strength Materials American
Concrete Institute Journal
AASHTO Guide for Design of Pavement Structures, American Association of State
Highway and Transportation Officials, Washington, D.C., 1986.
Ramme, B. W., Progress in CLSM: Continuing Innovation, Concrete International, V. 19,
No. 5, May 1997, pp. 32-33.
Adaska, W. S., Controlled Low-Strength Materials, Concrete International. 19, No. 4,
Apr. 1997, pp. 41-43.
IS 12269-2013 Indian Standard Specification for Ordinary Portland Cement-53 Grade
(First Revision) Bureau of Indian Standards, New Delhi
IS 383-1970 (Reaffirmed 1997) Indian Standard Specification for coarse and fine
Aggregates from Natural Source for Concrete Bureau of Indian Standards, New Delhi.
IS 9103-1999 Indian Standard Specification for Concrete Admixtures, Bureau of Indian
Standards, New Delhi.
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Controlled Low Strength Material (Clsm) As Robust Backfill Material
[8]
[9]
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[11]
[12]
IS 10262-2009 Indian Standard Concrete Mix Proportioning Guidelines (First Revision)
Bureau of Indian Standards, New Delhi.
IS 516-1959 Method of test for Strength of Concrete Bureau of Indian Standards, New
Delhi. India
K. V. Ramesh, R. Goutham and I. Siva Kishore An Experimental Study on Partial
Replacement of Bagasse Ash in Basalt Concrete Mix, International Journal of Civil
Engineering and Technology, 8(5), 2017, pp. 335–341.
K. Kiran and I. Siva Kishore, An Experimental Study On Partial Replacement of Cement
with Bagasse Ash In Concrete Mix. International Journal of Civil Engineering and
Technology, 8(1), 2017, pp. 452–455.
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Hydrogenated Low Strength Structural Steel Under Different Heat Treatment Conditions,
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Volume 5, Issue 4, April (2014), pp. 111-118
AUTHORS BIOGRAPY:
Anil Jadhav: is certified Concrete Technologist, holds Diploma, Bachelors, Degree in Civil
Engineering and PGPCM (Construction Management) from AICTE, PUNE UNIVERSITY
and NICMAR respectively. Presently working as Chief Consultant with NEXUS TECHNO
CONSULTANTS and visiting Industrial faculty for Advanced Concrete Technology with
MIT Academy of Engineering, Alandi, Pune. He has 10 years of experience with
Transportation Engineering and Concrete Technology. His Prime area of focus is to research
and develop Innovative Construction Materials and Technology.
Pramod Bongirwar, Retired in March 2003 in the capacity of Principal Secretary,
PWD.Was involved in executing several prestigious projects as Mumbai, Pune expressway,
50 Flyover in Mumbai, 25 ROB, Planning for 20000 tenements for project affected persons
etc. Introduced several cost effective and innovative designs of bridges After retirement
served as part time Advisor with IDFC for 11 years and now with Larsen and Toubro for last
12 years Has experience of 20 years on BOT projects and major highway projects Served as
members of several IRC Committees and Government advisory committees. Written several
articles in National and International conferences Recipient of Distinguished Alumnus Award
of IIT, Mumbai.
Rajendra Raut, Chief Engineer (Roads) Pune Municipal Corporation, is Graduate Civil
Engineer from Pune University having 28 years’ experience with almost 20 years in Road
department of PMC was involved in much technological innovative initiative undertaken by
PMC.
Deepak Patil: Deputy Engineer (BRTS) Pimpri Chinchwad Municipal Corporation is
Graduate Civil Engineer from Pune University having 15 years’ of experience. Currently
involved with BRTS Division of PCMC.
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