flexural behavior of fly ash-slag based reinforced … · · 2017-08-04vijay rangan et al[3],[4],...
TRANSCRIPT
International Journal of Theoretical and Applied Mechanics.
ISSN 0973-6085 Volume 12, Number 4 (2017) pp. 845-856
© Research India Publications
http://www.ripublication.com
Flexural Behavior Of Fly Ash-Slag Based Reinforced
Geopolymer Concrete Slabs Cured At Room
Temperature
Mahantesh NB 1, Amarnath. K2, Raghuprasad. B K3
1 Alliance University,Bangalore 2 & 3 The Oxford College of Engineering, Bangalore
Abstract
The Alkali activated low calcium fly ash & slag based reinforced structural
components are being popularized in the most consumed sector of concrete
construction industry. Slag by providing early age strength to geopolymer
concrete(GPC) fulfills the actual need of consumers of cast in situ
applications. The present research work outlines the efficacy of slag in
reinforced geopolymer flexural components. Reinforced GPC slabs using low
calcium fly ash & slag at 70:30 proportion, reinforced with HYSD steel bars
and cured at room temperature are tested by applying monotonically
increasing transverse loads. Slabs were subjected to central point load (CPL)
and UDL conditions. The computed and measured load vs. displacement
curves are found to be in close agreement. The flexural behavior of reinforced
GPC slabs follow distinct stages similar to OPC based RCC components.
Keywords:Geopolymer concrete, flexural behavior, Fly ash, GGBS, alkaline
solution, crack width.
1.0 PREVIOUS RESEARCH WORK.
From the early research groups of 21st century it was observed that low calcium fly
ash based geopolymer concrete (GPC) develops strength in proportion to the amount
of heat or steam provided during its early stage of polymerization. Although fly ash
based GPC has appreciable structural skills but heat/steam curing requirement has
become the major limiting factor in further developing the in-situ applications of
reinforced geopolymer concrete structural elements. Concluding investigations from
Vijay Rangan et al[3],[4], [18] & Radhakrishna[2] it is observed that fly ash - slag
846 Mahantesh NB, Amarnath.K, Raghuprasad.B K
based GPC develops significant early strength and very good structural skills at
ambient curing which are superior to OPC based RCC applications and thus opening a
broader way for in situ applications of Reinforced Geopolymer Concrete
2.0 MATERIAS AND MIX PROPORTIONS USED.
Fly ash used in this work collected from Raichur thermal power plant in Karnataka
has sp.gr 2.15,Silicon dioxide (SiO2) 61.98%,Aluminium oxide (Al2O3)
26.06%,calcium oxide(Cao) 3.05%. Slag is procured from Jindal Steel Plant Bellary-
Karnataka has sp.gr 2.62, Silicon dioxide (SiO2) 33.88%,Aluminium oxide (Al2O3)
18.02%,calcium oxide(Cao) 34.98%. M-Sand ,crushed from granite stone, having
Sp.gr 2.45 , Fineness Modulus (F.M) 2.70 & River
Sand of sand stone origin having F.M 2.62 confirming to Zone III of IS 383-1970 are
used. Coarse aggregates of granite origin of sizes 20mm,12.5mm & 4.75mm having
water absorption 0.5% by weight at room temperature (16 to 28 degree).
Sodium hydroxide of 97% purity and sodium silicates with Na2O=14.7%,
SiO2=29.412%, water = 59.9% by mass are used to form Alkaline Activator Solution
using ratio Na2Sio3/NaoH = 2.5 . Alkaline Activator Solution (AAS) is prepared 24
hours before mixing of concrete. Molarity of the NaoH solution (SHS) is determined
by the relation M=0.25PD , where M is the molarity of NaoH solution , P is
concentration of sodium , D is the density of SHS for P. Therefore to get 1liter of SHS
of 8,10 and 12 Molarity (255+745) ,(306+694) and (354+646) of ( Sodium
Hydroxide pallets in gms + water in gms) are added respectively. Sulphonated
naphthalene based super plasticizer i.e Conplast SP430 DIS distributed by FOSROC
chemicals is used. Reinforcement is of Fe500 grades.
3.0 SPECIMEN DETAILS AND LOAD TESTING:
The size ,reinforcement details ,compressive strength of GPC of slab concrete and
other relevant details of specimens are listed in Table 2 Three types of slabs with
aspect ratios 1, 1.5, and 2 were cast with 10 mm clear cover, compacted and cured at
room temperature 16 degrees at night and 28 degrees Celsius during peak day time.
Maximum temperature outside the room was 36 degrees during peak day time and 24
degrees celsius at night.
The specimen were tested under point load and udl system generated through 50Mton
self straining loading frame with electrically operated hydraulic jack. One
displacement transducer (LVDT) connected to multichannel digital automatic data
logger was fixed at the center bottom of the slab to measure the maximum deflection.
Digital load measuring system comprises of electronic load cell connected to
Flexural Behavior Of Fly Ash-Slag Based Reinforced Geopolymer Concrete… 847
automatic data logger. The automatic data logger is connected to computer interface
system with advanced menu driven software enabling automatic measuring, recording
and storing of load Vs displacement out puts in to computer.
Table 1: Mix Design
SN Materials Weight
kg Specifications
1 Fly ash 276 70% of total fly ash
2 GGBS (30%) 120 30% of total fly ash
3 20mm to 12mm size
CA 451 35% of total CA
4 12mmto 4.75mm CA 451 35% of total CA
5 4.75mm & down sizes 389 30% of total CA
6 River sand 111 20% of total FA
7 M-sand 444 80% of total FA
8 Sodium Hydroxide of
8M 45 97% purity (26.20%)
9 Sodium
Silicate(Na2sio3) 113 Na2O14.7%,SiO229.4%
10 Super plasticizer 3.6 SP430DIS (1.5%)
11 Extra water 4.0 Potable water
NOTATIONS; FA : Fine Aggregates , CA: Coarse Aggregates
Fig 1 : Typical Reinforcement Details And Stress Strain Diagrams
L=975 mm
B=650 mm
08mmdia - 04# 08mmdia - 06#
b
D
Section A-A
N A
Strain Diagram
Xu
d-Xu
d
ecu
esu
Stress Diagram
ecu :strain at top edge of concrete
Stress Strain Diagram at 0.67fck- Non Linear Cracked Phase
d : effective depth
d
0.67fck
T=fsu.Ast
fsu : Ultimate tensile stress in steel
C=0.67fck.b.Xu
0.416 Xu
848 Mahantesh NB, Amarnath.K, Raghuprasad.B K
4.0 FLEXURAL STRESS STRAIN BEHAVIOR OF CONCRETE AND STEEL
Among the most widely used and easily available aggregates , Granite holds the first
place having Young’s Modulus varying from 10 – 70 GPa - far above the values of
sand stone rocks i.e 1- 20 GPa . When Manufactured sand of granite origin as fine
aggregate mixed with coarse aggregates of granite origin , with fly ash : slag at 70:30
the resulting composite of granite based geopolymer concrete develops better
structural properties. The relations between compressive strength and flexural
strength, modulus of elasticity i.e., for fly ash:slab at 70:30 closely follow the
expressions fcr=0.7√fck [2] and Ec= 5000√fck after 28 days of ambient
curing.[18],[19]
All slabs are analyzed using conventional elastic theory for the applied loads and
provided boundary condition using geometrical & material properties like
compressive strength, steel strength etc. listed in Table 2. The flexural stress strain
relations of top compressive concrete follow distinct stages similar to OPC based
RCC flexural components. The basic flexural compressive stress strain relations
proposed by popovics with modified curve fitting factor suggested by Ganesan [5]
used to predict the flexural behavior of compression concrete. The failure loads
corresponding to first appearance of tension crack in concrete, yielding of tension
steel and peak compressive stress corresponding to 0.67fck and 0.85fck are
determined
Typical Slab analysis and structural design output after numerical computations are
described in following graphs using load deflection curves, stress and strains
developed at top edge of compressive concrete, stress and strains developed in steel .
Fig 2 a) Stress Vs Strain in Compressive
Concrete-Slab No.6
Fig 2 b) Stress Vs Strain in Tension steel -
Slab No. 6
Flexural Behavior Of Fly Ash-Slag Based Reinforced Geopolymer Concrete… 849
5.0 STRENGTH AND DEFORMATION BEHAVIOR
The measured Load vs Deflection relations at center bottom of slabs are represented
in figure (3) to (8).The flexural stiffness of RGPC decreases with the gradual increase
in applied loads similar to OPC based RCC flexural elements. Till the appearance of
first crack in tension concrete, whole section including reinforcements are effective
in producing linear elastic behavior with noticeably low profile deflections.
The appearance of first crack and further loading will noticeably reduce the effective
depth and will increase the crack depth and width making concrete in tension less
effective and therefore tension resistance offered by concrete is ignored. However the
membrane action developed is taken into account by considering effective moment of
inertia recommended by Indian RC designer.
The composite continues to be in linear elastic stage till yielding of tension steel.
Numerical computations indicate significant shift in neutral axis once the tension steel
yields. The deflections based on new effective section indicate the loss of flexural
stiffness similar to OPC based sections. The close agreement between measured and
calculated deflections indicate a healthy bond strength between reinforcement and
tension concrete justifying the negligence of tensile strength in concrete .
The specimen is said to have failed structurally when compression concrete reaches
0.67fck while it has already crossed yield strength of tension steel as all slabs were
under reinforced. Further loading at post failure stage develop significant deflections
which are slightly deviating from calculated ones based on effective moment of
inertia.
The numerical computations for flexural deflections do not include shear deflections
which are estimated to be less than 0.5% of flexural deflections.
All the specimens behaved to produce strain hardening flexural deflections.
Comparison of load Vs deflection for CPL and UDL from Fig (3) to Fig (8) , it is
observed that the calculated deflections for Central Point Loads differ more than the
measured ones while for UDL there is marginal difference. Thus confirming the
sensitiveness of Geopolymer Concrete for point loads
6.0 DUCTILITY INDICES
The performance of structural elements is well appreciated , when their ability to
absorb and dissipate energy by post elastic deformations subjected to several cycles of
loading are naturally imbedded at low cost. Reinforced Geopolymer Concrete
(RGPC) develop significant ductility along with steel reinforcement.
850 Mahantesh NB, Amarnath.K, Raghuprasad.B K
Ductility indices of flexurally deflected RGPC elements are compared with calculated
ones. The Ductility Index(calculated ) = ∆u / ∆y where ∆u & ∆y are measured
deflections corresponding to computed yield load Fy & ultimate load Fu.
Similarly Ductility Index (measured ) = ∆um/ ∆y , ∆um is the maximum deflection the
component under maximum applied load Fum. Ductility Index(calculated) represents
the minimum ductility the GPC will develop and Ductility Index (measured)
represents maximum ductility the GPC will develop.
The Average Displacement Ductility is the average ductility between these two values
which is more probable to develop under Normal Quality Control during GPC
production.
Fig 3a): Load Vs Deflections Curves of Slab 1
Under CPL
(Measured & Calculated)
Fig 3b): Crack Patterns slab 1
Fig 4a): Load Vs Deflections Curves of Slab
2Under CPL
(Measured & Calculated)
Fig 4b): Crack Patterns slab 2
Flexural Behavior Of Fly Ash-Slag Based Reinforced Geopolymer Concrete… 851
Fig 5a): Load Vs Deflections Curves of Slab 3
Under CPL
(Measured & Calculated)
Fig 5b): Crack Patterns slab 3
Fig 6a): Load Vs Deflections Curves of Slab 4
Under UDL
(Measured & Calculated)
Fig 6b): Crack Patterns slab 4
Fig 7a): Load Vs Deflections Curves of Slab 5
Under UDL
(Measured & Calculated)
Fig 7b): Crack Patterns slab 5
852 Mahantesh NB, Amarnath.K, Raghuprasad.B K
Fig 8a): Load Vs Deflections Curves of slab 6
Under UDL
(Measured & Calculated)
Fig 8b): Crack Patterns of slab 6
S.No. Details Slab 1& 4 Slab 2 & 5 Slab 3 & 6
1 Span Side Length 1.3m 0.975m 0.8m
2 Size : L mm X B mm X D mm 1300 x 650 x 75 975 x 650 x 75 800 x 800 x 75
3 L/D 17.33 13.00 10.67
4 Self weight in kg 147.65 & 147.25 110.4 & 110.1 111.25 & 111.75
5 Aspect Ratio 2 1.5 1
6 Molarity 8M 10M 12M
7 Curing days 36 26 22
8 fck 57.87 N/mm2
45.96 N/mm2
41.7 N/mm2
9Reinforcement Parallel to
Shorter & Longer Sides8mm-4# & 7# 8mm - 4# & 6 # 8mm - 5# & 5#
10 Reinforcement 0.507% 0.507% 0.515%
11 Yield Stress & Ultimate Stress 533.94 - 587.33 533.94 - 587.33 533.94 - 587.33
12 Test Results - Central Point Load S1 S2 S3
Support Conditions 2SSS 2SSS 2SSS
First cracking load & deflection 11.1 kN - 0.5 mm 15.76 kN - 0.35 mm 17.53 kN - 0.20 mm
Steel Yielding load &deflection 20.07 kN - 6.2 mm 31.6 kN - 5.74 mm 35.6 kN - 2.85 mm
Ultimate load &deflection 23.0 kN - 12.09 mm 36.2 kN - 6.92 mm 41.11 kN - 3.43 mm
Max.applied load & delfection 23.07 kN - 27.6 mm 37.9 kN - 7.6 mm 44.29 kN - 4.4 mm
Crack width at ultimate load 3.7 mm 1.5 mm 1.5mm
Ductility - Cal - Measured - Average 1.55 - 3.09 - 2.32 1.21 - 1.94 - 1.57 1.16 - 2.66 - 1.91
13 Test Results - UDL S4 S5 S6
Support Conditions 4SSS 2SSS 2SSR
First cracking load & deflection 42.84 kN-0.3 mm 26.13 kN - 0.36 mm 57.22 kN - 0.67 mm
Steel Yielding load &deflection 87.83 kN - 1.1 mm 55.04 kN -5.9 mm 128.7 kN - 3.8 mm
Ultimate load &deflection 99.46 kN - 1.7 mm 63.03 kN - 7.13 mm 146.8 kN - 4.4 mm
Max.applied load & delfection 125.86 kN - 3.4 mm 77.39 kN - 13.80 mm 189.27 kN - 9.6 mm
Crack width at ultimate load 1.9 mm 1.3 mm 1.2 mm
Ductility - Cal - Measured - Average 1.20 - 4.45 - 3.26 1.69 - 2.11 - 1.90 1.20 - 1.54 - 1.37
14 Average Ductility of all Specimens Calculated = 1.483 Measured = 2.633 Avearge = 2.058
Notations Used:4SSS- All 4 Sides Simply Supported ,2SSS- Two Shorter Sides Simply Supported and Other Edges free,2SSR- Two Short Edges Partially Restrained and remanining edges free, UDL- Uniformely Distributed Loading , CPL- Central Point load, M- NaoH Molarity
Table 2: Structural Details of Specimen Tested
Flexural Behavior Of Fly Ash-Slag Based Reinforced Geopolymer Concrete… 853
7.0 CRACK WIDTHS AND PATTERNS .
Developed crack widths within the range of strains in tension steel up to 0.87fy/Es
(0.0023 for Fe415 steel having yield stress 533.87 N/mm2) are within the acceptable
limits and are in agreement with calculated ones based on Indian and BS RC
Designers. Crack patterns follow load type and boundary conditions used and are in
consistency with similar OPC based RC elements. Crack widths beyond strain in steel
0.87fy/Es are in excess of calculated ones.
8.0 RESULTS AND DISCUSSIONS
In this research work GPC is prepared by manual mixing and cured at room
temperature 16 to 28 degrees celsius. Manual mixing up to 20 to 30 minutes increases
workability for further concreting activities. Manual mixing and compaction needs
careful observation to ensure normal quality control to enhance the basic strength
properties of concrete similar to OPC based concreting.
Since all slabs were under reinforced , tension failure of the specimens were noticed.
The appearance of first crack was little earlier than the calculated ones indicating
slightly less flexural strength of concrete compared to IS Code i.e fcr=0.7√fck. The
average peak strain in concrete at 0.67fck stress gives 0.002 to 0.0025 for parabolic
stress block suggested by Indian RC code and for 0.85fck stress it gives 0.003 to
0.0035 for rectangular stress block.
The flexural behaviour of all tested elements show distinct stages of behaviour similar
to OPC based RCC flexural elements like appearance of first crack, yielding of
tension steel and peak stress failure of compressive concrete as seen from the Fig (3)
to Fig (8) .
The stress strain behavior of compression concrete in Reinforced Geopolymer
Concrete Sections under increasing flexural stresses are in line with popovics model
with slight modification to curve fitting factor.
Load Vs Deflections of measured ones with calculated values based on effective
moment of inertia are found to differ within acceptable limits. Shear deflections being
very less do not show noticeable deflection profile
From fig (9) & fig (10) , it is observed that the developed crack widths co relate with
calculated crack widths based on IS 456-2000 code. Crack widths are found to be
within acceptable limits at service loads.
854 Mahantesh NB, Amarnath.K, Raghuprasad.B K
9.0 CONCLUSIONS
Following conclusions are drawn based on the above research work
Geopolymer concrete manufactured using low calcium based fly ash with slag can be used for in situ applications of reinforced geopolymer concrete flexural applications.
The flexural behavior of Reinforced Geopolymer Concrete is similar to Conventional RCC using OPC. Indian Code 456-2000 can be used to predict all structural design related output. Especially this seems to be more valid for fly ash: slag at 70:30 proportions.
Low calcium fly ash and slag (70:30) based geopolymer concrete , with coarse aggregates & M - sand of granite origin , With Fe500 grade reinforcement, Displacement Ductility of RGPC could be in the range 1.50 to 2.70. And The average displacement ductility of RGPC could be around 2.10
ACKNOWLEDGEMENTS:
The Authors wish to thank Management of Alliance University Bangalore And The
Oxford College of Engineering - Bangalore for their kind support while investigating
this research work.
Fig 9) Load Vs Crack widths - Central Point
Loads
Fig 10) Load Vs Crack widths : for UDL
Flexural Behavior Of Fly Ash-Slag Based Reinforced Geopolymer Concrete… 855
10.0 REFERENCES
1) Rajamane ‘et al’,” Flexural behavior of reinforced geopolymer concrete beams”,
International Journal of Civil and structural Engineering,Vol 2, No 1, 2011
2) Radhakrishna et al 2014,” Strength Characteristics of Open Air Cured
Geopolymer Concrete”, TRANSACTIONS OF THE INDIAN CERAMIC
SOCIETY,FEB 2014
3) Pradip Nath, Prabir Kumar Sarker (2014), “Effect of GGBFS on setting,
workability and early strength properties of fly ash geopolymer concrete cured in
ambient condition.” Department of Civil Engineering, Curtin University of
Technology, Australia
4) Vijay Rangan et al ,”Early Age Properties of low calcium fly ash geopolymer
concrete suitable for ambient curing”, The 5th International Conference of Euro
Asia Civil Engineering Forum,(EACEF-5),Sept 2015.
5) N Ganesan ‘et al’,” Development of stress block parameters for geopolymer
concrete “,The Indian Concrete Journal, September 2015, vol 89,Issue 9,pp 47-56.
6) Rangan B V ‘ et al”,” Modified Guide lines for Geopolymer Concrete Mix Design
Using Indian Standard “. Asian Journal of Civil Engineering( Building And
Housing) Vol 13,No3(2012).
7) Prakash Desai & K U Muthu,” A brief review on strength, deflection and
cracking of rectangular ,skew and circular reinforced concrete slabs”, Indian
Institute of Science , Mar-Apr 1988,91-108
8) Robert Park & Thomas Paulay,” Reinforced Concrete Structures”, John Wiley &
sons,INC.UK 2013
9) INDIAN STANDARD 456-2000.
10) Djwantoro Hardjito,” Studies on Fly Ash based Geopolymer Concrete”, Thesis
Report, Curtain University of Technology , November 2005.
11) Charles E Reynolds & James C Steedman, ”Reinforced Concrete Designer’s Hand
Book”,10th Edition
12) Magdy I. Salma “ Analysis of slabs spanning in two directions under concentrated
load”, HBRC Journal (2012) 8,212-216
13) Mahantesh et al,” Study on Flexural Behaviour of Fly Ash based reinforced
rectangular Geopolymer Concrete slabs “,International Journal of Engineering
Research & Technology (IJERT), ISSN: 2278-0181, Vol. 4 Issue 09, September-
2015
14) Mahantesh et al, ”Infleunce of Ambient Curing on Reinforced Geopolymer
Concrete Structural Elements “,International Journal of Engineering Trends and
Technology, Volume 28,Number 4,October 2015
856 Mahantesh NB, Amarnath.K, Raghuprasad.B K
15) Daguang Han,”Experimental and Theoretical Invetsigation of the crack behavior
of RC Slabs subjected to biaxial bending”, Institute of Structural Engineering for
structural concrete, University of Armed Forces Munich, December 2011.
16) Said M.Allan,” Evaluation of Tension Stiffening effect on the crack width
calculation of flexural RC member“,1110-
016,2013FacultyofEngineering,AlexandriaUniversity.Production and hosting by
Elsevier B.V http://dx.doi.org/10.1016/j.aej.2012.12.005
17) Rajamane N P & Jayalakshmi R ,”Quantities of Sodium Hydroxide Solids And
water to prepare sodium hydroxide solution of given molarity for geopolymer
concrete mixes “,ICI technical paper
18) Kadirnaikar ‘et al’, ”Stress strain Characteristics for Geopolymer Concrete-An
Experimental Approach CACE Volume 2, Issue 2 Apr. 2014 PP. 44-47,American
V-King Scientific Publishing,2014
19) Vijay Rangan,” Geopolymer Concrete for Environmental Protection”, The Indian
Concrete Journal, April 2014.
AUTHORS:
Prof.Mahantesh N B,Associtae Professor, Alliance University
Bangalore, has 10 years of Industrial Experience as Design Manager &
20 years teaching experience.He is a research scholar working on
alternate concrete technology .
Dr Amarnath .K, Prof & HOD Civil Dept, The Oxford Engg college
Bangalore (TOCE), has 30 years of experience in Teaching & Industry.
His research areas include concrete technology & tall buildings.He is
actively involved in guiding Ph.D & M.Tech thesis, material testing
and industry related consultations.
Dr Raghuprasad B K is working as Professor at The Oxford
Engineering College Bangalore(TOCE) .Formerly he was working as
Professor at Indian Institute of Science – Bangalore. He has guided
many Ph.D (27) & M.Tech thesis. His Areas of research: Fracture
Mechanics of Concrete, Structural Dynamics, Earthquake Resistant
Design, Finite Element and Boudary Element methods.