A study on the behaviour of Geopolymer concrete funicular shell

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A STUDY ON THE BEHAVIOUR OF GEOPOLYMER

CONCRETE FUNICULAR SHELL

Sriram Jagadeep

1

,

N. P. Rajamane

1

and D. Arul Prakash

2

1

SRM Institute of Science and Technology, Kattankulathur, India

2_{Department of Civil Engineering, SRM Institute of Science and Technology, Kattankulathur, India}

E-Mail: [email protected]

ABSTRACT

Compression structure provides an alternative construction technology which optimizes the use of building materials and natural resources. Geopolymer concrete is an eco-friendly and sustainable material which gives initial setting, elimination of water curing, good durability and mechanical properties. In the view of above considerations, present work is carried out for funicular shells of different spans from 1m to 2m with varying rises of L/10 to L/20 are analyzed by using SAP2000 software. Experimental study is carried for both conventional and Geopolymer concrete funicular shells of specimens of size 1m X 1m and the thickness of 30mm with and without Mesh Reinforcement. The solution with 0.55MR were prepared along with 50% Flyash and 50% GGBS are used instead of cement for the casting of cubes, cylinders and Geopolymer concrete funicular shells. UDL load is applied over the shell; load carrying capacity and deflection are measured. Analytical and experimental results are compared. Funicular shell with mesh reinforcement gives more strength than normal shell for both conventional and geopolymer concrete funicular shell.

Keywords: funicular shell, discretization, SAP software, geopolymer concrete, molar ratio.

INTRODUCTION

Environmental degradation witnessed today as a result of an irresponsible use of construction materials and natural resources [1]. It is one of the greatest environmental issues and has become the major concern during the last decade. The emission of CO2 in to

atmosphere causes the depletion of ozone layer. Among the greenhouse gases, 65% of carbon dioxide causes the global warming. The cement production causes the 6% of all CO2 emissions, because one ton of cement production

releases one ton of CO2 in to atmosphere. In spite of the

fact that the utilization of cement is as yet unavoidable until later on, numerous endeavors are being made so as to decrease the utilization of Portland cement in concrete production. These include the utilization of alternative cementing material such as Flyash, GGBS, silica fume, rice husk ash and metakaoline. A standout amongst the most ideal option is the utilization of antacid actuated fastener utilizing mechanical waste comprise of silicate material. In 1978, Davidovits suggested that the binding material could be delivered by a polymeric response of soluble base fluids with the silicon and aluminum in the source material or by modern waste, for example, flyash and GGBS. He named these materials as a geopolymer. The most common industrial by-product used is flyash (FA) and ground granulated blast furnace slag (GGBS) [2-5]. Considering the fact, that new way of designing buildings so that the materials used for the construction of buildings can be decreased leading to reducing in the construction cost. Funicular shell is a thin doubly curvature shell of shape which is purely in compression structure. These shells are used for both roofs as well as floors [6]. The stresses in the thin shell is transferred purely tension accompanied by shear and bending stresses. The funicular shell is a compression structure, which can be built by using were waste material and natural

resources. It can be conserved effectively and use of expensive steel and cement are optimized [7].

ANALYTICAL INVESTIGATION

Concrete funicular shell of square ground plan with doubly curvature surfaces and various thicknesses are analyzed by using finite element based software SAP2000.

Generating coordinates for funicular shells:

In the Present study, the funicular shell is designed based on the equation from the cl. no. 5.1.2 of IS 6332:1984, the equation to find the central rise is noted down:

Z =Zmax(a2− x_(a₂2_b) ∗ (b₂₎ 2− y2)

Where,

Z = height of funicular shell at point x, y Zmax = the maximum central rise of the shell

a = half of the length of the shell b = half of the width of the shell

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By placing X and Y values in the formula, the Z-organizes at various focuses can be obtained shown in Table-1.

Table-1. Co-ordinates of the funicular shell.

X Co-ordinate (m)

Y Co-ordinate (m)

Z Co-ordinate (m)

0 0 0.1

0 0.10 0.0960

0 0.20 0.0840

0 0.30 0.0640

0 0.40 0.0360

0 0.50 0

0.1 0.10 0.092160

0.2 0.20 0.070560

0.3 0.30 0.040960

0.4 0.40 0.012960

0.5 0.50 0

Execution of program

To contrast the test results and hypothesis, analytical study is conducted. The grade of concrete adopted as M30 and thickness considered as 40mm. The Funicular shell of 1000mm X 1000mm and rise of 100mm is developed by using SAP2000 software, which is shown in Figure-2. The shell is discretized in to the elements as shown in Figure-3.

Figure-2. Funicular shell Model in SAP2000 (3D View).

Figure-3. Finite Element Modeling.

From the analytical results, the avoidance of the funicular shell are determined and chart is plotted. The max. principle stress and min. principle stress are taken as tensile stress and compressive stress as shown in Figures 4 and 5 respectively.

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Figure-6. Max principal stress.

Figure-7. Min principal stress.

Figure-8. Deflection.

Central rise L/10 Central rise L/15 Central rise L/20

Shell 1 172.35 145.47 118.2

Shell 2 145.48 102.084 89.126

Shell 3 313.93 200.96 114.6

1 51 101 151 201 251 301 351

M

ax p

ri

n

ci

p

al

st

re

ss (N

/m

m

2)

Shell 1 175.138 212.25 218.24

Shell 2 180 217.765 322.26

Shell 3 216.75 322.26 620.03

0 100 200 300 400 500 600 700

M

in

p

ri

n

ci

p

al

st

re

ss (N

/m

m

2)

Shell 1 0.019 0.0207 0.0301

Shell 2 0.0047 0.0074 0.0187

Shell 3 0.0221 0.0318 0.0416

0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.1

D

e

fl

e

ction

(m

m

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EXPERIMENTAL INVESTIGATION

MATERIALS

Table-2. Materials Used.

Material Property Result

Cement

Conforming BIS Code IS:12269

Fineness Index(90Micron) 6%

Fineness Index(Blaine) 420m2/kg

Specific Gravity 3.15

Flyash

Conforming BIS Code IS:3812

Type Class - F

Fineness Index(Blaine) 389m2/kg.

Bulk Density 1010Kg/m3

GGBS

Fineness Index(Blaine) 400m2/kg.

Bulk Density 1200Kg/m3

Fine Aggregate (M-Sand)

Conforming BIS Code IS: 383-1970

Water Absorption 2.2

Bulk Density 1.75 kg/m3

Coarse Aggregate

Conforming BIS Code IS:383

Fineness Modulus 6.8

Water Absorption 1.2%

Bulk Density 1630 Kg/m3

Mesh Reinforcement Size 1m X 1m

Type Mild steel

Table-3. Chemical Composition of Binder Material.

Component SiO2 Al2O3 Fe2O3 Na2O CAO MgO K2O

Cement 30 11 3 0.6 46 4 0.4

Flyash 34 20 0.15 - 37 7 -

GGBS 55 26 7 0.6 9 2 0.6

Table-4. Properties of Reaction Generating Solution.

Chemical Formula Na2O : SiO2

% of Na2O 13.7

% of SiO2 29.4

H2O 55.9

Boiling Point 102 ֯C for 40% of Aqueous Solution

Density 1.2 Kg/l

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in Table-3. The mix is 1:2.34:2.52 and w/c is 0.40 is adopted and for better workability 1% super plasticizer (Conplast 430) were added. The solution with 0.55-0.60 Molar ratio is adopted. Firstly, Sodium hydroxide (NAOH) pellets and water are added and keep for 24hrs to reduce the temperature and then sodium silicate is added to the solution and again keeps the solution for 24hrs before casting. And then 50% flyash and 50% GGBS of cement content are taken and geopolymer concrete is prepared.

Table-5. Mix proportion.

Material Mix 1 Mix 2

Cement 393 Kgs -

Fine aggregate 920 Kgs 920 Kgs Coarse aggregate 992 Kgs 992 Kgs

Water 157 Litres -

Flyash - 196.5 Kg

GGBS - 196.5

RGL Solution - 157.2 kgs

Construction of Funicular Shells:

In Experimental setup, shell is made by Masonary Mould method.

FS1: Conventional Concrete Funicular shell without mesh reinforcement.

FS2: Conventional concrete Funicular shell with mesh Reinforcement.

FS3: Geopolymer Concrete Funicular shell without mesh Reinforcement.

FS4: Geopolymer Concrete Funicular shell with mesh Reinforcement.

The central rise of the funicular shell of square ground plan at various points is calculated (Figure-9)

Figure-9. Fixing the nails.

Figure-10. Finishing surface with cement mortar.

Mix ratio of mortar 1:4 (Cement: Fine aggregate) is taken to fill the nails. Finishing of edges and smoothening of surface is carefully done. The mortar which is filled over the nails is now left to set for some 4 to 7 days. The completion of the mould work is shown in the Figure-10. The finished Shell is coated with oil, Grease and any other releasing material. Concrete of specified mix is laid over the shell mould and thickness as per the design can be controlled by thickness gauges.

Figure-11. Conventional funicular shell.

Figure-12. Geopolymer concrete funicular shell.

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RESULTS AND DISCUSSIONS

Compression Test

The Conventional concrete and geopolymer concrete cubes of 150 mm x 150 mm x 150 mm were set up for every blend. After 24 hours, the samples were de-moulded and curing has been done for 7& 28 days.

Figure-13. Compression Test.

The compressive quality reported is the normal of three results got from three indistinguishable 3D shapes. For 7 and 28 days and the outcomes were tabled and represented in Table-6.

Table-6. Average Compressive Strength.

Duration

Average compressive strength (N/mm²)

Mix 1 Mix 2

7 days 19.2 15.7

28 days 41.4 36.5

Figure-14. Average Compression Test.

SPLIT TENSILE STRENGTH

The Conventional concrete and geopolymer concrete cylinders of the dimension 150 mm x 150 mm x 300 mm were set up for every blend. After 24 hours the examples were de-moulded and cured for 7& 28 days.

Figure-15. Split Tensile Test.

The split elasticity reported is the normal of three results got from three indistinguishable moulds. For 7 and 28 days and the outcomes were tabled and represented in Table-7.

Table-7. Average Split tensile strength.

Duration

Average Split tensile strength (N/mm²)

Mix 1 Mix 2

7 days 3.05 1.52

28 days 3.66 2.96

Mix 1 Mix 2

7 days 19.2 15.7

28 days 41.4 36.5

0 10 20 30 40 50

COMPRE

SSIVE

ST

RE

N

G

T

H

(N/MM

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Figure-16. Split Tensile strength.

FUNICULAR SHELL TESTING

The funicular shell was removed after a proper curing of 28 days and proceeded for the testing purpose. Considering the difficulty of placing the hydraulic jack over the shell, machine loading is avoided and hence only sand loading is given. Deflection meter is kept below the center span of the funicular shell. Sand bags of 25kg are collected and placed over the shell one by one. The values are noted from the deflection meter. The funicular shell is kept over the beam on two sides in which the beam is considered as the supports. The loading of sand bags over the shell and the deflection meter placed below the center span of the shell are shown in the Figure-17.

Figure-17. Sand Bags Loading.

From testing the shells FS1 and FS2, the estimations of avoidances for various loads were noted down. From the testing, results got out appeared in the Table-8.

Table-8. Test results on Funicular shells.

Description

Test Results Ultimate

Load(kgs) Deflection(mm)

FS1 360 1.42

FS2 570 1.19

FS3 310 1.6

FS4 465 1.21

Conventional concrete funicular shell with and without are loaded upto 310kgs and 495kgs and Geopolymer concrete funicular shell with and without fiber reinforcement are loaded upto 360 and 570kgs respectively.

Figure-18. Load Vs Deflection.

Mix 1 Mix 2

7 days 3.05 1.52

28 days 3.66 9.3

0 2 4 6 8 10

A

v

e

rag

e

S

p

li

t

te

n

si

le

str

e

n

g

th

(N

/m

m

²)

Split tensile Strength

0 0.5 1 1.5 2

0 100 200 300 400 500 600 700

Def

le

cti

o

n

(

mm

)

Load (kgs)

Load Vs Deflection

FS1

FS2

FS3

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CONCLUSIONS

a) The compressive strength of geopolymer concrete is almost same as conventional concrete as per the designed mix.

b) Max. Tensile stresses are formed at corners and compressive stresses are at edges of the doubly curved funicular shell.

c) The deflections and stresses are reduced with use of reinforcement in funicular shells.

d) The funicular doesn’t have reinforcement, so the corrosion is less and thickness is decreased.

e) The funicular shells are displayed great execution in one way slab action. The testing likewise demonstrated its value of two-way funicular shells for the one roof or floor construction. This derives the funicular shells are well reasonable for one way slab arrangement. This evades and replaces the development of cast insitu grid beams with precast/cast insitu beams.

f) It is concluded that an increment of 13.78 % of ultimate load (Pu) is observed in conventional concrete funicular shell without mesh when compared to Geopolymer concrete funicular shell without mesh.

g) Ultimate load (Pu) of 22.8% is observed in conventional concrete funicular shell with mesh when compared with Geopolymer concrete funicular shell with mesh.

h) Performance of regular funicular shell without work support is better when contrasted with geopolymer funicular shell without work fortification under udl.

i) Performance of regular funicular shell with work fortification is better when contrasted with geopolymer funicular shell with work support under udl because of higher evaluation of cement.

j) The deflection of conventional concrete funicular shell exhibits less compared to geopolymer concrete.

REFERENCES

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