MIX DESIGN AND RHEOLOGICAL PROPERTIES OF SELF -COM PACTING COCONUT SHELL AGGREGATE ... ·...

VOL. 13, NO. 4, FEBRUARY 2018 ISSN 1819-6608

ARPN Journal of Engineering and Applied Sciences ©2006-2018 Asian Research Publishing Network (ARPN). All rights reserved.

www.arpnjournals.com

1465

MIX DESIGN AND RHEOLOGICAL PROPERTIES OF

SELF-COMPACTING COCONUT SHELL

AGGREGATE CONCRETE

Idowu H. Adebakin, K. Gunasekaran and R. Annadurai

Department of Civil Engineering, Faculty of Engineering and Technology, SRM University, Kattankulathur, Tamil Nadu, India

E-Mail: [email protected]

ABSTRACT

This paper presents report of experimental works on the mix design and fresh properties of self-compacting

lightweight aggregate concrete (SCLWC) blended with fly ash using coconut shell as coarse aggregate. After 35 initial trial

mixes, 5 final mixtures were prepared with various amount of cement replacement with fly ash (0 – 25% by weight of

cement) at the same water/binder ratio of 0.33 and same percentage of superplasticizer (1.75% by weight of binder). The

fresh properties of SCLWC were investigated by means of slump flow, T500, V-funnel, L-box, wet sieve segregation and

wet density. Results showed that fly ash blended SCLWC with coconut shell as coarse aggregate performed satisfactorily

in flowability, viscosity and passing ability. In particular, mixtures with15% and 20% cement replacement with fly ash

gave very good results.

Keyword: coconut shell, concrete, fly ash, self-compacting, mix design, lightweight aggregate.

1. INTRODUCTION The usage of lightweight aggregate concrete

(LWC) for structural elements has been successfully

carried-out for many years. It has found acceptability

where light loading, low permeability and high thermal

strength will be beneficial. Lightweight aggregate (LWA)

is generally used in the production of LWC, and can either

be naturally sourced or artificially manufactured from the

by-products of some industrial process. Production of

artificial LWA involves heating the raw materials under

high temperature with its attendance high cost both

financially and environmentally [1].

Coconut shell (CS) can be classified as naturally

occurring lightweight aggregate from agricultural waste

just like palm kernel [2]. For many years, commercially

available LWA has been used widely for production of

LWC, however, issues of materials depletion and

environmental degradation make agricultural wastes like

coconut shell highly beneficial and sustainable in LWC

production.

Researches on normal concrete with coconut as

coarse aggregate revealed that there is good compatibility

of coconut shell-cement composite and there is no need for

pre-treatment [3,4]. It is also reported that though water

absorbing and moisture retaining capacity of CS is high, in

comparison to natural aggregate, CS does not deteriorate

over time once it is encapsulated into the concrete matrix,

hence coconut shell aggregate concrete is confirmed to be

very durable [5].

Self-compacting concrete (SCC) is a new

generation concrete that is highly flowable and hence can

be placed without vibration in narrow or heavily

reinforced formwork, while maintaining excellent

consistency and cohesiveness [6]. Self-compacting

lightweight aggregate concrete (SCLWC) combines the

good properties of lightweight and self-compacting to give

good and durable hardened concrete. Although, a good

number of researches have been made on SCLWC, but

using coconut shell aggregate (CSA) in the production of

SCLWC is a novel research.

2. THEORY

In order to produce good SCC, workability is a

very critical factor. Achieving SCC with good filling

ability, passing ability and high segregation resistance

requires careful mixture design. In the mix proportioning,

aside controlling aggregate quantities and low

water/binder ratio, it is common to apply high range water

reducing admixture to take care of flowability and a large

quantity of powder materials to achieve high resistance to

segregation [7].

The concept of SCC was first proposed by

Okamura in 1986, but it wasn’t until 1988 when the first

prototype was developed by Ozawa in Japan [8].

Basically, the physical properties of the gravel coupled

with the rheological properties of mortar defines SCC

characteristics. Hence, researches has shown that SCC

composed of two major phases: the gravel phase and the

suspending mortar phase [8].

Many mix design methods have been developed

for SCC, since design method for conventional concrete is

not practicable with SCC. Of all the methods, the rational

mix design method proposed by Okamura and Ozawa is

the simplest and most popular [9]. Though, other methods

such as blocking volume ratio, particle packing theory,

paste rheology theory, compression strength method have

been proved to be practicable too. However, all the mix

design methods were developed based on conventional

aggregates, but for LWA with diverse characteristics, there

is need for modification of any of the methods in other to

achieve self-compactability.

The design method proposed by Okamura et al

[10] was based on fixing coarse aggregate content at 50%

of the solid volume, and fine aggregate content at 40% of

the mortar volume. Then water/binder ratio and

superplasticizer’s dosage will be determined by trial

mailto:[email protected]




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mixes. Though simple, but requires rigorous laboratory

testing, especially with new materials like CS.

Concrete rheology defines the flow behaviour of

concrete based on its plastic viscosity (η) and yield stress (τ). Rheology is generally influenced by water/binder (w/b) ratio, type and volume of binder, hydration rate,

mixture temperature and, of course, superplasticizer (SP)

dosage [9]. Mineral admixtures and natural pozzolans are

used to improve rheological properties requirement of

SCC, majorly for improvement in cohesiveness and

segregation resistance. Heat of hydration and thermal

shrinkage are likewise regulated by the addition. The most

commonly used mineral admixture is low carbon class F

fly ash, which is a by-product of the pulverised coal

combustion in electric power generating plants. Fly ash is

finely divided powder with surface areas as low as

200m2/kg [11].

3. MATERIALS

3.1 Cementitious

*Ordinary Portland cement (OPC) 53 grade

conforming to the BIS 12269:1987 [12] was used

throughout this study while class ‘F’ fly ash (FA) sourced

from Tuticorin Thermal Power Station, Tamil Nadu India

was also used as mineral admixture. Table-1 shows the

chemical compositions, while Figures 1 and 2 are the

scanning electron microscopy (SEM) and energy

dispersive x-ray spectrometry (EDS) analysis of the

materials respectively.

Table-1. Physiochemical properties of OPC and Fly ash.

Composition

(% by mass)

OPC

(53 Grade)

Fly Ash

(Class F)

SiO2 21.0 64.03

Al2O3 5.1 15.50

Fe2O3 3.1 6.50

MgO 2.4 3.00

CaO 64.1 4.62

Na2O 0.3 -

K2O 0.7 -

SO3 2.2 -

Loss on ignition 0.6 4.35

Specific gravity 3.12 2.31

(a) (b)

Figure-1. OPC (a) SEM micrograph (10,000x) (b) EDS analysis.




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(a) (b)

Figure-2. Fly ash (a) SEM micrograph (5,000x) (b) EDS analysis.

3.2 Aggregates River sand sourced locally but conforming to

grading zone III as specified in BIS 383:1970 [13] was

used as fine aggregates. For coarse aggregates, freshly

seasoned coconut shells were crushed with the mechanical

crusher as shown in Figure-3. The crushed edges were

rough and spiky and the surface texture was fairly smooth

on one face and rough on the other (Figure-4).

(a) (b) (c)

Figure-3. (a) Coconut shell crusher (b) Freshly seasoned CS (c) Crushed CS.

Figure-4. CSA (12.5mm max. size with thickness of 2-8mm).




1468

Sizes that passed through 12.5 mm sieve but

retained in 4.75 mm were used in saturated surface dry

(SSD) condition throughout the study. Table-2 compares

the physical properties of the aggregates.

Table-2. Properties of aggregates used.

Physical and mechanical

properties

Coconut shell

aggregate (CSA) River sand

Maximum size (mm) 12.50 4.75 (passing)

Water absorption (%) 24.00 -

Specific gravity (SSD) 1.14 2.61

Fineness Modulus 6.54 3.72

Bulk density (kg/m3) 650 1700

Crushing value (%) 2.56 -

Impact value (%) 4.60 -

3.3 Superplasticizer

Type ‘F’ high range water reducing admixture

Conplast SP430 conforming to specifications in BIS:

9103-1999 [14] was used. Conplast SP430 is made of

Sulphonated Napthalene Formaldehyde with specific

gravity of 1.20 -1.22 at 30 °C

4. MIX DESIGN

4.1 Trial mixes

The constituents of the mixtures were

proportioned based on the principle recommended by

EFNARC [15] and modified version of Okamura and

Ozawa model. Because of its low bulk density and sizes

used, CSA content was fixed at 40% of the solid volume,

while fine aggregate content was fixed at 50% of the

mortar volume.

After laboratory determination of SP dosage to be

between 1.5-2.0 % of total powder content by weight, 35

trial mixes were carried out with cement content ranging

between 350kg/m3 and 510kg/m

3, fly ash replacement of

cement was between 5% and 30%, and w/b ratio between

0.3 and 0.4 by weight. The flowchart in Figure-5 served as

a guide throughout the research. Slump flow, T500, L-box,

V-funnel and GTM screen tests were carried out as

recommended by EFNARC to check for self-

compactability and 7 days compressive tests for strength

check on each trial. From the trials, it was discovered that

510kg/m3, 1.75% and 0.33 were the optimum values for

total powder content, SP dosage and w/b ratio

respectively.




1469

Figure-5. Design mix flowchart.

4.2 Final mixes

Finally, five sets of SCLWC were prepared using

CSA (40% of the solid volume) as coarse aggregate and

river sand (50% of the mortar volume) as fine aggregate.

Total powder content, SP dosage and w/b ratio were fixed

at 510kg/m3, 1.75% and 0.33 respectively. OPC was

replaced with FA at 0%, 10%, 15%, 20% and 25%

sequentially for the five sets.

Because of the high water absorption capacity of

coconut shell [3], CSA was initially soaked in clean water

for 24 hours and later allowed to dry under room

temperature to saturated surface dry (SSD) condition

before using for SCLWC. Figure-6 has the SEM images

showing saturated pores of the shell. Using CSA at SSD

state prevents absorption of mixing water by the aggregate

during mixing.

(a) (b)

Figure-6. SEM micrograph of CS at SSD condition (a) 255x (b) 2500x.

For homogeneity and uniformity in mixture, a

vertical-axis tilting mixer under laboratory condition was

used. Coarse and fine aggregates were mixed together for

30 sec at normal mixing speed of 24 rpm, after which




1470

about 30 % of the mixing water was added while mixing

was on-going for 1 min. The mixture was then allowed to

rest for 1 min so as to allow adsorption of the water by the

aggregates. Thereafter, cement and fly ash were added and

mixed for another 1 min before about 50 % of the mixing

water were added. The remaining 20 % mixing water was

added to SP and introduced to the wet mixture while

mixing continued for 3 min. 2 min resting was observed

before final 2 min mixing. This sequence follows the

recommendation by Khayat et al [16]. Table-3 is summary

of the mix proportions.

Table-3. Mix proportions (kg/m3).

S. No Mix ID CSA NFA Cement FA (%)

FA w/b Water SP %

1 SCLWC1 260 510 510 0 0 0.33 168.3 1.75

2 SCLWC2 260 510 459 10 51 0.33 168.3 1.75

3 SCLWC3 260 510 433.5 15 76.5 0.33 168.3 1.75

4 SCLWC4 260 510 408 20 102 0.33 168.3 1.75

5 SCLWC5 260 510 382.5 25 127.5 0.33 168.3 1.75

ID- Identification number, CSA- Coconut shell aggregate, NFA- Natural fine aggregate, FA- Fly ash, w/b- Water/binder,

SP- Superplasticiser.

5. EXPERIMENTAL PROCEDURES

With the EFNARC committee recommended

procedure as guide [15], the self-compactability properties

of the mixtures were evaluated using slump flow, T500, L-

box, V-funnel and GTM screen tests. Sketches of the test

apparatus is as shown in Figure-7.

Figure-7. SCLWC test apparatus sketches.

The slump flow test describes the flowability of

the fresh mix under gravity and in the absence of any

obstruction. It is the mean of two perpendicular diameters

of concrete flow after lifting the cone. The slump flow is a

primary check that must be carried-out on SCC, and there

are basically three classes of slump flow depending on the

range of applications as summarised in Table-4.

Table-4. Slump flow, viscosity and passing ability

guidelines by EFNARC [15].

Class Slump flow (mm)

Slump flow classes

SF1 550-650

SF2 660-750

SF3 760-850

1000 mm

1000 mm

.

500 mm

. 300 m

m.

200 mm

.

100 mm.

75mm

.

450 m

m.

150 m

m.

515 mm

.

65 mm

.

225 mm

.

600 m

m.

h1

200 mm

.

700 mm

.

400 mm

.

100 mm

.

150 m

m.

h2

Gate

3-12 mmØ smooth bars

L - Box

V- Funnel

Slump flow




1471

Class T500 (s) V-funnel time

(s)

Viscosity classes

VS1/VF1 ≤ 2 ≤ 8

VS2/VF2 >2 9-25

Passing ability

classes

PA1 ≥ 0.8 with two

rebar

PA2 ≥ 0.8 with three

rebar

For this study, the mixtures were designed to

have flow values within class 2 (SF2), that is, average

flow diameter between 660 and 750 mm. Meanwhile, the

time taken for the flow to reach the 500 mm circle from

the centre is noted as the T500, Figure-8 shows the test

procedure.

Figure-8. Slump flow test.

Figure-9. V-funnel test.

Times taken for the SCLWC to pass through the

V-funnel and T500 of the slump flow are measured and

used to assess the viscosity of the mix, Figure-9 is the V-

funnel test set-up.

Three bars L-box was used in the assessment of

the passing ability of the SCLWC, this is to ensure that

there will be neither segregation nor blocking when

SCLWC flows through closely spaced reinforcements or

in a confined area. Figure-10 is the test procedure.

Figure-10. L-box test.

Figure-11. Wet sieve segregation test.

Finally, the GTM screen test was carried out to

assess the stability of the SCLWC. Following EFNARC

guidelines [17], about 10 lit of fresh sample of each mix

was used to evaluate the mix resistance to segregation

using the set-up as shown in Figure-11, from where the

segregation ratio (SR) was determined. Accordingly, SR

should not exceed 15 % for the mix to be stable, though

the lower the value of SR, the more stable the mix should

be [18].




1472

6. RESULTS AND DISCUSSIONS

6.1 Slump flow

As indicated in Table 5, SCLWC produced are

within the slump flow range of 625 and 750 mm. Apart

from SCLWC1, other mixes fall within slump flow class

SF2 and according to EFNARC [15], this type of concrete

is suitable for normal elements like walls and columns. It

was also discovered that the flow diameter steadily

increased as the percentage of the fly ash increases, similar

observations has been made by some researchers too [8,

19- 21].

Table-5. Summary of fresh concrete test results.

Mix ID

Slump

flow

(mm)

T500

(sec)

V-

funnel

(sec)

PA SR

(%) Visual inspection

Wet density

(kg/m3)

SCLWC1 625 10.0 15 0.60 6.72 Heavy segregation 2151

SCLWC2 700 4.1 10.0 0.66 5.17 Bleeding & centre lump 2140

SCLWC3 730 4.0 8.1 0.95 3.38 Very stable & good

flow 2075

SCLWC4 750 4.2 8.3 0.88 3.54 Stable & good flow 2072

SCLWC5 755 4.5 8.5 0.80 4.03 Bleeding 2043

6.2 T500 and V-funnel flow times Figure-12 is a comparison between T500 flow and

V-funnel flow times which fell within the ranges of 4.0-

10.0 and 8.1-15.0 respectively. At this range, the viscosity

of the mixes will give sufficient segregation resistance and

at the same time formwork pressure would be moderate

[15, 7]. It is noticeable that the flow time reduces as the

percentage of fly ash increases up to 15 % replacement. It

is well reported in literatures that partial replacement of

cement with fly ash, to some level, improves the

rheological properties of SCC [22 - 25]. Fly ash particles

have spherical geometry and a coarse particle size, these

lead to reduction in adsorption of free water by the surface

area [25]. This ball bearing effect of the spherical particles

of fly ash must be the likely reason for reduction of mixes

flow time. Most of the SCLWC mixes investigated come

under VS2/VF2 class (Table-4) concrete mixture of this

class can be used for walls/piles with SF2 class of slump

flow [15].

Furthermore, Figure-13 shows that there is a

strong correlation between T500 flow and V-funnel flow

times, similar relationship has been reported for SCC with

different mineral additions [7, 25, 26]. Hence, for this

SCLWC, equation 1 is proposed for prediction of V-funnel

flow times.

𝑉𝑓 = . 7𝑇 + .9 (1)

Where 𝑉𝑓 the V-funnel flow time and T is the T500

flow time.

Figure-12. T500 and V-funnel flow times.

0

2

4

6

8

10

12

14

16

SCLWC1 SCLWC2 SCLWC3 SCLWC4 SCLWC5

Tim

e (s

ec.)

T500 flow time V-funnel flow time




1473

Figure-13. Correlation between V-funnel flow time and T500.

6.3 Blocking ratio (PA) and segregation ratio (SR)

L-box test used in evaluating the passing ability

of the mixes in congested rebar indicated PA ranging from

0.60 to 0.95 (Table-5). As per EFNARC, SCLWC1 and

SCLWC2 showed tendency of blockage in closely spaced

reinforcements. Other mixes showed no tendency of

blockage, with SCLWC3 having highest passing ratio of

0.95.

GTM screen stability test method was used to

evaluate the resistance of the mixtures to segregation

during haulage and after placement in formwork. The

result showed good resistance to segregation by all the

mixes with good stability as the percentage of fly ash

replacement increases. However, SCLWC3 mix has better

consistency than other mixes. Good correlation was also

observed between PA and SR as shown in Figure-14.

Figure-14. Correlation between SR and PA.

6.4 Wet density

The density of the fresh SCLWC was carried out

using the BS EN 12350 part 6 (2000b) [27] as a guide.

Three 100 mm cube moulds were prepared and weights

noted in kg. Then, the moulds were filled with fresh

SCLWC without compaction and the top trowelled

smooth. The weights were noted again in kg. The

difference between the two weights divided by the volume

of the mould in m3 gave the density for each. Average of

the three values was taken as the wet density for each mix

as shown in Table-5. The result indicated that as the

percentage of cement replacement with fly ash increases,

the wet density decreases but not at a constant rate. This is

likely due to the fact that the specific gravity of OPC used

(3.12) is higher than that of the fly ash (2.31).

y = 1.1037x + 3.924

R² = 0.9031

6

7

8

9

10

11

12

13

14

15

16

3 4 5 6 7 8 9 10 11

V-f

un

nel

flo

w t

ime

(sec

)

T500 (sec)

y = -9.0046x + 11.574

R² = 0.9005

2

2.5

3

3.5

4

4.5

5

5.5

6

6.5

7

0.5 0.6 0.7 0.8 0.9 1

SR

(%

)

PA




1474

Meanwhile, Figure-15 indicates a good correlation

between the flowability of the concrete and its wet density,

a similar observation was made by H. Zhao et al [28].

Figure-15. Correlation between wet density and slump flow diameter.

7. CONCLUSIONS Production of self-compacting lightweight

aggregate concrete using coconut shell and incorporating

fly ash as mineral admixture is not only eco-friendly in

terms of reduction in solid wastes load on the municipal

landfills, but also contributes to CO2 emission reduction as

cement quantity needed reduces. This study may serve

construction engineering society to develop sustainable

development on the production of self-compacting

coconut shell aggregate concrete. For this purpose, this

paper has reported mix design and rheological properties

of SCLWC using coconut shell as coarse aggregate and fly

ash as partial replacement of OPC at the rate of 0 %, 10 %,

15 %, 20 % and 25 %. The following conclusion can

therefore be drawn:

a) Tests on CS and its general performance in the

production of SCLWC mixes justified CSA as an

excellent material that requires no pre-treatment in the

production of flowable concrete.

b) Replacement of cement with fly ash increased the

slump flow and passing ratio values while there is

reduction in the flow rate, SR and wet density. It

generally showed that addition of fly ash has positive

effect on the passing ability, stability and flowability

of the fresh SCLWC.

c) Increasing fly ash content in the SCLWC mixes

generally results to an increase in viscosity which is

described by the T500 and V-funnel flow times.

Moreover, V-funnel times can be well correlated with

T500 data with a good correlation coefficient of 0.90.

d) Wet density of tested SCLWC fell within the range of

structural lightweight concrete as specified in both IS

and BS standards.

e) Results of this research show that fly ash blended

SCLWC using coconut shell as coarse aggregate can

practically be used in normal construction such as

slabs, beams, walls and columns without fear of

excessive bleeding, segregation or honeycomb.

However, mixes with 15% and 20% fly ash

replacement performed rheologically better than

others.

ACKNOWLEDGEMENTS

The authors would like to thank SRM University

Management for providing technical support,

Nanotechnology research centre, SRM university for their

assistant in SEM analysis and all those who were directly

or indirectly involved in this study. This research did not

receive any specific grant from funding agencies in the

public, commercial, or not-for-profit sectors. However, the

support of Nigeria Tertiary Education Trust Fund

(TETfund) and Yaba College of Technology, Nigeria, in

sponsoring the first author for his Ph.D. program at SRM

University is greatly appreciated.

REFERENCES

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[2] Gunasekaran K., Kumar P.S. and Lakshmipathy M. 2011. Study on properties of coconut shell as an aggregate for concrete. ICI journal July- Sept 2011: 27-33.

[3] Gunasekaran K. et al. 2011. Mechanical and bond properties of coconut shell concrete. Construction and Building Materials. 25: 92-98.

y = -0.7839x + 2654.4

R² = 0.7924

2020

2040

2060

2080

2100

2120

2140

2160

2180

600 650 700 750 800

Wet

den

sity

(k

gm

3)

Slump flow diameter (mm)




1475

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