mix design and rheological properties of self ... - ARPN Journals

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.

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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: adebakinidowu@gmail.com

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, T 500, 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

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www.arpnjournals.com 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].

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) SiO2

OPC (53 Grade) 21.0

Fly Ash (Class F) 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

-

3. MATERIALS

K2O

0.7

-

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

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) 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

(a)

(b) EDS analysis.

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).

(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).

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www.arpnjournals.com 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 Maximum size (mm)

Coconut shell aggregate (CSA) 12.50

4.75 (passing)

Water absorption (%)

24.00

-

Specific gravity (SSD)

1.14

2.61

Fineness Modulus

River sand

6.54

3.72

3

Bulk density (kg/m )

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/m3, 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, T 500, L-box, V-funnel and GTM screen tests were carried out as recommended by EFNARC to check for selfcompactability 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.

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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.

(a)

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.

(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

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www.arpnjournals.com 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

1

SCLWC1

260

510

510

FA (%) 0

FA

w/b

Water

0

0.33

168.3

SP % 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. of the mixtures were evaluated using slump flow, T 500, Lbox, V-funnel and GTM screen tests. Sketches of the test apparatus is as shown in Figure-7.

5. EXPERIMENTAL PROCEDURES With the EFNARC committee recommended procedure as guide [15], the self-compactability properties

100 mm. . mm

75

300 mm.

51

450 mm.

5m m.

10

00

. mm m.

50

0m

m. 0m

150 mm.

20

mm .

V- Funnel

10 22

5m m.

600 mm.

65

00

mm

Gate

Slump flow

h1

3-12 mmØ smoot h bars

10

0m m.

h2

40 70

150 mm.

0m m.

0m m.

L - Box

m. 0m

20

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

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www.arpnjournals.com T500 (s)

V-funnel time (s)

VS1/VF1

≤2

≤8

VS2/VF2 Passing ability classes

>2

9-25

Class Viscosity classes

PA1 PA2

≥ 0.8 with two rebar ≥ 0.8 with three rebar

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 Vfunnel 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.

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-10. L-box test.

Figure-8. Slump flow test.

Figure-11. Wet sieve segregation test.

Figure-9. V-funnel 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].

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www.arpnjournals.com 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.

SCLWC1

Slump flow (mm) 625

SCLWC2

700

4.1

10.0

0.66

5.17

SCLWC3

730

4.0

8.1

0.95

3.38

SCLWC4

750

4.2

8.3

0.88

3.54

Bleeding & centre lump Very stable & good flow Stable & good flow

SCLWC5

755

4.5

8.5

0.80

4.03

Bleeding

Mix ID

PA

SR (%)

Visual inspection

Wet density (kg/m3)

10.0

Vfunnel (sec) 15

0.60

6.72

Heavy segregation

2151 2140

2043

T500 (sec)

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 4.010.0 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

2075 2072

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.

16 14

Time (sec.)

12 10 8 6 4 2 0 SCLWC1

SCLWC2

T500 flow time

SCLWC3

SCLWC4

SCLWC5

V-funnel flow time

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

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www.arpnjournals.com 16 V-funnel flow time (sec)

15 y = 1.1037x + 3.924 R² = 0.9031

14 13 12 11 10 9 8 7 6 3

4

5

6

7 T500 (sec)

8

9

10

11

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.

7 6.5 6 y = -9.0046x + 11.574 R² = 0.9005

SR (%)

5.5 5 4.5 4 3.5 3 2.5 2 0.5

0.6

0.7

0.8

0.9

1

PA 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).

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www.arpnjournals.com 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].

2180

Wet density (kgm3)

2160 2140 2120 2100 y = -0.7839x + 2654.4 R² = 0.7924

2080 2060 2040 2020 600

650

700 750 Slump flow diameter (mm)

800

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 [1] Shafigh P. et al. 2013. Engineering properties of oil palm shell lightweight concrete containing fly ash. Materials and Design. 49: 613-621. [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.

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www.arpnjournals.com [4] Gunasekaran K. et al. 2012. Long term study on compressive and bond strength of coconut shell aggregate concrete. Construction and Building Materials. 28: 208-215.

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[6] Wu Z. et al. 2009. An experimental study on the workability of self-compacting lightweight concrete. Construction and Building Materials; 23:2087-2092. [7] Ranjbar M.M. et al. 2013. Effect of natural zeolite on the fresh and hardened properties of self-compacted concrete. Construction and Building Materials; 47: 806-813. [8] Wu Q. and An X. 2014. Development of a mix design method for SCC based on the rheological characteristics of paste. Construction and Build Materials. 53: 642-651. [9] Newman J. and Choo B. S. (eds). 2003. Advanced concrete technology- Process. Oxford, GB. Elsevier. [10] Shi C. et al. 2015. A review on mixture design methods for self-compacting concrete. Construction and Building Materials; 84: 387-398. [11] Kosmatka S.H., Kerkhoff B. and Panarese W.C. 2003. Design and control of concrete mixtures. 14th ed. Illinois, USA. Portland Cement Association. [12] IS: 12269. 1987. Specification for 53 grade ordinary Portland cement, Bureau of Indian Standards, New Delhi, India. [13] IS: 383. 1970. Specification for coarse and fine aggregate from natural sources for concrete, Bureau of Indian Standards, New Delhi, India. [14] IS: 9103. 1999. Indian Standard Code of PracticeConcrete Admixtures Specification. Bureau of Indian Standards, New Delhi, India. [15] The European guidelines for self-compacting concrete: Specification, production and use. 2005. EFNARC, UK.

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[16] Khayat K. H., Bickley J., and Lessard M. 2000. Performance of self-consolidating concrete for casting basement and foundation walls. ACI Materials Journal. 97, 374-80. [17] European Project Group. Specification and guidelines for self-compacting concrete. 2002. EFNARC, UK. [18] Güneyisi E. et al. 2015. Fresh and rheological behavior of nano-silica and fly ash blended selfcompacting concrete. Construction and Building Materials. 95: 29-44.

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