Influence of different types of polypropylene fibre on the mechanical properties of high-strength oil palm shell lightweight concrete

Construction and Building Materials 90 (2015) 36–43

Contents lists available at ScienceDirect

Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat

Influence of different types of polypropylene fibre on the mechanical properties of high-strength oil palm shell lightweight concrete Ming Kun Yew a,⇑, Hilmi Bin Mahmud a, Bee Chin Ang b, Ming Chian Yew c a

Department of Civil Engineering, Faculty of Engineering, University of Malaya, 50603 Kuala Lumpur, Malaysia Centre of Advanced Materials, Department of Mechanical Engineering, Faculty of Engineering, University of Malaya, 50603 Kuala Lumpur, Malaysia c Department of Mechanical and Material Engineering, Lee Kong Chian Faculty of Engineering & Science, Universiti Tunku Abdul Rahman, Cheras 43000 Kajang, Malaysia b

h i g h l i g h t s  Polypropylene fibres enhanced the strength of oil palm shell lightweight concrete.  PPTB1 of 0.5% fibre produced the highest compressive strength.  Addition of 0.5% PPTB1 fibre achieved the highest tensile strengths.  The highest residual compressive strength was found for 0.5% PPTB1 fibre.

a r t i c l e

i n f o

Article history: Received 8 May 2014 Received in revised form 6 March 2015 Accepted 12 April 2015 Available online 16 May 2015 Keywords: Lightweight concrete Oil palm shells Polypropylene fibres Mechanical property Density

a b s t r a c t This study aims to investigate the use of various polypropylene (PP) fibres with different aspect ratio and geometry to enhance the mechanical properties of oil palm shell fibre-reinforced lightweight concrete. The volume fractions (Vf) of 0.25%, 0.375% and 0.5% were studied for each fibre. As various PP fibres were added into oil palm shell fibre reinforced concrete, the marginal density reduction was reported. The effectiveness of new types of PP fibres to increase the compressive strength at later ages was more pronounced than at early age. It is found that low volume fractions of polypropylene twisted bundle (PPTB) fibres are more effective in improving the flexural strength of OPS concrete compared to its splitting tensile strength. The average modulus of elasticity (E value) is obtained to be 13.4 GPa for all mixes, which is higher than the values reported in previous studies. An increase in the percentage third load compressive strength of 0.5% PPTB fibre of up to 11% was reported. Hence, this new types of PP fibres is a promising alternative solution to compensate lower mechanical properties for lightweight concrete. Ó 2015 Elsevier Ltd. All rights reserved.

1. Introduction The current state of the structural lightweight aggregate concrete industry was born out of realization of sustainable construction. Development of sustainable structural lightweight concrete construction using oil palm shell (OPSLWC) is due to the density limit of 2000 kg/m3 [1]. The utilization of industrial and agricultural waste materials can be a breakthrough to make the industry more environmentally-friendly and sustainable. It has led to green and sustainable construction to improve the environmental friendliness of concrete by reducing the cost of construction materials and waste management. The utilization of waste materials, such as natural pumice, vermiculite, shale, slate, oil palm shell (OPS), fly ash, ground granulated blast furnace slag (GGBFS), silica fume, ⇑ Corresponding author. Tel.: +60 3 79675203; fax: +60 3 79675311. E-mail addresses: (M.K. Yew).

[email protected],

http://dx.doi.org/10.1016/j.conbuildmat.2015.04.024 0950-0618/Ó 2015 Elsevier Ltd. All rights reserved.

[email protected]

recycled concrete, recycled tyres, and recycled plastics, have been successfully used in concrete [2–4]. Recently, a large amount of lignocellulosic wastes OPS is generated due to the increasing number of plantations of oil palm trees in Malaysia, Indonesia, and Nigeria [5]. This waste is considered as one of the potential lightweight aggregate (LWA) in the development of lightweight aggregate concrete (LWAC). It is reported that Malaysia contributed some 18.79 million tonnes of crude palm oil on approximately 5 million hectares of land [6], making it a major producer of palm oil. Calculations show that 1.1 tonnes of shells, or 5.5% of the weight of the fresh fruit bunch, is produced annually from each hectare cultivated. There are many advantages of using OPS, especially when the material cost is minimized by utilizing the waste OPS aggregate in construction. These include savings in reinforcement, scaffolding, formwork and foundation costs. Furthermore, such concrete can be used for heat insulation, sound absorption, better fire resistance, superior anti-condensation properties and increased damping [7].

37

M.K. Yew et al. / Construction and Building Materials 90 (2015) 36–43

Air-dry density of oil palm shell concrete (OPSC) varies in the range of 1868–1988 kg/m3 with a corresponding 28-day compressive strength of more than 40 MPa [8–13]. In a past studies, the enhancement of mechanical properties of OPSC is dependent on the density, aggregate content, crushed or uncrushed particle size of OPS and heat treatment on OPS aggregate [8–10]. Other factors include water-cement ratio and incorporation of cementitious materials (silica fume, fly ash and ground granulated blast furnace slag). The influence of density on the compressive strength of OPSC can be observed from previous studies [8–13]. Alengaram et al. [14] showed that with a density of about 1900 kg/m3, a compressive strength of 37 MPa with the addition of silica fume (SF) can be produced. However, Yew et al. [10] reported that heat treatment on OPS aggregate, having a density of about 1945 kg/m3 achieved compressive strength of 49 MPa. Furthermore, Shafigh et al. [8,9] have successfully produced compressive strength of up to 53 MPa for a density of about 2000 kg/m3. It is generally known that, high compressive strength of LWAC results in brittleness and weak in tensile strength [15] and the density of LWAC is limited to 2000 kg/m3 [1]. As a result of these characteristics, LWAC could not support normal stresses and impact loads, where tensile strength is approximately one tenth of its compressive strength. It can be seen from recent research that, OPSLWAC can be reinforced with discontinuous (steel, polypropylene and nylon) fibres to overcome high potential tensile stresses and shear stresses at critical location in OPSLWC member [16–19]. However, the main disadvantage of adding steel fibres into OPSLWC in fresh state is its significant reduction in slump value and increased density. Furthermore, the inclusion of polypropylene and nylon insignificantly increased the mechanical properties of OPSC, particularly for the tensile strength [17]. One innovative method to improve the mechanical properties of OPSC without reaching the density limit is an addition of a new type of non-metallic fibre namely polypropylene twisted bundle (PPTB). This study is to access the effects of different types of PP fibre and aspect ratio at various volume fractions of 0.25%, 0.375% and 0.5% on mechanical properties of OPSC. The beneficial effects of new types of PP fibres are considered in the investigation on fibre-reinforced oil palm shell concrete (FROPSC). To the best of the authors’ knowledge, so far there are no reports on the effects of the different geometries (lengths and shapes) of PP fibres on the properties of OPSC incorporating fibres. In this study, the mechanical properties of OPSFRC containing fibres at three different percentages is evaluated and reported. The primary objective of this study is to investigate the effects of PPTB fibres at various volume fractions on the compressive strength of OPSFRC. The effects of different PP fibres on the splitting tensile strength, flexural strength, modulus of elasticity and residual compressive strength (RCS) are also investigated.

2. Experimental details 2.1. Materials 2.1.1. Cement The cement used in this study was ASTM type I ordinary Portland cement (OPC) [20] with a specific gravity of 3.14 g/cm3 and Blaine’s specific surface area of 3510 2 cm /g. The chemical compositions and physical properties of the OPC are given in Table 1. A cement content of 520 kg/m3 was used for all mixes.

2.1.2. Mineral admixture Silica fume (SF) is available in dry powder form and is procured from ScancemMaterials Sdn Bhd, Kuala Lumpur. The light gray, under the product name ‘‘Scancem’’ is available in 20 kg bags. The SF procured by the company satisfies all the requirements of the International Standards; ASTM C1240 [21] and AS 3582 [22]. The amount of densified SF at 5% of the cement weight was added as additional mineral admixture to enhance the mechanical properties of concrete.

Table 1 Chemical composition and physical properties of OPC. Chemical composition (%)

Physical properties

SiO2

Fe2O3

CaO

MgO

Al2O3

SO3

LOI

Specific gravity

Blain specific surface area (cm2/g)

21.28

3.36

64.64

2.06

5.60

2.14

0.64

3.14

3510

2.1.3. Water and superplasticizer (SP) Potable water to binder (w/b) ratio of 0.30 was used for all mixes. The SP used in this study was polycarboxylic ether (PCE) supplied by BASF, and complies with the ASTM C494/C494 M [23] specifications. The amount of SP was kept constant at 1.0% of the cement weight in order to improve workability. 2.1.4. Aggregate Local mining sand was used as the fine aggregate. The specific gravity, fineness modulus, water absorption and maximum grain size were found to be 2.68 g/cm3, 2.72, 0.97% and 4.75 mm, respectively. A sand content of 960 kg/m3 was used in all mixes. Old OPS were used as the coarse aggregate in this study, indicating that they had been discarded for more than six months. The old OPS were collected from a local crude palm oil producing mill. The percentage of fibres for old OPS (less than 2%) has been selected as an aggregate, which improves contact between the mortar and OPS grains and thus increases the compressive strength of the concrete. The advantages of using this aggregate in OPS concrete were reported by Shafigh et al. [8]. The OPS were washed and sieved using a 12.5 mm-sieve. The OPS aggregates retained in the sieve were collected and subsequently crushed using a stone-crushing machine in the laboratory. The crushed OPS aggregates were sieved using a 9.5 mm-sieve to remove OPS aggregates with sizes greater than 9.5 mm. The OPS aggregates were heat-treated at 60 °C over a period of 0.5 h using a temperature-controlled laboratory oven. Once cooled to room temperature, they were weighed under dry room conditions and immersed in water for 24 h. Due to the high water absorption of OPS, it was subsequently air dried in the laboratory to attain a saturated surface dry (SSD) condition before mixing. The difference in quality of the OPS surface between heat treatment and without heat treatment condition was reported by Yew et al. [10] and shown in Fig. 1. The OPS content was set constant at 330 kg/m3 for all mixes. The physical properties of the OPS used, are shown in Table 2. 2.1.5. Fibres The properties of different type of PP fibres are presented in Table 3. The three types of PP fibres are (i) polypropylene twisted bundle 1 (PPTB1); (ii) polypropylene twisted bundle 2 (PPTB2) and (iii) straight polypropylene 1 (PPS1), respectively, as tabulated in Table 3. 2.2. Mix proportions The proportions used for all mixes as described in Section 2.1. The volume fraction (Vf) of the fibres added to the concrete mix typically ranges from 0.1% to 3.0% [24]. It is noted that fibres with a high Vf tend to ‘ball’ in the mix and create workability problems. Therefore, low volume fractions (60.5%) were used for the PP fibres in this study. The volume fraction of the PPTB fibres was set as 0%, 0.25%, 0.375% and 0.5%. The amount of water and superplasticizer was kept constant for all mixes. 2.3. Test methods The procedure used to mix the fibre reinforced concrete is detailed as follows. Firstly, the OPS and sand were poured into a concrete mixer and dry mixed for 1 min. Following this, the cement was spread and dry mixed for 1 min. The fibres were then distributed and mixed for 3 min in the mix, based on the volume fraction specified above. Water and superplasticizer were then added with a mixing time of 5 min. Slump test was carried out prior to casting the specimens. The concrete specimens were cast onto oiled moulds and a poker vibrator was used to decrease the amount of air bubbles in the mix. For each mixture, 150 mm  150 mm  150 mm cubes were used to study the compressive strength and ultrasonic pulse velocity (UPV) at 1, 3, 7, 28, 56 and 90 days. Two cylinders (diameter: 150 mm, height: 300 mm) were used to examine the modulus of elasticity. Three cylinders (diameter: 100 mm, height: 200 mm) and three prisms of 100 mm  100 mm  500 mm were used to examine the 28-day splitting tensile strength and 28-day flexural strength, respectively. The specimens were demoulded approximately 24 ± 2 h after casting. The compression testing machine used was an ELE (Engineering Laboratory Equipment) with a load capacity of 3000 kN running of 3.0 kN/s in accordance to BS EN 12390-3:2009 [25]. Furthermore, RCS involves reloading the cube specimens for further 3 cycles after reaching maximum value, the failure in the compression test setting at 15% to ascertain the corresponding RCS.

38

M.K. Yew et al. / Construction and Building Materials 90 (2015) 36–43

(a)

(b)

Fig. 1. Surface quality of OPS aggregates (a) with heat treatment and (b) without heat treatment.

Table 2 Physical properties of OPS aggregates.

a

200 PPTB 1

OPS

OPSa

Maximum size (mm) Specific gravity (saturated surface dry) Compacted bulk density (kg/m3) Water absorption (24 h) (%) Aggregate impact value (%)

9.5 1.33 628 23.5 2.35

9.5 1.30 625 20.8 2.37

Heat-treated.

PPS1

y = -18.75x + 203.75 R² = 0.974

160 Slump (mm)

Physical property

PPTB 2

180

140

y = -17.15x + 202.85 R² = 0.9664

120 100

y = -14.5x + 200.5 R² = 0.9397

80

3. Results and discussion

60 0.000

0. 25 0

3.1. Workability (slump)

0 .3 7 5

0. 500

Volume fraction of PP fibre (%)

Slump tests were carried out to determine the consistency of fresh concrete. The use of fibres is well known to affect the workability and flowability of plain concrete intrinsically [26]. In this study, the quantity of water and SP were kept constant for all mixes in order to evaluate the effects of different PP fibres on the workability of OPC. From Fig. 2, it can be seen that the slump value of fresh OPSC decreases due to an increase in PP fibre volume fraction. The addition of fibres from 0% to 0.25%, 0.375% and 0.5% for PPTB1, PPTB2 and PPS1 reduces the range of slump values by approximately 11.1–64.3%, 13.9–82.7%, and 16.7–95.8%,

Fig. 2. Relationship between different PP fibre volume fraction and slump.

respectively. The results indicate that, the PPS1/0.25-0.5 of shorter length produced a lower slump in the range of 65–150 mm compared to PPTB1/0.25-0.5 (90–160 mm) and PPTB2/0.25-0.5 (75– 155 mm), respectively. Mehta and Monteiro [26] reported that a slump value for structural lightweight concrete in the range of 50–75 mm is comparable to an equivalent value of slump of 100–125 mm for NWC. This phenomenon might be attributed to the shorter length of fibres have higher effective surface area for

Table 3 Properties of different type of polypropylene fibres and aspect ratio. Fibre

Fibre type

Length (mm)

Aspect ratio

Specific gravity (g/cm3)

Tensile strength (MPa)

Monofilament-polypropylene twisted bundle 1 (PPTB1)

54

108

0.91

600

Monofilament-polypropylene twisted bundle 2 (PPTB2)

30

60

0.91

600

Monofilament-polypropylene straight 1 (PPS1)

20

40

0.91

600

39

M.K. Yew et al. / Construction and Building Materials 90 (2015) 36–43

the development of a fibre–matrix bond compared to longer fibres. The bond increases the viscosity which restrains the mixture from segregation and flow. The fibres have the tendency to absorb a higher amount of cement paste to wrap around due to the high fibre content and large surface area of fibres, which in turn, increases the viscosity of the mixture [27]. Hence, PP fibres of shorter length and higher volume fraction produced lower workability. The results of Yap et al. [17] showed that the slump value decreases upon addition of 0.5% Vf fibrillated (length: 19 mm, aspect ratio: 48) and multi-filament (length: 12 mm, aspect ratio: 240) polypropylene fibres into the OPS LWC. The reduction in slump value was found to be 47% and 60%, respectively. Several studies attempted to overcome this problem by producing more workable concrete. This was achieved by determining the optimum content of sand and adding superplasticizer [28]. The addition of superplasticizer improves the concrete’s flowability and workability without segregation [29–32]. Campione et al. [33] attained good workability in their mixtures by adding 1.5% of superplasticizer by cement weight for pumice and expanded clay LWACs reinforced with steel fibres. As a general rule, a low amount of fibres is recommended to achieve good workability for fibre reinforced concrete [34]. 3.2. Hardened density Two types of density (demoulded density (DD) and oven-dry density (ODD)) were measured for all mixes. The correlation between the demoulded and oven-dry densities as a function of fibre volume fraction is shown in Fig. 3. It can be observed that the concrete’s density decreases slightly with increasing fibre volume fraction, which is attributed to the fibres’ low specific gravity. All mixtures fulfilled the requirement of structural lightweight concrete by having an ODD and DD within the range of 1835– 1910 kg/m3 and 1897–1975 kg/m3, respectively. Newman and Owens [1] stated that, concrete with an oven-dry density (ODD) of not greater than 2000 kg/m3 is defined as structural lightweight concrete. This OPSFRC shows a close proximity value with the ODD reported in previous studies [18,19]. The results showed that, the addition of different type and geometry of PP fibres caused remarkable changes in the density reduction of OPSC. The inclusion of PPTB1, PPTB2 and PPS1 fibres produced density reduction in the ODD and DD of about 10– 75 kg/m3 and 12–78 kg/m3, respectively. From Fig. 3, the mixes with PP straight shape fibres produced a lower ODD and DD than the PPTB1 and PPTB2 geometry (twisted bundle) fibres. At 0.5% Vf, the PPS1 produced the lowest ODD and DD of about 1835 and 1897 kg/m3. In comparison to the density of normal weight PPTB1 (Demoulded)

PPTB2 (Demoulded)

PPS1 (Demoulded)

PPTB1 (Oven-dry)

PPTB2 (Oven-dry)

PPS1 (Oven-dry)

y = -10.25x + 1988.8 R² = 0.9806

Density (kg/m³)

1910

Mix code

Compressive strength (MPa)a 1d

y = -10.1x + 1924.4 R² = 0.9706

Control PPTB1/0.25 PPTB1/0.375 PPTB1/0.5 PPTB2/0.25 PPTB2/0.375 PPTB2/0.5 PPS1/0.25 PPS1/0.375 PPS1/0.5

y = -12.3x + 1985.7 R² = 0.9714

1890

y = -10.85x + 1923.2 R² = 0.9915

1870 y = -12.4x + 1924.1 R² = 0.9942

1850 1830 0.000

The results of the compressive strength at different ages (1 d, 3 d, 7 d and 28 d) are presented in Table 4 for all mixes. From the results of Table 4, the compressive strength of OPSC increased at all ages with an increase in PP fibres volume fraction. It can be seen that the early compressive strength of both OPSC and OPSFRC was achieved. It can be attributed to the addition of silica fume (SF) which reacts with calcium hydroxide (CaOH) liberated from hydration of the cement to produce calcium silicate hydrates (C–S–H) to improve aggregate-cement paste interface of concrete and consequently minimizes the induction of micro-cracks. It has been reported that, not all types of lightweight aggregate are suitable for production of HSLWC [35]. This investigation shows that the use of agriculture waste OPS aggregate for production of HSLWC is possible. Yew et al. reported that the use of heat treatment method on crushed OPS aggregate caused notable surface quality improvement and enhance adhesion between the OPS and cement paste [10]. A slight increase in compression strength was observed at 130 °C for 6 h has also been reported elsewhere [36]. The 28-days compressive strength of the OPSC and OPSFRC varies between 41 and 47 MPa, which fulfilled the high-strength lightweight concrete (HSLWC) requirements with respect to density and strength [37]. It was found that the compressive strength of specimen PPTB1/0.5 showed the highest compressive strength compared to control specimen, with a percentage increase of 15.4% at 28-days. A comparison of the strength at early and later ages indicate that the rate of strength development was greater as the age increased, especially for OPSC with higher PP fibres content. From the results of Table 4, it can be seen that the mixes from PPTB1/0.25 to PPTB1/0.5 increases the compressive strength by 5.9% and 10.0% at 1 d, 8.9% and 11.5% at 3 d, 7.0% and 10.6% at 7 d, 6.4% and 10.9% at 28 d, respectively. It can be observed that, the OPSFRC with twisted bundle shape and higher aspect ratio produced higher compressive strength as compared to the straight fibres. It may be due to the twisted bundle shape fibres which have good bond and anchorage in the matrix resulting in more strength. There is decrease in the strength with decrease in aspect ratio of same shape of fibre. All the mixtures attained about 90–93% of their 28 d compressive strength at the age of 7-days. In this study, the ratio of 1 d and 3 d strength to 28 d was 66–71% and 75–79%, respectively. Holm et al. reported [38] that the 7-day strength to 28-day strength ratio for HSLWC is between 86% and 92%. Furthermore, Fujji et al. [39] also reported that this ratio for HSLWC was between 80% and 90%.

y = -10.7x + 1988.3 R² = 0.99

1950 1930

3.3. Compressive strength

Table 4 Compressive strength development of control concrete and OPSFRC under continuous moist curing.

1990 1970

concrete (NWC) taken as 2350 kg/m3, the ODD and DD for all lightweight mixes are approximately 22% and 16% lower than of ordinary concrete. Hence, there is substantial cost savings by providing less dead load for LWC in this study.

0.250

0. 375

0.500

Volume fraction of PP fibre (%)

Fig. 3. Relationship between different PP fibre volume fraction and density.

a

28.9 28.6 30.3 31.4 28.9 30.0 31.2 30.1 29.8 30.4

3d (70.7%) (67.1%) (66.8%) (66.6%) (68.5%) (66.5%) (66.7%) (71.2%) (66.3%) (65.3%)

31.4 32.8 35.8 36.6 32.3 35.5 36.2 31.9 34.9 36.1

7d (76.7%) (77.1%) (78.9%) (77.5%) (76.6%) (78.6%) (77.3%) (75.3%) (77.6%) (77.4%)

38.1 39.3 42.1 43.5 39.0 41.8 43.3 38.5 41.6 43.2

28 d (93.0%) (92.4%) (92.8%) (92.1%) (92.5%) (92.6%) (92.5%) (90.9%) (92.5%) (92.7%)

40.9 42.6 45.3 47.2 42.2 45.1 46.8 42.4 44.9 46.6

The data in parentheses are percentage of 28 day compressive strength.

M.K. Yew et al. / Construction and Building Materials 90 (2015) 36–43

Fig. 4 shows the compressive strength development for OPSC containing PP with different geometry and length. The results indicate that control mix achieve saturated compressive strength after 28 d. It can be observed that, all mixes reinforced with different PP and aspect ratio showed improvement of compressive strength as the age increased (>28 d), especially for PPTB1/0.5 with highest fibre content. As can be seen from Fig. 4, there is notable difference between control and OPSFRC specimens containing different PP fibres and aspect ratio pertaining to 56 d and 90 d compressive strength increment. It was reported [17] that the OPSFRC with nylon fibres showed consistent compressive strength and slightly enhancement of about 3–6% compared to the control mix. However, the results of the present investigation showed that OPSFRC containing different PP fibres and aspect ratio increases the compressive strength significantly compared to the control specimen. The mixes from control to PPTB1/0.5, control to PPTB2/0.5 and control to PPS1/0.5 at 28 d consistently increases the compressive strength by about 4–15%, 3–14% and 4–14%, respectively. This observation may be attributed to the higher tensile strength of different type of the new PP and aspect ratio compared with other PP (fibrillated and multi-filament). In this study, an increasing compressive loading will initiate and advance the cracking on OPSC specimens. When the advancing crack approaches PP fibre, the debonding at the fibre–matrix interface begins due to the tensile stresses perpendicular to the expected path of the advancing crack. Once significant amount of tensile stress was introduced in concrete, micro-cracks and subsequently macro-cracks were formed [40–42]. This phenomenon showed that the addition of PP fibres improved aggregate-fibre-cement paste interface of the concrete and consequently increased the compressive strength.

The UPV is a non-destructive test method used to assess the quality of the concrete. This method can be used to estimate the strength of concrete test specimens and also useful on-site where destructive strength test is not applicable. As shown in Fig. 5, relationship between the UPV and the cube compressive strength was measured at the ages of 1 d, 3 d, 7 d, 28 d, 56 d and 90 d. The UPV method can be used to detect internal cracking, voids and

Compressive strength (MPa)

fcu = 0.733 (Ut)2.9 R2 = 0.97

50

40

30

20 3.40

3.50

3.60

3.70

3.80 UPV (km/s)

4.00

4.10

4.20

Fig. 5. Relationship between the UPV and compressive strength up to 90 days.

inhomogeneity of concrete, as well as changes in concrete such as deterioration due to aggressive chemical environment, freezing and thawing. It has been stated that concrete with UPV values within the range of 3.66–4.58 km/s are considered as concrete with ‘‘good’’ condition [43]. In general, it can be seen that the UPV of the control concrete and OPSFRC increased with increase in compressive strength and the values were found within the range of 3.45–4.16 km/s. From the results, it is evident that the specimens of different type of PP fibres have a positive effect on the UPV values of OPSFRC. It was found that UPV can be correlated with its corresponding cube compressive strength, as shown in Fig. 5, with a R2 value of 0.97. Eq. (1) is proposed to estimate the cube compressive strength based on the UPV values.

f cu ¼ 0:733ðU t Þ2:9

ð1Þ

3.5. Splitting tensile and flexural strengths In this study, the low dosage of different type of PP fibres and aspect ratio in concrete has positive effect on the splitting tensile and flexural strengths. From the results of Table 5, the addition of different types of PP fibres enhanced both splitting tensile and flexural strengths of OPSFRC. Furthermore, the increment of fibres

Control

PPTB1/0.25

PPTB1/0.375

PPTB1/0.5

PPTB2/0.25

PPTB2/0.375

PPTB2/0.5

PPS1/0.25

PPS1/0.375

PPS1/0.5

0

3.90

where fcu represents the cube compressive strength (MPa) and Ut represents the transverse ultrasonic pulse velocity (km/s).

3.4. Ultrasonic pulse velocity (UPV)

55 54 53 52 51 50 49 48 47 46 45 44 43 42 41 40 39 38 37 36 35 34 33 32 31 30 29 28 27 26 25

60 Compressive strength, fcu (MPa)

40

20

40

60

80

Age (days) Fig. 4. Development of compressive strength of control and OPSFRC.

100

41

M.K. Yew et al. / Construction and Building Materials 90 (2015) 36–43 Table 5 Mechanical properties of control concrete and OPSFRC. Mix code

Mechanical properties Splitting tensile strength (MPa)

Flexural strength (MPa)

Modulus of elasticity (GPa)

5.45 7.05 7.12 7.64 6.43 6.67 7.09 5.75 5.97 6.52

11.64 12.68 13.62 15.36 12.55 13.39 14.82 12.04 13.25 14.46

28 d 3.10 3.35 3.85 4.12 3.42 3.68 3.95 3.49 3.54 3.74

Fig. 6. Image of tested prism specimen – note the different type of PP fibres bridging across the crack.

volume fraction had a significant effect on both splitting tensile and flexural strengths. It can be seen that, the addition of different types of PP fibres greatly increased the splitting tensile strength of concrete. As found from this investigation, the addition of PPTB1/0.25–0.5%, PPTB2/0.25–0.5% and PPS1/0.25–0.5% fibres enhanced the splitting tensile strength up to 8–33%, 10–27% and 13–21% respectively compared to the control mix. On the other hand, the flexural strength of PPTB1, PPTB2 and PPS1 mixes produced significant improvement compared to the control concrete. The flexural strength of PPTB1, PPTB2 and PPS1 increased with an increase in fibres volume content. The average flexural strength for PPTB1/0.25–0.5%, PPTB2/0.25–0.5% and PPS1/0.25–0.5% increases by 7.3%, 6.7% and 6.1%, respectively. The addition of higher aspect ratio and twisted bundle shape of fibres provide added strength to the fibre–matrix interface which carry part of the applied load and the crack bridging effect as shown in Fig. 6. The content of fibres volume fraction used in this study is lower compared to previous studies [17–19]. However, PPS1 showed higher splitting tensile strength compared to PPTB2 and PPTB1 at 0.25% volume fraction. It might be attributed to the lower aspect ratio (L/d) of PPS1 fibres exhibiting higher effective surface area for the development of a fibre–matrix bond compared to PPTB2 and PPTB1 fibres. Thus, the greater surface area of PPS1 fibres was effective in transferring higher tensile stress compared to PPTB2 and PPTB1 fibres. The average splitting tensile and flexural strengths of PPTB1/0.25–0.5, PPTB2/0.25–0.5 and PPS1/0.25–0.5 mixes were found to be 22%, 19%, 16% and 33%, 23%, 12% higher, respectively than the control concrete. It can be seen that, low fibre volume fraction (up to 0.375%) are more effective in improving the flexural strength of OPSC compared to splitting tensile strength. This phenomenon might be attributed to the fibre geometry, which provides added strength to the matrix through reduces the stress concentration at the crack section and improves the crack growth resistance [44] and consequently, enhances the tensile strength of OPSFRC. The linear relationship between tensile strength (splitting tensile and flexural) and compressive strength for OPSFRC at the age of 28-day is correlated in Fig. 7. It can be observed that, the advantage of PP fibres in the enhancement of tensile strength is more evident in the OPSFRC with PPTB1 and PPTB2 compared to PPS1 fibres. It was stated that, different equations have been proposed to correlate splitting tensile strength to compressive strength of OPS LWAC by Shafigh et al. [45] and Yap et al. [17]. They predict splitting tensile strength based on the compressive strength of OPSC and OPSFRC as shown in Eqs. (2) and (3):

F - Flexural PPTB1-F 8.00

PPTB2-F

ST - Splitting Tensile PPS1-F

PPTB1-ST

PPTB2-ST

PPS1-ST

y = 0.1211x + 1.8162 R² = 0.7602 (PPTB1)

7.50 28-day tensile strength (MPa)

Control PPTB1/0.25 PPTB1/0.375 PPTB1/0.5 PPTB2/0.25 PPTB2/0.375 PPTB2/0.5 PPS1/0.25 PPS1/0.375 PPS1/0.5

7.00 y = 0.1369x + 0.6117 R² = 0.9039 (PPTB2)

6.50 6.00 y = 0.1739x - 1.6814 R² = 0.8766 (PPS1)

5.50 5.00

y = 0.1671x - 3.7518 R² = 0.9956 (PPTB1)

y = 0.1114x - 1.295 R² = 0.9734 (PPTB2)

4.50 4.00 3.50

y = 0.0559x + 1.0954 R² = 0.8129 (PPS1)

3.00 42

43

44

45

46

47

48

28-day compressive strength (MPa)

Fig. 7. Relationship between tensile strengths (splitting tensile and flexural strengths) and compressive strength.

where ft and fcu represents the splitting tensile and cube compressive strengths in MPa, respectively. An equation to correlate splitting tensile strength and compressive strength of OPSFRC is proposed in Eq. (4), whereby a higher coefficient of correlation is produced (accuracy = ±8%). Shafigh et al. reported that an accurate prediction of tensile strength of concrete imperative in mitigating cracking problems, minimize the failure of concrete in tension and increase shear strength prediction [45], is shown below:

qffiffiffiffiffiffi f t ¼ 0:55 f cu

ð4Þ

Different equations have also been proposed to correlate flexural strength to compressive strength of OPS LWAC by Alengaram et al. [46] in Eq. (5) and Yap et al. [17] in Eq. (6) for OPSFRC with PP and nylon fibres. A new equation, Eq. (7) is suggested for OPSFRC with different PP fibres to predict the flexural strength within ±12%.

f r ¼ 0:3

qffiffiffiffiffiffi 3 2 f cu

qffiffiffiffiffiffi 3 2 f r ¼ 0:385 f cu

ð5Þ

ð6Þ

qffiffiffiffiffiffi f t ¼ 0:4887 f cu

ð2Þ

f r ¼ 0:53

qffiffiffiffiffiffi f t ¼ 0:52 f cu

ð3Þ

where fr and fcu are the flexural and compressive strengths in MPa, respectively.

qffiffiffiffiffiffi 3 2 f cu

ð7Þ

42

M.K. Yew et al. / Construction and Building Materials 90 (2015) 36–43

3.6. Modulus of elasticity (E)

PPS1/0.5 PPS1/0.375

1=2

ð8Þ

1=2

ð9Þ

1=2

ð10Þ

Et1 ¼ 7:49f cu  36:39 Et2 ¼ 6:20f cu  27:89 Es1 ¼ 7:50f cu  36:86

where Et1, Et2, Es1 and fcu are the modulus of elasticity (GPa) of PPTB1, PPTB2 and PPS1 fibres and cube compressive strengths in MPa, respectively.

Modulus of elasticity ( GPa)

The residual compressive strength (RCS) is a simplified method to assess the residual strength toughness of concrete. The results from first compressive strength are further loaded into residual strength for second and third compressive strength. The RCS provides a clearer comparison on the beneficial effects of different type of PP fibres and volume fraction in enhancing the post-cracking of OPSFRC. As seen from Fig. 9, the control specimen of OPSC had the lowest RCS values as the specimen failed without fibre–matrix bond when the initial compressive loading was applied on the cube specimens. The post-failure compressive

PPTB1

PPTB2

PPS1

E = 7.49fcu ½ - 36.39 R2 = 0.923 (PPTB1) E = 6.20fcu½ - 27.89 R2 = 0.908 (PPTB2)

E = 7.50fcu ½ - 36.86 R2 = 0.986 (PPS1)

6.50

6.55

6.60

6.65

PPTB2/0.375 TLCS PPTB2/0.25

SLCS

PPTB1/0.5

FLCS

PPTB1/0.375 PPTB1/0.25 Control 0.00

10.00

Comparison of

1st,

20.00 2nd

and

3rd

30.00

40.00

50.00

load compressive strength at 28-days

Fig. 9. Comparison of 1st, 2nd and 3rd load compressive strength at 28-days.

strength values for second load compressive strength (SLCS) and third load compressive strength (TLCS) further reduced to 67.7% and 39.0%, respectively. The percentage TLCS of PPTB1/0.5 mixes produced the highest RCS values compared to PPTB2/0.5 and PPS1/0.5 with a value of 50.8%. It might be attributed to the higher aspect ratio, geometry as well as content of PPTB1 fibres. Similar to the previous observation, the crack bridging effect of fibres that are existent at the crack face is capable of sustaining a higher post-cracking to propagate further, compared to concrete with low volume fraction of fibres. This indicates that, the addition of fibres is expected to enhance the post-failure toughness of OPSC. In general, all OPSFRC mixes produced high RCS and this indicates the imperative of this type of PP fibres in improving the post-cracking characteristics. 4. Conclusion

3.7. Residual compressive strength (RCS)

15.6 15.4 15.2 15.0 14.8 14.6 14.4 14.2 14.0 13.8 13.6 13.4 13.2 13.0 12.8 12.6 12.4 12.2 12.0 11.8 6.45

PPS1/0.25 PPTB2/0.5 Mix

The modulus of elasticity (E) is an imperative test to assess the material properties of concrete as it provides useful information on the ability of concrete to deform elasticity in the design of concrete structures. From the results of Table 5, all OPSFRC have E in the range between 12.0 and 15.4 GPa. However, the control OPSC mix without any fibres produced a MOE of 11.6 GPa. It can be seen that, the 28-day MOE of the OPSC was found to increase with the addition of different types of PP fibres and aspect ratio as shown in Table 5. Similar finding for PP2 (multifilament) is reported by Yap et al. [17]. The increase of the E for PPTB1/0.25–0.5, PPTB2/0.25–0.5 and PPS1/0.25–0.5 mixes was in the range of 9– 32%, 8–27% and 3–24%, respectively. The addition of different types of PP fibres caused improvement of MOE due to higher aspect ratio and geometry of fibres in arresting the original shrinkage cracks in the concrete [47] and hence reduced the strain induced under compression loadings, and consequently improved the E of OPSFRC. As seen from Fig. 8, a good relationship is established between E and compressive strength of concrete. The following three equations is proposed for different type of PP fibres to relate the E and the cube compressive strength of OPSFRC.

6.70

6.75

6.80

6.85

6.90

Compressive strength (MPa ½)

Fig. 8. Relationship of compressive strength and modulus of elasticity (E) at 28days.

The effects of incorporating different types of PP fibres and aspect ratio at low volume fractions up to 0.5% on the mechanical properties of high-strength oil palm shell lightweight concrete have been investigated in this study. The following conclusions are drawn based on the experimental results: (1) PP fibres reduce the slump value of concrete. The reduction in slump value is within the range of 11–64% for different type of fibres. However, the reduction in slump value is less than that for fibrillated and multi-filament PP fibres at similar volume fractions. (2) The addition of this type of PP fibres contribution to density of concrete cannot be ignored, which reduces construction cost in foundation design, erection and installation (3) The compressive strength of OPSC increases with an increase in PP fibre content. Plain OPS concrete has a 28-day compressive strength of 41 MPa, and this value increases to 42–47 MPa when the concrete is reinforced with different types of PP fibres at volume fractions of 0.25–0.5%. (4) The addition of 0.5% Vf of PPTB1, PPTB2 and PPS1 fibres increases the splitting tensile strength of OPS concrete by 33%, 27% and 12%. Based on the results, it is recommended that the minimum volume fraction of the different type of PP fibres is 0.375% after reporting the results for 0.5%. (5) The effect of incorporating different type of PPTB fibres at low volume fractions in improving the flexural strength of OPS concrete is more pronounced compared to its effect on splitting tensile strength. (6) The specimens for both OPSC and OPSFRC can be categorized as ‘‘of good’’ condition after 7 days based on the UPV test results.

M.K. Yew et al. / Construction and Building Materials 90 (2015) 36–43

(7) Different types of PP fibres exhibit a positive effect on the modulus of elasticity of OPS concrete. It is found that the average E value measured in this study is 13.4 GPa for all mixes, which is comparable to the E values reported in previous studies. (8) The inclusion of different types of PP fibres at 0.5% volume fraction improved the post-failure toughness especially in comparison to the third residual compressive strength (RCS) of OPSFRC as compared to control specimen. The fibre–matrix bond enhanced the RCS values of OPSFRC, which is a sign of ductility.

Acknowledgements The authors gratefully acknowledge the financial support from University of Malaya under the Institute of Research Management and Monitoring (Project No.: PG007-2013A), University of Malaya Research Grant Scheme (Project No.: RP018/2012C and RP022C-13AET) and Fundamental Research Grant Scheme (Project No.: FP048-2013B). In addition, BCA would like to thank for the financial support of the Ministry of Higher Education, Malaysia through High Impact Research Grant MOHE-HIR D000008-16001. The authors extend special thanks to Mr. Yew See Hing for collecting the oil palm shell coarse aggregate species and Ir. Hong Chung Sin for providing the polypropylene fibres to this research.

References [1] Newman J, Owens P. Properties of lightweight concrete. Advanced concrete technology set. Oxford: Butterworth-Heinemann; 2003. p. 3–29. [2] Meyer C. The greening of the concrete industry. Cement Concr Compos 2009;31:601–5. [3] Federico LM, Chidiac SE. Waste glass as a supplementary cementitious material in concrete – critical review of treatment methods. Cement Concr Compos 2009;31:606–10. [4] Alengaram UJ, Muhit BAA, Jumaat MZ. Utilization of oil palm kernel shell as lightweight aggregate in concrete – a review. Concr Build Mater 2013;38:161–72. [5] Subiyanto B, Basri H, Sari LN, Rosalita TY. Chemical components of oil palm (elaeis guineensis Jacq.) shell and its effect on light concrete performance. J Trop Wood Sci Technol 2007;5(1):22–8. [6] MPOB expects CPO production to increase to 19 million tonnes this year. http://www.thestar.com.my/story.aspx/?file=%2f2013%2f1%2f15%2fbusiness% 2f12576771&sec=business [retrieved January 29, 2013]. [7] Shafigh P, Jumaat MZ, Mahmud H. Mix design and mechanical properties of oil palm shell lightweight aggregate concrete: a review. Int J Phys Sci 2010;5(14):2127–34. [8] Shafigh P, Jumaat MZ, Mahmud H. Oil palm shell as a lightweight aggregate for production high strength lightweight concrete. Concr Build Mater 2011;25:1848–53. [9] Shafigh P, Jumaat MZ, Mahmud H, Alengaram UJ. A new method of producing high strength oil palm shell lightweight concrete. Mater Des 2011;32:4839–43. [10] Yew MK, Mahmud H, Ang BC, Yew MC. Effects of heat treatment on oil palm shell coarse aggregates for high strength lightweight concrete. Mater Des 2014;54:702–7. [11] Yew MK, Mahmud H, Ang BC, Yew MC. Effects of oil palm shell aggregate species on high strength lightweight concrete. Sci World J 2014 [Article ID 387647:1-12]. [12] Yew MK, Mahmud H, Ang BC, Yew MC. Effects of low volume fraction of polyvinyl alcohol fibres on the mechanical properties of oil palm shell lightweight concrete. Adv Mater Sci Eng 2014 [Article ID 425236:1-11]. [13] Yew MK, Mahmud H, Shafigh P, Ang BC, Yew MC. Effects of polypropylene twisted bundle fibres on the mechanical properties of high-strength oil palm shell lightweight concrete. Mater Struct 2015:1–13. [14] Alengaram UJ, Jumaat MZ, Mahmud H, Shirazi SM. Effect of aggregate size and proportion on strength properties of palm kernel shell concrete. Int J Phys Sci 2010;5(12):1848–56.

43

[15] Khaloo AR, Sharifian M. Experimental investigation of low to high-strength steel fibre reinforced lightweight concrete under pure torsion. Asian J Civi Eng (Build Hous) 2005;6(6):533–47. [16] Shafigh P, Jumaat MZ, Mahmud H. Effect of steel fibre on the mechanical properties of oil palm shell lightweight concrete. Mater Des 2011;32:3926–32. [17] Yap SP, Alengaram UJ, Jumaat MZ. Enhancement of mechanical properties in polypropylene and nylon fibre reinforced oil palm shell concrete. Mater Des 2013;43:1034–41. [18] Mo KH, Yap SP, Alengaram UJ, Jumaat MZ, Bu CH. Impact resistance of hybrid fibre-reinforced oil palm shell concrete. Concr Build Mater 2014;50:499–507. [19] Yap SP, Bu CH, Alengaram UJ, Mo KH, Jumaat MZ. Flexural toughness characteristics of steel polypropylene hybrid fibre-reinforced oil palm shell concrete. Mater Des 2014;57:652–9. [20] ASTM C150/C150 M-12. Standard specification for Portland cement. Annual Book of ASTM Standards; 2012. [21] ASTM C1240-03a. Standard specifications for use of silica fume for use as a mineral admixture in hydraulic-cement, mortar, and grout. Annual Book of ASTM Standards; 2003. [22] AS 3582.3. Method of testing supplementary cementitious materials for use with Portland cement, method 3: determination of loss on ignition. Standards Australia; 1994. [23] ASTM C494/C494M-04. Standard specification for chemical admixture for concrete. Annual Book of ASTM Standards; 2004. [24] Kosmatka SH, Kerkhoff B, Panarese WC. Design and control of concrete mixtures. 14th ed. USA: Portland Cem Assoti; 2002. [25] BS EN 12390. Part 3 testing hardened concrete – compressive strength of test specimens. British Standard Institution; 2009. [26] Memon NA, Sumadi SR, Ramli M. Performance of high workability slag-cement mortar for ferrocement. Build Environ 2007;42:2710–7. [27] Mehta PK, Monteiro PJM. Concrete; microstructure, properties, and materials. 3rd ed. New York: McGraw-Hill; 2006. [28] Al-Harthy AS, Abdel Halim M, Taha R, Al-Jabri KS. The properties of concrete made with fine dune sand. Concr Build Mater 2007;21:1803–8. [29] Dawood ET, Ramli M. Flowable high-strength system as repair material. Struct Concr 2010;11:199–209. [30] Lu G, Wang K, Rudolphi TJ. Modeling rheological behavior of highly flowable mortar using concepts of particle and fluid mechanics. Cem Concr Compos 2008;30:1–12. [31] Okamura H, Ouchi M. Self compacting concrete. J Adv Concr Technol 2003;1:5–15. [32] Rossi P, Harrouche N. Mix design and mechanical behavior of some steel fibre reinforced concrete used in reinforced concrete structure. Mater Struct 1990;23:256–66. [33] Campione G, Miraglia N, Papia M. Mechanical properties of steel fibre reinforced lightweight concrete with pumice stone or expanded clay aggregates. Mater Struct 2001;34:201–10. [34] Sivakumar A. Influence of hybrid fibres on the post crack performance of high strength concrete: part I experimental investigations. J Civ Eng Constr Technol 2011;2(7):147–59. [35] Zhang MH, Gjorvl OE. Development of high-strength lightweight concrete. ACI Spec Publ 1990;121:667–82. [36] Yildiz S, Gezer ED, Yildiz UC. Mechanical and chemical behaviour of spruce wood modified by heat. Build Environ 2006;41:1762–6. [37] Hoff GC. Guide for the use of low-density concrete in civil works projects. US Army Corps of Engineers, Engineer Research and Development Center, ERDC/ GSL TR-02-13 (TR INP-02-07); 2002. [38] Holm TA, Bremner TW. State of the art report on high strength, high durability structural low-density concrete for applications in severe marine environments. US Army Corps of Engineers, Engineering Research and Development Center, ERDC/SL. TR-00-3; 2000. [39] Fujji K, Adachi S, Takeuchi MT, Kakizaki M, Edahiro H, Inoue T. Properties of high-strength and high-fluidity lightweight concrete. ACI Spec Publ 1998;179:65–84. [40] Song PS, Hwang S, Sheu BC. Strength properties of nylon- and polypropylenefibre-reinforced concretes. Cem Concr Res 2005;35:1546–50. [41] Han CG, Hwang YS, Yang SH, Gowripalan N. Performance of spalling resistance of high performance concrete with polypropylene fibre contents and lateral confinement. Cem Concr Res 2005;35:1747–53. [42] Yew MK, Othman I, Yew MC, Yeo SH, Mahmud H. Strength properties of hybrid nylon-steel and polypropylene-steel fibre-reinforced high strength concrete at low volume fraction. Int J Phys Sci 2011;6(33):7584–8. [43] Neville AM. Properties of concrete. 14th ed. Malaysia: CTP-VVP; 2008. [44] Banthia N, Gupta R. Influence of polypropylene fibre geometry on plastic shrinkage cracking in concrete. Cem Concr Res 2006;36:1263–7. [45] Shafigh P, Jumaat MZ, Mahmud H, Hamid NBAA. Lightweight concrete made from crushed oil palm shell: tensile strength and effect of initial curing on compressive strength. Concr Build Mater 2012;27:252–8. [46] Alengaram UJ, Jumaat MZ, Mahmud H. Influence of sand content and silica fume on mechanical properties of palm kernel shell concrete. In: International conference on construction and building technology ICCBT; 2008. p. 251–62. [47] Gao J, Sun W, Morino K. Mechanical properties of steel fibre-reinforced, highstrength, lightweight concrete. Cem Concr Compos 1997;19(4):307–13.