This study compares the effect of treated pineapple leaves fibres (T-PALF) with sodium hydroxide solution and untreated fibres (N-PALF) on the compressive and flexural strength of earth bricks stabilized with 3% and 5% cement. The fibre content ranged from 0% to 5% in steps of 1% by weight. The compressive strength tests were made at 7, 14, 21 and 28 days of curing; the flexural strength test were conducted at 28th day only. The results show that the T-PALF had a higher compressive strength when comparing to the N-PALF. The highest compressive strength of the bricks was obtained at 28 days of curing. The compressive strength at 28 days of stabilized brick at 3% and 5% of cement reinforced with T-PALF were 4.01 and 4.81 MPa, respectively, while the one reinforced with N-PALF was 3.19 and 4.63 MPa, respectively. The results further show that the highest flexural strength of both stabilized bricks at 3% and 5% of cement reinforced with T-PALF and N-PALF was obtained with the bricks stabilized with 5% of cement reinforced with T-PALF. This results show that bricks stabilized with 5% cement and reinforced with 3% of treated fibres content are good for construction of load bearing walls. It was observed; a significant improvement of the reinforced blocks under flexure than under compression.
Nowadays there is a growing attention in the development of research on natural fibre reinforced composites or bio-composites, in widespread applications, including automotive, construction and aerospace [
Reinforced soils are solid composites which consist of gathering two or more different structures in which their identities are preserved. The advantages of newly produced composites are higher specific strength, stiffness, and lower thermal conductivity (Kazemian et al., 2010) [
Pineapple leave fibre has been used for long time to reinforce composite and the results were significant; but due to lack of standards it has not yet been used properly in civil engineering field. Recently, some research started going in this direction of using pineapple to reinforce concrete [
Much effort has gone into improving the mechanical properties of laterites to enhance their performance in order to meet the demand for their wider applications [
The study was conducted at Jomo Kenyatta University of Agriculture and Technology (JKUAT) from February to June 2018. JKUAT is located in Juja township, 10 km West of Thika town and 45 km East of Nairobi, Kenya. The latitude, longitude and altitude of the location are 1.18˚S, 37˚E and 1460 m above sea level, respectively. Laterite soil and sand used for the study were procured from Juja and Nyeri, respectively. The soil was kept under polyetilene cover to ensure that it was neither too dry (by sun dry) nor too wet (by rain). In addition, Pozzolanic cement CEM IV/B 32.5R used in the study was formulated in accordance to the KS EAS 18-1:2001, which is adopted from the EN 197-1 European Standards. Finally, PALF which were the main material to be used for reinforcing the bricks were obtained from Hand Conifer Company Ltd, Mumbai, India. The fibres were extracted from the leaves by using mechanical extractor machine.
The physical properties for the soil that were examined included moisture content, maximum dry density, Atterberg limits and soil size particle distribution. The moisture content was determined according to BS 1377:1990. Dry density, Atterberg limits and the size distribution were analysed at JKUAT, as per to BS 1377-2:1990 [
In order to assess the chemical properties and tensile strength of the PALF it was necessary to treat the fibres in a 4% of sodium hydroxide (NaOH) solution over various durations. The NaOH treatment is one of the best treatment used for natural fibres. It helps to increase the fibre surface roughness by chemically modifying and cleaning the fibre surface [
1) Mix Design and Pineapple Leaf Fibre Reinforced Brick Preparation
The different specimens were prepared as follows. First, Portland cement, sand and laterite soil were mixed in proportions of 3%, 27% and 70% by mass, respectively, and water was added to form a paste of acceptable range of moisture content, where simple drop test in done according to the New Zealand Standard 4298 (1998) [
After mixing, the materials were poured into a manual stabilized soil block machine to make the bricks. The machine had a hydraulic pressure gauge and was set at a constant pressure of 10 MPa. The bricks were then wrapped with a plastic film to avoid rapid drying and stored under a sheltered area for 7 days. Thereafter, they were stored in the open air for 21 days for curing.
2) Determining the Mechanical Properties of the Bricks
Compressive strength of the bricks stabilized with 3% and 5% of cement and reinforced with N-PALF and T-PALF at 0% to 5% was determined. Servo-plus evolution testing machine was used for the test. Initially, the compressive strength was determined at 7, 14, 21 and 28 days of curing, and it was conducted in accordance to BS EN 772-1 (2011). Loading was done at a rate of 0.05 N/mm2∙s−1 until the brick failed and the maximum compressive stress recorded. On the other hand, the flexural strength was conducted according to ASTM C67-07 [
The results of the physical properties of the soil used in this study are shown in
Properties | Values |
---|---|
Proctor test: | |
Optimum moisture content (%) | 31.1 |
Maximum dry density (kg/m3) | 1351 |
Atterberg limits: | |
Liquid limit, wL (%) | 54 |
Plastic limit, wp (%) | 28 |
Plasticity index | 27 |
Soil classification (USCS): | CH |
Particle size distribution: | |
Gravel (20 - 2 mm) (%) | 2 |
Sand (2 - 0.06 mm) (%) | 20 |
Silt (0.06 - 0.002 mm) (%) | 58 |
Clay (<0.002 mm) (%) | 20 |
pH: | |
Value | 7.31 |
The particle size distribution of the soil corresponds to result of both dry sieving and hydrometer test (see
Chemical composition | Proportion (%) |
---|---|
SiO2 | 51.31 |
Al2O3 | 22.26 |
CaO | 1.33 |
MgO | 0.06 |
Na2O | 2.5 |
K2O | 1.7 |
TiO | 1.25 |
MnO | 0.34 |
Fe2O3 | 8.00 |
LOI | 10.00 |
The results for the chemical properties of the PALF are presented in
strength of the fibres increased after the treatment because non-cellulosic materials were removed from them [
The main purpose of the above treatment was to use the fibres with the highest tensile strength for soil reinforcement for making bricks. However, in this study the experimental value of 751.95 MPa corresponding to one (1) hour duration of treatment were selected. The numerical value was determined later after using the experimental value. Nevertheless, the difference between the experimental and numerical values is insignificant as the former is was just 1.99% less than the later. It is then recommended that future studies should establish the feasibility of using fibres with the numerically established tensile strength value.
Duration of treatment (min) | Chemical composition (%) | ||
---|---|---|---|
Cellulose | Hemi-cellulose | Lignin | |
0* | 78.676 | 70.775 | 10.321 |
30 | 75.76 | 68.443 | 9.300 |
60 | 74.87 | 67.551 | 9.26 |
120 | 74.23 | 67.48 | 9.15 |
180 | 74.005 | 66.812 | 9.055 |
*Corresponds to N-PALF while the rest (30-180) correspond to T-PALF.
The Scanning Electron Microscopy (SEM) results for the treated after (1) hour duration of treatment in NaOH solution and untreated pineapple leaves fibre are presented in
Compressive strength tests of four sets of bricks were made; the first and second sets were for bricks stabilized with 3% of cement reinforced with N-PALF and T-PALF, respectively, while the third and fourth sets were for bricks stabilized with 5% of cement reinforced N-PALF and T-PALF, respectively.
The relationship between the compressive strength of bricks stabilized with 3% cement and various proportions of T-PALF are shown in
The results for relationship between the compressive strength of bricks stabilized with 5% cement and various proportions of T-PALF are presented in
Based on the above results, the compressive strength increased with fibre content because the fibres within the bricks supported the applied load up to the 3% content level. However, above this level the compressive strength decreased because the amount of fibre in the mixture was high and instead of reinforcing the bricks the fibre started sticking together, forming waste matrix within the bricks making the bricks to loose strength. Similar observation was made by Humphrey Danso et al. [
The results also show that the bricks reinforced with T-PALF performed better than the N-PALF. This is due to the fact that NaOH solution treatment improved the tensile strength of the fibres and this improvement allowed the treated fibres to boost the strength of the bricks as compared to those reinforced with non-treated fibres. Similar observations were made by L. Uma Devi et al., 1996, and a significant improvement in the tensile strength was reported for polyester composites reinforced with treated PALF [
Finally, the results show that the performance of reinforced bricks stabilised with 5% of cement was higher than that with 3% of cement. Many other researchers (references) have found that 5% to 10% of cement is the best range to stabilize soil bricks, which supports the findings of this study. It is also important to mention that from this study with 5% of cement the fibre content is more suitable than with 3% since the fibres were added in terms of percentage weight of cement. The Standard Deviation (STDEV) of the compressive strength of the brick at 28 days are presented in
Fibre content (%) | Compressive strength of speciments at 28 days of curing | Mean | STDEV | |||
---|---|---|---|---|---|---|
3N-PALF | 3T-PALF | 5N-PALF | 5T-PALF | |||
0 | 2.91 | 2.91 | 3.04 | 3.04 | 2.975 | 0.06 |
1 | 2.43 | 2.34 | 3.36 | 3.89 | 3.005 | 0.65 |
2 | 2.98 | 3.38 | 3.58 | 3.88 | 3.455 | 0.33 |
3 | 3.19 | 4.01 | 4.63 | 4.81 | 4.16 | 0.63 |
4 | 2.39 | 3.26 | 3.14 | 3.31 | 3.025 | 0.37 |
5 | 2.19 | 2.92 | 2.83 | 3.01 | 2.7375 | 0.32 |
The flexural strength results are shown in
The flexural strength of bricks reinforced with T-PALF has shown a higher result as compare to those reinforced with N-PALF. At the optimum fibre content (3% of PALF) the flexural strength of the stabilized bricks with 5% of cement were 0.64 MPa and 0.92 MPa respectively for bricks reinforced with N-PALF and T-PALF, while for the control brick it was 0.43 MPa; so there is increased of 48.84% and 113.95% respectively with N-PALF and T-PALF over the unreinforced bricks. In the same manner, at the optimum fibre content (3% of PALF) the flexural strength of stabilized bricks with 3% of cement were 0.38 MPa and 0.49 MPa respectively for bricks reinforced with N-PALF and T-PALF, while for the control brick was 0.26 MPa; so there is increased of 46.15% and 88.46% respectively with N-PALF and T-PALF over the unreinforced bricks. The T-PALF have more restricted crack tip propagation and blunt the crack tip than N-PALF and this led to increase the flexural strength of the bricks better with T-PALF than with N-PALF.
The T-PALF have increased the strength of the bricks in flexure more than in compression, this is showing that the fibre acted more in traction than in compression within the composite as the case with steel reinforcement in concrete beam. More again, the best fibres content in the bricks is with 5% of cement.
Percentage of Increase compare to unreinforced bricks | ||||
---|---|---|---|---|
Fibres content (%) | 3 N-PALF | 3 T-PALF | 5 N-PALF | 5 T-PALF |
1 | 11.90 | 29.11 | 22.36 | 60.99 |
2 | 24.94 | 52.91 | 34.93 | 98.15 |
3 | 42.53 | 84.18 | 48.19 | 112.80 |
4 | 31.65 | 43.54 | 25.83 | 84.66 |
5 | 14.56 | 28.23 | 18.50 | 66.23 |
This study investigated the compressive strength of bricks stabilized with 3% and 5% of cement and reinforced with non-treated and treated pineapple leaf fibre. The results show that:
1) The soil had a high content of both clay and sand (20%) for making good bricks, and for that reason some sand was added to reduce the dominance of clay as this would lead to excessive drying shrinkage, and reduced durability and compressive strength. The soil is laterite as the Silica Sesquioxides ratio (SiO2/[Al2O3+Fe2O3]) is equal to 1.5.
2) The amount of cellulose, hemicellulose and lignin in the fibres decreased with increase in duration of treatment with sodium hydroxide solution. In addition, the treatment increased the tensile strength of the fibres up to an optimum of 766.9 MPa after 106.8 minutes.
3) Compressive strength of the fibre reinforced bricks increased with increase in fibre content up to 3%; thereafter it decreased. At 3% cement stabilization, 3% of treated fibres and 21 to 28 days of curing, the bricks attained enough compressive strength for construction of load bearing walls. However, better performance was obtained for 5% cement stabilized bricks at 3% fibre content. The bricks reinforced with sodium hydroxide treated fibres had higher compressive strength than non-treated fibres.
4) Flexural strength of the fibre reinforced bricks increased with increase in fibre content up to 3%; thereafter it decreased. The treated fibres have significantly improved the flexural strength of the bricks comparing to compressive strength.
This research was supported/partially supported by The Pan African University Institute of Basic Sciences Technology and Innovation (PAUISTI) of Kenya. We thank Mr. GARUGU for assistance with Laboratory material. We would also like to show our gratitude to Prof. Gabriel Nyamwamu Magoma, Director of PAUISTI.
S.H.C. conceived the study, designed experiments and interpreted the results; M.T. developed analytical tools and wrote the paper; N.C. analyzed data and wrote the paper.
This paper has been reviewed by 3 reviewers. 2 reviewers opted to be made public: FirstName1 LastName1, Affiliation1; FirstName2 LastName2, Affiliation2. The corresponding author is marked with *.
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The authors declare no conflicts of interest regarding the publication of this paper.
Vodounon, N.A., Kanali, C. and Mwero, J. (2018) Compressive and Flexural Strengths of Cement Stabilized Earth Bricks Reinforced with Treated and Untreated Pineapple Leaves Fibres. Open Journal of Composite Materials, 8, 145-160. https://doi.org/10.4236/ojcm.2018.84012