Adding plant fibers such as rice husks or sisals to the mortar is one of the main methods to reuse the agricultural wastes and reduce the energy consumption of building industry. However, recent research showed some limitation of the mortar mixed with plant fibers. In this paper, sisal fibers and rice husks were added together into cement mortar to investigate its mechanical properties and the optimum mixture ratio of sisal fiber and rice husk by mix ratio test and orthogonal test. The microstructure of the sisal fiber was observed using scanning electron microscopy (SEM) to understand how the properties of the mortar were affected. Results showed that adding sisal fiber and rice husk into cement mortar significantly improved the mechanic property, anticrack performance, and impermeability of the mortar. The highest compressive strength and flexural strength can reach 17.1 MPa and 3.3 MPa. The area of early cracks was reduced by 100%, and the maximum seepage pressure was 0.36 MPa. The microstructure analysis also indicated that adding rice husk and sisal fiber have a positive effect on the mortar. These results support that adding 0.1% volume admixture of 16 mm length sisal fiber with 35% rice husk into mortar is helpful for engineering application.
The rapid slumping of resources is attracting increasing social attention to environmental protection and sustainable development. In China, the energy consumption from building accounts for a large proportion [
There is a long history of the research studies on adding rice husk to mortar. Sun et al. [
Sisal fiber also has a significant effect on improving the mortar performance. Huang et al. [
According to previous studies, adding rice husk or sisal fiber to mortar can greatly improve the performance of the mortar. However, the low strength and easy cracking feature of the rice husk mortar limited its application. In order to solve this problem, rice husk and sisal fiber were added together into mortar in this study to search for the optimal mixture ratio that could meet the performance requirements of practical projects. The effects of sisal fiber and rice husk on the properties of mortar were discussed, and the mechanism of the hybrid fibers was studied.
The test raw materials are ordinary Portland cement P·O42.5; the maximum particle size of the engineering sand is 2.36 mm with modulus coefficient of 2.1; the rice husk is from Hubei Province, and its physical properties are shown in Table
Physical properties of the rice husk.
Category | Length (mm) | Width (mm) | Density (g/cm3) | Bulk density (g/cm3) | Thermal conductivity (W/m·K) |
---|---|---|---|---|---|
Rice husk | 5∼8 | 2.5∼5 | 720 | 83∼160 | 0.084∼0.209 |
Physical properties of the sisal fiber.
Fiber category | Density (g/cm3) | Elongation (%) | Tensile strength (MPa) | Tensile elasticity modulus (GPa) |
---|---|---|---|---|
Sisal fiber | 1.45 | 2.0∼2.5 | 511∼635 | 9.4∼22.0 |
The mixture ratios of test mortar are shown in Table
Mixture ratio of test mortar.
Sample | Sisal fiber content (%) | Sisal fiber length (mm) | Sisal fiber quality (kg) | Rice husk content (%) | Rice husk quality (kg) | Sand (kg) | Cement (kg) | Water (kg) |
---|---|---|---|---|---|---|---|---|
A0 | 0 | — | 0 | 0 | 0 | 1500 | 400 | 300 |
A1 | 0.10 | 8 | 1.45 | 35 | 35 | 975 | 400 | 300 |
A2 | 0.10 | 12 | 1.45 | 40 | 40 | 900 | 400 | 300 |
A3 | 0.10 | 16 | 1.45 | 45 | 45 | 825 | 400 | 300 |
A4 | 0.15 | 8 | 2.18 | 40 | 40 | 900 | 400 | 300 |
A5 | 0.15 | 12 | 2.18 | 45 | 45 | 825 | 400 | 300 |
A6 | 0.15 | 16 | 2.18 | 35 | 35 | 975 | 400 | 300 |
A7 | 0.20 | 8 | 2.90 | 45 | 45 | 825 | 400 | 300 |
A8 | 0.20 | 12 | 2.90 | 35 | 35 | 975 | 400 | 300 |
A9 | 0.20 | 16 | 2.90 | 40 | 40 | 900 | 400 | 300 |
Sisal fiber is easy to agglomerate when mixed into cement-based materials, which will result in uneven fiber distribution. In order to ensure the uniformity, continuity, and good workability of the material, after many attempts, the technological mixing process of sisal fiber rice husk mortar is formulated. Pour the sand and rice husk into the blender and keep stirring. Sisal fiber is added during stirring. Cement and water are added together and stirred in reverse direction for 2 minute. After mixing, the material is divided into three layers to cover the specimen mold, and a vibrator with the diameter of about 2 cm is used to slightly insert the vibrator layer by layer for 20 second. After smoothing, gently vibrate with both hands for 20 times and then rest. This process can effectively avoid the phenomenon of uneven mixing and floating of rice husk.
The size of sisal fiber husk mortar compression specimen is 70.7 mm × 70.7 mm × 70.7 mm. The specimens were loaded after 28 days of curing. The test was carried out in accordance with the requirements of JGJ-T70-2009 [
Compression test of sisal fiber husk mortar.
The sisal fiber husk mortar flexural test specimen is a prism of 100 mm × 100 mm × 400 mm. The test was carried out in accordance with the requirements of GB/T50081-2002) [
Flexural test of sisal fiber husk.
The test molds are shown in Figure
Test mold of early plastic shrinkage crack.
The test was carried out in accordance with the requirements of JGJ-T70-2009 [
Antipenetrability performance test of sisal fiber rice husk mortar.
The results of the mechanical test are shown in Table
Experimental results of test blocks.
Sample | Average compressive load (kN) | Compressive strength (MPa) | Average flexural load (kN) | Flexural strength (MPa) |
---|---|---|---|---|
A1 | 63.48 | 17.14 | 13.04 | 3.26 |
A2 | 52.12 | 14.07 | 10.87 | 2.72 |
A3 | 51.29 | 13.85 | 10.50 | 2.63 |
A4 | 54.67 | 14.77 | 8.60 | 2.15 |
A5 | 57.41 | 15.51 | 10.20 | 2.55 |
A6 | 52.21 | 14.09 | 10.88 | 2.72 |
A7 | 56.31 | 15.21 | 8.58 | 2.15 |
A8 | 53.38 | 14.41 | 9.11 | 2.28 |
A9 | 46.23 | 12.48 | 9.68 | 2.42 |
Compressive strength | Flexural strength | |||||
---|---|---|---|---|---|---|
Sisal fiber content | Sisal fiber length | Rice husk content | Sisal fiber content | Sisal fiber length | Rice husk content | |
K1 | 8.78 | 7.71 | 8.39 | 8.78 | 7.71 | 8.39 |
K2 | 7.65 | 7.69 | 7.73 | 7.65 | 7.69 | 7.73 |
K3 | 7.48 | 7.93 | 7.2 | 7.48 | 7.93 | 7.2 |
k1 | 2.93 | 2.57 | 2.80 | 2.93 | 2.57 | 2.80 |
k2 | 2.55 | 2.56 | 2.58 | 2.55 | 2.56 | 2.58 |
k3 | 2.49 | 2.64 | 2.4 | 2.49 | 2.64 | 2.4 |
R | 0.43 | 0.078 | 0.4 | 0.43 | 0.078 | 0.4 |
It can be seen from Table
As shown in Figure
Figure
Stress failure of cement can be considered to be a process in which the stress expansion of tiny cracks inside the specimen leads to gradual connection of internal cracks until a complete failure [
In 1962, Lyubimove et al. [
Songshan Jie’s model.
Measured from the SEM images, as shown in Figures
SEM of rice husk mortar surface. (a) Rice husk in mortar magnified 100 times. (b) Rice husk in mortar magnified 1000 times. (c) Rice husk in mortar magnified 50 times. (d) Rice husk in mortar magnified 500 times.
The hardness gradient of the ITZ can be explained from its formation process. The infiltration of moisture will be blocked at the surface of the aggregate to form a thicker water film. When the water enters the pores, most of the ions with strong diffusion ability during hydration will be combined with the water in the pores to form crystals. Based on these assumptions, an interface area model around the holes in rice husk is presented, as shown in Figure
Interface area model with the holes in rice husk.
According to current research, the strengthening effect of the fiber in the cement matrix mainly includes the following aspects [
There is also a fiber spacing theory represented by Romualdi and Batson [
Interface area of the sisal fiber and the cement mortar.
Test results of early plastic shrinkage crack performance and impermeability are shown in Table
Experimental results of anticrack performance and impermeability.
Sample | Crack area/mm2 | Fracture reduction factor (%) | Maximum seepage pressure (MPa) |
---|---|---|---|
A0 | 3016.33 | 0.19 | |
A1 | 0 | 100 | 0.36 |
A2 | 38.68 | 98.72 | 0.33 |
A3 | 53.36 | 98.23 | 0.35 |
A4 | 116.81 | 96.13 | 0.23 |
A5 | 122.36 | 95.94 | 0.22 |
A6 | 66.61 | 97.79 | 0.24 |
A7 | 179.85 | 94.04 | 0.17 |
A8 | 132.14 | 95.62 | 0.21 |
A9 | 158.34 | 94.75 | 0.19 |
The
The
Test A1.
Test A3.
Test A4.
As shown in Table
According to the
The test results showed in Table
Cavities in the mortar created by too many fibers.
In this paper, the effects of sisal fiber and rice husk on mechanical properties, early crack shrinkage, and impermeability of cement mortar were studied. The following conclusions were obtained from the experiments: The order of influence on compressive strength, from large to small, is the sisal fiber length, sisal fiber content, and rice husk content. The optimal mixture ratio of compressive strength is 0.10% volume admixture of 8 mm sisal fiber with 35% volume admixture of rice husk. The highest compressive strength can reach 17.1 MPa. The order of influence on flexural strength, from large to small, is the sisal fiber content, rice husk content, and sisal fiber length. The optimal mixture ratio is 0.10% volume admixture of 16 mm sisal fiber with 35% rice husk. The admixture amount of sisal fiber has a dominant contribution to the crack area and antipermeability property, while the length of sisal fiber contributes the least. The optimal mixture ratio of crack resistance and antipermeability property is 0.10% 16 mm sisal fiber volume admixture and 35% rice husk volume replacement rate. The area of early cracks is reduced by 100%, and the maximum seepage pressure is 0.36 MPa. Microstructure analysis showed that rice husk and sisal fiber release water in hydration process of cement which could improve the mechanical properties of the mortar. The water retention of rice husk and sisal fiber with high elastic modulus can support the interior structure of the mortar and improve its ductility.
All the data used to support the findings of this study are included within the article.
The authors declare that they have no conflicts of interest.
This study was financially supported by the National Natural Science Foundation of China (51474168).