Next Article in Journal
Are European Trees Prepared for Being Limited by Other Nutrients than Nitrogen?
Previous Article in Journal
An Evidence-Based Assessment of Biophilic Interior Design in a Traditional Context: The Case of the Kingdom of Saudi Arabia
Previous Article in Special Issue
Experimental Study on Static and Dynamic Characteristics of Sand–Clay Mixtures with Different Mass Ratios
 
 
Search for Articles:
Title / Keyword
Author / Affiliation / Email
Journal
Article Type
 
 
Advanced Search
 
Section
Special Issue
Volume
Issue
Number
Page
 
Journals
Sustainability
Volume 16
Issue 18
10.3390/su16187978
sustainability-logo
Submit to this Journal Review for this Journal Propose a Special Issue
► Article Menu

Article Menu

share Share announcement Help format_quote Cite question_answer Discuss in SciProfiles thumb_up
...
Endorse textsms
...
Comment
first_page
settings
Order Article Reprints
Font Type:
Arial Georgia Verdana
Font Size:
Aa Aa Aa
Line Spacing:
Column Width:
Background:
Article

Experimental Study on the Mechanical Properties of Rammed Red Clay Reinforced with Straw Fibers

by
Jianjun Guo
1,
Zhenwei Wu
2,*,
Wei Zhang
2 and
Heng Cao
2
1
National Engineering Research Center for Inland Waterway Regulation, Chongqing Jiaotong University, Chongqing 400074, China
2
College of River and Ocean Engineering, Chongqing Jiaotong University, Chongqing 400074, China
*
Author to whom correspondence should be addressed.
Sustainability 2024, 16(18), 7978; https://doi.org/10.3390/su16187978
Submission received: 8 August 2024 / Revised: 5 September 2024 / Accepted: 11 September 2024 / Published: 12 September 2024
(This article belongs to the Special Issue Advances in Sustainable Geotechnical Engineering and Civil Engineering)
Browse Figures
Versions Notes

Abstract

:
Earthen materials have been used as economic building materials since ancient times and continue to be used today, particularly in our modern society that pursues sustainability. As a form of agricultural waste, straw stalks are reused in civil engineering to avoid being burnt, which not only saves costs but also avoids environmental impacts. In the following paper, we present an experimental study on the mechanical properties of rammed red clay reinforced by straw fibers. Straw stalks were cut into different lengths and mixed evenly with red clay in different proportions before being compacted. The compressive strength, flexural strength, and shear strength of the stabilized rammed straw were analyzed. The results show that straw stalks, as a single reinforcing material, can significantly improve the mechanical properties of rammed red clay. Straw stalks had varying effects on improving the mechanical indexes of rammed red clay. When the length of the straw stalks was 15 mm and the straw stalk content was 0 Sust.3%, the straw stalks had the best effect on improving the mechanical properties of rammed red clay.

1. Introduction

Earthen materials are the earliest and longest-used building materials utilized by human beings [1]. Up to the present day, various new building materials have been continuously developed and promoted; however, natural earthen materials are still widely used [2,3], including, but not limited to, the fields of housing construction [4], military engineering [5], hydraulic engineering [6], etc. Earthen materials are mainly used as building materials in two ways. The first way involves the direct utilization of the physical and mechanical properties of earthen materials, such as earthen walls, earthen dams, earthen ridges (slopes), etc. The other way involves products derived from earthen materials, such as red bricks, ceramics, glass, and tiles. With the increasing awareness of environmental protection, humans have realized that products derived from soil, such as red bricks and tiles, easily form construction waste, which cannot be completely degraded over a short duration of time. The direct use of soil materials for building houses and structures has gradually become a sustainable choice; for example, houses made of soil for human habitation are still one of the main choices for modern buildings. Another example is a reservoir earthen dam built to regulate water resources. Due to the strong compressibility, low compressive strength, low shear strength, and low tensile strength of natural soil, it is common for its utilization to cause obvious sedimentation, cracking, and deformation of buildings; thus, there are potential safety hazards to its use in building construction. Therefore, people have continued to explore soil reinforcement technology, and, as a result, reinforced soil technology has come into being. Reinforced soil technology is a technology of high-performance composite soil composed of the appropriate amount of materials with high tensile strength in soil. Its use can quickly and effectively improve the properties and stability of soil and improve the safety rating of building structures. Therefore, it has been widely recognized in geotechnical engineering at home and abroad. Reinforcing materials that are frequently used to improve the mechanical properties of soil include cement [7], lime [8], polymer fibers [9], plant fibers [10,11,12], crushed concrete [13], granulated blast furnace slag [14], and even brown sugar [15].
Reinforced rammed earth has been used for the construction of infrastructure, such as buildings, shelters, defense structures, and hydraulic structures, with a history extending thousands of years. Examples include the Laohuling Dam in the Liangzhu Water Conservancy Engineering Site (2300 BC) [16,17], as shown in Figure 1, and Fujian Tulou, China (1100 AD) [18], as shown in Figure 2.
Human exploration and research work on reinforced rammed earth has never stopped. From the continuous expansion of new reinforced materials to the continuous expansion of engineering application fields, this technology is used creatively to solve various engineering problems. Successful practices often attract widespread attention. An increasing number of researchers use indoor and outdoor geotechnical tests, computer numerical simulation, observation with modern precision instruments, and other methods to conduct in-depth research on the mechanical properties, constitutive models, reinforcing effects, and mechanism of action of reinforced rammed earth.
Conversely, attempts have been made to use more materials as reinforcements in rammed earth in order to achieve better performance, lower costs, and more environmentally friendly and clean materials. In order to reduce greenhouse gas emissions associated with the building industry, granular industrial by-products and waste materials can be used in place of soil, such as crushed limestone, fly ash, ground granulated blast furnace slag, and silica fume, which can be used to improve the flexure and bond strength and other mechanical properties of rammed earth [19].
In a study, cement, waste phosphogypsum, fly ash, and quicklime were simultaneously used for rammed loess. The softening coefficient and flexural and compressive strength of the stabilized loess samples were studied, with the optimal mix proportions of the four materials being obtained [20]. The results of experimental studies show that 0.7% cement and 6.5% fly ash are the suitable stabilizer choice for rammed earth, with these materials being collected from an excavation site in Jamalzadeh district, Tehran, Iran [21]. Moderate amounts of recycled tire rubber and expanded shale aggregate can improve the thermal resistance and compressive strength of rammed-earth walls [22]. Using waste tire textile fibers in a cement-stabilized rammed-earth structure can improve its stabilization with cement and reduce the environmental impact [23,24]. Coir fibers can improve the post-peak behavior of cement-stabilized rammed earth [25]. Bamboo can enhance the load capacity of cement-stabilized rammed-earth columns [26]. The use of a straw fiber and earth mortar mix can increase the ductility of rammed-earth constructions that consist of sand, silt, clay, and gravel [3]. Sheep wool fibers can improve the mechanical performance of rammed soil, including clayey soil and volcanic sand [27]. Natural jute fabric applied with a stabilized cementitious matrix provides exceptional adhesion and adequate stiffness to rammed-earth structures [28]. Polypropylene fibers can improve the strength parameters of treated soils and improve swell-consolidation parameters [29]. Adding bagasse ash (GBA) and geo-polymerized quarry dust (GQD) together with shredded facemasks (FMs) into fat clay can improve its unconfined compressive strength and yield stress [30]. The authors of the above studies all focused on the reinforcement effect of multiple materials mixed with rammed earth. In most of the above studies, cement was the main reinforcing material used.
Of note, the research scope of rammed soil is constantly expanding. In addition to the main mechanical properties of rammed soil, such as its compressive strength [31,32], shear strength [33], and bending strength [34], some researchers have also focused on the capillary absorption characteristics [35], thermal performance [36], conductivity [37], seismic characteristics [38], durability [39], etc., of rammed soil. The types of evaluation methods used to assess the performance of reinforced rammed soil are becoming increasingly diverse, with non-destructive testing methods such as X-ray (XRD) infrared analysis [40] and sonic testing [41,42] being used to study the performance of reinforced rammed soil [43].
In summary, for natural materials from plants, such as straw fibers and jute fabric, or natural materials from animals, for example, sheep wool fibers, the reinforcement effect of each material used as the unique reinforcing material for rammed soil needs to be more widely studied. This area represents the development trend of modern architecture, which pursues closeness to nature, the use of fewer types of materials, and simple construction processes. Jute yarns can be woven into a mesh and attached to the surface of rammed-earth buildings to improve the overall performance of rammed-earth structures [31].
As a type of soil-reinforcing material, straw has a long history of application in China. Straw is usually added to plastic clay and then applied to the woven walls of fences, forming a dense and impermeable wall to resist wind and cold conditions, as shown in Figure 3. Of note, straw, as a natural material, is easy to obtain and degrades easily, making it extremely environmentally friendly. As a reinforcement material for rammed earth, it is more environmentally friendly compared with artificial fibers. With the promotion of sustainability and man’s higher pursuit of green building, straw, as a single reinforcing material, is put into plain soil and compacted to form rammed earth, representing a good choice of material. Straw fibers can improve the compressive, tensile, and shear strength of reinforced adobe masonry [2]. However, the current research focus on straw fibers as a reinforcement material of rammed earth is primarily aimed at adding straw fibers to stable soil (including lime-stabilized soil and cement-stabilized soil). At present, there is relatively little research on straw as a single reinforcement material in natural soil.
The aim of the present study was to investigate the strengthening performance of rammed red clay reinforced by only straw fibers. Unconfined compression tests, three-point bending tests, and direct shear tests were conducted to understand the response of rammed red clay, with the focus being on optimizing the compressive strength, bending strength, and shear strength of the material. The length of the reinforcing material and the proportion of the reinforcing material were used as key independent variables in the analysis of the mechanical properties of rammed red clay reinforced by straw stalks.

2. Materials and Specimen Preparation

The soil sample selected in the study presented herein was red clay widely distributed in southern China. This type of red clay has the advantages of strong plasticity, high compressive strength, and low compressibility, with it being widely used in building structure walls, foundations, and roadbeds. In order to further improve its mechanical properties, in recent years, some scholars have focused on adding polymers [44], epoxy emulsions [45], and other materials to red clay.
The specific geographical location of the soil samples taken in the experiment described herein was the Datian Community, Xiakou Town, Nan’an District, Chongqing City, China (106.6597° E, 29.5497° N). The data from the geotechnical investigation show that the geological strata of the soil sampling site were mainly composed of sandstone and mudstone of Quaternary silty clay (Qal + pl), Quaternary colluvial gravel soil (Qc), and the Ziliujing Formation of the Middle and Lower Jurassic (J1–2z). The moderately weathered rock layers were mainly composed of mudstone. The red clay was formed by the further weathering of mudstone, whose color was reddish brown (Figure 4). The natural moisture content of the raw material was ω = 15.33%, its natural density was ρ = 1.61 g/cm3, and its optimal compaction density was ρo = 2.10 g/cm3. The particle grading curve of the raw material is shown in Figure 5. This type of soil sample is highly suitable for rammed-earth buildings.
The straw used in the experiment was rice stalk, uniformly harvested in the same batch, and fully dried in the sun. In order to prevent excessive changes in the straw stalk diameter from having an influence on the test and fully assess the reinforcement effect of the straw on the rammed earth, only the lower part of the straw was used in the experiment. The diameter of this part of the straw stalks was uniform, with a size of 3 mm~5 mm. The cut straw stalks are shown in Figure 6.
In the experiment, the reinforcement effect of rammed earth was analyzed based on two factors: the length of the reinforcing material and the proportion of the reinforcing material. Based on previous research results and engineering applications, the lengths of the straw stalks selected for the experiment were 5 mm, 10 mm, 15 mm, and 20 mm, respectively. The percentages of the reinforcing materials were 0.1%, 0.2%, 0.3%, and 0.4%. The percentage of the reinforcing materials in the rammed earth was the dry straw mass/natural soil mass. During the sample preparation, the straw was cut into different lengths, based on the requirements of the different percentages of reinforcing materials in the red clay, and fully mixed with the red clay. The straw was evenly distributed in the red clay. The red clay containing the straw was loaded into a mold and rammed into three layers to achieve a density of 2.10 g/cm3.

3. Test Setup and Operation

3.1. Compressive Strength Tests

In order to explore the reinforcement effect of the length and percentage of the straw on the compressive strength of the rammed red clay specimens, the unconfined compressive strength test was used. The rammed red clay samples containing straw were molded into cylindrical specimens through a steel mold. The diameter of the specimens was Φ1 = 39.1 mm, and their height was h1 = 80 mm. According to engineering experience, we defined 17 different reinforcement conditions as GK01-GK17, as shown in Table 1. Three parallel tests were performed for each experimental condition; therefore, a total of 51 specimens were tested to determine their unconfined compressive strength. The process of the test is shown in Figure 7. Based on displacement control, the rate of the applied load was determined as vc = 0.01 mm/s until the vertical load reached its peak.
The unconfined compressive strength of each sample was calculated as follows:
σ = 4P/πd2
In the above formula, σ is the axial peak stress (MPa), P is the vertical peak load (N), and D is the diameter of the specimen (mm).

3.2. Bending Strength Tests

In order to explore the reinforcement effect of the length and percentage of the straw on the bending strength of the rammed red clay specimens, the three-point bending test was used. A total of 17 different reinforcement conditions were analyzed, and three parallel tests were carried out for each experimental condition; therefore, a total of 51 specimens were tested to determine their bending strength. The red clay samples containing straw were molded into rectangular specimens, with the length of the specimens being L = 200 mm, their width being b = 50 mm, and their height being h = 30 mm. The rate of the applied load was determined to be 0.01 mm/s until the vertical load reached its peak. The process of the test is shown in Figure 8.
The bending strength of each sample was calculated as follows:
f = 3FL0/2bh2
In the above formula, f is the bending strength of the specimen (MPa), F is the load applied when the specimen is destroyed (N), b is the width of the specimen (mm), h is the height of the specimen (mm), and L0 is the effective length of the specimen, which is the distance between the lower support points, standing at 150 mm.

3.3. Shear Strength Tests

In order to explore the reinforcement effect of the length and percentage of the straw on the shear strength of the rammed red clay specimens, the direct shear test was used. The red clay samples containing straw were molded into rectangular blocks. Once de-molded, a ring cutter was used to remove the specimens for use in the direct shear test. The diameter of the specimens was Φ2 = 61.8 mm, and their height was h2 = 20 mm. A total of 17 different reinforcement conditions were analyzed, and three parallel tests were carried out for each experimental condition by using the ZJ direct shear apparatus controlled by strain, as shown in Figure 9. The process of the test is shown in Figure 9. During the shearing process, the shear rate was vs = 0.8 mm/min, and the vertical loads were 100 kPa, 200 kPa, 300 kPa, and 400 kPa.

4. Results and Discussion

4.1. Compressive Strength Tests

The average unconfined compressive strength of the rammed red clay samples without straw fibers was 222.57 kPa. Once reinforced with straw fibers, the unconfined compressive strength of the rammed red clay samples increased to varying degrees. When the length of the straw stalks was 15 mm and the percentage of straw stalks for the reinforcing materials was 0.4%, the maximum value recorded was 277.47 kPa. Based on all of the experimental data, the relationship curves of the unconfined compressive strength with the length and percentage of the reinforcing material were plotted, as shown in Figure 10.
Based on the results presented in Figure 10, with the same percentage of straw stalks, and with the increase in the length of the straw stalks, the compressive strength of the rammed red clay samples showed a trend of first increasing and then decreasing. However, when the percentage of straw stalks was 0.1%, the compressive strength of the rammed red clay samples did not show a downward trend in the design condition of this experiment; however, the rate of increase evidently slowed down. The above results indicate that when the percentage of straw stalks added to rammed red clay is low, the peak value of the reinforcing effect of the straw fibers on the rammed red clay will be relatively delayed.
With the increase in the percentage of straw stalks added to the rammed red clay sample, the rammed red clay’s compressive strength showed an overall upward trend. When the percentage of straw stalks added to the rammed red clay sample was 0.4%, the compressive strength of the rammed earth increased the most. When the lengths of the reinforcing straw stalks were 5 mm, 10 mm, 15 mm, and 20 mm, the corresponding compressive strengths of the specimens were 260.79 kPa, 275.83 kPa, 277.47 kPa, and 276.26 kPa. The above results indicate that at these lengths, the mixing effect between straw stalks and red clay is the most efficient.
The reinforcement effect of the straw fibers on the rammed red clay was not proportional to the length of the straw stalks. According to our comprehensive analysis results, the reinforcement effect was greatest when the length of the reinforcing straw stalks was 15 mm. When the length of the straw stalks increased, although the effective bonding area of the soil particles and the straw stalks increased, the integrity of the soil was also compromised to a certain extent, the bonding area of the soil particles was reduced, and, subsequently, the compressive strength of the soil was reduced.
The reinforcement effect of straw stalks on rammed red clay not only improved the compressive strength of the rammed earth but also changed the failure mode of the rammed red clay specimens. In their study, Wei [46] scanned the surfaces of straw stalks using an electron microscope and found that the outer surfaces of the straw stalks were rough and covered with many hemispherical protrusions (Figure 11). This type of structure can increase the contact area between soil particles and the straw stalks, thereby enhancing the action of friction and bonding between the straw stalks and soil and effectively inhibiting the generation and development of cracks (Figure 12). As shown in Figure 13, due to the reinforcement provided by the straw stalks, no through-cracks occurred in the sample.

4.2. Bending Strength Tests

The relationship curves of the bending strength with the length and percentage of reinforcing material were plotted, as shown in Figure 14.
The average bending strength of the rammed red clay sample without straw fiber reinforcement was 41.75 kPa. Except for the reinforcement length of 5 mm and the straw stalk contents of 0.1% and 0.2%, the bending strength of rammed red clay reinforced by straw was lower than that of plain rammed red clay. In the other samples, the addition of straw stalks significantly improved the flexural strength of the rammed red clay. When the length of the straw stalks was 15 mm and the straw stalk content was 0.4%, the sample’s bending strength reached a maximum value of 77.55 kPa. When the length of the straw stalks was 5 mm and the straw stalk content was 0.2%, the bending strength of the sample was the lowest, decreasing to 37.45 kPa.
Based on the results presented in Figure 14, apart from the straw stalk content of 0.1%, with the increase in the length of the straw stalks, the flexural strength of the rammed red clay increased first. After reaching the peak value when the length of the straw stalk was 15 mm, the reinforcement effect of the straw stalks on the flexural strength of the rammed red clay specimens began to decrease. When the length of the reinforcing straw stalks was 5 mm, because the length of the straw stalks was too short, the bonding area between the soil particles and the straw stalks was not sufficient, and the beneficial effect of the straw on the resistance of the red clay to bending was not evident. When the length of the straw stalks was sufficiently long, there was a sufficient bonding area if cracks appeared in the specimen, the straw stalk could bear the pulling force, and the bending failure of the specimen could be delayed; thus, the flexural strength of the reinforced rammed red clay improved, as shown in Figure 15. When the proportion of reinforcing straw stalks remained stable, with the increase in the length of the straw stalks, the uniformity of the straw stalks in the rammed earth decreased, resulting in a decrease in the bending strength.
When the straw content that provided reinforcement was low, short straws were distributed in point-like and scattered shapes in the specimen, causing cracks to occur when the specimen was bent. In the early stages of crack development, the straws fell off because they were too short. Therefore, the mechanical properties of the soil and straw could not exert an effect, and this resulted in the flexural strength of the reinforced specimen being lower than that of the plain soil specimen. When the percentage of reinforcing material (straw fibers) was increased, namely, the number of straw stalks was increased, the straw stalks were distributed spatially in the rammed red clay and more evenly distributed, with the total adhesive area between the straw stalks and red clay increasing as well. If the specimen was subjected to an external force, the straw stalks exerted a reinforcing role, so the bending strength of the specimen began to increase. When the percentage of the reinforcing material increased to a certain value, the straw stalks were prone to overlap, and the voids generated between the straw stalks lacked bonding action; thus, the reinforcing effect of the bending strength became weaker.

4.3. Shear Strength Tests

Based on the experimental results reported above, the shear envelopes for the different tests are shown in Figure 16. The reinforcing effect of straw on the shear strength of rammed red clay was mainly reflected in the increasing cohesion of the rammed red clay; however, it had little effect on the internal friction angle. When the length of the straw stalks was 20 mm, the excessive percentage of the straw stalks slightly reduced the internal friction angle of the rammed red clay, with the lowest recorded value being 19.36°.
In order to further analyze the reinforcement effect of the straw stalks on the cohesion of the rammed red clay, a diagram showing these effects is shown in Figure 17.
Based on the results presented in Figure 17, when the length of the reinforcing straw stalks was 5 mm, the cohesion of the rammed red clay increased with the increase in the reinforcing straw stalk content, with a maximum value of 72.19 kPa. When the length of the reinforcing straw stalks was 10 mm, the cohesion of the rammed red clay increased with the increase in the reinforcing straw stalk content; however, this value decreased to 68.10 kPa after reaching a peak of 70.65 kPa. When the length of the reinforcing straw stalks was 15 mm, the cohesion of the rammed red clay increased with the increase in the reinforcing straw stalk content; however, the increasing trend gradually slowed down, with a maximum value of 69.41 kPa. When the length of the reinforcing straw stalks was 20 mm, the cohesion of the rammed red clay did not change considerably with the reinforcing straw stalk content. Even when the percentage of reinforcing straw stalks was 0.4%, the cohesion decreased to 67.89 kPa.
The enhancement of the shear performance of the straw stalks in the rammed red clay mainly involved inhibiting the generation and development of cracks by providing tension and limiting the deformation and displacement of local rammed red clay. When the length direction of the straw stalks crossed through the shear surface, the straw stalks in the shear surface could provide tension to resist shear, and the reinforcement effect of the straw stalks on the rammed red clay was the most evident at this point (Figure 18). The increase in the length and proportion of the reinforcing straw stalks in the rammed red clay increased the probability of the straw stalks passing through the shear surface, as shown in Figure 19, improving the shear performance of the rammed red clay. As the length and proportion of the reinforcing straw stalks in the rammed red clay increased, the overlap between the straw stalks destroyed the integrity of the rammed red clay and reduced the reinforcement effect of shear resistance, especially when the contact surface between the straw stalks occurred at the shear surface. Therefore, when the reinforcing straw stalk content was 0.4% and the length of the reinforcing straw stalks was 20 mm, the cohesion of the reinforced red clay decreased due to the excessive proportion of reinforcing straw stalks in the rammed red clay.
Based on the above test results, it can also be seen that the average compressive strength of the rammed red clay increased by 17.02%, its average bending strength increased by 49.92%, and its average cohesion increased by 84.61% when only reinforced with straw stalks. In the literature [27], when sheep wool fibers were added to reinforced rammed earth, the compressive strength of this material increased by 15%, and its bending strength increased by up to 16%. The above results are sufficient to prove that straw stalks can be used as a single reinforcing material in rammed-earth building structures. Moreover, compared with other reinforcing materials such as wool fibers and waste tire fibers, the combination of straw stalks and rammed earth is greater, and the strengthening effect is stable, with a wide range of sources and lower cost of processing.
As the proportion of reinforcing straw stalks in the rammed red clay increased, the compressive strength, flexural strength, and cohesion of the rammed red clay gradually increased; thereafter, the growth trend slowed down and even the mechanical parameters began to decline. The main reason for this phenomenon is that with the increase in the reinforcing straw stalk content, the straw stalks were prone to overlap, and the straws were connected to each other, forming a potential crack surface, reducing the bonding effect of the red clay, and resulting in the weakening of mechanical strength. If the proportion of reinforcing straw stalks in the rammed red clay remained unchanged when the length of the reinforcing straw stalks was 5 mm, the overlap between straw stalks could be avoided to some extent.
As the length of the reinforcing straw stalks in the rammed red clay increased, the rammed red clay’s compressive strength, flexural strength, and cohesion gradually increased. When the length of the reinforcing straw stalks was 15 mm, the compressive and flexural strength reached their peak. As the length of the reinforcing straw stalks in the rammed red clay continued to increase, the compressive and flexural strength began to decline, and the growth trend of cohesion slowed down. The reason for this phenomenon is that increasing the length of the reinforcement reduced the uniformity of the reinforced rammed red clay.

5. Conclusions

With the appropriate length and proportion of reinforcing material, as a single reinforcing material, straw stalks can effectively improve the mechanical properties of rammed red clay, such as its compressive strength, flexural strength, and shear strength. Compared with other types of reinforcement materials, straw fibers have advantages in terms of environmental and economic benefits.
As a single reinforcing material, straw stalks had different effects on improving the mechanical indexes of rammed red clay. The strengthening effect from high to low was cohesion > bending strength > compressive strength.
When the length of the reinforcing material was 15 mm, and the reinforcing material content was 0.3%, as a single reinforcing material, the straw stalks had the best effect on improving the mechanical properties of rammed red clay. A higher straw content is usually not used in engineering, and as the content increased, the reinforcement effect of most specimens decreased. Therefore, we did not continue to increase the content of the straw stalks.
The outer surfaces of straw stalks have a large number of hemispherical protrusions, which can increase the action of friction and bonding between straw stalks and particles and effectively inhibit the generation and development of cracks.

Author Contributions

Conceptualization, J.G.; methodology, J.G. and Z.W.; validation, J.G.; formal analysis, J.G.; investigation, Z.W. and W.Z.; resources, J.G.; data curation, Z.W.; writing—original draft preparation, J.G., Z.W. and W.Z.; writing—review and editing, H.C.; visualization, Z.W.; supervision, J.G.; project administration, J.G.; funding acquisition, J.G. All authors have read and agreed to the published version of this manuscript.

Funding

This research was funded by the Chongqing Water Conservancy Science and Technology Project (grant number: CQSLK-202329); the Natural Science Foundation of Chongqing, China (grant number: CSTB2022NSCQ-MSX0991); the Science and Technology Research Program of Chongqing Municipal Education Commission (grant number: KJQN202100742); and the Joint Training Base Construction Project for Graduate Students in Chongqing (grant number: JDLHPYJD20221004).

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

The dataset is available upon request from the authors.

Conflicts of Interest

The authors declare no conflicts of interest.

References

  1. He, L.; Khadka, B.; Sun, X.; Li, M.; Jiang, J. Compressive strength of rammed earth filled steel tubular stub columns. Case Stud. Constr. Mater. 2022, 17, e01379. [Google Scholar] [CrossRef]
  2. Abdulla, K.F.; Cunningham, L.S.M.; Gillie, M. Experimental study on the mechanical properties of straw fiber–reinforced adobe masonry. J. Mater. Civ. Eng. 2020, 32, 1–15. [Google Scholar] [CrossRef]
  3. Sabbà, M.F.; Tesoro, M.; Falcicchio, C.; Foti, D. Rammed earth with straw fibers and earth mortar: Mix design and mechanical characteristics determination. Fibers 2021, 9, 30. [Google Scholar] [CrossRef]
  4. Sameh, S.H. Promoting earth architecture as a sustainable construction technique in Egypt. J. Clean. Prod. 2014, 65, 362–373. [Google Scholar] [CrossRef]
  5. Rocha, M.; Faria, P.; Gago, A.S. Conservation of Defensive Military Structures Built with Rammed Earth. Buildings 2024, 14, 238. [Google Scholar] [CrossRef]
  6. Nan, S.; Ren, J.; Ma, Z.; Sui, J. Inversion of the seepage parameters of earth/rockfill dams considering the coupling effect of seepage and thermal transfer. Comput. Geotech. 2024, 165, 105882. [Google Scholar] [CrossRef]
  7. Narloch, P.; Woyciechowski, P. Assessing cement stabilized rammed earth durability in a humid continental climate. Buildings 2020, 10, 26. [Google Scholar] [CrossRef]
  8. Malkanthi, S.N.; Balthazaar, N.; Perera, A.A.D.A.J. Lime stabilization for compressed stabilized earth blocks with reduced clay and silt. Case Stud. Constr. Mater. 2020, 12, e00326. [Google Scholar] [CrossRef]
  9. Achenza, M.; Fenu, L. On Earth Stabilization with Natural Polymers for Earth Masonry Construction. Mater. Struct. 2014, 39, 21–27. [Google Scholar] [CrossRef]
  10. Koutous, A.; Hilali, E. Reinforcing rammed earth with plant fibers: A case study. Case Stud. Constr. Mater. 2021, 14, e00514. [Google Scholar] [CrossRef]
  11. Liu, L.; Yao, Y.; Zhang, L.; Wang, X. Study on the mechanical properties of modified rammed earth and the correlation of influencing factors. J. Clean. Prod. 2022, 374, 134042. [Google Scholar] [CrossRef]
  12. Pederson, F.; Florendo, R.; Khawaja, S.A.; Dimond, K.; Kim, H.J. Effects on the compressive strength of cement-stabilized rammed earth blocks with varied content of buffelgrass-based fibers in wet-dry conditions. Front. Built Environ. 2024, 10, 1362254. [Google Scholar] [CrossRef]
  13. Malkanthi, S.N.; Wickramasinghe, W.G.S.; Perera, A. Use of construction waste to modify soil grading for compressed stabilized earth blocks (CSEB) production. Case Stud. Constr. Mater. 2021, 15, e00717. [Google Scholar] [CrossRef]
  14. Toufigh, V.; Karamian, M.H.; Ghasemalizadeh, S. Study of stress–strain and volume change behavior of fly ash-GBFS based geopolymer rammed earth. Bull. Eng. Geol. Environ. 2021, 80, 6749–6767. [Google Scholar] [CrossRef]
  15. Luo, Y.; Zhong, H.; Bao, F.; Guo, Z.; Ni, P. Insights into natural and carbonation curing of ancient Chinese rammed earth mixed with brown sugar. Constr. Build. Mater. 2022, 317, 125969. [Google Scholar] [CrossRef]
  16. Liu, B. Liangzhu and Centennial Archaeology: The Underestimated Neolithic Age in China. Front. Hist. China 2022, 17, 247–266. [Google Scholar] [CrossRef]
  17. Liang, S.; Yuan, J.; Han, X. Study on Strength and Deformation of Grass-Wrapped Silt in Liangzhu Water Conservancy System. J. Hebei Univ. Eng. 2019, 36, 33–38. [Google Scholar]
  18. Liu, S.Y.; Wang, R.K.; Yu, J.; Cai, Y.Y.; Peng, X.Q. Physicochemical Characterization of the Render Layer of a Rammed Earth Wall in Fuyulou, China. J. Mater. Civ. Eng. 2023, 35, 04023125. [Google Scholar] [CrossRef]
  19. Meek, A.H.; Elchalakani, M.; Beckett, C.T.S.; Dong, M. Alternative stabilised rammed earth materials incorporating recycled waste and industrial by-products: A study of mechanical properties, flexure and bond strength. Constr. Build. Mater. 2021, 277, 122303. [Google Scholar] [CrossRef]
  20. Gu, K.; Chen, B. Loess stabilization using cement, waste phosphogypsum, fly ash and quicklime for self-compacting rammed earth construction. Constr. Build. Mater. 2020, 231, 117195. [Google Scholar] [CrossRef]
  21. Kosarimovahhed, M.; Toufigh, V. Sustainable usage of waste materials as stabilizer in rammed earth structures. J. Clean. Prod. 2020, 277, 123279. [Google Scholar] [CrossRef]
  22. Altaweel, M.D. The Effect of Recycled Tire Rubber and Expanded Shale Aggregate on the Thermal Resistance and the Compressive Strength of Rammed Earth Walls. Master’s Thesis, Nahrain University, Bagdad, Iraq, 2016. [Google Scholar]
  23. Nouri, H.; Safehian, M.; Hosseini, S.M.M.M. Rammed earth structures reinforced by waste tire textile fibers as an attempt to reduce the environmental impacts. Int. J. Environ. Sci. Technol. 2023, 20, 437–450. [Google Scholar] [CrossRef]
  24. Al-Subari, L.; Ekinci, A. Evaluation of Mechanical and Microstructural Properties of Waste Tire Improved Cemented Clay. J. Nat. Fibers 2024, 21, 2349750. [Google Scholar] [CrossRef]
  25. Rathod, R.S.B.; Reddy, B.V.V. Bond strength of coir fibers in cement-stabilized rammed earth matrix. J. Mater. Civ. Eng. 2021, 33, 04021293. [Google Scholar] [CrossRef]
  26. Tripura, D.D.; Singh, K.D. Mechanical behaviour of rammed earth column: A comparison between unreinforced, steel and bamboo reinforced columns. Mater. Constr. 2018, 68, e174. [Google Scholar] [CrossRef]
  27. Parlato, M.C.M.; Rivera-Gómez, C.; Porto, S.M.C. Reuse of livestock waste for the reinforcement of rammed-earth materials: Investigation on mechanical performances. J. Agric. Eng. 2023, 54, 1434. [Google Scholar] [CrossRef]
  28. Hamza, M.; Ijaz, N.; Fang, C.; Ijaz, Z. Stabilization of Problematic Expansive Clays Using Polypropylene Fiber Reinforcement. Jordan J. Civ. Eng. 2022, 16, 4. [Google Scholar]
  29. Ullah, I.; Khalid, U.; Rehman, Z.; Shah, M.M.; Khan, I.; Ijaz, N. Integrated recycling of geopolymerized quarry dust and bagasse ash with facemasks for the balanced amelioration of the fat clay: A multi-waste solution. Environ. Earth Sci. 2023, 82, 516. [Google Scholar] [CrossRef]
  30. Fagone, M.; Kloft, H.; Loccarini, F.; Ranocchiai, G. Jute fabric as a reinforcement for rammed earth structures. Compos. Part B 2019, 175, 107064. [Google Scholar] [CrossRef]
  31. Fagone, M.; Loccarini, F.; Ranocchiai, G. Strength evaluation of jute fabric for the reinforcement of rammed earth structures. Compos. Part B 2017, 113, 1–13. [Google Scholar] [CrossRef]
  32. Al-Jokhadar, A.; Soudi, Y.; Hashem, Y.A.; Masoud, A. Moisture Content and Compressive Strength of Rammed Earth Construction Mixtures in Hot Arid Regions: The Case of Amman, Jordan. J. Mater. Civ. Eng. 2024, 36, 04023584. [Google Scholar] [CrossRef]
  33. Xu, L.; Wong, K.K.; Fabbri, A.; Champiré, F.; Branque, D. Loading-unloading shear behavior of rammed earth upon varying clay content and relative humidity condition. Soils Found. 2018, 58, 1001–1015. [Google Scholar] [CrossRef]
  34. Gupta, R. Characterizing material properties of cement-stabilized rammed earth to construct sustainable insulated walls. Case Stud. Constr. Mater. 2014, 1, 60–68. [Google Scholar] [CrossRef]
  35. Indekeu, M.L.; Feng, C.; Janssen, H.; Woloszyn, M. Experimental study on the capillary absorption characteristics of rammed earth. Constr. Build. Mater. 2021, 283, 122689. [Google Scholar] [CrossRef]
  36. Chauhan, P.; Hajjar, A.E.; Prime, N.; Plé, O. Unsaturated behavior of rammed earth: Experimentation towards numerical modelling. Constr. Build. Mater. 2019, 227, 116646. [Google Scholar] [CrossRef]
  37. Abdulsamad, F.; Revil, A.; Prime, N.; Gnonnoue, P.Y.; Schmutz, M.; Plé, O. Complex conductivity of rammed earth. Eng. Geol. 2020, 273, 105697. [Google Scholar] [CrossRef]
  38. Romanazzi, A.; Oliveira, D.V.; Silva, R.A.; Candeias, P.X.; Costa, A.C.; Carvalho, A. Out-of-plane shake table test of a rammed earth sub-assembly. Bull. Earthq. Eng. 2022, 20, 8325–8356. [Google Scholar] [CrossRef]
  39. Ghasemalizadeh, S.; Toufigh, V. Durability of rammed earth materials. Int. J. Geomech. 2020, 20, 04020201. [Google Scholar] [CrossRef]
  40. Hussaini, S.M.S.; Toufigh, V. Strength and Fracture Behavior of Rammed-Earth Materials. J. Mater. Civ. Eng. 2019, 31, 04019228. [Google Scholar] [CrossRef]
  41. Zhou, T.; Zhang, H.; Li, B.; Zhang, L.; Tan, W. Evaluation of compressive strength of cement-stabilized rammed earth wall by ultrasonic-rebound combined method. J. Build. Eng. 2023, 68, 106121. [Google Scholar] [CrossRef]
  42. Rodríguez-Mariscal, J.D.; Zielińska, M.; Rucka, M.; Solís, M. Anisotropy and compaction gradient assessment on rammed earth specimens through sonic tomography approach. Eng. Struct. 2024, 309, 118058. [Google Scholar] [CrossRef]
  43. Khan, A.; Gupta, R.; Garg, M. Determining material characteristics of “Rammed Earth” using Non-Destructive Test methods for structural design. Structures 2019, 20, 399–410. [Google Scholar] [CrossRef]
  44. Kim, J.; Choi, H.; Rye, H.M.; Yoon, K.B.; Lee, D.E. A study on the red clay binder stabilized with a polymer aqueous solution. Polymers 2021, 13, 54. [Google Scholar] [CrossRef] [PubMed]
  45. Kim, J.; Choi, H.; Yoon, K.B.; Lee, D.E. Performance evaluation of red clay binder with epoxy emulsion for autonomous rammed earth construction. Polymers 2020, 12, 2050. [Google Scholar] [CrossRef]
  46. Wei, X.M. Study on Compressive Strength Test and Reinforcement Mechanism of Straw Reinforced Soil. Master’s Thesis, Chang’an University, Xi’an, China, 2020. [Google Scholar]
Sustainability 16 07978 g001
Figure 1. A section of grass-wrapped silt of the Laohuling Dam in the Liangzhu Water Conservancy Project Site.
Figure 1. A section of grass-wrapped silt of the Laohuling Dam in the Liangzhu Water Conservancy Project Site.
Sustainability 16 07978 g001
Sustainability 16 07978 g002
Figure 2. Bamboo bars and pine branches play a reinforcing role in the rammed-earth walls of the Fujian Tulou UNESCO World Heritage Site.
Figure 2. Bamboo bars and pine branches play a reinforcing role in the rammed-earth walls of the Fujian Tulou UNESCO World Heritage Site.
Sustainability 16 07978 g002
Sustainability 16 07978 g003
Figure 3. In the above photos, the fence wall was smeared with straw and mud.
Figure 3. In the above photos, the fence wall was smeared with straw and mud.
Sustainability 16 07978 g003
Sustainability 16 07978 g004
Figure 4. The soil sample used in the experiment.
Figure 4. The soil sample used in the experiment.
Sustainability 16 07978 g004
Sustainability 16 07978 g005
Figure 5. The particle grading curve of the soil sample.
Figure 5. The particle grading curve of the soil sample.
Sustainability 16 07978 g005
Sustainability 16 07978 g006
Figure 6. The cut straw stalks used in the experiment.
Figure 6. The cut straw stalks used in the experiment.
Sustainability 16 07978 g006
Sustainability 16 07978 g007
Figure 7. Equipment used for the unconfined compressive strength test for rammed red clay samples reinforced with straw. (Produced by Jiangsu Yongchang Science and Education Instrument Manufacturing Company, Jiangsu, China).
Figure 7. Equipment used for the unconfined compressive strength test for rammed red clay samples reinforced with straw. (Produced by Jiangsu Yongchang Science and Education Instrument Manufacturing Company, Jiangsu, China).
Sustainability 16 07978 g007
Sustainability 16 07978 g008
Figure 8. Equipment used for the three-point bending strength test for rammed red clay samples reinforced with straw: (a) three-point bending test loading process and (b) typical failure mechanism of the specimen.
Figure 8. Equipment used for the three-point bending strength test for rammed red clay samples reinforced with straw: (a) three-point bending test loading process and (b) typical failure mechanism of the specimen.
Sustainability 16 07978 g008
Sustainability 16 07978 g009
Figure 9. The shear strength test for rammed red clay samples reinforced with straw: (a) ZJ direct shear apparatus controlled by strain(Produced by Nanjing Soil Instrument Factory, Nanjing, China) and (b) specimens used for the direct shear test.
Figure 9. The shear strength test for rammed red clay samples reinforced with straw: (a) ZJ direct shear apparatus controlled by strain(Produced by Nanjing Soil Instrument Factory, Nanjing, China) and (b) specimens used for the direct shear test.
Sustainability 16 07978 g009
Sustainability 16 07978 g010
Figure 10. The relationship curves of unconfined compressive strength with the length and percentage of reinforcing material (straw fibers).
Figure 10. The relationship curves of unconfined compressive strength with the length and percentage of reinforcing material (straw fibers).
Sustainability 16 07978 g010
Sustainability 16 07978 g011
Figure 11. Scanning electron microscope image of the outer surface of a straw stalk (magnified 500 times).
Figure 11. Scanning electron microscope image of the outer surface of a straw stalk (magnified 500 times).
Sustainability 16 07978 g011
Sustainability 16 07978 g012
Figure 12. Action between hemispherical protrusions on the straw stalks and soil particles.
Figure 12. Action between hemispherical protrusions on the straw stalks and soil particles.
Sustainability 16 07978 g012
Sustainability 16 07978 g013
Figure 13. Typical crack patterns in the specimens from the unconfined compressive strength tests: (a) specimen without straw stalks and (b) specimen containing straw stalks.
Figure 13. Typical crack patterns in the specimens from the unconfined compressive strength tests: (a) specimen without straw stalks and (b) specimen containing straw stalks.
Sustainability 16 07978 g013
Sustainability 16 07978 g014
Figure 14. The relationship curves of bending strength with the length and percentage of reinforcing material (straw fibers).
Figure 14. The relationship curves of bending strength with the length and percentage of reinforcing material (straw fibers).
Sustainability 16 07978 g014
Sustainability 16 07978 g015
Figure 15. The reinforcement effect of bending strength with different lengths of reinforcing material: (a) the effect when the length of reinforcing material is too short and (b) the effect when the length of reinforcing material is moderate.
Figure 15. The reinforcement effect of bending strength with different lengths of reinforcing material: (a) the effect when the length of reinforcing material is too short and (b) the effect when the length of reinforcing material is moderate.
Sustainability 16 07978 g015
Sustainability 16 07978 g016
Figure 16. Curves between the cohesion and internal friction angle of rammed red clay reinforced by straw fibers: (a) results when the length of the straw stalks was 5 mm; (b) results when the length of the straw stalks was 10 mm; (c) results when the length of the straw stalks was 15 mm; and (d) results when the length of the straw stalks was 20 mm.
Figure 16. Curves between the cohesion and internal friction angle of rammed red clay reinforced by straw fibers: (a) results when the length of the straw stalks was 5 mm; (b) results when the length of the straw stalks was 10 mm; (c) results when the length of the straw stalks was 15 mm; and (d) results when the length of the straw stalks was 20 mm.
Sustainability 16 07978 g016
Sustainability 16 07978 g017
Figure 17. Contrast diagram for the reinforcing effect of straw stalks on the cohesion of rammed red clay; (a) results when the length of the straw stalks was 5 mm; (b) results when the length of the straw stalks was 10 mm; (c) results when the length of the straw stalks was 15 mm; and (d) results when the length of the straw stalks was 20 mm.
Figure 17. Contrast diagram for the reinforcing effect of straw stalks on the cohesion of rammed red clay; (a) results when the length of the straw stalks was 5 mm; (b) results when the length of the straw stalks was 10 mm; (c) results when the length of the straw stalks was 15 mm; and (d) results when the length of the straw stalks was 20 mm.
Sustainability 16 07978 g017
Sustainability 16 07978 g018
Figure 18. The straw is subjected to tension on the shear surface.
Figure 18. The straw is subjected to tension on the shear surface.
Sustainability 16 07978 g018
Sustainability 16 07978 g019
Figure 19. The length direction of the straw stalk crosses through the shear surface.
Figure 19. The length direction of the straw stalk crosses through the shear surface.
Sustainability 16 07978 g019
Table 1. Reinforcement conditions.
Table 1. Reinforcement conditions.
Percentage of Reinforcing Material
00.1%0.2%0.3%0.4%
Length of reinforcing material0GK01
5 mm GK02GK03GK04GK05
10 mm GK06GK07GK08GK09
15 mm GK10GK11GK12GK13
20 mm GK14GK15GK16GK17
Disclaimer/Publisher’s Note: The statements, opinions and data contained in all publications are solely those of the individual author(s) and contributor(s) and not of MDPI and/or the editor(s). MDPI and/or the editor(s) disclaim responsibility for any injury to people or property resulting from any ideas, methods, instructions or products referred to in the content.

Share and Cite

MDPI and ACS Style

Guo, J.; Wu, Z.; Zhang, W.; Cao, H. Experimental Study on the Mechanical Properties of Rammed Red Clay Reinforced with Straw Fibers. Sustainability 2024, 16, 7978. https://doi.org/10.3390/su16187978

AMA Style

Guo J, Wu Z, Zhang W, Cao H. Experimental Study on the Mechanical Properties of Rammed Red Clay Reinforced with Straw Fibers. Sustainability. 2024; 16(18):7978. https://doi.org/10.3390/su16187978

Chicago/Turabian Style

Guo, Jianjun, Zhenwei Wu, Wei Zhang, and Heng Cao. 2024. "Experimental Study on the Mechanical Properties of Rammed Red Clay Reinforced with Straw Fibers" Sustainability 16, no. 18: 7978. https://doi.org/10.3390/su16187978

Note that from the first issue of 2016, this journal uses article numbers instead of page numbers. See further details here.

Article Metrics

Back to TopTop