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Dosage method for unconfined strength and fatigue life of fiber-reinforced cement-treated sand

Abstract

Fiber-reinforcement has been reported as an effective and cost-attractive technique to improve the mechanical behavior of cemented soils. However, the dosage methodologies for these mixtures are still limited, especially regarding dynamic loading. The objective of this research was to analyze the dynamic response and strength behavior of fiber-reinforced cement-treated sand. In this sense, fatigue life, unconfined compressive strength, and split tensile strength tests were conducted. Results indicated that the mechanical behavior of the soil-cement mixtures was governed by fiber content, cement content and void ratio. The presence of fibers, the increase in cement content and the decrease in void ratio improved the overall mechanical behavior of all specimens. The porosity/cement content index resulted in a viable dosage method to predict both the monotonic and cyclic behavior of the mixtures. Lastly, the statistical analysis of variance corroborated the experimentally observed findings.

Keywords:
Polypropylene fibers; Portland cement; Soil-cement; Fatigue life; Rational dosage methodology

1. Introduction

Fiber-reinforcement and Portland cement stabilization have been widely utilized to improve the engineering properties of soils structures, such as embankments (Bieliatynskyi et al., 2021Bieliatynskyi, A., Krayushkina, K., Breskich, V., & Lunyakov, M. (2021). Basalt fiber geomats - modern material for reinforcing the motor road embankment slopes. Transportation Research Procedia, 54, 744-757. http://dx.doi.org/10.1016/j.trpro.2021.02.128.
http://dx.doi.org/10.1016/j.trpro.2021.0...
; Zhao et al., 2021Zhao, Y., Yang, Y., Ling, X., Gong, W., Li, G., & Su, L. (2021). Dynamic behavior of natural sand soils and fiber reinforced soils in heavy-haul railway embankment under multistage cyclic loading. Transportation Geotechnics, 28, 100507. https://doi.org/10.1016/j.trgeo.2020.100507.
https://doi.org/10.1016/j.trgeo.2020.100...
) and subgrade stabilization for footings (Nasr, 2014Nasr, A.M. (2014). Behavior of strip footing on fiber-reinforced cemented sand adjacent to sheet pile wall. Geotextiles and Geomembranes, 42(6), 599-610. http://dx.doi.org/10.1016/j.geotexmem.2014.10.004.
http://dx.doi.org/10.1016/j.geotexmem.20...
), pavements (Li et al., 2022Li, Y., Hao, P., & Li, N. (2022). Preparation and properties of a novel rejuvenator-loaded fiber for asphalt pavement. Construction & Building Materials, 324, 126687. http://dx.doi.org/10.1016/j.conbuildmat.2022.126687.
http://dx.doi.org/10.1016/j.conbuildmat....
; Ozturk & Ozyurt, 2022Ozturk, O., & Ozyurt, N. (2022). Sustainability and cost-effectiveness of steel and polypropylene fiber reinforced concrete pavement mixtures. Journal of Cleaner Production, 363(03), 132582. http://dx.doi.org/10.1016/j.jclepro.2022.132582.
http://dx.doi.org/10.1016/j.jclepro.2022...
), earth dams (Sangma & Tripura, 2020Sangma, S., & Tripura, D.D. (2020). Experimental study on shrinkage behaviour of earth walling materials with fibers and stabilizer for cob building. Construction & Building Materials, 256, 119449. http://dx.doi.org/10.1016/j.conbuildmat.2020.119449.
http://dx.doi.org/10.1016/j.conbuildmat....
), and barriers for landfills and containment pounds (Mukherjee & Kumar Mishra, 2021Mukherjee, K., & Kumar Mishra, A. (2021). Recycled waste tire fiber as a sustainable reinforcement in compacted sand-bentonite mixture for landfill application. Journal of Cleaner Production, 329, 129691. http://dx.doi.org/10.1016/j.jclepro.2021.129691.
http://dx.doi.org/10.1016/j.jclepro.2021...
). Cement addition increases strength and stiffness of the soils (Bruschi et al., 2022Bruschi, G.J., Santos, C.P., Levandoski, W.M.K., Ferrazzo, S.T., Korf, E.P., Saldanha, R.B., & Consoli, N.C. (2022). Leaching assessment of cemented bauxite tailings through wetting and drying cycles of durability test. Environmental Science and Pollution Research International, 29, 59247-59262. http://dx.doi.org/10.1007/s11356-022-20031-5.
http://dx.doi.org/10.1007/s11356-022-200...
; Bruschi, Santos, Ferrazzo, et al., 2023Bruschi, G.J., Santos, C.P., Ferrazzo, S.T., Araújo, M.T., & Consoli, N.C. (2023). Parameters controlling loss of mass and stiffness degradation of 'green' stabilized bauxite tailings. Proceedings of the Institution of Civil Engineers - Geotechnical Engineering, 176(3), 306-314. https://doi.org/10.1680/jgeen.21.00119.
https://doi.org/10.1680/jgeen.21.00119...
; Queiróz et al., 2022Queiróz, L.C., Batista, L.L.S., Souza, L.M.P., Lima, M.D., Danieli, S., Bruschi, G.J., & Bergmann, C.P. (2022). Alkali-activated system of carbide lime and rice husk for granular soil stabilization. Proceedings of the Institution of Civil Engineers - Ground Improvement, 1-37. Ahead of print. https://doi.org/10.1680/jgrim.21.00048.
https://doi.org/10.1680/jgrim.21.00048...
; Quiñónez Samaniego et al., 2021Quiñónez Samaniego, R.A., Scheuermann Filho, H.C., de Araújo, M.T., Bruschi, G.J., Festugato, L., & Consoli, N.C. (2021). Key parameters controlling strength and resilient modulus of a stabilised dispersive soil. Road Materials and Pavement Design, 24(1), 279-294. http://dx.doi.org/10.1080/14680629.2021.2013937.
http://dx.doi.org/10.1080/14680629.2021....
); however, it also increases brittleness, leading the enhanced soil to fail in a brittle way (Consoli et al., 2007Consoli, N.C., Foppa, D., Festugato, L., & Heineck, K.S. (2007). Key parameters for strength control of artificially cemented soils. Journal of Geotechnical and Geoenvironmental Engineering, 133(2), 197-205. http://dx.doi.org/10.1061/(ASCE)1090-0241(2007)133:2(197).
http://dx.doi.org/10.1061/(ASCE)1090-024...
, 2021a Consoli, N.C., Festugato, L., Miguel, G.D., & Scheuermann Filho, H.C. (2021a). Swelling prediction for green stabilized fiber-reinforced sulfate-rich dispersive soils. Geosynthetics International, 28(4), 391-401. http://dx.doi.org/10.1680/jgein.20.00050.
http://dx.doi.org/10.1680/jgein.20.00050...
). On the other hand, fiber addition increases the ductility and durability of the reinforced soil without compromising the strength of the composite (Festugato et al., 2017Festugato, L., Menger, E., Benezra, F., Kipper, E.A., & Consoli, N.C. (2017). Fibre-reinforced cemented soils compressive and tensile strength assessment as a function of filament length. Geotextiles and Geomembranes, 45(1), 77-82. http://dx.doi.org/10.1016/j.geotexmem.2016.09.001.
http://dx.doi.org/10.1016/j.geotexmem.20...
). The addition of fibers to cemented soils has been reported as an effective and cost attractive technique to increase the mechanical characteristics such as strength, ductility, and post-rupture bearing capacity (Chen et al., 2015Chen, M., Shen, S.-L., Arulrajah, A., Wu, H.-N., Hou, D.-W., & Xu, Y.-S. (2015). Laboratory evaluation on the effectiveness of polypropylene fibers on the strength of fiber-reinforced and cement-stabilized Shanghai soft clay. Geotextiles and Geomembranes, 43(6), 515-523. http://dx.doi.org/10.1016/j.geotexmem.2015.05.004.
http://dx.doi.org/10.1016/j.geotexmem.20...
; Consoli et al., 2009a,Consoli, N.C., Festugato, L., & Heineck, K.S. (2009a). Strain-hardening behaviour of fibre-reinforced sand in view of filament geometry. Geosynthetics International, 16(2), 109-115. http://dx.doi.org/10.1680/gein.2009.16.2.109.
http://dx.doi.org/10.1680/gein.2009.16.2...
2009b, 2011a ). Even though fiber-reinforcement has been proved effective, dosage methodologies for these mixtures are still limited.

Consoli et al. (2010)Consoli, N.C., Arcari Bassani, M.A., & Festugato, L. (2010). Effect of fiber-reinforcement on the strength of cemented soils. Geotextiles and Geomembranes, 28(4), 344-351. http://dx.doi.org/10.1016/j.geotexmem.2010.01.005.
http://dx.doi.org/10.1016/j.geotexmem.20...
created the first rational dosage methodology for fiber-reinforced cemented soil, considering the porosity/cement content ratio (η/Civ), as an appropriate parameter to evaluate the unconfined compressive strength (qu). Later, Consoli et al. (2013)Consoli, N.C., Moraes, R.R., & Festugato, L. (2013). Parameters controlling tensile and compressive strength of fiber-reinforced cemented soil. Journal of Materials in Civil Engineering, 25(10), 1568-1573. http://dx.doi.org/10.1061/(ASCE)MT.1943-5533.0000555.
http://dx.doi.org/10.1061/(ASCE)MT.1943-...
quantified the influence of the amount of cement, the porosity and the porosity/cement ratio in the assessment on tensile strength (qt) and compressive strength (qu) of fiber-reinforced artificially cemented sand, as well as in the changes of qt/qu relationships and particular increases in qt and qu due to fiber insertion. Festugato et al. (2017)Festugato, L., Menger, E., Benezra, F., Kipper, E.A., & Consoli, N.C. (2017). Fibre-reinforced cemented soils compressive and tensile strength assessment as a function of filament length. Geotextiles and Geomembranes, 45(1), 77-82. http://dx.doi.org/10.1016/j.geotexmem.2016.09.001.
http://dx.doi.org/10.1016/j.geotexmem.20...
studied a dosage methodology based on the tensile and compressive strength of fiber-reinforced cemented soils, considering the fiber length. Authors indicated that the length of the filaments and the porosity/cement ratio are key parameters in the evaluation of the tensile strength and the compressive strength of the mixture studied. For each fiber length, there is a linear proportionality between the tensile and compressive strength, being independent of the porosity/cement ratio. As a consequence, rational dosing methodologies can be centered on tensile or compression tests on reinforced or unreinforced samples.

Despite these extensive findings, most of the experimental work regarding the mechanical behavior of fiber-reinforced cemented soils and their dosage methodologies entails exclusively the analysis of these composites under monotonic/static loading. The porosity/cement content ratio (η/Civ) dosage framework has recently started to be investigated for mixtures under dynamic loading. Festugato et al. (2021)Festugato, L., Venson, G.I., & Consoli, N.C. (2021). Parameters controlling cyclic behaviour of cement-treated sand. Transportation Geotechnics, 27, 100488. http://dx.doi.org/10.1016/j.trgeo.2020.100488.
http://dx.doi.org/10.1016/j.trgeo.2020.1...
studied mixtures of unreinforced cemented sand and showed such ratio was able to assess resilient modulus and fatigue life. Piuzzi et al. (2021)Piuzzi, G.P., Scheuermann Filho, H.C., Villena Del Carpio, J.A., & Consoli, N.C. (2021). The effects of porosity, asphalt content and fiberglass incorporation on the tensile strength and resilient modulus of asphalt concrete blends. Geotextiles and Geomembranes, 49(3), 864-870. http://dx.doi.org/10.1016/j.geotexmem.2021.01.002.
http://dx.doi.org/10.1016/j.geotexmem.20...
observed the porosity/cement ratio could be used for the assessment of asphalt concrete mixtures mechanical behavior under cyclic loading. However, the use of η/Civ has not yet been investigated for the study of fiber reinforced cement mixtures behavior under not monotonic loading. Dynamic loading is especially important on pavement design, reinforcement of areas susceptible to earthquakes, foundations of coastal structures, and even wind turbines. Pavements design, for instance, usually considers the fatigue life of the subgrade constituent materials. Fatigue is the process of localized progressive permanent structural change which occurs in a point of the material subjected to stresses of variable amplitude, below the ultimate strength of the material, that causes cracks that lead to failure after a certain number of cycles (ASTM, 2013ASTM E1823-13. (2013). Standard Terminology Relating to Fatigue and Fracture Testing. ASTM International, West Conshohocken, PA. https://doi.org/10.1520/E1823-21.
https://doi.org/10.1520/E1823-21...
).

In this sense, the objective of this research was to analyze dynamic response and strength behavior of fiber-reinforced cement-treated sand. To that extent, fatigue life, unconfined compressive strength, and split tensile strength tests were conducted on fiber-reinforced and non-reinforced cemented mixtures. In addition, all results were correlated with the porosity/cement content index to create a rational dosage methodology for the stabilized mixtures.

2. Materials and methods

2.1 Materials

The soil utilized in this research was a clean sand, known as Osorio sand (OS). The material was collected nearby Porto Alegre, in southern Brazil. OS was classified as a poorly graded sand (SP) in accordance with the Unified Soil Classification System (USCS) (ASTM, 2020ASTM D2487. (2020). Standard Practice for Classification of Soils for Engineering Purposes (Unified Soil Classification System). ASTM International, West Conshohocken, PA. https://doi.org/10.1520/D2487-17E01.
https://doi.org/10.1520/D2487-17E01...
) with a specific weight of grains of 2.65 g/cm3 [D854 (ASTM, 2014ASTM D854. (2014). Standard Test Methods for Specific Gravity of Soil Solids by Water Pycnometer. ASTM International, West Conshohocken, PA. https://doi.org/10.1520/D0854-14.
https://doi.org/10.1520/D0854-14...
)]. This sand is composed of approximately 99.5% quartz (Consoli et al., 2009aConsoli, N.C., Festugato, L., & Heineck, K.S. (2009a). Strain-hardening behaviour of fibre-reinforced sand in view of filament geometry. Geosynthetics International, 16(2), 109-115. http://dx.doi.org/10.1680/gein.2009.16.2.109.
http://dx.doi.org/10.1680/gein.2009.16.2...
). For the cementing agent, high initial strength Portland cement (type III) was utilized, with a specific weight of grains of 3.15 g/cm3. This cement was selected considering its high capacity of generating considerable strength over short periods of time. Regarding the fiber-reinforcement, monofilament polypropylene fibers were applied. These fibers presented average dimensions of 50 mm length and 0.1 mm diameter, with a specific weight of grains of 0.91 g/cm3, elastic modulus of 3 GPa, tensile strength of 120 MPa, and strain failure of 80%. The materials physical properties are summarized in Table 1, while Figure 1 shows the grain size distribution.

Table 1
Materials physical properties.
Figure 1
Grain size distribution.

2.2 Molding and curing procedures

For unconfined compressive strength and split tensile strength tests, triplicates of specimens of 10 cm diameter and 20 cm in height were utilized. As for fatigue life tests, duplicates of cylindrical specimens of 10 cm in diameter and 5 cm in height were applied. The cement addition was 1, 2, 3, 5, and 7%, in accordance with the indications of the Portland Cement Association (PCA, 1992Portland Cement Association - PCA. (1992). Soil-cement construction handbook. PCA.) and previous studies (Consoli et al., 2020Consoli, N.C., Carretta, M.S., Leon, H.B., Schneider, M.E.B., Reginato, N.C., & Carraro, J.A.H. (2020). Behaviour of cement-stabilised silty sands subjected to harsh environmental conditions. Proceedings of the Institution of Civil Engineers -. Geotechnical Engineering, 173(1), 40-48. http://dx.doi.org/10.1680/jgeen.18.00243.
http://dx.doi.org/10.1680/jgeen.18.00243...
; Consoli & Tomasi, 2018Consoli, N.C., & Tomasi, L.F. (2018). The impact of dry unit weight and cement content on the durability of sand-cement blends. Proceedings of the Institution of Civil Engineers - Ground Improvement, 171(2), 96-102. http://dx.doi.org/10.1680/jgrim.17.00034.
http://dx.doi.org/10.1680/jgrim.17.00034...
). The fiber addition was 0.5% for all samples. Previous studies shown the increase of fiber content improves materials mechanical behavior up to a limit, from which mixing and compaction processes become not effective and reinforcement benefits are negatively affected. For the studied polypropylene fibers, considering mixture preparation and compaction, an optimum value of 0.5% observed (e.g. Festugato et al., 2018Festugato, L., Peccin da Silva, A., Diambra, A., Consoli, N.C., & Ibraim, E. (2018). Modelling tensile/compressive strength ratio of fibre reinforced cemented soils. Geotextiles and Geomembranes, 46(2), 155-165. http://dx.doi.org/10.1016/j.geotexmem.2017.11.003.
http://dx.doi.org/10.1016/j.geotexmem.20...
, 2021Festugato, L., Venson, G.I., & Consoli, N.C. (2021). Parameters controlling cyclic behaviour of cement-treated sand. Transportation Geotechnics, 27, 100488. http://dx.doi.org/10.1016/j.trgeo.2020.100488.
http://dx.doi.org/10.1016/j.trgeo.2020.1...
). To explore a wide range of porosities and its effect on the mechanical properties, three void ratios were also selected (0.64, 0.70, and 0.78) based on Proctor compaction tests under standard energy (ASTM, 2021ASTM D698-12. (2021). Standard Test Methods for Laboratory Compaction Characteristics of Soil Using Standard Effort (12 400 Ft-lbf/ft3 (600 KN-m/m3)). ASTM International, West Conshohocken, PA. https://doi.org/10.1520/D0698-12E02.
https://doi.org/10.1520/D0698-12E02...
). All specimens were molded with the 9% optimum moisture content from the compaction tests. The fiber reinforced compacted cemented soil specimens were prepared by hand-mixing, in this order, dry soil, cement, water and polypropylene fibers. It was found important to add water prior the addition of fibers to prevent their floating. The quantity of fibers for each mixture was calculated by the mass of dry soil plus cement. Visual and microscope examination of exhumed specimens showed the mixtures to be satisfactorily uniform. The molding procedures followed the undercompaction method proposed by Ladd (1978)Ladd, R.S. (1978). Preparing test specimens using undercompaction. Geotechnical Testing Journal, 1(1), 16-23. http://dx.doi.org/10.1520/GTJ10364J.
http://dx.doi.org/10.1520/GTJ10364J...
. After confection specimens were measured and stored at 23 ± 2°C and 95 ± 2% controlled moisture for 7 days curing. The acceptance criteria were as follows: degree of compaction between 99% and 101%; water content within 0.5% of the target value; diameter within 0.5 mm of the target value; and height within 1 mm of the target value. Figure 2 depicts the aspect of a prepared specimen after fatigue life testing.

Figure 2
Typical aspect of tested specimen.

2.3 Unconfined compressive strength (qu)

Unconfined compression strength (qu) tests were conducted in accordance with the procedures of ASTM D2166 (ASTM, 2016ASTM D2166/D2166M. (2016). Standard Test Method for Unconfined Compressive Strength of Cohesive Soil. ASTM International, West Conshohocken, PA. https://doi.org/10.1520/D2166.
https://doi.org/10.1520/D2166...
), with an automatic loading machine (50 kN load capacity and 1.14mm/min displacement rate).

2.4 Split tensile strength (qt)

Split tensile strength tests (qt) tests were conducted in accordance with the procedures of ASTM D6931 (ASTM, 2017ASTM D6931. (2017). Standard Test Method for Indirect Tensile (IDT) Strength of Bituminous Mixtures. ASTM International, West Conshohocken, PA. https://doi.org/10.1520/D6931-12.2.
https://doi.org/10.1520/D6931-12.2...
); performed in an automatic loading machine with a maximum load capacity of 50 kN, with a ring of 10 kN load capacity and resolution of 0.005 kN.

2.5 Fatigue life (Nf)

Fatigue life tests were conducted in accordance with the procedures of BS EN 12697-24 (BSI, 2016BSI EN 12697-25. (2016). Bituminous mixtures — test methods. British Standards Institution, London, United Kingdom. https://doi.org/10.3403/30288544U.
https://doi.org/10.3403/30288544U...
). The cyclic load (haversine-shaped pulse of 2 Hz) was applied with a pneumatic load machine. The magnitude of the applied load was 90% of the specimens’ tensile strength. A 10 kN loading cell with a resolution of 0.0001 kN was employed to measure the applied load. In addition, two linear variable differential transformers (LVDT) located on the opposite side of the specimens, were responsible to measure radial displacements with a resolution of 0.001 mm.

2.6 Porosity/cement content index (η/Civ)

Resilient modulus, split tensile strength, and durability results were also expressed in function of the porosity/cement index proposed by Consoli et al. (2007)Consoli, N.C., Foppa, D., Festugato, L., & Heineck, K.S. (2007). Key parameters for strength control of artificially cemented soils. Journal of Geotechnical and Geoenvironmental Engineering, 133(2), 197-205. http://dx.doi.org/10.1061/(ASCE)1090-0241(2007)133:2(197).
http://dx.doi.org/10.1061/(ASCE)1090-024...
and defined by Equations 1 and 2.

η = 100 - 100 γ d OS 100 + F 100 OS 100 γ s OS + F 100 γ s F (1)
Civ = V C V = m C γ s C V (2)

Porosity (η) is a function of the dry unit weight (γd) and unit weight of solids (γsOS and γsF) of the Osorio sand (OS) and the fibers (F). The cement content (Civ) results from the volume occupied by Portland cement (PC) divided by the total volume of the sample. This index allows the unification of all experiments in a single relation, resulting in a rational dosage methodology for cemented soil mixtures. However, such equations are valid for the cemented mixtures studied herein and are only functional if the boundary conditions of the applied variables are ensured.

3. Results and discussion

3.1 Unconfined compressive strength (qu)

The unconfined compressive strength results are presented in Figure 3. The data was presented as a function of the porosity/cement content index (η/Civ).

Figure 3
Unconfined compressive strength.

For all studied combinations, the increase in cement content and decrease in porosity (lower η/Civ values) resulted in higher qu. Cement content presented a considerable effect on qu, for both unreinforced and fiber-reinforced specimens. The increase in cement content (1% to 2% and latter to 3%, 5% and 7%) also increased the hydrated products of the mixture, contributing to the further development of a stiffer soil-cement matrix and, consequently, an increase in strength (Consoli et al., 2007Consoli, N.C., Foppa, D., Festugato, L., & Heineck, K.S. (2007). Key parameters for strength control of artificially cemented soils. Journal of Geotechnical and Geoenvironmental Engineering, 133(2), 197-205. http://dx.doi.org/10.1061/(ASCE)1090-0241(2007)133:2(197).
http://dx.doi.org/10.1061/(ASCE)1090-024...
, 2011bConsoli, N.C., Zortéa, F., Souza, M., & Festugato, L. (2011b). Studies on the dosage of fiber-reinforced cemented soils. Journal of Materials in Civil Engineering, 23(12), 1624-1632. http://dx.doi.org/10.1061/(ASCE)MT.1943-5533.0000343.
http://dx.doi.org/10.1061/(ASCE)MT.1943-...
; Festugato et al., 2018Festugato, L., Peccin da Silva, A., Diambra, A., Consoli, N.C., & Ibraim, E. (2018). Modelling tensile/compressive strength ratio of fibre reinforced cemented soils. Geotextiles and Geomembranes, 46(2), 155-165. http://dx.doi.org/10.1016/j.geotexmem.2017.11.003.
http://dx.doi.org/10.1016/j.geotexmem.20...
); a small addition of cement was enough to generate significant gains in strength. Regarding the porosity effect, the reduction in mixtures void ratio resulted in an increase in the rate of qu gain with cement content (Carvalho Queiróz et al., 2022Carvalho Queiróz, L., Dias Miguel, G., Jordi Bruschi, G., & Deluan Sampaio de Lima, M. (2022). Macro-micro characterization of green stabilized alkali-activated sand. Geotechnical and Geological Engineering, 40, 3763-3778. http://dx.doi.org/10.1007/s10706-022-02130-9.
http://dx.doi.org/10.1007/s10706-022-021...
; Pereira dos Santos et al., 2022Pereira dos Santos, C., Bruschi, G.J., Mattos, J.R.G., & Consoli, N.C. (2022). Stabilization of gold mining tailings with alkali-activated carbide lime and sugarcane bagasse ash. Transportation Geotechnics, 32, 100704. https://doi.org/10.1016/j.trgeo.2021.100704.
https://doi.org/10.1016/j.trgeo.2021.100...
; Queiróz et al., 2022Queiróz, L.C., Batista, L.L.S., Souza, L.M.P., Lima, M.D., Danieli, S., Bruschi, G.J., & Bergmann, C.P. (2022). Alkali-activated system of carbide lime and rice husk for granular soil stabilization. Proceedings of the Institution of Civil Engineers - Ground Improvement, 1-37. Ahead of print. https://doi.org/10.1680/jgrim.21.00048.
https://doi.org/10.1680/jgrim.21.00048...
). At lower porosities the contact area between particles is enlarged, enhancing the interlocking phenomenon and friction mobilization resulting in an increase in strength, and so the effectiveness of the cement and the fibers is greater (Festugato et al., 2017Festugato, L., Menger, E., Benezra, F., Kipper, E.A., & Consoli, N.C. (2017). Fibre-reinforced cemented soils compressive and tensile strength assessment as a function of filament length. Geotextiles and Geomembranes, 45(1), 77-82. http://dx.doi.org/10.1016/j.geotexmem.2016.09.001.
http://dx.doi.org/10.1016/j.geotexmem.20...
). This physical-chemical phenomenon has also been evidenced in different cemented geotechnical materials (Bruschi et al., 2021Bruschi, G.J., Santos, C.P., de Araújo, M.T., Ferrazzo, S.T., Marques, S., & Consoli, N.C. (2021). Green stabilization of bauxite tailings: a mechanical study on alkali-activated materials. Journal of Materials in Civil Engineering, 33(11), 1-25. http://dx.doi.org/10.1061/(ASCE)MT.1943-5533.0003949.
http://dx.doi.org/10.1061/(ASCE)MT.1943-...
; Carvalho Queiróz et al., 2022Carvalho Queiróz, L., Dias Miguel, G., Jordi Bruschi, G., & Deluan Sampaio de Lima, M. (2022). Macro-micro characterization of green stabilized alkali-activated sand. Geotechnical and Geological Engineering, 40, 3763-3778. http://dx.doi.org/10.1007/s10706-022-02130-9.
http://dx.doi.org/10.1007/s10706-022-021...
; Pereira dos Santos et al., 2022Pereira dos Santos, C., Bruschi, G.J., Mattos, J.R.G., & Consoli, N.C. (2022). Stabilization of gold mining tailings with alkali-activated carbide lime and sugarcane bagasse ash. Transportation Geotechnics, 32, 100704. https://doi.org/10.1016/j.trgeo.2021.100704.
https://doi.org/10.1016/j.trgeo.2021.100...
; Quiñónez Samaniego et al., 2021Quiñónez Samaniego, R.A., Scheuermann Filho, H.C., de Araújo, M.T., Bruschi, G.J., Festugato, L., & Consoli, N.C. (2021). Key parameters controlling strength and resilient modulus of a stabilised dispersive soil. Road Materials and Pavement Design, 24(1), 279-294. http://dx.doi.org/10.1080/14680629.2021.2013937.
http://dx.doi.org/10.1080/14680629.2021....
; Silva et al., 2022Silva, A., Festugato, L., Daronco, J.V.L., & Menger, E.S. (2022). Mechanical response of a sand, reclaimed-asphalt pavement, and Portland cement mixture. Journal of Materials in Civil Engineering, 34(9), 520-533. http://dx.doi.org/10.1061/(ASCE)MT.1943-5533.0004361.
http://dx.doi.org/10.1061/(ASCE)MT.1943-...
; Tonini de Araújo et al., 2021Tonini de Araújo, M., Tonatto Ferrazzo, S., Bruschi, G.J., & Cesar Consoli, N. (2021). Mechanical and environmental performance of eggshell lime for expansive soils improvement. Transportation Geotechnics, 31(2), 100681. http://dx.doi.org/10.1016/j.trgeo.2021.100681.
http://dx.doi.org/10.1016/j.trgeo.2021.1...
; Bruschi et al., 2023Bruschi, G.J., Santos, C.P., Ferrazzo, S.T., Araújo, M.T., & Consoli, N.C. (2023). Parameters controlling loss of mass and stiffness degradation of 'green' stabilized bauxite tailings. Proceedings of the Institution of Civil Engineers - Geotechnical Engineering, 176(3), 306-314. https://doi.org/10.1680/jgeen.21.00119.
https://doi.org/10.1680/jgeen.21.00119...
).

When comparing non-reinforced and fiber-reinforced specimens, the average qu of reinforced specimens was 18% higher than non-reinforced ones, indicating that fiber addition contributed for strength development. Consoli et al. (2009b)Consoli, N.C., Vendruscolo, M.A., Fonini, A., & Rosa, F.D. (2009b). Fiber reinforcement effects on sand considering a wide cementation range. Geotextiles and Geomembranes, 27(3), 196-203. http://dx.doi.org/10.1016/j.geotexmem.2008.11.005.
http://dx.doi.org/10.1016/j.geotexmem.20...
claim that the efficiency of fiber reinforcement is governed by several factors, such as: fiber content, orientation, geometry, mechanical characteristics, and properties of the soil such as grading, mineralogy, and grain shape. Fiber reinforcement in cemented soils is only effective when the fiber length is large when compared to the grain size of the soil (Michalowski, 2008Michalowski, R.L. (2008). Limit analysis with anisotropic fibre-reinforced soil. Geotechnique, 58(6), 489-501. http://dx.doi.org/10.1680/geot.2007.00055.
http://dx.doi.org/10.1680/geot.2007.0005...
; Michalowski & Čermák, 2003Michalowski, R.L., & Čermák, J. (2003). Triaxial compression of sand reinforced with fibers. Journal of Geotechnical and Geoenvironmental Engineering, 129(2), 125-136. http://dx.doi.org/10.1061/(ASCE)1090-0241(2003)129:2(125).
http://dx.doi.org/10.1061/(ASCE)1090-024...
). Furthermore, Festugato et al. (2017)Festugato, L., Menger, E., Benezra, F., Kipper, E.A., & Consoli, N.C. (2017). Fibre-reinforced cemented soils compressive and tensile strength assessment as a function of filament length. Geotextiles and Geomembranes, 45(1), 77-82. http://dx.doi.org/10.1016/j.geotexmem.2016.09.001.
http://dx.doi.org/10.1016/j.geotexmem.20...
indicated that an increase of fiber reinforcement length directly improves the strength of cemented soils.

Fair correlations were identified between the η/Civ index and qu, as shown by Equations 3 and 4. For the non-reinforced mixtures the determination coefficient (R2) was 0.98, while for the reinforced ones the coefficient was 0.92. This suggests that through these equations it becomes possible to predict the qu of the fiber-reinforced cement-treated mixtures over a wide range of porosities and cement contents, avoiding unnecessary testing on practical soil-cement applications. Furthermore, this index has also been shown to work on the prediction of qu in different fiber-reinforced cemented soils (Consoli et al., 2011aConsoli, N.C., Moraes, R.R., & Festugato, L. (2011a). Split tensile strength of monofilament polypropylene fiber-reinforced cemented sandy soils. Geosynthetics International, 18(2), 57-62. http://dx.doi.org/10.1680/gein.2011.18.2.57.
http://dx.doi.org/10.1680/gein.2011.18.2...
, 2017aConsoli, N.C., Nierwinski, H.P., Peccin da Silva, A., & Sosnoski, J. (2017a). Durability and strength of fiber-reinforced compacted gold tailings-cement blends. Geotextiles and Geomembranes, 45(2), 98-102. http://dx.doi.org/10.1016/j.geotexmem.2017.01.001.
http://dx.doi.org/10.1016/j.geotexmem.20...
; Mazhar & GuhaRay, 2021Mazhar, S., & GuhaRay, A. (2021). Stabilization of expansive clay by fibre-reinforced alkali-activated binder: an experimental investigation and prediction modelling. International Journal of Geotechnical Engineering, 15(8), 977-993. http://dx.doi.org/10.1080/19386362.2020.1775358.
http://dx.doi.org/10.1080/19386362.2020....
).

Unreinforced cemented mixture: qu (kPa) = 2 .7×10 4 η Civ -1 .3 (3)
Fiber-reinforced cemented mixture: qu (kPa) = 3 .2×10 4 η Civ -1 .3 (4)

3.2 Split tensile strength (qt)

Results of split tensile strength tests are presented in Figure 4. Once again, the data was expressed in function of the porosity/cement content index (η/Civ).

Figure 4
Split tensile strength.

As in the case of the compressive strength results, the decrease in the porosity/cement content index led to an increase in split tensile strength. The mechanism by which the reduction in porosity influences the soil-cement strength is again related to the existence of a larger contact area between particles of the cemented mixture, enhancing the interlocking phenomenon. As for the cement content, its increase enhances the cementitious reactions happening on the mixtures, contributing for strength development (Piuzzi et al., 2021Piuzzi, G.P., Scheuermann Filho, H.C., Villena Del Carpio, J.A., & Consoli, N.C. (2021). The effects of porosity, asphalt content and fiberglass incorporation on the tensile strength and resilient modulus of asphalt concrete blends. Geotextiles and Geomembranes, 49(3), 864-870. http://dx.doi.org/10.1016/j.geotexmem.2021.01.002.
http://dx.doi.org/10.1016/j.geotexmem.20...
).

The average qt of reinforced specimens was 20% higher than non-reinforced ones, indicating that fiber addition also contributed for split tensile strength development. Fiber-reinforcement seems to be more efficient for tensile strength than for compressive strength; similar findings were presented by Festugato et al. (2017)Festugato, L., Menger, E., Benezra, F., Kipper, E.A., & Consoli, N.C. (2017). Fibre-reinforced cemented soils compressive and tensile strength assessment as a function of filament length. Geotextiles and Geomembranes, 45(1), 77-82. http://dx.doi.org/10.1016/j.geotexmem.2016.09.001.
http://dx.doi.org/10.1016/j.geotexmem.20...
, while studying the compressive and tensile strength of fiber-reinforced soils.

Adequate correlations between split tensile strength and η/Civ index were shown for all studied combinations. The determination coefficients (R2) were 0.94 and 0.92 for the unreinforced and fiber-reinforced specimens, respectively, indicating the viability of the η/Civ index on the prediction of the split tensile strength for the analyzed conditions. This viability has also been proven for other cemented geotechnical materials (Consoli et al., 2016Consoli, N.C., Samaniego, R.A.Q., & Villalba, N.M.K. (2016). Durability, strength, and stiffness of dispersive clay-lime blends. Journal of Materials in Civil Engineering, 28(11), 04016124. http://dx.doi.org/10.1061/(ASCE)MT.1943-5533.0001632.
http://dx.doi.org/10.1061/(ASCE)MT.1943-...
, 2017bConsoli, N.C., Quiñónez, R.A., González, L.E., & López, R.A. (2017b). Influence of molding moisture content and porosity/cement index on stiffness, strength, and failure envelopes of artificially cemented fine-grained soils. Journal of Materials in Civil Engineering, 29(5), 04016277. http://dx.doi.org/10.1061/(ASCE)MT.1943-5533.0001819.
http://dx.doi.org/10.1061/(ASCE)MT.1943-...
, 2018Consoli, N.C., Pasche, E., Specht, L.P., & Tanski, M. (2018). Key parameters controlling dynamic modulus of crushed reclaimed asphalt paving-powdered rock-Portland cement blends. Road Materials and Pavement Design, 19(8), 1716-1733. http://dx.doi.org/10.1080/14680629.2017.1345779.
http://dx.doi.org/10.1080/14680629.2017....
, 2021b Consoli, N.C., Festugato, L., Miguel, G.D., Moreira, E.B., & Scheuermann Filho, H.C. (2021b). Fatigue life of green stabilized fiber-reinforced sulfate-rich dispersive soil. Journal of Materials in Civil Engineering, 33(9), 04021249. http://dx.doi.org/10.1061/(ASCE)MT.1943-5533.0003842.
http://dx.doi.org/10.1061/(ASCE)MT.1943-...
; Piuzzi et al., 2021Piuzzi, G.P., Scheuermann Filho, H.C., Villena Del Carpio, J.A., & Consoli, N.C. (2021). The effects of porosity, asphalt content and fiberglass incorporation on the tensile strength and resilient modulus of asphalt concrete blends. Geotextiles and Geomembranes, 49(3), 864-870. http://dx.doi.org/10.1016/j.geotexmem.2021.01.002.
http://dx.doi.org/10.1016/j.geotexmem.20...
).

Unreinforced cemented mixture: qt (kPa) = 4 .1×10 3 η Civ -1 .3 (5)
Fiber-reinforced cemented mixture: qt (kPa) = 4 .9×10 3 η Civ -1 .3 (6)

3.3 Fatigue life (Nf)

Fatigue life results are presented in Figure 5 also expressed in function of the porosity/cement content index (η/Civ).

Figure 5
Fatigue life.

Analogous to the behavior evidenced for split tensile and compressive strength, a reduction in porosity and increase in cement content led to the improvement of fatigue life for both fiber-reinforced and non-reinforced specimens. This behavior is attributed to the greater friction mobilization and higher contact area between particles, as the porosity decreases and cement content increases. Similar trends have also been reported for fatigue life studies (Consoli et al., 2021cConsoli, N.C., Tebechrani Neto, A., Correa, B.R.S., Quiñónez Samaniego, R.A., & Cristelo, N. (2021c). Durability evaluation of reclaimed asphalt pavement, ground glass and carbide lime blends based on unconfined compression tests. Transportation Geotechnics, 27, 100461. http://dx.doi.org/10.1016/j.trgeo.2020.100461.
http://dx.doi.org/10.1016/j.trgeo.2020.1...
; Piuzzi et al., 2021Piuzzi, G.P., Scheuermann Filho, H.C., Villena Del Carpio, J.A., & Consoli, N.C. (2021). The effects of porosity, asphalt content and fiberglass incorporation on the tensile strength and resilient modulus of asphalt concrete blends. Geotextiles and Geomembranes, 49(3), 864-870. http://dx.doi.org/10.1016/j.geotexmem.2021.01.002.
http://dx.doi.org/10.1016/j.geotexmem.20...
).

Regarding the effect of fiber reinforcement, non-reinforced specimens resulted in average Nf values 78% lower than fiber reinforced ones. The cement addition increases strength of soil; however, it also increases brittleness, which leads to brittle-like failure. In opposition, fiber addition increases the ductility of the cemented soil, without considerably compromising its strength. In the case of this research, fiber addition enhanced the bridging effect between particles, playing a critical role in the initiation and extension of cracks. This effect can be related to the hydrophilic characteristics and surface roughness of the fibers (Consoli et al., 2012Consoli, N.C., Ruver, C.A., Girardello, V., Festugato, L., & Thomé, A. (2012). Effect of polypropylene fibers on the uplift behavior of model footings embedded in sand. Geosynthetics International, 19(1), 79-84. http://dx.doi.org/10.1680/gein.2012.19.1.79.
http://dx.doi.org/10.1680/gein.2012.19.1...
; Festugato et al., 2017Festugato, L., Menger, E., Benezra, F., Kipper, E.A., & Consoli, N.C. (2017). Fibre-reinforced cemented soils compressive and tensile strength assessment as a function of filament length. Geotextiles and Geomembranes, 45(1), 77-82. http://dx.doi.org/10.1016/j.geotexmem.2016.09.001.
http://dx.doi.org/10.1016/j.geotexmem.20...
). The inclusion of fibers was able to mitigate internal stresses in distinctive orientations, contributing for a more distributed stress field, thus avoiding local fractures.

Satisfactory correlations were identified for both non-reinforced and fiber reinforced specimens and the η/Civ index. For both the non-reinforced and fiber reinforced specimens, R2 was 0.9. The elevated R2 indicate the viability of the index in also predicting Nf of the cemented mixtures, providing a rational dosage methodology for a wide range of porosities and cement contents.

Unreinforced cemented mixture: Nf (cycle) = 8 .1×10 5 η Civ -1 .9 (7)
Fiber-reinforced cemented mixture: Nf (cycle) = 5 .1×10 6 η Civ -1 .9 (8)

3.4 Statistical analysis

Unconfined compressive strength, split tensile strength and fatigue life results were statistically analyzed with an analysis of variance (ANOVA). This analysis included three main factors (fiber content, cement content, and void ratio) and their second-order interactions. ANOVA results are illustrated through Pareto charts (Figure 6) and main effects plots (Figure 7). The significance of the analysis is shown in the Pareto charts; the horizontal bars portray the magnitude of the studied effects while the dotted vertical line is associated with the significance level (95% confidence) of the analysis. Values exceeding the vertical line represent factors that have significant effects over the mechanical behavior. As for the main effects charts (Figure 7), the dotted line represents the mean result of the tests.

Figure 6
Pareto charts: (a) unconfined compressive strength; (b) split tensile strength; (c) fatigue life.
Figure 7
Main effect plots: (a) unconfined compressive strength; (b) split tensile strength; (c) fatigue life.

For unconfined compressive strength tests, the Pareto charts (Figure 6) show that all main factors (B, C, and A) were statistically significant, while their second-order interactions showed no influence on the response variable. As for split tensile strength tests, only the main factors (B, C, and A) and the second order interaction BC (cement content and void ratio) were statistically significant. Finally, for fatigue life tests all main factors (A, B, and C) and their second-order interactions (AB, AC, and BC) presented a significant influence. As for the main effects (Figure 7) an increase on fiber and cement content and decrease in void ratio resulted in a positive effect for all tests (compressive strength, split tensile strength and fatigue life). The statistical analysis corroborates the mechanical results, in which qu, qt, and Nf were governed by fiber content, cement content, and void ratio. It is important to highlight that, fiber content was the main factor that presented the most influence over fatigue life results, once again corroborating the presented results.

4. Conclusions

This study investigated the fatigue life and strength behavior of fiber-reinforced cement-treated sand. In addition, a rational dosage methodology (porosity/cement content index) was also investigated. Based on the findings of this study, for the studied materials and conditions (polypropylene fiber reinforced fine sand cemented with type III Portland cement under unconfined monotonic and cyclic loading), the following conclusions can be disclosed:

a) Fiber-reinforcement improved the mechanical behavior of both monotonic (unconfined compressive strength and split tensile strength) and dynamic loading (fatigue life) tests. This improvement was more pronounced for the fatigue life tests, considering that fiber addition enhanced the bridging effect between particles, playing a critical role in the initiation and extension of cracks;

b) Statistical analysis showed that the mechanical behavior of the fiber-reinforced cemented sand was governed by fiber content, cement content and void ratio of the mixtures. An increase in fiber and cement content and decrease in void ratio resulted in a positive effect while a decrease in void ratio on fatigue life, unconfined compressive strength and split tensile strength;

c) The porosity/cement content index (η/Civ) was shown to be an appropriate parameter to evaluate the stabilization of fiber-reinforced cemented sand in terms of fatigue life, unconfined compressive strength and split tensile strength. The provided equations allow the selection of the best combination of void ratio and cement content for a wide range of options, replacing trial and error experiments with a rational dosage methodology for both monotonic and dynamic loading.

List of symbols

qt split tensile strength

qu unconfined compressive strength

Civ cement content

F fibers

LVDT linear variable differential transformer

OS Osorio Sand

PC Portland cement

PCA Portland cement association

SP poorly graded sand

γd dry unit weight

γsF unit weight of solids fibers

γsOS unit weight of solids Osorio sand

η Porosity

η/Civ porosity/cement content ratio

Data availability

All data produced or examined in the course of the current study are included in this article.

Acknowledgements

Authors wish to express their gratitude to the Brazilian Research Council CNPq for supporting the research group (grants # 307289/2018-4 and 402572/2021-1).

  • Discussion open until November 30, 2023.

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    » http://dx.doi.org/10.1061/(ASCE)MT.1943-5533.0001819
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    » http://dx.doi.org/10.1080/14680629.2017.1345779
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    » http://dx.doi.org/10.1680/gein.2012.19.1.79
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Publication Dates

  • Publication in this collection
    21 July 2023
  • Date of issue
    2023

History

  • Received
    29 June 2022
  • Accepted
    27 Apr 2023
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