Increase In Unconfined Compressive Strength Research Articles

Use of lignocellulose-degrading enzyme bio-cemented soils in the construction industry

In their activity, termites break down biomass into glucose, forming cementitious compounds. This results in rainfall-resistant mounds for their shelters, which interests the construction industry. This study explored the potential application of the abundant naturally bio-cemented termite mound soils in highway construction. Experimental investigations compared these mound soils to surrounding soils, revealing that mound soils are 68.2% finer in particle size distribution and have 81.4% lower organic content. Atterberg limits indicated 14.6% higher plasticity and a 5.3% increase in specific gravity for mound soils. Atomic Absorption Spectroscopy (AAS) showed no significant difference in chemical composition. Proctor tests indicated that the compaction characteristics of the soils were comparable, confirming their engineering viability without modifications. Mound soils exhibited a twofold increase in Unconfined Compressive Strength (UCS) and a 33.9% increment in California Bearing Ratio (CBR) strength. One-way ANOVA tests confirmed these differences with p-value ranges of 0.0056-0.0361 below the 0.05 significance threshold. The study advocates utilising eco-friendly naturally bio-cemented mound soils in highway construction, meeting minimum standards. Mound soils from one acre can construct up to 2,500m highway, optimising resource use, promoting sustainability by repurposing natural materials, and significantly reducing carbon emissions. Further research on soil improvement using lignocellulose-degrading enzymes is recommended.

Stress-Strain Behavior of Soft Soil Stabilized with Nickel Slag, Limestone, and Aluminum Hydroxide

Soil stabilization by combining several minerals is a form of material engineering aimed at increasing the bearing capacity of the soil to a higher level. The development of waste-based materials and the utilization of local potential are part of environmentally conscious construction. This study aims to analyses the mechanical behaviour of soil stabilized with several pozzolanic materials derived from nickel processing waste and limestone, which are local materials with very large deposits. ASTM standards were used in this study for both physical and mechanical testing. Unconfined compressive strength (UCS) tests were conducted to compare the mechanical behaviour of stabilized soil with that of natural soil. The test samples used were cylindrical with a diameter of 35 mm and a height of 70 mm. The binding materials consisted of nickel slag, aluminium hydroxide, and limestone, with the amount of each material based on the dry soil weight (γdry). The addition of lime in this study was varied at 2%, 4%, and 6%. The test results generally show that lime variations and curing time affect the increase in unconfined compressive strength (qu), with the highest value of 30.91 kg/cm² observed at 6% lime content after 28 days of curing.

Impact of soil density on biomineralization using EICP and MICP techniques for earthen sites consolidation

Enzyme-induced calcium carbonate precipitation (EICP) and microbially-induced calcium carbonate precipitation (MICP) techniques represent emerging trends in soil stabilization. However, the impact of soil density on biomineralization, particularly in historical earthen sites, remains unclear. This study compares the consolidation effects of EICP and MICP on cylindrical samples (10 cm × 5 cm) with three densities (1.5 g/cm3, 1.6 g/cm3, and 1.7 g/cm3) derived from the soil near the UNESCO World Cultural Heritage Site of Suoyang Ancient City, Gansu Province, China. Results showed that calcium carbonate production increased across all densities through bio-cementation, with higher densities producing more calcium carbonate. MICP-treated specimens exhibited larger increases in calcium carbonate production compared to those treated with EICP. Specimens with a density of 1.7 g/cm³ showed a wave velocity increase of 3.26% (EICP) and 7.13% (MICP), and an unconfined compressive strength increase of 8% (EICP) and 26% (MICP). These strength increases correlated with the generation of calcium carbonate. The findings suggest that biomineralization can be effectively utilized for in situ consolidation of earthen sites, emphasizing the importance of considering soil density in biologically-based conservation technologies. Furthermore, MICP shows potential advantages over EICP in providing stronger, compatible and more sustainable soil reinforcement.

Feasibility of compacted attapulgite/diatomite amended clayey soils as gas barrier materials

Compacted clay liners are extensively used as barriers to control the upward diffusion of vapors of volatile or semi-volatile organic contaminants released from unsaturated contaminated soils at industry-contaminated sites. This study aimed to investigate the gas diffusion barrier performance of compacted clayey soils amended with three agents including attapulgite and diatomite individually, and attapulgite/diatomite mixture. The properties including water retention, volumetric shrinkage, gas diffusion, and unconfined compressive strength were evaluated through a series of laboratory tests of amended compacted clayey soils. The results demonstrate that the decrease in volume proportions of inter-aggregate pores leads to an increase in unconfined compressive strength (qu). Both hydrophilic groups and microstructures of attapulgite and diatomite result in an increase in water retention percent (Wt) of compacted clayey soil specimens after amendment regardless of the type of agent or initial water content (w0). Furthermore, the ratio of the gas diffusion coefficient (De) to the gas diffusion coefficient in the air (Da) was significantly reduced owing to a decrease in volume proportions of inter-aggregate pores, hydrophilic group, and microstructures of attapulgite and diatomite. Scanning electron microscope analyses revealed that rod-shaped attapulgite filled the inter-aggregate pores formed by clay particles, whereas the disc-shaped diatomite particles, characterized by micropores, failed to obstruct the inter-aggregate pores due to their larger particle size. Mercury intrusion porosimetry (MIP) analyses showed a reduction in pore volume in the inter-aggregate pores, leading to a reduction in the total pore volume for both the attapulgite and attapulgite/diatomite mixture amended clays, which is in accordance with the scanning electron microscope (SEM) results. The findings are pertinent to the practical application of compacted clay liners as gas barriers against the upward migration of volatile or semi-volatile organic contaminants at contaminated sites.

Stabilization of an iron ore tailings by-product with perlite waste geopolymer

In the field of engineering, sustainable solutions that can generate lower environmental impacts, either through material replacement or reuse, are increasingly sought after. In Brazil, in the geotechnical area, there is a demand to find solutions to avoid the disposal of tailings sludge destined for structures, following the recent dam ruptures of Fundao in 2015 and Corrego do Feijao in 2019. One of the recent investments is in the treatment of tailings, generating by-products. To improve the mechanical properties of these by-products, geopolymer utilization has been employed. Geopolymers are products resulting from reactions between aluminosilicate precursors and alkaline activators. The objective of this study is to evaluate the unconfined compressive strength of an iron ore tailings by-product stabilized with a geopolymer that utilizes perlite waste as a precursor and sodium hydroxide as an activator through a two-part alkali-activation process. Two molar concentrations of activators, 2M and 5M, and two sample compositions were evaluated: one with 20% geopolymer and 80% iron ore tailings by-product, and another with 30% and 70%. An increase in unconfined compressive strength was observed with higher concentrations of the activator solution and a greater percentage of geopolymer in material stabilization. Thus, it can be stated that the use of geopolymers in by-product stabilization is promising, but finding the optimal dosage and evaluating other variables such as curing time and temperature is necessary.

Effect of Polymeric Agent on the Strength and Water Stability of Cement-Stabilized Construction Waste Soil

Due to the large output of construction waste soils, it has become an enormous challenge for human society and the ecological environment. The purpose of this paper is to discuss the possibility of using a stabilized waste soil in road engineering. Cement and polymer stabilizers were added to the waste soil, and the effect of the stabilizer on the strength and water stability of the stabilized soil was studied. The structure and morphology of the specimens were analyzed using an X-ray diffractometer (XRD) and a scanning electron microscope (SEM). The results show that the unconfined compressive strength increases by 25.0% and the 28-day water stability coefficient, K increases by 59.6% after the addition of the stabilizer. The XRD curve shows that the addition of the new stabilizer does not produce a new characteristic peak, but the diffraction peak strength of some minerals can be improved. SEM shows that the surface of stabilized soil particles is covered by materials, and the particles show obvious agglomeration, forming a network structure, which improves the strength and water stability of the soil.

Enhancing the Strength of Mine Residue Soil by Bioremediation Combined with Biopolymers

Traditional soil stabilization methods are usually associated with high energy consumption, carbon emissions, and long-term environmental impact. Recent developments have shown the potential use of bio-based techniques as eco-friendly alternatives for soil stabilization. The present work studies the effects of the addition of the biopolymers xanthan gum (XG) or carboxymethyl cellulose (CMC) to a mine residue soil, combined or not with biostimulation and bioaugmentation techniques, in terms of compressive stress–strain behavior. Unconfined compressive strength (UCS) tests were performed on previously disturbed samples (two cycles of percolation, extraction and homogenization) to evaluate if the biostimulation and bioremediation remain active in a real adverse scenario. The results allowed for us to conclude that both biopolymers, when applied individually (with a content of 1%), are effective stabilizers (CMC allows for unconfined compressive strength increases of up to 109%), showing better results for CMC than Portland cement. The biostimulation of the autochthonous community of the mine residue soil was revealed to be a non-effective technique, even when combined with the biopolymers. However, good results were observed when the bioaugmentation was combined with xanthan gum, with unconfined compressive strength improvements of up to 27%. The study revealed that these bio-based techniques are promising soil engineering techniques, offering environmentally friendly alternatives for sustainable soil stabilization and contributing to a greener and more sustainable future.

IMPROVEMENT OF HIGH PLASTICITY CLAY BY USING FILTER SLUDGE

Filter sludge (FS) is a waste material that occurs during sugar production in the sugar industry, and since it is not used anywhere, it creates a problem due to storage costs and environmental damage. In the present study, high plasticity clay was stabilized with a filter sludge which has never been used for soil stabilization in field cases. The changes in the geotechnical properties of a high plasticity clay (CH) with the additive of filter sludge (FS) were investigated. The amount of FS mixed into CH soil is 3-6-9-12-15% by dry weight of the soil. Changes in geotechnical properties such as consistency limits, compaction parameters, strength, swelling potential, CBR value of improved soils were determined. The plastic limit and optimum water content increase as the FS content added to the soil increases; liquid limit, plasticity index, and maximum dry density decrease. Improved soil strength increases as the curing time and FS amount increase, and the highest strength was obtained with 15% of FS. At the optimum additive ratio, the unconfined compressive strength increases by 33%. The swelling percentage of CH clay decreases from 42.5% to 20%. According to the wet CBR test results, the bearing capacity of the improved soil increased from %1.1 to %4.4. As a result of this study, it was seen that the FS waste material improved the geotechnical properties of the soil.

Strength and Mechanism of Granite Residual Soil Strengthened by Microbial-Induced Calcite Precipitation Technology

High rainfall environmental conditions can easily cause erosion or collapse of the granite residual soil slope. However, traditional slope reinforcement methods have drawbacks such as poor landscape effect, high energy consumption of raw materials, and environmental pollution. This study studied the application of microbial-induced calcite precipitation (MICP) in the reinforcement of granite residual soil. The consolidation effect of various methods was investigated, and the influence of cementing liquid concentration and pH value on consolidation under optimal curing conditions was explored. The results showed that the bacteria concentration reached OD600 = 3.0 and urease activity was 31.64 mM/min, which positively impact the production of calcium carbonate and the stability of crystal morphology. In addition, the soaking method was found to have the most effective consolidation effect on the surface soil samples, with the lowest disintegration rate. On the other hand, the peristaltic pump grouting method is the most effective in strengthening depth. This method resulted in a 513.65% increase in unconfined compressive strength (UCS), a 297.98% increase in cohesion, and a 101.75% increase in internal friction angle. This study also found that after seven rounds of grouting, the highest UCS was achieved in consolidated soil samples with a 0.5 mol/L cementing solution concentration, reaching 1.602 MPa. The UCS of soil samples increases as the pH value of the cementing fluid increases within the range of 6–8. As the pH value reaches 8–9, the strength increases and stabilizes gradually. These research findings can serve as an experimental basis for strengthening granite residual soil slopes and a guide for improving microbial geotechnical strengthening methods.

Mechanical Properties and Microscopic Study of Steel Slag–Fly Ash-Solidified Loess under Alkaline Conditions

To address the geological hazard posed by unstable loess slopes prone to collapse and landslides, a high-strength geopolymer cementing material was developed utilizing green steel slag–fly ash as its primary constituent and activated through the application of sodium silicate alkalinity. The mechanical properties and microstructure changes of loess under varying dosages of steel slag–fly ash geopolymers and curing age were investigated through a series of tests, including unconfined compressive strength, direct shear, disintegration, electron microscope scanning, and X-ray diffraction. The findings indicate that the incorporation of geopolymers can significantly enhance the internal friction angle, cohesion, and unconfined compressive strength of loess, while mitigating the disintegration quantity and rate of stabilized soil. When 20% geopolymer is mixed into the solidified soil and cured for 28 days, the resulting solidified soil exhibits an internal friction angle of 31.12°, a cohesion of 81.09 kPa, and an unconfined compressive strength of 570.86 kPa. These values are 1.62 times, 1.76 times, and 3.36 times higher than those of loess, respectively. Moreover, the solidified soil shows minimal disintegration within 1800 s, with only 1.97% disintegration. The curing age of solidified soil has a significant impact on its curing effect. Enhancing the curing time can considerably enhance the mechanical properties of solidified soil. When the geopolymer content is 20% and the curing time is extended to 28 days, the internal friction angle, cohesion, and unconfined compressive strength increase by approximately 0.23 times, 0.48 times, and 1.61 times, respectively, compared to a curing time of 7 days. By analyzing SEM and XRD, it was found that the hydration of steel slag–fly ash geopolymer produces C-S-H and C-A-S-H cementing materials, which effectively fill the gaps between soil particles and enhance the mechanical properties of solidified soil. The research findings can serve as a theoretical foundation for the consolidation of loess subgrade utilizing steel slag–fly ash geopolymer.

Effect of Basalt Fiber Content and Length on the Strength and Crack Development of Polyvinyl Alcohol/Basalt Hybrid Fiber-Reinforced Cement Soil.

Polyvinyl alcohol (PVA) fiber is widely used in geotechnical engineering because of its excellent physical and mechanical properties; however, PVA fibers are prone to aging, while basalt fiber has a natural anti-aging ability, which can be added to cement material to effectively eliminate the effects of aging on PVA fiber. Previous experiments identified that the optimum content of PVA fiber is 0.5% (mass fraction, the same below). Based on this, we continued to add basalt fibers of different lengths (3 mm, 6 mm, 9 mm, 12 mm, 18 mm, 30 mm) and different contents (0%, 0.25%, 0.5%, 0.75%, 1%) to study the effect of both length and content of basalt fibers on the strength of cement soil specimens. It was concluded that adding 0.5 % of 9 mm basalt fiber results in the greatest increase in unconfined compressive strength (UCS). The UCS reached 12.59 MPa, which was 71% higher than specimens without fiber, and a regression analysis was carried out to obtain the relationship among them. The ratio of cement soil in the highest UCS and the relationship among the UCS, the length, and the content of basalt fiber can be used as a reference for practical projects. In addition, digital image correlation (DIC) technology was used to analyze the surface cracks and horizontal strain field when the peak strain was reached at each content and length of the basalt fiber. Finally, the curing mechanism for hybrid fiber cement soil was analyzed by combining the results of the UCS test, DIC test, and SEM test.

The Effectiveness of Residual Soil, Orashi River Sand, and Sombrero River Sand as Stabilizing Agents for Subgrade Soil of Highway Pavement

The study investigated the effect of different stabilization materials, including residual soil and river sands, on the properties of subgrade soil for road and pavement structures. The results showed that the chemical composition of the subgrade soil was dominated by calcium, aluminum, and silicon, indicating a mineral clay soil. The use of stabilization materials led to a decrease in fines content and an increase in maximum dry density. The behavior of optimum moisture content was non-linear, and the liquid limit of the stabilized subgrade soil decreased significantly for all three materials, indicating a decrease in soil swelling ability. The study also revealed that the use of composite materials of cement and residual soil or river sand can improve the properties of subgrade soil and lead to an increase in unconfined compressive strength. The findings of this study can aid in the selection of appropriate stabilization materials and methods, and in the optimization of the use of these materials in road construction for improved strength and durability. Further research is needed to fully understand the characteristics of subgrade soil and determine the most effective methods for its stabilization and management. This study investigates the effects of residual soil and river sands on the mechanical properties of subgrade soil, with a focus on liquid limit, plastic limit, plasticity index, and unconfined compressive strength. The results suggest that residual soil, Orashi River sand, and Sombrero River sand are effective stabilizing agents for subgrade soil, with an increase in strength observed with increasing percentages of stabilizing material. However, there is an optimum content of stabilization material required to achieve maximum strength values, beyond which the strength decreases. The study also highlights the importance of considering the effect of soaking on the strength of subgrade soil and demonstrates the effectiveness of using composite .........

Efficiency comparison of mixture formulations in the stabilisation/solidification of the loess silt contaminated with zinc in terms of mechanical properties

The effectiveness of various types of binders in stabilizing/solidifying (S/S) contaminated soils is strongly dependent on the type of soil and contaminants present. The literature abounds with studies of stabilisation/solidification of clayey soils, which provides a background for initial assumptions in design of the method application for contamination of this type of soil. However, studies on the stabilisation/solidification of loess silt contaminated with heavy metals are not available. Filling this deficiency is important in order to ensure the rapid adoption of the most effective remedies in case of contamination and their immediate implementation in the subsoil. This paper has enabled the determination of the most effective mixture among the examined for the remediation of loess silt contaminated with zinc in terms of compressive strength. Strengths were determined with the implementation of 30% Portland cement (2.63 MPa), 30% of fly ash-cement mixture (2.21 MPa), an incinerated sewage sludge ash-cement mixture (0.93 MPa) and mixtures in which cement was replaced by an MgO activator (0.18 MPa for fly ash and 0.63 MPa for incinerated sewage sludge ash). In addition, the determination of strength was carried out for samples containing a mixture of fly ash, activator and cement (0.26 MPa) and incinerated sewage sludge ash, activator and cement (0.26 MPa), with weight ratios of 5:4:1 respectively. In summary, fly ash and cement in a 2:1 ratio can be considered the most effective binding mix in terms of unconfined compressive strength increase.

Sodium Carboxymethyl Cellulose-Enhanced GCLs in Freshwater Reservoirs

Biopolymers that are environmentally friendly organic products are increasingly used in geotechnical applications instead of synthetic polymers and other chemical additives. Cellulose is a biopolymer that is obtained from the cell walls of plants. In order to evaluate its effect on internal erosion, triaxial permeability tests were performed on a sodium carboxymethyl cellulose-enhanced geosynthetic clay liner (GCL) with Ca bentonite that was placed over a coarse gravel with an average grain diameter of 2.5 cm and permeated with tap water. Furthermore, unconfined compression tests were conducted on the cellulose-added bentonite component of the GCL in order to evaluate the mechanical effect of sodium carboxymethyl cellulose addition to the GCL on internal erosion. Test results indicated that 2% cellulose addition by dry weight maintained sufficient hydraulic and mechanical performances with almost 2.5 orders of magnitude decrease in permeability and 10 times increase in unconfined compressive strength. However, cellulose addition had only a slight enhancement against internal erosion. All the tested GCLs resisted against internal erosion up to a hydraulic head of 25 m. But 30 m hydraulic head resulted in internal erosion for the GCLs enhanced with up to a content of 2% cellulose.

Bio-stabilisation of soft soil using cattle manure

Environmentally friendly materials are being explored as alternatives to lime and cement binders in ground improvement. Biological treatment methods are environmentally friendly as they rely on the natural activity of ubiquitous microbes to produce extracellular polymeric saccharides (EPS) and calcite cements. EPS extruded by microbes exhibit strong adhesion from growth of fibrous bridges and bonds between surfaces. In situ polysaccharide secretion in soils to improve their engineering properties has not been examined. In this study, pulverised dried cattle manure (CM) are is used for in situ EPS production in a synthetic soft soil specimen. The indigenous facultative anaerobes and aerobes in animal waste produce negatively charged EPS molecules in the soil specimen. Bridging of sand particles and embedment of CM fibres in kaolinite aggregates caused an immediate increase in unconfined compressive strength (UCS) of the stabilised specimen. EPS cementation improved soil strength by filling pores and engulfing kaolinite aggregates into bonded mass. Fibre reinforcement and bio-stabilisation by CM increased the UCS of the soil by 740%. Replacing C-intensive lime/cement binders by CM as a stabilising agent has the potential to prevent release of 1 t of carbon dioxide to the atmosphere per tonne of lime/cement consumed.

Synergistic solidification of lead-contaminated soil by magnesium oxide and microorganisms

Although microbially induced carbonate precipitation (MICP) technology effectively promotes the remediation of heavy metal contaminated soils in low concentrations, the high concentration of heavy metals has a toxic effect on microorganisms, which leads to the decline of carbonate yield and makes the soil strength and environmental safety after remediation no up to the standard. This study describes the synergistic curing effect of MgO and microorganisms on soil contaminated with high concentrations of heavy metals. The experimental results with MgO showed 2–6 times increase in unconfined compressive strength (UCS) compared to bio-cemented samples without MgO. Toxicity characteristic leaching procedure experiments indicated that Pb-contaminated soil at 10,000 mg/kg with quantitative MgO for synergistic solidification could meet the international solid waste disposal standards, which leachable Pb2+ are less than 5 mg/L. In addition, the microscopic results showed that the introduction of MgO promoted the formation of magnesium calcite and dolomite, improved the solidification efficiency of heavy metal contaminants, and demonstrated the presence of Pb2+ in carbonate minerals. This study suggests that MgO and microorganisms have broad application prospects for synergistic solidification of Pb2+ soil.

Comparative study on engineering properties of cement-based backfill material for sustainable urban area

• Relative permittivity of CLSM decreases with curing time during step II and III. • Compressional-wave velocity exponentially increases with curing time during step III. • Relative permittivity increases with FC because silts lead to water absorption. • Silts on force chain and pore distribution by FC affect compressional-wave velocity. • Strength can be expressed as a function of the wave velocity and the permittivity. Backfill materials used in urban areas should have suitable mechanical properties (e.g., strength and flowability) for safety and serviceability of constructed geo-infrastructures. The objective of this study was to estimate the relative permittivity and compressional-wave velocity to correlate them with the unconfined compressive strength of a controlled low-strength material (CLSM) for backfill. CLSMs with fines content (FC) of 30 %, 50 %, and 90 % were prepared in sensing molds instrumented by a time domain reflectometry probe and piezo disk element. The test results show that the relative permittivity decreases with respect to the curing time, whereas the compressional-wave velocity and unconfined compressive strength increase. In addition, the relative permittivity increases as the FC increases owing to the water content, while the compressional-wave velocity and unconfined compressive strength decrease owing to the FC effect on the force chain. In this context, the FC might disturb the load-carrying matrix, and it results in remaining water and delays the curing time within 672 h. From the correlations, the relationship between the unconfined compressive strength and compressional-wave velocity with respect to the relative permittivity can be reliably constructed at an R 2 of 0.83. For this reason, it is considered that the water content from the relative permittivity can improve the relationship between strength and stiffness. Consequently, the time domain reflectometry probe can be effectively used for reliable assessment of CLSM strength during curing.

Study on Performance of Retarded Composite Semi-Rigid Base Mixed with Rubber Powder.

In order to solve the problem of poor crack resistance and frost resistance of semi-rigid base, rubber powder and retarder were added to a semi-rigid base mixture. First, 61 mixing ratios were determined. Then, through the unconfined compressive strength, splitting strength, and other tests, the mechanical, crack, and frost resistance properties of the retarded composite semi-rigid base coarse mixture with rubber powder were studied. Finally, the macro and micro properties of the two kinds of admixture composite semi-rigid base coarse mixtures were studied by means of SEM and industrial CT. The results show that rubber powder and retarder can effectively improve the cracking and freezing resistance of the mixture. After five freeze–thaw cycle tests, the strength of the retarded composite semi-rigid base material mixed with rubber powder decreased slightly compared with the mixture without additives. It can be seen that rubber powder improved the frost resistance of the mixture. When the content of rubber powder was 1.5%, the BDR value of the mixture increased by 8.8%. With the increase of unconfined compressive strength, splitting strength, and flexural tensile strength at 28 d and 90 d, it was found that the retarder improved the middle and late strength of the mixture. When the content of retarder was 0.09%, the increase of unconfined compressive strength at 28 d reached 3.9%. The addition of rubber powder and retarder improved the distribution of internal pores, the proportion of large pores decreased, and the proportion of small pores increased. The retarder changed the morphology of hydration products, formed a dense network supporting structure, further refined the pores, and reduced the porosity of the mixture. The proportion of pores with a volume greater than 100 mm3 in the total pore volume decreased by 26.01%, and the proportion of medium pores increased by 13.07%, thereby improving the mechanical properties of the mixture.

Impact of Mixing Methods and Cement Dosage on Unconfined Compressive Strength of Cement-Stabilized Macadam

The technology of vibratory mixing has been applied to improve the compressive strength of cement-stabilized macadam (CSM). The aim of this study is to investigate the effect of vibration acceleration and cement dosage on the unconfined compressive strength and density of CSM. The mixtures with four cement dosages (2%, 3%, 4%, and 5%) were prepared by conventional mixing (0 g) and vibratory mixing (1 g, 2 g, and 3.5 g). The unconfined compressive strength was tested under different mixing methods. And the microstructure of CSM was analyzed by scanning electron microscope. The results indicate that samples using vibratory mixing have higher strengths, lower coefficient of variation, and denser microstructures, compared with the conventional compulsory mixing. Compared with 15% in conventional mixing, the strength variable coefficient of CSM is less than 10% in the vibratory mixing method. As the cement dosage and the vibration acceleration increase, the unconfined compressive strength increases. However, cement dosage has a more significant influence on improving the unconfined compressive strength than the mixing method. With the increase of every 1% in cement dosage, the 7-day strength of conventional mixing and in vibratory mixing average increased by 59% and 38%, respectively. However, the maximum improvement rate of the UCS value is 20–56.7% when vibration acceleration increased from 0 to 1 g. Especially when cement dosage is high, the effect of vibratory mixing on improving strength is limited. Besides, vibratory mixing reduces the original cement dosage by over 1.6% with the qualified unconfined compressive strength at vibration acceleration of 2 g, which is recommended in construction practice.

An experimental study on evaluation of fiber Reinforced-Fly ash stabilized black cotton soil as a sustainable subgrade material

With population escalation and the reduction in availability of land, there is a growing demand for structures on weak or soft soils. Black cotton (BC) soil has been considered as a problematic soil because of high swelling potential. Pavements constructed on BC soil subgrade suffer from severe rutting and cracking on the pavement surface. With a focus on avoiding this type of failure in the BC soil, stabilization with reinforcement is preferred recently. The aim of the current work is to check the efficiency of Poly Vinyl Chloride (PVC) fiber reinforced-fly ash stabilized black cotton soil as a sustainable subgrade material. PVC fiber as reinforcing material and Fly ash as the admixture for stabilizing the BC soil is used. For minimizing the impact of fly ash on environment, use of waste products in construction work is inevitable and a sustainable solution.In the current research work, Black cotton soil from three different places of Odisha have been collected and treated with different percentage of fly ash and PVC fiber so as to improve different properties of soil. From the results it is found that there is an increase in Unconfined Compressive Strength (UCS) and California Bearing Ratio (CBR) values of the treated soil and the optimum value of fly ash is found to be 30% and PVC fiber to be 1.5%.