Unconfined Compressive Strength Of Samples Research Articles

Experimental study of the mechanical and thermal properties of metakaolin based geopolymer stabilized soil during low temperature curing

To address the challenges associated with significant thermal disturbance and carbon emissions resulting from the conventional stabilization of frozen soil using cement, geopolymer material is used to replace cement to stabilize frozen soil. The unconfined compressive strength (UCS) of the geopolymer stabilized soil was investigated in relation to the proportions of metakaolin (MK), calcium carbide slag (CCS), curing temperature, and curing age. Microscopic analysis was conducted to unveil the stabilized mechanism. The UCS, shear strength, thermal conductivity, hydration products and microstructure of geopolymer stabilized soil and cement soil were compared in parallel. A total of 240 experiments were conducted in this study. The outcomes indicate that the optimal content of MK and CCS is 10% and 6% respectively. The UCS of samples with the optimal content after 28d of curing at 20 °C, −2 °C, and − 10 °C are 3.783 MPa, 1.164 MPa, and 0.901 MPa respectively. The primary causes of the rise in UCS of the geopolymer stabilized soil are the production of amorphous calcium silicate hydrate and calcium aluminate hydrate gel as a result of the stimulation of MK based geopolymer with CCS. The UCS of the geopolymer stabilized soil decreases with a decrease in curing temperature. In frozen conditions, the expansion of ice crystals in the soil creates voids and promotes crack growth, leading to a decrease in the efficiency of geopolymerization reactions. After 28d of curing at room temperature and low temperature, the geopolymer stabilized soil with the optimal content exhibits higher UCS, failure strain, shear strength, cohesion, and internal friction angle compared to the cement soil. At all curing temperatures and ages, the geopolymer stabilized soil has a lower thermal conductivity than the cement soil. The geopolymer stabilized soil is less susceptible to low temperature curing than cement soil, demonstrating a larger amount of hydration products and a denser microstructure, according to experimental results from XRD and SEM. The results of this work offer a theoretical foundation for using geopolymer in place of cement to stabilize soils in permafrost regions.

Silica fume stabilized loess: Mechanical properties, microstructural evolution and environmental analysis

The stabilization of loess is gaining increasing attention due to some of its physical properties which are highly prone to trigger some geological hazards. Common stabilizers (lime, cement and fly ash) release a significant proportion of greenhouse gases during their production, so it is becoming increasingly important to find an environmentally friendly or industrial waste material to stabilize loess. Silica fume is one such industrial waste material that can be used as a stabilizer in the stabilization of loess foundations. In this work, the unconfined compression strength of samples with different silica fume contents was measured, suggested that silica fume remarkably improved the strength for the samples. Fourier Transform Infrared Spectroscopy (FTIR), X-ray diffraction (XRD), Scanning Electron Microscope (SEM), and energy-dispersive X-ray spectroscopy (EDXS) techniques were used to explore the microstructure and quantify the microstructural parameters through Image-Pro Plus (IPP) software to explain the variation in mechanical properties of samples with different silica fume content. The results indicated that the stabilization of the loess by silica fume consisted of both chemical and physical stabilization. Chemical stabilization was the reaction between silica fume and loess particles to produce C-S-H gels, while physical stabilization was the addition of silica fume which filled the pore volume and caused a variation in the shape and angle of the pores, thereby increasing the mechanical strength. The environmental impact of stabilizing 1 m3 of loess with a common stabilizer was studied by life cycle assessment (LCA) under similar unconfined compressed strength conditions, thus demonstrating the need to promote the use of silica fume in the loess foundation stabilization market.

Graphene stabilized loess: Mechanical properties, microstructural evolution and life cycle assessment

More attention has been paid to graphene as an emerging stabilizer due to its advanced mechanical properties. The aim of this work investigates the stabilizing and environmental performance of graphene as a loess stabilizer towards a cleaner treatment. The unconfined compression strength of samples with different graphene contents was measured, indicating that graphene significantly enhanced the strength of the loess. A series of microstructural techniques were used to explore the microstructure and thus explain the variation in mechanical properties of samples with different graphene content. The results show that the addition of graphene does not chemically react with the loess to produce new substances, but mainly produces physical stabilization of the loess structure. As the graphene content increases, the pore area in the sample decreases and the inter-aggregate pores tend to flatten out, which have a positive correlation with the increase in sample strength. This study also compares the results of graphene production by electrochemical exfoliation and chemical oxidation and found that graphene produced by chemical oxidation showed significant advantages in terms of greenhouse gas emissions and cumulative energy demand.

Study on Mechanical Characteristics and Failure Modes of Coal–Mudstone Combined Body with Prefabricated Crack

There are normally pre-existing cracks that can be observed in the coal seam and immediate roof that influences the stability of the rib spalling and the movement law of overlying strata. In this study, comprehensive research methods (e.g., theory analysis, experimental tests and numerical simulations) were adopted to reveal the mechanical characteristics, acoustic emission behaviors and failure modes of a coal–mudstone combined body with a single prefabricated non-penetrating crack. The results show that the influence of the crack angle on the elastic modulus of the coal–mudstone combined body samples was limited. With the increase in the crack angle, the unconfined compressive strength of samples decreased first and then increased in a V-shaped trend. In addition, the minimum unconfined compressive strength could be observed at a crack angle of 45°. Moreover, the number of acoustic emissions significantly increased with the process of continuous loading. In addition, the stress reduction zone could be observed in both ends of the prefabricated cracks at the initial stage of loading. The high- and low-stress zones were transformed with the process of continuous loading. Under an unconfined compression test, the failure models of the coal body part in the samples were mainly caused by shear failure, and only a few cracks occurred in the upper tip of the prefabricated cracks of the mudstone part. Therefore, airfoil cracks could be observed in the samples due to the strength difference of the coal mass and mudstone.

Effect of the Curing Time and Combination of Corncob (Zea Mays L.) Ash With Swelling Clay on Mechanical Properties of Soil in Forest Road

ABSTRACT Swelling soil such as clay soil is known as unsuitable material for forest transportation due to the high volume change and mechanical defects. The aim of this study was to investigate the effects of corncob ash as a biologic additive on mechanical properties of clayey soil in forest roads of Bahramnia forestry plan in Golestan province. Different content of corncob ash and curing time were the treatments of study. Corn wastes were collected from farmlands and nodes of corncob with high silica content were used to produce ash. Soil samples were collected from the road construction area to conduct testing. First set of soil samples without additives and second set contained 5%, 10%, 15%, and 20% of corncob ash. Atterberg limits, standard proctor, and unconfined compressive strength were carried out on 7, 14, and 28 days curing times. Findings showed that the plastic index decreased by increasing corncob ash to 5%. Adding ash up to 5% can cause dramatic increase in plastic index. Addition of ash to the soil decreased dry bulk density and increased optimum moisture content. Maximum dry density (1.73 g cm−3) was recorded in optimum moisture of 28.5% and ash content of 5%. Unconfined compressive strength of samples increased until adding 5% of ash, and then the compressive strength decreased by increasing the ash content. There wasn’t significant difference between the curing times of 14 and 28 days in mechanical properties of soil samples. It was concluded that ash content of 5% and curing time of 14 days were the optimum values which maximum improvements in mechanical properties of swelling clay soil are occurred.

The Influence of Nanosilica on Unconfined Compressive Strength of Frost-Susceptible Soil

In engineering practice there are numerous methods to improve the mechanical properties of subsoil. The paper presents the analysis of changes in the unconfined compressive strength of frost-susceptible soils stabilised with nanosilica (NS). Tests were conducted on samples of fine-grained soil at the maximum dry density (MDD) and optimum moisture content (OMC). Four variants of samples were prepared: soil without additive, soil with 1% NS, soil with 3% NS and soil with 5% NS. Due to the frost-susceptible character of the soil, tests were conducted on non-frozen samples and on samples subjected to ten cycles of freezing and thawing. Cyclic freezing and thawing of soil mixtures allowed for determination of the additive effectiveness in the temperature conditions encountered during the winter season. Based on the research results of unfrozen samples, it was determined that the addition of nanosilica leads to the increase in their unconfined compressive strength. On the other hand, the strength of pure soil samples after ten cycles of freezing and thawing decreased. This is a commonly known trend that results from the soil and soil mixtures freezing. However, in the same conditions, the unconfined compressive strength of samples stabilised with nanosilica demonstrated a significant increase with the increase of the additive content. The highest values were noted for samples stabilised with 5% addition of nanosilica. In order to explain the obtained results, further tests are required. However, the preliminary research has shown the effectiveness of nanosilica as an independent additive stabilising frost-susceptible soils, although it is not commonly used in engineering practice.

Effect of VOCs pollutants on strength of cemented soil

Based on the soil conservation project of a chemical plant in Zhenjiang, the effects of volatile organic compounds (VOCS) pollutants on the strength of cement soil were studied experimentally. Xylene was utilized for indoor experiment. The specimen was made of water, xylene solvent, gray yellow clay and 42.5 ordinary Portland cement in a certain proportion. Firstly, the influence of the content of xylene on the unconfined compressive strength of cemented soil with time was analyzed, and then the effect of cement blending ratio on the unconfined compressive strength of samples containing xylene was studied with the increase of time. The results showed that the unconfined compressive strength of cement-soil samples increase with the increase of time and decreased with the increase of xylene content in similar curing time; the same xylene incorporation and the unconfined compressive strength of cement soil samples increased with the increase of cement incorporation ratio. In addition, the author also verified the impact of VOCs pollutants on cement-soil retaining walls by simulating actual engineering, and proposed two solutions which were expected to advise the engineering.

Effect of Ca/Al Ratio on Stabilization/Solidification of Lead-Contaminated Soil by Ettringite

Ettringite is commonly used for the stabilization/solidification for heavy metal-contaminated soils, and its treatment effect will be influenced by Ca/Al mole ratio. Lead-contaminated soil samples were solidified using ettringite with different Ca/Al mole ratios. The pH value, unconfined compressive strength of solidified samples, and leaching concentration were investigated to understand the influence of Ca/Al mole ratio on properties of ettringite-solidified contaminated soils. The microstructural characteristics of solidified contaminated soils were also explored. The results show that lead leaching concentration decreases dramatically with increasing the content of lime and curing time. Lead concentration drops from 49.89 mg/L to 0.19 mg/L when Ca/Al mole ratio increases from 4 : 3 to 10 : 3 at 28 days and from 36.57 mg/L to near 0 mg/L at 90 days. In addition, the unconfined compressive strength of samples drops at first and then increases with the increase of Ca/Al mole ratio. Besides, the pH values of solidified soil and leachate rise with the increase of content of lime. The pH values of solidified soil increase from 9.68 to 11.34, and there is little difference between 28 days and 90 days. However, the pH values of leachate increase from 5.56 to 8.59 at 28 days, and 90-day pH values increase from 5.65 to 9.44. The results of SEM, XRD, and EDS tests also indicate that Ca/Al mole ratio affects the shape of ettringite, the stabilization/solidification effectiveness of contaminated soil, and the pore of solidified soil. When Ca/Al mole ratio equals to 8 : 3, ettringite content has a substantial increase, and lead leaching concentration is lower than 5 mg/L.

Mechanical Evaluation of Bottom Ash from Municipal Solid Waste Incineration Used in Roadbase

As a by-product from the incineration of municipal solid waste, bottom ash has a broad application prospect of resource utilization. In this study, bottom ash was selected as partial aggregate alternative and used as roadbase materials. The cemented aggregate containing bottom ash was evaluated through both experimental and numerical analysis. According to the results, the unconfined compressive strength of samples increases with the curing time, and the failure strain of sample decreases with the curing time. The unconfined compressive strength and failure strain of samples are influenced by the types of bottom ash. The increase of compressive strength with the curing time can be attributed to that the hydration reaction of cement will be more complete when the curing time is longer. The representative value (7 days) of unconfined compressive strength of samples meets the strength requirement (≥2.5 MPa) of the road subbase layer of heavy traffic highway in China. Subsequently, the surface settlement decreases with the increase of the modulus and thickness of roadbase and the distance from the centerline, while the settlement increases with vehicle load increasing. The modulus of the roadbase is not the main influences on the pavement settlement, under the condition that the strength of samples meets the requirements. However, increasing the thickness of roadbase can reduce the settlement at the center of the pavement effectively.

Research on pavement performance of mixed filler with alkaline residue-expansive soil

The expansive soil, a special clay, can cause crack, bulge, landslides and other accidents in the highway subgrade. To reduce the harm of expansive soil and realize the resource utilization of alkaline residue which is industrial solid waste, different ratio of alkaline residue and expansive soil with medium expansive potential are mixed as subgrade filling. A series of experiments are carried out for the pavement performance of the mixture. The results show that the swelling ratio of the mixture decreases significantly with the mixing rate. The longer the curing time is, the lower the swelling ratio will be. And the expansibility is completely eliminated in 28 days. The unconfined compressive strength(UCS) heightens with the growth of mixing rate, and when the mixing rate reaches 30%, the increasing level gradually stabilizes. Similarly, the curing time has an obvious effect on the unconfined compressive strength. After cured for 14 days, the UCS of samples is twice of that not cured. And the cohesion goes up in first stage, then decreases, and peaked as the mixing rate reaches to 30%. However, the internal friction angle changes little. The CBR increases with the increase of mixture ratio and the curing time. In addition, the mechanism of alkali residue modifying curing expansive soil is mainly based on the substitution effect of alkali residue, coagulation reaction and ion exchange of alkali residue - expansive soil.

Cement-Based and AC-Based Solidification/Stabilization Processes of Aliphatic Hydrocarbons Contaminated Soils in Kharg Island Oil Terminal

In this study, the efficiency of solidification and stabilization (S/S) processes of aliphatic hydrocarbons (AHs) contaminated soil in the Kharg island oil terminal was investigated using Portland cement and activated carbon (AC) and, thus, the best mix design was determined based on the pollution leaching and unconfined compressive strength. Regarding the unconfined compressive strength of samples with a curing time of 28 days, the compressive strength decreased with increasing the AC; also, the maximum unconfined compressive strength belonged to the sample contains of 25% cement, 1% AC (C25 AC1) and strength of 4441 kPa. The leaching test results through the toxicity characteristic leaching procedure method demonstrated that an increase in amount of AC leads to decrease in leaching of aliphatic compounds; however, the same trend was not perceived in the case of cement; indeed, the reduction of aliphatic compounds was not observed in all samples containing the increased amount of cement. The synergistic approach for cement and AC is needed to reach an ideal stabilization of AHs. Therefore, the amount of 25% cement and 3% AC (C25 AC3) was concluded as the best mix design of S/S for AHs contaminated soils.

Stabilization of problematic silty sands using microsilica and lime

In this study, to stabilize problematic silty sand soils, Microsilica-Lime admixture was used as an additive. Various samples containing 0, 1, 2, 5, 10 and 15% (by weight) Microsilica and 0, 1, 3 and 5% (by weight) Lime were prepared. To investigate the role of the studied additives on the stabilization of the sandy soils, unconfined compressive strength of the materials and their swelling potential, were considered. To do this, unconfined compressive strength test, California Bearing Ratio, also, swelling tests were carried out. As a result, the unconfined compressive strength of samples with 10% Microsilica and 3% Lime in curing time of 28 days was obtained about 50 times larger than the strength of the untreated samples. On the other hand, the samples stabilized only with 1% Lime showed considerable swelling potential while adding only 1% Microsilica caused a considerable reduce in the amount of swelling. Unconfined compressive strength of samples containing 1% Microsilica and 1% Lime was about 12 times larger than the strength of the untreated samples and these samples showed less swelling potential. Then, these amounts are considered as the optimal amounts, which are used in the road construction projects. Also, the results obtained from scanning the samples using electron microscope illustrated that the Microsilica causes to form crystalline micro-structures in the soil which is the main cause for increasing the strength of stabilized samples.

An Experiment for Effects of Different Additives on Strength of Sediment Solidification

The solidification method is a significant and resultful method for the disposal of dredged sediment. Solidified agents can be employed to improve the unconfined compressive strength (UCS) of sediment solidification. In this work, considering of economy and practicability, three kinds of optimized compound additives are selected and investigated on the effects of UCS of sediment solidification. 7d., 14d.and 28d. solidification stadium were taken to test the UCS of samples. Results showed that the activator had the best effect on increasing the UCS. The comparative tests also indicated that adding any kind of additive into the cement-based materials could improve the UCS of sediment solidification, the highest value of UCS was 11.02MPa (SCAHR). By means of scan electron microscope (SEM) technology, the microstructure images of the raw sample and solidified sample were obtained, which help to understand the development of UCS of the solidified sediments.

Effect of Static Soaking under Different Temperatures on the Lime Stabilized Gypseous Soil

This study concerns with the effect of long-term soaking on the unconfined compressive strength, loss in weight and gypsum dissolution of gypseous soil stabilized with (4%) lime, take into account the following variables: initial water content, water temperature, soaking duration.The results reveals that, the unconfined compressive strength was dropped, and the reduction in values was different according to the initial water content and water temperature, so that the reduction of the unconfined compressive strength of samples soaked in water at low temperatures (5° and 25° C) was greater than those soaked in water temperatures at (490 and 600 C). The results obtained shows that the increase in soaking period decreases the percentage amount of gypsum and loss in weight for all water temperatures and soaking durations.

Microstructural Development of Stabilized Fly Ash as Pavement Base Material

Microstructural, chemical, mineralogical, and thermal analysis was carried out in a study to use Eraring Power Station (New South Wales, Australia) fly ash as pavement base material. The fly ash was stabilized with cement and lime separately. The effects of cement and lime stabilization were examined in terms of chemical composition, crystalline structures, and hydration products. Unconfined compressive strength of samples was also measured to observe the effect of stabilization over time. The results obtained from cement and lime-stabilized samples showed that the hydration products that account for strength gain of the stabilized fly ash are almost the same for both types of stabilizing agents. The discrepancies between the resulting strengths are due to the proportion and density of these products.

Characterization of lime sludge for engineering applications

Chemical composition and engineering properties of 20 samples of lime sludge, produced from the lime calcining process, were determined in order to evaluate its potential applications as an engineering construction material. The results indicate that lime sludge is composed mainly of calcium (51.48%), silica (8.30%), and aluminum (3.24%). Iron, magnesium, and sulfur each make up less than 3% by weight, while zinc, chromium, selenium, lead, cadmium, barium, and silver collectively make up less than 0.01% of the total composition. The loss on ignition (LOI) is 34.4% by weight of the total composition. Engineering tests show that lime sludge can be considered as a uniformly-graded, nonplastic silt (ML) with an average liquid limit of 48, average natural water content of 90%, average maximum dry density of 64 pcf (1.03 Mg/m 3), average optimum water content of 50%, and an average friction angle of 27 degrees. The average permeability and unconfined compressive strength of samples compacted to at least 90% of maximum dry density are 2 × 10 −5 cm/sec and 38 psi (0.26 MPa), respectively. Because of its high natural water content, low density, and poor strength characteristics, lime sludge in its natural state is considered unsuitable for engineering construction. However, when lime sludge was mixed with varying percentages of a silty soil, it was found that the density of the admixtures increased and the permeability decreased with an increase in soil content. This suggests that lime sludge-soil admixtures may have potential for such engineering applications as daily landfill cover, hydraulic barriers, and structural fill material.