Increase In Unconfined Compressive Strength Research Articles

Analysis of Influencing Factors and Mechanism of Strength of Cement-Modified Silty Sand

The unconfined compressive strength of cement-modified silty sand in Jilin Province was investigated in this study. For this purpose, various tests were conducted, including the screening test, compaction test, CBR test, X-ray fluorescence detection, and unconfined compressive strength test. Effects of compaction degree, soil quality, water quality, cement content, and curing age were considered. The results show that CBR value is positively correlated with compactness. Two kinds of different water qualities have little effect on unconfined compressive strength of cement-improved soil; with the increase in cement content, the unconfined compressive strength increases, and the power function equation established by the two is significantly correlated. The logarithmic relationship between cement-soil strength and curing age is approximately linear. Through regression analysis, the comprehensive characterization parameters of cement-soil strength, such as water-cement ratio, cement content, and curing age, are put forward. The unconfined compressive strength of cement-modified silty sand has a good power function relationship with the comprehensive characterization parameters, and the fitting degree between the strength prediction formula and the existing research and test data exceeds 90%, which verifies the effectiveness of the comprehensive characterization parameters.

Undrained cyclic loading response of lignosulfonate treated high plastic clay

In this study, a non-traditional and environment friendly chemical stabilizer, lignosulfonate has been used to stabilize high plastic clay and its effectiveness has been investigated through a series of static and cyclic loading tests. Unconfined compression tests were conducted for various percentages of lignosulphonate contents (0.5, 0.75, 1.5, 2.0, 2.5 and 3.0%) by weight of dry soil at curing periods of 5, 10 and 21 days. Shear strength and deformation characteristics of stabilized specimens were examined, corresponding to optimum content of lignosulfonate at which unconfined compressive strength was maximum, for different confining pressures and cyclic stress levels under unconsolidated undrained conditions. Test results indicated a significant increase in unconfined compressive strength and shear strength under static loading; whereas, reduction in axial strains and rate of permanent strain development, and increased resilient modulus under cyclic loading. In addition, SEM analysis has also been conducted to understand the microstructural changes occurring in the soil due to addition of lignosulfonate.

The long-term performance of concrete amended with municipal sewage sludge incineration ash

Municipal sewage sludge incineration ash (MSSIA) is commonly used as a raw material in concrete, but few studies have focused on the long-term environmental tolerance of municipal sewage sludge incineration ash concrete (MSSIAC). In this study, acid rain leaching, salt erosion, and freezing–thawing tests were used to evaluate the long-term environmental behavior of the optimal MSSIAC formulation. One optimal MSSIAC formulation replaces 5% MSSIA, and results in a 7.2% increase in unconfined compressive strength (UCS), indicating that MSSIA-amended concrete can have enhanced UCS. Only Zn was released from the optimal MSSIAC formulations (replacing 5% or 10% MSSIA) in the acid rain leaching test, but only up to 0.071 mg Zn L−1, which was within the acceptable environmental range. No heavy metals were released at concentrations above the method detection limits in the salt erosion and freezing–thawing tests. The optimal MSSIAC formulations have excellent long-term environmental tolerance while meeting the requirement of UCS, and provide a valuable use for MSSIA.

The carbonation of a lime-treated soil: experimental approach

This paper presents an experimental study of the carbonation consequences on the macroscopic properties of a lime-treated silty soil. The classical cure in the lab confirms a slow increase in unconfined compressive strength (UCS) over time. Accelerated carbonation leads to a similar final value but the kinetic is different, showing a rapid increase of UCS then no further evolution with time. Samples stored outside also showed a rapid increase of the strength but the final UCS value is lower. Physico-chemical and microstructure analysis highlighted the rapid carbonation of Portlandite during carbonation. Carbonation was limited to the surface of the Portlandite nodules. In samples stored in lab, reaction of lime nodules with soil leads to formation of C–(A)–S–H gel. These two very different scenarios both led to a similar UCS increase, although at a different rate. On the contrary, samples stored outsides were shown to undergo carbonation of the C–(A)–S–H gel, hence explaining the lower increase in UCS.

Experimental Investigation on Small-Strain Dynamic Properties and Unconfined Compressive Strength of Gyeongju Compacted Bentonite for Nuclear Waste Repository

Gyeongju bentonite is a Ca-bentonite and a highly compacted buffer material primarily considered in Korea, as a part of an engineered barrier system (EBS) of high-level radioactive waste (HLW) repository. During the repository lifetime, the buffer material should guarantee the safe disposal of HLW against any external mechanical impact, including seismic activity. Therefore, the dynamic deformation properties of buffer material is crucial to validate its lifetime effectiveness and performance. Even though there are some researches to investigate the dynamic properties of the bentonite buffer, there has been no researches for the Korean bentonite buffer. For this reason, the paper aims to evaluate the dynamic properties at small-strain of Gyeongju bentonite and correlate the small-strain deformation properties with unconfined compressive strength using seismic and static laboratory tests. Three sets of compacted cylindrical bentonite specimens with varying dry densities (1.50 g/cm3 to 1.77 g/cm3) were produced using a cold isostatic pressing technique under three different pressing loads. Free-free resonant column (FFRC) tests and unconfined compressive (UC) tests were performed. The FFRC tests measured deformation properties at small strain, including unconstrained and constrained compression velocities, Young's modulus (Emax), constrained modulus (Max), material damping ratio (Dmin), and Poisson's ratio. The UC tests evaluated the compressive strength and secant modulus (E50) at large-strain. In this study, it was found that the deformation properties (Emax and Mmax) and unconfined compressive strength increase with the increase in a design rage of dry density. Poisson's ratio measured at constrained boundary yields relatively constant value close to 0.4 for specimens at a range of dry density higher than 1.5 g/cm3. In addition, it was found that the elastic moduli have an almost linear relationship with the unconfined compressive strength. Finally, empirical equations between elastic moduli and unconfined compressive strength for Gyeongju compacted bentonite are proposed for a Koeran design guideline.

Mechanical Properties and Microstructure of Fibre-Reinforced Clay Blended with By-Product Cementitious Materials

Clayey soils endure adverse changes in strength and volume due to seasonal changes in moisture content and temperature. It has been well recognised that high cement content has been successfully employed in improving the mechanical properties of clayey soils for geotechnical infrastructural purposes. However, the environmental setbacks regarding the use of high cement content in soil reinforcement have necessitated the need for a greener soil reinforcement technique by incorporating industrial by-product materials and synthetic fibres with a reduced amount of cement content in soil-cement mixtures. Therefore, this study presents an experimental study to investigate the mechanical performance of polypropylene and glass fibre-reinforced cement-clay mixtures blended with ground granulated blast slag (GGBS), lime and micro silica for different mix compositions and curing conditions. The unconfined compressive strength, linear expansion and microstructural analysis of the reinforced soils have been studied. The results show that an increase in polypropylene and glass fibre contents caused an increase in unconfined compressive strength but brought on the reduction of linear expansion of the investigated clay from 7.92% to 0.2% at fibre content up to 0.8% for cement-clay mixture reinforced with 5% Portland cement (PC). The use of 0.4–0.8% polypropylene and glass fibre contents in reinforcing cement-clay mixture at 5% cement content causes an increase in unconfined compressive strength (UCS) values above the minimum UCS target value according to American Society for Testing and Materials (ASTM) 4609 after 7 and 14 days curing at 20 °C to 50 °C temperature. Therefore, this new clean production of fibre-reinforced cement-clay mixture blended with industrial by-product materials has great potential for a wide range of applications in subgrade reinforcement.

Mechanical behavior of Vinh Long soil mixed with cement

Recently, deep soil mixing has been constructed in Vietnam. However, the researchers applying this solution to reinforce soft ground with geological conditions of Vinh Long are not common. This paper concentrates on study of mechanics of soil samples which are compatile with Vinh Long geological conditions. Experiments on unconfined compressive strength were performed to analyze mechanical behaviors in the duration of curing samples. Soils taken from two layer of researching area were mixed with cement with the content from 150 kg/m3 to 250 kg/m3, then were curing in duration of 7 days, 14 days, 28 days and 60 days. Results of tests at specified timeline show that unconfined compressive strength of most mixing samples increases with the cement content and curing period. The secant modulus of elasticity is determined from the deformation resistance test, then the loading capacity of samples can be deduced. The secant modulus of elasticity increases when the unconfined compressive strength increases. This article is a valuable reference in the design of cement-reinforced soft soil for application in infrastructure engineering.

Influence of in-house produced biochar on geotechnical properties of expansive clay

The current study aims to explore geotechnical properties of expansive soil amended with in-house produced biochar. Biochar was produced in-house using slow pyrolysis (at constant temperature of 500 °C) of commonly available Prosospis Juliflora (invasive weed) in a muffle furnace. This study also motivates alternative use of Prosospis Juliflora, whose reduction can help to minimize transmission of malaria and also threat to bio-diversity. The biochar was uniformly mixed with expansive black cotton soil at 5% and 10% content. Both basic and geotechnical properties (CBR and unconfined compressive strength) was determined for modified and unmodified soil samples. Based on results, it can be concluded that the plasticity index of an expansive soil is reduced significantly with an increase in biochar content. On the other hand, change in shrinkage limit was negligible. There is an increase in unconfined compressive strength and also reduction in free swell index of expansive soil amended with biochar. This is despite the significantly lower specific gravity and higher porous structure of biochar particles. The result is contrary to application of biochar in sandy soils in literature. The possible mechanism could be due to formation of bonds between negatively charged surface functional groups of biochar and positively charged ions of an expansive soil.

Durability and strength improvement of clayshale using various stabilized materials

In Indonesia, the study of clayshale has begun to be widely discussed. Clayshale is well known as a degradable material. The process of degradability in clayshale shows the weakening of the shear strength. This clayshale characteristic leads to several failures in the geotechnical design. To avoid degradability, soil stabilization testing was carried out by using cement, lime and rice husk ash. In the soil stabilization study, the use of cement and lime is already common and effective for some type of problematic soil, but the cost of material production is expensive and not environmentally friendly. Rice husk ash as agricultural waste material has the potential as a stabilizing material because it is availability and reaction ability with lime as known pozzolanic reaction. From the test results, each mixture has different response and potency. Cement has better resistance to wetting and drying with a significant increase in unconfined compressive strength. Whereas the lime itself did not significantly increase durability and unconfined compressive strength, but the effect of rice husk ash to the soil-lime mixture increasing durability despite the reduction in unconfined compressive strength.

Freeze-thaw performance of a cement-treated expansive soil

This experimental study presents an attempt on the effect of cement addition to expansive soil on its deformation and strength behaviours when subjected to freezing–thawing (F–T) action. A series of laboratory tests on cemented-treated expansive clay samples after 28–d curing periods were conducted. The experimental program involved freezing–thawing test, volume measurement, and unconfined compression test. The effects were evaluated by focusing on the water loss, volume change, stress-strain response, unconfined compression strength, resilient modulus and strain at failure after a sequence of freeze–thaw cycles. Eight groups of expansive soil samples were prepared with four different cement contents (i.e. 0%, 3%, 5% and 7% by weight of soil) and subjected to 0, 1, 2, 3, 5, 7, 9, and 12 F–T cycles, respectively. The analysis of experimental results indicated that: 1) Cement additive makes expansive soil become less sensitive to moisture and cement–induced hydration reaction will reduce swelling–shrinkage characteristics triggered by F–T cycles; 2) The inclusion of cement within expansive soil causes an increase in unconfined compressive strength, resilient modulus, but a decrease in strain at failure. However, such effect induced by cement will be diluted by F–T cycles; 3) Cement can retard the degradation of resilient modulus but increase a faster strength reduction against F–T weathering. 4) Upon F–T cycles, un–cemented expansive soil will become more brittle, while cement-treated soils more ductile before 1st F-T cycle. A power function, independent of F–T cycles and cement contents, exists between the strain at failure and UCS. The results obtained from the study are fairly promising to employ cement additive against freeze–thaw resistance of expansive soils.

Investigating the Properties of Foamed Mixture Lightweight Soil Mixed with Bauxite Tailings as Filler

To make better use of large amounts of discarded bauxite tailings (BTs), a foamed mixture lightweight soil mixed with BTs as filler (FMLSB) was proposed. Using the orthogonal experimental design method, the effects of various contents of cement, BTs, and foam on the fluidity, wet density, unconfined compressive strength, water absorption, and microstructure of FMLSB were studied. The experimental results indicate that the wet density and unconfined compressive strength increase as the contents of cement and BTs increase but decrease as the foam content increases. Water absorption increases with the reduction of the wet density, but the unconfined compressive strength exponentially increases as the wet density increases. With an increase in the contents of cement and BTs and a decrease in the foam content, fewer pores are present, and the pores are not connected with each other. The results of the range analysis show that the main factor affecting the wet density and unconfined compressive strength of the FMLSB is the foam content, followed by the cement content, and meanwhile, BTs can maintain the lightweight and high strength of FMLSB. Based on the intended engineering applications and standard specifications, the optimum composition of the FMLSB mixture is proposed. Overall, the results indicate that BTs have the potential to be used as filler to produce FMLSB and that applications of FMLSB will lead to great economic and environmental benefits in engineering construction.

Access the Suitability of Local Soil and Demolishing Waste for Rammed Earth

Rammed earth is an ancient building technique used in many regions of the world using natural raw materials such as earth, chalk, lime or gravel. It is a monolithic construction and the process involves compact the soil in progressive layers in a rigid formwork. The paper focusing on the use of locally available material which are not energy intensive. Also demolishing waste and flyash is used to replace the natural sand. The properties of cement stabilized rammed earth was studied in terms of density and strength. The effect of varying percentage of demolishing waste, flyash and their effect to increase of unconfined compressive strength is studied. The rammed samples were made and stabilised with cement at fix percentages of cement as 8 %. Based on the results of this study and from the earlier investigations it is clear that the clay content predominantly in non swelling soil is an important parameter of rammed earth to improve bond strength. Also the presence of courser material such as gravel and sand is play an important role in strength gaining is noted.

Research on Strength and Microstructure Characteristics of Cement Solidified Cadmium Contaminated Expansive Soil

Depending on the laboratory test of consolidation expansive soil polluted by heavy metal Cd, we can use cement to cure expansive soil artificially polluted by cadmium nitrate in different concentration. The paper discussed how the heavy metal concentration, cement dosage and curing age influence the unconfined compressive strength by solidified expansive soil polluted by heavy metal and micro-structure properties were tested. The study results show that, as the curing age and cement concentration increases, the unconfined compressive strength increases; as the concentration of heavy metal increases, the unconfined compressive strength decreases; the effect of heavy metal concentration on strength is different, the effect of high concentration on strength is greater than the effect of low concentration; Through the change rules of the micro-structure characteristics, the results on micro-structure analyzing show that the reason of strength increases is the porosity decreases after adding cement.

Development of Alternative Stabilization Methods for Transportation Infrastructure Based on Geopolymers

Current soil stabilization methods are often limited by durability and leaching issues and do not always offer sustainable treatments. This research explores the use of geopolymers to stabilize clays in the North Texas area. In recent years, geopolymer has received much attention as an eco-friendly and sustainable alternative to conventional chemical additives, since it can be processed at room temperature from aqueous solutions by utilizing waste materials and/or abounded natural sources. Two subgrade soils from North Texas were treated with GP mix at a ratio of 8 wt% dry GP to dry soil. GP is shown to reduce swelling and shrinkage potential of soil considerably while an increase in unconfined compressive strength is observed as well. Therefore, further studies are recommended to understand the mechanism of GP and soil bonding resulting in said changes.

EXPERIMENTAL STUDY ON UNCONFINED COMPRESSIVE STRENGTH OF SOIL AND EPS PARTICLES MIXTURES

This paper aims to study the density, strength and deformation characteristics of soil and EPS particles mixtures that is a type of light weight soil. It carried out the density tests and unconfined compressive strength tests of the mixed soil with different cement content, EPS content, age and water content. The results show the following findings. When volume ratio of EPS particals is 20% to 60%, the density range of the light weight soil is about 0.64g·cm-3~1.46g·cm-3. The amount of EPS particles has the greatest impact on the light weight soil density. When the volume rate of EPS particles is increased by 10%, the density of EPS particles light weight soil is decreased by about 0.15g·cm-3~0.23g·cm-3, which shows that it is feasible to realize the light weight of mixed soil by adding EPS particles. Cement content and water content have less influence on density of light weight soil. But age has little effect on density of light weight soil. In addition, when the volume ratio of EPS is 50%, the density of light weight soil is similar to that of water. The range of unconfined compressive strength of EPS particles light weight soil in this test is 103.2 kPa~1359.0 kPa, while the unconfined compressive strength of plain soil is 79.98 kPa. So it can be stated that the light soil in the proportioning of this test has better strength properties relative to the plain soil. The unconfined compressive strength of light weight soil increases exponentially with the increase of cement content. However, the larger the volume ratio of EPS particles, the smaller the unconfined compressive strength and the linear relationship between them. In the case of more than the optimal water content, with the increase of water content, the relationship between the unconfined compressive strength is reduced exponentially. The increase of age makes the unconfined compressive strength increase in hyperbolic form. The stress-strain relationship characteristics of EPS particles light weight soil are mainly characterized by strain softening type. However, the increase of water content and the increase of the content of EPS particles can make the stress-strain relationship curves of the light weight soil change gradually to the hardening type. Damage strain and average deformation model are used to describe the deformation characteristics of soil. The damage strain of light weight soil decreases with the increase of cement content, but the volume ratio of EPS particle is opposite. The greater the water content, the greater the damage strain of light weight soil. However, the increase of the age makes the damage strain of the sample decrease. When the volume ratio of EPS particles is more than 50%, the damage strain of light weight soil is greatly increased, and its brittleness is obviously weakened. The average deformation modulus is a parameter to characterize the stiffness of EPS particles light weight soil. The larger the cement content, the larger the average deformation modulus of light weight soil. However, the average deformation modulus of light weight soil decreases linearly with the increase of the volume ratio of EPS particles. The increase of water content can reduce the stiffness of light weight soil, and the longer the age, the greater the stiffness.

Laboratory Investigation of the Effect of Nano-Silica on Unconfined Compressive Strength and Frost Heaving Characteristics of Silty Clay

In order to investigate the effect of nano-silica on the unconfined compressive strength and frost heaving characteristics of silty clay, a series of indoor tests of unconfined compressive strength, frost heaving, and mercury intrusion porosimetry (MIP) was done on silty clay with different nano-silica content. The unconfined compressive strength of silty clay increased with increases in nano-silica content, and increased by 6.65 times when the nano-silica content was 5.0%. However, the frost heaving displacement decreased with increases in the nano-silica content. The results of MIP tests illustrated that the volume and number of large pores decreased, and the volume and numbers of small pores increased with increases in the nano-silica content. An increase in the nano-silica content increased the porosity and decreased the average pore diameter. The formation of viscous gel by addition of nano-silica into silty clay enhanced the bonding and filled the gaps between particles of silty clay and blocked the migration of water in the soil. The microscopic pore structure of the sample was generally uniform with increasing nano-silica content, which resulted in an increase in unconfined compressive strength and a decrease in frost heaving displacement.

Study on Unconfined Compressive Strength of High Volume Cement Stabilized Macadam

This paper mainly studies the effects of different cement content (5%, 7%, 9%, 11%, 13%, 15%) on the unconfined compressive strength of cement stabilized macadam base materials. The effects of different cement content on the compressive properties of the mixture were compared by unconfined compressive strength test analysis. The results show that the influence of cement content on the early strength of the road base layer is greater than the impact on the later strength. When the age is 1 day, the cement content increases from 9% to 11%, and the unconfined compressive strength increase rate of the test piece is the largest (35.93%).

Chemical Stability and Leaching Behavior of One-Part Geopolymer from Soil and Coal Fly Ash Mixtures

Aluminosilicate minerals have become an important resource for an emerging sustainable material for construction known as geopolymer. Geopolymer, an alkali-activated material, is becoming an attractive alternative to Portland cement because of its lower carbon footprint and embodied energy. However, the synthesis process requires typically a two-part system for alkali activation wherein the solid geopolymer precursor is mixed with aqueous alkali solutions. These alkali activators are corrosive and may be difficult to handle in the field-scale application. In this study, a one-part geopolymer in which coal fly ash was mixed with solid alkali activators such as sodium hydroxide and sodium silicate to form a powdery cementitious binder was developed. This binder mixed with soil only requires water to form the soil-fly ash (SO-CFA) geopolymer cement, which can be used as stabilized soil for backfill/foundation. This geopolymer product was then evaluated for chemical stability by immersing the material with 5% by weight of sulfuric acid solution for 28 days. Indication suggests that the geopolymer exhibited high resistance against acid attack with an observed increase of unconfined compressive strength even when the immersion time in acidic solution was increased to 56 days. The mineralogical phase, microstructure, and morphology of the material were characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, and scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDX), respectively. Results not only confirmed the formation of gypsum due to acid attack but also indicated the dissolution of anorthite and albite that may have caused the microstructure to be composed of sodium aluminosilicate hydrate (N–A–S–H) and calcium (alumino) silicate hydrate (C(–A)–S–H) with poly(ferro-sialate-siloxo) and poly(ferro-sialate-disiloxo) networks. A column leaching test with deionized water was also performed on the soil-fly ash geopolymer to study the leachability of metals in the material. Results showed that arsenic exhibits higher mobility in the geopolymer as compared to that of cadmium, chromium, and lead.

Predicting the Effective Depth of Soil Stabilization for Marine Clay Treated by Biomass Silica

Reclamation and development towards the oceanic area had become a trend of modern days, where the marine soil need to be treated prior construction. The increase in unconfined compressive strength of marine clay treated by Biomass Silica, ‘SH-85’ has been demonstrated by several investigations. This paper studies the stress-strain behavior of marine clay treated with 12% of SH-85 with different curing periods and confining pressures. The results show that the strength parameters of the stabilized soil are greatly improved during the early stage of the curing period under higher confining pressures. In addition, the XRD analysis and microstructure study confirm the appearance of a new reflection peak at 29° in the treated soils indicating the formation of Calcium Silicate Hydrate (CSH). The curing period of 7 days at a confining pressure of 400 kPa was found to be an optimum combination for in situ stabilization. The effective stabilization depth predicted at each location can be defined as the depth ensuing the mentioned confining pressure. The approach of this research can be applied in construction activities associated with marine clay to help engineers in risk assessment, feasibility study and planning of the developments.

Coal Fly Ash–Carbide Lime Admixtures as an Alternative to Concrete Masonry Blocks: Influence of Ash Grounds

AbstractCompacted blocks of coal fly ash and carbide lime (two industrial by-products) have a great potential as building products. This admixture can be used as an alternative to weight-bearing or nonstructural concrete masonry blocks due to the pozzolanic reactions occurring between silica and/or alumina in amorphous phases (found in the fly ash) and Ca++ (existent in carbide lime) in an alkaline environment. However, pozzolanic reactions are notoriously slow at ambient temperatures, requiring long curing periods to achieve the necessary strength for certain applications. Therefore, this study aims to verify the influence of coal fly ash ground towards the increase of unconfined compressive strength (qu) in fly ash–carbide lime blends. Results have shown that the ash grounds allowed an increase in qu for coal fly ash–carbide lime admixtures. It was found that coal fly ash ground for a short period of time (up to 2 h) increases the specific area of the fly ash grains by about 50%, while the strength at a...