Free Expansion Rate Research Articles

Experimental Study on Modification of Grouting Material for Joints of Prefabricated Buildings

In order to apply grouting material to the joints of fabricated buildings and make it meet the performance demands of low shrinkage, strong bond, and high toughness of joint materials for prefabricated buildings, the expansion agent (EA), neoprene latex (NL), and rubber particles (RP) were used to modify the grouting material, and the effects of different dosages of the three components on the working performance, mechanical properties, and expansion or shrinkage properties of the grouting material were investigated. The results show that the EA decreases the flexural strength-to-compressive strength ratio (FCR) of the grouting material and enhances the vertical expansion rate and bond strength. The dosage of EA and the curing conditions have a significant effect on the expansion rate of the hardened grouting material. The grouting material can still maintain its 0.0022% free expansion rate with a 7% EA dosage at 120 d. The NL significantly inhibits the vertical expansion of the fresh mortar but inhibits the drying shrinkage of the grouting material after hardening, improves the FCR and bond strength; the 7 d bond strength under a 5% NL dosage can reach 4.27 MPa. The RP inhibits the vertical expansion of the fresh mortar and the drying shrinkage after mortar hardening; with the increase of its dosage, the bond strength of the grouting material increases first and then decreases, the 28 d FCS of the grouting material peaked at 0.173 at 10% dosage.

Influence of Different Industrial Waste Residues on Engineering Properties of High Liquid Limit Soil and Its Microscopic Mechanism

High liquid limit soil has unfavorable engineering geological characteristics, such as strong disintegration, dry shrinkage and easy cracking, and easy uplift when encountering water, which will cause various problems to the engineering. At present, the relationship between the physical and mechanical properties of high liquid limit soil and the characteristics of water-soil interaction is still not clear enough. In this study, the high liquid limit soil of Zhanjiang Avenue was selected to explore the influence of different ratios of three kinds of industrial waste residues (blast furnace slag, carbide slag, and tailing sand) on the high liquid limit soil. Aiming at the common adverse engineering geological phenomena of high liquid limit soil, such as easy disintegration, dry shrinkage crack, and easy uplift in water, the effects of different industrial waste residues on the water-soil interaction characteristics of high liquid limit soil are explored through disintegration and crack tests. In addition, the effects of different kinds and ratios on the free expansion rate, pH, unconfined compressive strength, and shear strength parameters of high liquid limit soil were studied. The improvement mechanism of different industrial waste residues on the engineering properties of high liquid limit soil is discussed in terms of mineral composition and microstructure. Based on the experimental results of this study and considering the cost and engineering practice, it is suggested that the modified carbide slag optimal ratio of high liquid limit soil of Zhanjiang Avenue is 8%. The results can provide certain guidance for the improvement and application of different industrial waste residues on high liquid limit soil to achieve the effect of sustainable development.

Weak Expansive Soil Physical Properties Modification by Means of a Cement-Jute Fiber

Sixteen groups of comprehensive tests have been conducted to investigate the modifications in the physical properties of a weak expansive soil due to the addition of a cement jute fiber. The tests have been conducted to analyze the liquid plastic limit, the particle distribution and the free expansion rate. The results show that: (1) With an increase in the cement-jute fiber content, the free expansion rate of the modified expansive soil gradually decreases, however, such a rate rebounds when the fiber content exceeds 0.5% and the cement content exceeds 6%. (2) With an increase in the cement percentage, the particle unevenness coefficient (Cu) and curvature coeffi- cient (Cc) of the modified expansive soil tend to grow gradually. The Cc coefficient reaches 1.0 when the cement content is 6%. The unevenness coefficient of 16 soil samples is greater than 5.0, however, the Cu coefficient decreases when the cement content reaches 6%. (3) The plastic limit of soil increases as the cement content is made higher, while the liquid limit and plastic index decrease gradually. When the content of the modified material is 2% + 0.1%~2% + 0.7% (Cement content + jute fiber content), the change of particle size distribution is most obvious. (4) When the contents of cement and jute fiber are is 6% and 0.5%, respectively, the modification induced in the physical properties of soil samples corresponds to the best case.

Study on Expansion Characteristics and Expansion Potential of Gypsum Rock

In this study, the relationship between four expansion indices and the expansion potential of gypsum rock was studied; on this basis, a criterion for judging expansion potential is established for gypsum rock. The results show that the free expansion rate is unsuitable for grading gypsum rocks’ expansion potential. Setting the gypsum rock in the Wuzhishan tunnel as the research subject, the ultimate expansion rate is 24.28% on the 7th day and 34.08% on the 30th day; the ultimate expansion rate on the 7th day of the indoor rock sample can be estimated by the fitting formula on the 30th day, the ultimate expansion force is 304.51 kPa, and the BET-specific surface area is 6.31 m2/g. The ultimate expansion ratio and BET-specific surface area have an excellent linear relationship with the ultimate expansion force. Setting the ultimate expansion force, ultimate expansion ratio and BET-specific surface area as the standard, the criterion for judging the expansion potential of gypsum rock is determined, which is more convenient and accurate than existing standards. The standard in this paper can predict the potential disasters that may occur in underground engineering.

Effects of the Layer Charge Location and Interlayer Cation on Rectorite Swelling Properties: Comparison between Molecular Dynamics Simulations and Experiments

Understanding the swelling properties of clay minerals is of great significance to environmental science and engineering applications, including environmental remediation, oil and gas wellbore collapse, geological disasters, and commercial additives. The vast majority of experimental and molecular simulation studies have mainly focused on pure clays. However, 70% of clays are mixed-layer clays (MLCs), and the most frequent MLCs is illite-montmorillonite (I-MMT). In this research, grand canonical Monte Carlo and molecular dynamics simulations were used to study the effects of the layer charge location (tetrahedral and octahedral substitution), interlayer cation type (Na+, Cs+, and Ca2+), and water contents on the swelling and hydration properties of rectorite (R1 type I-MMT) and compared with the experimentally measured basal spacing by water vapor adsorption and X-ray diffraction. It turned out that the free swelling ratio was positively correlated with water contents. The order of the three cations’ free expansion rate was Na+, Ca2+, and Cs+. The swelling process of rectorite (REC) was revealed from porosity changing with water contents. The surface of tetrahedral substitution (T-substitution) clay was more likely to bind to interlayer cations to form an inner-sphere surface complex (ISSC), the number of fully hydrated cations of the T-substitution clay was less than that of octahedral substitution (O-substitution), and REC was more swelling in O-substitution, which was supported by the basal spacing, atomic density distribution, and radial distribution function. The cation radius, the hydration energy, and the preference of the inner/outer-sphere surface complex (ISSC/OSSC) all affected REC swelling. Because of the presence of asymmetric charges in the REC layer, interlayer cations tended to distribute on the surface of illite and formed an ISSC when they formed 1-, 2-, and 3-layer (1, 2, and 3 W) hydrate states. When the layer charge density of illite and Mmt was constant, only the layer charge position in Mmt was changed, and the REC swelling behavior was transformed into pure Mmt. The interlayer cations and the layer charge location significantly impacted the REC swelling.

The Effects of Salt-Lake Salt Solution on the Strength of Expansive Soil

Expansive soils are widely distributed and often cause serious damage to structures. Hanzhong expansive soil and Yulin salt-lake solution were adopted to investigate the effect of salt-lake salt solution on the strength of expansive soil. Expansive soils modified with salt-lake salt solutions with different concentrations (0.1, 0.5, and 1.0 mol/L) were evaluated by X-ray diffraction (XRD), Atterberg limit, free swelling, no load swelling ratio, and triaxial compression tests. The improved expansive soil research using salt-lake salt solution was carried out based on the macroscopic mechanical characteristics. Test results showed that the addition of salt-lake solution effectively inhibited the expansibility of soil. With the increase of the concentration of salt-lake solution, liquid limit, plastic limit, plastic index, free expansion rate, no load swelling, cohesion, and internal friction angle of expansive soil were decreased in varying degrees, and stress-strain relationship curve gradually showed strain softening trend. The reason for the above results was believed to be that salt-lake salt solution reduced the force between particles on shear surface and reduced mutual hindrance.

Insights to compressive strength, impermeability and microstructure of micro-expansion steel slag cement under constraint conditions

This work aims at evaluating the influence of steel slag as partial replacement of cement on the mechanical properties and impermeability of cement-based materials under constraint conditions. The results show that, compared with the raw steel slag, the setting time of the wet-grinding steel slag system is shortened, and the free expansion rate is increased. When the wet-grinding steel slag content is 10%, the compressive strength of the specimen (constraint) after 28 days of curing is the highest, reaching 68.5 MPa, which is 9.3% higher than that of the free curing specimen, and the impermeability is also the best. Under the constraint conditions, the expansion strain produced by steel slag leads to the compact sample structure and reduced porosity, which is conducive to the mechanical properties and compactness of the pore structure of cement paste.

A novel expansive soil hardener: performance and mechanism of immersion stability.

Aiming at the existing problems of poor treatment effect and immersion stability of expansive soils, a slag soil hardener (SSH, developed by Wuhan University, China) was combined with different additives to dispose in this study. The free expansion rate, compressive strength, and immersion stability of samples were compared, and the influences of different additives, curing age, and dry density on the process and mechanism of improvement were discussed. The experimental results indicated that SSH combined with quicklime had the best improvement effect on expansive soils, in which the mass ratio of raw materials was: expansive soil/SSH/quicklime = 92/4/4, and the free expansion rate decreased from 45.90% to 4.4%, compressive strength increased from 2.53 MPa to 6.69 MPa, and there was no splitting after immersion under this ratio. FTIR spectroscopy, XPS and SEM were performed to analyze the characteristic functional groups, structural forms, and morphology of samples to study the mechanism of improvement, which showed that SSH greatly reduced the proportion of montmorillonite in the whole system and further enhanced the mechanism of ion exchange, soil particle connection, and coating protection. The research can provide theoretical reference for engineering the application of expansive soil area in rainy climate and has dual economic and environmental benefits.

Experimental Study on Physical-Mechanical Properties of Expansive Soil Improved by Multiple Admixtures

The treatment of expansive soil is always a difficult problem in engineering. Using coal gangue, fly ash, and other solid waste to treat expansive soil has gradually become a new way of energy saving and environmental protection. Most of the existing studies focus on using one or two kinds of admixtures to improve expansive soil, but there are few studies on improving expansive soil with multiple admixtures. In this paper, the expansion and shrinkage deformation and strength characteristics of expansive soil modified by coal gangue, fly ash, and lime are studied experimentally. Nine groups of different mixing schemes were designed through orthogonal tests, and the physical and mechanical properties of the improved expansive soil under different mixing ratios were tested. The sensitivity analysis of the test results was carried out to study the effect of each admixture on the improved expansive soil under different mixing ratios, and the optimal mix ratio under different conditions was obtained. The optimal mix ratio is 8% for coal gangue, 11% for fly ash, and 6% for lime. Further scanning electron microscopy (SEM) tests were carried out to analyze the microstructure of the improved expansive soil and explore the improvement mechanism of the multiadmixture. The results show that the optimal moisture content and the maximum dry density of the expansive soil with ash are decreased, and the properties of liquid plastic limit, free expansion rate, shear strength, and unconfined compressive strength of the expansive soil are improved obviously. Through the analysis of the comprehensive balance method, it is found that the content of lime has the greatest influence on the improvement effect of expansive soil, followed by that of coal gangue, and the least is that of fly ash. SEM structure analysis reveals that the particles of improved expansive soil are mainly aggregates, the soil structure is dense, particle agglomeration increases, and the overall structure is stronger. The research results can provide reference for the improvement of expansive soil with various admixtures and the resource utilization of coal gangue, fly ash, and other solid wastes.

Strength and Expansion and Deformation Characteristics of Modified Expansive Soil by Octadecylamine

Octadecylamine was used as a primary water repellent and mixed into the remodeled expansive soil, and modified expansive soils with different water contents and octadecylamine contents were configured. The water repellency level of the modified expansive soil was determined by the drip penetration time method, the corresponding free, unloaded, and loaded swelling rate tests were carried out, and the law of the influence of octadecylamine content and water content on the expansion and deformation of expansive soil was obtained. It can be shown that the modified expansive soil with an octadecylamine content of 0.8% (mass fraction) had an extreme water repellent grade, and the water repellency remained stable. The more the water content and octadecylamine content, the lower the free swelling rate, and the unloaded swelling rate and loaded swelling rate of modified expansive soil tended to be stable. When the octadecylamine content was 0.5% and 0.8%, the free expansion rate was significantly reduced, and the maximum drop was 42%. When the octadecylamine content was increased from 0% to 0.8%, the uncharged expansion stability duration was shortened from 97 h to 47 h, and the expansion rate was reduced from 12.9% to 9.4%. When the mass fraction of octadecylamine was 0.8%, the modified expansive soil with a water content of 20% would decrease its load expansion rate from 2.14% at 50 kPa to 0.01% at 400 kPa. When the load was small, the octadecylamine content and initial water content had a greater impact on the loaded expansion rate; when the load was large, the load became the main factor affecting the loaded expansion rate. Under the same overburden pressure, the more the octadecylamine content was, the lower the soil shear strength was and the more it tended to be stable.

Preliminary study on microbially modified expansive soil of embankment

The improvement of expansive soils has crucial academic research significance and engineering application value. The regular practice using chemical improvement methods may be helpful to improve the expansive soil; however, at the cost of inconvenient material acquisition, troublesome mixing methods, expensive construction, and polluting the soil environment. To this end, based on the microbial induced calcium carbonate precipitation (MICP) technology, we carry out a series of soil modification tests on the expansive soil for the roadbed filling in Nanning, Guangxi. Considering the problematic behaviors of the expansive soil and its significant adverse effect on engineering, this paper focuses on the soil improvement; particularly, we aim to study the improved soil's physical properties, limit moisture content and swelling and shrinkage rates under the action of dry and wet cycles. It is found that the swelling index of the improved expansive soil has been decreased significantly, the free expansion rate drops to 14.9%, such that the samples fall into the category of non-expansive soil. The liquid limit and plastic limit of soil samples decreased to 47.2% and 20.4%, respectively, after 6 times of microbial treatment. Moreover, after several high-pressure consolidation tests under dry-wet cycle conditions, the hydrophilic capacity of the improved expansive soil is significantly weakened, and its corresponding water absorption induced swelling rate and drainage-induced shrinkage rate are significantly reduced. The above research results show that it is feasible to use the MICP technology to improve the swelling and shrinkage characteristics of the expansive soil; in particular, after six treatments with the microbial solution, all indices of the expansive soil achieve the best improvement effect.

Effect of freeze-thaw cycles on the physical and dynamic characteristic of modified Na-bentonite by KCl

The method of electrokinetic ion-exchange–modified bentonite can not only shorten the test period but also improve the efficiency of cation exchange. In this study, the X-ray fluorescence spectroscopy test, freeze-thaw (FT) cycle test, CT scan test, and dynamic triaxial test were performed on bentonite before and after modification. The results showed that cation exchange occurred between the bentonite layers and the free expansion rate was significantly reduced. With the increase in the number of FT cycles, the Na-bentonite samples did not change significantly, while the K-bentonite gradually appeared cracks, and the cracks developed significantly as the number of FT cycles increased. The FT cycles had a significant impact on the dynamic parameters of two bentonites, especially the first two FT cycles. When the strain was constant, the dynamic shear modulus of the two bentonites decreased first and then increased with the increase of the number of FT cycles, and then tended to be stable. The damping ratios of the two bentonites showed the opposite trend: the damping ratio of the Na-bentonite increased first and then decreased with the increase of the FT cycles, and the K-bentonite first decreased, then increased and then stabilized, indicating that the structure of K-bentonite was more stable. By comparison, it was found that the effects of FT cycles on the dynamic parameters of K-bentonite were smaller than those of Na-bentonite.

Strength and Microfabric of Expansive Soil Improved with Rice Husk Ash and Lime

Expansive soil has harmful effect on engineering. Rice husk ash (RHA) has high pozzolanic activity, so it can form new cementing material with lime or cement to solidify soil. In this paper, the tests of free expansion rate, water ratio limit, and optimum moisture content (OMC) are carried out; then, RHA and lime were added to artificial soil in different proportions of 5, 10, 15, and 20% by weight, in which the ratio of RHA to lime is 80 : 20. The unconfined compressive strength (UCS) in different curing age is measured, and the improvement effect of RHA and lime to expansive soil can be obtained. Finally, the reason of improvement effect is explained by using the scanning electron microscope (SEM). The results of the study show that (1) for the best utilization effect, the optimum percentage of RHA is 12% and lime is 3%; (2) the UCS is 2.6 times of the pure soil after curing of 14 d under the optimum percentage; (3) the curing age has a significant effect on strength; (4) the main reason for the strength increase of the modified soil is that the crystal produced by the pozzolanic activity fills the pores of the soil.

Stabilization Mechanism of Calcium Lignosulphonate Used in Expansion Sensitive Soil

A series of tests were performed to investigate the macroscopic properties and the stabilization mechanism of calcium lignosulphonate modified expansive soil. Compared with natural soil, soil modified by 4% calcium lignosulphonate showed 56.5% increased 28 days unconfined compressive strength and 23.8% decreased free expansion rate. The X-ray diffraction analysis results indicate the existence of cation exchange and the reduction of montmorillonite interplanar spacing. The X-computed tomography results demonstrate that calcium lignosulphonate decreased the porosity and optimized the pore distribution. The calcium lignosulphonate also increased the stability of the suspension system according to the Zeta potential results. Moreover, the results of rheological tests show that the moderate amount of calcium lignosulphonate enhanced the yield stress and the plastic viscosity, proving the formation of a strong connection between soil particles.

Anisotropic expansions of a strongly interacting Fermi superfluid containing a vortex

We present a study of static and expansion properties of strongly interacting Fermi superfluids containing a vortex initially trapped by cylindrically symmetric potentials. Based on the order-parameter equation in the framework of the Gross–Pitaevskii equation, a unified expression for the energy of a vortex line in the crossover from a Bardeen–Cooper–Schrieffer superfluid to a molecular Bose–Einstein condensate is analytically presented. Numerical simulations show that the combined effects of interactions and trap configurations lead to an interesting property that the free expansion rate of the vortex core radius is smaller than that of the radius of the superfluid in the radial direction, when the strongly interacting Fermi superfluid containing a vortex is released from a cigar-shaped trap. The effects of the trap anisotropy and vortex on the Efimovian expansions of a unitary Fermi superfluid in real experimental setups are also predicted.

Study on Expansion Mechanism of Mudstone Under Structural Strength

As the structural swelling soft rock, mudstone’s expansion mechanism is similar to expansive soil, but it has its own particularity. In this paper, based on the analysis of the difference between the undisturbed and remolded samples of mudstone in terms of expansion and deformation, the expansion mechanism considering the strength of mudstone structure was proposed, and the verification test was designed. The following research results were obtained: In judging the potential of mudstone expansion, it is defective to rely solely on the free expansion rate, and its structural strength should be fully considered; The expansive force of mudstone is divided into the external expansive force resisting the external action and the internal expansive force resisting the interaction between internal particles. The external expansive force is the main reason of the increase of the volume of mudstone, and the internal expansive force is related to the cementation strength inside mudstone; The expansion theory based on free expansion rate, expansion force and uniaxial compressive strength is proposed.

Physical and Mechanical Characteristics of Soft Rock Tunnel and the Effect of Excavation on Supporting Structure

The problem of large deformation is very prominent in deep-buried tunnel excavation in soft rock, which brings serious potential safety hazards and economic losses to projects. The knowledge of deformation law and support measures is the key to ensure the rational design and safe construction in a large deformation tunnel of soft rock. This paper describes rock physical and mechanical tests and field monitoring is employed to investigate the cause and development process of large deformation in Dongsong hydropower station in Sichuan Province, China. The results show that the free expansion rate of the rock sample is 20.0%, the average expansion stress of the rock sample is 11.0 kPa, and the expansibility of the rock is low. Large deformation of surrounding rock mainly comes from the dilatancy effect with high geostress and relaxation deformation with weak support. Shotcrete sealing exposed surrounding rock, and early strength support avoiding water immersion are useful to deal with the three main factors (weathering, water and confining pressure) that affect the strength of surrounding rocks. The second lining applied in time can effectively limit the further development of stress and deformation of initial support, and prevent the cracking and large deformation of concrete. Clearance convergence is suggested to be the main monitoring work in construction, because of its advantages of intuitive results, easy quality assurance of instrument installation and high accuracy.

Freely Expanding Knots of X-Ray-emitting Ejecta in Kepler’s Supernova Remnant

Abstract We report measurements of proper motion, radial velocity, and elemental composition for 14 compact X-ray-bright knots in Kepler’s supernova remnant (SNR) using archival Chandra data. The knots with the highest speed show both large proper motions (μ ∼ 0.″11–0.″14 yr−1) and high radial velocities (v ∼ 8700–10,020 km s−1). For these knots the estimated space velocities (9100 km s−1 ≲ v 3D ≲ 10,400 km s−1) are similar to the typical Si velocity seen in supernovae (SNe) Ia near maximum light. High-speed ejecta knots appear only in specific locations and are morphologically and kinematically distinct from the rest of the ejecta. The proper motions of five knots extrapolate back over the age of Kepler’s SNR to a consistent central position. This new kinematic center agrees well with previous determinations, but is less subject to systematic errors and denotes a location about which several prominent structures in the remnant display a high degree of symmetry. These five knots are expanding at close to the free expansion rate (expansion indices of 0.75 ≲ m ≲ 1.0), which we argue indicates either that they were formed in the explosion with a high density contrast (more than 100 times the ambient density) or that they have propagated through regions of relatively low density (n H < 0.1 cm−3) in the ambient medium. X-ray spectral analysis shows that the undecelerated knots have high Si and S abundances, a lower Fe abundance, and very low O abundance, pointing to an origin in the partial Si-burning zone, which occurs in the outer layer of the exploding white dwarf for models of SNe Ia. Other knots show lower speeds and expansion indices consistent with decelerated ejecta knots or features in the ambient medium overrun by the forward shock. Our new accurate location for the explosion site has well-defined positional uncertainties, allowing for a great reduction in the area to be searched for faint surviving donor stars under non-traditional single-degenerate SNe Ia scenarios; because of the lack of bright stars in the search area the traditional scenario remains ruled out.

Laboratory study on engineering geological characteristics and formation mechanism of altered rocks of Henan Tianchi pumped storage power station, China

Concentrations of biotite flakes were distributed at multiple locations during the site investigation for the Tianchi Pumped Storage Power Station project in Henan Province, China. Rock mass was highly weathered on both sides of a prominent fault, and a large number of white and gray, locally yellow–brown, argillaceous agglomerations were observed. The local core at the end of the ZK44 hole presented a gray and white sandstone structure. Petrochemical tests, which included sheet identification, scanning electron microscopy, electron probe analysis, and X-ray diffraction, showed that the main alteration types were mica-rich-type altered rocks and clay-type altered rocks, which were accompanied by chlorite, epidote, actinolite, and other alteration minerals. According to the mechanical test results, the smallest antidisintegration index was 84 %, disintegration was easily accomplished, the maximum axial free expansion rate was 0.00204 %, the maximum free expansion rate in the radial direction was 0.0178 %, and maximum lateral constrained expansion rate was 0.0194 %. The swelling pressure of all the specimens did not exceed 10 kPa, and the clay-type altered rocks exhibited three large expansion parameters. Uniaxial and triaxial compression tests showed that the strength of granite, as reflected by its deformation and elastic moduli, decreased to values even lower than those of highly weathered rocks because of alteration. The poor characteristics of the altered rock presented great challenges for support or lining during the construction and operation stages. After excavation, the expanded altered rocks should be cleaned up immediately, the support or lining should be in place immediately, and water should be drained in time.

Study on Expansion of Circulating Fluidized Bed Combustion Coal Ash

Expansive hydration products of circulating fluidized bed combustion (CFBC) ash with different finesses are investigated in this paper. The results show that expansion occurred in hardened paste of CFBC ashes is mainly due to formation of dihydrate gypsum and ettringite. Besides, the free lime does indirectly cause expansion due to its effects on crystallization of ettringite. It also has been observed that linear free expansion rate of paste with ground CFBC ash is higher than that of paste using original ash at 1 day of hydration, but lower than paste with original ash 3 days and longer period of hydration later.