Compaction Voids Research Articles

Interpretation of undrained shear strength observed in confined triaxial compression tests on compacted clay

This paper presents an interpretation technique to quantify the effects of compaction state and matric suction on the undrained shear strength of compacted clay under confined undrained triaxial compression. This novel technique is based on the mathematical frameworks of the “stress history and normalized soil engineering property” (SHANSEP) method for saturated soil and the “Barcelona basic model” (BBM) for unsaturated soil. Test data of compacted Calgary till were analyzed and interpreted using the proposed technique. The interpretation technique is very useful in delineating the relative impacts of the factors on the behavioural trends in measured undrained shear strength. It was found that in addition to the initial compacted void ratio and suction, soil structure and failure mode exert significant influence on the undrained shear strength of compacted clay. This technique is attractive to engineering practitioners because the confined undrained compression tests (with no pore-air and pore-water pressure measurement) are much simpler and less time-consuming compared to rigorous laboratory tests on unsaturated soil.

Review of Sprayability of Wet Sprayed Concrete

Abstract Wet sprayed concrete quality is affected by more production factors than cast concrete, particularly due to the propulsion through the nozzle and the flash set caused by the set accelerator. Practitioners often use the term “sprayability” to describe these factors. We propose a definition of “sprayability” that relates the application to the final properties of the hardened sprayed concrete and review factors affecting it: concrete constituents, proportioning, and application mechanics. These factors affect the hardening and the structure of the hardened sprayed concrete – the porosity, permeability and durability. We consider improving sustainability through proportioning with increased share of supplementary cementitious materials, calculate the placed composition and focus on factors that affect water transport, and hence durability. Due to the spray application and flash-set, irregular compaction voids dominate the macro pore structure of sprayed concrete. Studies of permeability of sprayed concrete have shown that it is possible to obtain low permeabilities given adequate composition and curing. Presumably these samples have been well-cured, uncracked and with non-percolating macro voids. Given observations of cracks in sprayed concrete linings and the macro voids, important further studies will be on the effect of accelerator, compaction porosity and cracking on permeability.

Study on the Construction Performance of Zeolite Asphalt Mixture Based on Macro‐Micro Scale

In order to explore the construction performance of zeolite asphalt mixture, the microproperties of zeolite and the macroproperties of zeolite asphalt mixture were studied. The structure composition, surface properties, and pore characteristics of zeolite were analyzed by infrared spectroscopy and pressure pump method. The structure, composition, and thermal stability of zeolite were analyzed by differential scanning calorimetry and thermogravimetry, the mechanism of moisture absorption and loss of water was explored, and the properties of moisture absorption and loss of water were studied. The effect of the type and amount of zeolite on the viscosity of asphalt was studied by the viscosity test. According to the mixing current and the compaction void ratio, the influence of zeolite on the construction performance of zeolite asphalt mixture was studied. The results show that zeolite contains special zeolite water and the pore content of zeolite is much higher than that of mineral powder. Zeolite loses water at 90°C∼120°C, which is the necessary condition for zeolite to be used in warm mix asphalt mixture. The water absorption and loss capacity of zeolite mainly depend on pore volume. The larger the pore volume is, the stronger the water holding capacity of zeolite is. Meanwhile, the water holding capacity and loss capacity of zeolite are related to pore size distribution. According to the viscosity temperature equation, the mixing and compaction temperature of the asphalt mixture are determined. The mixing and initial pressure temperature of the zeolite asphalt mixture are lower than those of the hot asphalt mixture. Based on the principle of mixing current equivalence, the mixing temperature of zeolite asphalt mixture can be reduced by 20°C compared with that of hot asphalt mixture. The better the water loss performance of zeolite is, the easier the mixture is to be compacted. For the base asphalt mixture, the compaction temperature of the mixture is 120–130°C, and, for the modified asphalt mixture, the compaction temperature is 130–140°C.

Ettringite induced heaving in stabilized high sulfate soils

Stabilization of expansive soils using lime and cement additives have been used by practitioners over the years. However, recent heaving and premature pavement failures in lime and cement-treated subgrades containing sulfates led to questioning the use of calcium-based stabilization methods for these soils. Annually, millions of dollars are spent to repair pavements distressed by this Ettringite induced heaving. Based on the past studies, researchers and practitioners have proposed various methods to treat sulfate soils. Applicability of these methods is mostly limited to soils with sulfate levels below 8000 ppm. Soils with sulfate content above 8000 ppm are termed as “high sulfate” soils, and chemical treatment of such soils is currently not considered. A research study was designed to aid in understanding the heaving phenomenon in soils with sulfate contents above 8000 ppm and to develop practical techniques to stabilize such soils. High sulfate soils were sampled and treated with lime at varying mellowing periods and treated soils were then subjected to the engineering and chemical tests. Tests results were analyzed to understand the effectiveness of mellowing period on the heaving phenomenon of these soils. Treated soils at higher mellowing periods showed reduced sulfate-induced heaving when sulfate levels are lower than 30,000 ppm. Sulfate levels in excess of 30,000 ppm did not result in effective treatment of soils. It was also observed that compaction void ratios and soil clay mineralogy have a significant impact on the swell behavior of chemically treated high sulfate soils. An innovative method comprising of aerial technologies is used to monitor the pavement heaving. This keynote paper provides a comprehensive review of stabilization of high sulfate soils and methods studied to mitigate sulfate heaving.

Closure laws of void in the core of cross wedge rolling shaft based on the floating-pressure method

In order to improve the internal quality of cross wedge rolling (CWR) shaft, the floating-pressure method (FPM) using high-pressure gas to compact void in CWR shaft is adopted in this paper. Firstly, the theoretical relations between each influencing factor and flow stresses are deduced by establishing the mechanical model of void closure based on FPM. Then, the laws of stress variation, metal flow, void shape variation, and microstructure evolution are all analyzed by DEFORM-3D finite element software, and the mechanism of void closure based on FPM is clarified. By means of hot isostatic pressing equipment, the FPM experiments are conducted, and it is illustrated that the outer dimensions of CWR shaft are hardly affected and its internal void can be effectively eliminated. Finally, the tests of specimens’ mechanics performance show that the tensile strength of the specimen is improved and its surface hardness is slightly reduced. The research results provide a new way for improving the yield and mechanical properties of CWR shaft.

Multi-step triaxial compressive creep behaviour and induced gas permeability change of clay-rich rock

Clay-rich rocks are potential geological barriers for geological repositories of radioactive waste. The long-term safety of a repository requires a full characterisation of the time-dependent thermal hydro-mechanical behaviour of the clay-rich rocks. This paper investigates the creep deformation and induced permeability change of the Callovo-Oxfordian (COx) claystone by a series of multi-step triaxial compressive creep tests. The effects of confining pressure and deviatoric stress are both studied. Three values of effective confining pressure are 2 MPa, 6 MPa and 12 MPa, according to the in situ stress estimation at the Bure underground research laboratory in France. In each test, the deviatoric stress is progressively loaded in five steps so that the primary, secondary and tertiary stages of creep can be evaluated. In the last loading step, the tested sample may exhibit a creep failure process. During the creep tests, the gas permeability of the partially saturated COx claystone is measured by a transient pulse decay method in concurrence with the material creep deformation. The results obtained show that both the confining pressure and deviatoric stress have important effects on the time-dependent deformation and permeability evolution of the claystone. Analysis of creep strain rates during the last creep step indicates that there exists a threshold for the creep-induced failure of the COx claystone. The permeability evolution in the triaxial creep process is closely related to the microstructural evolution of rock, including the closure of pre-existing micro-cracks, the compaction voids and the creation, propagation and coalescence of micro-cracks.

Quantification of Coarse Aggregate Angularity by a Newly Developed Auto Grader Machine

The physical properties of aggregates have a direct correlation to the performance of a pavement. Stiffness, fatigue response, shear resistance and permanent deformation are some of the distresses for which aggregate form, texture and angularity have an influence. Angularity is an important property of aggregate shape, more angular are the particles there will be better interlocking, inter friction and greater mechanical stability, hence better pavement distress resistance. A debate has a risen over several methods to capture this physical property either directly or indirectly such as aggregate imaging system (AIMS), Un compacted void content of coarse aggregate (AASHTO T326), University of Illinois Aggregate Image Analyzer (UIAIA) and Indian manual coarse aggregate angularity test. Some are costly some are laborious and time consuming; hence there is a need for better methods that are cost effective, accurate, rapid in measuring aggregate angularity. The research conducted in this study introduces cost effective Aggregate Auto-grader and evaluates the effective set of time and speed for this automated machine to obtain minimum percentage air voids between aggregates (estimation of perfect interlocking) by shaking sample of coarse aggregates in orbital motion. In addition to measure accuracy of automate Aggregate Auto-grader test results are compared to other manual coarse aggregate angularity test. The trend followed by results of aggregate Auto-grader is as same as the manual test, hence based on results a new equation is proposed for obtaining coarse aggregate angularity by Aggregate Auto-grade machine which has more accuracy, reputability and reproducibility compare to the manual test.

Trapped Modes in Piezoelectric and Elastic Waveguides

We derive a sufficient condition for the existence of trapped modes in a cylindrical piezoelectric waveguide $\varOmega$ with a compact void $\varTheta$ . An infinite part $\varGamma_{D}$ of the exterior boundary $\partial\varOmega$ is clamped along an electric conductor and the remaining part $\varGamma_{N}=(\partial\varOmega\setminus \varGamma_{D})\cup\partial\varTheta$ is traction-free and is in contact with an insulator, e.g., a vacuum. The condition permits the limit passage either to an elastic or a compound waveguide but it crucially differs from the pure elastic case due to the involved electric enthalpy instead of the energy functional. Examples of concrete waveguides and voids supporting trapped modes are given, and open questions are formulated. In particular, in contrast to a pure elastic waveguide where “almost” any crack traps a wave, no example of a crack trapping a wave in a piezoelectric waveguide is known yet.

The Certainties of History and the Uncertainties of Representation in Post-Holocaust Writing

The Certainties of History and the Uncertainties of Representation in Post-Holocaust Writing

Several Factors Affecting the Strength and Deformation Characteristics of Cement-Mixed Gravel

ABSTRACT Related to the construction of a new type bridge abutment having the backfill of cement-mixed gravel, effects of moulding water content, wi, compaction energy level, cement-to-gravel ratio by weight, c/g, and curing period on the stress-strain behaviour of compacted cement-mixed gravel and their correlations were investigated. A series of drained triaxial compression tests were performed on a well-graded gravel of crushed sandstone from a quarry mixed with ordinary Portland cement. Possible effects of inherent anisotropy produced by compaction in different directions were evaluated to a limited extent. The following results were obtained. With a fixed c/g, the maximum compressive strength is attained when compacted at wi=the optimum water content, wopt, for a given compaction energy level, while the compressive strength is not an unique function of compacted dry density of solid, ρd (or compacted void ratio, e). These trends of behaviour are analysed in terms of positive effects of higher ρd (or lower e) of cement-mixed gravel and an associated increase in the cement amount per total volume for a fixed c/g as well as effects of the amount and strength of cement paste, both being a function of moulding water content. The benefits of compaction at wi=wopt for a fixed compaction energy level in achieving higher compressive strengths increase with an increase in c/g and the curing period. The pre-peak stress-strain behaviour tends to become more linear with curing period. The effects of in-herent anisotropy are not as significant as those with air-pluviated unbound sand.

Strength and Deformation Properties of Compacted Cement-Mixed Gravel Evaluated by Triaxial Compression Tests

To achieve as possible as a high cost-effective construction of important civil engineering structures, such as bridge abutments, using cement-mixed gravel (CMG) for the backfill, a series of drained triaxial compression (TC) tests were performed on CMG specimens. Two types of well-graded gravels were used. Axial and lateral strains were measured locally on the lateral surface of solid cylindrical specimens. It was found that, for a same cement to gravel ratio by weight, the peak strength qmax tends to become the maximum when compacted at the optimum water content, w opt, for a given compaction energy level. This trend is due largely to the smallest compacted void ratio and partly due to the largest cement content per unit volume associated with the maximum dry density. The other influencing factors include an incidental optimum combination of strength and amount of cement paste that may be attained when compacted at w = wopt· The relationship between the ratio of "qmax at a certain molding water content, w" to "qmax at wopt, qmax.OMC" and the normalized deviation ratio of w from “wopt, | w- wopt | / wopt” is rather unique whether compacted at dry or wet of optimum, for different compaction energies and for the two types of gravel. It is also shown that the initial Young's modulus tends to become the maximum when compacted at wopt while the pre-peak stiffness and post-peak ductility generally increase with an increase in the molding water content. Based on the test results, it is recommended to compact a given type of cement-mixed gravel around at wopt ensuring that the compaction is not made dry of optimum for a given compaction energy.

Swell versus Saturation for Compacted Clay

The purpose of this study is to investigate the relationship between swell and degree of saturation for a compacted clay. Laboratory tests indicate that the percent swell increases in direct proportion to the degree of saturation at the end of the test. The linear relationship does not intercept the initial compacted degree of saturation. The coefficient of swell can be affected by the compacted effort. The dry, hard clods are broken down by the higher compactive effort. This reduction in interclod voids probably causes the significantly different coefficient of swell. Swell tests compacted to low, dry densities have a final saturation degree below 90%, even after two cycles of secondary swell. This indicates the presence of entrapped air. The main factor governing entrapped air for this soil appears to be the initial compacted void ratio. By itself, the degree of saturation does not seem to reliably indicate future potential for swell. One problem is the presence of entrapped air, which can result in a s...

Permeability of Roller Compacted Concrete

Water‐permeability measurements were made on 50 mm diameter and 100 mm long cored cylinders obtained from a roller compacted concrete pavement that was 160 mm in average thickness. A triaxial permeability cell was used. The effect of water‐cement ratio, silica fume addition, use of a finer cement, curing technique, etc. on coefficients of permeability were investigated. Roller compacted concrete was found to be considerably more permeable than conventionally proportioned and placed concrete and somewhat more permeable than conventional mass concrete. The use of silica fume and finer cement appeared to reduce the coefficient of permeability to some extent. However, the method of curing did not make any appreciable difference. When observed under a microscope, roller compacted concrete was found to have a number of interconnected compaction voids, hollow aggregate‐paste boundaries, and interfaces that were porous and undeveloped.