Equivalent Volume Method Research Articles

Influence of Recycled Concrete Aggregate Type on Rheological Behaviour of Mixtures Proportioned Using the Equivalent Volume Method

The ever-growing urgency to combat climate change has led the civil construction industry to develop and adopt sustainable construction materials and methods. The so-called recycled concrete aggregate (RCA) emerges as an alternative to decrease the carbon footprint of new concrete construction, the disposal of waste concrete, and the use of non-renewable natural resources such as cement and aggregates. RCA can be produced from crushing waste concrete; yet challenges remain when using RCA in concrete especially its fresh state behaviour due to its distinct multi-phase nature and microstructure (i.e., presence of residual mortar (RM)/residual cement paste (RCP)). In this context, this work presents a comprehensive study of the rheological behaviour of recycled concrete mixtures through the use of a planetary rheometer (IBB). The recycled mixtures were proportioned using the Equivalent Volume (EV) method, a mixture proportioning technique that accounts for the RM and RCP, respectively, and improves the recycled mixture's hardened state properties, incorporating distinct: 1) coarse RCA having various inner qualities (i.e., 25 MPa, 35 MPa and 45 MPa) and mineralogy (i.e., limestone and granite) and 2) fine RCA made from natural or manufactured sand while having different degrees of processing (i.e., crushed once vs continuously crushed). All recycled mixtures produced in this study present shear-thinning profiles, suggesting that these mixtures are suitable for applications under high torque regimes such as vibrated or pumped concrete. Additionally, they were produced with 100% recycled concrete aggregate (either fine or coarse RCA), classifying them as low embodied energy mixtures.

Influencing factors of the mixing performance of a near-nozzle continuous mixer for 3D concrete printing: An analysis based on spatial Lacey mixing index (SLMI)

3D concrete printing, as a vital construction method for future development, has lately received significant attention. Unlike classic pumped concrete material extrusion process, a near-nozzle continuous mixer reduces mixing energy by eliminating long conveying distances. However, there has been limited research on it mixing quality. In the study, the first mixing phase of an innovative near-nozzle continuous mixer is explored by full-scale numerical simulation. In order to improve the mixing process of additive 3D concrete printing, it is necessary to compare the mixing efficiencies and performances of continuous mixers with different configurations under various working conditions. Sixty cases with four parameters (sideward angle, the number of paddles, rotation speed, and mixture's composition ratio in different levels) are analyzed in the discrete element method (DEM) simulation. The influences of these parameters on overall and local mixing performances are determined with the modified Lacey mixing index, the spatial Lacey mixing index (SLMI). For unequal particles introduced in this study, SLMl is combined with the equivalent volume method. Qualitative and quantitative analysis results reveal that the four-15°-paddle conveyor mixer performs better above a certain rotation speed, regardless of the mixture's composition ratio. This paper increases the understanding of the mixing process for preparing well-mixed dry materials in a continuous conveying state, which is crucial for efficient near-nozzle mixing in 3D concrete dosing.

Development and application of a new ballast water system for immersed tunnel installation: A case study of the Yuliangzhou tunnel in Xiangyang, China

Ballast water systems are an indispensable part of the installation of immersed tunnels and are utilized to increase or reduce the total weight of immersed tunnel elements in the processes of floating transportation, mooring and sinking. Traditional ballast water systems generally utilize rigid tanks, which consist of retaining walls made of steel-wood parts, for water supply and discharge. However, there are many drawbacks to the traditional ballast water system based on rigid tanks. For example, the construction of rigid ballast tanks is a complex process that is not very efficient and but is very costly. In addition, the processes of installing and dismantling the steel panels of rigid ballast tanks involve substantial welding work and many fire operations, which result in a substantial amount of smoke and dust inside the tunnel elements, resulting in a construction environment that is harmful to human health. Based on the Yuliangzhou Immersed Tunnel, which extends across the Hanjiang River in Xiangyang, China, a new type of ballast water system with flexible water-filled containers was developed to address the abovementioned problems. The equivalent volume method was proposed to determine the geometric size of the flexible water-filled containers. Field stability tests of the flexible water-filled containers were conducted on a 4.8% slope. The experimental results showed that the designed flexible container could meet the actual water demand of tunnel element immersion, without sliding or rolling during water injection, and that the relationship between the water amount and water pressure was approximately parabolic. In view of the specific functions in different installation stages of tunnel elements, the equipment layout of the new type of ballast water system was determined. Based on the processes of tunnel element installation, water supply and discharge technologies were designed. This system has been successfully applied in the Yuliangzhou Immersed Tunnel project, which supports the use of these technologies in immersed tunnel construction.

Investigation of the thermal conductivity of composite materials with a spherical filler

In the light of the disadvantages of existing methods for determining the thermal conductivity of composite materials, the major practical issue is the need for creating more advanced calculation methods that take into account the geometry of the dispersed inclusions and their properties, i.e., those capable of evaluating the heat-conducting parameters of the composite with consideration of the properties of its components and their relative positions. In this paper, the analytical formulas, containing the ratio of the thermal conductivity coefficients of the base material and the filler, are derived for calculating the thermal conductivity of composite. The proposed model uses averaging of parameters at the "matrix-dispersed inclusion" phase boundary. We consider several well-known models developed by domestic and foreign researchers in recent years, which allows us to calculate the coefficient of thermal conductivity of such composites. The results of comparison of these models with the analytical dependence obtained in this paper are presented, and its applicability intervals are specified for different ratios of the inclusion thermal conductivity coefficient and the matrix material. The main goal is to fill the lack of information on thermal conductivity of spherical filler composites. The model considered in this paper is based on a change in the thermal resistance at the phase boundary. Since most materials used in industry contain inclusions with different geometric characteristics, then it is necessary to use the equivalent volume method - the reduction of various geometric inclusions to a given spherical one - which makes it possible to determine a change in the thermal conductivity coefficient for different physical and geometric values of the matrix material and filler. Various dependences of the change in the thermal conductivity coefficient of composite materials on the volume content of the spherical inclusion are compared with the numerical and experimental results. The analytical dependence given in this paper is consistent with the experimental and numerical results for relatively small values of the thermal conductivity coefficient and the inclusion diameter.

Strength Time–Varying and Freeze–Thaw Durability of Sustainable Pervious Concrete Pavement Material Containing Waste Fly Ash

Pervious concretes, as sustainable pavement materials, have great advantages in addressing a number of environmental issues. Fly ash, as the industrial by-product waste, is the most commonly used as cement substitute in concrete. The objective of this paper is to study the effects of waste fly ash on properties of pervious concrete. Fly ash was used to replace cement with equivalent volume method at different levels (3%, 6%, 9%, and 12%). The control pervious concrete and fly ash modified pervious concrete were prepared in the laboratory. The porosity, permeability, compressive strength, flexural strength, and freeze–thaw resistance of all mixtures were tested. The results indicated that the addition of fly ash decreased the early-age (28 d) compressive strength and flexural strength, but the long-term (150 d) compressive strength and flexural strength of fly ash modified pervious concrete were higher than that of the early-age. The adverse effect of fly ash on freeze–thaw resistance of pervious concrete was observed when the fly ash was added. The porosity and permeability of all pervious concrete mixtures changed little with the content of fly ash due to the use of equal volume replacement method. Although fly ash is not positive to the properties of pervious concrete, it is still feasible to apply fly ash as a substitute for cement in pervious concrete.

Laboratory Evaluation of Eco-Friendly Pervious Concrete Pavement Material Containing Silica Fume

Pervious concretes, such as sustainable pavement materials, have great advantages in solving urban flooding, promoting urban ecological balance, and alleviating urban heat island effect, due to its special porous structure. However, pervious concrete typically has high porosity and low strength. The insufficient strength and poor freeze-thaw durability are important factors that restrict its wide application, especially in seasonal frozen areas. Improving the strength and freeze-thaw resistance of pervious concrete will expand its application. Silica fumes, as an industrial by-product waste and supplementary cementitious material, play an important role in improving concrete performance. The objective of this paper was to study the effects of silica fumes on properties of sustainable pervious concrete. Silica fumes were used to replace cement with the equivalent volume method at different levels (3%, 6%, 9%, and 12%). The control pervious concrete and silica fume-modified pervious concrete mixtures were prepared in the lab. The porosity, permeability, compressive strength, flexural strength, and freeze-thaw resistance properties of all mixtures were tested. The results indicated that the addition of silica fumes significantly improved the strength and freeze-thaw resistance of pervious concrete. The porosity and permeability of all pervious concrete mixtures changed little with the content of silica fumes due to the adoption of the equal volume replacement method.

Particle size cut performance of aerodynamic cyclone separators: Generalized modeling and characterization by correlating global cyclone dimensions

To generalize the characterization of particle-size cut performance for aerodynamic cyclones, a data-driven modeling approach using two varied correlating strategy Ψ0.5=Cc1/2dp0.5/D and Stk0.5=(Ccρpdp0.52vi)/(18 μD) was proposed. This approach correlated the global influencing parameters including cyclone dimensions, operating conditions and multiphase properties which have not ever completely included before. The proposed models integrated the external geometrical dimensions (cyclone inlet area (ab/D) and vortex finder diameter De/D) into a annular Reynolds number Rea=ρgQ(D-De)/[μ(ab)], and used a special body dimensionless parameter DB/D derived from an equivalent volume method to characterize effect of the cyclone body dimensions: vortex finder length S/D, cyclone height H/D, cylinder height h/D and particle outlet diameter B/D. Results showed that the proposed Ψ0.5–based correlation improves the predictive ability and generalization performance compared to the other corresponding theoretical and regression models. Furthermore, the influence of cyclone dimensions and operating parameters on particle cutoff size was quantitatively addressed based on the proposed model. The result may provide a reference for performance assessment, design improvement and global optimization of aerodynamic cyclones applied both industrial process and aerosol sampling.

A New Method for Predicting the Hydrocyclone Efficiency with the Light Dispersed Phase

In this study, a new method for predicting the hydrocyclone efficiency with the light dispersed phase has been developed. The equivalent volume method is employed to simplify the effective region of the hydrocyclone into a cylindrical shape, the influence of structural complexity on the method is reduced. Based on the analysis of the dispersed phase droplets and the assumption of determining the droplets been separated, a residence time model of the droplets in the effective separating region is theoretically developed. This method can be expressed as a simple function including the cyclone dimension and operating parameters. By compared with the previous experimental data, it is showed that the calculated value is close to the experimental value when the separation rate is more than 10%. When inlet velocity is not too large, cause the dispersed phase droplet breakage is not obvious, the applicability of this method is better.

Prediction of gas-particle separation efficiency for cyclones: A time-of-flight model

Modeling the particle separation efficiency has been a topic of interest since the air cyclones was introduced for gas-particle separation in the fields of environmental science and chemical engineering. In this work, a new simple time-of-flight model is theoretically developed to predict the particle separation efficiency in cyclones. In this model, the equivalent volume method is employed to geometrically modify the cylindrical-conical type cyclone as a right cylindrical cyclone in order to overcome the nonuniform effect on the particle separation distance. Based on the analysis of the gas flow pattern and the particle dynamics in the cyclone separator, the differential equation for the time-of-flight model is established according to the principle of particle mass balance. The model can be finally expressed as a simple explicit function including the main cyclone dimensions and operating parameters, without the need for solving complex equation of mathematical physics. The influences of the short-circuit flow near the bottom of cyclone outlet duct and the exchange flow between outer and inner vortex flow are comprehensively considered to revise the effective residence time of gas flow, a key parameter in the present model. By comparisons with experimental data as well as other classical separation models for the cyclones with different geometrical configurations and operating conditions, the results show that the present model has a relatively high predicted accuracy with the mean squared error of 0.0158. It is demonstrated that the present model has considerable availability for predicting the particle separation efficiency for cyclone separators.

Determination of the relationship between strength and test method for glass fibre epoxy composite coupons using Weibull analysis

Glass fibre epoxy composite test coupons exhibit variability in their tensile strength data dependent on the test method used. The three common test standards are for tensile, three-point flexure and four-point flexure and it is accepted that flexure tests yield higher strengths than tensile tests. Tests were carried out on coupons of a woven E-glass epoxy composite for each type of test. The data for each test was found to fit a two-parameter Weibull distribution. The Weibull moduli for each of the test methods were approximately the same. This Weibull modulus is used to relate the strengths for different test methods using an equivalent volume method. It was found that the strength variability is dependent only on the equivalent volumes of test coupons and thus, a method is proposed for the prediction of tensile strengths from flexural strength tests and vice versa.