Conversion of fly ash into geopolymers/concrete. Display omitted
•An overview of geopolymer is presented alongwith its processing parameters.•The hardened properties and durability of geopolymer ...concrete are discussed.•The design guidelines for OPC concrete are applicable to geopolymer concrete also.•Geopolymeric building products developed at CSIR-CBRI are highlighted.•Ambient cured single component geopolymer may enhance its wider use in the field.
An overview of advances in geopolymers formed by the alkaline activation of aluminosilicates is presented alongwith opportunities for their use in building construction. The properties of mortars/concrete made from geopolymeric binders are discussed with respect to fresh and hardened states, interfacial transition zone between aggregate and geopolymer, bond with steel reinforcing bars and resistance to elevated temperature. The durability of geopolymer pastes and concrete is highlighted in terms of their deterioration in various aggressive environments. R&D works carried out on heat and ambient cured geopolymers at CSIR-CBRI are briefly outlined alongwith the product developments. Research findings revealed that geopolymer concrete exhibited comparative properties to that of OPC concrete which has potential to be used in civil engineering applications.
Based on the Nernst–Planck model for ion transport, the electroosmotic flow of a non-Newtonian fluid near a surface potential heterogeneity is studied numerically. The objectives of this study are to ...highlight the limitations of the linear slip-model and the nonlinear Poisson–Boltzmann model at various flow conditions as well as to develop vortical flow to promote mixing of neutral solutes within the micro-channel. A power-law fluid, both shear-thinning and shear-thickening, for the pseudoplastic behavior of the non-Newtonian fluid or viscoplastic fluid with yield stress is adopted to describe the transport of electrolyte, which is coupled with the ion transport equations governed by the Nernst–Planck equations and the Poisson equation for electric field. The viscoplastic fluid is modeled as either Casson, Bingham or Hershel–Buckley fluid. A pressure-correction based control volume approach has been adopted for the numerical computations of the governing equations. The nonlinear effects are found to be pronounced for a shear thinning liquid, whereas, the electroosmotic flow is dominated by the diffusion mechanisms for the shear thickening liquid. A maximum difference of 39% between the existing analytic solution based on the Debye–Hückel approximation and the present numerical model is found for a shear thinning power-law fluid. A vortex, which resembles a Lamb vortex, develops over the potential patch when the patch potential is of opposite sign to that of the homogeneous surface potential. Enhanced mixing of a neutral solute is also analyzed in the present analysis. The yield stress reduces the electroosmotic flow however, promotes solute mixing.
In this article, we introduce a model featuring a Lévy process in a bounded domain with semi-transparent boundary, by considering the fractional Laplacian operator with lower order non-local ...perturbations. We study the wellposedness of the model, certain qualitative properties and Runge type approximation. Furthermore, we consider the inverse problem of determining the unknown coefficients in our model from the exterior measurements of the corresponding Cauchy data. We also discuss the recovery of all the unknown coefficients from a single measurement.
Seismic stability analysis is an important aspect for design of safe retaining walls in earthquake prone areas. In this study, limit equilibrium method is used for rotational stability analysis of ...gravity retaining wall on rigid foundation supporting dry cohesionless backfill with modified pseudo-dynamic seismic forces. Proposed method satisfies the zero stress boundary condition at free ground surface and considers the amplification of acceleration. Stability factor FW is proposed to determine the safe weight of the retaining wall against rotational failure under seismic conditions. If the safe weight of the retaining wall is known under static condition then by simply multiplying that with FW can give the safe weight of the retaining wall against rotational failure under seismic condition. Present study shows that wall-soil interaction in various seismic conditions may or may not be in-phase for the entire duration of the input motion. It depends on the properties of the backfill soil, properties of the wall material and also on the frequency content of the input motion. A modified rotating block method is proposed to obtain the rotational displacement under seismic conditions. Present results give higher values of rotational displacements of the wall when compared with the available results by pseudo-static analysis. Hence the present study may be used to design seismically stable retaining wall.
•Modified pseudodynamic method satisfies boundary conditions•Amplification of acceleration is inherent to soil properties•Seismic active earth thrust and its point of application for gravity retaining wall•Seismic stability factors for retaining wall against rotational mode of failure•Rotational displacement of gravity retaining wall under seismic conditions
This paper investigates the influence of different amounts of recycled coarse aggregates obtained from a demolished RCC culvert 15 years old on the properties of recycled aggregate concrete (RAC). A ...new term called “coarse aggregate replacement ratio (CRR)” is introduced and is defined as the ratio of weight of recycled coarse aggregate to the total weight of coarse aggregate in a concrete mix. To analyze the behaviour of concrete in both the fresh and hardened state, a coarse aggregate replacement ratio of 0, 0.25, 0.50 and 1.0 are adopted in the concrete mixes. The properties namely compressive and indirect tensile strengths, modulus of elasticity, water absorption, volume of voids, density of hardened concrete and depth of chloride penetration are studied. From the experimental results it is observed that the concrete cured in air after 7 days of wet curing shows better strength than concrete cured completely under water for 28 days for all coarse aggregate replacement ratios. The volume of voids and water absorption of recycled aggregate concrete are 2.61 and 1.82% higher than those of normal concrete due to the high absorption capacity of old mortar adhered to recycled aggregates. The relationships among compressive strength, tensile strengths and modulus of elasticity are developed and verified with the models reported in the literature for both normal and recycled aggregate concrete. In addition, the non-destructive testing parameters such as rebound number and UPV (Ultrasonic pulse velocity) are reported. The study demonstrates the potential use of field recycled coarse aggregates (RCA) in concrete.
The main focus of this paper is on direct data driven synthesis and design of controllers. We show that the complete set of stabilizing proportional-integral-derivative (PID) and first-order ...controllers for a finite dimensional linear time-invariant plant, possibly cascaded with a delay, can be calculated directly from the frequency response (Nyquist/Bode) data P(jomega) for omega epsi 0, infin) without the need of producing an identified analytical model. It is also shown that complete sets achieving guaranteed levels of performance measures such as gain margin, phase margin, and Hinfin norms can likewise be calculated directly from only Nyquist/Bode data. The solutions have important new features. For example it is not necessary to know the order of the plant or even the number of left half plane or right half plane poles or zeros. The solution also identifies, in the case of PID controllers an exact low frequency band over which the plant data must be known with accuracy and beyond which the plant information may be rough or approximate. These constitute important new guidelines for identification when the latter is to be used for control design. The model free approach to control synthesis and design developed here is an attractive complement to modern and post modern model based design methods which require complete information on the plant and generally produce a single optimal controller. A discussion is included, with illustrative example, of the sharp differences between model-free and model based approaches when computing sets of stabilizing controllers. For example, it is shown, that the identified model of a high order system can be non-PID stabilizable whereas the original data indicates it is PID stabilizable. The results given here are also a significant improvement over classical control loop-shaping approaches since we obtain complete sets of controllers achieving the design specifications. It can enhance fuzzy and neural approaches which are model free but cannot guarantee stability and performance. Finally, these results open the door to adaptive, model free, fixed order designs of real world systems.
A numerical study is made on the mixed convection of copper–water nanofluid inside a differentially heated skew enclosure. Co-ordinate transformations are used to transform the physical domain to the ...computational domain in an orthogonal co-ordinate. The finite volume based SIMPLEC algorithm is used to solve the transformed equations for fluid flow and heat transfer equations in the computational domain. The fluid flow and heat transfer characteristics are studied for a wide range of skew angles (30°⩽λ⩽150°), nanoparticle volume fraction (0.0⩽ϕ⩽0.2) and Richardson number (0.1⩽Ri⩽5) at a fixed value of Reynolds number. The entropy generation and Bejan number are evaluated to demonstrate the thermodynamic optimization of the mixed convection. It is shown that the heat transfer rate increases remarkably by the addition of nanoparticles. The flow field is sensible to the skew angle variation. Our results show that the heat transfer augmentation through nanoparticles with lower rate in entropy generation enhancement can be achieved in a skewed cavity.
An enhanced electroosmotic flow through a surface-modulated microchannel is considered. The microchannel is modulated by periodically arranged rectangular grooves filled with polyelectrolyte ...materials. The flat surface of the walls is maintained at a constant charge density. A nonlinear model based on the Poisson–Nernst–Planck equations coupled with the Darcy–Brinkman–Forchheimer equation in the polyelectrolyte region and Navier–Stokes equations in the clear fluid region is adopted. Going beyond the widely employed Debye–Hückel linearization, we adopt numerical methods to elucidate the effect of pertinent parameters on electroosmosis in the patterned channel. The patterned microchannel results in an enhancement in the average EOF by creating an intrinsic velocity slip at the polyelectrolyte–liquid interface. An analytical solution of the EOF for a limiting case in which the groove width is much higher than the channel height is obtained based on the Debye–Hückel approximation. This analytical solution is in good agreement with the present numerical model when a low charge density and a thin Debye layer are considered. We have also established an analogy between the EOF in a polyelectrolyte-filled grooved-channel with the EOF in which the grooves are replaced by the charged slipping planes.
The electrophoresis of a charged colloid particle embedded in a charged hydrogel medium is studied based on the numerical computation of Stokes–Nernst–Planck–Poisson equations. In this study, no ...prior assumption on surface charge density of the particle, Debye length and imposed external electric field are made. We have compared our computed results for a lower range of surface charge density with the existing analytical solution based on the weakly charged particle and found them in good agreement when the fixed charge density of the hydrogel is low. Nonlinearity effects in gel electrophoresis is pronounced for a thick Debye length and higher values of particle ζ-potential. Even in the absence of a gel medium (free-solution), the numerical procedure used in this work yields mobilities different from the previous theoretical analysis based on the Debye–Hückel approximation when the scaled ζ-potential exceeds 2 and the Debye length is in the order of the particle size. The strong background electroosmotic flow (EOF) for a high fixed charge density of the polyelectrolyte hydrogel with a mesh size comparable to the particle radius drags the particle along the direction of the EOF. In this case, the electrophoretic velocity of the particle varies with its size. The particle electrophoretic velocity and forces are determined for a wide range of intrinsic parameters values.
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•Numerical study based on the Stokes–Nernst–Planck–Poisson equations.•Impact of double layer polarization and convective transport of ions.•Background EOF drags the negatively charged particle along the imposed electric field.•Size-selectivity in a highly charged gel medium is demonstrated.
