Screening of Soil Amendments for Efficient Water-Holding Capacity Based on a Rainfall-Infiltration Model in a Vertisol

A simulation study was conducted with five soil amendments, viz., goat manure, coir pith, phosphogypsum, polyacrylamide, and a control at two rainfall intensities of 60 and 120?mm?h?1 under dry and wet soil conditions in a clay loam vertisol with the objective of identifying a superior soil amendment for maximum infiltration and suitable soil aggregate stability. The F-test based on analysis of variance of infiltration data indicated that soil amendments, rainfall intensities, and soil conditions were significantly different from each other. Based on least significant difference test, polyacrylamide was found to be superior with a significantly higher infiltration, compared to all other amendments. An exponential model of infiltration over a time interval was calibrated for each soil amendment under dry and wet soil conditions. Based on the model, polyacrylamide and phosphogypsum were found to have a better soil aggregate stability compared to other soil amendments. The exponential model gave a significant predictability of instantaneous infiltration ranging from 0.75 to 0.99 under different situations. A grouping of treatments based on mean and coefficient of variation of infiltration in comparison with soil aggregate stability values indicated that polyacrylamide was superior under different situations in the study. Phosphogypsum was found to be the second best soil amendment with a relatively lower infiltration compared to polyacrylamide, but with a better soil aggregate stability compared to other soil amendments. Coir pith, goat manure, and control gave a significantly lower infiltration with a relatively higher variation compared to polyacrylamide and phosphogypsum, and also had a relatively lower soil aggregate stability under different situations examined in the study.     

Response of high performance concrete plates to impact of non-deforming projectiles

The relatively recent technology, which enables the production of high strength concrete (HSC), makes HSC a prospective material for the construction of impact-resisting barriers. However, current penetration formulae are based on test data of normal strength concrete (NSC) and their extrapolation to higher concrete strengths is unsafe. The response of 80×80 cm high performance concrete (HPC) plate specimens to an impact of non-deforming steel projectiles was examined in an experimental study. The tests were planned with an aim to observe the influence of the concrete mix ingredients and amount and type of reinforcement on the performance of HSC under this type of loading. The variants that were examined were the aggregates (different types and maximum size), addition of micro-silica (MS) and steel fibers, and reinforcement details. The main findings show that design of HPC barriers to withstand impact loads involves several aspects. These are aimed at achieving enhanced properties of the structural element, where only one of which is the concrete's compressive strength.     

Study of self-aggregation of coal derived asphaltene in organic solvents: A fluorescence approach

Fluorescence spectra of coal derived asphaltenes sourced from Barari coke plant situated at Dhanbad, India, have been studied as a function of concentration in benzene, toluene and carbon tetrachloride with an eye to study the self-aggregation of the solute. Aggregation has been found to be a gradual process and the concentration characterizing onset of aggregation process coincide for the solvents. The critical aggregation constants (CAC) appear to be ca 90-100 and 180-200 for all the solvents. A small red shift of fluorescence band is observed when traces of water (∼0.05%, v/v) are present in carbon tetrachloride solution.     

Image analysis method for determining 3-D shape of coarse aggregate

A 3-D method for particle shape determination of coarse aggregates using image analysis, IA, is presented. It is based on the measures the axial length of all three axis of every particle in a coarse aggregate sample. Two images of the entire aggregate sample are taken, in lying and standing positions. Since the particle's intermediate axes are measured in both images they can be used to couple the shortest and longest axial dimensions for each particle. The method allows an interpretation of length/thickness, length/width and width/thickness ratios of all the particles and is thus comparable to the flakiness and shape index tests.     

Effect of elevated temperatures on geopolymer paste, mortar and concrete

Geopolymers are generally believed to provide good fire resistance due to their ceramic-like properties. Previous experimental studies on geopolymer under elevated temperatures have mainly focused on metakaolin-based geopolymers. This paper presents the results of a study on the effect of elevated temperature on geopolymer paste, mortar and concrete made using fly ash as a precursor. The geopolymer was synthesized with sodium silicate and potassium hydroxide solutions. Various experimental parameters have been examined such as specimen sizing, aggregate sizing, aggregate type and superplasticizer type. The study identifies specimen size and aggregate size as the two main factors that govern geopolymer behavior at elevated temperatures (800 °C). Aggregate sizes larger than 10 mm resulted in good strength performances in both ambient and elevated temperatures. Strength loss in geopolymer concrete at elevated temperatures is attributed to the thermal mismatch between the geopolymer matrix and the aggregates.     

Chemical and Structural Investigations of Biomimetically Grown Fluorapatite–Gelatin Composite Aggregates

Deeper understanding of the basic principles of biomineralization is a major challenge for present and future research. The high complexity of in‐vivo conditions calls for simplified model systems that still involve dynamic processes like reorganization, formation, self‐organization, and development of patterns, respectively. The present contribution deals with hierarchically ordered spherical aggregates of fluorapatite–gelatin composites with fractal architecture that are grown in gelatin matrices. The model system was chosen to mimic formation conditions on a lower level of complexity compared with the natural formation of calcified tissue (bone, teeth). In order to gain insight into structure formation and the motif for this special kind of morphogenesis we investigated the interaction of the organic and inorganic components of aggregates in different growth stages by detailed chemical analyses, thermoanalytical measurements, X‐ray diffraction on solitary particles, and scanning electron microscopy (SEM) as well as transmission electron microscopy (TEM) investigations. The close relation of the results and observations to calcified tissue may stimulate advanced interests in the fields of medical and materials development.     

Floc rupture and turbulence: a framework for analysis

The paper focuses on the physical character of flocs. This is developed through analysis of the impact of hydrodynamic stress on floc size. Theory is developed on the basis of an energy criterion which balances the turbulent kinetic energy against the energy expenditure associated with rupture. For turbulence, the kinetic energy per unit volume is moulded by the velocity scale (νε)^1/4 and the d/η ratio in which ν, ε, η refer to the kinematic viscosity, the rate of energy dissipation per unit mass and the Kolmogorov length, respectively. The distance scale, d, is equivalent to the maximum floc size. In its most rudimentary form, floc structure is based on the model S∝k?/d³ in which k is the number of bonds broken and ? the potential energy expenditure per bond broken. With appropriate development, this transforms to S=S₀(d/d₀)^D−3 in which d₀ is the primary particle size, D the fractal dimension, and S₀ is a scaling factor controlling the mechanical strength. From the energy criterion, analytical expressions are derived for d in the form d=γε^−m/2 in which γ and m are constants. Beside the proposal of models for S, a valuable advance is the development of rupture theory for the whole domain of d/η. Theory is examined using a number of published data sets in which there exists knowledge of parameters γ, m and D. The paper demonstrates how the model can be used as an analytical tool for dissecting the factors which control S₀. The theory establishes a framework which can be developed further, and applies to flows containing fractal aggregates in both industry and the natural environment.     

Distribution analyses of multi-modal dynamic light scattering data

A method of data analysis for dynamic light scattering is proposed to evaluate the weight fraction, w(R_h), of a small amount of large aggregates in a dilute solution, where R_h is the hydrodynamic radius. We examined the time-correlation function of scattering intensity for model multi-modal systems, i.e., mixtures of latex solutions having different particle sizes and of polystyrene standard solutions having different molecular weights, by properly taking into account the unknown fractions, w(R_h), and scattering intensities of individual components. We derived an equation to evaluate the weight fractions of the components. The validity of this method was verified by successfully reconstructing the observed correlation functions having fast and slow modes. As a demonstration, the fraction of aggregates in a thermosensitive polymer solution in water was evaluated as a function of temperature.     

Spherical harmonic-based random fields for aggregates used in concrete

Two non-Gaussian random field models are developed for characterizing the geometry of star-like inclusions in two-phase or multi-phase materials. For illustration, the models are calibrated to the geometrical features of a population of 128 similar ASTM C57 aggregates used in concrete. The first model is a sum of spherical harmonic functions with random non-Gaussian coefficients. The second model is a nonlinear memoryless mapping of a sum of spherical harmonic functions with Gaussian coefficients.The two random field models are used to develop Monte Carlo algorithms for generating virtual aggregates. By construction, the virtual aggregates capture essential statistics of the target population of aggregates. The performance of the proposed models is assessed by quantitative and qualitative metrics.     

Stochastic Priority Model for Aggregate Blending

Aggregate blending models that incorporate the optimization of two objectives with their priority levels are presented. The two objectives include the minimization of the mean deviation (or mean absolute deviation) from the midpoint of specification limits and the minimization of the unit cost of the blend. The models are applicable to any number of aggregates and can be used to provide the optimum proportions corresponding to a given priority level or to establish trade‐off curves between mean deviation and cost. The stochastic elements of aggregate gradations are formulated and incorporated into the models. Both the deterministic and stochastic models are applied to a numerical aggregate blending problem, and extensions of the models to accommodate some practical cases are presented.