Narayanan Neithalath

Acoustic performance and damping behavior of cellulose-cement composites

Abstract This paper describes the influence of morphologically altered cellulose fibers on the acoustic and mechanical properties of cellulose–cement composites. Three fiber morphologies were considered (macro-nodules, discrete fibers, and petite nodules). The main parameters studied include the normal incident acoustic absorption coefficient (α), specific damping capacity (ψ), loss tangent (tanδ), storage modulus (E′), and loss modulus (E′′=E′tanδ). The acoustic absorption coefficient was found to increase with an increase in fiber volume for all three fiber types investigated, though “macro-nodule” fibers were found to be the most effective. Stiffness–loss relationships are reported for these composites and the behavior of cellulose–cement composites with soft cellulose fiber inclusions was found to be similar to a Voigt (series) composite model. Low volumes of fibers had a minimal effect on the loss tangent; however the stiffness was considerably reduced. Predictive equations for loss modulus as a function of fiber volume at different moisture conditions were developed. These relations compare well with the experimental values as well as the idealized Voigt composite behavior. This suggests that there is an optimum fiber volume, which maximizes the loss modulus for saturated composites while the loss modulus is practically independent of fiber volume for dry composites.

Stereology- and Morphology-Based Pore Structure Descriptors of Enhanced Porosity (Pervious) Concretes

In the structural and functional performance of enhanced porosity concrete (EPC) (or pervious concrete) and other macroporous materials, porosity, pore sizes and their distribution, connectivity, and specific surface area and other pore structure features play dominant roles. Analysis of such EPC features is dealt with in this paper using mathematical morphology and stereological techniques. Similar porosity values for the studied mixtures were provided by a morphological method based on two-point correlation and stereological methods based on area and line fractions. Lower porosity was shown by single-sized aggregate EPC mixtures than blended aggregate mixtures. Smaller pore sizes are found to result from higher proportions of smaller sized aggregates in the mixture. There is definition of an effective pore diameter based on a critical size based on opening granulometric density function, a two-point correlation based characteristic size, and pore size distribution of equivalent diameters. The pore sizes of the blended aggregate mixtures lie in between those of mixtures in which single-sized aggregates make up the blend. Good correspondence is seen between the inverse of the specific surface areas of pores and the effective pore diameter and correlation lengths, whereas there is linear relation of the mean free spacing between pores and these quantities. There is comparison of stereology-based three-dimensional pore distribution density indicating preconnectivity and a hydraulic connectivity factor for permeability, and the latter is shown to be a more sensitive parameter through which EPC specimens made with different size aggregates can be distinguished.

Water Vapor Sorption in Cementitious Materials—Measurement, Modeling and Interpretation

The rate and extent of uptake and release of moisture are critical in controlling the behavior of cementitious materials ranging from fluid transport to hygral deformations. While classically determined using an equilibrium (static) salt solution method (Baroghel-Bouny in Cem Concr Res 37:414–437, 2007), advanced capabilities offered by gravimetric dynamic vapor sorption (DVS) analyzers, are now permitting acquisition of sorption spectra at microgram (

Understanding the Energy Implications of Phase-Change Materials in Concrete Walls through Finite-Element Analysis

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Confined Water in Layered Silicates: The Origin of Anomalous Thermal Expansion Behavior in Calcium-Silicate-Hydrates

μg) resolution on the order of a few weeks. This work highlights new multicycle determinations of adsorption/desorption isotherms, acquired using a custom-built DVS analyzer for well-hydrated alite and ordinary portland cement pastes over a range of water-to-solid ratios (

Observations on the rheological response of alkali activated fly ash suspensions: the role of activator type and concentration

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