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Abstract: A radar nondestructive testing (NDT) technique using an airborne horn antenna operating in the far-field condition is developed for detecting damages such as debonding and concrete cracking in glass fiber reinforced polymer (GFRP)-wrapped concrete columns. The far-field airborne radar (FAR) NDT technique is advantageous for distant measurement in practical applications where contact/near-contact measurement becomes an issue. In this technique the radar antenna operates in inverse synthetic aperture radar (ISAR) mode. Laboratory measurements at the frequency range 8–18GHz are made on artificially damaged GFRP–concrete specimens for a preliminary validation of this technique. Collected frequency–angle measurements are further processed by the fast backprojection algorithm to render range–cross-range imagery for damage detection. From the reported measurements and imaging results the proposed FAR NDT technique is conceptually validated; the potential of this technique is shown in identifying defects and debonding in the GFRP–concrete interface regions of the concrete columns wrapped with these composite materials. [Copyright &y& Elsevier]

This work investigates the synergetic effect of nano-silica, NS, (up to 2% by weight) and metakaolin, MK, (up to 9.75% by weight) on the pore- and micro-structure of hardened Ordinary Portland Cement (OPC) pastes after 28 days of curing time. By addition of NS, it was observed that ultra-fine porosity of the cementitious matrix was formed due to the plombierite phase observed via synchrotron XRD analysis. The inclusion of MK along with NS facilitated formation of Calcium-Aluminum-Silicate-Hydrate (C-A-S-H) based crystal structure of wairakite . Mean chain length (MCL) values showed that addition of NS to MK helped in increasing the MCL values up to 7.8, while decreasing the Ca/Si ratio contributed to a higher degree of silicate polymerization that facilitated Calcium-Silicate-Hydrate (C-S-H)/C-A-S-H formation. Water adsorption analysis detected that the inclusion of NS to OPC increased the specific surface area up to 163.5 m 2 /g suggesting probable densification of the cementitious matrix. [ABSTRACT FROM AUTHOR]

This work investigates the effectiveness of the use of volcanic ash along with silica fume as a partial replacement for Portland cement. Multiple mix combinations of volcanic ash, silica fume and Portland cement were examined using various pore and microstructure characterization techniques. Hardened cement pastes were cured for 28 days and their pore and microstructures were examined using X-ray Microtomography, Magic Angle Spinning (MAS) Nuclear magnetic resonance (NMR) for 27 Al and 29 Si, X-ray Diffraction (XRD) and Fourier transform infra-red spectroscopy (FTIR). Microstructure examination of mixes prepared with volcanic ash, silica fume and Portland cement revealed the co-existance of calcium silicate hydrate (C-S-H) and calcium–alumino-silicate-hydrate (C-A-S-H) gels, along with other hydration products that led to a reduction in porosity and densification of the cement matrix. These findings indicate that volcanic ash along with silica fume is a viable substitute for Portland cement up to 40% and provides a sustainable, cost effective and environmentally friendly solution to volcanic ash disposal. [ABSTRACT FROM AUTHOR]

Raman Spectroscopy was used to track the free water and the cementitious gel phases when Ordinary Portland Cement (OPC) and tricalcium silicate (C 3 S) were partially substituted by natural pozzolanic volcanic ash. Two different particle sizes of volcanic ash (VA), (namely 17 and 6 μm) were each used to substitute 10%, 30% and 50% of OPC and C 3 S by weight. Particle size and concentration of VA significantly affected the hydration behavior of cement paste by influencing the water dynamics during the course of hydration. Increase in concentration of VA also led to an increase in “free water” during the course of hydration. Calcium silicate hydrate (C-S-H) phases along with calcium/magnesium based zeolites were detected as the concentration of volcanic ash increased in the mix. This work shows that Raman spectroscopy is a powerful tool to examine the hydration process when Portland cements are substituted by volcanic ashes of different sizes. [ABSTRACT FROM AUTHOR]

In recent years, continuum and atomistic modeling of cementitious materials has provided significant advances towards studying the durability of civil infrastructure. An important frontier to understanding structure-property relationships is the “mesoscale”, which represents the bridge between underlying (e.g. molecular) processes and bulk macroscale behavior. This review highlights examples of a mesoscale approach within biological materials and emphasizes their applicability to the study and design of sustainable cement-based materials at multiple length scales. We propose a methodology focused on the coupling of computation and experiment for furthering our understanding of the microstructural properties that control the durability of hardened cement paste. [ABSTRACT FROM AUTHOR]

The use of volcanic ash as a partial substitute to Portland cement can be a viable alternative for producing sustainable and durable cementitious materials. This study investigates the effect of early and late age curing of hardened cement pastes made with volcanic ash and Ordinary Portland Cement (OPC). Pore and microstructure studies were performed on hardened cement pastes prepared with 10% incremental substitution of volcanic ash up to 50% substitution of OPC. Densification in hardened cement pastes was attributed to formation of Calcium Silicate Hydrate (C-S-H) and Calcium-Alumino-Silicate-Hydrate (C-A-S-H) gels, while the development of Magnesium-Silicate-Hydrates (M-S-H) led to decalcification of C-S-H and C-A-S-H gels which resulted in an increase in porosity of the cementitious matrix. A combination of bulk and surface characterization techniques was used to facilitate effective usage of volcanic ash as a potential substitute for Portland cement that provides a sustainable construction material, and environmentally friendly solution to volcanic ash disposal. [ABSTRACT FROM AUTHOR]

Abstract: Fiber reinforced polymer (FRP) materials have been increasingly used in the last two decades to improve various structural characteristics of reinforced concrete (RC) bridges, buildings and other structures. Ductility of the resulting FRP–concrete system plays an important role in structural performance, especially in certain applications such as earthquake resistant design of structures, where ductility and energy dissipation play a vital role. Wrapping RC columns with FRP has been shown to generally result in significant increase in ductility due to the confinement of concrete by the FRP. Other applications such as flexural strengthening of beams involve tradeoffs between ductility and the desired load capacity. Furthermore, environmental factors may adversely affect the FRP–concrete bond raising concerns about the ductility of the system due to possible premature failure modes. Characterization of these effects requires the use of more involved mechanics concepts other than the simple elastic or ultimate strength analyses. This paper focuses on characterizing ductility of the FRP–concrete systems at different length scales using a combined experimental/computational mechanics approach. Effects of several parameters on ductility, including constituent material properties and their interfaces, FRP reinforcement geometry at the macro- and meso-level, and atomistic structure at the molecular level are discussed. Integration of this knowledge will provide the basis for improved design strategies considering the ductility of FRP–concrete systems from a global as well as local perspective including interface bond behavior under various mechanical and environmental conditions. [Copyright &y& Elsevier]

• Small angle neutron scattering and inelastic neutron scattering investigation of cement paste. • Engineering volcanic ash in Portland cement using fractal insights and water dynamics. • Concentration, along with the particle size of the volcanic ash, influences the initiation of gelation in cement paste. Hydration behavior of cements with additives is complicated due to the multifarious nature of hydration products formed at various stages of hydration. Neutron-based scattering techniques are useful in detecting both the microstructural evolution and water dynamics of hydrating cement pastes. This work investigates the effect of early-age hydration on microstructural evolution of cement paste with local volcanic ash using neutron-based beamline techniques. Early-age hydration dynamics of Portland cement paste with volcanic ash was examined via inelastic neutron scattering (INS), while the evolution of microstructure was observed with small angle neutron scattering (SANS). The data obtained from the ratio of volume fractal to surface fractal clearly showed that greater than 30% substitution of volcanic ash leads to unreacted volcanic ash and coarser morphology, which could influence the chemo-mechanical properties of the resulting hydration products. INS results showed that the effect of finer-particle-sized volcanic ash contributes to initiation of gelation, which accommodates higher conversion of free water to bound water. The multi-scale analysis that combines a time-resolved study of water dynamics along with microstructure is found to provide a basis for effectively utilizing engineered additives for the local cement industry. [ABSTRACT FROM AUTHOR]