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Early-age hydration kinetics of Portland cement with nano-additives such as nano-silica (NS) was examined using quasielastic neutron scattering (QENS). Cement pastes with different ratios of Portland cement to NS were prepared. The concentration of the NS played a major role in controlling the free and bound water during the hydration of the cement paste. Additionally, the effects of metakaolin (MK) with NS in Portland cements revealed that MK acts as a retarder by decreasing the bounding water capacity during the early age of hydration. An increase in the concentration of NS affected the degree of hydration by reducing the amount of free and mobile water in the gel pores when compared to Portland cement paste. Here, we show that the concentration of NS governs the early-age hydration process in Portland cements. [ABSTRACT FROM AUTHOR]

In recent years, the construction of tall buildings has been increasing in many countries, including Kuwait and other Gulf states. These tall buildings are especially sensitive to ground shaking due to long period seismic surface waves. Although Kuwait is relatively aseismic, it has been affected by large (Mw > 6) regional earthquakes in the Zagros Fold-Thrust Belt (ZFTB). Accurate ground motion prediction for large earthquakes is important to assess the seismic hazard to tall buildings. In this study, we first analyze the observed ground motions due to two earthquakes widely felt in Kuwait: the 08/18/2014 Mw 6.2 earthquake, 360 km NNE of Kuwait City, and the 11/12/2017 Mw 7.3 earthquake, 642 km NNE of Kuwait City. The peak spectral displacement periods of the ground motion from the 08/18/2014 Mw 6.2 earthquake matched well with the ambient vibration spectra of the tallest building—the Al-Hamra Tower. We calculate the ground motions from potential regional and local earthquakes. We use a velocity model obtained by matching the observed seismograms of the 2014 and 2017 earthquakes. We calculate ground motions in Kuwait due to a regional Mw = 7.5 earthquake, and a local Mw = 5.0 earthquakes. Our study shows that a significant source of seismic hazard to tall buildings in Kuwait comes from the regional tectonic earthquakes. However, local earthquakes have the potential to generate high peak ground accelerations (~ 98 cm/s2) close to their epicenters. [ABSTRACT FROM AUTHOR]

This study investigates the early ages of hydration behavior when basaltic volcanic ash was used as a partial substitute to ordinary Portland cement using ultra-small-angle X-ray scattering and wide-angle X-ray scattering (WAXS). The mix design consisted of 10, 30 and 50% substitution of Portland cement with two different-sized volcanic ashes. The data showed that substitution of volcanic ash above 30% results in excess unreacted volcanic ash, rather than additional pozzolanic reactions along longer length scales. WAXS studies revealed that addition of finely ground volcanic ash facilitated calcium-silicate-hydrate related phases, whereas inclusion of coarser volcanic ash caused domination by calcium-aluminum-silicate-hydrate and unreacted MgO phases, suggesting some volcanic ash remained unreacted throughout the hydration process. Addition of more than 30% volcanic ash leads to coarser morphology along with decreased surface area and higher intensity of scattering at early-age hydration. This suggests an abrupt dissolution indicated by changes in surface area due to the retarding gel formation that can have implication on early-age setting influencing the mechanical properties of the resulting cementitious matrix. The findings from this work show that the concentration of volcanic ash influences the specific surface area and morphology of hydration products during the early age of hydration. Hence, natural pozzolanic volcanic ashes can be a viable substitute to Portland cement by providing environmental benefits in terms of lower-carbon footprint along with long-term durability. [ABSTRACT FROM AUTHOR]

Organic–inorganic interfaces exist in many natural or synthetic materials, such as mineral–protein interfaces found in bone and epoxy–silica interfaces found in concrete construction. Here, we report a model to predict the intrinsic strength between organic and inorganic materials, based on a molecular dynamics simulation approach combined with the metadynamics method, used to reconstruct the free energy surface between attached and detached states of the bonded system and scaled up to incorporate it into a continuum model. We apply this technique to model an epoxy–silica system that primarily features nonbonded and nondirectional van der Waals and Coulombic chemical interactions. The intrinsic strength between epoxy and silica derived from the molecular level is used to predict the structural behavior of epoxy–silica interface at the macroscopic length scale by invoking a finite element approach using a cohesive zone model which shows a good agreement with existing experimental results. [ABSTRACT FROM PUBLISHER]