Time filter

Source Type

Chesapeake City, MD, United States

Munoz J.F.,National Research Council Italy | Yao Y.,SES Group and Associates LLC | Youtcheff J.,Turner Fairbank Highway Research Center | Arnold T.,Turner Fairbank Highway Research Center
Cement and Concrete Composites | Year: 2014

This study explored the effect of two combinations of silicon and aluminum oxides, nanosilica-nanoboehmite and nanosilica-gibbsite, on the hydration reaction of cement and the porosity of the interfacial transition zone (ITZ). The influence of sols on the cement hydration reaction was investigated using isothermal calorimetry while their effect on the porosity of the aggregate-paste interface was validated using scanning electron microscopy. The nanosilica-nanoboehmite mixtures were found to accelerate the hydration reaction to a higher degree than the individual components, nanosilica and nanoboehmite. Further, the effect was also found to be dependent on the stoichiometry of the mixture of nanoparticles. The nanosilica-gibbsite combinations not only accelerated the reaction but also increased the cumulative heat of hydration. In this case, the enhancement is attributed to the seeding effect of the gibbsite particles, being more prominent at the smaller particle sizes. Lastly, when these materials were applied as nanoporous thin films on the aggregates, all sol mixtures not only helped to decrease the overall porosity but also contributed to refinement of the porosity in the cement paste adjacent to the aggregate. These effects were observed up to 250 μm away from the surface of the aggregate thus not restricted to the typical length of the interfacial transition zone in concrete (40-50 μm). © 2013 Elsevier Ltd. All rights reserved. Source

Kim H.,SES Group and Associates LLC | Goulias D.G.,University of Maryland University College
Journal of Materials in Civil Engineering | Year: 2015

In the current trend of sustainability, the concrete community has been aggressively looking into adopting green construction material practices and at the same time improving concrete quality and performance for extensive service life and adaptive reuse. Concrete is the construction material most used in the world, with an estimated yearly production of 2.35 billion tons worldwide. In the United States, it is estimated that on average approximately 5% of the ready-mix concrete produced is unused and returned to the plant with only a small portion reused. Such a material when further processed, identified as crushed returned concrete aggregate (CCA), has a significant residual value because among other things it is free of contaminants and has better quality than recycled concrete aggregate (RCA). The objective of this study was to assess the shrinkage behavior of CCA concrete mixtures produced with aggregate from returned concrete. The aggregate was prepared from concrete of different strength. The virgin aggregate (stone) was replaced either partially or at 100% level in the concrete mixtures. The response of the hyperbolic shrinkage prediction model was examined, and based on the experimental results an alternative model is proposed. The proposed model and methodology can be used to estimate the drying shrinkage of CCA mixtures, and eventually can be adopted for assessing the shrinkage behavior of these concrete mixtures in other regions. © 2014 American Society of Civil Engineers. Source

Williams A.J.,University of Nevada, Las Vegas | Buck B.J.,University of Nevada, Las Vegas | Beyene M.A.,University of Nevada, Las Vegas | Beyene M.A.,SES Group and Associates LLC
Soil Science Society of America Journal | Year: 2012

Biological soil crusts (BSCs) are bio-sedimentary complexes that play critical ecological roles in arid landscapes; however, the interactions between component biota and sediments are poorly understood. A detailed micromorphological investigation of BSC development and crust microstructure in the Muddy Mountains Wilderness Area, Nevada, examined features in thin section using petrographic microscopy, light microscopy, scanning electron microscopy, and energy dispersive x-ray spectroscopy. The >1800 microscopic observations were linked to crust macroscale features and soil geomorphology. Complex bio-sedimentary structures of BSCs reflect a dynamic genetic history and diverse formative processes, including: (i) stabilization and authigenic mineral precipitation; (ii) wetting-drying and expansion-contraction; (iii) dust capture; (iv) microscale mass wasting; and (v) vesicular (Av) horizon formation. A new conceptual model for hot deserts illustrates how these processes co-develop with BSC succession, during countless wet-dry cycles, to build up pinnacle microtopography while simultaneously forming Av horizons in the bio-rich and bio-poor zones. Complex surficial and internal bio-sedimentary structures, which vary as a function of crust morphology, trap surface water for uptake by crust organisms, while dust influx provides a source of nutrients. These phenomena influence landscape-scale water dynamics and biogeochemical cycling, increasing the availability of soil resources during times of biotic stress. Biological soil crusts uniquely facilitate the accumulation, morphology, and ecosystem function of dust and should, therefore, be considered critical agents in arid pedogenesis and landscape development. © Soil Science Society of America,. Source

Meininger R.C.,FHWA Office of Infrastructure Research and Development | Stokowski S.J.,SES Group and Associates LLC | Stokowski S.J.,Turner Fairbank Highway Research Center
Public Roads | Year: 2011

Sand, gravel, crushed stone, and, increasingly, industrial byproducts and reclaimed construction materials are the foundation of the Nation's transportation infrastructure. Collectively referred to as aggregates, these materials are essential to constructing, preserving, and rehabilitating roads and bridges. Ensuring a sustainable supply of aggregates requires advance planning and balancing a complex matrix of engineering, geographical, and geological variables and community interests. In general, natural aggregates are mined from stone quarries and from sand and gravel pits. Increasingly, however, agencies are using recycled, reclaimed, and alternative byproduct aggregate materials, such as blast furnace and steel slag, other mining or industrial byproducts, and reclaimed asphalt pavement and recycled concrete aggregate. FHWA estimates the US transportation industry's need for aggregates for pavements at about 700 million tons per year. Other objectives of Alaska's program include development of performance standards that the department can apply to material sites and to facilitate geotechnical asset management to drive long-term decision making concerning these material assets. Source

Balachandran C.,SES Group and Associates LLC | Olek J.,Purdue University | Rangaraju P.R.,Clemson University | Diamond S.,Purdue University
Transportation Research Record | Year: 2011

About 15 years after the introduction of alkali-acetate and alkali-formate deicers, premature deterioration was observed on some airfield pavements that had been exposed to the deicers. A characteristic map cracking pattern was observed on pavement surfaces that had experienced repeated applications of these deicers, and the suspected cause of this cracking pattern was accelerated alkali-silica reaction (ASR). Laboratory-based research indicated that alkali-silica reactive aggregates may undergo active deterioration when intimately exposed to such deicers under conditions promoting accelerated reaction. Investigations were conducted on cores collected from an airport whose deicing operations involved repeated applications of potassium acetate deicer. Detailed microscopic investigation indicated that uniform distress existed throughout the depth of the pavement, although in one, the distress resulted from alkali-carbonate reaction rather than from ASR. However, investigations on the depth of penetration of deicer into these pavement cores showed only limited incursion. A companion laboratory study estimated the extent of deicer penetration under different laboratory exposure conditions. Even in a relatively aggressive wetting and drying exposure regime, ingress of the deicer was limited. Thus, it was concluded that although the potassium acetate deicer can induce severe ASR under aggressive laboratory conditions, penetration into field airport pavements may be so limited in some cases that the potassium acetate deicer does not seem to aggravate the ASR distress should one already exist. Source

Discover hidden collaborations