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Zachary Grasley

Bio: Zachary Grasley is an academic researcher from Texas A&M University. The author has contributed to research in topics: Cementitious & Viscoelasticity. The author has an hindex of 25, co-authored 100 publications receiving 2119 citations. Previous affiliations of Zachary Grasley include Virginia Tech & University of Illinois at Urbana–Champaign.


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TL;DR: In this paper, carbon nanotubes (CNTs) and carbon nanofibers (CNFs) are added to cement matrix composites in concentrations of 0.1 and 0.2% by weight of cement.
Abstract: Carbon nanotubes (CNTs) and carbon nanofibers (CNFs) are quickly becoming two of the most promising nanomaterials because of their unique mechanical properties. The size and aspect ratio of CNFs and CNTs mean that they can be distributed on a much finer scale than commonly used microreinforcing fibers. As a result, microcracks are interrupted much more quickly during propagation in a nano- reinforced matrix, producing much smaller crack widths at the point of first contact between the moving crack front and the reinforcement. In this study, untreated CNTs and CNFs are added to cement matrix composites in concentrations of 0.1 and 0.2% by weight of cement. The nanofilaments are dispersed by using an ultrasonic mixer and then cast into molds. Each specimen is tested in a custom-made three-point flexural test fixture to record its mechanical properties; namely, the Young's modulus, flexural strength, ultimate strain capacity, and fracture toughness, at 7, 14, and 28 days. A scanning electron microscope (SEM) is used to discern the difference between crack bridging and fiber pullout. Test results show that the strength, ductility, and fracture toughness can be improved with the addition of low concentrations of either CNTs or CNFs. DOI: 10.1061/(ASCE)MT.1943-5533.0000266. © 2011 American Society of Civil Engineers.

278 citations

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TL;DR: In this article, the effects of functionalized carbon nanotubes (CNTs) and carbon nanofibers (CNFs) on the mechanical properties of cement composites, both untreated and treated CNFs and CNTs were added to cement paste in concentrations of 0.1% and 0.2% by weight of cement.
Abstract: To study the effects of functionalized carbon nanotubes (CNTs) and carbon nanofibers (CNFs) on the mechanical properties of cement composites, both untreated and treated CNFs and CNTs were added to cement paste in concentrations of 0.1% and 0.2% by weight of cement. The surface-treated nanofilaments were functionalized in a solution of sulfuric acid (H2SO4) and nitric acid (HNO3). The nano- filaments were dispersed by using an ultrasonic mixer and were then cast into molds. Each specimen was tested in a custom-made three-point flexural test fixture to record the mechanical properties (i.e., the Young's modulus, flexural strength, ductility, and modulus of toughness) at the age of 7, 14, and 28 days. The microstructure was analyzed by using a scanning electron microscope. Untreated CNTs and CNFs were found to enhance the mechanical properties of cementitious materials, whereas the acid-treated CNTs and CNFs degraded the mechanical properties. DOI: 10.1061/(ASCE)NM.2153-5477.0000041. © 2012 American Society of Civil Engineers. CE Database subject headings: Nanotechnology; Cement; Mechanical properties; Carbon. Author keywords: Carbon nanotubes; Carbon nanofibers; Cement; Surface treatment; Mechanical properties.

141 citations

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TL;DR: In this paper, the effect of using superplasticizers accompanied by sonication on the dispersion of carbon nanofibers in water and paste was investigated and suggestions were made for achieving enhanced dispersal.
Abstract: Carbon nanofibers (CNFs) and nanotubes (CNTs) are known to be extremely strong and stiff, and their potential as reinforcement has been of interest to many investigators in the past decade. One of the most important keys for fully harnessing the properties of any type of fiber is to control the distribution in the material matrix. As far as CNFs-CNTs are concerned, the strong attraction among nanoscale fibers due to van der Waals forces makes this task difficult. This study focuses on some of the problems that prevent a uniform distribution of CNFs-CNTs in cement paste and the methods used in the past to enhance dispersion. The first phase of the experimental program investigates the effect of using superplasticizers accompanied by sonication on the dispersion of CNFs in water and paste. The second phase focuses on the problem of cement grain size and limitations that the use of fine grain cement causes. Finally, on the basis of results and past studies, suggestions are made for achieving enhanced dispers...

141 citations

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TL;DR: In this article, the role of pore fluid pressure changes on the thermal dilation coefficient of hardened cement paste and concrete is investigated through internal relative humidity measurements, and the additional thermal strain caused by changes in pore fluids pressure was modelled using internal RH measurements as a primary parameter.
Abstract: The coefficient of thermal dilation (CTD) of hardened cement paste and concrete is a function of the state of internal moisture in the pore system. It has been theorized that changes in the pore fluid pressure induced by temperature change causes additional dilation when the material is partially saturated. Drying shrinkage stresses in early-age concrete also evolve from changes in the pore fluid pressure. The Kelvin-Laplace equation relates changes in the pore fluid pressure to the measured internal relative humidity (RH). This research investigated the role of pore pressure changes on the CTD through internal RH measurements. A maximum change in humidity (ΔRH) due to temperature change (ΔT) was measured when the initial humidity was at an intermediate value. Likewise, the maximum CTD was also measured at an intermediate initial RH. Based on these findings, the additional thermal strain caused by changes in pore fluid pressure was modelled using internal RH measurements as a primary parameter.

112 citations

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TL;DR: In this paper, a simple model was developed to estimate the stress gradient associated with drying in both free and fully restrained concrete specimens, and the model predicts that the stresses in the surface layer of restrained concrete exceed the tensile strength of the material prior to complete specimen failure.
Abstract: A moisture gradient develops as concrete dries, inducing a drying shrinkage stress gradient that can lead to early-age cracking in restrained concrete. A new internal relative humidity measurement system was used to quantify the moisture gradient in early-age concrete exposed to drying. A simple model was developed to estimate the stress gradient associated with drying in both free and fully restrained concrete specimens. The model predicts that the stresses in the surface layer of restrained concrete exceed the tensile strength of the material prior to complete specimen failure. Comparison of the model and experimental results indicate that the fully restrained specimens with the most severe drying stress gradients failed at the earliest ages.

103 citations


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6,278 citations

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TL;DR: In this paper, the reinforcing effects of graphene oxide (GO) on portland cement paste are investigated, and it is discovered that the introduction of 0.03% by weight GO sheets into the cement paste can increase the compressive strength and tensile strength of the cement composite by more than 40%.
Abstract: In this experimental study, the reinforcing effects of graphene oxide (GO) on portland cement paste are investigated. It is discovered that the introduction of 0.03% by weight GO sheets into the cement paste can increase the compressive strength and tensile strength of the cement composite by more than 40% due to the reduction of the pore structure of the cement paste. Moreover, the inclusion of the GO sheets enhances the degree of hydration of the cement paste. However, the workability of the GO-cement composite becomes somewhat reduced. The overall results indicate that GO could be a promising nanofillers for reinforcing the engineering properties of portland cement paste.

604 citations

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TL;DR: In this article, the effect of incorporating nanomaterials in low dosages to the fabrication, workability, hydration, microstructure, and mechanical properties of cement-based composites are comprehensively reviewed.

512 citations

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TL;DR: In this paper, two types of cement-based sensors, one with carbon fibers alone and the other carrying a hybrid of both fibers and nanotubes, were considered and their ability to sense an applied compressive load through a measureable change in resistivity was investigated.
Abstract: Electrically conductive cementitious composites carrying carbon fibers and carbon nanotubes were developed and their ability to sense an applied compressive load through a measureable change in resistivity was investigated. Two types of cement-based sensors, one with carbon fibers alone and the other carrying a hybrid of both fibers and nanotubes, were considered. Direct comparisons were also made with traditional strain gauges mounted on the sensor specimens. Sensing experiments indicate that under cyclic loading, the changes in resistivity mimic both the changes in the applied load and the measured material strain with high fidelity for both sensor types. The response, however, is nonlinear and rate dependent. At an arbitrary loading rate, the hybrid sensor, containing a combination carbon fibers and nanotubes, produced the best results with better repeatability.

466 citations