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International Concrete Abstracts Portal

Showing 1-5 of 11 Abstracts search results

Document: 

SP335

Date: 

October 9, 2019

Author(s):

Mahmoud Reda Taha and Mohamed T. Bassuoni

Publication:

Symposium Papers

Volume:

335

Abstract:

Many of the papers presented in this volume were included in the two-part session Nanotechnology for Improved Concrete Performance, sponsored by ACI Committee 241, Nanotechnology of Concrete at the ACI Convention in Philadelphia, PA, on October 26, 2016. In line with the practice and requirements of the American Concrete Institute, peer review, followed by appropriate response and revision by authors, has been implemented.

DOI:

10.14359/51721384


Document: 

SP-335_06

Date: 

September 20, 2019

Author(s):

Su-Jin Lee, Shiho Kawashima, and Jong-Pil Won

Publication:

Symposium Papers

Volume:

335

Abstract:

In this study, nanosilica was applied to the surface of polypropylene (PP) fibers to introduce self-healing abilities when incorporated into cement-composites. When the fiber is at the site of a crack, the nanosilica can form additional hydration products through pozzolanic reaction to effectively seal the crack. Nanosilica was synthesized onto the fibers through a sol-gel process. Then the fibers were dried at room temperature or 50°C (122°F) to remove the excess solution and adhere the nanosilica particles onto the fiber surface. The existence of nanosilica was confirmed by observing the mass change before and after the sol-gel process, water absorption, soluble matter loss and microscopy. The self-healing performance of cement-composites reinforced with treated and untreated macro and micro PP fibers at dosages of 1.8kg/m3 (3.0lb/yd3) and 0.9kg/m3 (1.5lb/yd3), respectively, were evaluated through flexural strength testing according to ASTM C348. To evaluate strength recovery, samples were loaded to 60% of the peak load to induce cracking. The cracked specimens were cured for 28 days under laboratory conditions to undergo self-healing. A significant recovery in flexural strength (112.8%) was observed by using nanosilica treated micro PP fibers dried at room temperature.

DOI:

10.14359/51720216


Document: 

SP-335_05

Date: 

September 20, 2019

Author(s):

Sumanta Das, Pu Yang, Sudhanshu S. Singh, James C.E. Mertens, Xianghui Xiao, Nikhilesh Chawla and Narayanan Neithalath

Publication:

Symposium Papers

Volume:

335

Abstract:

A  detailed  microstructural  and  micromechanical  study  of  a  fly  ash‐based  geopolymer  paste  including: (i) synchrotron x‐ray tomography (XRT) to characterize the pores (size > 0.74 m) that are influential in fluid transport, (ii) mercury intrusion porosimetry (MIP) to capture the volume fraction of smaller  pores,  (iii)  high  resolution  scanning  electron  microscopy  (SEM)  combined  with  a  multi‐label  thresholding method to identify and characterize the solid phases in the microstructure, and (iv) nanoindentation  to  determine  the  component  phase  elastic  properties  using  statistical  deconvolution  techniques, is reported in this paper. The 3D pore structure from XRT is used in a computational fluid transport  model  to  predict  the  permeability  of  the  material.  The  pore  volume  from  XRT,  solid  phase  volumes from SEM, and the phase elastic properties are used in a numerical homogenization framework to determine the homogenized macroscale elastic modulus of the composite. The homogenized elastic moduli are in good agreement with the flexural elastic modulus determined on macroscale paste beams. It  is  shown  that  the  combined  use  of  microstructural  and  micromechanical  characterization  tools  at  multiple scales provides valuable information towards the material design of fly ash‐based geopolymers.

DOI:

10.14359/51720215


Document: 

SP-335_09

Date: 

September 20, 2019

Author(s):

A. M. Yasien, A. Abayou, and M. T. Bassuoni

Publication:

Symposium Papers

Volume:

335

Abstract:

In cold regions, freezing temperatures limit the construction season to few months, usually between May and September. The use of nanoparticles, which have high specific surface and vigorous reactivity, may potentially enhance the performance of concrete placed at low temperatures. Therefore, this study focused on developing concrete mixtures incorporating nano-silica which were mixed, placed and cured at -5°C (23°F) without any insulation or protection targeting field applications in late fall and early spring periods. Eight mixtures incorporating general use (GU) cement, fly ash (up to 25%), and nano-silica (up to 4%) were tested for this purpose, with water-to-binder ratios of 0.32 and 0.4. All mixtures contained a combination of calcium nitrate and calcium nitrite as an antifreeze admixture. Testing involved concrete setting time (placement), 7 and 28 days compressive strengths (hardened properties) and resistance to freezing-thawing cycles (durability). Moreover, mercury intrusion porosimetry, thermal analysis and scanning electron microscopy were performed to corroborate the trends from the macro-scale tests. It was found that nano-silica significantly improved the overall performance of concrete placed and cured at -5°C (23°F), which implicates its promising use for construction applications under low temperatures.

DOI:

10.14359/51720219


Document: 

SP-335_03

Date: 

September 20, 2019

Author(s):

Joshua Hoheneder, Ismael Flores-Vivian and Konstantin Sobolev

Publication:

Symposium Papers

Volume:

335

Abstract:

Fiber additions in portland cement composites is a regular practice for crack prevention and for increasing the flexural strength. In this research, fiber-reinforced composites (FRC) with polyvinyl alcohol (PVA) fibers and carbon nanofibers (CNF) or carbon nanotubes (CNT) were investigated. Specimens were tested to measure their flexural strength, water absorption and electrical conductivity in water or sodium chloride solution. It was found that the developed composites, depending on applied stress and exposure to chloride solutions, exhibit some electrical conductivity. These dependencies can be characterized by piezoresistive and chemo-resistive coefficients demonstrating that the material possesses self-sensing capabilities. The sensitivity to strain,  crack formation, and chloride solutions can be enhanced by incorporating small amounts of CNF or CNT into a composite structure. Conducted research has demonstrated a strong dependency of electrical properties of the composite on crack formation in moist environments. The developed procedure is scalable for industrial application in concrete structures that require nondestructive stress monitoring, integrity under high service loads and stability in harsh environments.

DOI:

10.14359/51720213


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