International Concrete Abstracts Portal

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.

Due to the ubiquity of concrete in the urban environment and the upscaling of nanomaterial production, the incorporation of nanoparticles into cementitious materials has gained increased attention. This study compares the performance of various titania (TiO₂) and silica (SiO₂) nanoparticles-modified coatings, including their photocatalytic performance and the quality of their adhesion to the cementitious substrates. The photocatalytic performance with respect to air purification and self-cleaning are evaluated by nitrogen oxide (NO_x) and methylene blue (MB) dye photodegradation, respectively. The results show that the Portland cement (OPC)-based cementitious materials exhibit greater photocatalytic efficiency than calcium aluminate cement (CAC)-based ones. It is proposed that the superior performance is due to a greater proportion of finer porosity and the presence of high surface area calcium silicate hydrates (C-S-H) in OPC-based cementitious materials. Interactions between coatings and cementitious substrates are examined through wettability and adhesion. The results show that the inclusion of silica layer can affect the interaction of coated cementitious surface with water, as well as the bond strength between coating and cementitious substrate.

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.

Nanomaterials like nanosilica, nanoalumina and nanoclay have shown improvement in workability and increased compressive strength when used with cement. However, the potential of using nanoclay to alter the elastic modulus and limit creep of oil-well cement (OWC), specifically when cured under high temperature and pressure, has not been explored. In this investigation, Type-G cement mixed with 1.0 wt.%, 3.0 wt.% and 5.0 wt.% nanoclay and with water/cement ratio of 0.45 was prepared and cured for 7 days under high temperature and pressure of 80 ℃ (176 ℉) and 10 MPa (1500 psi) respectively. Dynamic mechanical analysis was conducted under high temperature to reveal the evolution of the elastic modulus and creep compliance of the different cement-nanoclay mixture with curing time. Thermogravimetric analysis, Scanning Electron Microscope and X-ray Diffraction measurements were performed to support observations of elastic modulus and creep compliance evolution of OWC incorporating nanoclay explaining the microstructural changes that take place in OWC mixture incorporating nanoclay when hydrated under high temperature and pressure.

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.