International Concrete Abstracts Portal

This CD-ROM consist of 9 papers sponsored by ACI Committee 236, at the Fall 2009 Convention in New Orleans, LA, in November 2009. The papers included cover a broad range of subjects related to the nanotechnology and material science of concrete with focus on nanostructure characterization, synthesis, design, and modeling of cement based materials, as well as application of nano-materials in concrete technology. Note: The individual papers are also available. Please click on the following link to view the papers available, or call 248.848.3800 to order. SP-267

Recent developments in nanotechnology paved the way for deepening the modeling level of science-based kernels and enabling new opportunities in terms of understanding the formation of hydration products and their contribution to the microstructure. Based on these developments next generation models are considered to have the potential to design new advanced materials that contribute to sustainable construction. One of the activities currently running in this field is the Codice (Computationally Driven design of Innovative Cement-based materials) project which is a multi-scale modeling research project established within the European research arena FP7. The project has the ambition to bridge the nanoscale to the microscale by applying advanced computational simulation modeling techniques for cementitious materials. Nano-based models will be connected to the microscale level within the framework of the Hymostruc model. It is the objective of the CODICE project to provide more insight into the role of the fundamental building blocks of CSH gel (basically 5nm sized nanoparticles) and the mechanisms that govern their aggregation into high-density (HD) and low-density (LD) C-S-H varieties. Thus, the project aims to refine the microstructure of the Hymostruc model (Breugel 1991) so as to recognize the two types of C-S-H aggregates. The new computational scheme is expected to be a perfect tool to design new cementitious materials with improved mechanical properties.

In this study, the development of cementitious nanocomposites reinforced with multiwall carbon nanotubes (MWCNTs) at water-cement ratios of 0.3 and 0.5 was investigated. The effect of carbon nanotubes at low concentrations on the fracture properties, nanoscale properties and microstructure of the nanocomposite materials was studied. The morphology and the microstructure of nanocomposite samples were investigated using an ultra high resolution field emission scanning electron microscope. A special type of nanoindenter, along with in-place scanning probe microscopy imaging, was used to determine the local nanoscale mechanical properties. The results show that the mechanical properties of cementitious matrices can be increased by the incorporation of very low amounts of CNTs. Nanoimaging of the fracture surfaces of cement nanocomposites have shown that CNTs reinforce cement paste by bridging the nanocracks and pores. Additionally, nanoindentation results suggest that CNTs modify and reinforce the nanostructure of cement paste by increasing the amount of high stiffness C-S-H and reducing the porosity.

The authors aim to investigate the effect of using colloidal nano-silica on the properties of concrete especially for the case of fly ash concrete. The study includes a laboratory study on six concrete mixtures in which three have 30% of the cement content replaced with fly ash, while the others were normal cement concrete mixtures. Two ratios of colloidal nano-silica were added to concrete with and without fly ash to examine its effect. Testing was conducted to assess the reactivity and the durability of the studied mixtures, including adiabatic temperature test, compressive strength test, splitting tensile strength test, and rapid chloride penetration test. Results show the addition of nano-silica can enhance the reactivity and early age strength of fly ash concrete mixtures to match normal concrete mixtures. Furthermore, the use of nano-silica improved the mechanical properties and reduced the permeability of concrete.

With the advent of nano technology, materials have been developed that can be applied to high performance concrete mix designs. Nano silica reacts with calcium hydroxide to develop more of the strength carrying structure of cement paste, calcium silica hydrate. In this paper, predictive relationships have been developed to distinguish the strength benefits when using different sizes of nano silica in cement paste. An extensive regime of experimental analysis was carried out to determine the effect of nano silica in the cement paste. Through these experiments the heat of hydration of multiple cement mix designs were measured. After that, the concentration of calcium hydroxide was recorded through X-ray diffraction. Then, the crystallographic structures were examined through scanning electron microscopy. Finally, the compressive strength was determined for each cement paste mixture. Through these experiments it was found that as the silica particles decreases in size and incorporate a wider gradation of sizes, the calcium silicate hydrates became more rigid; this increased the compressive strength.