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

This work presents results from an on-going investigation on the microstructural properties of cement-based materials in the presence of very low concentration of polymeric nano-aggregates. The hereby discussed properties are mainly porosity and permeability of mortar specimens, containing 0.5 g/L (0.03 lb/ft3 ) (mixing water) Poly(ethylene oxide)-block-Polystyrene (PEO113-b-PS218) stabilized micelles. The coefficient of water permeability, K, for the samples cast with nano-aggregates was found to be significantly lower, 3.65 e–14 m/s, compared to the control specimen, 3.7 e–8 m/s. Apparently, even a very low concentration of PEO113-b-PS218 micelles is able to significantly reduce water permeability at early ages. The phenomena are most likely denoted to re-distribution and transformation of hydration products in the matrix, the micelles contributing to restructuring of the pore space and altering the cement hydration mechanisms due to their specific amphiphilic properties.

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.

The effect of nano-anatase titanium dioxide (TiO2) powder on early age hydration kinetics of tricalcium silicate (C3S) was investigated. Isothermal calorimetry was performed on C3S pastes with 0, 10, and 15% of TiO2 addition by weight, and two mathematical models-the Avrami model and the boundary nucleation model (BN model)-were fitted to the data. The addition of TiO2 accelerated the rate of hydration, increased the peak reaction rate, and increased the degree of hydration at 12 and 24 hours. The model fits demonstrate that the BN model better captures the kinetics of the reaction, particularly in the deceleration period, than the Avrami model. The increase in the ratio of rate parameters (kB/kG) of the BN model with TiO2 addition suggests that hydration product is formed on or near the surfaces of TiO2 particles, as well as on the C3S surface. These results demonstrate that the addition of TiO2 nanoparticles accelerates the early hydration by providing additional nucleation sites, forming the foundation for future optimization of photocatalytic and other nanoparticle-containing cements.

The effects of small dosages of nano-silica as a partial cement replacement material on the Ca ion leaching resistance of cement pastes exposed to deionized water is reported in this paper. Plain and modified cement paste specimens (containing either 6% or 9% of silica fume, or 0.5% or 1.5% of nano-silica) are subjected to leaching in deionized water for different durations after 56 days of curing in saturated limewater. The mass loss, change in porosity, and the changes in calcium hydroxide (CH) and C-S-H contents from thermogravimetric analysis between the specimens cured under saturated limewater for the entire duration and the specimens leached for different times are used to bring out the beneficial effects of these cement replacement materials when pastes are exposed to a leaching medium. The nano-silica modified cement pastes are observed to demonstrate lower mass loss and a lower increase in porosity when subjected to leaching. Using the changes in CH and C-S-H contents between the saturated and the leached pastes, it is shown that leaching and continuing cement hydration and/or pozzolanic reaction are essentially coupled, especially for the modified pastes. The paste with higher nano-silica content is seen to demonstrate increased C-S-H contents when undergoing leaching. The net Ca ion loss from both CH and C-S-H phases are seen to be lower for the pastes incorporating nano-silica as compared to those containing silica fume. The plain paste is seen to suffer the highest amount of Ca ion loss. A simplified method of calculating the apparent depth of the CH dissolution front is also reported, which is seen to highlight the influence of nano-silica and silica fume in improving the leaching resistance of pastes.