International Concrete Abstracts Portal

This volume consists of ten papers that were presented at a technical session, sponsored by ACI Committee 236, Materials of Science of Concrete, at the ACI Fall 2007 Convention in Denver, CO. Papers include “ Nanotechnology in Construction: A Roadmap for Development”, “ Nanotechnology and Concrete: Research Opportunities”, “Molecular Engineering of the Cohesion in Neat and Hybrid Cement Hydrates”, and “Use of Atomic Force Microscopy and Nanoindentation for Characterization of Cementitious Materials at the Nanoscale”.

Compared with other major industrial sectors, the construction industry has lagged behind in awareness of the potential for exploitation of nanotechnology. Both the awareness and actual exploitation in construction are now increasing; however, progress is uneven, especially in the current early stages of its practical exploitation. A roadmap then becomes a useful tool, a template, for predictions of trends and developments connecting nanotechnology and construction. The Roadmap for Nanotechnology in Construction (RoNaC) outlined in this paper is aimed at facilitating identifications of desirable aims/destinations for construction research and technical development (RTD) over a short-to-medium timescale (up to 25 years). The RoNaC was developed as an aid for forecasting research and investment directions. It provides guidance to construction industry, investors, and national/international bodies supporting research and development about the diverse pathways toward current nanotechnology-linked expectations, aims, and targets in this very large and economically significant domain. The complexity of the construction domain is such that a single overall chart would be far too general in a scale so large that it would become incomprehensible. Sectorial or "topical" charts have been developed instead of a single "map", and three examples of such charts have been worked out to illustrate this approach. Requirements for adequate research infrastructures, effects of appropriate drivers, and diverse vehicles for RTD are considered together with an assessment of the "environment" conducive to progress along the pathways and directions indicated in the charts.

In this research, sample preparation techniques were developed to image the nano- and microstructure of hardened cement paste and to determine local mechanical properties. An atomic force microscope (AFM) was used to image the nanostructure of hardened cement paste. AFM and a Hysitron Triboindenter equipped with an in-situ scanning probe microscopy were used to determine the Young’s modulus of cement paste at the nanoscale.

On the basis of recent molecular simulation or experimental studies, we discuss two possible strategies for improving the mechanical properties of cementitious materials by modifying the bonding scheme in the hydrates at molecular level. We focus on the calcium silicate hydrates (C-S-H). A first strategy would be based on the strengthening of the cohesion forces acting between the individual C-S-H lamellae or between their crystallites. Monte Carlo simulations in the primitive model framework and ab initio atomistic calculations suggest that the cohesion of C-S-H is mainly due to a combination of sub-nano range ionic-covalent forces and meso-range ionic correlation forces. Both types of forces may be modified, at least in theory, by changing the nature of the interstitial ions, their hydration state, or the charge density on the C-S-H lamellae.

Nanotechnology is one of the most active research areas that encompasses a number of disciplines including civil engineering and construction materials. The most active fields are electronics, biomechanics, and coatings. Interest in nanotechnology concept for portland-cement composites is steadily growing. Currently, the most active research areas dealing with cement and concrete are: understanding of the hydration of cement particles and the use of nano-size ingredients such as alumina and silica particles. There are also a limited number of investigations dealing with the manufacture of nanocement. If cement with nanosize particles can be manufactured and processed, it will open up a large number of opportunities in the fields of ceramics, high-strength composites ,and electronic applications. This will elevate the status of portland cement to a high-tech material in addition to its current status of the most widely used construction material. Very few inorganic cementing materials can match the capabilities of portland cement in terms of cost and availability. The main objective of this paper is to outline promising research areas. Basic background information on nanotechnology research, state of the art on use of this technology in concrete, opportunities, and challenges are discussed.