International Concrete Abstracts Portal

Nano-technology based on depth-sensing microindentation apparatus was used to evaluate the elastic modulus and micro-hardness of the interfacial transition zone (ITZ) and to estimate the extent of the ITZ around the aggregate-matrix interface for underwater concrete (UWC) and around steel reinforcement for selfconsolidating concrete (SCC) and vibrated concrete. The micromechanical properties of ITZ near to aggregates of concrete cast in water were lower than those of concrete cast in air. The modulus elasticity and the microstrength of concrete cast in water were lower than those of concrete cast in air. It is attributed to the dilution of paste cement and fines particles in water causing reduction of strength and increasing the porosity of concrete. The results of the interfacial properties between selfconsolidating concrete and conventional concrete revealed that the elastic modulus and the micro-strength of the ITZ were lower on the bottom side of a horizontal steel bar than on the top side, particularly for the vibrated reference concrete. The difference of ITZ properties between top and bottom side of the horizontal steel bar appeared to be less pronounced for the SCC mixtures than for the corresponding control mixtures.

The present paper addresses several topics in regard to the sustainable design and use of concrete and the role of nanotechnology. First, major features concerning the sustainable aspects of the material concrete are summarized. Then the major constituent, cement, (from an environmental point of view), is discussed in detail, particularly the hydration and application of slag cement. The intelligent combining of mineral oxides, which are found in clinker, slag, and fly ashes, is designated as mineral oxide engineering. It results, among others, in environmentally friendly binders, recipes for soil stabilization (new building products), and impermeable/durable concretes. Subsequently, the mixture design of concrete is treated, whereby distinction is made between self-consolidating concrete and earthmoist concrete. By combining the particle sizes of all components, including the powders (cement, fillers), optimum mixtures in regard to workability/compactability and hardened state properties are obtained. This so-called particle size engineering results in concretes that meet all technical requirements, but that also make optimum use of the cement it is containing. This paper concludes with summarizing the opportunities and challenges involved with the introduction of both approaches, viz. mineral oxide engineering and particle size engineering, in the construction industry.

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.

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.

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.