This CD contains the proceedings from the Twelfth International Conference on Recent Advances in Concrete Technology and Sustainability Issues held in Prague, Czech Republic, in October 2012. The 34 papers include Advances in Geological CO2 Sequestration and Co-Sequestration with O2; Self-Compacting High-Performance Concretes; Dynamic Performance of Eco-Friendly Prestressed Concrete Sleeper; Parameters Influencing the Performance of Shrinkage-Compensating Concrete, and much more. 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-289

Geopolymers constitute a potential sustainable alternative to Portland cement. They are amorphous silica-aluminates products of the reaction of metakaolin or fly ashes with an alkali silicate solution. The usage of geopolymer pastes as cementing materials is hindered by a lack of data, understanding and control concerning the rheology of the paste before hardening. As a first step, using diverse methods such as Nuclear Magnetic resonance (NMR) and Small Angle X-ray Scattering, we showed that the high viscosity of the alkali solutions can be rationalized by ion pairing and molar excess volume considerations. This allows further studies on the evolution of the rheology of the fresh geopolymer as a function of time and temperature and suggests possible ways to improve the workability of the geopolymer pastes.

This paper investigates the properties of the foamed concrete containing Nano silica, as compared with the foamed concrete containing micro silica, as well as comparing the properties of these two concretes with the concrete witness concrete. To conduct this study, Nano silica with an average size of 12nm and 1 to 6% of the cement weight was used; in addition, micro silica with an average size of 230nm and 1 to 6% of the cement weight was utilized. In this study the size of the air-voids in the hardened concrete ranged from 0.1 to 1 mm. The air voids were due to the protein- based foaming agent. The Type 1 cement used in this project was based upon ASTM C 150 .The samples were produced in two forms, that is, with and without sand. The compressive strength test was conducted for the samples at the ages of 7 and 28 with an approximately dried density of 600 and 1600 kg/m3.The SEM images were obtained from the failure section. The results indicated that in initial days, samples containing Nano silica have greater compressive strength than those containing micro silica and also the no-sand samples containing Nano silica show a greater increase in the amount of compressive strength than those containing micro silica and witness samples. The micro structural examination of the foamed concrete by using the SEM images suggests the improvement in the concrete micro structure and mechanical properties containing Nano silica.

Ground bottom ash (GBA) from Municipal Solid Wastes Incinerators (MSWI) does not perform as well as other mineral additions -such as silica fume or fly ash produced by coal burning- due to the presence of aluminium metal particles which react with the lime formed by the hydration of portland cement and produce significant volume of hydrogen in form of gas bubbles which increase the porosity of concrete and reduce its strength. Due to this drawback, a new process was developed to separate the aluminium metal particles through a mechanical removal of metals and a wet grinding of bottom ashes. At the end of the process, GBA was used as aqueous slurry to replace portland cement. In the present work GBA with a maximum size of 1.7 mm (0.07 min) was used to replace about 10% of portland cement in self-compacting concretes (SCC). Mixtures with shrinkage-reducing admixture (SRA) and a CaO-based expansive agent were also manufactured to reduce the drying shrinkage and the related cracks. Moreover, an alternative way to reduce both number and length of cracks was adopted by using SRA combined with polyvinyl alcohol (PVA) macrosynthetic fibres. Corresponding mixtures with silica fume or fly ash were also manufactured. GBA performed as well as silica fume in terms of mechanical properties, durability and crack behavior, and much better than fly ash.

The paper describes a new technology for recycling residual fresh concrete at the ready-mixed plant, which transforms the unset residual concrete from the construction site into granular materials, in short period of time and without production of waste. The method employs organic polymers and setting accelerators, which are added directly into the truck mixer and transform the residual concrete into aggregates which, after curing, can be reused for the production of new concrete. The new technology represents a significant contribution to the area of reduction of waste at the ready-mixed plant. It also contributes to the protection of natural resources, in accordance with the guidelines of the European Directive on wastes.