International Concrete Abstracts Portal

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

Nowadays, many nuclear power plants are approaching their designed lifetime and the question of their decommissioning is being increasingly discussed. In connection with the dismantling of the nuclear facilities large quantities of typical decommissioning waste material are produced. Among this waste material, there is a significant amount of radioactive steel. Its level of radioactivity just slightly exceeds the regulatory limits set for unconditional release into the environment and, moreover, contains radionuclides with relatively short half-life. Disposal of all this kind of steel in specialized repositories would require considerable financial investments. Therefore, re-melting and reuse of this steel in the construction of bridges seems like an advantageous alternative. The article deals particularly with the possibilities of using slightly radioactive steel in concrete bridges construction and the risks related to this issue.

This study examines the early-age and durability properties of mortars made with Dredged Marine Sand (DMS). Both physical and mechanical properties of the DMS mortars were investigated and compared to those of mortar prepared with conventional aggregates. Results showed that the substitution of Standardized Sand (SS) with DMS had no significant effect on mortar hydration. For a rate substitution of 25%, the mechanical properties of mortars increased, particularly in case of air curing. The increasing of substi¬tution rate of SS with DMS, slightly decreased the mortar density and increased entrapped air and total porosity. For a substitution rate of 50% and more, a decrease of the mechanical properties was measured. Chloride migration coefficients of tested mortars followed similar trends.

The use of superabsorbent polymers as internal curing agents in high performance concrete has gained much interest in research and slowly gaining interest among industrial producers. Although there have been many publications on the microstructure of internally cured system, little interest has developed in the actual mechanisms of absorption and desorption of superabsorbent polymers in high pH systems and how they are related to the structure of the polymers themselves. Results in the literature indicate that the polymer structure actively interacts with the ions present in the solvent, which results in a strong ion filtration effect. This paper demonstrates that this ion filtration effect is due to electrostatic interaction. The timing and dominance of this effect can heavily influence the effectiveness in internal curing. In particular, concrete containing superabsorbent polymers demonstrate different strength gain behaviors when cured in lime-saturated water.

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.