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

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.

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.

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.

Lias Delta clay was calcined on production scale in a rotary kiln. Subsequently it was ground and tested as type II addition in combination with three different cements. Workability and strength development were investigated. These physical tests were accompanied by microstructural analysis of the calcined clay and cement paste made with and without the addition of calcined clay. After a hydration of 28 d major differences could neither be detected by means of SEM nor by XRD in the mineral phases present in mixes made with or without. Only the content of portlandite was reduced due to the pozzolanic reaction of the calcined clay. Parallel tests using marble flour for comparison ruled out that strength increase was due to physical filler effects.

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.

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.

Limestone quarry dusts are fine materials obtained during the process of crushing rock to produce gravel. The effects of dust content in crushed limestone sand on the properties of fresh and hardened self-compacting mortar are not well known. An experimental study was undertaken to find out the effect limestone dust content on the properties of fresh and hardened self-compacting mortar (SCM). SCM mixtures were prepared using crushed limestone sand partially replaced with limestone dust at varying percentages (0, 5, 10, 15, 20, 25 and 30%). Tests used to characterize the properties of mortars include: slump flow, flow time, viscosity measurements, compressive strength and flexural strength at 3 and 28 days of age. Results indicate that the crushed limestone dust significantly improves the rheological and mechanical properties of SCM with a content ranging from 10 to 15% of limestone dust.

High strength self-compacting concrete (HS-SCC) has increasing demand in infrastructure works where high compressive strength of up to 100 MPa is achieved with a special type of superfluid concrete mixture. SCC was developed in Japan at the end of the 1990’s and the scientific rules to manufacture SCC were developed by Japanese Scientists. Concrete mixture proportions for HS-SCC have been varied widely depending on many factors and sensitive interactions between components. Statistical mixture design (SMD) methods can be used to enhance our understanding of concrete mixtures by providing cost effective fresh and hardened concrete properties. In this study, the optimization results of HS-SCC mixture proportions in C100/115 concrete class using SMD methods were compared with the scientific rules of Okamura and coworkers to manufacture SCC. As a result of this study, suggested concrete mixture proportions through SMD method were confirmed by Okamura’s Rules.

Marl was calcined at temperatures between 600 and 1000 ºC and compressive strength of mortars was tested after 28 days curing at 20 ºC, when 20% of OPC was replaced by calcined marl at equal w/c-ratios. The clays were hold for 45 min. at the respective temperatures and the optimum calcination temperature with respect to reactivity as pozzolan seemed to be 800 °C. Higher replacement levels were tested for the most reactive temperature and even with a replacement level of 50% OPC the same strength as without cement replacement could be achieved. The 1-day strength for mortar with 50% calcined marl replacing cement was sufficient for demoulding concrete in field practice. Pozzolanicity was tested on pastes of calcined marl and calcium hydroxide in different ratios with an alkaline solution by the use of thermal analysis, XRD and SEM. Ca(OH)2 consumption and formation of hydration products was analysed after curing for 28 days and 6 month at 20 & 38 ºC.