Experiments with Externally Prestressed Continuous Composite Girders

Steel-concrete composite girders have attractive potentials when applied in bridge construction. The serviceability performance of continuous composite girders is becoming more and more a deterministic parameter in the design of this type of structures. An effective method for improving this performance is to apply prestressing to control or completely eliminate concrete deck cracking caused by static and time dependent actions. Little literature has been found addressing the experimental analysis of continuous girders prestressed by means of external deviated tendons. The current research aims to investigate the behavior of a double-span steel composite beam externally prestressed by means of continuous tendons in terms of cracking characteristics, load deflection response, and load carrying capacity. The efficiency of prestressing is evaluated by comparing the results to those of a non-prestressed beam with similar cross sections and spans

Influence of Different Drying Conditions on High Strength Concrete Compressive Strength

The influence of different drying conditions on the compressive strength and strength development rates of high strength concrete up to an age of 28 days was evaluated. Two HSC mixes with and without silica fume addition were used to cast cubes of 10 cm size. The cubes were stored in different drying conditions until the age of testing at 3, 7, 28 days

HYDROTHERMAL REHYDROXYLATION OF KAOLINITE STUDIED BY THERMAL ANALYSIS

The effect of hydrothermal conditions on process of kaolinite rehydroxylation at 180°C and 230°C and for soaking times from 1 to 200 hour was studied by thermal analysis (DTA, DSC, TG). It is shown that the kaolinite dehydroxylation of rehydroxylated samples shifts to lower temperatures compared to the original kaolinite. Amounts of kaolinite in rehydroxylated samples were calculated from TG curves. The curve of the kaolinite mass gain (Δm) plotted against the time of hydrothermal treatment indicates a two stage process with a different mass gain rate representing short and long-time measurements. Multiple dehydroxylation was studied by repeated calcinations (2 h at 600°C) and hydrothermal treatments (10 h at 230°C). It was proved that values of activation energy (Ea) of multiple dehydroxylations decreased with the increasing number of repeated treatments. Conclusions of the study were applied for the investigation of kaolinite origin in archaeological samples from Roztoky near Prague

Effect of nanosilica-based activators on the performance of an alkali-activated fly ash

This paper assesses the effect of the use of an alternative activator based on nanosilica/MOH (M = K+ or Na+) blended solutions on the performance of alkali-activated fly ash binders. Binders produced with commercial silicate activators display a greater degree of reaction, associated with increased contents of geopolymer gel; however, mortars produced with the alternative nanosilica-based activators exhibited lower water demand and reduced permeability, independent of the alkali cation used. Na-based activators promote higher compressive strength compared with K-based activators, along with a refined pore structure, although K-activated samples exhibit reduced water demand. Zeolite type products are the major crystalline phases formed within these binders. A wider range of zeolites is formed when using commercial silicate solutions compared with the alternative activators. These results suggest that there are variations in the availability of Si in the system, and consequently in the alkalinity, depending on the silicate source in the activator, which is important in determining the nanostructure of the geopolymer gel.This study was sponsored by the Ministerio de Ciencia e Innovacion of Spain (Project GEORES MAT2010-19934 and research scholarship BES-2008-002440), European regional development fund (FEDER), and the Universitat Politecnica de Valencia (Spain). The participation of SAB and JLP was funded by the Australian Research Council (ARC), including partial funding through the Particulate Fluids Processing Centre, a Special Research Centre of the ARC. A special acknowledgement is also due to the Centre of Electron Microscopy of the Universitat Politecnica de Valencia and Pedro Garces from the Universidad de Alicante for support in some experiments.Rodriguez Martinez, ED.; Bernal, SA.; Provis, JL.; Paya Bernabeu, JJ.; Monzó Balbuena, JM.; Borrachero Rosado, MV. (2013). Effect of nanosilica-based activators on the performance of an alkali-activated fly ash. Cement and Concrete Composites. 35(1):1-11. doi:10.1016/j.cemconcomp.2012.08.025S11135

Feasibility Study of Material-modified Precast Element Used in the Railway Industry

Fiber reinforced concrete (FRC) is a material whose utilization in the concrete industry has been rapidly increasing recently. The use of this specific material over conventional forms of concrete can lead to many benefits at some applications. The contribution is focused on the feasibility study of FRC use for precast irregular plates utilized in the railway industry. Nowadays, the existing irregular plates are made of conventional reinforced concrete. The aim of the study is to verify the feasibility of the modified plate made of self compacted fiber reinforced concrete (SCFRC) without conventional reinforcement instead of reinforced concrete. The whole procedure including the design and manufacture of the modified plate is described. The manufacturing technology of SCFRC is also demonstrated, as well as the numerical analysis of material-modified plate on a nonlinear model. Three different load conditions - dismantling, transport to the building site and intended use were analyzed. Besides, the informative material tests were conducted in order to obtain the properties of concrete composite at 28 days that was used for the manufacture. The static loading tests of the SCFRC irregular plate have not been performed yet as the applied research is in the phase of cost effective pilot study which has to only verify the feasibility of the modified plate

Influence of Different Drying Conditions on High Strength Concrete Compressive Strength

The influence of different drying conditions on the compressive strength and strength development rates of high strength concrete up to an age of 28 days was evaluated. Two HSC mixes with and without silica fume addition were used to cast cubes of 10 cm size. The cubes were stored in different drying conditions until the age of testing at 3, 7, 28 days

Study on pervious recycled aggregate fibre reinforced concrete for airfield pavement

For the last several years, the attention has been devoted to the development of eco-friendly construction materials with the aim to reduce the environmental impact of construction. The integral part of this development is to find applications for which the recycled materials could be used efficiently. The presented study deals with the development of recycled aggregate fibre reinforced concrete which is going to be used for an innovative precast concrete pavement system. The system is being developed recently at Czech Technical University in Prague with the aim to provide a system for airfield pavement with rapid construction and recycled material utilization. The investigated material is going to be used for construction of a sub-base course which is underneath a surface course of precast concrete elements. Within the scope of the work, standard laboratory tests were conducted with the aim to observe mechanical properties of recycled aggregate fibre reinforced concrete. The obtained findings showed that the material exhibits ductile behaviour likely due to very long polypropylene fibres used for strengthening concrete matrix. On the contrary, the tested material has low modulus of elasticity in comparison with conventional concrete. Subsequently, the pilot construction of the sub-base course was carried out in order to examine both concrete mixture preparation and concrete course installation in practice. The obtained findings showed that a compaction ratio of the material is about 20 %. Moreover, a flat surface of the sub-base course was hard to achieve considering the used manufacturing technology