Abstract: This paper deals with the possibility of safe incorporation fluidised bed combustion fly ash (waste material) into cement matrix together with next commonly used secondary raw material, which is high-temperature fly ash. Both of these materials have a very high pozzolanic ability, and the right combination could bring important improvements in both the physico-mechanical properties and the better durability of a cement composite. This paper tries to determine the correct methodology for designing green concrete by using modern methods measuring rheology of fresh concrete and following hydration processes. The use of fluidised bed combustion fly ash in cement composite production as an admixture is not currently common, but there are some real possibilities for its potential. The most striking negative aspect is its chemical composition which supports the development of new product formation, influencing the durability of the composite. Another disadvantage is the morphology of grains, which have a negative effect on consistency. This raises the question of how this waste can be used in concrete production to emphasize its positive properties and eliminate negatives. The focal point of the experiment carried out on cement pastes was particularly on the progress of hydration processes, aiming for the possible acceleration of pozzolanic reactions of both types of fly ash.
Abstract: The paper is focused on monitoring of dependencies
of different composition concretes on elastic modulus values.
To obtain a summary of elastic modulus development in dependence
of concrete composition design variability was the objective
of the experiment. Essential part of this work was initiated
as a reaction to building practice when questions of elastic moduli
arose at the same time and which mostly did not obtain the required
and expected values from concrete constructions.
Abstract: The paper a summary of the results of concretes with
partial substitution of natural aggregates with recycled concrete is
solved. Design formulas of the concretes were characterised with 20,
40 and 60% substitution of natural 8-16mm fraction aggregates with
a selected recycled concrete of analogous coarse fractions. With the
product samples an evaluation of coarse fraction aggregates influence
on fresh concrete consistency and concrete strength in time was
carried out. The results of concretes with aggregates substitution will
be compared to reference formula containing only the fractions of
natural aggregates.
Abstract: This paper introduces selected composition of conventional concretes and their resulting mechanical properties at different ages of concrete. With respect to utilization of mineral admixtures, fly ash and ground limestone agents were included in addition to pure Portland binder. The proposal of concrete composition remained constant in basic concrete components such as cement and representation of individual contents of aggregate fractions; weight dosing of admixtures and water dose were only modified. Water dose was chosen in order to achieve identical consistence by settlement for all proposals of concrete composition. Mechanical properties monitored include compression strength, static and dynamic modulus of concrete elasticity, at ages of 7, 28, 90, and 180 days.
Abstract: Paper focuses on experimental testing of possibilities of mechanical activation of fly ash and observation of influence of specific surface and granulometry on final properties of fresh and hardened concrete. Mechanical grinding prepared various fineness of fly ash, which was classed by specific surface in accordance with Blain and their granulometry was determined by means of laser granulometer. Then, sets of testing specimens were made from mix designs of identical composition with 25% or Portland cement CEM I 42.5 R replaced with fly ash with various specific surface and granulometry. Mix design with only Portland cement was used as reference. Mix designs were tested on consistency of fresh concrete and compressive strength after 7, 28, 60 and 90 days.