Sandra Juradin

Experimental Testing of the Effects of Fine Particles on the Properties of the Self-Compacting Lightweight Concrete

The self-compacting lightweight concrete (SCLC) is a combination of the Self compacting concrete (SCC) and the Lightweight concrete. It combines all the good properties of those two materials and is extremely convenient for the construction of buildings that require low mass and do not require high compressive strength, for example restoration works in old structures (e.g., replacement of wooden floors), prefabricated elements that require transportation, and for structures and elements where the concrete surface should be visible. In this paper the effect of the amount of fine particles on the properties of the self-compacting lightweight concrete (SCLC) in the fresh and hardened state was explored. For this purpose, sets of specimens with different combinations of admixtures of silica fume, fly ash, and filler were prepared and tested. Slump flow and flow time of fresh concrete, as well as the dynamic elastic modulus and compressive strength of hardened concrete, were measured at different ages of concrete. The processes of manufacturing and methods of testing are described, as well as the obtained results.

Determination of rheological properties of fresh concrete and similar materials in a vibration rheometer

A vibration rheometer has been developed for the purpose of determining the viscosity coefficient and the yield value of fresh concrete under vibration. The main parts of the apparatus, a test specimen and a vibration source form a unitary oscillatory system whose parameters can be measured with sufficient precision. Two types of fine grained reference material have been prepared and examined; one with a high coefficient of viscosity and the other with a high yield value. The rheological properties of reference materials have been determined in a capillary tube viscometer. Since there is no analytical solution to the flow in the vibration rheometer, the constants of the vibration rheometer have been determined by experiment, for each position of the apparatus piston within the measuring range. The parameters of the flow depend on the maximum acceleration of the vibration source. An increase in acceleration causes an increase in the yield value as well as a reduction in the plastic viscosity coefficient of the material specimen. A testing of fresh mortar has been carried out as well. The obtained results have been compared with the impact on reference materials, which makes the results of our research applicable to fresh vibrated concrete.

Comparison of Methods of Dosage and Effect of the Composition on the Properties of Fresh and Hardened Self-Compacting Concrete

Self-compacting concrete has to have a high flowability and ability to fill the gaps of reinforcement and corners of molds without vibration. The composition of self-compacting concrete (SCC) has a significant impact on his properties so mix design criterions are mostly focused on the type and mixture proportions of the constituents. In this work, a designe method for SCC proposed by Nan Su eat al. [1] was tested and compared with CBI method [2,3]. For this purpose, several mixtures of self-compacting concrete were prepared and tested. Properties of fresh mixture were determined by slump flow method, visual assessment of stability, T50 time, V-funnel method, L-box method and J-ring method. In hardened state, the elastic modulus of elasticity and compressive strengths after 7 and 28 days were determined.

Utjecaj veličine ispitnog uzorka na mehanička svojstva mlaznog betona

U radu su opisana laboratorijska ispitivanja uzoraka mlaznog betona ugrađivanog u primarni podgradni sustav tunela Sveti Ilija. Promatran je utjecaj dimenzija ispitnih uzoraka mlaznog betona na tlacnu cvrstocu i dinamicki modul elasticnosti obicnog i mikroarmiranog betona izrađenog in situ. Pregledom dobivenih rezultata analizirana je i opravdanost procjene tlacne cvrstoce na temelju rezultata dinamickog modula elasticnosti.

Effect of test specimen size on mechanical properties of shotcrete

U radu su opisana laboratorijska ispitivanja uzoraka mlaznog betona ugrađivanog u primarni podgradni sustav tunela Sveti Ilija. Promatran je utjecaj dimenzija ispitnih uzoraka mlaznog betona na tlacnu cvrstocu i dinamicki modul elasticnosti obicnog i mikroarmiranog betona izrađenog in situ. Pregledom dobivenih rezultata analizirana je i opravdanost procjene tlacne cvrstoce na temelju rezultata dinamickog modula elasticnosti.

Influence of Cement Type and Mineral Additions, Silica Fume and Metakaolin, on the Properties of Fresh and Hardened Self-compacting Concrete

Proportioning and mixing self-compacting concrete is a challenging task because the concrete mixture has to be stable and has to have the ability to fill formwork and to bypass obstacles under the influence of its own weight. Besides that, the final product has to be quality hardened concrete. It is known that even a little alteration of any component can significantly change characteristics of fresh and hardened concrete. In this work, the influences of the type of cement and additions, namely silica fumes and metakaolin on the workability and compressive strength of self-compacting concrete, are experimentally examined. For this purpose, several mixtures of self-compacting concrete were prepared and tested. The properties of fresh mixture were determined by the slump flow method, visual assessment of stability, T50 time, V-funnel method, L-box method and J-ring method. Also, in the hardened state, compressive strengths after 7 and after 28 days were determined. Results obtained in this work were compared with the results of other authors.

UTJECAJ STAROSTI I SKLADIŠTENJA CEMENTA NA NJEGOVU KVALITETU

Cement koji je nepropisno uskladisten nakon godine dana gubi i do 50% svoje cvrstoce. U radu su ispitana svojstva uskladistenih uzoraka cementa starih 30 godina. Radi usporedbe, ispitana su i dva nova cementa: jedan lose uskladisten, a drugi uzet iz tek otvorene vrece. Rezultati ispitivanja uspoređeni su s vrijedecim standardima i referentnim rezultatima iz vremena proizvodnje cemenata.