THE INFLUENCE OF CONCRETE SHRINKAGE ON BOND STRENGTH BETWEEN FIBRES AND CEMENT MATRIX

V diplomskem delu je predstavljen vpliv induciranih tlačnih napetosti v cementni matrici na jakost vpetja vlaken, na prenos obremenitve iz matrice na vlakna in na mehanske lastnosti vlaknastega cementnega kompozita med obremenitvijo. Tlačno napetost zaradi krčenja betona smo izmerili s posebej za ta namen razvitim merilcem. Študije smo opravili na vzorcih s cementno malto, v katero smo dodali dodatek aeranta. Med procesom mešanja malte so se kot posledica delovanja aeranta v matrici formirali zračni mehurčki, ki so zaradi povečane poroznosti povzročili precejšnje krčenje cementne matrice in s tem pritiske pravokotno na vlakna. S tem se je povečalo tudi trenje na mejni površini. S pomočjo izvlečnih testov smo na eksperimentalnih preizkušancih v časovnih intervalih izmerili izvlečno silo in opisali vpliv zaradi krčenja povzročenih bočnih pritiskov. Tendenca izmerjenih rezultatov notranjih deformacij se giblje v skladu z navedbami literature. The purpose of present diploma thesis was to describe the impact of induced normal stresses inside the cement matrix on interfacial bond strength, load transfer between fibres and matrix and mechanical properties of fibrous cement composites during loading. Internal compressive stresses due to shrinkage of concrete were measured with the measuring device developed for this purpose. Studies were performed on samples of cement mortar with addition of an air entraining agent. Air bubbles formed inside the mortar mix as a result of added air entraining agent increased porosity and caused substantial shrinkage of cement matrix and subsequent pressure perpendicular to the fibers. This also increased the interfacial friction. Composite bond characteristics were evaluated with conventional pull-out tests. The results of the fibre pull-out tests were then combined with measured and calculated values of shrinkage induced lateral pressure. The results of measurements performed in this study are in accordance with findings of the literature.