Faculty of Mining, Geology and Petroleum Engineering University of Zagreb
Abstract
The mechanical properties of chrushed rock aggregates are greatly influenced by the petrographic characteristics of parent rock. The main objective of this study was to determine the relation between the petrographic characteristics of some volcanic and subvolcanic (silicate) rocks from Croatia, and the chrushing resistance of aggregates produced by their comminution. The aggregate resistance to chrusing was tested by means of the Los Angeles abrasion test. During this testing, an aggregate is subjected to dynamic load by impact and abrasion. The petrographic characteristics were examined with the petrographic and scanning electron microscope and by X-ray powder diffraction with CuKa (1,54 A) radiation. In order to obtain the most correct evaluation of aggregates chrushing resistance, four different values had been used - the recrushing index (Ir), the reduction ratio (RR), the Los Angeles abrasion value (LA) and the Los Angeles abrasion value residue (LAr). On the basis of the obtained results, the following petrographic factors have been revealed as the most important ones for rock aggregates resistance to crushing: a - the size of crystals, b - the form, arrangement and dimensions ratio of crystals, and, especially c - the presence of microfractures in parent rock.Petrografska obilježja ishodišne stijene bitno utječu na mehanička svojstva drobljenih kamenih agregata. Glavni cilj ovog rada bio je utvrditi odnose između petrografskih obilježja nekih vulkanskih i subvulkanskih (silikatnih) stijena i otpornosti prema drobljenju agregata dobivenih njihovih usitnjavanjem. Otpornost prema drobljenju ispitivana je metodom "Los Angeles". Tijekom ispitivanja agregat je izložen dinamičkim opterećenjima na udar i habanje. Mineralni sastav i druga petrografska obilježja određeni su petrografskim i elektronskim mikroskopom, te metodom rendgenske difrakcije na prahu vertikalnim rendgenskim goniometrom s CuKu (1,54 A) zračenjem. Kako bi se što točnije ocijenila otpornost prema drobljenju ispitivanih agregata korištena su četiri različita pokazatelja: koeficijent Los Angeles (LA), koeficijent Los Angeles ostatka (LAr), indeks pregranulacije (Ir) i stupanj usitnjavanja (PR). Na temelju dobivenih rezultata kao najvažnija petrografska obilježja kamenih agregata u pogledu otpornosti prema drobljenju izdvojeni su: a- veličina kristala; b- oblik, prostorni raspored i međusobni odnos veličine kristala; i, posebice c - prisustvo mikropukotina u ishodišnoj stijeni
