Abstract | Predmet istraživanja doktorskog rada je benkovački prirodni kamen, tanko slojeviti vapnenac
gornjoeocenske starosti, koji se eksploatira u znatnijim količinama u obliku tankih ploča u kamenolomima
smještenim u blizini grada Benkovca. Ciljevi istraživanja doktorskog rada bili su sljedeći:
1. odrediti mineralno-petrografska, fizičko-mehanička, tehničko-tehnološka i kemijska svojstva
benkovačkoga prirodnoga ili arhitektonsko-građevnog kamena;
2. odrediti strukturno-teksturne i petrografske značajke kamena koje utječu na njegova svojstva;
3. odrediti stupanj teksturne anizotropije prirodnoga kamena s obzirom na raspodjelu fizičkih svojstava
u uzorcima;
4. utvrditi postojanost benkovačkoga prirodnoga kamena na djelovanje kristalizacije soli, smrzavanje i
toplinske promjene;
5. utvrditi utjecaj mineralno-petrografskih, kemijskih i fizičko-mehaničkih svojstava na postojanost
benkovačkoga prirodnoga kamena.
Na temelju ispitivanja benkovačkoga prirodnoga kamena izdvojena su tri litotipa: zrnski, mikritni i
laminirani litotip. Pri tome je, benkovački prirodni kamen, prema petrografskim značajkama, determiniran kao
laminirani litotip, zbog izmjene lamina zrnskog i mikritnog litotipa. S komercijalnog i tržišnog gledišta
laminirani litotip predstavlja glavni varijetet benkovačkoga prirodnoga kamena. Zrnski i mikritni litotip se
razlikuju prema boji, mineralnom i kemijskom sastavu, vrsti strukturnih sastojaka te prema strukturnoteksturnim
karakteristikama i fizičko-mehaničkim svojstvima. Prema tome svojstva laminiranog litotipa
značajno ovise o zrnskom i mikritnom litotipu, te o njihovom položaju i udjelu u uzorcima. Dominantan mineral
zastupljen u svim uzorcima je kalcit. Zrnski litotip se pretežno sastoji od vrlo dobro sortiranih karbonatnih
intraklasta te od siliciklasticnog detritusa, koji je prisutan u kolicini manjoj od 1 mas. %, a između njih se nalazi
krupnokristalasti sparikalcitni cement. Dijagenetski procesi u zrnskom litotipu su: rekristalizacija primarnog
karbonatnog matriksa, cementacija sparitom, dolomitizacija i dedolomitizacija. Mikritni litotip pokazuje gustu
homogenu mikritnu strukturu. Međutim, uočeni su i rekristalizirani dijelovi kao i bioturbacija. U uzorcima
mikritnog litotipa nema dolomita, ali su, u malim količinama, određeni minerali glina (smektit, kaolinit,
mješanoslojni klorit-vermikulit).
Kod laminiranog litotipa bitna je njegova heterogena građa u smislu izmjene lamina/slojeva različitog
sastava zrnskog i mikritnog. Granice između lamina u laminiranom litotipu su oštre i nepravilne. U uzorcima
laminiranog litotipa je uočena laminacija, granica između lamina dva litotipa i diskontinuiteti (mikropukotine)
koje ukazuju na teksturnu anizotropiju (heterogenost) uzoraka. Primjenom nedestruktivne prognozne metode
određivanja svojstava kamena (metoda ultrazvuka) određen je koeficijent teksturne anizotropije prirodnog
kamena. Tijekom ispitivanja ustanovljeno je da teksturna anizotropija (laminacija), prisutnost mikropora i
mikropukotina, dijagenetske promjene u benkovačkom prirodnom kamenu utječu na gustoću, poroznost,
povećano upijanje vode, smanjenje tlačne i čvrstoće na savijanje, usporavanje brzine prolaza UZV-a, te
smanjenje postojanosti kamena pri kristalizaciji soli i smrzavanja.
Na uzorcima zrnskog, mikritnog i laminiranog litotipa od fizičko-mehaničkih svojstava određeni su:
boja, gustoća, prostorna masa, otvorena i ukupna poroznost, upijanje vode pri atmosferskom tlaku, kapilarno
upijanje vode, sušenje kapilarno zasićenih uzoraka, čvrstoća na tlak i savijanje, brzina prolaza ultrazvučnih
valova te otpornost na habanje i klizanje klatnom. Nakon kapilarnog upijanja uzorci su podvrgnuti sušenju
prema nenormiranoj metodi. Fizičko-mehanička svojstva prirodnog kamena su ispitivana prema hrvatskim i
europskim ispitnim normama, a dobiveni rezultati su statistički obrađeni. Od tehničko-tehnoloških svojstava
obavljena je probna obrada pri jednolikim udarcima prikladnim alatom i obrada pri piljenu i brušenju.
Naglasak u doktorskom radu je bio na djelovanju fizičkog propadanja benkovačkoga prirodnoga
kamena te je određena postojanost uzoraka tri litotipa na djelovanje kristalizacije soli, smrzavanje i toplinske
promjene. Utvrđena je razlika između sva tri litotipa prema navedenim svojstvima i njihovoj postojanosti.
Mikritni i zrnski litotip su postojani na djelovanje kristalizacije soli, smrzavanje i toplinske promjene. Za razliku
od njih, laminirani litotip nije postojan na djelovanje kristalizacije soli i smrzavanje. Pri kristalizaciji soli raspalo
se pet od dvanaest uzoraka laminiranog litotipa, a pri smrzavanju jedan. Uzorci su se raspali duž diskontinuiteta
(mikropukotina) ili na granici između zrnskog i mikritnog litotipa jer duž svake teksturne anizotropije kamena
jače je djelovanje kristalizacijskih tlakova i veća su oštećenja. Ipak, kod svih uzoraka tijekom ispitivanja
postojanosti na djelovanje kristalizacije soli, smrzavanje i toplinske promjene došlo je do promjena u unutrašnjoj
građi, povećanja pornog prostora, proširenja prirodnih diskontinuiteta te kod nekih uzoraka (laminiranog litotipa)
i do pucanja po diskontinuitetima. |
Abstract (english) | Benkovac natural stone is attractive thinly bedded limestone excavated in the wider area of Benkovac,
Croatia. All the quarries and deposits are located in the zone of Eocene layers. Raw material is excavated in the
shape of thin slabs and because of its decorativity, platy texture, physical and mechanical properties it is
traditionally used in building industry. Material requires minimal processing and it is applied in numerous stone
constructions such as fences, roof tiles, paving and façade decoration etc. Today; this famous natural stone, is
recognized as a special brand in Croatian stone industry and stone market.
The objectives of thesis are:
1. determination of mineralogical, petrographical, physical, mechanical, technical and chemical properties
of benkovac natural or building stone
2. determination of textural and petrographical features which have impact on stone properties
3. assignment of textural anisotropy in natural stone
4. observation of benkovac natural stone resistance to salt crystallization, frost and ageing due to thermal
shock
5. linking mineralogical, petrographical, chemical, physical and mechanical properties of benkovac
natural stone with its durability.
Mineralogical and petrographical analyses were performed at Faculty of Mining, Geology and
Petroleum Engineering. Benkovac natural stone was characterized as laminated lithotype where grainy and
micritic lithotype layers alter in macro scale. Benkovac natural stone can also occur in the form of grainy and
micritic lithotype. The laminated lithotype alteration is the main commercially used variety of benkovac natural
stone. Grainy and micritic lithotypes can be distinguished by color, mineral and chemical composition, by
structural and textural characteristics and by the physical and mechanical properties. The properties of laminated
lithotype depend on properties of grainy and micritic components, their position and proportion in the structure.
X-ray diffraction confirmed calcite to be the dominant mineral present in all samples. Grainy lithotype
consists of very well-sorted carbonate intraclasts and siliciclastic detritus, which is present in amount of less than
1 wt. %. Intraclasts and detritus are bound by coarsely crystalline sparicalcite cement. During the diagenesis of
grainy lithotype a primary recrystallization of carbonate matrix, sparitic cementation, dolomitization and
dedolomitization appeared. Micritic lithotype is characterized by dense homogeneous micritic structure with
signs of recrystallization and bioturbation. The micritic lithotype samples are free of dolomite and contain small
quantities of clay minerals such as smectite, kaolinite and intercalated chlorite-vermiculite.
In order to describe visual heterogeneity and textural anisotropy of stone the textural characteristics and
petrographic properties were studied. The laminated lithotype is characteristic by profoundly heterogenic
structure. The boundaries between two laminas are sharp and uneven and discontinuities (microcracks) are
observed. Textural anisotropy (lamination), micropores, microcracs, and alteration by diagenetic processes
directly influence density, porosity, water absorption, uniaxial compressive strength, flexural strength, sound
speed propagation as well as durability to salt crystallization, frost and ageing by thermal shock.
Stone samples were selected for physical, mechanical, technical and durability testing after macroscopic
and microscopic analysis. Testing took part at IGH d.d. Stone samples were treated according to Croatian and
European standards in order to determine:
− real and apparent density
− total and open porosity
− water absorption at atmospheric pressure
− water absorption by capillarity action
− water desorption
− uniaxial compressive strength
− flexural strength
− sound speed propagation
− abrasion and slip resistance.
Testing was carried on each lithotype. Deviation from standard procedure was introduced by desorption
at atmospheric conditions after capillary absorption tests. The deviation is noted in the thesis. Results were
statistically elaborated and interpreted.
Durability and physical degradation of benkovac natural stone were tested in respect to salt
crystallization, frost and ageing by thermal shock. After the testing, the uniaxial compressive strength and
ultrasound speed propagation were measured in order to detect possible degradation of stone. The ultrasound
method (propagation of ultrasound waves through samples) is nondestructive method for prediction of stone
properties such as textural anisotropy index. Properties and durability of all three lithotypes of stone were
determined. Micritic and grainy lithotypes are resistant to all tested weathering processes. The laminated lithotype is sensitive to salt crystallization. Visual inspection revealed that five of twelve samples were crumbled
before the end of salt crystallization test. The impact of freezing cycles was milder, only one sample of
laminated lithotype showed delamination along an existent fracture.
Benkovac platy stone samples show considerable textural anisotropy and discontinuity in the structure.
Microcracks, pores, fractures or even a contact between two lithotypes influence mechanical properties and
durability of stone greatly. The large area of pore space together with natural discontinuities (microcracks)
enables the material to absorb liquid. Saturation in conjunction with crystallization lead to expansion in the
structure of laminated lithotypes and ruptures along discontinuities appear. |