Istraživanje svojstva svežeg i očvrslog samozbijajućeg betona sa mineralnim dodacima na bazi industrijskih nusprodukata

Abstract

Beton, kao jedan od najčešće upotrebljavanih materijala u građevinskojindustriji evoluirao je sa razvojem građevinarstva, od početaka primene dodanašnjih dana. Konvencionalni beton se ugrađuje pomoću vibrirajućeopreme kako bi se u njemu redukovao sadržaj zaostalog vazduha,eliminisala mogućnost pojave kaverni i drugih šupljina na kontaktima saarmaturom i oplatom (takozvani normalno vibrirani beton, Normal VibratedConcrete – NVC). Na taj način beton postaje kompaktniji, gušći ihomogeniji, što je osnov za njegovo prihvatljivo ponašanje u konstrukciji.Tehnološka operacija kompaktiranja tradicionalno igra ključnu ulogu uproizvodnji kvalitetnog betona sa optimalnom čvrstoćom i trajnošću.Razvoj hemijskih dodataka tipa superplastifikatora omogućio je lakšeugrađivanje betona, pošto se malim doziranjem ovakvog hemijskog dodatkamogu smanjiti sile trenja između čvrstih čestica, što za rezultat dajepokretljivije i obradljivije betone (betone tečnijih konzistencija) koje jelakše ugraditi, uz zadržavanje iste količine vode. Ekstrapolacijom konceptaupotrebe superplastifikatora u pravcu dobijanja betona tečnijih konzistencijadošlo se do koncepta samozbijajućeg betona (Self-compacting Concrete -skraćeno SCC). Samozbijajući beton se može definisati kao beton, koji ćebez primene mehaničkih sredstava za ugrađivanje popunjavati sve ugloveoplate i uzane prostore između gusto raspoređenih šipki armature, samo poddejstvom sopstvene težine, tako da se u završnoj fazi dobije kompaktanbeton veće trajnosti.U sastav samozbijajućeg betona, po pravilu, ulaze veoma fini mineralnidodaci, od kojih su najčešće primenjivani krečnjačko i dolomitno brašno,kao i leteći pepeo. U okviru eksperimentalnog rada u ovoj disertaciji je,osim letećeg pepela (poreklom iz dve termoelektrane, TE "Kolubara" i TE"Kostolac") upotrebljen i sprašeni reciklirani beton (dobijen rušenjemdotrajalih armiranobetonskih konstrukcija, odnosno drobljenjem kontrolnihlaboratorijskih kocki) i sprašeni elementarni sumpor (koji se dobija kaonusprodukt u naftnoj industriji, u Rafineriji nafte Pančevo).U okviru eksperimentalnog rada spravljeno je i detaljno ispitivano 11mešavina SCC: dve referentne SCC mešavine sa krečnjačkim brašnom kaomineralnim dodatkom, pet mešavina sa letećim pepelom, tri mešavine sasprašenim recikliranim betonom i četiri mešavine sa sprašenim sumporom.Prethodno je prilikom definisanja recepture za SCC mešavine spravljeno iispitano 12 probnih (pilot) mešavina. Sve navedene mešavine, osim dveprobne (pilot) mešavine, imale su svojstva koja karakterišu samozbijajuće...

Concrete, as one of the most commonly used materials in the constructionindustry, has evolved with the development of construction, from thebeginning to the present day. Placing of conventional concrete is usuallydone with the use of vibrating equipment to help in reduction of entrainedair content, eliminating the possibility of cavities occurrence in contact withreinforcement and formwork (the so-called Normal Vibrated Concrete,NVC). Concrete becomes more compact, denser and more homogeneous,which are the basic aspects for an acceptable behavior in the structure. Thisoperation, compaction, traditionally plays a key role in the production ofhigh quality concrete, with optimum strength and durability.Development of superplasticizers (chemical admixtures for concrete)allowed easier placing of concrete with stiffer consistency; a small dosageof this type of chemical admixtures can reduce the friction between theparticles, which results in more mobile and workable concrete (concretewith fluid consistency) that is easier to place in formwork, whilemaintaining the same amount of water. Extrapolation of the concept of thesuperplasticizers use towards obtaining concrete with fluid consistency ledto the concept of Self-compacting Concrete - SCC for short. Selfcompactingconcrete, is defined as a concrete mix that can be placed purelyby means of its own weight, with little or no vibration and is a highlyflowable concrete that spreads into place, fills formwork, and wraps eventhe most congested reinforcement, and showing no signs of segregation.Typically, SCC contains certain quantities of very fine mineral additions;the most commonly applied are limestone and dolomite powder and fly ash.Within the experimental work in this thesis, besides fly ash (originatingfrom two power plants, "Kolubara" and "Kostolac"), recycled pulverizedconcrete (obtained by demolition of old concrete structures) and powderedelemental sulfur (which is obtained as a by-product of the petrol industry, inPancevo Oil Refinery).Within this experimental work, 11 mixtures of SCC were prepared, tworeference SCC mixtures with limestone powder as mineral addition, fivemixtures with fly ash, three mixtures with ground recycled concrete andfour mixtures with ground elemental sulfur. Also, during the proces ofdefining the composition of SCC mixtures, 12 test (pilot) mixutures weremade and investigated. All mixtures, except two test mixtures, could becharacterized as self-compacting concrete, based on their fresh properties.The applied extensive testing of fresh and hardened SCC (with respect tothe designed properties of fresh SCC, the research findings of the recent...