Povećanje žilavosti i udarne otpornosti betona putem mikro-armiranja

The paper deals with actual methodology and relevant technical regulation in the field of toughness (i.e. ductility) testing of fiber-reinforced concrete subjected to static load (flexural or wedge-splitting test), as well as testing of material's resistance to dynamic - impact load. The improved performance of fiber-reinforced concrete, compared to composite materials made without the addition of fibers, is most significant when the enhancement of fracture energy absorption capacity (i.e. improvement of toughness) is concerned. The results obtained during these tests can be very important, especially in order to compare the properties of different types of composites, but also to solve specific practical engineering problems.U radu su obrađeni aktuelna metodologija i relevantna tehnička regulativa iz oblasti ispitivanja žilavosti (duktilnosti) mikro-armiranih betona pri statičkom opterećenju (savijanju ili cepanju pomoću klina), kao i otpornosti predmetnih materijala pri dinamičkom - udarnom opterećenju. Poboljšane performanse mikro-armiranih betona, u odnosu na kompozite spravljene bez dodatka vlakana, najviše su izražene u domenu povećanja njihovog kapaciteta da apsorbuju energiju tokom loma (tj. u vidu povećanja žilavosti). Rezultati dobijeni na osnovu ovakvih ispitivanja mogu da budu veoma značaj ni, pre svega kod poređenja svojstava kompozita različitog sastava, ali takođe i kod rešavanja specifičnih inženjerskih problema u praksi

Uticaj dodatka polipropilenskih vlakana na atheziju maltera za podlogu

The results of own experimental explorations conducted in order to determine adhesion of mortar made with addition of polypropylene fibers are presented in this paper. The priciest concrete plates were used as a base material over which the mortar was cast in 3 cm thick layers. Six different series of specimens - cylinders were treated, depending on type and amount of used fibers, as well as on preparation techniques of surface between old and new material. The testing of adhesion was conducted using axial tension method. The obtained results showed significant improvement of this physical-mechanical property on specimens made with polypropylene fibers compared to control specimens (mortar without micro reinforcement).U radu su prikazani rezultati sopstvenih eksperimentalnih istraživanja koja su imala za cilj određivanje veličine athezije (prianjanja) za podlogu maltera spravljenih sa dodatkom polipropilenskih vlakana. Kao podloga su korišćene prefabrikovane betonske ploče preko kojih je ugrađivan sloj maltera debljine 3 cm. Ukupno je tretirano šest serija uzoraka - kernova, u zavisnosti od vrste i količine upotrebljenih vlakana, kao i različite pripreme površine na kontaktu između starog i novog materijala. Ispitivanje athezije vršeno je pri čistom aksijalnom zatezanju. Ostvareni rezultati pokazuju značajno poboljšanje predmetne fizičko-mehaničke karakteristike kod maltera ojačanih polipropilenskim vlaknima, u odnosu na etalonske uzorke (malter bez dodatka mikroarmature)

Povećanje žilavosti i udarne otpornosti betona putem mikro-armiranja

The paper deals with actual methodology and relevant technical regulation in the field of toughness (i.e. ductility) testing of fiber-reinforced concrete subjected to static load (flexural or wedge-splitting test), as well as testing of material's resistance to dynamic - impact load. The improved performance of fiber-reinforced concrete, compared to composite materials made without the addition of fibers, is most significant when the enhancement of fracture energy absorption capacity (i.e. improvement of toughness) is concerned. The results obtained during these tests can be very important, especially in order to compare the properties of different types of composites, but also to solve specific practical engineering problems.U radu su obrađeni aktuelna metodologija i relevantna tehnička regulativa iz oblasti ispitivanja žilavosti (duktilnosti) mikro-armiranih betona pri statičkom opterećenju (savijanju ili cepanju pomoću klina), kao i otpornosti predmetnih materijala pri dinamičkom - udarnom opterećenju. Poboljšane performanse mikro-armiranih betona, u odnosu na kompozite spravljene bez dodatka vlakana, najviše su izražene u domenu povećanja njihovog kapaciteta da apsorbuju energiju tokom loma (tj. u vidu povećanja žilavosti). Rezultati dobijeni na osnovu ovakvih ispitivanja mogu da budu veoma značaj ni, pre svega kod poređenja svojstava kompozita različitog sastava, ali takođe i kod rešavanja specifičnih inženjerskih problema u praksi

Eksperimentalna ispitivanja određenih termo-fizičkih i mehaničkih svojstava EPS betona

In this paper the experimental results obtained during testing of certain important properties of EPS concrete as a type of lightweight composite material - regarding Civil engineering physics are presented. Most of the attention has been paid to actual problems of thermo-insulation, steam conduction, capillary absorption and behavior of the material when exposed to low temperatures. After numerous laboratory tests, the authors concluded that Simprolit - as a represent of the EPS group of light concrete composites made of Portland cement, expanded polystyrene granules and special additives - satisfies high demands necessary for contemporary thermo-insulation and steam conduction materials. This composite material is characterized by relatively low density and good thermo-insulation properties, as well as high frost resistance. Simprolit system for thermo-insulation and steam conduction fulfils all the required conditions - both from the aspects of bearing capacity and Civil engineering physics.U ovom radu prikazani su rezultati sopstvenih eksperimentalnih ispitivanja nekih od važnijih svojstava lakoagregatnih kompozita tipa EPS betona - sa stanovišta građevinske fizike. Akcenat je stavljen na aktuelne probleme termoizolacije, odvođenja vodene pare, kapilarnog upijanja i ponašanja materijala u uslovima niskih temperatura spoljašnje sredine. Nakon obavljenih brojnih laboratorijskih testova, autori su došli do zaključka da Simprolit - kao reprezent grupe EPS betona spravljenih na bazi portland cementa, granula ekspandiranog polistirena i specijalnih aditiva - zadovoljava visoke zahteve koji se postavljaju pred savremene termoizolacione i paropropusne materijale. Ovaj kompozit karakterišu relativno niska zapreminska masa i dobre termoizolacione performanse, kao i visoka otpornost na dejstvo mraza. Simprolit sistem za termoizolaciju odvođenje vodene pare sa ravnih krovova ispunjava neophodne uslove - kako sa aspekta nosivosti, tako i sa aspekta građevinske fizike

Eksperimentalna ispitivanja određenih termo-fizičkih i mehaničkih svojstava EPS betona

In this paper the experimental results obtained during testing of certain important properties of EPS concrete as a type of lightweight composite material - regarding Civil engineering physics are presented. Most of the attention has been paid to actual problems of thermo-insulation, steam conduction, capillary absorption and behavior of the material when exposed to low temperatures. After numerous laboratory tests, the authors concluded that Simprolit - as a represent of the EPS group of light concrete composites made of Portland cement, expanded polystyrene granules and special additives - satisfies high demands necessary for contemporary thermo-insulation and steam conduction materials. This composite material is characterized by relatively low density and good thermo-insulation properties, as well as high frost resistance. Simprolit system for thermo-insulation and steam conduction fulfils all the required conditions - both from the aspects of bearing capacity and Civil engineering physics.U ovom radu prikazani su rezultati sopstvenih eksperimentalnih ispitivanja nekih od važnijih svojstava lakoagregatnih kompozita tipa EPS betona - sa stanovišta građevinske fizike. Akcenat je stavljen na aktuelne probleme termoizolacije, odvođenja vodene pare, kapilarnog upijanja i ponašanja materijala u uslovima niskih temperatura spoljašnje sredine. Nakon obavljenih brojnih laboratorijskih testova, autori su došli do zaključka da Simprolit - kao reprezent grupe EPS betona spravljenih na bazi portland cementa, granula ekspandiranog polistirena i specijalnih aditiva - zadovoljava visoke zahteve koji se postavljaju pred savremene termoizolacione i paropropusne materijale. Ovaj kompozit karakterišu relativno niska zapreminska masa i dobre termoizolacione performanse, kao i visoka otpornost na dejstvo mraza. Simprolit sistem za termoizolaciju odvođenje vodene pare sa ravnih krovova ispunjava neophodne uslove - kako sa aspekta nosivosti, tako i sa aspekta građevinske fizike

Uticaj vrste i količine polipropilenskih vlakana na mehanička svojstva kompozita tipa maltera i betona

Reinforcement of different brittle materials using fibers in order to improve their mechanical properties is an age-old concept. This concept is especially actual in the last two decades, when a large number of new fiber types have been developed. Among these are fibers made of steel (ordinary or stainless), polymeric compounds (polypropylene, polyethylene, nylon, etc.), mineral materials (asbestos, glass) and naturally occurring materials (cellulose, sisal, bamboo, coconut, etc.). This paper deals with results of experimental investigations of fiber-reinforced mortar - composite material made with addition of polypropylene fibers. On the basis of own explorations, the conclusion can be derived that the addition of relatively small amount of polypropylene fibers (volume fraction ~ 0,1%) improves certain mechanical properties of mortar and concrete composites, such as compressive strength, flexural strength, and shear strength.Ojačanje različitih vrsta krtih materijala pomoću vlakana, u cilju poboljšanja njihovih mehaničkih svojstava, predstavlja koncept koji je poznat i primenjivan od davnina. Ovaj koncept je naročito aktuelan u poslednje dve dekade, kada je razvijen i uveden u upotrebu veliki broj novih vrsta vlakana (ili tzv. mikroarmature). Od svih tipova vlakana, kao najznačajnije možemo izdvojiti sledeće: čelična (od običnog ili nerđajućcg čelika), polimerna (polipropilenska, polietilenska, najlonska i dr.), mineralna (azbestna, staklena), kao i vlakna od prirodnih materijala (od celuloze, konoplje, bambusa, kokosa, itd.). U ovom radu prikazani su rezultati eksperimentalnih ispitivanja svojstava maltera - kompozita spravljenih na bazi dodatka polipropilenskih vlakana. Na bazi sopstvenih istraživanja, može se izvući zaključak da dodatak relativno male količine polipropilenskih vlakana (~ 0,1% od ukupne zapremine), poboljšava pojedina mehanička svojstva kompozita tipa maltera i betona, kao što su čvrstoća pri pritisku, čvrstoća pri savijanju i čvrstoća pri smicanju

Mikroarmirani malteri i betoni - mogućnost poboljšanja fizičko-mehaničkih svojstava

Basic properties of fiber reinforcement mortar and concrete type composites have been represented in the paper. The results of authors' own laboratory testing of two concrete types as well as two mortar types are shown. Some of the series were made with the addition of hooked steel fibers. Furthermore, testing conducted on mortar specimens made with ordinary sand and crushed brick aggregate are presented. Certain specimen series were made with the additional of monofilament polypropylene fibers. During the testing the following properties were considered: density, compressive and flexural strength as well as shrinkage of mortar. The obtained experimental results pointed to the significant improvement of mechanical properties of the composites with reinforcement.U radu je dat prikaz osnovnih svojstava mikro­armiranih kompozita tipa maltera i betona. Prikazuju se rezultati sopstvenih laboratorijskih ispitivanja dobijeni na dva tipa maltera kao i na dva tipa betona. Kod nekih od ovih serija korišćena su čelična vlakna zakrivljena na krajevima. Dalje, prikazuju se rezultati ispitivanja dobijeni na uzorcima spravljenim sa polipropilenskim vlaknima i to kao sa rečnim agregatom, tako i sa agregatom od drobljene opeke. Pri ispitivanjima praćena su sledeća svojstva: zapreminska masa, čvrstoća pri pritisku, čvrstoća pri savijanju kao i skupljanje. Rezultati eksperimentalnih ispitivanja pokazuju značajno poboljšanje mehaničkih svojstava kompozita izrađenih sa mikroarmaturom

Pebble dynamics and accretion onto rocky planets. II. Radiative models

We investigate the effects of radiative energy transfer on a series of nested-grid, high-resolution hydrodynamic simulations of gas and particle dynamics in the vicinity of an Earth-mass planetary embryo. We include heating due to the accretion of solids and the subsequent convective motions. Using a constant embryo surface temperature, we show that radiative energy transport results in a tendency to reduce the entropy in the primordial atmosphere, but this tendency is alleviated by an increase in the strength of convective energy transport, triggered by a correspondingly increased super-adiabatic temperature gradient. As a consequence, the amplitude of the convective motions increase by roughly an order of magnitude in the vicinity of the embryo. In the cases investigated here, where the optical depth towards the disk surface is larger than unity, the reduction of the temperature in the outer parts of the Hill sphere relative to cases without radiative energy transport is only $\sim$100K, while the mass density increase is on the order of a factor of two in the inner parts of the Hill sphere. Our results demonstrate that, unless unrealistically low dust opacities are assumed, radiative cooling in the context of primordial rocky planet atmospheres can only become important after the disk surface density has dropped significantly below minimum-mass-solar-nebula values.Comment: 5 pages, 4 figures, 2 appendices; MNRAS Letters, accepte

Savremene metode i tehnike ispitivanja betona i betonskih konstrukcija

This paper presents several contemporary nondestructive methods and techniques used for testing of concrete and concrete structures. These methods provide prompt and simple 'in situ' determination of fresh and/or hardened concrete properties, The obtained results can be used as additional proof of concrete quality (together with laboratory testing of specimens) for reinforced concrete structures monitoring or to determine possible causes of built in materials degradation.U radu su prikazane neke od savremenih nedestruktivnih metoda i tehnika ispitivanja betona i betonskih konstrukcija. Ove metode omogućavaju vrlo brzo i jednostavno određivanje pojedinih karakteristika svežeg i/ili očvrslog betona 'in situ'. Njihovom primenom dobija-ju se rezultati koji mogu da se koriste kao dopunski dokaz o kvalitetu betona (uz ispitivanje probnih tela u laboratoriji), za praćenje stanja armirano betonskih konstrukcija (tzv. 'monitoring') ili za utvrđivanje mogućih uzroka degradacije materijala ugrađenih u ove konstrukcije

Solidified waste water treated sludge as partial replacement of cement in concete composites

In this research, tests of mortar and porous concrete made with solidified waste water treatment sludge (SWWTS) used in two forms as a partial replacement of cement were carried out. SWWTS mainly consisted out of CaCO3 and Ca(OH)2, having no pozzolanic properties. For this reason, it was used both, as produced, and modified by adding Al2O3 and Mg3Si4O10(OH)2 in certain percentages. One mortar type and two types of porous concrete were tested. For each of the three products two mixtures were prepared: the reference mixture and the mixture made with 30% replacement of cement, while the other components remained the same. Based on the given comparative analysis, conclusions were drawn regarding the structure of porous concrete slabs, which refer to individual analyzed properties, but also to the possibility of applying energy-efficient materials. The obtained results point to the conclusion that the use of SWWTS reduces the values of almost all tested properties of porous concrete (flexural and compressive strength, pull-off strength, abrasion resistance), but also that the modification of SWWTS led to a smaller difference in the results of the samples made with 30% of cement replacement and the reference samples. Although, the use of SWWTS led to the reduction of mechancal properties of concretes, the most important benefit is development of possible way for reuse of this waste material and avoid its disposal in the landfills