Search

In this scientific research, the definition of appropriate neutron shielding parameters is presented and the results of calculations or measurements of these parameters are presented for four selected types of concrete that are used in protection against neutron radiation. A method for calculating the fast neutron effective removal cross section is considered, which has its own specificities because it takes into account different types of interactions of fast neutrons with the materials from which the selected types of concrete are made. In addition, the values of macroscopic neutron absorption cross section for thermal neutrons, macroscopic neutron scattering cross section and total macroscopic neutron attenuation cross section, which includes scattering of fast neutrons and absorption of thermal neutrons, are presented for the selected types of concrete. Based on the analysis of neutron shielding parameters, type of concrete with coarse-fine aggregate limonite-limonite has a higher level of ability to protect against neutron radiation compared to concrete with coarse-fine aggregate magnetite-limonite and concrete with barite-barite.

Quantity of waste rubber generated by automobile tires is growing, posing an environmental threat. Rubber tire recycling was studied for usage in asphalt and waterproofing systems during past few decades. Globally, concrete is the most widely used building material. About 7% of CO2 emissions come from the cement production. The purpose of this research is to assess if using waste rubber and Portland cement together in composite material for structural applications is feasible. Waste tires (shredded to 0/1 mm) were used as fine aggregate replacement (in 2.5 and 7.5 %), together with PC and natural stone. An investigation of properties in fresh (slump test, bulk density, air content) and hardened state (bulk density, compressive strength) was performed on the rubberized concrete. The compressive strength decreased by increasing the rubber content for all w/c ratios (0.55-0.4). The addition of fine-sized rubber did not cause a retardation in cement hydration mechanism. According to the obtained compressive strengths, all designed rubberized concretes belong to a group of structural concretes.

Waste tires have long been a challenge for waste disposal. In an effort to mitigate the impact of solid waste on the environment and recycle it as much as possible, research has been conducted into the possibility of using this waste in concrete mixes. However, the use of these waste materials in concrete is still not popular due to the lack of knowledge of the properties that can be obtained with this material. Hence, the aim is to use waste material in the production of concrete, and that concrete mixes with this material have satisfactory performance. The paper presents the results of research on concrete in which volume replacement of fine aggregate with crumb rubber was performed in the amount of 5%, and this concrete was compared with the control concrete mix and aerated concrete. All concrete are made with a water-cement factor of 0.45. The performance of fresh concrete was monitored for 10, 30 and 60 min. In the case of concrete with the addition of crumb rubber, after 60 min, higher values of air content were obtained, and lower values of volume mass of fresh concrete compared to the initial measurements. The obtained test results of hardened concrete indicate that concrete with crumb rubber has a lower compressive strength compared to the control concrete mix, while compared to aerated concrete, they obtain approximate compressive strength values.

Donošenjem Pravilnika o tehničkim zahtevima za beton odgovornost za stavljanje / isporuku betona na tržište preuzima proizvođač betona, kome se nameću znatno veće obaveze, nadležnosti i zahtevi koje mora ispuniti. Očekujemo da Pravilnik doprinese poboljšanju kvaliteta betona i povećanju uređenosti na tržištu ovih građevinskih proizvoda. Ovim radom predstavljeni su osnovni aspekti ocenjivanja i verifikacije stalnosti performansi betona, u skladu sa Pravilnikom o tehničkim zahtevima za beton. Objašnjene su obaveze proizvođača i imenovanog sertifikacionog tela za fabričku kontrolu proizvodnje.

This study compared the performance of self-compacting concrete (SCC) based on fly ash addition and limestone filler. A SCC prepared with Portland cement, river sand, and limestone filler was used as a reference sample. Additional experimental self-compacting concretes with different types of fine aggregates, fillers, and special additives for increasing freeze-thaw resistance were prepared and optimized. The correlation between mix design, i.e., percentage of barite sand and additives, on properties of hardened SCC (compressive and flexural strengths), were investigated and discussed.

Self-compacting concrete (SCC), a non-shaped composite building material, has improved microstructure packing, strength, and durability thanks to the use of fly ash, a highly effective mineral additive. Performances of SCC with fly ash and conventional SCC with limestone filler were compared. Additional experimental self-compacting concretes were made and adjusted with various types of fine aggregates, fillers, and unique additives to increase freeze-thaw resistance. The relationship between the proportion of barite sand and additives and the properties of SCC was investigated and discussed. Tests of freeze-thaw resistance with and without de-icing salts are the main focus of these articles.

The impacts of nano-silica addition, steel micro-reinforcement, and aggregate type on the mechanical properties and durability of ultra-high-performance concrete (UHPC) were studied. As aggregates, quartz and barite were used. The amounts of steel fibers and nano-silica were alternated. Six concrete mixes were produced with quartz sand, and the remaining six concrete mixes were designed with barite sand. Fibers made about 3-5% of the concrete composition’s mass. In a 2-5% concentration, nano-silica was used as a cement replacement. The inclusion of nano-silica significantly boosted the compressive strength of UHPC. The compressive and flexural strengths were also positively impacted by fiber supplementation ranging from 3% to 5%. The amount of fiber utilized proved to be more influential than the aggregate used. The UHPC concrete's durability was increased as all samples were highly resistant to freezing and thawing cycles. UHPC designed with barite aggregate demonstrated good X and gamma ray absorption at energies below 300 keV.

Fly ash is a highly efficient mineral additive whose role is reflected in improvements of microstructure packing, strength and durability of non-shaped composite building materials such as self-compacting concrete (SCC). A comparative study of performances of SCC with fly ash and standard SCC with limestone filler was conducted.Additional experimental self-compacting concretes with different types of fine aggregates, fillers, and special additives for increasing freeze-thaw resistance were prepared and optimized. The correlation between percentage of barite sand and additives, and properties of SCC, were investigated and discussed. Main topic of these article is testing the resistance of concrete to penetration of water under pressure.

Betonske konstrukcije su često u eksploataciji izložene spoljašnjim uticajima. Preporuke koje definiše evropski stan-dard SRPS EN 206 za korišćenje betona u pojedinim klasa-ma izloženosti nisu dovoljne i iz tog razloga je usvojen i standard SRPS U.M1.206 koji predstavlja nacionalni doda-tak za njegovu primenu. Dejstvo mraza značajno utiče na trajnost betonske konstrukcije jer može da dovede do raza-ranja strukture betona. Zaštita se postiže dodavanjem hemij-skih dodataka koji uvlače vazduh u svež beton. U radu je prikazana mogućnost primene novog dodatka Sika Aer Solid. Ispitivana je otpornost betona na dejstvo mraza, mraza u prisustvu soli za odmrzavanje, prodiranje vode pod pritiskom i koeficijent migracije hlorida u laboratorijskim uslovima i uzorcima izvađenim iz betonskih prefabrikovanih elemenata. Betoni sa Sika Aer Solid su za istu klasu konzistencije u odnosu na aerirane betone imali bolja svojstva i u svežem i u očvrslom stanju.

During the implementation of procedures for designing building barriers for protection against gamma and X radiation, the unavoidable question of choosing construction materials with appropriate mechanical and radiation characteristics for protective barriers arises. Based on engineering practice, it is necessary to compare different types of concrete used for the construction of facilities where there are sources of gamma and X radiation, such as in cases where radiation sources appear in medical facilities with linear accelerators, cyclotron installations for accelerating nuclear particles, in the environment of nuclear reactors, in radioactive waste storages, or in radiation sterilization unit s. In the cost-benefit analysis, several criteria are used to evaluate the characteristics of the concrete, so that in addition to the mechanical characteristics, the radiation characteristics of the construction material are also considered. One of the most important characteristics of concrete for radiation protection is its total mass attenuation coefficient. In this paper, computer code XCOM was used for the calculation of the total mass attenuation coefficients in energy range from 0.01MeV to 100 MeV for three types of concrete: ordinary concrete, concrete with barite and concrete with limonite and steel. Based on the comparison of calculation results, it was concluded that concrete with limonite and steel has greater protective power than other two concrete types for the gamma and X radiation energy less than 30 keV. The second important conclusion is that the concrete with barite has greater protective power than other two concrete types in the range of photon energy from 30 keV to 300 keV, and for photon energy greater than 6 MeV. A detailed analysis of the calculation results found that in the energy range of 400 keV to 6 MeV values for the total mass attenuation coefficients are approximately the same for three different types of concrete.

During the implementation of construction barrier design procedures for protection against gamma and X radiation, the inevitable question arises of choosing building materials with suitable mechanical and radiation characteristics for protective barriers. Based on engineering practice, it is necessary to compare different types of concrete used for the construction of buildings in which there are sources of gamma and X radiation, as in cases where radiation sources appear in medical institutions with linear accelerators, cyclotron installations for the acceleration of nuclear particles, in the environment of nuclear reactors, in radioactive waste warehouses or in radiation sterilization units. In the analysis of costs and benefits, several criteria are used to evaluate the characteristics of concrete, so that, in addition to the mechanical ones, the radiation characteristics of the building material are also taken into account. One of the most important characteristics of radiation shielding concrete is its overall mass attenuation coefficient. In this paper, the XCOM computer code was used to calculate the total mass attenuation coefficients in the energy range from 0.01 MeV to 100 MeV for three types of concrete: ultrahight properties concrete (UHPC), concrete with barite and concrete with magnetite and steel. Based on the comparison of the calculation results, it was concluded that concrete with magnetite and steel has a greater protective power than the other two types of concrete for gamma and X radiation energy lower than 30 keV. Another important conclusion is that concrete with barite has a higher protective power than the other two types of concrete in the photon energy range from 30 keV to 300 keV, and for photon energy greater than 6 MeV. A detailed analysis of the calculation results revealed that in the energy range from 400 keV to 6 MeV the values for the total mass attenuation coefficients are approximately the same for three different types of concre

Compared to traditional concrete, self-compacting concrete (SCC) demonstrates greater flowability, which is achieved by including an extra high percentage of ultra-fine particles. As a result, the required high paste content is obtained while the cement content is strictly limited. The coal combustion byproduct (fly ash) is one of the most efficient SCC fillers because it extends the lifecycle of SCC by improving its microstructural properties, strength, and durability. In this study, the amounts of fly ash in SCC compositions varied. The changes in physical and mechanical characteristics of fresh SCC samples related to variations in the water/binder ratio were monitored.

Leteći pepeo je visoko efikasan mineralni aditiv čija se uloga ogleda u poboljšanju mikrostrukture, čvrstoće i izdržljivosti kompozitnih građevinskih materijala kao što je samozbijajući beton (SCC). Referentni SCC je projktovan sa portland cementom, rečnim agregatom i krečnjačkim filerom. Eksperimentalni program obuhvatao je proizvodnju pet samozbijajućih betona sa različitim vrstama sitnog agregata, filera i specijalnog dodatka za povećanje otpornosti na dejstvo mraza. Ispitivani su i diskutovani efekti koje baritni pesak i dodaci imaju na svojstva svežeg SCC (sleganje rasprostiranjem, test V-levka i test L-kutije) i čvrstoću pri pritisku.

A comparative study of performances of self compacting concrete (SCC) with fly ash and limestone filler was conducted. The experimental program included the production of reference SCC designed with Portland cement, river sand and limestone filler and four experimental self compacting concretes with different types of fine aggregates, fillers and special additive to increase freeze-thaw resistance. The effects that different sand and additions have on the properties of fresh SCC (slump-flow test, V-funnel test, and L-box test) and compressive strengths in early ages (3 and 7 days) were investigated and discussed.

Self-compacting concrete (SCC) exhibits increased flowability in comparison with the conventional vibrated concrete. This is most often achieved through the incorporation of high amounts of extra-fine particles (i.e. mineral fillers) in the composition of self-compacting concrete. The purpose is to limit the share of cement while reaching the required large paste content. The components and their proportions, as well as type and particle size of filler, casting, manufacturing and curing conditions of SCC, significantly influence the concrete’s fresh and hardened properties. Among fillers employed in SCC, fly ash is one of the most frequent due to its availability and the low cost. Fly as is an industrial by-product and a highly efficient mineral additive whose role is reflected in improvements of microstructure packing, strength and durability of non-shaped composite building materials such as self-compacting concrete. A comparative study of performances of SCC with different quantities of fly ash and standard SCC with limestone filler was conducted in this study. The experimental program included the production of reference self-compacting concrete based on Portland cement and limestone filler (P1) and additional three experimental self-compacting concrete mixtures (P2, P3, P4) with different quantities of fly ash addition. Behaviour of self-compacting concrete in the fresh state is primarily influenced by type of mineral additive used. The effect that fly ash addition has on the physical behaviour and mechanical properties of fresh experimental SCC concrete samples was discussed. The properties and technology of self-compacting concretes in their fresh state in regard to the alternations in water/cement (w/c) ratios are monitored and explained in this paper. Concrete mixtures with fly ash had lower density in comparisons with the referent concrete. For the same class of consistency, higher amount of water was needed for preparation of SCC mixture with fly ash. Inc

Global warming and the emission of CO2 into the atmosphere is becoming a bigger problem in the world every year. The desire for a global increase in production and the ever-increasing development of industry are the cause of the increased amount of waste in landfills and environmental pollution. Concrete is the most used construction material in the world, and the production of its main ingredient, cement, is responsible for about 7% of CO2 emissions in the world. Application of waste materials and by-products that end up as waste during some industrial process in production can find further application in concrete. Such materials can be used as mineral additives or as aggregate fillers, for partial or complete replacement of natural stone aggregate and/or cement. In this work, volume replacement of the fine fraction with 2.5 and 7.5 % crushed rubber was performed. Based on the test results of fresh concrete, in concrete with rubber addition, the slump consistency and bulk density decrease, and the air content increases. A drop in compressive strength of concrete was observed with an increase in the rubber content of 7.5%.

During the implementation of procedures for designing building barriers for protection against gamma and X radiation, the unavoidable question of choosing construction materials with appropriate mechanical and radiation characteristics for protective barriers arises. Based on engineering practice, it is necessary to compare different types of concrete used for the construction of facilities where there are sources of gamma and X radiation, such as in cases where radiation sources appear in medical facilities with linear accelerators, cyclotron installations for accelerating nuclear particles, in the environment of nuclear reactors, in radioactive waste storages, or in radiation sterilization unit s. In the cost-benefit analysis, several criteria are used to evaluate the characteristics of the concrete, so that in addition to the mechanical characteristics, the radiation characteristics of the construction material are also considered. One of the most important characteristics of concrete for radiation protection is its total mass attenuation coefficient. In this paper, computer code XCOM was used for the calculation of the total mass attenuation coefficients in energy range from 0.01MeV to 100 MeV for three types of concrete: ordinary concrete, concrete with barite and concrete with limonite and steel. Based on the comparison of calculation results, it was concluded that concrete with limonite and steel has greater protective power than other two concrete types for the gamma and X radiation energy less than 30 keV. The second important conclusion is that the concrete with barite has greater protective power than other two concrete types in the range of photon energy from 30 keV to 300 keV, and for photon energy greater than 6 MeV. A detailed analysis of the calculation results found that in the energy range of 400 keV to 6 MeV values for the total mass attenuation coefficients are approximately the same for three different types of concrete.

The paper presents the influence of the use of different types of fibers on the properties of concrete. All concrete samples were made with same component materials and compositions, except for the amount of fibers, which was varied. After hardening, the concrete samples were tested for compressive strength, tensile splitting strength and water penetration depth under pressure. Based on the test results, depending on the type, shape, amount and arrangement of fibers, the tensile and compressive strength values as well as the depth of water penetration under pressure were analyzed. Based on the tests performed, the best mechanical properties were achieved with the use of "Dramix 3D" steel fibers.

The paper shows the influence of steel fibers obtained from steel wire separated in the recycling process of waste car tires on the properties of concrete. The reference concrete was prepared, as well as concretes with the addition of steel fibers, which were varied in contents at 20 kg/m3 and 40 kg/m3. The slump test of fresh concrete was performed using the Webe method, where it was established that with an increase in the amount of fibers, concretes with a stiffer consistency are obtained. Concrete beams were tested for strength during flexure tension (limit of proportionality (LOP) and residual flexural strength). Can be concluded that the residual flexure strength greater than 1.5 MPa at a CMOD of 0.5 mm is already achieved with the addition of 20 kg of fibers per m3 of concrete, while both conditions for the residual bending strengths are satisfied with the addition of 40 kg of fibers per m3 of concrete and that they amount to 2.4 MPa at a CMOD of 0.5 mm and 1.4 MPa at a CMOD of 3.5 mm.

The phyllosilicate mineral pyrophyllite can be utilized in cementitious composites design to replace quartz powder and boost workability, early strengths, and refractoriness. Employed as a mineral additive or microfiller, pyrophyllite is stable at high temperatures owing to its thermal conversion into mullite. In this study, mortar samples were prepared using andalusite as aggregate, high-alumina cement as a binder, and pyrophyllite as an additive (15%, 25%, and 35%). Compressive and flexural strengths, both at normal and elevated temperatures (samples were thermally treated at 1000°C) were tested on the samples, along with the refractoriness. The effects of pyrophyllite addition on the mineral composition, microstructure, and bonding and sintering mechanisms were studied using instrumental analytical techniques. Pyrophyllite acted as additional pozzolana during cement hydration as it formed microreinforcement in the shape of crystalline folia within the microstructure, which improved the compressive strengths of mortars. The differential thermal analysis highlighted that pyrophyllite did not negatively interfere with the cement hydration route; moreover, this mineral additive behaved as pozzolana. The investigation demonstrated that pyrophyllite additions of up to 25% can be used in cementitious composites without affecting their performance.

The experimental study included the design and production of ultra-high-performance steel fiber-reinforced concrete (UHPFRC). The physical and mechanical properties of UHPFRC were investigated in a laboratory setting. To investigate the properties of UHPFR concrete, three types of concrete and over 70 samples were used. Following that, samples were created to test the anchors' load-bearing performance. Six concrete slabs with a total of 108 pre-installed anchor samples and six concrete slabs with 108 post-installed chemical anchor samples were created. The analysis of the test findings comprised all individual results as well as the definition of the relationship between the anchor's tensile load capacity and other parameters. To accurately determine the individual influence of the investigated factors as well as their combined impact, a factorial experiment, and artificial neural networks were used in addition to normal statistical numerical studies. It was determined that both approaches offer advantages. The results obtained show matches in certain parts. Due to the way data is processed in different ways, there are also significant differences between them.

Ponašanje struktura pod delovanjem različitih vrsta opterećenja određene su njenim deformacionim karakteristikama, globalnim deformacionim karakteristikama – pomeranjima i rotacijama i lokalnim deformacionim karakteristikama - dilatacijama u materijalu strukture. Poznavanjem globalnih i lokalnih deformacionih karakteristika strukture ostvarujemo mogućnost da pratimo ponašanje strukture u celini ili nekog njenog segmenta. Osnovni cilj ovog istraživanja je provera algoritma proračuna za dobijanje vertikalnih pomeranja - ugiba strukture, na osnovu poznatih vrednosti dilatacija u materijalu strukture, pri delovanju opterećenja. Provera algoritma sprovodi se poređenjem numeričkih i eksperimentalnih rezultata.

The paper presents the possibility of using recycled aggregate from precast concrete paving elements and kerbs in the production of concrete kerb units. Experimental work included several types of concrete consistency class S1, made with different amounts of cement and coarse recycled concrete aggregate. The influence of percentage and grain size of recycled concrete aggregate on concrete compressive strength at different ages was observed. Based on the experimental results, it can be concluded that the use of recycled concrete as an aggregate creates a new composite material that can be used for the production of precast elements. The results show that the replacement of the coarse natural aggregate with aggregate from crushed concrete is possible to produce concrete curbs that meet the requirements of EN 1340, but the class depends on the replacement percentage of the natural aggregate with recycled ones. In this way, the production waste is turned back to process, and the newly created concrete is certainly ecological material.

The possibility of using tailings from the iron mine (IOT) in the production of concrete elements for the pedestrian areas is shown in this paper. To determine the impact of the amount of tailings on the compressive strength of concrete, samples with varying percentage of replacement of aggregate fractions were made. Based on the testing results it was assumed that it is possible to produce the concrete elements with tailings from iron mine as concrete component. The results show that partial replacing natural aggregate with IOT produces concrete elements which meet the requirements of EN 1338.

Tehničko rešenje predstavlja poboljšanu konstrukciju zaštićene grejne ploče (hotguarded plate) za merenje toplotne provodljivosti termoizolacionih materijala postavljanjem ispitnog uzorka iznad i ispod grejne ploče (standardna simetrična ispitna konfiguracija). Merenje toplotne provodljivosti vrši se u skladu sa standardom SRPS U.A2.020. Ovim rešenjem toplotna provodljivost se proračunava na osnovu vrednosti izmerenog toplotnog fluksa korišćenjem dva tanka toplotna fluksmetra na toploj i hladnoj strani ispitivanih uzoraka. Prednost korišćenja fluksmetara na grejnoj i rashladnoj ploči u odnosu na uobičajen metod za određivanje toplotne provodljivosti (hot-guarded plate) je u periodu dostizanja stacionarnog stanja koji je znatno kraći. Na taj način bi se ostvarila sva zahtevana merenja toplotne provodljivsti termoizolacionih materijala usled povećane potražnje za ovakvom vrstom ispitivanja u Republici Srbiji. Kod metoda merenja sa toplotnim fluksmetrima, uobičajeno je da se koristi jedan fluksmetar na zaštićenoj grejnoj ploči. Kod ovog tehničkog rešenja koriste se dva toplotna fluksmetra na površini uzorka. Na taj način se precizno može utvrditi srednja vrednost toplotnog fluksa kroz ispitivani uzorak tj. srednji toplotni fluks kroz sam uzorak je tačnije određen. Fluksmetri za ovakvu vrstu merenja su odabrani sa velikom mernom površinom da bi se dobile što merodavnije vrednosti raspodele toplotnog fluksa po mernoj površi, pri čemu uobičajeno korišćenje znatno manjih toplotnih fluksmetara. Novi koncept grejne ploče ne odgovara uobičajenim grejnim pločama koje su opisane u standardima. Specifičnost ovog dizajna ploče je u smanjenom toplotnom prekidu – prostor između unutrašnje zaštićene (hot) i spoljašnje zaštitne (guard) ploče koje zajedno čine predmet ovog tehničkog rešenja. Veličinom toplotnog prekida od 1 mm popunjenog dvokomponentnim termoizolacionim lepkom, određena je i minimalna dozvoljena debljina uzorka. Na taj način je omogućeno merenje tanjih termoizolacija

Da bi se obezbedila trajnost betona, potrebno je zaštititi betonske infrastrukturne objekte u zemljama u kojima se smenjuju godišnja doba i različiti vremenski uslovi, jer je njihovo izlaganje ciklusima zamrzavanja i odmrzavanja (eng. FTC – freezing and thawing cycles) u prisustvu soli za odmrzavanje jedan od najagresivnijih mehanizama za propadanje betona. Šteta od mraza, progresivno pogoršanje koje započinje ljuštenjem površinskog maltera i završava potpunim urušavanjem betonskih elemenata, glavna je briga kada se beton koristi u hladnijim regionima. Ponavljanjem ciklusa zamrzavanja i odmrzavanja javljaju se prsline i pukotine, a beton postepeno gubi svoja prvobitno projektovana svojstva. Betoni koji će biti izloženi dejstvu mraza u svom sastavu imaju veće količine cementa, a problem primene veće količine cementa se poslednjih godina posebno naglašava zbog sve većeg zagađenja životne sredine i stvaranja efekta staklene bašte. Betoni koji se izlažu dejstvu mraza i/ili mraza i soli štite se aeriranjem. To često nije garancija da će se postići projektovan sadržaj vazduha u svežem betonu. Zbog toga se htelo doći do rešenja nekim drugim sredstvima zaštite betona izloženih dejstvu mraza. Jedno od rešenja je Sika Aer Solid. Kako bi ovaj materijal mogao da se primenjuje na našem podneblju i sa našim materijalima, obavljena su ispitivanja svojstava betona u svežem i očvrslom stanju, sa posebnom osvrtom na trajnost betona. Primenom Sika Aer Solid kao zamene za aerant, moguće je proizvesti betonske elemente čija svojstva zadovoljavaju zahtevane klase izloženosti koje su definisane prema SRPS EN 206 i SRPS U.M1.206. Dodavanjem Sika Aer Solid u beton postiže se trajnost betonskih prefabrikovanih elemenata kroz postizanje otpornosti na dejstvo mraza, otpornosti na dejstvo mraza u prisustvu soli za odmrzavanje, otpornosti na penetraciju vode pod prisitkom, kao i otpornosti na migraciju hloridnih jona.

Concrete in which the air entraining admixture was used can exhibit behavior which alternate from the ‘standard’ concrete behavior when employed in the structural design. The origin of this problem can be found in the changeable properties of the componential materials, incompatibility of the utilized raw materials, influence of extreme conditions on the concrete curing (i.e., increased temperature), etc. The possibility of using other additives for the concrete exposed to various environmental influences was investigated. Sustainability of concrete production and resource efficiency urged the searching for an adequate waste material or an industrial byproduct which would improve freezing/thawing resistance of concrete. In this paper the possibility of Sika Aer Solid powdery additive and recycled rubber as a substitute for the air entraining admixture was investigated. Four mixtures were designed: referent concrete with no air entraining admixtures, concrete with Sika Aer Solid, concrete with recycled rubber, and concrete with air entraining admixture. The properties of fresh and hardened concrete were examined. The obtained results of compressive strength, resistance to freezing/thawing cycles and depth of water penetration under pressure for altered concretes indicate that it is possible to use alternative additives as substitutes for air entraining admixture.

The paper presents the influence of the application of different types of fibers in concrete beams on the flexural tensile strength. All concrete beams were made of the same component materials and composition, except for the amount of fiber, which is varied. After hardening, the height of the concrete beams in the central part was reduced to 125 mm by cutting. The measurement of flexural tensile strength by was performed according to SRPS EN 14651. Based on the test results, depending on the type, shape, quantity and distribution of fibers, the values of ultimate and residual strengths were analyzed.

The Guarded hot plate method (GHP) is a widely used technique to measure thermal conductivity of thermal insulation specimens in steady-state conditions. In this paper, an advance of GHP has been developed in the Laboratory for Thermal technique and fire protection in Institute IMS. The innovative GHP has been applied for measuring thermal conductivity using additional heat flux meters. The design of this GHP is similar to the design of the plate for GHP apparatus; however, it has different design: smaller width of thermal barrier, which is filled with insulation glue. Heaters inside hot and guard plates are built from wire for thermocouples, which is a unique type of heater. Geometry of heater has been optimized inside plates to achieve uniform temperature distribution along the specimen surface. Temperature uniformity of guarded hot plate and energy balance were experimentally determined. The verification and validation results of improved GHP have been shown. The test method was validated comparing test results of thermal conductivity with results of the round-robin test. Four national companies participated in the round-robin comparison on thermal conductivity measurement by guarded hot plate method. The measurement was performed on the same specimen of thermal insulation material (expanded polystyrene) according to SRPS EN 12667 at temperatures ranging between 10℃-40℃. The measured thermal conductivity of all participants in the round-robin test was input data for statistical processing according to SRPS ISO 5725-2 and ISO 13528. To evaluate the performance of the participants, the “z” score has been used. Measurements were conducted successively for all participants. Since 2020, the Accreditation Body of Serbia also approved this test method.

The guarded hot plate (GHP) method is a widely used technique to measure thermal conductivity of thermal insulation specimens in steady-state conditions. In this paper, an advance of GHP has been developed in the Laboratory for Thermal Technique and Fire Protection in Institute IMS. The innovative GHP has been applied for measuring thermal conductivity using additional heat flux meters. The design of this GHP is similar to the design of the plate for GHP apparatus, however, it has different design: smaller width of thermal barrier, which is filled with insulation glue. Heaters inside hot and guard plates are built from wire for thermocouples, which is a unique type of heater. Geometry of heater has been optimized inside plates to achieve uniform temperature distribution along the specimen surface. Temperature uniformity of GHP and energy balance were experimentally determined. The verification and validation results of improved GHP have been shown. The test method was validated comparing test results of thermal conductivity with results of the round-robin test. Four national companies participated in the round-robin comparison on thermal conductivity measurement by GHP method. The measurement was performed on the same specimen of thermal insulation material (expanded polystyrene) according to SRPS EN 12667 at temperatures ranging between 10-40 °C. The measured thermal conductivity of all participants in the round-robin test was input data for statistical processing according to SRPS ISO 5725-2 and ISO 13528. To evaluate the performance of the participants, the “z” score has been used. Measurements were conducted successively for all participants. Since 2020, the Accreditation Body of Serbia also approved this test method.

The influence of the application of different types of fibres on the flexural strength of beams cut from slabs of sprayed concrete is presented in the paper. Fibres of different materials, shapes and dimensions were used. All types of concrete were made of the same component materials and composition, except the amount of fibres that is varied. Slabs of dimensions 60x60x10 cm were made using a concrete spraying machine. After curing, the beams of 75x125x500 mm were cut from the beams. Flexural strength of the beams was tested according to SRPS EN 14488-3 at the age of 28 days. Based on the test results, depending on the type, shape, amount and distribution of fibres, values of ultimate and residual strengths were analysed. The highest values of ultimate and residual strength at deformations of 0.5-1, 0.5-2 and 0.5-4 mm had sprayed concrete (or shotcrete) with the addition of 40 mm polypropylene fibres.