Staff

Abstract:
For possible application of gamma radiation in processing of fresh concrete, like surface processing at precast plants or 3D printing, it is essential to evaluate effects of irradiation on the early hardening of cementitious binders. The influence of gamma irradiation with the dose rate of 4.6 kGy/h on the early strength, pore size distribution and qualitative phase composition of mortar was investigated. The range of investigation comprises the effects selected micro- and nano-additions to Portland cement mortar used to control the kinetic of setting and early hardening of cement. Results show that gamma irradiation of hardening mortar results in the early strength increase of about 56–100%, in reduction of capillary porosity and pore size refinement. The gamma-irradiation sensitivity of early strength of cement mortar is equivalent to increased temperature wet curing. A correlation of heat evolution characteristics of hardening mortar and the temperature-equivalent of gamma irradiation is discussed.

Keywords:
boron minerals, early hardening, gamma irradiation, pore size distribution, strength, temperature equivalent

Abstract:
The article describes an experimental study of the properties of concrete designed for the construction of the bottom layer of two-layered road pavement with the exposed aggregate surface. Two types of materials were studied: industrially-produced concrete placed on a highway trial section using slip form technology and concrete produced in a laboratory setting, containing CEM II/A-V and CEM II/A-S Portland cement. The tested mixes contained granite or limestone coarse aggregate. The following basic performance properties were studied: compressive strength and split tensile strength, air void characteristics, freeze-thaw resistance, water absorption rate and chloride penetration. The mechanical properties and freeze-thaw resistance results obtained on the laboratory specimens were similar to those obtained on the cores drilled from the pavement. Despite the observed changes in the air void system parameters, mineral admixtures to Portland cements did not reduce the freeze-thaw resistance of concrete. The compressive strength was higher by up to 19% and sorptivity decreased by up to 22% in concrete containing cement with mineral admixtures.

Keywords:
air-entrained concrete, air void characteristics, CEM I, CEM II/A-S, CEM II/A-V, durability, freeze-thaw resistance, road pavement, sorptivity

Abstract:
The effects of gamma irradiation on concrete properties during early hardening were studied towards radioactive waste storage or accelerated processing at precast plants. Concrete mixtures containing different mineral aggregates (baryte, magnetite, amphibolite) were investigated. During initial 16 hours of hardening the mixes were irradiated using 60Co gamma source at the rate of 3.5 kGy/h. The mechanical properties and microstructural features of irradiated early-age concrete were tested: the secant elastic modulus, the compressive strength, the porosity and pore size distribution. XRD and SEM analysis were also performed. The results indicate both the stiffening and pore refinement in concrete due to early gamma irradiation. Effects of early irradiation on microstructural features of cement matrix were found in the subsurface layer up to the depth of 2 mm. The influence of different mineral aggregates in concrete on the radiation-induced changes of early age properties is discussed.

Abstract:
Durability of concrete designed for radiation shielding structures is an important issue in nuclear power plant safety. An investigation of the permeability of concrete containing heavyweight aggregates and water-bearing aggregates was performed with respect to gaseous and liquid media. Mix design was developed using Portland and slag cement, crushed magnetite and serpentine aggregate. The use of slag cement in concrete containing magnetite and serpentine aggregates resulted in the substantial improvement of the compressive strength in comparison with Portland cement concrete. The application of slag cement was found to reduce the chloride ingress, regardless of the special aggregate use. The coefficient of chloride migration was within the range 5 ÷ 8 × 10^−12 m^2/s and 17 ÷ 25 × 10^−12 m^2/s for slag cement concrete and Portland cement concrete, respectively. At the same time, the carbonation depth was increased twice for slag cement concrete in comparison to Portland cement concrete. However, the maximum carbonation depth after one year of exposure to 1% CO2 was only 14 mm for slag cement concrete, and 7 mm for reference concrete. The total pore volume evaluated using mercury intrusion porosimetry was influenced by the type of special aggregate used. It was shown that concrete with various contents of magnetite aggregate and slag cement achieved the smallest total pore volume. While serpentine coarse aggregate caused an increase in total pore volume in comparison to concrete with magnetite aggregate.

Keywords:
chloride permeability, carbonation, slag cement, radiation shielding concrete, microstructure, MIP, mix design, Portland cement, magnetite

Abstract:
The purpose of introducing air into the concrete mix is to increase the freeze-thaw and scaling resistance of hardened concrete. The utility of the sequential pressure method (Super Air Meter - SAM) for assessment of the air entrainment quality was verified by comparing the results obtained with this method with the results of the air-void analysis of hardened concrete. The results of the tests carried out on mixes designed and produced at a laboratory and the mixes produced on an industrial scale during expressway construction are considered. Furthermore, the relationships between the SAM number and the micro air-void content A300 in hardened concrete and the freeze-thaw and de-icing salt resistance are analysed as part of this research. A clear co-relation between the SAM number, a parameter that characterises the air-entrainment of the concrete mix, and the microvoid content has been demonstrated.
Napowietrzenie mieszanki betonowej stosuje się w celu podwyższenia mrozoodporności betonu i jego odporności na złuszczenia powierzchniowe. Przeprowadzono badania możliwości charakteryzowania jakości napowietrzenia mieszanki betonowej za pomocą pomiarów metodą sekwencyjno-ciśnieniową, oceniając zgodność jej wyników z wynikami pomiaru charakterystyki porów w betonie stwardniałym. Przedstawiono wyniki badań mieszanek zaprojektowanych i wykonanych w laboratorium, jak i mieszanek wykonanych przemysłowo na budowie drogi ekspresowej. Analizowano relację tzw. liczby SAM mieszanki betonowej w odniesieniu do zawartości mikroporów A300 w stwardniałym betonie oraz odporności na cykliczne działanie mrozu w obecności soli odladzających. Wykazano wyraźną korelację między parametrem charakteryzującym napowietrzenie mieszanki betonowej (liczba SAM) a zawartością mikroporów w betonie stwardniałym.

Keywords:
air-entrainment, air-void parameters, concrete, freeze-thaw resistance, microvoid content, sequential pressure method, surface scaling / beton, charakterystyka porów, metoda sekwencyjno-cioenieniowa, mrozoodporność, napowietrzenie, zawartość mikroporów, złuszczenia powierzchniowe

Abstract:
Results of measurements of the specific heat and the thermal conductivity of concrete with blended special aggregate for neutron and gamma radiation shielding are presented. Experimental tests were performed on concrete with heavyweight aggregate (magnetite, barite), hydrogen-bearing aggregate (serpentine) and amphibolite aggregate. The thermal properties of concrete were determined using a nonstationary method. The highest specific heat was found for concrete with serpentine aggregate. Simple models for predicting the specific heat and the thermal conductivity on the basis of concrete mix design were evaluated to include the blends of heavyweight and hydrogen-bearing aggregates. The thermal conductivity of concrete was found to be linearly dependent on the concrete density in the range from 2200 to 3500 kg/m3. Its increase due to water saturation of concrete was not dependent on the open porosity of concrete. It was found that the specific heat can be fairly well predicted using the rule of mixtures formula. The thermal conductivity of concrete can be approximately predicted using a parallel model in the case of water-saturated concrete. The thermal conductivity prediction for dry concrete is also discussed.

Keywords:
blended aggregate, concrete mix design, density, non-stationary method, open porosity, thermal properties, thermal conductivity, specific heat, radiation shielding

Abstract:
The suitability of the sequential air pressure method (SAM) to evaluate the quality of air entrainment in concrete mix to support prediction of durability of hardened concrete was studied. The experiments included both laboratory-produced mixes and on-site trials on mixes delivered for highway pavement construction. The fresh air content and the air void distribution was tested using the SAM apparatus. The air content and the air void characteristics in hardened concrete was tested using the microscopic analysis on polished sections. Standard fresh mix properties were also tested and the compressive strength and salt-scaling resistance of concrete was determined. Effects of type and proportion of admixtures, type of crushed aggregate, timing of SAM measurements and the method of mix consolidation were analyzed. The relationship between the SAM number and the air void characteristics in hardened concrete was critically evaluated. The relationship between SAM number and the content of microvoids (A300) is found for the laboratory mixes and confirmed with few field test results. The criterion of SAM number ≤ 0.4 is proposed for the target microvoids content A300 ≥ 1.5% and the enhanced salt scaling resistance of concrete.

Keywords:
air entrainment, air void distribution, concrete durability, fresh concrete, frost-salt scaling, microvoids content, mix design, sequential pressure method, spacing factor, test methods

Abstract:
Fly ashes from coal combustion in circulating fluidized bed boilers in three power plants were tested as a potential additive to cement binder in concrete. The phase composition and microstructure of cement pastes containing fluidized bed fly ash was studied. The fractions of cement substitution with fluidized bed fly ash were 20% and 30% by weight. X-ray diffraction (XRD) tests and thermal analyses (derivative thermogravimetry (DTG), differential thermal analysis (DTA) and thermogravimetry (TG)) were performed on ash specimens and on hardened cement paste specimens matured in water for up to 400 days. Quantitative evaluation of the phase composition as a function of fluidized bed fly ash content revealed significant changes in portlandite content and only moderate changes in the content of ettringite.

Keywords:
clean coal combustion, fluidized bed fly ash, microstructure, phase composition, portlandite, unburned carbon

Abstract:
The effect of the composition of industrial concrete designed for radiation shielding structures on the air permeability and the diffusion of moisture was studied. The mix design for heavyweight concrete of bulk density 3168–3317 kg/m3 was developed using barite and magnetite aggregate and cements blended with fly ash and blastfurnace slag. Structural elements, like columns of a height of 4 m and massive blocks made of mixtures with different cements were manufactured using ready mixed concrete pumped into the formwork. Core specimens were taken from the elements at different locations. The air permeability index was tested using Autoclam device. Evaluation of the quality of concrete on the basis of API results varied from “very good” to “good”. The moisture distribution inside concrete specimens was equilibrated to RH = 60 ± 5%. Observation of RH changes allowed to determine the moisture diffusion coefficient. Significant differences of the permeability and moisture diffusion coefficient depending on the location of the core specimens drilling and mix design of concrete were found. The D coefficient provided a good reflection of the different quality of heavyweight concrete in structural elements.

Keywords:
Air permeability, Autoclam, Barite, Blended cement, Cracking, Heavyweight aggregate, Magnetite, Moisture diffusion, Radiation shielding concrete, Relative humidity

Keywords:
nuclear reactor, concrete shield, radiation influence

Abstract:
Modelling studies in laboratory of the effect of curing on the mechanical properties and durability of the concrete pavement with exposed aggregate are presented. Air-entrained concrete was designed as the top layer of a motorway pavement with the use of two types of cements: CEM I and CEM III/A. The w/c increase (from 0.34 to 0.37) and change of cement type (CEM I 42.5N and CEM III/A 42.5 N) in properly air-entrained concrete did not influence significantly the internal frost resistance F200 - a decrease of the compressive strength after 200 freeze-thaw cycles was in the range from 4 to 12%. The lowest reduction of strength was observed for concrete with CEM I, w/c=0.34 and proper air entrainment. The properly air-entrained concrete layer with exposed aggregate, which was cured with a curing agent with closure capacity > 85%, was characterized by a very good resistance to surface scaling - the mass of scales m56 was equal to 0.10-0.12 kg/m2, irrespective of the type of cement and w/c ratio. However, there was a significant increase in the water absorption rate, surface scaling and chloride permeability, which caused with inadequate curing

Keywords:
air entrained concrete, curing, durability, exposed aggregate pavement, frost resistance, road pavement, permeability, scaling resistance

Abstract:
W artykule opisano podstawowe wyniki uzyskane w trakcie realizacji projektu badawczego „Trwałość i skuteczność betonowych osłon przed promieniowaniem jonizującym w obiektach energetyki jądrowej” [1]. Przedstawiono też wytyczne techniczne i kryteria oceny betonu osłonowego. Uzyskane wyniki mogą stanowić podstawę dalszych prac przy projektowaniu obiektów elektrowni jądrowych, składowisk materiałów radioaktywnych i innych miejsc powstawania, stosowania lub przechowywania materiałów wytwarzających promieniowanie jonizujące. Artykuł obejmuje zagadnienia związane z wymaganą skutecznością betonowych konstrukcji osłonowych przez zapewnienie bezpieczeństwa personelu i otoczenia przed oddziaływaniem promieniowania jonizującego. Rozpatrzono również trwałość osłon betonowych, tzn. zachowanie właściwości mechanicznych i nieprzepuszczalności w okresie przewidzianej eksploatacji pod wpływem przewidywanych oddziaływań zewnętrznych i procesów starzenia, a także przy podwyższonej temperaturze i promieniowaniu jonizującym. Artykuł nie obejmuje zagadnień integralności osłon pod obciążeniami wyjątkowymi, spowodowanymi awarią reaktora, uderzeniem samolotu, działaniami terrorystycznymi itp.

Abstract:
The influence of blended cements containing calcareous fly ash (W) on the strength and permeability of air entrained concrete was studied. Moderately active calcareous fly ash of CaO content of 26% and loss on ignition of 2%, obtained from lignite fired power station in Poland, was selected. Ternary cement compositions including siliceous fly ash (V) and ground granulated blast furnace slag (S) were also studied. Air void analysis in hardened concrete was used to evaluate the effectiveness of air entraining process. Pore size distribution was characterized by mercury intrusion porosimetry (MIP). The presence of calcareous fly ash in cement resulted in a moderate increase in the compressive strength of concrete and an increase of the category of resistance to chloride ion migration. Test results revealed a linear relationship between the capillary porosity measured by MIP and the chloride migration coefficient (Dnssm). The permeability was lower for increased clinker replacement level which was due to formation of smaller diameters of the capillary pores.

Keywords:
Air entrained concrete, Air void characteristics, Calcareous fly ash, Chloride ion migration, Multicomponent cements, Pore size distribution, Strength

Abstract:
The objective of this paper is to examine the possible use of new blended cements containing calcareous fly ash in structural concrete, potentially adequate for structural elements of nuclear power plants. The investigation included five new cements made with different contents of non-clinker constituents: calcareous fly ash, siliceous fly ash, ground granulated blastfurnace slag, and a reference cement—ordinary Portland cement. The influence of innovative cements on the resistance of concrete to chloride and carbonation exposure was studied. Additionally, an evaluation of the microstructure was performed using optical microscopy on concrete thin sections. Test results revealed a substantial improvement of the resistance to chloride ion penetration into concrete containing blended cements. The resistance was higher for increased clinker replacement levels and increased with curing time. However, concrete made with blended cements exhibited higher depth of carbonation than the Portland cement concrete, except the Portland-fly ash cement with 14.3% of calcareous fly ash. The thin sections analysis confirmed the values of the carbonation depth obtained from the phenolphthalein test. Test results indicate the possible range of application for new cements containing calcareous fly ash.

Keywords:
blended cements, calcareous fly ash, chloride migration, carbonation, durability, nuclear shielding concrete, thin sections

Abstract:
We present a review of freeze-thaw durability requirements laid down in both European standards and in the national specifications in relation to concrete for road structures. The principles of material selection for concrete mix are presented. We discuss local variations in the severity of the winter season and the extent of frost action in the components of road structures. The characteristic parameters of the test procedure for direct assessment of the resistance of concrete to internal damage are analysed, with particular attention paid to the specimen cooling rate. The temperature distribution in specimens was determined in standard freeze-thaw resistance tests carried out at two accredited laboratories. We discuss the criteria used in indirect assessment of freeze-thaw durability of air-entrained concrete on the basis of air void characteristics. Based on the determined temperature distribution in concrete specimens we postulate an improvement of the standard test procedure to clearly specify the cooling rate. It would be beneficial to distinguish frost impact zones depending on the severity of action of frost and de-icing salts on concrete in road structures.

Keywords:
air void characteristics, concrete, cooling rate, durability, internal frost resistance, mix design, performance specification, test methods

Abstract:
W artykule przedstawiono wyniki badań parametrów termicznych procesu twardnienia mieszanek betonowych, z których dwie wykonano z wykorzystaniem kruszyw stosowanych w produkcji betonów osłonowych (kruszywo magnetytowe oraz serpentynitowe), a trzecią, referencyjną, z wykorzystaniem kruszywa amfibolitowego. Na podstawie analizy dokonanych pomiarów temperatury wyznaczono parametry procesu twardnienia betonu (m.in. maksymalny przyrost temperatury, maksymalny gradient i in.). Jednocześnie rozwiązując numerycznie tzw. zagadnie-nie odwrotne wyznaczono parametry cieplne betonu w trakcie pierwszych 72 godzin twardnienia. Tą samą metodą wyznaczono również wartości funkcji źródła ciepła, a następnie na jej podstawie oszacowano ilość ciepła wydzieloną w procesie hydratacji cementu. Uzyskano dobrą jakościową zgodność postaci funkcji źródła ciepła oraz wykresów zmian temperatury w mieszankach. W toku analiz uzyskanych wyników wyraźnie zaznaczył się wpływ zróżnicowania parametrów cieplnych zastosowanych kruszyw. W przypadku mieszanki z kruszywem serpentynitowym dały się także zauważyć istotne różnice w przebiegu przyrostu temperatury (opóźnienie) w stosunku do pozostałych mieszanek

Keywords:
młody beton, beton osłonowy, ciepło hydratacji, ciepło właściwe, współczynnik przewodzenia ciepła

Abstract:
Przedstawiono wyniki badań podciągania kapilarnego (PK), porowatości dostępnej dla wody (E) oraz współczynnika migracji jonów chlorkowych w stanie nieustalonym (Dnssm). Zakres badań obejmował betony z kruszywem magnetytowym, barytowym, serpentynitowym oraz kruszywem referencyjnym w postaci grysu amfibolitowego, które wcześniej poddane zostały selektywnemu kruszeniu i przesiewaniu, tak by zapewnić jednakowe krzywe uziarnienia/stosy okruchowe. Prze analizowano wpływ mikrostruktury porów wyznaczonej za pomocą porozymetrii rtęciowej z odpornością na wnikanie jonów i cieczy w matrycę cementową. Z badań wynika, że betony z kruszywami specjalnymi osiągają wskaźniki przepuszczalności porównywalne lub nieco gorsze niż próbki referencyjne. Nie zaobserwowano systematycznego wpływu porowatości kapilarnej na wyniki badań przepuszczalności.

Keywords:
podciąganie kapilarne, migracja jonów chlorkowych, kruszywo magnetytowe, kruszywo barytowe, kruszywo serpentynitowe, porowatość

Abstract:
The paper presents a method of pore connectivity analysis applied to specimens of cement based composites differing in water to cement ratio. The method employed X-ray microtomography (micro-CT). Microtomography supplied digitized three-dimensional radiographs of small concrete specimens. The data derived from the radiographs were applied as an input into the application based on the algorithm called ‘random walk simulation’. As the result a parameter called diffusive tortuosity was established and compared with estimated porosity of examined specimens.

Artykuł prezentuje metodę wyznaczania parametru charakteryzującego intensywność połączeń mikroporów w zastosowaniu do próbek kompozytów z matrycą cementową, różniących się stosunkiem wodnocementowym. Metoda bazuje na wynikach badań z zastosowaniem mikrotomografii rentgenowskiej. Analizowano zdigitizowane zestawy danych, opisujące trójwymiarową reprezentację mikrostruktury niewielkich próbek wykonanych z betonu. Przygotowane w ten sposób skany mikrostruktury zastosowano jako dane wejściowe wprowadzone do oprogramowania wykorzystujacego algorytm ‘przypadkowo migrujących cząstek wirtualnych’. W ten sposób wyznaczono parametr mikrostruktury znany jako krętość dyfuzyjna. Parametr ten porównano z porowatością obserwowaną wyznaczoną dla zbadanych próbek przy wykorzystaniu analizy jasności voxeli w analizowanych próbkach.

Keywords:
X-ray tomography, concrete microstructure, diffusive tortuosity

Abstract:
In the paper two advanced methods for testing cement based composites are described and compared. These are X-ray microtomography and optical microscopy. Microtomography supplies three-dimensional images of small concrete specimens. In the tomograms all cracks, pores and other voids and inclusions, that exceed a few micrometers, are shown. Such visualisation can become a valuable tool for analysis of the basic material properties. Images obtained on thin sections and analysed with various methods on optical microscopes supply additional information on material microstructure that cannot be obtained in tomograms. For example it is relatively easy to determine zone penetrated by CO2 ingress. These two methods, presented on examples of tests, complete each another in order to supply a set of information on composition and defects of tested composite materials.

Keywords:
cement matrix composites, concrete deterioration, X-ray tomography, microscopic analysis, concrete microstructure

Abstract:
The paper presents results of the investigation of the air void characteristics and the resistance to cyclic freezing and thawing of air-entrained concrete containing calcareous fly ash. The frost resistance was tested also under the presence of de-icing salts to check the resistance to frost-salt scaling and without de-icing salts. The range of investigation included air entrained concrete mixes with the specified water-binder ratio of w/b=0.45 with addition of calcareous fly ash or made using blended cements with calcareous fly ash (W), and also siliceous fly ash (V) and ground granulated blast-furnace slag (S). The coarse aggregates used were crushed granodiorite and crushed limestone. The air-void system parameters were determined by microscopic image analysis and the effect of addition of calcareous fly ash was assessed. The effect of concrete age and presence of fly ash W on the strength and freeze-thaw resistance was also studied. The tests have shown that the use of calcareous fly ash as one of the main constituents of blended cements does not affect the frost salt scaling resistance nor the resistance to internal frost damage provided that the air void system is adequate.

Keywords:
air-void system parameters, blended cements, calcareous fly ash, freeze-thaw resistance, scaling resistance

Abstract:
The investigation of concrete microstructure and phase composition was performed on concrete specimens produced with and without calcareous fly ash obtained from Bełchatów Power Station. The used calcareous fly ash (designated “W”) was either unprocessed or ground to assumed specific surface and added to concrete mix to substitute 30% of the binder by weight. The following testing methods were used in this research: scanning electron microscopy, differential thermal analysis (DTA) and multiple microindentation. The characteristic features of the investigated microstructures are discussed and the effect of calcareous fly ash on the content of non-evaporable water and portlandite in cement matrix is analysed. The results of microindentation and compressive strength testing were used as the basis for evaluation of the efficiency of calcareous fly ash added to concrete mix.

Keywords:
calcareous fly ash, microindentation, microstructure, non-evaporable water, phase composition, portlandite, strength

Abstract:
Przedstawiono wyniki badań wytrzymałości na ściskanie, odporności na wnikanie chlorków oraz odporności na powierzchniowe łuszczenie w obecności soli odladzających betonów napowietrzonych z popiołem lotnym wapiennym (W). Próbki betonu dojrzewały w odmiennych warunkach wilgotnościowych. Zakres badań obejmował betony napowietrzone o współczynniku w/c=0,45 wykonane z cementów portlandzkich wieloskładnikowych z dodatkiem popiołu W oraz z dodatkami popiołu lotnego krzemionkowego V i mielonego granulowanego żużla wielkopiecowego S. Próbki dojrzewały przez 28 i 90 dni, z czego połowa w wodzie, natomiast druga połowa po 3 dniowej pielęgnacji w powietrzu w wilgotności RH=40%. Charakterystyka porów powietrznych w stwardniałym betonie została oznaczona metodą mikroskopowej analizy obrazu. Z badań wynika, że przy zbliżonych parametrach charakterystyki porów powietrznych zmiana warunków pielęgnacji próbek obniża w znaczący sposób trwałość betonu. Największy wpływ zmiennych warunków i czasów dojrzewania zaobserwowano w odniesieniu do odporności betonu na agresję mrozu i środków odladzających.

Keywords:
charakterystyka porów, napowietrzenie, penetracja chlorków, popiól lotny wapienny, powierzchniowe złuszczenie

Abstract:
Przedstawiono wyniki kompleksowych badań eksperymentalnych cementów żużlowo-wapiennych, wytworzonych przez zmieszanie klinkieru portlandzkiego z granulowanym żużlem wielkopiecowym i kamieniem wapiennym o różnym rozdrobnieniu. Wykonane z nich zaprawy poddano badaniu wytrzymałości na ściskanie oraz badaniu mikrostruktury porów za pomocą porozymetrii rtęciowej. Po ekspozycji próbek na agresję jonów siarczanowych i chlorkowych przez okres 360 dni dokonano obserwacji produktów korozyjnych w mikroskopie skaningowym. Zaprojektowano mieszanki betonowe napowietrzone i nie-napowietrzone z cementem hutniczym oraz wybranym cementem żużlowo-wapiennym. Przeprowadzono badania wytrzymałości na ściskanie, nasiąkliwości, mrozoodporności oraz mikrostruktury betonów. Stwierdzono, że częściowe zastąpienie klinkieru kamieniem wapiennym powoduje poprawienie urabialności mieszanki. Dodatek kamienia wapiennego obniżył wytrzymałość na ściskanie zapraw i betonów, a ich odporność na działanie środowisk agresywnych była podobna jak w przypadku cementu CEM III/A 32,5N-LH-HSR/NA

Abstract:
Stabilność właściwości mieszanki betonowej od momentu wymieszania do wbudowania wpływa na trwałość wykonanej konstrukcji. W przypadku betonu klasy projektowanego na agresję środowiska XF4 szczególnie istotna jest stabilność pęcherzyków powietrza wprowadzanych za pomocą domieszki napowietrzającej. Przedstawione badania rozważają wpływ stosowania cementów z dodatkami mineralnymi CEM II/A-V 42,5R, CEM II/B-S 42,5N i CEM III/A 42,5N na dystrybucję porów w mieszance betonowej przeznaczonej na górną warstwę nawierzchni betonowej. Przeanalizowano zmiany charakterystyki porów w betonie od wykonania do wbudowania. Próbki pobrano bezpośrednio po wykonaniu mieszanki, po godzinie bezruchu i po wysokoenergetycznym mieszaniu po godzinie bezruchu. Określono właściwości mieszanki betonowej, charakterystykę porów, właściwości mechaniczne, szybkość absorpcji wody i rezystywność betonu. Przeprowadzone badania wykazały utratę do 0,55% całkowitej zawartości powietrza w betonie po godzinie bezruchu. Wysokoenergetyczne mieszanie zwiększyło całkowitą zawartość powietrza o 1,57%, 1,02%, 0,92% odpowiednio w betonie z cementem CEM I, CEM II/A-V i CEM II/B-S. W betonie z CEM III/A zawartość powietrza zmniejszyła się o 0,69%. Wysokoenergetyczne mieszanie zwiększyło udział mikroporów - A300 w całkowitej zawartości powietrza w betonie z cementami żużlowymi przyczyniając się do zwiększenia o 8-12% tak wytrzymałości na ściskanie, jak i rozciąganie przy rozłupywaniu po 28 dniach dojrzewania. Pomiary rezystywności pozwoliły zaobserwować zwiększenie przepuszczalności próbek po dodatkowym mieszaniu. The stability of air bubbles in concrete mixture from homogenization to final embedding in pavement is necessary. The presented paper examine effect of using cements with supplementary cementitious materials, as CEM II / A-V 42.5R, CEM II / B-S 42.5N and CEM III / A 42.5N, on the air void distribution in the concrete mix intended for the upper layer of the concrete pavement. The fluctuation of air voids characteristics in concrete from homogenization to casting were analyzed. The specimens after mixing, one hours of inactivity and high-energy mixing after inactivity were taken. The concrete mix properties, air voids characteristics, mechanical properties, water absorption and hardened concrete resistivity were determined. The investigation revealed a loss up to 0,55% of total air content in concrete after one hour of inactivity. The high-energy mixing increased the total air content by 1.57%, 1.02%, 0.92% in concrete with CEM I, CEM II/A-V and CEM II/B-S respectively. The air content in CEM III/A concrete decreased by 0.69%. The high-energy mixing increased the share of micropores - A300 in the total air content in concrete with slag cements, contributing to 8-12% increase in both compressive and splitting strength after 28 days of curing. The resistivity measurements shown an increase in sample permeability after additional mixing.

Abstract:
Prolonged durability of concrete structures is closely related to the minimization of the transport of liquids in cement matrix. Capillary suction is a dominant mechanism of liquid transport, especially in moderate climate, where cyclic wetting-drying and freeze-thawing cycles occur. Air-entraining of concrete is the efficient way to prevent deterioration impact from environment. However, the influence of air voids distribution on the capillary suction is not well known. The purpose of the research was to assess the water absorption properties of the air entrained concrete. The concrete mixes with the air content from 1% to 16% and similar proportion of micropores to large air voids (A300/A) were prepared. The water absorption tests were performed using ASTM C1585 procedure. The following parameters were determined: Si – initial rate of water absorption, Ss – secondary rate of water absorption, tn – time of nick point, In - water absorption for tn, I60 – initial 60 seconds of water absorption. The results were compared with the air content in concrete. Additionally the compressive strength, porosity accessible to water and concrete resistivity were measured. The linear relationships between initial and secondary rate of water absorption and the air content in concrete were found. A significant changes of rate of water absorption in concrete when the air content change more than 6% were observed.

Keywords:
water absorption, air-entrained concrete, nick point, concrete resistivity, porosity accessible to water

Abstract:
The risk of occurrence of deleterious alkali-silica reaction (ASR) in concrete should be properly minimized in major highway pavements and bridges. Real-life experiences show that even in concrete made with aggregates potentially not susceptible to ASR, it may occur under unfavourable conditions of external alkali supply at wet conditions and heavy traffic load. An experimental investigation was performed to study the susceptibility of selected Polish mineral aggregates to ASR at external alkali supply. The test method „60°C concrete test with external alkali supply” covered by draft procedure RILEM AAR-12 was implemented at IPPT PAN laboratory. Air entrained concrete specimens were exposed to cyclic temperature changes and wet-dry exposure as well as NaCl solution exposure. Several combinations of coarse crushed aggregate and fine natural aggregate were tested in concrete designed as for heavy duty highway pavement. SEM evaluation of microstructure of concrete with glacial deposit aggregate revealed visible alkali-silica gel. The effects of fine aggregate on the expansion of concrete were also revealed.

Keywords:
air entrained concrete, alkali-silica reaction, cyclic exposure, external alkali, highway pavement

Abstract:
Salt solutions are used to ensure safe driving conditions during winter. NaCl deicer is the most often used brine in Polish climatic zone. The chemical effects of this type of chloride-based deicer in wetting and drying (WD) and temperature cycles on concrete need to be better understood. This research was focus to study the microstructure of air-entrained pavement concrete after combined chemical (10% of NaCl) and physical (WD and 60°C) exposure conditions. The adopted WD and temperature regime was designed to verify the hypothesis that regularly alternating wetting and drying cycles with external alkali supply from deicer salt will provoke the Alkali-Silica Reaction (ASR). The aggregates varied their origin and mineralogical composition. The microscopic examination was carried out on concrete specimens using SEM with EDX. The microscopic analysis has shown that main reason for concrete deterioration during cyclic chemical and physical exposure conditions was both physical influence - WD cycles and the chemical influence – ASR (primarily, the fine aggregate which lead to form of alkali-silica gel). The expansive gel was shown to be capable of destroying the test specimens. Also differences in mineralogical composition of coarse aggregates influenced on the concrete prism expansion due to ASR.

Abstract:
Przedmiotem referatu jest przydatność zmodyfikowanej metody ciśnieniowej do wyznaczenia charakterystyki porów w napowietrzonej mieszance betonowej w warunkach polowych na miejscu budowy nawierzchni drogowej. Metoda polegająca na stopniowym zwiększaniu ciśnienia na mieszankę, w określonej sekwencji, pozwala wyznaczyć parametr zwany liczbą SAM. Zgodnie z oczekiwaniem wynalazców metody powinna być skorelowana ze wskaźnikiem rozmieszczenia porów w betonie. Przeprowadzone badania doświadczalne obejmowały rozpoznanie w warunkach laboratoryjnych powtarzalności metody oraz pomiary napowietrzenia mieszanki na dolną i górną warstwę betonu w nawierzchni odcinków dróg ekspresowych. Na próbkach stwardniałego betonu wyznaczono wskaźnik rozmieszczenia porów zgodnie z PN-EN 480-11 i przeanalizowano zgodność charakterystyki napowietrzenia betonu stwardniałego z charakterystyką napowietrzenia mieszanki na podstawie liczby SAM. Wykonanie pomiarów w warunkach budowy dwuwarstwowej nawierzchni drogi ekspresowej nie nastręczało kłopotów technicznych. Jednakże w wielu przypadkach stwierdzono niewystarczającą korelację charakterystyki porów w mieszance i w betonie stwardniałym. Przeanalizowano czynniki wpływające na zaobserwowane niezgodności.

Abstract:
Penetration of external alkalis from deicing salts into concrete pavement can promote deleterious alkali-silica reaction (ASR) and therefore reduce its long-term performance. In severe exposure conditions (wet and heavy traffic load) the susceptibility of aggregates to ASR may be aggravated. To study this phenomenon on concrete specimens the combined cyclic exposure method was developed at VDZ Düsseldorf. Such a cyclic wet-dry-external alkali exposure was used on air entrained concrete specimens to investigate its influence on the microstructure and the permeability of concrete. Air voids characteristics, mercury intrusion porosimetry, porosity accessible to water and water absorption of concrete was tested. Concrete microstructure was observed in scanning electron microscope to reveal the specific features. The applied cyclic wetdry-external alkali exposure induced a marked decrease of total porosity of concrete and the appearance of ASR gel in cement matrix. An increase of the rate of water absorption of concrete was also found.

Keywords:
alkali-silica reaction, VDZ test, microstructure, permeability, water absorption

Abstract:
Exposed aggregate concrete (EAC) pavement technology is used in Poland for construction of major highways and expressways. When properly executed, it is an efficient technique to provide desired friction for skid resistance without compromising the noise limitations. Concrete mix uniformity, proper dosing of retarding agent and optimal time to brush with a mechanical broom are supposed to have a major impact on the properties of the upper pavement layer. An experimental investigation was performed on exposed aggregate concrete specimens manufactured in the laboratory in a way to simulate the industrial production of two-layer concrete slab with exposed aggregate. The texture depth was determined using a laser profiler. The compressive strength of concrete, the water absorption rate, and permeability of chloride ions through concrete were also determined. The freeze-thaw resistance and surface scaling resistance were tested and analyzed with respect to air void characteristics. Results revealed an increase in surface scaling for EAC slabs with higher w/c ratio and slabs simulating local bleeding. The most efficient method to determine indirectly the durability of EAC slabs was the set of permeability tests comprised of measurements of chloride migration and rate of water absorption. The change of macrotexture depth with increase of w/c ratio and retarding admixture type was found.

Keywords:
highway pavement, exposed aggregate concrete, surface retarder, durability, concrete preparation parameter, water absorption, chloride migration, surface scaling, macrotexture

Abstract:
The use of exposed aggregate concrete (EAC) in the upper layer of two-lift pavements is spread over many European countries including Poland. However, the EAC technology is considered difficult to apply because of inevitable dependence on operator's experience to control the whole process properly. The proper timing of technological operations is critical. The investigation on the performance of EAC was performed to gain a better understanding of material and environmental factors involved. EAC slabs were manufactured in the laboratory following the procedure applied at the construction site. Air entrained concrete mix design included a variable water to cement ratio and cement type while the type and the content of aggregate was constant. The effects of curing intensity were studied. The strength properties, air void characteristics of hardened concrete, the freeze-thaw resistance and the salt-scaling resistance were tested of specimens cored from the slabs, using the European standard methods. EAC permeability was also evaluated using the methods covered by ASTM C1585 and NT Build 492. Such permeability indicators and frost durability were applied to evaluate the differences in EAC layers performance. The environmental vulnerability of EAC mixes used in the upper layer of two-lift pavements is discussed.

Keywords:
air entrainment, blended cement, concrete durability, curing technology, highway pavement, mix design, permeability

Abstract:
Nuclear reactor containments must maintain high durability since they restrict the spread of radiation and radioactive contamination to the general public, which could have significant consequences. The containment integrity and impermeability for potentially contaminated media is ensured using sophisticated structural and materials solutions including prevention of early age cracking of concrete. The results of numerical and experimental investigation on thermal behavior of early age concrete are presented. Concrete mixes were prepared with low-heat blended cements and various mineral aggregates. Special aggregates were selected for enhancing the radiation shielding capacity of concrete, including minerals of high atomic weight and of increased content of bound water. The proposed approach consisted of several stages, consisting mainly of measurements of the one-dimensional heat distribution in cylindrical concrete elements and solving the equation of one-dimensional heat transferto determine thermal properties of hardening concrete. The proposed model of temperature distribution in hardening concrete is based on the non-linear inverse heat transfer problem solution. The obtained experimental results and numerically determined material characteristics are discussed in respect to the concrete mix design.

Keywords:
durability, heat transfer, hardening concrete, inverse solution, temperature, thermal properties

Abstract:
The paper presents the results of investigation of the specific heat and the thermal conductivity of shielding concrete and the specific heat of selected crushed aggregates used to produce them. The results of the specific heat were obtained by two methods: a stationary method, using a calorimeter, and a non-stationary method. The obtained results were compared to the results available in the literature. In addition, in the case of measuring the specific heat, the results obtained with the two methods were compared and attempt has been made to explain the differences between them.

Keywords:
shielding concrete, heavy aggregates, specific heat, thermal conductivity

Abstract:
In the paper a method of X-ray microtomography (micro-CT) was employed for a direct insight into a microstructure of concrete with a practical resolution of approx. 10 micrometers3. Two sets of specimens were subjects of examination. The spatial concentration of air pores was investigated in three concretes differing in the amount of the supplement of high calcium fly ash (HCFA). The parameter of pore connectivity called diffusive tortuosity was determined in three other concretes made of the same ingredients but differing in water to cement ratio. The quantitative results obtained with application of described procedures are applicable in material characterization.

Keywords:
X-ray microtomography, concrete, microstructure

Abstract:
The relationship between the internal pore characteristic and the non-steady state chloride migration coefficient (Dnssm) was investigated for concrete mixes made with blended cement containing high calcium fly ash (HCFA). Air entrained concrete mixes were made usinggranodiorite and crushed limestone as coarse aggregate. Designed surface scaling resistance was confirmed with standard test. The pore structure was determined using mercury intrusion porosimetry (MIP) and digital image analysis techniques. Phase composition of hydration products was examined using the XRD analysis. Chloride ion transportvelocity was measured using a rapid chloride migration test.The test has shown a relationship between the chloride migration coefficient and poresizecharacteristic derived from MIP tests. Effect of aggregate type on the course of relationship as shown differences curve for both type of aggregates. Increase amount of additives in blended cements caused decrease of critical and average pore size obtained by MIP method.

Keywords:
HCFA, blended cement, chloride ions migration, MIP, scaling resistance

Abstract:
The construction of Żarnowiec Nuclear Power Plant (NPP) facilities was discontinued in 1989, despite the high level of work advancement. Already a large part of the concrete structures was built, now submerged in water from Żarnowieckie Lake. These structures were exposed over 30 years to the environmental conditions (rain, and varying high and low temperatures) without any special maintenance treatment. The technological documentation archives are not available. Experimental testing of specimens drilled out from different concrete structure elements was performed in September 2014.
The goal of the research was the identification of the composition of concrete and its present properties, especially the recognition of the effects of long-term environmental impact. The scope of the research covered macroscopic and microscopic analysis of concrete, compressive strength test, permeability test defined as the rate of chloride ions migration and water absorption. Unfortunately, the most important parts of the concrete structure are not available for testing because they are under water level. The obtained results allowed to classify the concrete structural elements in nuclear power plants buildings as of a quite good quality.

Keywords:
durability, old concrete, strength, microstructure, permeability

Abstract:
The results of microscopic analysis on thin sections of aggregates intended for nuclear shielding concrete are presented. The petrographic analysis was performed on different barite, magnetite and hematite aggregates used as the high-density aggregate to absorb gamma radiation. Both optical microscopy and accelerated expansion tests were used to recognise the potential for alkali-reactivity of the aggregates. The mineral composition of the tested aggregates was analysed on thin sections in transmitted cross-polarized light and XRD tests were additionally performed. Expansion tests of mortar bars exposed to 1 N NaOH solution at the temperature of 80°C were also performed following ASTM C1260. The high-density aggregates contained ore deposits - metallic opaque phases providing the required shielding properties. These aggregates also contained various amounts of non-metallic phases, with both innocuous non-ore minerals and deleterious, potentially reactive materials. Barite aggregates contained siderite, fluorite and hawleyite in varying amounts, apart from the barium sulphate being the principal component. Moreover, particularly reactive cristobalite and muscovite were identified in barite aggregates from certain quarries. Tests according to ASTM C1260 performed on mortars showed the expansion above the accepted criterion for non-reactive aggregate and confirmed the threat due to the presence of cristobalite in barite aggregates.

Keywords:
high-density aggregate, heavy concrete, alkali-silica reaction, thin section, XRD

Abstract:
The possibility of using the high calcium fly ash (HCFA) as type II concrete additive is not well established, especially in relation to the durability of concrete structures in aggressive environment. The paper presents results of microstructural characterization of air-entrained concrete containing high calcium fly ash from lignite combustion. Frost resistant concretes were designed with different content of fly ash use for cement replacement by 15% and 30%. Different kinds of HCFA were used: raw (unprocessed) and grinded during 10, 15 and 28 minutes. The evaluation of the microstructure was performed using SEM and optical microscopy on thin sections and plane sections. All thin sections were impregnated with epoxy containing fluorescent dye and were examined using ordinary light, crossed polarized light and UV light. The thin section evaluation involved petrographic characterization of aggregates and examination of paste quality. Automatic air-void analysis on plane sections revealed air-content, specific surface, spacing factor and the content of micropores in the hardened concrete. Significant differences in particle shape and size before and after grinding of the HCFA were revealed by SEM analysis. The results of thin section analysis of the high calcium fly ash concrete showed that its microstructure was more dense than that of the ordinary concrete. The influence of specific surface of fly ash on air void content in HCFA concrete was found.

Keywords:
high calcium fly ash (HCFA), air-entrained concretes, microstructural characterization

Abstract:
Przeprowadzono badania doświadczalne przepuszczalności powietrza przez beton przy zastosowaniu nieniszczącej metody Torrenta. Zaprojektowano i wykonano płyty betonowe z mieszanek o jednakowym stosie okruchowym i zróżnicowanym spoiwie poprzez zastosowanie dodatków popiołowych. Wykonane elementy próbne pielęgnowano w warunkach normowych wysokiej wilgotności, a później poddano suszeniu w warunkach laboratoryjnych. Przeprowadzono pomiary współczynnika gazoprzepuszczalności kT oraz oporu elektrycznego sondą Wennera. Ponadto, przeprowadzono normowe określenie wytrzymałości betonu na ściskanie. Jak stwierdzono, współczynnik gazoprzepuszczalności kT betonu zwiększał się o dwa rzędy wielkości wskutek wysychania elementów próbnych. Przydatność sondy Wennera do pośredniego określenia wilgotności betonu była ograniczona. Stwierdzono istotny wpływ modyfikacji popiołowych na współczynnik przepuszczalności powietrza przez beton.

Keywords:
beton, gazoprzepuszczalność, popiół lotny, wilgotność, wytrzymałość na ściskanie

Abstract:
Możliwości zastosowania popiołów lotnych wapiennych jako dodatków typu II do betonów konstrukcyjnych nie są dostatecznie rozpoznane, szczególnie w zakresie zagadnień trwałości betonów zawierających takie popioły. Referat przedstawia wyniki badania stabilności porów powietrznych w mieszankach betonowych, zawierających popiół lotny wapienny oraz wyniki badania charakterystyki porów powietrznych w betonie stwardniałym. Mieszanki betonowe napowietrzne zaprojektowano zgodnie z wymaganiami wysokiej odporności betonu na agresję mrozu i środków odladzających. Część cementu portlandzkiego zastępowano popiołem lotnym wapiennym, przy założeniu współczynnika efektywności dodatku. Na wykonanych próbkach betonu przeprowadzono badania parametrów mikrostruktury porów powietrznych i sformułowano wnioski dotyczące możliwości napowietrzania mieszanek zawierających popiół lotny wapienny.

Keywords:
charakterystyka porów powietrznych, dodatek typu II, mrozoodporność, napowietrzanie, popiół lotny wapienny, trwałość