Staff

Abstract:
An alkali–silica reaction (ASR) is a chemical process that leads to the formation of an expansive gel, potentially causing durability issues in concrete structures. This article investigates the properties and behaviour of ASR products in mortar with the addition of low-purity calcined clay as an additional material. This study includes an evaluation of the expansion and microstructural characteristics of the mortar, as well as an analysis of the formation and behaviour of ASR products with different contents of calcined clay. Expansion tests of the mortar beam specimens were conducted according to ASTM C1567, and a detailed microscopic analysis of the reaction products was performed. Additionally, their mechanical properties were determined using nanoindentation. This study reveals that with an increasing calcined clay content, the amount of the crystalline form of the ASR gel decreases, while the nanohardness increases. The Young’s modulus of the amorphous ASR products ranged from 5 to 12 GPa, while the nanohardness ranged from 0.41 to 0.67 GPa. The obtained results contribute to a better understanding of how the incorporation of low-purity calcined clay influences the ASR in mortar, providing valuable insights into developing sustainable and durable building materials for the construction industry.

Keywords:
alkali–silica reaction, ASR products, calcined clay, mortar, expansion

Abstract:
Research on the durability of structural concrete requires careful selection of aggregates, particularly considering their reactivity to alkali-silica reaction (ASR). The Miniature Concrete Prism Test (MCPT) allows for shortened testing time
and eliminates the need for aggregate crushing, making it a practical alternative to other methods. The aim of the research is to evaluate the reactivity of aggregate mixtures with varying mineral compositions. Research results confirm
the significant impact of fine aggregates on concrete expansion in the MCPT method in NaOH solution at 60°C. The observed expansion correlates with a reduction in concrete’s elastic modulus.
Badania nad trwałością betonu konstrukcyjnego wymagają starannej selekcji kruszyw, szczególnie uwzględniającej ich reaktywność na reakcję alkalia-krzemionka (ASR). Metoda Miniature Concrete Prism Test (MCPT) pozwala na skrócenie
czasu badania i eliminację konieczności rozdrabniania kruszywa, co czyni ją praktyczną alternatywą dla innych metod. Celem badań jest ocena reaktywności mieszaniny kruszyw o zróżnicowanym składzie mineralnym. Wyniki badań potwierdzają
znaczący wpływ kruszywa drobnego na ekspansję betonu w metodzie MCPT w roztworze NaOH w temp. 60°C. Obserwowana ekspansja koreluje z redukcją modułu sprężystości betonu.

Keywords:
alkali-silica reaction (ASR), concrete expansion, MCPT method, fine aggregate, durability, reakcja alkalia-krzemionka (ASR), ekspansja betonu, metoda MCPT, kruszywo drobne, trwałość

Abstract:
Przedstawiono wyniki oceny diagnostycznej posadzki przemysłowej przy wykorzystaniu metodyki ilościowej oceny mikrostruktury betonu. Objawy uszkodzeń obejmowały pylenie powierzchniowe i delaminację warstwy utwardzonej. Przeprowadzono analizę petrograficzną składu betonu w próbkach-odwiertach. Zaobserwowano nadmierne napowietrzenie betonu, gromadzenie się porów powietrznych i występowanie ukierunkowanych spękań, miejscową zmienność składu fazowego produktów hydratacji cementu, w tym występowanie obszarów o intensywnej karbonatyzacji, co wpływało na przedwczesne uszkodzenia powierzchniowe.
Diagnostic assessment of industrial floor using the methodology of quantitative evaluation of concrete microstructure is presented. Symptoms of damage included surface dusting and delamination of the top layer. A petrographic analysis of the concrete composition in core specimens was carried out. Excessive air content, accumulation of air voids and the occurrence of oriented cracks, local variability of the phase composition of cement hydration products, including the occurrence of carbonated areas were observed and associated with the premature surface damage.

Keywords:
delaminacja, mikroskopia ilościowa, porowatość, posadzki betonowe, utwardzenie powierzchniowe, delamination, quantitative microscopy, porosity, concrete floors, surface hardening

Abstract:
Potential use of marginal fine aggregate in concrete is hindered by prescriptive quality requirements for concrete constituents. Experimental tests were performed on eleven mixtures of coarse and fine aggregates of variable susceptibility to alkali silica reaction (ASR). The miniature concrete prism test was applied for evaluation of ASR-induced expansion and associated changes of elastic properties were evaluated using the resonance modulus testing. Substitution of nonreactive sand with sands of moderate reactivity resulted in a relative increase in concrete expansion by 19–112% and substantial reduction of its elastic properties during the exposure to accelerated ASR environment. The Kolmogorov-Avrami-Mehl-Johnson model, modified to incorporate separately the effects of moderate reactivity of coarse and fine aggregate fractions, successfully described the kinetics of ASR-induced expansion. Beneficial effects of blastfurnace slag used for partial replacement of Portland clinker in blended cements were captured for aggregate combinations.

Keywords:
Aggregate mixture reactivity, Alkali-silica reaction, Fine aggregate, Kinetic model, Miniature concrete prism test, Slag-blended cement

Abstract:
Results of experimental investigation on the mitigation of alkali–silica reaction (ASR) by low-grade calcined clay are presented. Domestic clay with an Al2O3 content equal to 26% and SiO2—58% was used. The calcination temperatures were as follows: 650 °C, 750 °C, 850 °C and 950 °C, which were chosen much more widely than presented in previous studies. Pozzolanity of the raw and calcined clay was determined with the Fratini test. The performance of calcined clay to mitigate ASR was evaluated according to ASTM C1567 using reactive aggregates. A control mortar mixture was prepared with 100% Portland cement (Na2Oeq = 1.12%) as a binder with reactive aggregate, and test mixtures were made with 10% and 20% of calcined clay as a cement replacement. The microstructure of the specimens was observed on the polished sections using scanning electron microscope (SEM) operated in backscattered mode (BSE). The results of expansion of mortar bars with reactive aggregate showed that replacing cement with calcined clay reduced the expansion of the mortar bars. The greater the cement replacement, the better results in terms of ASR mitigation. However, the influence of the calcination temperature was not as clear. The opposite trend was found with the use of 10% or 20% calcined clay.

Keywords:
alkali–silica reaction (ASR), expansion, low grade calcined clay, mitigation, Fratini test, microscopic analysis

Abstract:
This article examines the problem of the service life of reinforced concrete structures intended for nuclear power plants and radiation waste storage bunkers when exposed to radiation. This research focused on assessing the corrosion resistance of steel bars under conditions of simultaneous exposure to gamma radiation and various environmental conditions affecting the rate of carbonation. Electrochemical measurements of steel bars were carried out on samples in three environmental conditions: in a laboratory–dry; enclosed in a can at RH = 50%; and enclosed in a can at RH = 100%. The durability of the passivation layer of steel on non-irradiated and irradiated specimens after 8 months of exposure to gamma radiation was compared. A lower degradation effect of gamma radiation was visible in fully water-saturated specimens

Keywords:
corrosion of steel, relative humidity variability, carbonation condition, EIS, polarization curve

Abstract:
Alkali-silica reaction (ASR) is a phenomenon that causes irreversible damage to concrete structures. Since 1940, research has continued to investigate the possibility of eliminating these negative effects. The lack of availability of non-reactive aggregates requires the use of reactive aggregates, characterized by satisfactory physical and mechanical properties, with the introduction of innovative solutions to mitigate the effects of ASR expansion. Recently, fibre-reinforcement has shown to be a promising approach, even if the type and the volume of fibres used to reduce, or eliminate, the deleterious effects of expansion are not well established. For this reason, Miniature Concrete Prism Tests (MCPT) were performed on 4 series of expansive concrete prisms without any fibres and with 0.5% in volume of polypropylene fibres, steel fibres, and recycled carbon fibres, respectively. In addition, 4 series of non-expansive mortar prisms, with and without fibres, were tested in bending. As a result, by using recycled carbon fibres a moderate expansion can be observed after 56 days, in contrast to the high expansion of un-reinforced concrete. The same positive effect cannot be observed in concrete reinforced with steel or polypropylene fibres. This is due to the absence of the deflection hardening capacity of the fibre-reinforcement, as confirmed by both mechanical tests on non-expansive mortars, and by the analysis of microstructure on the post-mortem specimens.

Keywords:
Mortar, Concrete, Bending tests, Miniature Concrete Prism Tests (MCPT), Expansion Microstructure

Abstract:
This article presents the results of an experimental investigation into the mitigation of the alkali–silica reaction (ASR) resulting from using low-grade clay calcined at 850 °C. The clay used in the experiment was domestic clay with an Al2O3 content equal to 26% and a SiO2 content of 58%. The performance of calcined clay in ASR mitigation was evaluated according to ASTM C1567 using reactive aggregates. The control mortar mixture consisted of 100% Portland cement (Na2Oeq = 1.12%) binder and reactive aggregate. The test mixtures used the same reactive aggregate and binders, in which part of the cement was replaced with either 10%, 20% or 30% calcined clay. The microstructure of specimens was examined on the polished sections using a scanning electron microscope (SEM) operated in the backscattered mode (BSE). The results of expansion obtained from the mortar bars made with the reactive aggregate showed that replacing cement by calcined clay reduced their expansion, with the level of expansion decreasing with the increase in the level of cement replacement.

Keywords:
calcined clay, alkali–silica reaction, expansion, mitigation, microstructure

Abstract:
During the wintertime, concrete pavements experience harsh exposure conditions due to the presence of both the freezing–thawing and wetting–drying cycles. Airport concrete pavements are commonly de-iced using chloride-free organic salts such as potassium formate or potassium acetate. However, these materials contain alkali ions which can have harmful effects on both the cement matrix and the aggregate. Specifically, there is an increased risk of occurrence of the alkali–silica reaction (ASR). The goal of this research was to estimate the influence of potassium formate on the potential of causing alkali–silica reaction in aggregates with different categories of reactivity (R0, R1, R2). The accelerated mortar bar test and its modification (which involves replacing sodium hydroxide solution with a potassium formate solution) were used. Detailed SEM-EDS examinations were performed to confirm the presence of alkali–silica reaction and to analyze the influence of potassium formate on the microstructure of mortar.

Keywords:
alkali–silica reaction,potassium formate,de-icing agent,reactive aggregate

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:
A viable prediction of service life of reinforced concrete structures exposed to irradiation environment is necessary to support a license extension for currently operating nuclear power plants as well as to support concrete mix optimization for new builds. An experimental study was carried out to evaluate the corrosion performance of mild steel reinforcing bars under gamma irradiation at environmental conditions favoring accelerated carbonation. in elevated temperature. The electrochemical impedance spectroscopy and potentiodynamic electrochemical tests were performed to assess the corrosion rates on the rebar surfaces. Effects of irradiation were also examined in regard to capillary pore size distribution by mercury intrusion porosimetry and mesopore distribution based on nitrogen desorption data. Companion tests were performed to determine the compressive and flexural strength of mortar exposed to gamma irradiation. Relative effects of gamma irradiation are reported for mortar specimens containing fly ash or limestone powder used for partial replacement of Portland cement up to 40% by mass. Gamma irradiation dose up to 2 MGy was found to affect the properties of passive layer of steel in comparison to non-irradiated specimens. A decrease of corrosive potential and passivation potential was found. An increase of corrosion current density by an order of magnitude due to gamma irradiation was observed. Parameters of polarization curves of steel indicated unstable passive layer on steel reinforcement in irradiated mortars.

Keywords:
gamma irradiation, steel corrosion, supplementary cementitious materials, modification, electrochemical impedance spectroscopy, corrosion potential, Barrett-Joyner-Halenda porosity

Abstract:
Prediction of carbonation progress in concrete exposed to ionizing radiation is important for the durability assessment of nuclear power plants, eventually needed for operational license extension. The objective of this work is to reveal the influence of gamma irradiation on the carbonation development and resulting microstructural features of cement mortar. The composition of mortar was varied by using mineral additions. Canned specimens at elevated CO2 concentration environment were exposed to gamma irradiation up to the absorbed dose of 1.6 MGy in the vicinity of spent nuclear fuel rods in pool of research reactor. Micromechanical properties of carbonation reaction products were determined using nanoindentation tests. The carbonation depth was found to increase with increasing absorbed γ dose. The size of calcite crystals was about three times greater in irradiated specimens. Gamma irradiation improved the micromechanical properties of carbonation products. Effects of mineral additives on the characteristics of irradiated mortar are discussed.

Keywords:
calcite, carbonation, cement mortar, gamma irradiation, microstructure, mineral additions, nanoindentation

Abstract:
Diagnostic tests were carried out on specimens drilled from a section of jointed, unreinforced highway pavement after 15 years of service. The section of highway was exposed to heavy road traffic, environmental actions of wet-freeze climate zone and associated winter maintenance including application of deicing salt. Premature pavement damage was manifested by visible cracking, mostly along transverse joints and in slab corners. Tests performed on core specimens included petrographic analysis of concrete and its components, using optical and scanning electron microscopy, also evaluation of elastic and transport properties, expansion potential, cracks and air void system. Numerous cracks in the grains of coarse quartzite aggregate were found. Reactive forms of quartz in quartzite aggregate - microcrystalline and cryptocrystalline quartz - were abundant. The gel-like products in cracks in quartzite grains and in surrounding cement paste were identified as alkali-silica reaction products. Expansion of specimens exposed to an alkali-silica reaction-promoting environment indicated the potential for further development of such reaction. Substantial cracking and reduction of modulus of elasticity was correlated with the presence of reactive quartz in quartzite aggregate. The role of additional destructive factors, such as the impact of heavy vehicles traffic and freeze-thaw aggression was indicated by greater cracks in the slow traffic lane compared than in the emergency lane, associated with local marginal air entrainment of concrete.

Keywords:
alkali-silica reaction, concrete, cracking, durability, highway pavement

Abstract:
Sand used as fine aggregate in concrete may, under unfavorable environmental conditions, cause alkali-silica reaction and the consequent deterioration of durability and functional properties of concrete. The aim of this work is to compare alkali-silica reactivity of 18 natural sands of various origin. The potential reactivity of sands was tested according to the procedures PB/1/18 and PB/3/18 established in the Technical Guidelines issued by the General Directorate for National Roads and Motorways. Mineral composition of aggregate was analyzed in order to identify reactive minerals. Mortar bar expansion tests and microscopic analyses of the products of alkali-silica reaction were performed. The research indicated that 6 (33%) out of 18 tested aggregates should be classified as “moderately reactive” and 12 (67%) aggregates should be classified as “non-reactive”. It was demonstrated that the origin of sand affects its susceptibility to alkali-silica reaction.

Keywords:
alkali-silica gel, expansion, fine aggregate, reactive minerals, sand

Abstract:
Premature damage to the concrete pavement of a trunk road section after 15 years of its service life was noticed. The damage manifested itself in cracking along transverse joints and in the corners of slabs. Diagnostic investigations, covering a petrographic analysis of concrete and mineral aggregates by means of optical and scanning microscopy, an evaluation of the elastic properties, the degree of cracking and air-void parameters and an identification of the alkali-silica reaction products, were carried out on core samples. Multiple cracks in coarse quartzite aggregate particles and in cement matrix were found. A significant presence of microcrystalline and cryptocrystalline quartz in quartzite particles was detected. Typical alkali-silica reaction products were unambiguously identified. The considerable cracking and the substantial decrease in the modulus of elasticity were correlated with the presence of reactive quartz in the quartzite aggregate and the alkali-silica reaction was found to be the main cause of the damage. Additional damaging factors, such as heavy traffic loads and frost aggression, are discussed.

Keywords:
concrete, road pavement, pavement evaluation, aggregate, quartzite, alkali-silica reaction, cracks, service life

Abstract:
The design of concrete for radiation shielding structures is principally based on the selection of materials of adequate elemental composition and mix proportioning to achieve the long-term durability in nuclear environment. Concrete elements may become radioactive through exposure to neutron radiation from the nuclear reactor. A selection of constituent materials of greatly reduced content of long-lived residual radioisotopes would reduce the volume of low-level waste during plant decommissioning. The objective of this investigation is an assessment of trace elements with a large activation cross section in concrete constituents and simultaneous evaluation of susceptibility of concrete to detrimental alkali-silica reaction. Two isotopes 60Co and 152Eu were chosen as the dominant long-lived residual radioisotopes and evaluated using neutron activation analysis. The influence of selected mineral aggregates on the expansion due to alkali-silica reaction was tested. The content of 60Co and 152Eu activated by neutron radiation in fine and coarse aggregates, as well as in four types of Portland cement, is presented and discussed in respect to the chemical composition and rock origin. Conflicting results were obtained for quartzite coarse aggregate and siliceous river sand that, despite a low content, 60Co and 152Eu exhibited a high susceptibility to alkali-silica reaction in Portland cement concrete. The obtained results facilitate a multicriteria selection of constituents for radiation-shielding concrete.

Keywords:
alkali-silica reaction, concrete durability, low-level radioactive waste, neutron activation analysis, radiation shielding concrete, trace elements

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:
The assessment of the aggregate suitability for concrete pavements applies mainly to coarse aggregate. However, even fine aggregate can significantly affect the long-term durability of concrete when it is susceptible to alkali-silica reaction (ASR). The sustainable use of available fine aggregates for the production of concrete, while reducing the effects of ASR, requires special preventive measures. The paper proposed different procedures to determine the chemical composition of aggregate and the related ASR risk. The study covers various properties of natural fine aggregates from glacial deposits. The experiments included determination of chemical composition by prompt gamma activation analysis (PGAA), quantitative mineralogical characterisation on thin sections using digital image procedure (DIP) and expansion measurements in mortar bar test (MBT). The strong correlation of sand origin and its susceptibility to ASR was observed. Content of micro- and cryptocrystalline quartz in siliceous sand was found to have a crucial effect on its performance in AMBT.

Keywords:
fine aggregate, alkali-silica reaction, mineral composition, prompt gamma activation analysis, digital image procedure, glacial deposit

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:
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:
The paper presents investigations into the reactivity of aggregates from igneous rock, carried out in accordance with the procedures contained in the GDDKiA General Technical Specification "Concrete pavements". The aim of the investigations was evaluation of the suitability of the aggregates for road structures and pavements built using cement based concrete technology. Aggregates produced from extrusive rocks (basalt, melaphyre and porphyry) and from intrusive rocks (granite and gabbro) were analysed. The mineral composition of the aggregates was evaluated with regard to their reactive SiO2 content. Expansion tests on mortar bar and concrete prism specimens with analysed aggregates and a microscopic analysis of the alkali-aggregate reaction products were carried out. A considerable amount of reactive minerals: chalcedony, tridymite and microcrystalline quartz and volcanic glass were found in the grains of the porphyry and melaphyre aggregates. On the basis of the conducted investigations the two aggregates made of igneous rocks (melaphyre and porphyry) were classified into category R1 (moderately reactive). The basalt aggregate, the granite aggregate and the gabbro aggregate were assigned to category R0 (non-reactive).
W artykule przedstawiono badania reaktywności kruszyw ze skał magmowych przeprowadzone zgodnie z procedurami ujętymi w instrukcjach GDDKiA OST "Nawierzchnie betonowe" w celu oceny ich przydatności do stosowania w technologii betonu cementowego na drogowe konstrukcje inżynierskie i nawierzchnie. Analizie poddano kruszywa ze skał wylewnych: bazalt, melafir i porfir oraz ze skał głębinowych: granit i gabro. Przeprowadzono ocenę składu mineralnego kruszyw z uwagi na zawartość reaktywnych minerałów krzemionkowych. Przeprowadzono badania wydłużenia próbek zapraw i betonów z kruszywami oraz analizę mikroskopową produktów reakcji alkalia-kruszywo. Stwierdzono występowanie znacznej ilości reaktywnych minerałów w ziarnach kruszywa z porfiru i melafiru: chalcedonu i trydymitu oraz kwarcu mikrokrystalicznego i szkliwa wulkanicznego. Na podstawie przeprowadzonych badań dwa kruszywa ze skał magmowych (melafir oraz porfir) zaklasyfikowano do kategorii R1 - umiarkowanie reaktywne. Kruszywo bazaltowe, granit oraz gabro przypisano kategorii R0 - niereaktywne.

Keywords:
aggregate, alkali reactivity, alkali silica gel, cristobalite, igneous rocks, microcrystalline quartz, reactive minerals / alkaliczny żel krzemionkowy, kruszywo, krystobalit, mikrokrystaliczny kwarc, minerały reaktywne, reaktywność alkaliczna, skały wulkaniczne

Abstract:
The paper presents the results of investigations into the reactivity of domestic aggregates produced from selected sedimentary rocks, carried out using the new testing methods, consistent with the RILEM and ASTM methods, implemented by GDDKiA (Polish General Directorate for National Roads and Motorways) documents. The range of the investigations covered coarse crushed aggregates produced from limestone, dolomite, sandstone and greywacke rocks, potentially suitable for making strong and durable concrete. No reactive forms of quartz were found in the mineralogical composition of the limestone aggregates and the dolomite aggregates. Micro- and cryptocrystalline quartz occurred in the particles of the greywacke aggregates and the sandstone aggregates. On the basis of the expansion of mortar and concrete specimens the aggregates produced from the sedimentary rocks were classified into the reactivity categories: R0, R1 and R2. A sodium-potassium-calcium silicate gel, whose composition (consistent with that reported in the literature) was characteristic of the alkali-silica reaction products, was found. The investigations resulted in a consistent assessment of the reactivity of the aggregates.
W pracy przedstawiono wyniki badań reaktywności krajowych kruszyw z wybranych, litych skał osadowych przy wykorzystaniu nowych metod badawczych wdrożonych w dokumentach technicznych Generalnej Dyrekcji Dróg Krajowych i Autostrad (GDDKiA), zgodnych z metodami RILEM i ASTM. Zakres badań obejmował kruszywa grube łamane o potencjalnej przydatności do wykonania wytrzymałego i trwałego betonu, wyprodukowane ze skał wapienia, dolomitu, piaskowca i szarogłazu. W składzie mineralnym kruszyw z wapieni i dolomitu nie stwierdzono obecności reaktywnych form kwarcu; w ziarnach kruszywa z szarogłazów i piaskowca występował kwarc mikro- i kryptokrystaliczny. Na podstawie wydłużenia próbek określono następujące kategorie reaktywności wybranych krajowych kruszyw ze skał osadowych: R0, R1 i R2. Zaobserwowano występowanie żelu krzemianu sodowo-potasowo-wapniowego o składzie charakterystycznym dla produktów reakcji alkalia-kruszywo, zgodnym z danymi literaturowymi. Uzyskano spójną ocenę reaktywności kruszyw.

Keywords:
alkali-aggregate reaction, cement, concrete, dolomite aggregate, expansion, greywacke, limestone, quartz, reactive minerals, sandstone / beton, cement, kruszywo dolomitowe, kruszywo wapienne, kwarc, minerały reaktywne, piaskowiec, reakcja alkalia-kruszywo, szarogłaz, wydłużenie

Abstract:
W referacie przedstawiono wyniki badań betonu poddanego cyklicznym oddziaływaniom zmiennej temperatury i wilgotności wraz z zewnętrznym oddziaływaniem soli odladzającej. Warunki badania odzwierciedlają oddziaływania środowiskowe na beton w nawierzchniach dróg ekspresowych i elementach drogowych obiektów inżynierskich, określone kategorią środowiska E3. Próbki wykonano według receptur laboratoryjnych oraz pobrano na placu budowy kilku odcinków nawierzchni dróg ekspresowych w Polsce. Przeprowadzono pomiary ekspansji próbek betonu, zmiany masy i zmiany rezonansowego modułu sprężystości w funkcji czasu. W przypadku betonu nawierzchniowego pobranego na budowie, zawierającego kruszywa grube i drobne spełniające kryteria niereaktywności potwierdzono stabilność objętościową i stałość właściwości sprężystych. Wyniki badań próbek laboratoryjnych ujawniły zróżnicowaną podatność betonu na uszkodzenia wskutek ASR w warunkach zewnętrznego oddziaływania soli odladzającej, związaną z obecnością minerałów reaktywnych w kruszywach. Przeprowadzone międzylaboratoryjne badania porównawcze pod auspicjami BASt wykazały biegłość laboratorium.

Abstract:
Results of experimental investigations on the reactivity of crushed aggregates produced from sedimentary and igneous rocks are presented. Applied test methods, consistent with RILEM and ASTM standards are implemented in technical specifications of Polish national highway administration. The range of the investigations covered coarse aggregates produced from crushed limestone, dolomite, sandstone and greywacke rocks, as well as from basalt, melaphyre, porphyry, granite and gabbro. The aggregates were selected on the basis of their mechanical and physical properties to be adequate for making durable concrete for highway applications. The mineral composition of the aggregates was evaluated with regard to their reactive SiO2 content. A considerable amount of reactive minerals: chalcedony, tridymite and microcrystalline quartz were found in the grains of the porphyry and melaphyre aggregates. No reactive forms of quartz were found to be present in the mineralogical composition of the limestone aggregates and the dolomite aggregates. Micro- and cryptocrystalline quartz occurred in the particles of the greywacke aggregates and the sandstone aggregates. On the basis of the expansion of mortar and concrete of specimens, the coarse aggregates produced from crushed rocks were classified into three reactivity categories. A sodium-potassium-calcium silicate gel was found and its composition was consistent with that reported in the literature as characteristic of the alkali-aggregate reaction products. The tests revealed consistent assessment of the reactivity of the aggregates.

Keywords:
alkali silica gel, expansion tests, microcrystalline quartz, petrographic analysis, technical specifications

Abstract:
Alkali silica reaction (ASR) is a harmful phenomenon occurring as a result of chemical interactions between sodium and potassium hydroxides in the pore solution and reactive minerals contained in the aggregate. Reactive minerals like microcrystalline, cryptocrystalline or strained quartz dissolve in the alkaline solution and form an expansive gel product. Proper selection of concrete constituents is necessary to ensure the durability of concrete structures. The proper recognition of the aggregate mineralogical composition is a very important element in the process of selection of concrete components due to the risk of ASR occurrence. This paper presents the results of detailed microscopic analysis of alkali-silica reactivity of domestic fine aggregates of various origins. Six siliceous sands from different locations in Poland and one limestone sand were tested. Detailed petrographic analysis was performed on thin sections. In all siliceous sands micro- and cryptocrystalline quartz was recognized as a reactive mineral. Digital image analysis was performed for quantitative assessment of the potential of reactivity of sands. It revealed, that siliceous river sands were the most susceptible to an alkali-silica reaction, which was confirmed by mortar bar expansion test performed according to the standard test method.

Abstract:
During the decommissioning of nuclear power plants, a significant amount of cement based composites should be disposed as radioactive waste. The use of material with low-activation constituents could effectively reduce radioactivity of concrete. The subject of the paper is the content of trace elements with large activation cross section in concrete constituents due to their ability to be activated in radiation shielding structures. Various Portland cement specimens were subjected to elemental analysis by neutron activation analysis and prompt gamma activation analysis to assess the dominant long-lived residual radioisotopes. Concentrations of the radionuclides, such as Europium-152, Cobalt-60 and Caesium-134 were assessed. Their half-life time is 13.5, 5.27, and 2.07 years, respectively. On the basis of the obtained results, recommendations for cement selection for low-activation concrete are proposed in order to economize decommissioning cost by reducing a radioactive concrete waste.

Abstract:
In the present study the potential of alkali-silica reaction (ASR) in fine fraction of aggregate was analyzed. The investigation was focused on mineral composition of siliceous sand and its influence on ASR. Three siliceous sands from different origin and localization in Poland were tested. Petrographic analysis on thin sections was conducted. The automatic image analysis was used to estimate the content of reactive minerals (micro- and crypto-crystalline quartz). The XRD measurements were performed. Alkali-silica reactivity of fine aggregate was tested by mortar-bar test according to ASTM C1260 Standard. Petrographic analysis showed that all tested siliceous sands contained reactive form of quartz, micro- and cryptocrystalline. Mortar-bar tests according to ASTM C1260 indicated that one from the selected sands exceeded expansion over the limit and was considered as reactive. The content of reactive minerals in sands estimated by automatic image analysis corresponded to ASTM C1260 results. The higher content of reactive form of quartz in siliceous sand, the larger expansion of mortar-bar test.

Keywords:
Siliceous sand, Alkali-Silica Reaction (ASR), digital image analysis, micro- and cryptocrystalline quartz, expansion

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:
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:
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