Influence of Surface Retarders on Texture Profile and Durability of Upper Layer of Exposed Aggregate Concrete Pavement

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

Wpływ mrówczanu sodu i potasu na podatność kruszywa granitowego na reakcję alkaliczną

Use of de-icing agents is necessary in winter to maintain appropriate quality of road and airport surfaces. Formate or acetate de-icing agents are safer for aircraft and the environment than the commonly used sodium chloride, but may cause an alkali-silica reaction in concrete. The study investigated the influence of sodium formate and potassium formate on the occurrence of ASR (alkali-silica reaction) in mortars with granite aggregate. Accelerated mortar-bar tests at 80°C using various de-icing agents were performed and detailed studies of the SEM-EDS microstructure were carried out.Stosowanie środków odladzających jest niezbędne do zimowego utrzymania odpowiedniej jakości betonowych nawierzchni drogowych i lotniskowych. Środki odladzające na bazie mrówczanów lub octanów są bezpieczniejsze zarówno dla środowiska, jak i statków powietrznych niż powszechnie stosowany chlorek sodu, jednak mogą wywoływać reakcję alkaliczno-krzemionkową kruszywa w betonie. W pracy analizowano wpływ mrówczanu sodu i mrówczanu potasu na potencjał wystąpienia ASR (alkali-silica reaction) w zaprawach z kruszywem granitowym. Przeprowadzono badania ekspansji w 80°C z zastosowaniem różnych środków odladzających oraz przeprowadzono szczegółowe badania mikrostruktury SEM-EDS

Effect of boron-containing aggregates on setting and hardening of Portland cement mortars

Multicomponent cement-based composites are known as versatile structural materials for enhanced radiation shielding. The use of selected elements, like boron, cadmium, or rare earth elements, provides an increased neutron shielding capacity. Because of profusion, reasonable costs and large cross-section for neutron capture, boron containing minerals are suggested as aggregates for radiation shielding concrete. Despite many advantages, boron additives may act as cement setting retarders. Uncontrolled setting and hardening is not acceptable in radiation shielding concrete technology. In this work we present results from isothermal calorimetry measurements on cement mortars with boron-containing aggregates. Four types of boron aggregates were used in the studies: colemanite, ulexite, borax and boron carbide. Based on calorimetric curves, the beginning of setting time was determined. Additionally early mortar strength was investigated and linear relationship between the heat generated in the isothermal calorimeter and the early compressive strength has been observed. The use of isothermal calorimetry allowed us to estimate the limits for the content of boron compounds to be used cement mortar

Laboratory investigations on fine aggregates used for concrete pavements due to the risk of ASR

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

Microscopic analysis of the alkali-silica reactivity of various origin fine aggregate

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

Alkali-silica reaction and microstructure of concrete subjected to combined chemical and physical exposure conditions

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

Influence of Calcination Temperature and Amount of Low-Grade Clay Replacement on Mitigation of the Alkali–Silica Reaction

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