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.
The aim of the study was to generate rules for the prediction of the chloride resistance of concrete modified with high calcium fly ash using machine learning methods. The rapid chloride permeability test, according to the Nordtest Method Build 492, was used for determining the chloride ions’ penetration in concrete containing high calcium fly ash (HCFA) for partial replacement of Portland cement. The results of the performed tests were used as the training set to generate rules describing the relation between material composition and the chloride resistance. Multiple methods for rule generation were applied and compared. The rules generated by algorithm J48 from the Weka workbench provided the means for adequate classification of plain concretes and concretes modified with high calcium fly ash as materials of good, acceptable or unacceptable resistance to chloride penetration.
Long-term exposure of concrete to nuclear reactor environments may enhance the ageing phenomena. An investigation concerning a possible deleterious alkali-silica reaction (ASR) in concrete containing high-density aggregates is presented in this paper. The scope of this investigation was limited to heavy aggregates that could be used for the construction of the first Polish nuclear power plant (NPP). Five different high-density aggregates were selected and tested: three barites, magnetite, and hematite. Mineralogical analysis was conducted using thin section microscopic observation in transmitted light. The accelerated mortar beam test and the long-time concrete prism test were applied to estimate the susceptibility of heavy aggregates to ASR. X-ray diffraction (XRD) and scanning electron microscopy (SEM) analyses were conducted on aggregates and mortars. The quartz size in aggregate grains was evaluated using image analysis. Application of the accelerated mortar beam method confirmed the observations of thin sections and XRD analysis of high-density aggregates. The microcrystalline quartz in hematite aggregate and cristobalite in one of barite aggregate triggered an ASR. The composition of ASR gel was confirmed by microscopic analysis. The long-term concrete test permitted the selection of innocuous high-density aggregates from among the other aggregates available, which showed practically no reactivity.
In the present study, the potential for the alkali-silica reaction (ASR) in radiation shielding concrete containing special aggregates is presented. The tests were performed on two kinds of aggregate: (1) high-density aggregate to absorb the gamma radiation (barite, magnetite, and hematite) and (2) mineral with high bound water content to attenuate the neutron flux (serpentinite). The optical microscopy in transparent light on thin sections, XRD and XRF method, was used to assess the mineral composition of aggregates. ASTM C1260 test method for potential alkali reactivity of aggregates was applied also to investigate the effect of different content and crystal size of silica on the expansion due to ASR.The tests revealed that all tested aggregates, such as barite, magnetite, hematite, and serpentinite, were characterized by low solubility at high pH. The XRD and XRF results have shown presence of silica in all tested aggregates, but the microscopic observations enhanced size and composition of SiO 2 crystals. The aggregates were not deleterious themselves, but the different content and size of SiO 2 crystals in the aggregate influenced their potential for alkali-silica reaction. The quartz in heavy kinds of rocks and in the serpentinite used for radiation shielding was just as much potentially susceptible to deleterious ASR as quartz in common rocks used in concrete technology. In the hematite, silica crystals were classified as microcrystalline, so it should be considered as potentially reactive. The expansion tests confirmed that hematite was highly reactive. Other aggregates after 14 days of testing did not exceed 0.1% elongation limit. The microstructural analysis of thin sections prepared from mortars after ASTM C1260 test confirmed expansion of aggregate grains due to ASR.
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.
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