Karolina Gibas

Influence of Blended Cements with Calcareous Fly Ash on Chloride Ion Migration and Carbonation Resistance of Concrete for Durable Structures

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.

Prediction of the Chloride Resistance of Concrete Modified with High Calcium Fly Ash Using Machine Learning

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.

Influence of calcerous fly ash on concrete resistance to migration of chlorides

The use of caleerous fly ash from brown coal combustion in Belchatow Power Plant in Poland as additive to concrete mix was studied. The strength and the resistance to chloride penetration into concrete was investigated at water to binder ratio from 0.45 to 0.60. Caleerous fly ash both in unprocessed form and grinded to specified specific surface was used for partial replacement of cement up to 30% of mass. To evaluate the concrete resistance to chloride ion penetration the standard method of determination of chloride migration coefficient from non-steady-state migration test according to NT Build 492 was used. Test results revealed a substantial improvement of the resistance to chloride penetration into concrete containing calcerous fly ash. The resistance was higher for increased replacement level and decreased water-to-cement ratio.

Potential for Alkali–Silica Reaction in Radiation Shielding Concrete Containing Special Aggregates

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 SiO2 crystals. The aggregates were not deleterious themselves, but the different content and size of SiO2 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.