Effects of limestone replacement ratio on the sulfate resistance of Portland limestone cement mortars exposed to extraordinary high sulfate concentrations

A comparative study has been performed on the sulfate resistance of Portland limestone cement (PLC) mortars exposed to extraordinary high sulfate concentrations (200 g/l). PLCs have been prepared by using two types of clinkers having different C₃S/C₂S ratios and interstitial phase morphologies. Blended cements have been prepared by replacing 5%, 10%, 20% and 40% of clinker with limestone. Cubic (50 × 50 × 50 mm) and prismatic (25 × 25 × 285 mm) cement mortars were prepared. After two months initial water curing, these samples were exposed to three different sulfate solutions (Na₂SO₄ at 20 °C and 5 °C, MgSO₄ at 5 °C). Solutions were not refreshed and pH values of solutions were monitored during the testing stage. The compressive strength and length changes of samples have been monitored for a period of 1 year. Additional microstructural analyses have been conducted by XRD and SEM/EDS studies. Results indicated that in general, limestone replacement ratio and low temperature negatively affect the sulfate resistance of cement mortars. Additionally, clinkers of high C₃S/C₂S ratios with dendritic interstitial phase structure were found to be more prone to sulfate attack in the presence of high amounts of limestone.From the results, it is postulated that in the absence of solution change, extraordinary high sulfate content modified the mechanism of sulfate reactions and formation of related products. At high limestone replacement ratios, XRD and SEM/EDS studies revealed that while ettringite is the main deterioration product for the samples exposed to Na₂SO₄, gypsum and thaumasite formation were dominant products of deterioration in the case of MgSO₄ attack. It can be concluded that, the difference between reaction mechanisms of Na₂SO₄ and MgSO₄ attack to limestone cement mortars strongly depends on the pH change of sulfate solutions.     

Compatibility of a polycarboxylate-based superplasticiser with different set-controlling admixtures

The compatibility of specific combinations of chemical admixtures for cement pastes and mortars have been investigated. The consistency, setting time and compressive strength of cement pastes and mortars incorporating a polycarboxylate-based plasticizing admixture (PCA) with four different set-controlling admixtures (SCA); calcium formate (CF), tri-ethanolamine (TEA), mixture of calcium nitrite and nitrate salts (CNN blend) and sodium aluminate (SA) have been determined within the scope of this study. Fifty-two mortar and paste specimens with different amounts of PCA and SCA combinations have been prepared. Water/cement ratios of cement paste and mortar mixtures were 0.24 and 0.50, respectively. The paste mixtures have been prepared to determine the setting time data and the mortar mixtures have been used to determine the consistency and compressive strength values. Test results indicated that the PCA employed in this study, retards the setting time, improves consistency and reduces the early strength development of all paste and mortar mixtures at dosages greater than 0.4% by mass of cement. However, the use of different set-controlling admixtures in combination with PCA caused drastic changes in the performances of the mixtures depending on the type and amount of SCAs. It was concluded that, in order to reduce the setting time and increase the early strength of PCA incorporated mortars without causing consistency loss, the combination of PCA, and SCA should be optimized according to their types. A new 3D box-plot method has been used to determine the optimum admixture combinations for the desired properties. Maximum flow, shortest setting time and highest early strength criterion were the targets of the optimization. The most effective combination to obtain desired set acceleration and high early strength values was 1.8% PCA with 1.6% nitrite and nitrate salts based SCA by mass of cement. If consistency lost is in secondary importance, 1.8% PCA based plasticiser with 1% sodium aluminate based SCA may be an alternative combination. The proposed method can be used to optimize the targeted properties for a specific combination of cement, PCA and SCA.     

Effects of porosity and related interstitial phase morphology difference on the grindability of clinkers

The effects of regional clinker porosity and interstitial phase morphology differences on grindability of clinkers have been investigated within the scope of this study. Porosity and phase characteristics of two clinkers from different furnaces which are using the same raw materials were determined by the application of image processing techniques on SEM images of polished surfaces. Comparison of interstitial phase compositions of two clinkers showed that, clinkers with similar phase compositions may have different grindability due to the porosity and phase morphology differences. Porous clinkers usually exhibit a dendritic interstitial phase morphology with an improved grindability. Increasing porosity also leads to greater incidence of the dendritic morphology in porous regions and lower incidence of alkali in the aluminate in dendritic regions.     

Polymorphism of Alpha-Synuclein Amyloid Fibrils Depends on Ionic Strength and Protein Concentration

Protein aggregate formation is linked with multiple amyloidoses, including Alzheimer‘s and Parkinson‘s diseases. Currently, the understanding of such fibrillar structure formation and propagation is still not sufficient, the outcome of which is a lack of potent, anti-amyloid drugs. The environmental conditions used during in vitro protein aggregation assays play an important role in determining both the aggregation kinetic parameters, as well as resulting fibril structure. In the case of alpha-synuclein, ionic strength has been shown as a crucial factor in its amyloid aggregation. In this work, we examine a large sample size of alpha-synuclein aggregation reactions under thirty different ionic strength and protein concentration combinations and determine the resulting fibril structural variations using their dye-binding properties, secondary structure and morphology. We show that both ionic strength and protein concentration determine the structural variability of alpha-synuclein amyloid fibrils and that sometimes even identical conditions can result in up to four distinct types of aggregates.     

Characterization of antimicrobial polylactic acid based films

Olive leaf extract (OLE) (Olea europaea L.), which has antimicrobial effect on many food pathogens, was incorporated as antimicrobial agent into polylactic acid (PLA) films. Antimicrobial activities of films were tested against Staphylococcus aureus. Increasing amount of the OLE in the film discs from 0.9 mg to 5.4 mg caused a significant increase in inhibitory zones from 9.10 mm to 16.20 mm, respectively. Moreover, incorporation of OLE and/or increasing the amount in the film formulation significantly enhanced the water vapor permeability (WVP). The water solubility and the degradation rates of films increased up to 19.3% and 22.4%, respectively. Thus, OLE incorporated PLA films have a prospectively potential in antimicrobial food packaging to reduce post-process growth of S. aureus with improved properties.     

The effect of fly ash and limestone fillers on the viscosity and compressive strength of self-compacting repair mortars

Today, self-compacting mortars are preferred for repair purposes due to the application easiness and mechanical advantages. However, for self-compactability, the paste phase must meet some certain criteria at fresh state. The cement as well as the ingredients of the paste, powders with cementitious, pozzolanic or inert nature and plasticizing chemical admixtures should be carefully chosen in order to obtain a suitable paste composition to enrich the granular skeleton of the mix. The physical properties of powders (shape, surface morphology, fineness, particle size distribution, particle packing) and physico-chemical (time-dependent hydration reactions, zeta potentials) interactions between cement powder and plasticizer should be taken into consideration. All these parameters affect the performance of fresh paste in different manners. There is no universally accepted agreement on the effect of these factors due to the complexity of combined action; thus, it is hard to make a generalization.This study deals with the selection of amount and type of powders from the viewpoint of fresh state rheology and mechanical performance. The influence of powder materials on self-compactability, viscosity and strength were compared with a properly designed set of test methods (the mini-slump, V-funnel tests, viscosity measurements and compressive strength tests). It may be advised that, for each cement-powder-plasticizer mixture, a series of test methods can be used to determine the optimum content and type of materials for a specified workability.     

Effects of fibre type and matrix structure on the mechanical performance of self-compacting micro-concrete composites

The compatibility of matrix and fibre properties is one of the key parameters in the successful design of fibre reinforced cementitious composites. In order to achieve the desired performance, the properties of each constituent of composite should be properly configured. The aim of this study was to investigate the performance of two polymer based micro-fibres (polypropylene and polyvinyl alcohol) in different matrices (high strength and comparatively low strength with fly ash incorporation) which were designed to contain considerably high amounts of fibres (1% by volume) while maintaining their self-compactability. The fresh state thixotropic behaviour of fibre reinforced matrices was minimised by proper adjustment of water/cementitious material ratio and admixture dosage. The mechanical properties (first crack strength and displacement, flexural strength and relative toughness) of prismatic composite samples were compared by three point flexural loading test. The typical behaviours of selected composites and collapse mechanisms of PP and PVA fibres in these matrices were characterised by microstructural studies. It was concluded that, a high strength matrix with a high strength fibre give the best performance from the view point of flexural strength and toughness performance. However, incorporation of fly ash did not cause a significant reduction in composite performance possibly due to its enhancing effect on matrix–fibre interface adhesion. The possibilities and suggestions to further improve the performance of the composites were also discussed.     

Effect of ettringite morphology on DEF-related expansion

In this study, time dependent ettringite formation in heat-cured mortars has been investigated. In order to clarify the effect of formation place and morphology of ettringite on expansion, secondary electron images of cracked surfaces of mortars at three ages were analysed by SEM–EDS. Also, the X-ray microtomography analysis has been performed to observe the crack formation. The expansive role of delayed formed ettringite was related with its time dependent morphology as a function of formation place. From these observations, mechanism of ettringite reformation after heat curing has been proposed. Alumina rich species were the primary sources of ettringite formation as the starting nuclei. At later ages, if S and Al sources are readily available, the mentioned alumina rich nuclei will grow up and build ball ettringite. At long term, ball type ettringites (non-expansive) converted to massive type (expansive). These conversions can only take places if the form of available space is narrow (preformed micro-cracks). Massive ettringites exert pressure in these narrow spaces and cause expansion of mortar. If the form of the available space is spherical (entrapped air voids) ball ettringites preserve their initial form and do not cause any expansion.     

Temperature-Dependent Structural Variability of Prion Protein Amyloid Fibrils

Prion protein aggregation into amyloid fibrils is associated with the onset and progression of prion diseases—a group of neurodegenerative amyloidoses. The process of such aggregate formation is still not fully understood, especially regarding their polymorphism, an event where the same type of protein forms multiple, conformationally and morphologically distinct structures. Considering that such structural variations can greatly complicate the search for potential antiamyloid compounds, either by having specific propagation properties or stability, it is important to better understand this aggregation event. We have recently reported the ability of prion protein fibrils to obtain at least two distinct conformations under identical conditions, which raised the question if this occurrence is tied to only certain environmental conditions. In this work, we examined a large sample size of prion protein aggregation reactions under a range of temperatures and analyzed the resulting fibril dye-binding, secondary structure and morphological properties. We show that all temperature conditions lead to the formation of more than one fibril type and that this variability may depend on the state of the initial prion protein molecules.     

Effect of Ionic Strength on Thioflavin-T Affinity to Amyloid Fibrils and Its Fluorescence Intensity

The formation of amyloid fibrils is linked to multiple neurodegenerative disorders, including Alzheimer’s and Parkinson’s disease. Despite years of research and countless studies on the topic of such aggregate formation, as well as their resulting structure, the current knowledge is still fairly limited. One of the main aspects prohibiting effective aggregation tracking is the environment’s effect on amyloid-specific dyes, namely thioflavin-T (ThT). Currently, there are only a few studies hinting at ionic strength being one of the factors that modulate the dye’s binding affinity and fluorescence intensity. In this work we explore this effect under a range of ionic strength conditions, using insulin, lysozyme, mouse prion protein, and α-synuclein fibrils. We show that ionic strength is an extremely important factor affecting both the binding affinity, as well as the fluorescence intensity of ThT.