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The main aim of this research is to assess different fly ashes as raw materials for the manufacturing of geopolymers. Three different fly ashes have been investigated. First, a conventional fly ash from the Skawina coal power plant (Poland), obtained at a temperature of 900–1100 °C. Second, ultra-fine fly ash from a power plant in China; the side product received at 1300 °C. The third fly ash was waste was obtained after combustion in incineration plants. To predict the properties and suitability of materials in the geopolymerization process, methods based on X-ray analysis were used. The applied precursors were tested for elemental and chemical compounds. The investigations of geopolymer materials based on these three fly ashes are also presented. The materials produced on the basis of applied precursors were subjected to strength evaluation. The following research methods were applied for this study: density, X-ray fluorescence (XRF), X-ray diffraction analysis (XRD), Scanning Electron Microscopy (SEM), flexural and compressive strength. The obtained results show that materials based on fly ashes had a similar compressive strength (about 60 MPa), while significant differences were observed during the bending test from 0.1 to 5.3 MPa. Ultra-fine fly ash had a lower flexural strength compared to conventional fly ash. This study revealed the need for process optimization for materials based on a precursor from a waste incineration plant. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • This is a recycled cementitious material. • Calcium fluoride sludge has the potential instead of cementing materials. • Calcium fluoride sludge has the cementitious capacity. • Sludge replacement cement was suggested to be limited below 10%. Abstract This study was aimed to investigate calcium fluoride sludge waste resource reuse, and explore the feasibility of calcium fluoride sludge in cement-based materials used to replace the cement. The mechanical properties and durability of cement-based materials containing calcium fluoride sludge were performed using resistance test, absorption test, initial surface absorption tests, dry shrinkage test, compressive strength test, mercury intrusion porosimetry and scanning electron microscopy observation. The results indicated that partially replacing cement with calcium fluoride sludge improved the compressive strength, permeability and pore-structure, as well as 10% replacement of cement seems to give superior mechanical properties and durability due to the denser microstructures. Such dense microstructures observed in scanning electron microscopy images and narrow pore size distribution determined by mercury intrusion porosimetry. [ABSTRACT FROM AUTHOR]

Abstract: Rock wool is an inorganic fibrous substance produced by steam blasting and cooling molten glass. As with other industrial by-products, rock wool particles can be used as cementitious materials or ultra fine fillers in cement-based composites. This study investigated the microstructure of mortar specimens produced with cement-based composites that include various forms of rock wool particles. It conducted compressive strength testing, rapid chloride penetration tests, X-ray diffraction analysis, thermo-gravimetric analysis, and scanning electronic microscopy to evaluate the macro- and micro-properties of the cement-based composites. Test results indicate that inclusion of rock wool particles in composites improved compressive strength and reduced chloride ion penetration at the age of 91days due to the reduction of calcium hydroxide content. Microscopic analysis confirms that the use of rock wool particles contributed to the formation of a denser, more compact microstructure within the hardened paste. In addition, X-ray diffraction analysis shows few changes in formation of pozzolanic reaction products and no new hydrations are formed with incorporating rock wool particles. [Copyright &y& Elsevier]

• S/A is a valuable reference for the SCC mix design. • Higher S/A means more fine aggregates to fill in the pores. • Increasing S/A undermines efforts to reduce the area affected by ITZ. • Higher S/A produces concrete of greater compactness and higher durability. In this study, it evaluated the effects of sand/aggregate (S/A) ratio on the flowability, strength, durability, and microstructures of self-compacting concrete (SCC). Testing was performed on specimens using five S/A ratios: 51%, 52%, 53%, 54%, and 55%. Slump flow tests, slump tests, and box tests were used to characterize the rheological properties of the concrete as well as the mechanical properties, including compressive strength, splitting strength, slant shear strength and ultrasonic pulse velocity. Durability was evaluated using tests of absorption, resistivity and initial surface absorption. Microstructures were examined using mercury intrusion porosimetry (MIP) and scanning electron microscopy (SEM). The test results indicate that a higher S/A ratio improved flowability. A greater proportion of coarse aggregate (i.e., a decrease in S/A ratio) improved the mechanical properties by 10% compared to the control specimens (S/A ratio: 52%) at 56 days. A higher S/A ratio was shown to improve bonding capacity by enhancing the roughness of the particles and thereby increasing adhesion strength. A higher S/A ratio was also shown to improve the durability of the specimens by permitting denser packing; however, a higher S/A ratio resulted in a thinner interfacial transition zone. MIP analysis did not reveal a correlation between S/A ratio and the interfacial transition zone, whereas SEM photos indicated that a lower S/A ratio reduces the size of the interfacial transition zone. [ABSTRACT FROM AUTHOR]

In this study, we coated fine recycled concrete aggregate (FRCA) with fly ash, slag, or polyvinyl alcohol (PVA) (viscosity: 44–50 cps), replaced 25% of the natural fine aggregate in concrete with the coated FRCA, and examined the durability and microscopic properties of the flesh concrete and hardened concrete. We then examined the effects of the various types of coating as well as the thickness on the properties of concrete. Our test results indicate that coating FRCA with fly ash or PVA increases the workability of the fresh concrete, whereas slag coatings slightly reduce the workability. Slag coatings increased the compressive strength, splitting strength, and durability of specimens to a greater degree than do fly ash or PVA coatings, regardless of the water-cement ratio. Furthermore, thicker coatings were shown to produce better results. Scanning electron microscopy images and mercury intrusion porosimetry tests verified that specimens containing FRCA coated with slag resulted in superior engineering properties. [ABSTRACT FROM AUTHOR]

Most previous experiments conducted on water-saturated clay-rich gouges sheared under extreme deformation conditions (including seismic slip rates e.g., 1 m/s, and displacements exceeding several meters) relied on gouge confinement using Polytetrafluoroethene (Teflon). Use of Teflon restricts such experiments to low normal stresses (≤2 MPa), which represents a significant limitation in our understanding of earthquake physics and seismic hazard assessment. To understand how normal stress and fluid affect the frictional behavior and deformation processes of clay-rich slipping zones, we performed rotary shear experiments using a purpose-built sample holder on water-saturated kaolinite gouges at a slip rate of 1 m/s and normal stresses ranging from 2 to 18 MPa. Results show that the apparent friction coefficient, μ , increases up to a peak value, μ p , of ~0.17–0.46, associated with marked gouge compaction. This is followed by dramatic weakening with increasing displacement to a steady-state value, μ ss , ~0.02–0.26 accompanied by gouge dilation. In-situ synchrotron X-ray diffraction and field-emission scanning electron microscopy show that clay aggregates within the gouge layer have a random fabric and do not experience mineral phase changes. On the basis of temperature measurements made during the experiments combined with a thermo-hydro-mechanical model, our results suggest that pore fluids within the gouge layer were mainly in liquid form during shearing. We conclude that dramatic weakening of kaolinite gouges at seismic rates under impermeable conditions is due to thermal pressurization, resulting in fluidization of the gouges. Our new experimental approach could be used to better understand earthquake physics and frictional processes of geological and civil interest. • Water-saturated kaolinite samples were frictionally investigated at seismic rates. • A gouge sample holder was built to expand the experimental condition of normal stress. • In impermeable condition, kaolinite has a dynamic weakening behavior during sliding. • In addition, the presence of water inhibits the temperature rise in kaolinite. • The weakening mechanism is thermal pressurization, resulting in fluidization of gouge. [ABSTRACT FROM AUTHOR]