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Construction and demolition waste (CDW) is the third-most abundant waste generated annually in the countries of the European Union. One of the alternatives to the use of these wastes is geopolymeric materials. Partial replacement of commonly used raw materials for the production of these materials can help reduce the number of landfills and the consumption of natural resources. In this study, the authors partially replaced metakaolin and fly ash with clay bricks and concrete debris. The research method in article is connected with analysis of microstructures and the mechanical and physical properties of the geopolymers. The results obtained show the possibility of manufacturing useful construction materials based on industrial byproducts (fly ash) and CDW. Compressive strength and flexural strength were, for samples containing metakaolin, 20.1 MPa and 5.3 MPa, respectively. Geopolymers containing fly ash displayed 19.7 MPa of compressive strength and 3.0 MPa of flexural strength. The results for both synthesized materials give them perspectives for future applications in the construction industry. [ABSTRACT FROM AUTHOR]

[Display omitted] • We demonstrated the feasibility of using RUFA for the preparation of geopolymers. • We conducted in-depth analysis into the microstructure of RUFA geopolymers. • Sodium-hydroxide-activated geopolymer presented superior mechanical properties. • We produced RUFA geopolymer with compressive strength exceeding 97.6 MPa. This study used reactive ultra-fine fly ash (RUFA) as the primary raw materials in the preparation of a novel RUFA geopolymer. Note that the solution to binder weight ratio was maintained at the same level by varying the concentration of the NaOH solution. Extensive analysis was conducted to characterize the flowability and mechanical properties. X-ray diffraction (XRD), Scanning Electron Microscope-Energy Dispersive Spectrometer (SEM-EDS), Fourier transform infrared spectroscopy (FT-IR), mercury intrusion porosimetry (MIP), thermogravimetric (TG), and zeta potential analyses were used to examine the microstructure of RUFA geopolymers. Increasing the concentration of NaOH also led to an increase in compressive strength. A high NaOH concentration of 12 mol/L resulted in compressive strength of 97.6 MPa at 28 days. Finally, increasing the concentration of NaOH increased the formation of the primary reaction geopolymerization product, N-A-S-H gel, resulting in a denser microstructure with lower porosity. [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]

Our objective in this study was to promote the recycling of industrial by-products by combining ground granulated blast-furnace slag (G) and circulating fluidized bed co-fired fly ash (FA). We then added sodium silicate as an alkali activator (A) to a combination of G and FA (GFA) to create a novel cement-free cementitious material (AGFA). One of our main research aims was to explore the influence of the activator on GFA in terms of working and mechanical properties and drying shrinkage behavior. Hydration products were analyzed using XRD and SEM-EDS. The setting time of GFA was longer than that of AGFA, and the water absorption and fluidity were both higher. Adding sodium silicate to the GFA was shown to greatly improve mechanical properties through the formation of hydration products containing C–S–H, C-A-S-H, and C–N-A-S-H gels, which intertwined to form a dense microstructure. Compared to AGFA, the GFA was less affected by dry shrinkage, due to the expansive formation of ettringite (from anhydride) during the hydration process. Note that the reaction of the alkaline agent in AGFA with the anhydride in FA reduced the amount of ettringite that formed. The alkaline agent also promoted the depolymerization of vitreous G and FA particles, resulting in the formation of large quantities of gel, the process of which consumed much of the free water, resulting in further shrinkage. Further, it provides a good feasibility and application prospect in environmentally friendly building material of GFA and AGFA cementless composites and is expected to replace traditional cement-based composites. • This study developed an environmentally-friendly cementless composite. • Co-fired fly ash and GGBS can be combined to act as a full replacement for cement. • A novel cement-free cementitious material without activators was presented. • Sodium-silicate activated composites presented better mechanical properties. • The compressive strength of activated composite could reach more than 70 MPa. [ABSTRACT FROM AUTHOR]

• 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]

There are considerable resource reuse and environmental concerns regarding SiC sludge (SiCS) that results from cutting silicon ingots into wafers. In the current study, the effect of the Na2SiO3 solution/sodium hydroxide solution (NS/SS) mass ratio and SiCS amount on metakaolin geopolymers was found during geopolymerization system performance. The results indicate that while NS/SS ratio was relatively low, increasing the NaOH content resulted in a sufficient amount of OH− in the system to increase the solubility and hinder polycondensation, as indicated by the bulk density and setting-time results; since the polycondensation was inhibited, the mechanical strength was reduced. This study demonstrated that a geopolymer can be formed from a substitution of 10% SiCS and with an NS/SS ratio of 1.6, and that this geopolymer is a feasible material. [ABSTRACT FROM AUTHOR]

Abstract: The present study aimed to establish the durability indices of cement-based composites containing supplementary cementitious materials. The influences of compressive strength, permeability, and microstructure of cement-based composites containing fly ash and silica fume were discussed. The relationship between pore structure and corrosion behavior was investigated and compared. The results demonstrate that the addition of silica fume in cement-based composites resulted in a higher compressive strength, a lower absorption, a lower critical pore size, a lower chloride diffusion coefficient, and a lower corrosion rate. The composites containing 10% silica fumes performed better in permeability than composites containing 5% silica fumes, because silica fumes can narrow down the size of large capillary pores and densify the pore structure. The addition of fly ash in composites also enhanced the compressive strength and the permeability but was not as effective as silica fume. Unhydrated fly ash grains caused a looser pore structure and reduced the permeability. The combination of fly ash and silica fume enhanced the compressive strength and the permeability and specimens containing 5% silica fume and 10% fly ash had increased more in compressive strength and decreased more in permeability than specimens containing 5% silica fume or 15% fly ash. Moreover, the corrosion rate, the chloride diffusion coefficient, and the critical pore size were suitable for evaluating the durability of cement-based composites. A regression analysis found that the probability of rebar corrosion was greater than 90%, when the corrosion rate was 11.54μm/yr, the chloride diffusion coefficient was 0.62×10−12 m2/s, or the critical pore size was 26.71nm. [Copyright &y& Elsevier]