Alkali-activated Granulated Blast Furnace Research Articles

Influence of secondary carbon fiber on the mechanical behaviour and microstructure of alkali-activated granulated blast furnace slag-based composites

This study aimed to investigate the mechanical behaviour and microstructure of an environmentally friendly fibre-reinforce alkali-activated composites. The composites were obtained from alkali-activated granulated blast furnace slag reinforced with chopped secondary carbon fibres (SCFs) coming from the aircraft industry carbon fiber reinforced plastics waste. Three types of surfactants and two concentrations of SCFs were investigated. The compressive and bending strengths were measured to evaluate the mechanical behaviour of specimens. Moreover, the polycondensation products, pore structure, and microscopic morphology of the composites were analyzed using X-ray diffraction (XRD), method of standard contact porosimetry (MSCP), and scanning electron microscopy (SEM). It was found that tetraethylammonium bromide and a superplasticizer agent Glenium-51® increase compressive strength for reference granulated blast furnace slag-based alkali-activated matrix approximately by 60 % and lead to lower open porosity from 16 to 5 %. The experimental results showed that the incorporation of 0.7 vol. % SCFs had an optimal influence on mechanical behaviour and microstructure of composite. Based on the test results, it can be clearly said that using of Glenium-51® is improving the compressive strength of slag based alkali-activated composites reinforced SCFs.

Cements with supplementary cementitious materials for high-temperature geothermal wells

This paper discusses self-healing ability, characterized by the strength recovery and crack sealing, thermal shock and acid resistance of several cementitious composites in water, alkali carbonate or geothermal brine at 300 °C. The tested formulations included a common high-temperature OPC/SiO2 formulation, a calcium-aluminate cement with alkali activated FAF blend (TSRC), alkali-activated granulated blast furnace slag (GBFS/SiO2) and fly ash C/fly ash F (FAC/FAF) cementitious blends. Compressive strength recoveries and visual observations of cracks sealing using 3D imaging after the compressive damage and then after the 5-day healing period were used to evaluate the self-healing abilities of these composites. The strength recoveries were evaluated for composites after 1-, 5-, 10-, 15-, and 30- day initial curing periods at 300 °C and after repeated damage and 5-day healing treatments. The nature of the failure was classified depending on the Young’s modulus (YM) of the tested blends. Composites with moderate values of YM, such as OPC/SiO2 and TSRC developed slim cracks while brittle and very brittle FAC/FAF and GBFS/SiO2 cementitious blends produced multidirectional cracks or near-fragment failures resulting in poor strength recoveries. In comparison with the common high-temperature OPC/SiO2 blend, composites with alkali activated pozzolanic materials demonstrated a decrease in crack size during the short healing periods. Fly ash-containing composites showed better acid resistance surviving 28 days in sulfuric acid (pH 0.2) at 90 °C. The TSRC demonstrated the best thermal shock resistance losing only about 20 % of the original strength in five 350 °C heat→25 °C water thermal cycles. In all the tests the TSRC outperformed the rest of the composites with average strength recoveries of more than 85 %. Alkali carbonate was the most favorable for both strength recovery and crack sealing. The short-term strength recoveries could be further improved to above 100 % by addition of micro-glass fibers (MGF). However, the MGF raised the brittleness of the samples after longer initial curing times, which decreased recovery rates of the aged samples. Crystalline phase analysis demonstrated that different products assisted in strength recoveries and crack sealing. The later included for the most part silica and analcime while the former were hydrogrossulars (ferrian) with various stoichiometries, iron-magnesium minerals, cancrinite, quartz and boehmite. These phases formed thanks to the slow high-temperature alkaline reactions of fly ash and glass fibers for MGF-modified samples.

Effect of polyacrylic resin on mechanical properties of granulated blast furnace slag based geopolymer

The mechanical performances of alkali-activated granulated blast furnace slag (GBFS) based geopolymer modified with polyacrylic resin were investigated in this paper. The water-to-binder ratio, alkaline activator content (Na2O wt%) and SiO2/Na2O molar ratio in this experiment maintained at 0.5, 6% and 0.8, respectively. Geopolymer samples were synthesized by alkaline solution and GBFS with incorporating amount of 0.25, 0.5, 0.75, 1.0, 3.0 and 5.0wt% polyacrylic resin. The mechanical properties of samples were measured using compression tests, flexure tests and bending toughness tests. The results show that the compressive and flexural strength were both up to the maximum value while doping 1wt% polyacrylic resin, the ratio of flexural-compressive strength and bending toughness at curing 28days were increased by 36.3% and 104.6% respectively, compared with the control samples. The structural evolutions of specimen after incorporating polyacrylic resin were characterised by FTIR as well as 29Si NMR spectroscopy. It indicated that a new absorption peak namely SiOC bond at wavenumber of about 1180cm−1 in the FRIR spectra appeared while incorporating polyacrylic resin whatever 1wt% or 5wt%, the chemical shifts corresponding resonance peaks of siliceous species moved towards to low field, and the polymerization degree of Si transformed from Q3, Q4 to Q0, Q1, Q2.

Engineering and durability properties of concretes based on alkali-activated granulated blast furnace slag/metakaolin blends

The effects of activation conditions on the engineering properties of alkali-activated slag/metakaolin blends are examined. At high activator concentration, compressive strengths at early age are enhanced by the inclusion of metakaolin in the binder. A similar effect is observed in the flexural strength of the concretes, as dissolution and reaction of metakaolin is favoured under higher-alkalinity activation conditions. Increased metakaolin contents and higher activator concentrations also lead in most cases to reduced water sorptivity and lower chloride permeability. The correlation between the outcome of the rapid chloride permeability test (RCPT) and a directly-measured chloride diffusion coefficient is weak, revealing the limitations of the RCPT when applied to alkali-activated concretes. Accelerated carbonation, induced by exposure to elevated CO2 concentrations, leads to a reduction in compressive strength and an increased permeability; however, there is not a linear relationship between carbonation depth and total porosity, indicating that CO2 diffusion is not the only parameter controlling the carbonation of these materials.

Microstructure of Alkali-Activated Granulated Blast Furnace Slag-Based Geopolymer

The microstructure of alkali-activated granulated blast furnace slag-based geopolymer was studied by means of field emission scanning electron microscope (FESEM) coupled with energy dispersive X-ray analysis (EDXA). FESEM images showed that the geopolymer material has worm-like microstructure in the nanoscale with an average particle size of 20 nm. EDXA results demonstrated that the Na-based and Ca-based geopolymers were produced via the disintegration of amorphous phases and some minerals in GBFS and polycondensation reaction of oxygen-silicon and oxygen-aluminum tetrahedrons under alkaline condition.

The alkali–silica reaction in alkali-activated granulated slag mortars with reactive aggregate

The expansion of alkali-activated granulated blast furnace slag (AAS) cement mortars with reactive aggregate due to alkali–silica reaction (ASR) was investigated. The alkaline activator used was NaOH solution with 4% Na 2O (by mass of slag). These results were compared to those of ordinary portland cement (OPC) mortars. The ASTM C1260-94 Standard Test Method based on the NBRI Accelerated Test Method was followed. The nature of the ASR products was also studied by SEM/EDX. The results obtained show that the AAS cement mortars experienced expansion due to the ASR, but expansion occurs at slower rate than with OPC mortars under similar conditions. The cause of the expansion in AAS cement mortars is the formation of sodium and calcium silicate hydrate reaction products with rosette-type morphology. Finally, in order to determine potential expansion due to ASR, the Accelerated Test Method is not suitable for AAS mortars because the reaction rate is initially slow and a longer period of testing is required.