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•Reusing industrial byproducts prepares the new cementitious material for CPB.•UCS and microstructure of CPB are studied under low temperature-atmospheric pressure.•CPB under 5 ℃ with ...50, 75 kPa exhibits lower UCS than those under 20 ℃ with 101 kPa.•Looser microstructure with large porosity forms inside CPB under 5 ℃ with 50 kPa.
To promote application of cemented backfill mining in underground mines located at high-altitude regions, there is a necessary to investigate mechanical performance of cemented paste backfill (CPB) under low temperature and low atmospheric pressure. In this study, the orthogonal experiment was first scheduled to synthesize the new cementitious material by combining industrial byproducts of blast furnace slag (BFS), carbide slag (CS), desulfurization gypsum (DG) with cement clinker (CC). Then, CPB samples were prepared with the new cementitious material and cured under different temperatures of 5, 10, 20 ℃ and atmospheric pressures of 50, 75, 101 kPa for 3, 7 14, and 28 days. Unconfined compressive strength (UCS) and microstructural analyses were conducted to evaluate strength and microstructure evolution of CPB. Experimental results indicate that UCS values of CPB increase with BFS, but decrease with CS and DG. The optimal proportion of the new cementitious material is determined as: 70 wt% BFS, 12 wt% CS, 1 wt% DG, and 17 wt% CC. Under curing of low temperature and low atmospheric pressure, CPB samples exhibit lower UCS values than those under 20 ℃ with 101 kPa. Especially, the coupling of low temperature and low atmospheric pressure exerts significantly adverse influence on the later strength of CPB after curing of 14 and 28 days. The declines of 57.99 % and 41.75 % are observed from UCS values of 14-day and 28-day CPB under 5 ℃ with 50 kPa, respectively. Regardless of curing temperature and atmospheric pressure, UCS values increase with the ratio of cementitious material to tailings and curing time. Low curing temperature and low atmospheric pressure reduce the hydration degree of the new cementitious material. The amount of hydration products decreases, the number of micropores (0.1 ∼ 1 μm) and the total porosity increases, as well as more loose microstructure forms among solid particles. This is the underlying reason behind performance degeneration of CPB under low temperature and low atmospheric pressure.
The recycling of agricultural wastes in cementitious products has recently been a trendy approach for the sustainability goals of the world as it ensures economic and ecological advantages in ...addition to the safe disposal of these wastes. In this regard, the potentiality of a biomass ash obtained from the incineration of pistachio shell to serve as a supplementary cementitious material is documented in the present study. An increase of up to 30% in the amount of pistachio shell ash resulted in the proportional increase of both water requirement and setting time of the ordinary Portland cement by up to 54% and 300%, respectively. The incorporation of up to 20% pistachio shell ash into the cement yielded specimens of comparable or higher compressive strength values relatively varying between 98% and 117% at the 28 days and later curing ages. Beside the cementitious property, it was observed that a presence of graphitic structures in the pistachio shell ash remarkably improved the mechanical and the microstructural properties of cement mortars. In conclusion, at least 10% incorporation of this ash into the cement is highly recommended for the cement industry as it is beneficial in achieving the highest ultimate (400-day) compressive strength and promotes no loss on the early (2-day) compressive strength.
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•The pistachio shell ash (PSA) was used as a supplementary cementitious material (SCM).•The presence of graphitic structures in PSA contributed to the early strength properties of cement.•10% PSA incorporation improved the compressive strength value of cement by 17% at 400 days.•The 28 days and the later age strength values were found to be satisfactory at even 20% PSA.•The use of PSA is strictly recommended for sustainability goals of the cement industry.
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•Analysis of synergistic effect of scouring abrasion and sulfate attack on concrete.•An abrasion-erosion testing system based on natural conditions of the environment was ...proposed.•Testing the macro properties, micromorphology, phase transformation, and pore structure of the eroded specimens.•Relating the volumetric sediment concentration and the velocity of the scouring flow to the abrasion rate of concrete.
The conventional tests of dynamic water scouring abrasion (DWSA) on lining concrete for hydraulic discharge tunnel do not consider concomitant sulfate ions that may exist in aggressive aqueous environment and alter the mechanisms and deterioration kinetics of DWSA. In this study, an abrasion-erosion testing system based on natural conditions of the environment has been used to evaluate the influence of volumetric concentration of sediment and the velocity of the scouring flow on abrasion-erosion synergism of lining concrete. To this end, lining concretes were subjected ambient conditions similar to that in drainage tunnel, spillway and stilling basin geographic locations, while implementing abrasion and accelerated external sulfate attack (ESA) test alternately prior to various physical and microstructural analyses. A dynamically decrease of properties on a macroscopic scale was observed, as well as an increase of precipitated ettringite, leached calcium, harmful pore (>200 nm) and sheeted radial micro-cracks, in lining concretes exposed to sediment-laden flow simulated for discharge, which were involved in the co-occurrence of complex degradation mechanisms in specimens exposed to DWSA-ESA. Results indicate that a water body with a high-velocity flow and a high sediment concentration significantly accelerates the sulfate attack on concrete. In contrast, a water body with a low-velocity flow and a low concentration of sediment alleviates the traverse of sulfate ions in concrete due to the inside-out pressure potential. The implications of these synoptic findings may informatively improve the design of abrasion and erosion resistance for concrete when dual exposure to ESA and abrasion is occurred in hydraulic tunnel engineering.
Using of magnetized water (MW) in the manufacturing of Portland cement concrete has shown promising effects in recent decades. This research investigates the effect of using alkaline activator (AA) ...solution prepared with MW on producing fly ash (FA) and silica fume (SF) based geopolymer concrete. The MW was prepared by passing tap water (TW) through two permanent magnetic fields of 1.4 and 1.6 Tesla intensities. Sodium hydroxide (SH), potassium hydroxide (PH), and sodium silicate (SS) solutions were the AA used. In total, 28 geopolymer concrete mixes were produced and tested in this study. Half of the mixes was made with the proposed MW (activator and added water), and compared with the other half that made with TW (activator and added water). Variables like; water type (TW or MW), SF content (10%−100%), AA type (SH+SS or PH+SS), AA concentration, AA to cementitious materials (AA/C) ratio, and water to cementitious materials (W/C) ratio were applied in this study. Physical and chemical properties of the utilized water and AA were measured. Concrete fresh and hardened mechanical properties were measured including workability, compressive strength, tensile strength, flexural strength, bond strength, and water absorption. Ultrasonic pulse velocity non-destructive testing was also conducted on the produced concrete. Scanning electronic microscope (SEM), energy dispersive X-ray (EDX), and X-ray diffraction (XRD) analyses were carried out on selected mixes to closely investigate the microstructure of the introduced geopolymer concrete. The results showed that compared with TW, utilizing MW in preparing the AA of geopolymer concrete caused notable increase in the concrete slump with an average of 14%, compressive strength increase by up to 64%, tensile strength increase by up to 60%, flexural strength increase by up to 41%, bond strength increase by up to 40%, and water absorption decrease by up to 38%.
•Geopolymer concrete alkaline activator (AA) was made with magnetized water (MW).•Sodium hydroxide, potassium hydroxide, sodium silicate solutions were the AA used.•Twenty-eight mixes were tested for fresh and hardened mechanical properties.•MW increased slump with average of 14%, increased compressive strength by up to 64%.•MW increased tensile strength by up to 60%, decreased water absorption by up to 38%.
Chloride diffusion within concrete is proved to reveal an impact on the service life of reinforced concrete structures, however, its penetration within recycled concrete has not been fully ...comprehended. To clarify this process, the chloride transport in recycled concrete over time was investigated through experimental and theoretical work, and the outcomes were further interpreted by microstructural analyses. The results indicate that unlike normal concrete, different chloride transport behaviors were seen in recycled concrete, which resulted from the high porosity of recycled aggregates. Meanwhile, the high porosity of recycled aggregates resulted in a quicker rise in the maximum chloride concentration over time in the drying-wetting environment, but a slower rate of decrease in the chloride diffusion coefficient. In addition, the relationship between several parameters related to chloride diffusion within recycled concrete (e.g., the chloride diffusion coefficient and the chloride binding capacity) was established. Finally, a more sophisticated model that could well describe the chloride diffusion within recycled concrete was proposed, which considered a number of key indexes.
•A total of 9 GCs with/without cold-bonded LWFA were produced.•Na2SiO3/NaOH was determined as 2.5 by weight in all mixtures.•Replacement of quartz aggregate with LWFA increased the workability of ...GCs.•LWFA up to 25% developed the physical, mechanical and durability properties of GCs.•The results also were supported by the microstructural analysis of GCs.
In this study, effects of cold-bonded lightweight fine aggregate (LWFA) on the geopolymer composites (GCs) were investigated in terms of fresh, physical, mechanical and durability properties. LWFA and different diameters quartz aggregates were used in the production of fly-ash-based GCs. However, LWFA was only replaced with the quartz aggregate of 1.2–2.5 mm. A mixture of 12 M NaOH and Na2SiO3 solution was prepared as 1/2.5. Unit weight, specific gravity, water absorption, apparent porosity, compressive and flexural strengths, ultrasonic pulse velocity and water sorptivity coefficient of GCs were determined. According to the test results, workability of GCs improved as the usage rate of LWFA increased. Due to the surface characteristics of LWFA, the mechanical properties of GC were enhanced by the geopolymerization reaction conducted between LWFA with alkali activators. Thus, the compressive strength of GC with 25% LWFA was 39.6% higher than that of the control GC at 28th day. This conclusion supported by TGA/DTA and FTIR analysis indicated that N-A-S-H gel of GC incorporating 25% LWFA was higher compared to control mixture. Also, GCs incorporating 40% and higher LWFA showed lower performance than control GC.
The development of sustainable building materials and construction to decrease environmental pollution in both production and operational stages of the materials’ life cycle is appealing to great ...interest in the construction industries worldwide. This study evaluated the negative effect of temperature up to 1000 °C on the compressive strength and microstructure of fly ash and petroleum sludge ash (PSA) geopolymer mortar. A sodium silicate and sodium hydroxide mixture is used as an activator. The synthesized mortar was investigated using X-ray Diffraction (XRD), Fourier Transformation Infrared Spectroscopy (FTIR), Mercury Intrusion Porosimetry (MIP), and Field Emission Scanning Electron Microscopy (FESEM). As the temperature increased, the compressive strength of the geopolymer mortar decreased. The strength degradation is due to the damage to microstructure because of the temperature-induced dehydroxylation, dehydration thermal incompatibility between geopolymer aggregate and paste of geopolymer mortar at high temperatures. With an increase in temperature, the cumulative pore volume increased. The FESEM image showed the decomposition of the geopolymer matrix started at a temperature of 600 °C. Incorporating PSA in geopolymer mortar could result in an eco-friendly and sustainable environment that may reduce the problems associated with sludge disposal.
In this research, the effects of adding graphene nanoplatelets (GNPs) on the flexural properties of fiber metal laminates (FMLs) under marine environmental conditions were investigated. The FMLs were ...fabricated with alternating layers of Al6061 and glass fiber reinforced epoxy (GFRE) with different concentrations of GNPs (0.25, 0.5, and 1.0 wt%). The samples were immersed in the 3.5 wt% NaCl solution for different immersion times (7, 14, and 28 days) at room temperature. The addition of GNPs led to decreasing the water absorption of samples after immersion in the 3.5 wt% NaCl solution; the lowest absorbed water was for the samples with 0.25 wt% GNPs. Although the flexural properties of samples decreased by increasing the immersion time, the lowest reduction in flexural properties was obtained for the sample with 0.25 wt% GNPs. Results showed that by adding GNPs and immersing the specimens in the 3.5 wt% NaCl solution for 28 days, the flexural strength and modulus, and strain values of specimens containing 0.25 wt% GNPs were respectively about 128%, 63%, and 1.85 times higher than those of samples without GNPs. Also, the reduction of the flexural properties caused by immersion in NaCl solution was lower than that of samples without GNPs. Moreover, the water uptake of samples with 0.25, 0.5, and 1.0 wt% GNPs was about 38%, 31%, and 37% lower than that of samples without GNPs after 28 days of immersion. Microstructural analyses revealed that the improvements in the metal/polymer adhesion and mechanical properties of the polymeric part of FMLs resulting from various mechanisms were the main reasons for the improved performance of samples with GNPs under marine conditions.
New Ti alloys are being developed to obtain materials with better properties for biomedical applications. In order to avoid complications caused for the presence of Al and V ions in the blood stream, ...novel alloys have been developed without these two elements. Mo and Nb are two non-toxic β-stabilizing elements used in Ti alloys because they decrease the elastic modulus and improve corrosion resistance. Thus, this study investigated the influence of Nb addition in Ti-xNb-5Mo alloy (x = 0, 10, 20, 30 %wt) on microstructure, structure, and selected mechanical properties. The samples were characterized after annealing, and the results showed the decrease of α phase and growth of β phase with the addition of Nb. The ω phase in the alloy containing 20% Nb was also detected. The samples’ elastic modulus and microhardness tended to decrease with increasing of the β phase, except for the Ti–20Nb–5Mo alloy due to phase hardening ω. The average crystallite size of the α and β phases increased with the addition of Nb.
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•Long term micro function of modified-SWSSC at various influential factors was studied.•Gradual improvement of microstructural zonation in tidal exposed SWSSC due to SF,•pH reduction, ...SF reaction, magnesium sulphate decomposed chloride-containing phases.•MgO and CaO in SCMs reacted with CO2, forming dolomite CaMg(CO3)2, SWSSC strength loss.•C-S-H physical properties increased the chloride binding capacity of MK&SF-mixed SWSSC.
In tidal zones, the transfer of conductive ions accelerates concrete deterioration due to dry-wet cycles, temperature, and humidity gradients over time. Thus, this study investigates the effects of ground granulated blast furnace slag (GGBS), silica fume (SF), and metakaolin (MK) on the deterioration rate of seawater SeaSand concrete (SWSSC) exposed to tidal conditions for four years caused by carbonation, sulphate and chloride penetration. Results showed continuous exposure to MgSO4, reduced Fe content and converted AFm into AFt, contributing to an increase in total SWSSC porosity of 12.9% while reduced to 10.2%, 7.4% and 7.3% with the optimal addition of GGBS, SF and MK. In combined sulphate and chloride-rich conditions, enhanced gel phase physical properties were more influential than AFm phases in increasing chloride binding capacity. SF suppressed AFt expansion, formed dense C-S-H with optimal Ca/Si ratio and physically increased the chloride binding capacity of SWSSC.
Similarly, despite its high alumina content, MK restricted chloride mobility mainly through C-S-H and, subsequently, AFm phases. Additionally, through its initial acceleration of calcium-hydroxide consumption, SF reduced alkalinity and minimized the formation of CaCO3, outperforming MK in mitigating carbonation. Higher CaO and MgO in GGBS-mixed samples led to dolomite formation in severely carbonated zones, causing long-term mechanical strength reduction. In summary, SF significantly enhanced SWSSC durability and served as an effective additive in tidal-exposed SWSSC.
