In construction engineering and mining engineering, CaCl2 is the most commonly used calcium source in microbial-induced carbonate precipitation (MICP) technology because it can generate CaCO3, which ...has a high degree of crystallization and is thermodynamically stable, in tailings or soil. However, this calcium source is not the best choice for biocement. This study aims to compare the stability, strength, NH3 emission, and other effects of CaCl2, Ca(CH3COO)2, and Ca(NO3)2 in bio-cement to determine the best calcium source for bio-cement. The results indicate that after curing for 28 days, the strength of bio-cement with Ca(CH3COO)2 as its calcium source is higher than that with CaCl2 and Ca(NO3)2 as calcium sources. After adding cement to three calcium sources (CaCl2, Ca(CH3COO)2, and Ca(NO3)2), the CH3COO− sample is more stable and has higher biomass and urease activity than the Cl− and NO3− samples. Since CH3COO− is a weak acid, CH3COOH generated by CH3COO− can easily react with NH3 under the alkaline condition provided by cement, reducing NH3 emissions. When Ca(CH3COO)2 was used as a calcium source, the NH3 emission of its sample decreased by 54.2% and 51.4% compared with CaCl2 and Ca(NO3)2. Therefore, CH3COO−, as an anionic calcium source, will have more application prospects than CaCl2 and Ca(NO3) in bio-cement production.
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•Ca(CH3COO)2 used as the calcium source is more suitable than others for biocement.•Part of CH3COO− reacts with NH3 to generate CH3COONH4, reducing NH3 emissions.•CH3COO− improves the mineralization rate of MICP because of its large relative molar mass.•Ca(CH3COO)2 helps to generate more CaCO3 to improve the compactness of biocement.•The stability of Ca(CH3COO)2 in biocement is higher than that of CaCl2 and Ca(NO3)2.
From infrastructure to national defense construction, concrete has been a key enabler in human history. While as the main binding material, ordinary Portland cement production indirectly threatens ...the human health due to the CO
2
emissions contributing to the greenhouse effect. Alkali-activated materials show great promise to be one type of feasible alternative binder. Blast furnace slag (BFS) is one of the commonly used precursors that used to preparation alkali-activated slag (AAS) due to the higher content of glassy components. Accelerating the wide application of AAS requires the reaction behavior of BFS to be clearly understood. Such reaction behavior is strongly related to the BFS structure. Thus, it is crucial to identify and decipher how the basic structure of BFS control their engineering properties. Here, we review some of the recent efforts in this direction. In the present review, we report how the BFS structure controls the reaction kinetics and reaction products as well as the mechanical properties of AAS. We also envisage a perspective in which the BFS reaction behavior can be investigated and interpreted by combining topology constraint theory, machine learning and atomic simulation.
To improve the properties of cemented ultra-fine tailings backfill (CUTB), the authors intend to outline the framework of the effect of steel slag (SS) on the properties of CUTB. Therefore, ...flowability, unconfined compressive strength (UCS), hydration products, and pore structure were used to investigate the properties of CUTB samples. The results showed that the incorporation of SS increased the flow spread by increasing the water film thickness (WFT). Unconfined compressive strength (UCS) was observed to be enhanced when the content of SS did not exceed 20 wt%. Hydration phase evolution tested by X-ray diffraction, thermogravimetry, and thermodynamic modeling indicated the additional formation of hydrotalcite-like phases (Ht). This contributed to a denser microstructure. Besides, lower total porosity and critical pore diameter (dcr) obtained by mercury intrusion porosimeter tests were observed in samples with SS addition, which could favor the strength development. On the other hand, toxicity characteristic leaching procedure (TCLP) results indicated that the CUTB exhibited good environmental performance.
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•Adding SS increased the flowability of UCTB slurry through enhancing the WFT value.•The addition of SS increased the UCS of UCTB samples after curing for 28 days.•Incorporating SS reduced the C-S-H formation but increased the Ht generation.•Refined pore structure due to the addition of SS was observed.
High-volume replacement of ordinary Portland cement (OPC) by FA usually results in comparatively lower compressive strength and delayed setting. We investigated the effect of superfine blast furnace ...slags (S-BFS) on the properties of high-volume FA cement. The flowability, initial setting time, mechanical properties and the hydration phase assembles as well as the pore structure were investigated. The results showed that the addition of S-BFS could significantly enhance the unconfined compressive strength (UCS) while decrease the flowability. This problem was alleviated by the incorporation of polycarboxylate superplasticizers (PCEs). X-ray powder diffraction (XRD), thermogravimetric (TG) analysis and mass balance calculations indicated the formation of more hydrotalcite like phases (Ht) with the addition of S-BFS, contributes to the development of UCS due to the reduction in cumulative pore volume. With the incorporation of S-BFS and PCEs, the binders offer low cost with improved environmental performance.
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•S-BFS decreased the flowability of the slurry with fast initial setting.•Coupling S-BFS with PCEs enhanced the UCS to more than 75% of PC strength.•Formation more Ht and pore structure refinement contributed to higher strength.
This paper investigated the effect of blast furnace slags (BFS) characteristics on the properties achievement after being alkali activated. The physical and chemical characteristics of BFS were ...determined by X-ray fluorescence (XRF), X-ray Diffraction (XRD) and laser granulometry. Multi-technical characterizations using calorimetry, XRD, Fourier Transform Infrared Spectroscopy (FTIR), Thermogravimetry (TG-DTG), scanning electron microscope (SEM), nitrogen sorption and uniaxial compressive strength (UCS) were applied to give an in-depth understanding of the relationship between the reaction products, microstructure and BFS characteristics. The test results show that the microstructure and mechanical properties of alkali activated blast furnace slags (BFS) highly depend on the characteristics of BFS. Although the higher content of basic oxide could accelerate the hydration process and result in higher mechanical properties, a poor thermal stabilization was observed. On the other hand, with a higher content of Fe, the hydration process in alkali activated BFS2 lasts for a longer time, contributing to a delayed compressive strength achievement.
•Using CQD as activator increased the quantity of Ht phase significantly.•Decreased the Al incorporated in C-S-H gels was observed when using CQD as activator.•CQD based binders presented better ...compressive strength after long curing periods.•All binders showed good immobilization effects but better capacity was observed at CQD activated binders.
With this present work, the authors intend to outline the framework of the properties of calcined quarry dust (CQD) activated binders. Compressive strength, phase assembles, and the pore structure were investigated and compared with CaO activated binder. The research work has brought about a discovery that CQD activated binders presented higher compressive strength than CaO activated binders after long curing periods due to the formation of abundant hydrotalcite (Ht) like phases, although relative lower compressive strength was found. Besides, decreased Al content was observed in C-S-H when utilization of CQD acted as activator. Furthermore, all binders in the present work exhibited satisfactory mine tailings immobilization capacity although better performance was detected in CQD based binders.
In this paper iron tailing sand (TS) are used as aggerate to develop ultra high-performance concrete (UHPC). The mix proportion of UHPC is designed and TS were added by 25%, 50%, 75% and 100% (wt.%, ...i.e., weight percentage) to replace natural river sand. Firstly, the influence of TS on the slurry behavior was carried out. The experimental result indicates that with the continuously increasing content of TS, the workability of slurry decreases, while the air content increases. Considering the workability, the optimal replacing dosage of TS should be less than 50%. Then, tests for the hardened specimens were taken. The compressive behavior and micro-porosity deteriorate with increasing content of TS, and the compressive strength had a positive linear relationship with the workability, which indicated that the decline the compressive behavior is mainly due to the loss of flowability. Finally, autogenous shrinkages of UHPC with different TS dosage were also tested. At the same time, the micro-structure of specimens was discussed, which was deteriorate with the increasing dosage of TS. Therefore, comprehensively considering the compressive behavior, micro-structure and shrinkage behavior, as much as 50% of the aggregate could be replaced by TS when developing UHPC.
This article investigated the potential of fly ash (FA)/blast furnace slag- (BFS-) based geopolymer as a novel backfilling material. The effects of NaOH concentration and FA/BFS mass ratio were ...explored through XRD, FTIR, and TG-DTG analyses. The results indicated that the reaction products and strengths of geopolymer depended on the NaOH concentration and types of source materials. Slump, final setting time, and setting ratio increased as a function of FA content. However, the increase in FA content reduced the compressive strength and microstructure of the backfilling material (BM) due to the lower reactivity than BFS. Microstructure analysis reveals that the matrix tends to be denser with the BFS content and NaOH concentration increase.
Numerous waste iron tailings worldwide require eco-friendly treatment methods, with biotechnology being a promising option. However, bacteria survival in cemented paste backfill has been a persistent ...challenge. This study presents a method that adjusts the cementing solution composition (e.g. urea and calcium ions) to enhance
Bacillus licheniformis
biomass in backfill. This approach, free from additives, aims to determine the optimal cementing solution concentration for bacterial growth in backfill. The results indicate that a solution with 1.0 mol/L urea and 1.2 mol/L calcium ions has the highest strength, surpassing the control group by 4.56%. Quantitative analysis reveals that this solution enhances the production of calcium carbonate while reducing the content of calcium hydroxide (CH), the hydration product. The interplay between biomineralization and hydration reactions is explained by the fact that CH in hydration reactions contributes calcium ions to the biomineralization process, establishing a complementary relationship between hydration and mineralization products. This discovery opens up a novel path to integrate MICP with waste iron tailings recycling for cemented paste backfill.
Graphical Abstract
Mining operations in permafrost or cold region have an urgent need to understand the behavior of frozen cemented foam backfill for its practical application. The aim of this paper is to ...experimentally investigate the strength and deformation behavior of frozen cemented foam backfill (FCFB) that contains cementitious material, foaming agent and aggregates with different particle size distributions in sub-zero environment (−10 °C). Several techniques have been used to examine the mechanical properties and the microstructure. The experimental results show that the strength and elastic modulus of FCFB increases as the ultra-fine particles content of building stone waste in FCFB increases. With the extended freezing time, FCFB exhibits more ductility due to strain-hardening. The mechanical strength of FCFB has a slighter increment with increased freezing interval time. Freeze-thaw cycles lower mechanical strength by deteriorating the structure. Additionally, FCFB with a higher content of ultra-fine portion presents a higher degree of cement hydration because of more contained unfrozen water, and the significant reduction of hydration rate occurs at an early age due to large amount of water freezing into ice. These findings will provide technical information for the optimal design of cemented foam backfill in cold-region.
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