scholarly journals Recycling and Application of Mine Tailings in Alkali-Activated Cements and Mortars—Strength Development and Environmental Assessment

2020 ◽  
Vol 10 (6) ◽  
pp. 2084 ◽  
Author(s):  
Nuno Cristelo ◽  
João Coelho ◽  
Mafalda Oliveira ◽  
Nilo Cesar Consoli ◽  
Ángel Palomo ◽  
...  
Keyword(s):  
Mine Tailings ◽  
Sodium Intake ◽  
Sodium Sulphate ◽  
Strength Development ◽  
Strength Increase ◽  
Fine Aggregate ◽  
Reaction Products ◽  
X Ray ◽  
Alkali Activated

Mine tailings (MT) could represent a step forward in terms of the quality of the aggregates usually used in civil engineering applications, mostly due to its high density. The Portuguese Neves Corvo copper mine, owned by the Lundin Mining Corporation, produces approximately 3 million tonnes per year. Nevertheless, it cannot be used in its original state, due to its high levels of sulphur and other metals (As, Cr, Cu, Pb, Zn). This paper focuses on the stabilisation/solidification of high-sulphur MT, without any previous thermal treatment, using alkali-activated fly ash (FA). The variables considered were the MT/FA ratio and the activator type and concentration. A fine aggregate was then added to the pastes to assess the quality of the resulting mortar. Maximum compressive strengths of 14 MPa and 24 MPa were obtained for the pastes and mortars, respectively, after curing for 24 h at 85 °C. Thermogravimetric analysis, scanning electron microscopy, X-ray energy dispersive spectroscopy, X-ray diffraction, and infrared spectroscopy were used to characterize the reaction products, and two types of leaching tests were performed to assess the environmental performance. The results showed that the strength increase is related with the formation of a N-A-S-H gel, although sodium sulphate carbonate was also developed, suggesting that the total sodium intake could be optimized without strength loss. The solubility of the analysed metals in the paste with 78% MT and 22% FA was below the threshold for non-hazardous waste.

scholarly journals Microstructural and Mechanical Properties of Alkali Activated Materials from Two Types of Blast Furnace Slags

Materials ◽  
2019 ◽  
Vol 12 (13) ◽  
pp. 2089 ◽  
Author(s):  
Jun Xing ◽  
Yingliang Zhao ◽  
Jingping Qiu ◽  
Xiaogang Sun
Keyword(s):  
Mechanical Properties ◽  
Compressive Strength ◽  
Blast Furnace ◽  
Thermal Stabilization ◽  
Hydration Process ◽  
Reaction Products ◽  
Basic Oxide ◽  
X Ray ◽  
Physical And Chemical ◽  
Alkali Activated

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.

scholarly journals Unsaturated Response of Clayey Soils Stabilised with Alkaline Cements

Molecules ◽  
2020 ◽  
Vol 25 (11) ◽  
pp. 2533
Author(s):  
Nuno Araújo ◽  
Manuela Corrêa-Silva ◽  
Tiago Miranda ◽  
António Topa Gomes ◽  
Fernando Castro ◽  
...  
Keyword(s):  
Triaxial Tests ◽  
Strength Increase ◽  
Soil Water Retention ◽  
Experimental Procedure ◽  
Retention Curve ◽  
Curing Conditions ◽  
Strength Tests ◽  
Before And After ◽  
Alkali Activated

The influence of suction on the mechanical behaviour of unsaturated chemically stabilised soils is still mostly unknown and unquantified. This is also motivated by the difficulties associated with the experimental procedure required to fully characterise the unsaturated response of the soil, including its direct influence on traditional strength tests. The present paper presents the soil water retention curves obtained for a Portuguese soil before and after being stabilised with Portland cement (OPC) and an alkali-activated cement (AAC). Saturated undrained triaxial tests were also performed for the same curing conditions (0, 28, and 90 days). Previous attempts to characterise the retention curve of soils stabilised with AAC are unknown, and the results showed that the pore volume structure is already formed after 28 days, prior to the full development of the gel matrix responsible for the strength increase between 28 and 90 days. The curve changed after stabilisation, and with each binder, as the OPC presented a higher air-entry value and a narrower suction range compared to the AAC solution. The significant differences between the curves obtained from each binder suggest the future development of a methodology to assess the quality of the AAC stabilisation.

scholarly journals Role of Curing Conditions and Precursor on the Microstructure and Phase Chemistry of Alkali-Activated Fly Ash and Slag Pastes

Materials ◽  
2021 ◽  
Vol 14 (8) ◽  
pp. 1918
Author(s):  
Marija Nedeljković ◽  
Bahman Ghiassi ◽  
Guang Ye
Keyword(s):  
Fly Ash ◽  
Analytical Techniques ◽  
Limited Information ◽  
Reaction Products ◽  
Curing Conditions ◽  
X Ray ◽  
Phase Recognition ◽  
Phase Chemistry ◽  
Alkali Activated

Understanding the role of curing conditions on the microstructure and phase chemistry of alkali-activated materials (AAMs) is essential for the evaluation of the long-term performance as well as the optimization of the processing methods for achieving more durable AAMs-based concretes. However, this information cannot be obtained with the common material characterization techniques as they often deliver limited information on the chemical domains and proportions of reaction products. This paper presents the use of PhAse Recognition and Characterization (PARC) software to overcome this obstacle for the first time. A single precursor (ground granulated blast-furnace slag (GBFS)) and a binary precursor (50% GBFS–50% fly ash) alkali-activated paste are investigated. The pastes are prepared and then cured in sealed and unsealed conditions for up to one year. The development of the microstructure and phase chemistry are investigated with PARC, and the obtained results are compared with independent bulk analytical techniques X-ray Powder Fluorescence and X-ray Powder Diffraction. PARC allowed the determination of the type of reaction products and GBFS and FA’s spatial distribution and degree of reaction at different curing ages and conditions. The results showed that the pastes react at different rates with the dominant reaction products of Mg-rich gel around GBFS particles, i.e., Ca-Mg-Na-Al-Si, and with Ca-Na-Al-Si gel, in the bulk paste. The microstructure evolution was significantly affected in the unsealed curing conditions due to the Na+ loss. The effect of the curing conditions was more pronounced in the binary system.

scholarly journals X-ray CT Analysis of FNS Mortars Mixed with Converter Slag Fine Aggregate

2021 ◽  
pp. 1-7
Author(s):  
Won Jung Cho ◽  
Ji Seok Kim
Keyword(s):  
Converter Slag ◽  
Fine Aggregate ◽  
X Ray ◽  
Natural Aggregate ◽  
Global Demand ◽  
The Future ◽  
Ct Analysis ◽  
Alternative Sources ◽  
Natural Aggregates

Aggregate is an indispensable component in concrete occupying nearly 65-80% of the total volume, whose effects on concrete performance are rarely studied [1]. Due to their inert and impervious characteristics, the durability of concrete is also influenced by the quality of aggregates. To meet the global demand for concrete in the future, it is becoming a more challenging task to find suitable alternatives to natural aggregate for preparing concrete [2]. Hence, the use of alternative sources for natural aggregates is becoming increasingly important.

scholarly journals Strength Development and Microstructure of Alkali-activated Slag-MgO in Air Curing Condition

2018 ◽  
Vol 186 ◽  
pp. 02003
Author(s):  
Chao-Lung Hwang ◽  
Duy-Hai Vo ◽  
Mitiku Damtie Yehualaw ◽  
Vu-An Tran
Keyword(s):  
Compressive Strength ◽  
Strength Development ◽  
X Ray Diffraction ◽  
Alkali Activated Slag ◽  
X Ray ◽  
Binder Ratio ◽  
Curing Condition ◽  
Activated Slag ◽  
Water To Binder Ratio ◽  
Alkali Activated

The aim of this study is to analysis the effect of MgO on strength development and microstructure of alkali-activated slag (AAS) in air curing condition. Four mixtures of AAS are prepared using different MgO content (0%, 5%, 10%, and 15 % by weight of slag) at water to binder ratio of 0.4. The flow, compressive strength, scanning electron microscopy, and X-ray diffraction are tested under relevant standards. The addition of MgO significantly accelerated the hydration rate of AAS. AAS with adding MgO tended to increase the compressive strength and to reduce the flow. The higher adding MgO content was associated with higher hydrotalcite-like phase (Ht) formation which improved the microstrure of AAS in the air curing condition.

scholarly journals Stabilisation of high-sulphide tailings with alkali activated fly ash – mechanical performance

2019 ◽  
Vol 274 ◽  
pp. 02001
Author(s):  
Cristelo Nuno ◽  
Coelho João ◽  
Miranda Tiago ◽  
Sousa Luis ◽  
Fernández-Jiménez Ana ◽  
...  
Keyword(s):  
Compressive Strength ◽  
Fly Ash ◽  
Mine Tailings ◽  
Industrial Waste ◽  
Mechanical Performance ◽  
Specific Weight ◽  
Sulphide Tailings ◽  
Alkali Activated ◽  
Construction Works

Mine tailings could represent a step forward in terms of the quality of the aggregates that usually accepted in civil engineering applications, due to their specific weight and compressive strength. The Neves-Corvo copper mine produces approximately 3 million tons of tailings every year, which could supply several construction works, at least in the south of Portugal. Nevertheless, this industrial waste requires stabilisation, not only due to their high sulphur content, but also due to mechanical performance demands. This paper focus on the stabilisation, without previous thermal treatment, of the mine tailings from Neves-Corvo.

scholarly journals Improvement of Pavement Subgrade by Adding Cement and Fly Ash to Natural Desert Sand

2021 ◽  
Vol 6 (11) ◽  
pp. 151
Author(s):  
Talal S. Amhadi ◽  
Gabriel J. Assaf
Keyword(s):  
Fly Ash ◽  
Shear Failure ◽  
Poor Quality ◽  
Fine Aggregate ◽  
Lateral Shear ◽  
X Ray ◽  
Pavement Distress ◽  
Manufactured Sand ◽  
Desert Sand

Soil characteristics are paramount to design pavements and to assess the economic viability of a road. In the desert, such as that found in southern Libya, the very poor quality of soils leads to important pavement distress such as cracks, rutting, potholes, and lateral shear failure on the edges. To improve the strength of desert sand, an innovative approach is proposed, consisting of adding manufactured sand, ordinary Portland cement (OPC), and fly ash (FA) as a binder. OPC and FA improve the characteristics of mixes of crushed fine aggregate (CFA) and natural desert sand (NDS). These results are based on a gradation of two sand sources to determine the particle distribution and X-ray fluorescence (XRF) to determine their chemical and physical properties, respectively. This research assesses the effect of cement and fly ash on the geotechnical behavior of two mixtures of fine desert and manufactured sands (30:70% and 50:50%). The mix composed of 26% of CFA, 62% of NDS, 5% of OPC, and 7% of FA shows optimal results in terms of strength, compaction, and bearing capacity characteristics.

Electrochemical Deposition of Selenium on Copper

2016 ◽  
Vol 682 ◽  
pp. 189-196 ◽  
Author(s):  
Karolina Kołczyk ◽  
Remigiusz Kowalik ◽  
Krzysztof Mech ◽  
Piotr Żabiński
Keyword(s):  
Copper Substrate ◽  
Sodium Sulphate ◽  
X Ray Diffraction ◽  
Voltammetric Analysis ◽  
X Ray ◽  
Sulphate Electrolyte ◽  
Electrolysis Potential ◽  
Influence Of Ph

The present work concerns studies aiming at determination of optimal parameters of obtaining selenium coatings on a copper substrate through the cathodic reduction from sulphate and citrate solutions. The voltammetric analysis was performed in selected solutions to define electrode reactions within the examined range of potentials as well as an influence of pH on their kinetics. The range of potentials in which selenium is reduced to Se0, and then to Se2- was determined. The next stage was performing several electrolysis, where the working electrode was copper. It was to define an influence of citric acid, sodium sulphate, electrolyte pH and the electrolysis potential on the quality of the obtained coatings. The coatings were analysed with the use of X-ray spectrofluorimetry, X-ray diffraction and scanning electron microscopy.

scholarly journals Effects of CO2 Curing on Alkali-Activated Slag Paste Cured in Different Curing Conditions

Materials ◽  
2019 ◽  
Vol 12 (21) ◽  
pp. 3513 ◽  
Author(s):  
Yubin Jun ◽  
Seong Ho Han ◽  
Tae Yong Shin ◽  
Jae Hong Kim
Keyword(s):  
Compressive Strength ◽  
Co2 Concentration ◽  
Strength Development ◽  
X Ray Diffraction ◽  
Curing Conditions ◽  
Alkali Activated Slag ◽  
X Ray ◽  
Compressive Strength Development ◽  
Activated Slag ◽  
Alkali Activated

The effect of CO2 curing on alkali-activated slag paste activated by a mixture of sodium hydroxide and sodium silicate solutions is reported in this paper. The paste samples after demolding were cured in three different curing environments as follows: (1) environmental chamber maintained at 85% relative humidity (RH) and 25 °C; (2) 3-bar CO2 pressure vessel; and (3) CO2 chamber maintained at 20% CO2 concentration, 70% RH and 25 °C. The hardened samples were then subjected to compressive strength measurement, X-ray diffraction analysis, and thermogravimetry. All curing conditions used in this study were beneficial for the strength development of the alkali-activated slag paste samples. Among the curing environments, the 20% CO2 chamber was the most effective on compressive strength development; this is attributed to the simultaneous supply of moisture and CO2 within the chamber. The results of X-ray diffraction and thermogravimetry show that the alkali-activated slag cured in the 20% CO2 chamber received a higher amount of calcium silicate hydrate (C-S-H), while calcite formed at an early age was consumed with time. C-S-H was formed by associating the calcite generated by CO2 curing with the silica gel dissolved from alkali-activated slag.

scholarly journals Alkali-Activated Binders Based on Tungsten Mining Waste and Electric-Arc-Furnace Slag: Compressive Strength and Microstructure Properties

CivilEng ◽  
2020 ◽  
Vol 1 (2) ◽  
pp. 154-180
Author(s):  
Naim Sedira ◽  
João Castro-Gomes
Keyword(s):  
Compressive Strength ◽  
Electric Arc ◽  
Mining Waste ◽  
Arc Furnace ◽  
Reaction Products ◽  
X Ray ◽  
Eaf Slag ◽  
Electric Arc Furnace Slag ◽  
Furnace Slag ◽  
Alkali Activated

The valorization and reusing of mining waste has been widely studied in recent years. Research has demonstrated that there is great potential for reusing mining waste for construction applications. This work experimentally investigated the strength development, pore structure, and microstructure of a binary alkali-activated binder. This is based on tungsten mining waste mud (TMWM) and electric-arc-furnace slag (EAF-Slag) using different proportions of TMWM (10, 20, 30, 40, and 50 vt.%). The precursors were activated using sodium silicate (Na2SiO3) and potassium hydroxide (KOH 8M) as alkaline activator solution with solid:liquid weight ratio = 3. Pastes were used to assess the compressive strength of the blended binder and their microstructure. The reaction products were characterized by X-ray diffraction (XRD), scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDS), and Fourier transform infra-red (FT-IR) spectroscopy, while the porosity and the pores size properties were examined by mercury intrusion porosimetry (MIP). The results show that the partial replacement of TMWM with EAF-Slag exhibited better mechanical properties than the 100TM-AAB. A maximum strength value of 20.1 MPa was obtained in the binary-AAB sample prepared with 50 vt.% TMWM and EAF-Slag. The pastes that contained a higher dosage of EAF-Slag became more compact with lower porosity and finer pore-size distribution. In addition, the results obtained by SEM-EDS confirmed the formation of different types of reaction products in the 100TM-AAB, 100FS-AAB, and the binary-AABs mixtures such as N-A-S-H, C-A-S-H and (N, C)-A-S-H gels frameworks in the system as the major elements detected are Si, Al, Ca, and Na.

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