Effects of waste glass on alkali-activated tungsten mining waste: Composition and mechanical properties

Increasingly more research is being directed towards the valorisation of waste materials as precursors for synthesising alkali-activated binders (AABs). For this study, varying blends of tungsten mining waste (TMW) and waste glass (WG) are activated using a combined sodium hydroxide (SH) and sodium silicate (SS) alkali solution. The activating solution itself is also varied with respect to the quantities of SS and SH to determine their effect on reactant formation and mechanical strength of TMW-based AABs. The results show that an increased WG content can effectively provide an additional source of reactive silica, contribute to the formation of (C, N)-A-S-H gel products and thus significantly improve the mechanical strength. High strength TMW-WG AABs were attributed to a faster TMW dissolution rate and dense microstructure. Such structures were characteristic of formulations with low alkali modulus (SiO2/Na2O <2) combined with a SS/SH weight ratio of 2.8. For the latter, not only was a characteristic slower strength development with increasing alkali content observed, but there was also a limit of alkali metal concentration (Na2O∼3.1%) beyond which the strength deteriorated. Furthermore, SEM micrographs disclose that unreacted particles of WG reinforced the matrix by acting as a filler.This study was funded by the European Commission Horizon 2020 MARIE Skłodowska-CURIE Research and Innovation Staff Exchange Scheme (grant agreement number 645696). Brunel University London and Thomas Gerald Gray Charitable Trust provided a bursary and fees, respectively to support the first author's PhD study

FPZ evolution of mixed mode fracture in concrete: Experimental and numerical

Digital image correlation (DIC) technique is applied to study the evolution of fracture process zone (FPZ) of mixed mode fracture in concrete. By testing a series of beams of various sizes under four-point shearing, the opening and sliding displacements on the crack surfaces are the fracture process by introducing a crack propagation criterion. The opening and sliding displacements on the crack surfaces obtained from numerical analysis exhibit a reasonable agreement with the experimental results, which verifies the DIC technique presented in the study. By combining experimental observations with numerical simulations, the evolution of the FPZ during the whole crack propagation process of mix mode fracture is investigated and elaborated in depth. The results indicate that the ratio of crack opening to sliding displacement remains approximately constant as crack propagates before reaching a peak load. Meanwhile, the FPZ evolution during the complete fracture process is influenced by the specimen ligament length and the ratio of mode I to II stress intensity factor component. With the decrease of ligament length and the ratio of mode I to II stress intensity factor component, the full FPZ length decreases. However, when the ligament length is less than 63 mm or ratio of mode I to II stress intensity factor component is less than 0.11, the FPZ cannot fully develop, but keeps increasing as crack propagates

Study on accelerated microbial corrosion of concrete by artificially intensified sewage

In this study, the artificially intensified sewage with different levels of chemical oxygen demand (COD) were prepared, and the changes in weight and strength, as well as the micro morphology, mineral compositions and pore structure of concrete specimens immersed in the artificially intensified sewage and water were investigated in comparison. In parallel, the COD, pH, H2S and O2 values, as well as the microbial species and contents of sewage were monitored in the corrosion process. Furthermore, the microbial structure and activities within biofilm developed on concrete surface were also analyzed. The results indicated that the increase of COD concentration of sewage from 300 to 9000 mg/L led to the decline of sewage pH from 6.4 to 2.3 and increase of biofilm thickness from 300 to 800 μm, as well as the substantial growth of dominant microorganisms (Bacteroidete, Proteobacteria, etc.). The drop of pH level and O2 concentration within biofilm also indicated the high activities of sulfate-reducing and sulfur-oxidizing reaction. Correspondingly, after 150 days of immersion both the mass loss and strength decline rate of concrete increased from 0.32% to 1.78% and from 10.6% to 31.7%, respectively. Furthermore, the microstructure of the specimens in sewage became loose and porous. The CH content of specimens in sewage was significant lower than that of specimens in water, and both the cumulative mercury quantity and harmful macropore proportion of specimens in intensified sewage were significantly larger than that of specimens in water, which indicated the chemical reaction between CH and some acid substance. Overall, the sewage concentration increased by 30 times can triple the corrosion rate of concrete. The results obtained are expected to explore a fast and realistic method to simulate the concrete corrosion in full flow sewer pipes

Lightweight Alkali-Activated Material from Mining and Glass Waste by Chemical and Physical Foaming

A foamed alkali-activated material (FAAM), based on tungsten mining waste (TMW) and municipal waste glass (WG) was fabricated by using aluminium powder and organic surfactant foaming agents. The compressive strength and density of the FAAM were investigated in terms of different parameters of production and formulation including curing temperature as well as the dosage of Na2O, foaming agent, foam catalyzing agent and stabilizing agent. FAAM made with aluminium powder consisted of smaller open macropores and exhibited higher compressive strength in comparison with those of larger closed macropores obtained by the organic surfactant counterparts. The final aluminium powder based FAAM reached a 7-day compressive strength in excess of 3 MPa and a density below 0.7 g/cm3 25 . The implementation of an appropriate amount of foam stabilizer led to a further 15% increase in compressive strength, 6% reduction in density and a thermal conductivity below 0.1 W/mK. The FAAM explored in this study represents an ideal material for building envelop insulation.European Commission Horizon 202

Quantifying the influence of elliptical ring geometry on the degree of restraint in a ring test

A novel elliptical ring test method has been proposed to replace the traditional circular ring test method for the purpose of shortening test duration for assessing cracking tendency of concrete and more conveniently examining crack evolution in concrete rings. To further explore the mechanism of this new test method, a numerical model was established to analyse stress development and crack initiation in concrete rings in which a fictitious temperature field simulated the externally applied mechanical effects of concrete shrinkage on concrete causing the same strain as shrinkage does. The proposed numerical model was validated against experimental results and was then used to evaluate the effects of ring geometry on the degree of restraint to concrete. Moreover, a series of numerical experiments were conducted to derive the expression of the degree of restraint to elliptical rings. Through the error analysis of the degree of restraint on concrete properties and ring geometry, the expression was verified so that it can be used to calculate the degree of restraint provided by the internal steel ring. According to the derived expression, the restrained elliptical ring test can be designed to quantitatively simulate the service condition of concrete in an engineering structure more accurately.The financial support of the National Natural Science Foundation of China under the grants of NSFC 51478083 and NSFC 51421064, the UK Engineering and Physical Sciences Research Council under the grant of EP/I031952/1, the Fundamental Research Funds for the Central Universities of China under the grants of DUT17LK06, and the Natural Science Foundation of Liaoning Province of China under the grant of 20170540183 is gratefully acknowledged

A Review on Mineral Waste for Chemical-activated Binders: Mineralogical and Chemical Characteristics

This review discusses the potential of alkali-activated materials obtained from mineral waste. A brief historical background on alkali-activated materials is presented. Recent advances in the develop-ment of binders obtained from mineral wastes and alkali-activated solutions are described. The scope of this state of the art review is to identify current knowledge in support that mineral waste can be used for the production of alkali-activated binders. In addition, this review identifies the chemical activators that can be effectively utilized for such purposes in the age when wastes are still viewed by industry as dis-posable. Some mineral wastes which are discussed can be viewed as a new resource for recycling and recovery which will offer important economic and social benefits.European Commission under Horizon 2020, Marie Skłodowska-Curie Actions, Research and Innovation Staff Exchange (RISE), by REMINE – “Reuse of Mining Waste into Innovative Geopolymeric-based Structural Panels, Precast, Ready Mixes and Insitu Applications”, Portuguese national funds through FCT - Foundation for Science and Technology, IP, within the research unit C-MADE, Centre of Materials and Building Technologies (CIVE-Central covilhã-4082), University of Beira Interior, Portugal

Mechanical and Thermal Performance of Macro-Encapsulated Phase Change Materials for Pavement Application

Macro-encapsulated phase change material (PCM) lightweight aggregates (ME-LWA) were produced and evaluated for their mechanical and thermal properties in road engineering applications. The ME-LWAs were first characterised in terms of their physical and geometrical properties. Then, the ME-LWAs were investigated in detail by applying the European Standards of testing for the Bulk Crushing Test and the Polished Stone Value (PSV) coefficient as well as Micro-Deval and laboratory profilometry. In addition, the thermal performance for possible construction of smart pavements with the inclusion of ME-LWAs for anti-ice purposes was determined. The crushing resistance of the ME-LWAs was improved, while their resistance to polishing was reduced. Thermal analysis of the encapsulated PCM determined it to possess excellent thermal stability and a heat storage capacity of 30.43 J/g. Based on the research findings, the inclusion of ME-LWAs in surface pavement layers could be considered a viable solution for the control of surface temperatures in cold climates. Road safety and maintenance could benefit in terms of reduced ice periods and reduced treatments with salts and other anti-ice solutions.variou

Preparation conditions for the synthesis of alkali-activated binders using tungsten mining waste

This study evaluated the results of preparation conditions for the production of an alkali-activated binder (AAB) based on a binary mixture of tailings from tungsten mine waste (TMW), and waste glass (WG) activated with a mixture of sodium silicate (SS) and sodium hydroxide (SH). A 40% by weight WG increased the amorphous nature of the binary blend by 21% without initiating the alkali-silica reaction. The SS-SH activator solution was subjected to a variation of mixing times, and its sensitivity was measured using temperature monitoring and Fourier transform infrared spectroscopy (FTIR). After 20 min of mixing, the SS-SH activator solution showed a 3.13°C reduction in temperature and a 21.4% increase in unbound water content, and as a result imparted a 26% drop in the mechanical strength of TMW-WG AAB at 28 days. The TMW-WG AAB was also determined to develop the highest compressive strength when cured at 80°C for 24 h in sealed conditions. The following conditions, supported by X-ray diffraction (XRD) and FTIR, are responsible for the most significant dissolution of the aluminosilicate oxides.Partial financial support from the European Commission Horizon 2020’s MARIE Skłodowska-CURIE Research and Innovation Staff Exchange Scheme through the Grant 645696 (i.e., REMINE project) is greatly acknowledged. The first author thanks Thomas Gerald Gray Charitable Trust and Brunel University London for providing fees and a bursary to support his Ph.D. study

Sustainable Calcination of Magnesium Hydroxide for Magnesium Oxychloride Cement Production

Effects of varying calcination conditions on the chemical and physical properties of magnesium oxide (MgO), an essential component of magnesium-based cement, were investigated using the more sustainable precursor material of magnesium hydroxide [Mg(OH)2Mg(OH)2]. Extremely pure and thus more reactive MgO was obtained using a 17.6% less-energy-intensive calcination regime compared with industrial-grade MgO obtained from the calcination of dolomitic lime. As a result, the magnesium oxychloride cement (MOC) that was produced from the sustainably sourced MgO obtained a 50% increase in flexural strength and 22% increase in compressive strength. This was mostly due to its homogenous microstructure, consisting predominantly of the phase-5 hydration product, verified visually using a scanning electron microscope (SEM) and crystallographically using X-ray diffraction (XRD). Based on these findings, it has been revealed that the calcination therapies currently used in industry are impractical for both economic and sustainability purposes; MgO can be manufactured in a more sustainable and thus more competitive means, as discovered in this study.European Commission Horizon 2020 Research and Innovation Programm

An experimental study on crack propagation at rock-concrete interface using digital image correlation technique

The digital image correlation (DIC) technique is employed to investigate the fracture process at rock-concrete interfaces under three-point bending (TPB), and four-point shearing (FPS) of rock-concrete composite beams with various pre-crack positions. According to the displacement fields obtained from experiment, the crack width, and propagation length during the fracture process can be derived, providing information on the evolution of the fracture process zone (FPZ) at the interface. The results indicated that under TPB, the fracture of the rock-concrete interface is mode I dominated fracture although slight sliding displacement was also observed. Under FPS, the mode II component may increase in the case of a small notched crack length-to-depth ratio, resulting in the crack kinking into the rock. It was also observed that the FPZ length at the peak load is far longer for a specimen under FPS than under TPB.The financial support of the National Natural Science Foundation of China under the grants of NSFC 51478083, NSFC 51421064 and NSFC 51109026, and partial financial support from the UK Royal Academy of Engineering through the Distinguished Visiting Fellow Scheme under the grant DVF1617_5_21 is gratefully acknowledged