Aggregate Production Research Articles

The impact of slag on the process of geopolymerization and the mechanical performance of mine-tailings-based alkali-activated lightweight aggregates

Alkali-activated lightweight aggregates (LWAs) made of alkali-activated aluminosilicate-rich mine tailings (MTs) offer a promising alternative to natural lightweight aggregates. The comprehensive investigation of lightweight aggregate production using aluminosilicate-rich MTs in combination with commercial slag as a reactive aluminosilicate remains largely unexplored. In this study, mixtures of MTs and slag were pelletized through the application of a pan pelletizer machine. The study focused on examining the impact of different slag concentrations on the chemical, physical, mechanical, mineralogical, and morphological properties of the produced LWAs. Furthermore, a comparison was made between the physical and mechanical characteristics of the resulting LWAs and those of flay-ash (FA)-based LWAs. The results revealed that the inclusion of slag in LWAs, as compared to FA, led to the production of LWAs with superior physical and mechanical properties. Specifically, as the slag content increases, the water absorption, dissolution, and porosity of LWAs significantly decreased, while the bulk density and compressive strength increased. It is important to note that these changes occur without affecting the specific gravity of the LWAs. The scanning electron microscope (SEM) images clearly showed that the addition of slag, similar to FA, especially at concentrations of more than 20% and higher, promoted uniform geopolymerization within the specimens. Furthermore, the energy-dispersive X-ray spectroscopy (EDS) analysis revealed that all LWAs with concentrations of 20% slag and higher exhibited a Si:Al ratio exceeding three, indicating a higher likelihood of geopolymer backbone formation. The X-ray diffraction (XRD) and Fourier-transform infrared spectroscopy (FTIR) analyses revealed that the alkali activation process led to the depletion of gypsum, originally present in the MTs, and the emergence of sodalite and zeolite in the LWAs. Thermogravimetric analysis (TGA) tests provided additional confirmation of the ongoing geopolymerization process in slag-based LWAs, particularly those containing 20% slag or higher.

Magnetic Separation of Lunar Regolith as its Beneficiation for Construction Effort on the Moon

Abstract A concept of magnetic separation of regolith for production of lunar aggregate is presented in the paper. Future construction effort on the Moon will require significant amounts of concrete-like composites. The authors formulate a hypothesis that magnetic separation of regolith would be a very efficient beneficiation procedure solving multiple civil engineering problems associated with properties of raw lunar soil. For the research program, 10 lunar soil simulants were used. The magnetic separation was feasible in majority of cases. Acquired lunar aggregate would be useful for both concrete-like composite production and covering the surface of a habitat. The aims of future research are pointed out in the paper.

Quantifying the Macroeconomic Impact of COVID-19-Related School Closures through the Human Capital Channel

This paper uses a new measure of human capital, which distinguishes both quality and quantity components, to estimate the long-term effect of the COVID-19-related school closures on aggregate productivity through the human capital channel. Productivity losses build up over time and are estimated to range between 0.4% and 2.1% after 45 years, for 12 weeks and 2 years of school closure, respectively. These results appear to be broadly consistent with earlier findings in the literature. Two opposing effects might influence these estimates. Online teaching would lower economic costs while learning losses in tertiary education (not considered here) would inflate them. Policies aimed at improving the quality of education and adult training will be needed to offset or, at least, alleviate the impact of the pandemic on human capital.

Production, properties and life cycle assessment of artificial lightweight aggregates produced with corn straw ash (CSA) and concrete slurry waste (CSW)

Open burning of corn straw has been a long-standing environmental problem in developing agricultural countries. The development of the concrete material industry supplies a feasible consumption outlet for the bulk solid wastes from agriculture and construction fields. In this study, therefore, corn straw and concrete waste were turned into available cementitious materials: corn straw ash (CSA) and concrete slurry waste (CSW) powder. Then CSA and CSW were reused to be artificial lightweight aggregates (ALAs) by cold-bonding pelletization and carbonation curing. A multi-criteria decision-making model for ALAs was finally proposed to comprehensively evaluate the technical, environmental, and economic factors and select the most valuable candidate. The findings indicate that it is technically feasible to produce ALAs by using CSA and CSW. The optimal mechanical parameters of the disc granulator are 35 rpm and 45° inclination in the cold-bonding pelletization process of ALA production. From a technical point of view, with the increase of CSA content in ALAs, the strength of ALAs increased first and then decreased, reaching the optimum value of 14.2 MPa with the addition of 5% CSA. According to the sustainability score, the descending order of ALAs is C1, C4, C3, C2 and C0. Sustainability results show that the ALAs of the mixture of 5 wt% CSA and 95 wt% CSW is the optimal solution. The ALAs with dual-function in terms of reducing CO2 emissions and capturing CO2 is a promising candidate for low-carbon concrete production. The decision model could be suitable for the sustainable selection of artificial aggregates or recycling construction materials.

Import License, Misallocation, and Aggregate Total Factor Productivity in the Chinese Steel Industry*

This paper examines how import license restriction‐induced resource misallocation affects industry aggregate total factor productivity (TFP). We apply a recently proposed consistent estimator to micro‐level data from the Chinese steel industry, considering material price heterogeneity. We back out the potential extent of misallocation, finding the importers' TFP is not significantly higher than that of the nonimporters, and resource misallocation caused by the iron‐ore import license lowers aggregate productivity. Our analysis indicates that removing the trade barrier counterfactually would increase the industrial TFP by 76.8%, on average.

Informality and aggregate labor productivity growth: Does ICT moderate the relationship?

This paper attempts to understand whether digitization, measured in terms of ICT capital and penetration of the internet, helps reduce the negative impact of informality on labor productivity growth, especially in emerging & developing countries. Informality is argued to be a drag on productivity growth in emerging & developing countries. We argue that increased use of digital technologies can help informal sector reduce transaction and coordination costs; enhance the linkages between the informal and formal sectors; facilitate the integration of the informal sector in the global value chain; and also increase the potential for the formalization of the economy in general - all of these are likely to contribute to aggregate productivity growth. Our econometric analysis using panel data for 118 countries from 1997-2017 provides some evidence of ICT capital deepening helping to reduce informality's negative impact on aggregate productivity growth. However, the moderating effect is modest compared to the magnitude of the negative impact of informality, indicating the need for a faster and more intense digitization efforts in emerging & developing economies. Moreover, investments in complementary factors including skills and infrastructure are imperative to fully unleash the potential of ICT in reducing the negative impact of informality.

PH-controlled sulfuric acid washing enhancing heavy metal stabilization in lightweight aggregate production from municipal solid waste incineration fly ash

Municipal solid waste incineration fly ash (FA) is a pressing issue in urban development. In FA treatment, washing is a common dechlorination pre-treatment. During washing, considerable heavy metal would leach due to the abundant alkaline substances, posing challenges to the heavy metal stabilization. Also, with high alkalinity, FA has potential to co-dispose of waste sulfuric acid (hazardous waste). Addressing these, our study presented a novel pH-controlled sulfuric acid washing for FA dechlorination during the sintering preparation of lightweight aggregate (LWA). It was aimed at enhancing heavy metals stabilization and enabling the co-recycling of FA and waste sulfuric acid. By controlling a pH of 10.50 during sulfuric acid washing, the leaching rate of Pb, Cd, Zn, Cu, Ba, and Cr was below 2%, which was a marked improvement over conventional water washing. Sulfuric acid washed FA (SFA) can be used to produce standard-compliant LWA by sintering with bentonite and SiC. The SFA-based LWA stabilized heavy metals more effectively than LWA using FA and water-washed FA. At a 30 wt% addition rate, the stabilized rate of Pb and Cd increased from 11.7% (using FA) to 72.4% (using SFA), and from 6.3% (using FA) to 49.0% (using SFA), respectively. During washing and sintering, XPS analysis further investigated the transformation of Pb, Cu, and Zn into stable states (Pb-glass, Cu2O/CuO, and ZnAl2O4), enhancing their stabilization. Our study introduces a novel method for co-recycling FA and waste sulfuric acid, offering enhanced environmental sustainability and deeper insights into the mechanism of heavy metal stabilization.

Foreign Exchange Rate Management and Macroeconomic Performance in Nigeria: Autoregressive Distributed Lag (ARDL) Bound Testing Approach

This paper examined the impact of real exchange rate on economic performance in Nigeria for the period (1981-2021) using a modified and extended aggregate production model and Autoregressive Distributed Lag (ARDL) Bound Testing Approach for analysis. The results indicated that the real exchange rate had a positive and significant effect on economic performance in the long run and a negative but insignificant impact in the short run. As for the control variables, in the long-run capital stock, labour force and foreign direct investment had a positive and significant impact on economic performance, real interest rate and broad money supply exerted a positive but insignificant effect on economic performance, whereas inflation rate and trade openness displayed a negative but insignificant effect on economic performance. In the short-run, capital stock, inflation rate, foreign direct investment and broad money supply impacted positively on economic performance, while labour force, real interest rate, trade openness and government expenditure had a negative effect. It was recommended, among others, that government policies should be directed toward increasing productivity in Nigeria; and that Nigeria should refine a good chunk of crude oil locally, increase agricultural production and revive the manufacturing sector for increased manufacturing output to meet the country’s need for petroleum, agricultural and manufactured products.

A review on aggregate production planning under uncertainty: Insights from a fuzzy programming perspective

It is essential to address uncertainties in different production planning strategies, notably aggregate production planning, which is a critical medium-term strategy. In this context, uncertainties typically appear as vagueness or impreciseness, leading to the prevalent adoption of fuzzy numbers to represent uncertain attributes. However, despite its significance, no dedicated study has exclusively examined aggregate production planning from the perspective of fuzzy mathematical programming. Thus, this review analyzed the published literature on fuzzy aggregate production planning and presented a classification scheme. In this review, various digital databases were explored, yielding a selection of 44 most relevant articles. Furthermore, this study thoroughly analyzed and reported various characteristics such as modelling and solution approaches, objective functions, fuzzy attributes, membership functions, aggregate operators, etc. The review revealed that fuzzy linear programming and fuzzy goal programming were the most utilized modelling approaches, with optimization solvers and metaheuristics standing out as the predominant solution approaches. Additionally, triangular fuzzy numbers emerged as the preferred method for the crisp formulation of fuzzy numbers. This review provides valuable insights into the existing research on fuzzy aggregate production planning and offers guidance to researchers to streamline their future research endeavors.

Sustainable strategies for reducing environmental impact in concrete block manufacturing: a comprehensive life cycle assessment

ABSTRACT This study delves into the environmental impact of concrete block manufacturing, focusing on embodied energy, CO2 emissions, and water consumption. The research addresses the pressing need to understand the ecological implications of concrete block production for sustainable development. We use a comprehensive life cycle assessment (LCA) methodology to assess embodied energy, CO2 emissions, and water consumption throughout the concrete block production lifecycle. The study draws upon primary data from industry sources and secondary data from research studies to ensure accuracy and reliability. Findings reveal that concrete block manufacturing demands significant energy, primarily attributed to cement and aggregate production and transportation. The process generates substantial CO2 emissions from limestone calcination during cement production. Water consumption is a critical concern during the curing and washing stages. The study explores diverse strategies and technologies aimed at mitigating the environmental impact. Implications of this research highlight the importance of adopting sustainable practices within the concrete block industry to address environmental impact. This study emphasizes the concrete block industry's potential to contribute to a greener and more sustainable future by implementing environmentally friendly measures. This study's comprehensive analysis and actionable recommendations aim to attract readers and stakeholders, encouraging further interest and investment in sustainable practices.

Language diversity, gender inequality, and aggregate productivity in Canada

AbstractIdentifying sources of barriers to occupational mobility is central to evaluating the efficiency of the labor market. In this paper, we present an augmented Roy model in which workers self‐select into occupations, subject to labor market barriers that are specific to their socio‐linguistic group. Our findings provide evidence of differences in labor market outcomes across gender and linguistic groups in Canada. We argue that these differences could be attributed to barriers to labor mobility and that the reduction of these disparities would result in higher aggregate productivity in the country. In the augmented Roy model, the frictions result in inefficient allocation of labor across occupations. The study quantifies the change in aggregate productivity that would result from reducing the friction. The elimination of the frictions increased aggregate output on average by 6.2% and 4.4% in 1991 and 2011, respectively. This finding highlights the importance of reducing language barriers and gender inequality in the labor market. We provide policy recommendations for mitigating the disparities in socioeconomic outcomes between gender and linguistic groups.

Allocative Efficiency between and within the Formal and Informal Manufacturing Sectors in Zimbabwe

Abstract Resource misallocation has the potential to reduce aggregate total factor productivity and undermine industrial development. Aggregate productivity losses are found to be particularly pronounced in emerging economies where large market frictions impede efficient resource allocation. Available estimates, however, almost entirely exclude firms in the informal sector that in some countries, such as Zimbabwe, make up a high share of overall production and employment. The exclusion of informal firms can result in either an over- or under-estimate of the aggregate productivity losses from misallocation. This paper, therefore, uses firm-level survey data to analyze how market distortions contribute to the misallocation of resources within and between the formal and informal manufacturing sectors in Zimbabwe. Applying the approach developed by Hsieh and Klenow (2009) to firm-level microdata, the results reveal extensive resource misallocation in both the formal and informal manufacturing sector. Market shares of informal firms are found to be low relative to their productivity—an outcome associated with relatively large capital market distortions. Misallocation is also more pronounced among relatively productive firms, thus exacerbating aggregate losses in total factor productivity (TFP). Estimates indicate that aggregated gains in TFP of 151.4 percent can be realized through efficient resource allocation.

Glibenclamide-Loaded Nanoparticles Reduce NLRP3 Inflammasome Activation and Modulate miR-223-3p/miR-7-1-5p Expression in THP-1 Cells.

The anti-hyperglycemic drug glibenclamide (Glb) might represent an interesting therapeutic option in human neurodegenerative diseases because of its anti-inflammatory activity and its ability to downregulate activation of the NLRP3 inflammasome. Bi-functionalized liposomes that can cross the blood-brain barrier (BBB) may be used to release Glb into the central nervous system (CNS), overcoming its poor solubility and bioavailability. Here, we analyzed in vitro the effect of Glb-loaded nanovectors (GNVs) and Glb itself on NLRP3 inflammasome activation using a lipopolysaccharide- and nigericine-activated THP-1 cell model. Apoptosis-associated speck-like protein containing a CARD (ASC) aggregation and NLRP3-related cytokine (IL-1β, caspase 1, and IL-18) production and gene expression, as well as the concentration of miR-223-3p and miR-7-1-5p, known to modulate the NLRP3 inflammasome, were evaluated in all conditions. Results showed that both GNVs and Glb reduced significantly ASC-speck oligomerization, transcription and translation of NLRP3, as well as the secretion of caspase 1 and IL-1β (p < 0.05 for all). Unexpectedly, GNVs/Glb significantly suppressed miR-223-3p and upregulated miR-7-1-5p expression (p < 0.01). These preliminary results thus suggest that GNVs, similarly to Glb, are able to dampen NLRP3 inflammasome activation, inflammatory cytokine release, and modulate miR-223-3p/miR-7-1-5p. Although the mechanisms underlying the complex relation among these elements remain to be further investigated, these results can open new roads to the use of GNVs as a novel strategy to reduce inflammasome activation in disease and rehabilitation.

On the geography of inequality: labour sorting in general equilibrium

ABSTRACT We study how cities’ amenities and limited housing supply contribute to aggregate wage inequality and affect housing prices through the sorting of heterogeneous skilled workers. We develop a general equilibrium model where workers differ along a continuum of skills and compete for limited housing. Our analysis suggests that spatial sorting accounts for 7.5% of the aggregate wage dispersion, increases average housing prices by 20–40% in constrained cities, and makes the economy 1.9% more productive. In addition, we evaluate a place-based policy that aims to expand the supply of houses in 1% of constrained cities and find that it improves aggregate productivity between 0.2% and 0.4%. However, the place-based policy has the unintended consequence of aggravating aggregate wage inequality by the same magnitude.

Aggregate productivity slowdown and share of temporary workers

Aggregate productivity slowdown and share of temporary workers

Absolute configuration assignment of highly fluorinated carboxylic acids via VCD and MRR spectroscopy

Chiral analysis has become a crucial step in studying the stereospecific synthesis of Active Pharmaceutical Ingredients (APIs). Both Vibrational Circular Dichroism (VCD) and Molecular Rotational Resonance (MRR) spectroscopy are capable of determining absolute configurations (ACs) via comparison of experimental and calculated data. In this regard, each technique has its own caveats. In VCD analysis, accurate prediction of the normal modes as well as rigorous conformational searches of both the analyte and potential (self-)aggregation products are required to optimally match experimental spectra. In MRR analysis, chiral species are resolved through complexation with a chiral tag to prepare spectrally distinct diastereomeric complexes. Although individual complex isomers can be distinguished, spectral assignments need to be matched to unique isomer geometries for unambiguous AC assignment. In this work, the ACs of two highly fluorinated carboxylic acids were successfully assigned using VCD and MRR spectroscopy. In the VCD analysis, the M06-2X functional was demonstrated to be superior to B3LYP and B3LYP-GD3 in accurately predicting the C–F normal modes and both monomeric and dimeric spectral contributions were observed. In a similar analysis with broadband MRR, most experimentally identified geometries had more than one possible computational match. Nevertheless, careful consideration of the chiral tag, as well as additional isomer assignments, resulted in successful assignment of the AC. This comparative study demonstrates the power of contemporary VCD analysis and the unique contributions of MRR to the analytical toolbox.

Suitability of marble powders in production of high strength concrete

A tremendous amount of non-biodegradable waste is created during mining and processing tasks of layered stones like marble. Over time, this has become a global problem because it harms the environment in multiple ways. Hence, it is necessary to find an alternate way to securely dispose and reuse marble wastes. The construction sector is one of the significant consumers of natural resources for the production of material binders and aggregates. As a result, in recent years, number of researchers have carried out studies in which various kinds of marble waste have been incorporated into concrete with the intention of substituting either cement or aggregates or both. This paper presents the effect of two locally sourced waste marble powders Kadapa marble powder (KMP) and Bethamcherla marble powder (BMP) as partial replacement of cement on mechanical and durability properties of high strength concrete (HSC). Their effect at different replacement levels in HSC is evaluated in compressive, indirect tensile and flexural strengths, elastic modulus, chloride penetration resistance and freeze–thaw durability properties. Micro-structural investigation is also conducted to evaluate their impact on the matrix of HSC containing waste marble powders as additional cementitious materials. Results show that the HSC consisting of KMP and BMP content of 10% and 15%, respectively exhibited higher mechanical and durability properties than the control HSC. Micro-structural investigation also supports this finding. It can be concluded that the use of marble powders as partial replacement of cement does not have any adverse impact on the properties of concrete. The use of KMP and BMP reduces the vast amount of energy required to produce cement, cost and time with reduction in environmental hazards.

Optimal allocations in growth models with private information

This paper considers a class of growth models with idiosyncratic human capital risk and private information about individual effort choices (moral hazard). Households are infinitely-lived and have preferences that allow for a time-additive expected utility representation with a one-period utility function that is additive over consumption and effort as well as logarithmic over consumption. Human capital investment is risky due to idiosyncratic shocks that follow a Markov process with transition probabilities that depend on effort choices. The production process is represented by an aggregate production function that uses physical capital and human capital as input factors. We show that constrained optimal allocations are simple in the sense that individual effort levels and individual consumption growth rates are history-independent. Further, constrained optimal allocations are the solutions to a recursive social planner problem that is simple in the sense that exogenous shocks are the only state variables. We also show that constrained optimal allocations can be decentralized as competitive equilibrium allocations of a market economy with a simple tax- and transfer scheme. Finally, it is always optimal to subsidize human capital investment in the market economy.

Effect of microwave radiation temperature and content of different solid waste on the microstructure and physicomechanical properties of lightweight aggregates

Microwave radiation in the production of lightweight aggregates, it has not yet been thoroughly explored. Therefore, the main goal of the research is to analyze the possibility of using various types of waste, such as waste rock (0–30 %) and glass cullet (10 %), fly ash (50–80 %) and waste solution using different microwave temperature (1000, 1050, 1100 °C) in order to obtain lightweight aggregates. Above factors and, chemical and mineral composition of the waste materials, affect the microstructure and physico-mechanical parameters of the aggregates.). The thermophysical behavior (DTG/TG), grain composition, chemical composition (XRF), phase composition (XRD) and microstructure (SEM, μ-CT) were analyzed. The microstructure, as well as the related characteristics of aggregates, i.e. water absorption, density, and compressive strength, depend on the sintering temperature, chemical composition and mineral waste raw material. The best properties were obtained for a raw material mixture containing 80 % coal fly ash, 10 % glass cullet, 10 % clay and 48 g of the waste solution (per 100 g of raw mixture), sintered in the microwave at 1100 °C. The aggregates were characterized by water absorption of 6.96 %, bulk of 1.70 g/cm3, loose bulk density 0.60 g/cm3, and compressive strength 5.95 MPa. Closed porosity determined by micro-CT was 8.41 %, open - 0.24 %, sphericity 0.62. The total porosity depends on the loose bulk density and particle density of lightweight aggregates.Furthermore, washout tests meet environmental requirements. The proposed technology, moreover, enables a short time of thermal processing of raw materials, and thus energy savings and a sustainable approach to the production of green pellets. Thanks to the high strength, the obtained aggregates can replace commercial aggregates.

A REVIEW OF THE EFFECT OF ADDITIVES ON THE MECHANICAL PROPERTIES OF LIGHTWEIGHT CONCRETE

Many organizations around the world have recognized lightweight, long-lasting, cost and environmentally-friendly construction materials as a future necessity. The lightweight concrete is manufactured mainly either by replacing the original aggregate with lightweight aggregate or addition foam production materials to concrete mixtures. These additions lead to a decrease in the lightweight concrete density and change mechanical properties such as compressive strength. Therefore, there is much experimental research has been conducted to add different material types that can improve lightweight concrete compressive strength while maintaining low density. In this review, the effect of various additions such as steel fiber, product waste materials, and nano-materials on the lightweight concrete compressive strength and density have been explained. The various effects of these additive materials on lightweight concrete properties, some additives lead to improving the properties of lightweight concrete, while other materials lead to a decrease in those properties, and this depends on the type and amount of material additive, the method lightweight concrete manufacturing, and their mixture composition.