Aggregate Production Research Articles

Productivity Paradox in Africa: Does Digitalization Foster Labor Productivity in African Economies?

AbstractHow the advancement of information and communications technologies (ICT) and digitalization affect labor productivity is subject of an ongoing debate. While parts of the literature find the expected positive effects, other studies have found no effect, resulting in the so-called productiviy paradox. As most of the studies have focused on economically advanced economies such as OECD countries, evidence for less developed economies has been sparse. We use a digitalization composite index from a balanced panel of 40 Sub-Saharan African (SSA) economies, using data from 2006 to 2021, to assess the effect of digitalization on aggregate labor productivity in SSA economies. We employ generalized least squares (GLS) and system generalized methods of moments (GMM) methods to capture the effects of digitalization on labor productivity levels in agriculture, manufacturing, and service sectors. Our results show a weak association between digitalization and overall labor productivity. However, when sectors are analyzed separately, digitalization has a positive effect on labor productivity in agriculture and manufacturing sectors, whereas we find evidence for the productivity paradox in the service sector, with even a negative effect of digitalization on labor productivity.

Artificial lightweight aggregate made from alternative and waste raw materials, hardened using the hybrid method

Lightweight aggregates are a material used in many industries. A huge amount of this material is used in construction and architecture. For the most part, lightweight construction aggregates are obtained from natural resources such as clay raw materials that have the ability to swell at high temperatures. Resources of these clays are limited and not available everywhere. Therefore, opportunities are being sought to produce lightweight artificial aggregates that have interesting performance characteristics due to their properties. For example, special preparation techniques can reduce or increase the water absorption of such an aggregate depending on the needs and application. The production of artificial lightweight aggregate using various types of waste materials is environmentally friendly as it reduces the depletion of natural resources. Therefore, this article proposes a method of obtaining artificial lightweight aggregate consolidated using two methods: drum and dynamic granulation. Hardening was achieved using combined methods: sintering and hydration, trying to maintain the highest possible porosity. Waste materials were used, such as dust from construction rubble and residues from the processing of PET bottles, as well as clay from the Bełchatów mine as a raw material accompanying the lignite overburden. High open porosity of the aggregates was achieved, above 30%, low apparent density of 1.23 g/cm3, low leachability of approximately 250 µS. The produced lightweight aggregates could ultimately be used in green roofs.

Preparation of carbon-negative artificial lightweight aggregates by carbonating sintered red mud (SRM): CO2 sequestration, microstructure and performance

This study investigated the possibility of employing CO2 curing for the production of cement-free artificial aggregates using low-value sintering red mud (SRM) and fly ash (FA). The effects of different curing methods (CO2 and air curing) and varying FA dosages on the properties of SRM artificial aggregates were analyzed. For SRM artificial aggregates subjected to CO2 curing, the calcium silicates depleted accompanied by precipitation of calcite and aragonite. The carbonated SRM artificial aggregates (CRAAs), exhibited a denser microstructure, with the pores of the SRM filled with carbonation products. For CRAAs with 100 wt% SRM, up to 9.67 wt% CO2 was sequestered and in turn produced calcium carbonate, which resulted in a 149.0% enhancement in crushing strength and a 29.5% reduction in water absorption compared to the similar aggregates under air curing. The introduction of FA led to an accelerated strength development in the CRAAs during subsequent air curing, which was attributed to the formation of carboaluminates as a result of the hydration between the carbonation products and aluminates derived from FA. From the perspective of environment, CRAAs was carbon-negative, with a potential reduction of up to 40.2 kg of CO2 per ton of CRAAs production, presenting a cleaner and sustainable alternative to natural aggregates. The results of the study provided a feasible solution for the effective treatment of SRM on a large scale and can be used as a reference for subsequent studies.

Plant litter as a heavy metal migration strategy following application of sewage sludge to subtropical forest soils

The environmental risks of migration of heavy metals (HMs) following applications of sewage sludge (SS) to forest soils are garnering increased attention. Plant litter at the forest floor may modify HM migration pathways through impacts on soil aggregates and water/soil erosion; however, HM migration responses to plant litter are poorly understood. The aim of this study was to determine the effects of plant litter cover on HMs migration, and water and soil erosion following the application of SS to subtropical forest soils. Effects of addition of SS along and SS plus plant litter at 0.75 or 1.5 kg m−2 on the migration of cadmium, chromium, copper, nickel, lead, and zinc in surface runoff, soil interflow, and sediments were quantified across nine simulated rainfall events in a laboratory experiment and following natural intense rain events in a field experiment. Addition of SS elevated HM concentrations in surface runoff by 38.7 to 98.5 %, in soil interflow by 48.3 to 312.5 %, and in sediment by 28.5 to 149.4 %, and increased the production of sediment aggregates <0.05 mm that led to greater cumulative migrations of HMs in surface runoff and sediment; sediment accounted for 89.5 % of HM migrations. Addition of plant litter reduced cumulative migration of HMs by 87.1–97.27 %; however, the higher rate of plant litter led to a decrease in surface runoff and sediment yield, and an increase in soil interflow. Addition of plant litter shifted the main pathway of HM migration from sediment to surface runoff and soil interflow. The potential ecological HM risk index was “low” for each treatment. We found consistency in HM concentrations and migrations via surface runoff between the field and laboratory experiments. Overall, the addition of plant litter with SS mitigated soil erosion and reduced total migration of HMs, resulting in a 88.7–97.3 % decrease in the ecological risk index of the six HMs. We conclude that the addition of plant litter may provide a management strategy for the mitigation of HM risks to environmental safety for the disposal of SS in subtropical forest systems.

Quantifying the productivity effects of education-job mismatch: a cross-country analysis

ABSTRACT This study addresses the relationship between education-job mismatch and aggregate labor market performance in a cross-country setting. We examine the effect of education-job mismatch on aggregate productivity across 15 countries using data from the OECD Survey of Adult Skills (PIAAC). We measure mismatch levels and compute their incidence across countries. Next, the paper develops a model linking mismatch to aggregate productivity. In the model the allocation of labor across the types of mismatch is derived from the endogenous process. The findings show that reducing mismatch results in increases in output per capita. This provides evidence for an important role of the allocation of workers according to jobs that match their fields of study and qualification levels not only for individual earnings but also for aggregate outcomes.

Family migration and structural transformation

AbstractThis paper integrates the migration decisions of married couples into a multi‐sector spatial model, investigating their impact on structural transformation, productivity and gender wage gap. Focusing on China, a country characterized by a higher share of agricultural employment and a lower share in services compared with countries with similar income, we uncover a significant gender gap in migration costs among rural married couples. Furthermore, while migration costs have decreased for all demographic groups from 2000 to 2010, the decline was least pronounced for married couples when both partners left agriculture. We find that reducing migration costs for married couples who migrate together would lead to a decline in agricultural employment, a rise in service sector employment, an increase in aggregate productivity and a narrowing of the gender wage gap. Eliminating the gender differences in migration costs would also increase service sector employment and reduce the gender wage gap.

Occupational choice, human capital and financial constraints

AbstractWe study the aggregate productivity effects of firm‐level financial frictions. Credit constraints affect not only production decisions but also household‐level schooling decisions. In turn, entrepreneurial schooling decisions impact firm‐level productivities, whose cross‐sectional distribution becomes endogenous. In anticipation of future constraints, entrepreneurs underinvest in schooling early in life. Frictions lower aggregate productivity because talent is misallocated across occupations and capital is misallocated across firms. Firm‐level productivities are also lower due to schooling distortions. These effects combined account for between 36% and 68% of the US–India aggregate productivity difference. Schooling distortions are the major source of aggregate productivity differences.

What if? The macroeconomic and distributional effects for Germany of a stop of energy imports from Russia

AbstractThis paper discusses the economic effects of a potential cut‐off of the German economy from Russian energy imports. We use a multi‐sector open‐economy model and a simplified approach based on an aggregate production function to estimate the effects of a shock to energy inputs. We show that the effects are likely to be substantial but manageable because of substitution of energy imports and reallocation along the production chain. In the short run, a stop of Russian energy imports would lead to an output loss relative to the baseline situation, without the energy cut‐off, in the range 0.5% to 3% of GDP.

The growth rate of senile plaques is determined by the competition between the rate of deposition of free Aβ aggregates into plaques and the autocatalytic production of free Aβ aggregates

The formation of amyloid beta (Aβ) deposits (senile plaques) is one of the hallmarks of Alzheimer’s disease (AD). This study investigates what processes are primarily responsible for their formation. A model is developed to simulate the diffusion of amyloid beta (Aβ) monomers, the production of free Aβ aggregates through nucleation and autocatalytic processes, and the deposition of these aggregates into senile plaques. The model suggests that efficient degradation of Aβ monomers alone may suffice to prevent the growth of senile plaques, even without degrading Aβ aggregates and existing plaques. This is because the degradation of Aβ monomers interrupts the supply of reactants needed for plaque formation. The impact of Aβ monomer diffusivity is demonstrated to be small, enabling the application of the lumped capacitance approximation and the derivation of approximate analytical solutions for limiting cases with both small and large rates of Aβ aggregate deposition into plaques. It is found that the rate of plaque growth is governed by two competing processes. One is the deposition rate of free Aβ aggregates into senile plaques. If this rate is small, the plaque grows slowly. However, if the rate of deposition of Aβ aggregates into senile plaques is very large, the free Aβ aggregates are removed from the intracellular fluid by deposition into the plaques, leaving insufficient free Aβ aggregates to catalyze the production of new aggregates. This suggests that under certain conditions, Aβ plaques may offer neuroprotection and impede their own growth. Additionally, it indicates that there exists an optimal rate of deposition of free Aβ aggregates into the plaques, at which the plaques attain their maximum size.

Short communication: Bifidobacterium abundance in the faecal microbiota is strongly associated with milk traits in dairy cattle

The performance of dairy cows is influenced by the microbial communities hosted within their digestive tract. While the rumen microbiota has long been associated with host phenotypes, the impact of the faecal microbiota remains elusive. In this study, we collected 697 faecal samples from commercial Holstein cows and analysed them with 16S rRNA gene analyses. For each animal, routinely recorded data, i.e., milk yield, fat yield, protein yield, fat content, protein content, and an aggregate production trait (pINEL) based on the French economic dairy index, were available to assess the links between the faecal microbiota and host production. Our findings revealed a strong and significant association between the structure of the bacterial and prokaryote community (β-diversity) and dairy production. In addition, differential abundance analyses identified 48 genera whose abundances were significantly associated with pINEL, milk, fat and protein yield. Among these genera, the increased abundance of Bifidobacterium, and particularly an amplicon sequence variant with a 16S rRNA V3-V4 gene region identical to B. globosum and B. pseudolongum, was found to be the most important for high-yielding animals. Bifidobacterium seemed to be a potential key member of the bovine faecal microbiota that should be further investigated. Conversely, the p-1088-a5 gut group genus was found more abundant in low-productive cows. In conclusion, this study demonstrates significant associations between the faecal microbiota and the performance of dairy cows at the whole lactation scale. A better understanding of the physiology of the gut microbiota could help to improve dairy cow production.

Global decarbonization potential of CO2 mineralization in concrete materials

CO2 mineralization products are often heralded as having outstanding potentials to reduce CO2-eq. emissions. However, these claims are generally undermined by incomplete consideration of the life cycle climate change impacts, material properties, supply and demand constraints, and economic viability of CO2 mineralization products. We investigate these factors in detail for ten concrete-related CO2 mineralization products to quantify their individual and global CO2-eq. emissions reduction potentials. Our results show that in 2020, 3.9 Gt of carbonatable solid materials were generated globally, with the dominant material being end-of-life cement paste in concrete and mortar (1.4 Gt y-1). All ten of the CO2 mineralization technologies investigated here reduce life cycle CO2-eq. emissions when used to substitute comparable conventional products. In 2020, the global CO2-eq. emissions reduction potential of economically competitive CO2 mineralization technologies was 0.39 Gt CO2-eq., i.e., 15% of that from cement production. This level of CO2-eq. emissions reduction is limited by the supply of end-of-life cement paste. The results also show that it is 2 to 5 times cheaper to reduce CO2-eq. emissions by producing cement from carbonated end-of-life cement paste than carbon capture and storage (CCS), demonstrating its superior decarbonization potential. On the other hand, it is currently much more expensive to reduce CO2-eq. emissions using some CO2 mineralization technologies, like carbonated normal weight aggregate production, than CCS. Technologies and policies that increase recovery of end-of-life cement paste from aged infrastructure are key to unlocking the potential of CO2 mineralization in reducing the CO2-eq. footprint of concrete materials.

Tax Heterogeneity and Misallocation

There is substantial asymmetry in effective corporate income tax rates across firms. While tax asymmetries would reduce productivity in frictionless economies, they can improve efficiency in a distorted economy if taxes alleviate other economic frictions. We develop a framework to estimate to what extent tax asymmetries affect productivity in distorted economies. Using US firm-level balance sheet data alongside measures of effective marginal tax rates, we find a positive correlation between tax rates and factor productivity, suggesting that tax asymmetry exacerbates the distortions from other economic frictions. Eliminating tax rate asymmetries would raise aggregate productivity by 3 to 4 percent if taxes distort capital costs alone. Models where taxes also distort the marginal cost of labor predict potential gains as high as 9 percent.

Business cycles in Colombia: stylized facts

The purpose of this article is to examine the economic cycles in Colombia and to empirically corroborate the fulfillment of nine stylized facts documented in the specialized international literature. For this purpose, the retropolated series 1975-2013 and the series 2005:1-2022:4 of the National Administrative Department of Statistics (DANE) were analyzed using the Hodrick-Prescott filter. Thus, the occurrence of four economic cycles is recorded between 1975 and 2013 with an average duration of 9.3 years with an expansionary phase of 5.0 years and a contractionary phase of 5.3 years. Similarly, between 2005:1 and 2022:4 there were three cycles with an average duration of 21.7 quarters, with an expansionary phase of 14.7 quarters and a contractionary phase of 7.0 quarters. It should also be said that the cyclical fluctuations of employment and unemployment are closely related to effective demand and domestic demand in accordance with Keynesian theory; for example, the positive correlation between the real GDP cycle and the implicit GDP deflator cycle suggests that the cycles were not due to shifts in the aggregate production function as the dominant theory stresses, but to shifts in the aggregate demand function.

Обоснование технологии получения заготовки для ножа исполнительного органа геохода

Introduction. In the construction of the geohod, a blade executive body is used as a working body, which is an element of screw blades rigidly connected to each other in the center of the geohod. The shape of the body is proposed to be made in a helicoid shape, taking into account the specifics of the operation of the underground unit. Therefore, at present, the development and justification of technological solutions for the manufacture of knives of various shapes of the executive body is an urgent task. Materials and methods. The paper considers the main methods for obtaining a body blank of the executive body of the geohod, based on the structural, functional and technological features of the geohod design. To determine the rational variant of the casting method, the main technological capabilities of the casting methods are analyzed. To assess the effectiveness of casting methods, such indicators as: the material utilization factor and the technological cost of the work piece are considered. It is noted that one of the traditional approaches for obtaining a billet is the method of metalworking by pressure. To obtain a blank of the body, the possibility of using rolling and bending technology is considered. The choice of pressure treatment technology is justified. Research results and their discussions. The results of calculations of the technological cost of the casting billet show that it is advisable to use shell casting to obtain a body billet in the conditions of mass production of underground aggregates. Also, the results of determining the technological cost of the work piece by pressure treatment show that it is advisable to use the bending method to obtain a body blank in conditions of small-scale production and medium-scale production of equipment. Conclusion. To choose a method for obtaining a blank body of the executive body, it is necessary to take into account a number of features of the application of methods for obtaining a blank. First of all, it is necessary to take into account the type of production, the degree of ensuring accuracy and quality, especially in terms of strength characteristics, the possibility of using high-performance equipment to increase the productivity of the enterprise. Resume. The article presents the results of research to determine the choice of a method for obtaining a body blank of the executive body of the geohod. It is established that when choosing a method for obtaining a work piece, it is necessary to take into account the type of production, the degree of accuracy and quality, especially in terms of strength characteristics, and the possibility of using high-performance equipment to increase production productivity. Suggestions for practical application and direction of future research can be made in the implementation of the body manufacturing technology of the executive body of the geohod, taking into account the optimal geometry of the cutting edge of the body and the type of production of tunneling units.

Improved Artificial Aggregates for Use in Green Roof Design

The development of surfaces in cities, as a result of progressive urbanization, not only reduces the natural retention capacity of the environment but also causes changes in the water balance. In urbanized areas, the amount and intensity of rainwater discharged to receivers increase, and the time of water outflow from the catchment area shortens. Low retention does not provide effective responses to the local water deficit and does not limit the effects of excess water during flood periods. Furthermore, aging drainage systems do not always have the required hydraulic efficiency in absorbing runoff after intense and heavy rainfall or snowmelt. The aim of the work was to determine the possibility of obtaining flat aggregates with a grain size of 2–16 mm from clay-silt fractions from sedimentation tanks using selected mechanical processing methods (crushing and screening in a crusher-screener system with recycling). An important issue was the examination of the physical and mechanical properties of the produced aggregates after firing, where the work required a detailed material analysis using various research techniques, such as XRD, XRF, SEM and digital microscopy. The obtained results will allow for further research on developing the concept of technology for the production of lightweight aggregates used, for example, on building roofs. Particular attention was paid to the flat shape of the aggregate, which affects a number of its properties. To obtain a flat-shaped aggregate, the authors used a patented sieving method. The obtained materials had high cavernosity of 69% on average, water absorption of 40.7% and low bulk density of 0.82 g/cm3.

LCA applied to comparative environmental evaluation of aggregate production from recycled waste materials and virgin sources

Nowadays, all productive sectors, including the construction industry, are facing the challenge of reducing their environmental impact. To achieve this objective, numerous actions are being carried out to access greater levels of environmental and economic sustainability. Techniques as Life Cycle Assessment contribute to quantifying environmental impacts, promoting a circular economy in a sector that consumes a high volume of resources, materials, and energy while generating large amounts of gaseous, liquid, or solid emissions. The present study aims to deepen our understanding of aspects that demonstrate the benefits of using RA instead of natural aggregates. This study not only quantifies the environmental impact but also explores the effects of potential improvements in the productive system and their impact on reducing environmental harm. The Life Cycle Assessment methodology is applied to quantify and compare the environmental impacts generated in the production of a ton of mixed recycled aggregates (MRA) from construction and demolition wastes, based on the data provided by plant managers. This is compared to the environmental impacts generated in the production of one ton of natural aggregates extracted from a quarry. The results revealed that the production of mixed recycled aggregate is more environmentally beneficial, confirming a reduction of 70.66% in environmental impacts during the production of recycled aggregates, in comparison to the natural aggregates extraction. Furthermore, the economic analysis demonstrates the economic advantage since the cost of producing recycled aggregates is over 30% cheaper than natural aggregates, being more competitive even when the transportation distances from the plant to the work sites exceed those of natural aggregates.Graphical

Corporate Tax Rates, Allocative Efficiency, and Aggregate Productivity

Abstract This paper quantifies the impact of effective corporate tax rates on aggregate total factor productivity (TFP). Using Chilean manufacturing data, we document a large dispersion in the effective tax rate faced by firms and a mass of firms facing a 0 percent tax rate. We integrate these findings into a standard monopolistic competition model, where firms are subject to corporate taxation and also face output and capital wedges, which represent all other distortions present in the economy. We find that eliminating corporate tax rates increases TFP between 4 and 11 percent. We consider counterfactual policies in which firms face a uniform flat tax rate and find a monotonically decreasing relationship between the level of the tax rate and TFP.

Bifunctional halloysite nanotube-based Ripk1 siRNA delivery system rescues cognitive impairment by targeting amyloid β plaques for clearance and reducing necrotic neurons in Alzheimer’s disease mice

Alzheimer’s disease (AD) is exacerbated by abnormal accumulation of toxic β-amyloid (Aβ) aggregates and Aβ-mediated neuronal cell death. Currently, no effective drugs for AD treatment are mainly due to the blood–brain barrier hindrance, which limits the most drugs for application in AD treatment. Accumulating evidence suggests that increased levels of Ripk1 and enhancement of Ripk1-mediated neuronal necroptosis are known to play an important role in neuronal death in AD. Targeting Ripk1 by pharmacological or genetic inhibition of Ripk1 has been demonstrated to prevent neuronal necroptosis and improve memory deficits in AD mice models. Here, we showed that halloysite (HNTs), one of the nanoclays, absorbed Aβ and reduced toxic Aβ aggregate production by inhibiting fibril formation and promoting the clearance of Aβ plaques. We also presented evidence that RVG29, a brain-penetrating peptide, bound directly to Aβ species and inhibited Aβ aggregation. In addition, Ripk1 is more dramatically expressed around Aβ plaques than those far from plaques in the brain of AD mice. Therefore, we designed a novel Aβ plaque-targeted nanomedicine (SH-RVG/siRipk1) via functionalizing with RVG29 onto short HNTs (SH) and loading Ripk1 siRNA (siRipk1) into the lumen of SH to prevent siRipk1 degradation. As we expected, SH-RVG/siRipk1 not only reduced plaques and improved memory impairment but also rescued necrotic neuronal loss around plaques by reducing Ripk1 expression around plaques in AD mice. These findings indicate that SH-RVG/siRipk1 may be an effective strategy for the treatment of AD.

Informality and aggregate productivity: The case of Mexico

This paper develops and estimates a quantitative model to analyze the aggregate productivity consequences of informality in Mexico. While informality is typically viewed as prevailing solely among small firms, we use rich census data to document a high and rising share of large informal firms between 1998 and 2013. The model is quantified using the observed size and productivity distributions of both informal and formal firms. We use the model to assess the role of changes in labor market regulations, entry costs and enforcement in contributing to the rise in informality and decline in TFP in Mexico from 1998 to 2013. We find that the factors most important for the decline in aggregate productivity were not important drivers of the increase in informality, and conversely, the factors most important for the increase in informality had little impact on aggregate productivity. Regulatory changes during the 2000s contributed to over a third of the observed rise in the informal employment share, but with small aggregate productivity consequences. In contrast, rising entry costs account for a third of the decline in TFP from 1998 to 2013, but had little impact on informality.

Utilization Of Buton Asphalt Solid Waste (ASW) Waste Bitumen Extraction In Concrete

Indonesia has 650 million tons of Buton Rock Asphalt (Asbuton) deposits. �The mineral residue, known as Asphalt Solid Waste (ASW). The extraction left ASW by 65-90% of asbuton�s weight. However, 770 thousand tons/year of ASW remain underutilized, causing environmental pollution due to its hydrocarbon content. Based on XRD results, Asbuton minerals were dominated with 46% CaCO3, which are potential as a subtitute material in concrete. However, its hydrocarbon content at 68,911 ppm raises concerns. To prevent ASW hydrocarbons from contaminating concrete, solidification was attempted. This study investigates solidification by making Artificial Coarse Aggregate (ACA) products and using ASW as a subtitute for gravel in concrete. The ACAs were produced from a mixture of ASW and cement, molded into 50 x 100 mm cylinders, crushed after twenty eight-days moist curing, and tested according to ASTM C33 standard of gravel. ASW replaced 0-12.5% by volume of sand and ACA replaced 0-12.5% by volume of gravel in concrete with a target compressive strength of 45 MPa at twenty eight-days. Heat of hydration and shrinkage were tested to indentify the impact of CaCO3 from ASW on concrete. The results showed that ACA could reduce 9% of ASW hydrocarbons. However, the ACA produced did not meet the gravel standard in ASTM because ACA absorption reached 6.75% and abrasion test up to 57%. Neverthless, ASW�s high absorption reduced heat hydration by 10% and shrinkage by 83% compared to normal concrete.