Search Results (36)

This study investigates the production and economic feasibility of biochar for smallholder and family farms in Central Amazonia, with potential implications for other tropical regions. The costs of construction of a prototype mobile kiln and biochar production were evaluated, using small-sized biomass from acai (Euterpe oleracea Mart.) agro-industrial residues as feedstock. The biochar produced was characterised in terms of its liming capacity (calcium carbonate equivalence, CaCO_3eq), nutrient content via organic fertilisation methods, and ash analysis by ICP-OES. Field trials with cowpea assessed economic outcomes, as well scenarios of fractional biochar application and cost comparison between biochar production in the prototype kiln and a traditional earth-brick kiln. The prototype kiln showed production costs of USD 0.87–2.06 kg⁻¹, whereas traditional kiln significantly reduced costs (USD 0.03–0.08 kg⁻¹). Biochar application alone increased cowpea revenue by 34%, while combining biochar and lime raised cowpea revenues by up to 84.6%. Owing to high input costs and the low value of the crop, the control treatment generated greater net revenue compared to treatments using lime alone. Moreover, biochar produced in traditional kilns provided a 94% increase in net revenue compared to liming. The estimated externalities indicated that carbon credits represented the most significant potential source of income (USD 2217 ha⁻¹). Finally, fractional biochar application in ten years can retain over 97% of soil carbon content, demonstrating potential for sustainable agriculture and carbon sequestration and a potential further motivation for farmers if integrated into carbon markets. Public policies and technological adaptations are essential for facilitating biochar adoption by small-scale tropical farmers. Full article

This study explores the potential of using sustainable materials in brick manufacturing by designing a novel brick mix in the laboratory, incorporating sand, lime kiln dust (LKD) waste, tyre rubber, and ground granulated blast furnace slag (GGBFS) waste. These cementless bricks blended LKD–GGBFS wastes as the binder agent and fine crumb rubber from waste tyres as a partial replacement for sand in measured increments of 0%, 5%, and 10% by volume of sand. Ordinary Portland cement (OPC) and fired clay bricks were sourced from the industry, and their properties were compared to those of the laboratory bricks. Tests performed on the industry and laboratory bricks included compressive strength (CS), freeze-thaw (F-T), and water absorption (WA) tests for comparison purposes. Additionally, scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) analyses were performed on the bricks to assess the morphological and mineralogical changes responsible for the observed strengths and durability. The CS and WA values of the engineered bricks were 12, 6, and 4 MPa, and 7, 12, and 15%, respectively, for 0, 5, and 10% crumb rubber replacements. The industry bricks’ average CS and WA values were 13 MPa and 8%, respectively. From the results obtained, the green laboratory bricks passed the minimum strength requirements for load-bearing and non-load-bearing bricks, which can be used to construct small houses. Lastly, the engineered bricks demonstrated strength and durability properties comparable to those of the industry-standard bricks, indicating their potential as a sustainable alternative to help divert waste from landfills, reduce the pressure on natural fine sand extraction, and support eco-conscious brick production for a sustainable environment. Full article

Ensuring efficient long-term quality control of the raw mix remains a priority for the cement industry, supporting initiatives to lower the CO₂ footprint by incorporating significant amounts of alternative fuels and raw materials in clinker production. This study presents an effective method for creating a robust auto-tuner for proportional–integral–differential (PID) controller control of the lime saturation factor (LSF) of the raw mix using artificial neural networks (ANNs). This auto-tuner, combined with a previously studied robust PID controller, forms an integrated system that adapts to process changes and maintains low long-term variance in LSF. The ANN links each of the three PID gains to the process dynamic parameters, with the three ANNs also interconnected. We employed the Levenberg–Marquardt method to optimize the ANNs’ synaptic weights and applied the weight decay method to prevent overfitting. The industrial implementation of our control system, using the auto-tuner for 16,800 h of raw mill operation, shows an average LSF standard deviation of 2.5, with fewer than 10% of the datasets exceeding a standard deviation of 3.5. Considering that the measurement reproducibility is 1.44 and assuming a low mixing ratio of the raw meal in the silo equal to 2, the LSF standard deviation in the kiln feed approaches the analysis reproducibility, indicating that disturbances in the raw meal largely diminish in the kiln feed. In conclusion, integrating traditional, well-established tools like PID controllers with newer advanced techniques, such as ANNs, can yield innovative solutions. Full article

This paper presents a study on the ring formation phenomenon in lime kilns using simulation. The research focuses on the chemical recovery cycle integrated into the pulp production process at a pulp mill, with particular emphasis on the calcium cycle within the lime kilns. Lime kilns are critical components, as their unavailability can significantly impact the overall cost-effectiveness of the facility. The calcination of lime sludge occurs in a rotary kiln, where calcium carbonate in the lime sludge is converted into calcium oxide (lime). Under certain conditions, material can progressively accumulate, leading to ring formation and eventual kiln clogging, resulting in operational downtime. To investigate this issue, the authors developed a physics-based model using a finite-dimensional, one-dimensional approach that considers only longitudinal variation. Several approximations were made to maintain a reasonable simulation time without compromising accuracy. Simulations based on real operational data identified fluctuations in fuel flow rate and sulfur content from non-condensable gases as key contributors to ring formation. The results showed that these fluctuations caused instability in the temperature profiles of the solids and gas beds, leading to periods of cooling before the lime sludge reaches the outlet to the coolers. This cooling promotes the recarbonation of lime and, consequently, the formation of rings. The findings highlight that stabilizing fuel flow and managing sulfur content could mitigate ring formation and improve kiln efficiency. The developed model provides a valuable tool for predictive analysis and process optimization, potentially supporting the development of a digital twin to enhance real-time monitoring and operational control. Full article

The Yucatán Peninsula, a key region of the ancient Maya civilization, has long presented challenges in establishing absolute chronological frameworks for its cultural practices. While the central regions of Mesoamerica have been extensively studied, the southern areas, including the Yucatán, remain underexplored. Limekilns, integral to lime production in pre-Hispanic Maya society, are well suited for archaeomagnetic studies due to the high temperatures (>700 °C) required for their operation. This study analyzed 108 specimens from 12 limekilns near Mérida, Yucatán, using rock-magnetic experiments and progressive alternating field demagnetization to refine the absolute chronology and determine the continuity of the lime production technology. Thermoremanent magnetization was predominantly carried by magnetite-like phases. Archaeomagnetic directions were successfully obtained for ten kilns with robust precision parameters. Age intervals were calculated using global geomagnetic models (SHA.DIF.14K, SHAWQ.2K), local paleosecular variation curves, and a Bootstrap resampling method. The analysis identified apparently two distinct chronological clusters: one between 900 and 1000 AD, associated with the Late–Terminal Classic period, and another near 1500 AD, just prior to the Spanish conquest. These findings reveal an apparent 500-year hiatus in lime production, followed by the potential reuse of kilns. Our study refines the chronological framework for Mayan lime production and its cultural and technological evolution. The integration of archaeomagnetic methods demonstrates their far-reaching applicability in addressing questions of continuity, reuse, and technological adaptation, contributing to broader debates on ancient pyrotechnological practices and their socioeconomic implications. Full article

The thermal stabilization of expansive soils has emerged as a promising and sustainable alternative to conventional chemical stabilization methods, addressing the long-standing challenges associated with soil swelling and shrinkage. This review critically evaluates the mechanisms, applications, and advancements in thermal stabilization techniques, with a particular focus on both traditional approaches (e.g., kiln heating) and emerging innovations such as microwave heating. This study synthesizes recent research findings to assess how thermal treatment modifies the mineralogical, physical, and mechanical properties of expansive soils, reducing their plasticity and improving their strength characteristics. Comparative analysis highlights the advantages, limitations, and sustainability implications of different thermal methods, considering factors such as energy efficiency, scalability, and environmental impact. While thermal stabilization offers a viable alternative to chemical treatments, key challenges remain regarding cost, field implementation, and long-term performance validation. The integration of thermal treatment with complementary techniques, such as lime stabilization, is explored as a means to enhance soil stability while minimizing environmental impact. By addressing critical research gaps and providing a comprehensive perspective on the future potential of thermal stabilization, this review contributes valuable insights for researchers and engineers seeking innovative and sustainable solutions for managing expansive soils. Full article

In the municipality of La Granja d’Escarp, for over thirty years, an important natural cement factory was in operation. In 1876, the Girona family, who were businessmen and bankers from Barcelona, opened the factory with modern industrial facilities. It included kilns, mills, and crushers, alongside warehouses, a small railway for internal transportation of the various materials used, and even a housing area for workers. The neighboring Ebro River allowed distribution by river transport at first. Later, with the use of railways, transport to consumption points was possible. This industrial complex became a center of significant importance in Catalonia in the production of cement, which was used for building hydraulic and civil works. During the first decade of the twentieth century, the factory stopped its activity and the facilities were abandoned. Nowadays, this industrial heritage site is in a state of neglect, without any kind of protection or maintenance. In turn, this has caused the collapse of some buildings in recent times and the loss of historical value of the architectural ensemble. We have carried out initial geomatic research, which has highlighted the constructive properties of the kilns. We have also tested five samples from different buildings using XRD and TGA/DSC, which showed the use of lime mortars in their construction. This is the first study to be carried out at this site, with the aim of showing the historical importance of the ensemble. The goal of the study was to highlight the value of this industrial heritage site and illustrate that it was once a pioneer in the production of natural cement and a driving force for Catalonia. Full article

The process of purifying agricultural products, at various food processing plants, generates waste materials that consist of precipitated calcium carbonate, organic debris, and trace amounts of soil and agricultural contaminants. A specific food-processing waste, hereafter referred to as a food industry byproduct, FIBP, is typically stockpiled on land adjacent to the corresponding food processing facilities due to its large volume and chemical composition. The FIBP also contains commercially available unspent lime products, which makes its reuse viable in various applications. An example is construction applications where an organic content of up to 5% by weight is allowed, such as treating expansive clays. Traditionally, lime stabilization has been used for improving the properties of expansive clays, where ground improvement methods are necessary for a large area. However, the process of producing lime is resource- and energy-intensive as it includes crushing and heating limestone in kilns to extract lime. Therefore, one specific doubly sustainable application is the treatment of expansive clays using the FIBP instead of lime. The main application tested here is the treatment of expansive clayey soils underneath a stretch of State Highway 95 near Marsing, ID. Other potential applications are in road and embankment construction. To evaluate the potential of expansive clay stabilization utilizing the FIBP, a series of geotechnical and environmental laboratory testing were conducted to measure the engineering properties (e.g., swell potential, permeability, and strength properties) of expansive clay amended with FIBP. Preliminary testing on blends with an expansive clay suggests benefits such as decreased swelling potential, increased density, and leachate immobilization. Full article

The treatment and resource utilization of sludge from municipal sewage treatment plants is an important environmental issue. Cement kiln co-processing offers a promising solution, but challenges remain, particularly regarding sludge properties and feasibility in kiln systems. This study analyzes the characteristics of three pretreated sludges: mechanically dewatered sludge, deeply dewatered sludge, and lime-dried sludge. Using techniques such as thermogravimetric analysis (TGA) and X-ray diffraction (XRD), this study investigates their calorific values and raw material utilizability in co-processing. As the sludge moisture content decreases from interstitial to bound water, energy consumption per ton of evaporated water rises, particularly below 30%. At 10 °C/min heating, energy consumption for mechanically dewatered sludge at 80%, 30%, and 10% moisture was 3573, 8220, and 34,751 kJ/kg, respectively; for deeply dewatered sludge at 60%, 30%, and 10%, the values were 4398, 7550, and 11,504 kJ/kg. Keeping moisture content above 30% before kiln entry reduces energy use and enhances calorific value. Sludge utilizability as a raw material depends on its pretreatment. The ash composition of deeply and mechanically dewatered sludge resembles iron-rich raw materials, while lime-dried sludge aligns more with limestone. The utilizable ash content was 23.3%, 8.1%, and 46.3%, respectively, with lime-dried sludge showing the highest potential. This study provides insights into sludge properties and their co-processing potential in cement kilns, offering scientific and technical support for practical applications. Full article

This study aimed to investigate the behavior of accelerated carbonation-cured laboratory specimens using the ultrasonic non-destructive testing (UNDT) method and compare the results with the destructive testing (DT) method. The materials used in the study included a blend of lime kiln dust and ground granulated blast furnace slag (LKD-GBFS) wastes, natural fine aggregate (sand), and alternative fine aggregates from waste tires. The chemical analysis of the LKD and GBFS samples highlighted them as suitable alternatives to OPC, hence their utilization in the study. A 60:40 (LKD-GBFS) blending ratio and a 1:2 mix design (one part LKD-GBFS blend and two part sand) was considered. The natural fine aggregate was partially replaced with fine waste tire rubber crumbs (TRCs) in stepped increments of 0, 5, and 10% by the volume of the sand. The samples produced were cured using three curing regimens: humid curing (HC), accelerated carbonation curing (ACC) with no water curing (NWC) afterwards, and water curing after carbonation (WC). From the results, an exponential model was developed, which showed a direct correlation between the UNDT and DT results. The developed model is a useful tool that can predict the CS of carbonated samples when cast samples are unavailable. Lastly, a total CO₂ uptake of 15,912 g (15.9 kg) was recorded, which underscores ACC as a promising curing technique that can be utilized in the construction industry. This technique will bring about savings in terms of the time required to produce masonry units while promoting a change in the basic assumptions of a safer and cleaner environment. Full article

Although soil stabilization with cement and lime is widely used to overcome the low shear strength of soft clay, which can cause severe damage to the infrastructures founded on such soils, such binders have severe impacts on the environment in terms of increasing emissions of carbon dioxide and the consumption of energy. Therefore, it is necessary to investigate soil improvement using sustainable materials such as byproducts or natural resources as alternatives to conventional binders—cement and lime. In this study, the combination of cement kiln dust as a byproduct and zeolite was used to produce an alkali-activated matrix. The results showed that the strength increased from 124 kPa for the untreated clay to 572 kPa for clay treated with 30% activated stabilizer agent (activated cement kiln dust). Moreover, incorporating zeolite as a partial replacement of the activated cement kiln dust increased the strength drastically to 960 and 2530 kPa for zeolite ratios of 0.1 and 0.6, respectively, which then decreased sharply to 1167 and 800 kPa with further increasing zeolite/pr to 0.8 and 1.0, respectively. The soil that was improved with the activated stabilizer agents was tested under footings subjected to eccentric loading. The results of large-scale loading tests showed clear improvements in terms of increasing the bearing capacity and decreasing the tilt of the footings. Also, a reduction occurred due to the eccentricity decreasing as a result of increasing the thickness of the treated soil layer beneath the footing. Full article

Quicklime, rich in CaO(s), is generated by calcining limestone at high temperatures. Parallel-flow regenerative lime kilns are the most energy-effective industrial method available today. To prevent major disruptions in such kilns, a high raw material quality is necessary. Under some conditions, impurity-enriched material may adhere to limestone pebbles and enter the kiln. In this study, limestone and corresponding quicklime were analyzed to evaluate the extent and composition of surface impurities and assess the effect on quicklime product quality, here defined as free CaO. This was performed by sampling and analyzing limestone, quarry clay, laboratory-produced quicklime, and industrially produced quicklime with XRF, SEM/EDX, and XRD; interpretations were supported by thermodynamic equilibrium calculations. In the laboratory-produced quicklime, the surface impurities reacted with calcium forming Larnite, Gehlenite, Åkermanite and Merwinite, reducing the quicklime quality. The results showed that the limestone surface layer comprised 1.2 wt.-% of the total mass but possessed 4 wt.-% of the total impurities. The effect on industrially produced quicklime quality was lower; this indicated that the limestone surface impurities were removed while the material moved through the kiln. Multicomponent chemical equilibrium calculations showed that the quarry clay was expected to be fully melted at 1170 °C, possibly leading to operational problems. Full article

The global challenge faced due to the impact of the construction industry on climate change, along with the issues surrounding sustainable waste disposal, has necessitated various research on using waste products as eco-friendly alternatives in construction. In this study, the avoidance of waste disposal through landfills in Australia was encouraged by incorporating lime kiln dust (LKD) and tire rubber waste (TRW) into masonry mixes to manufacture green bricks. Furthermore, the investigations in this article highlight the use of mercury intrusion porosimetry (MIP) to determine the durability of the LKD-TRW bricks when exposed to freeze–thaw (F-T) cycles by examining the pore size distribution within the bricks. The LKD waste was blended with ground granulated blast furnace slag (GGBFS) at a 70:30 blending ratio and combined with the TRW in stepped increments of 5% from 0 to 20% to produce these eco-friendly bricks. The compressive strength (CS), flexural strength (FS), frost resistance (FR), pore size distribution according to mercury intrusion porosimetry (MIP), and the water absorption (WA) properties of the bricks were assessed. The CS and FS values at 28 days of curing were recorded as 6.17, 5.25, and 3.09 MPa and 2.52, 2, and 1.55 MPa for 0, 5, and 10% TRW contents, respectively. Durability assessments using the F-T test showed that the bricks produced with 0% TRW passed as frost-resistant bricks. Furthermore, the results from the MIP test showed a total pore volume of 0.033 mL/g at 3 µm pore size for the 0% TRW content, further confirming its durability. Hence, the 0% LKD-TRW bricks can be utilized in cold regions where temperatures can be as low as −43 °C without deteriorating. Lastly, WA values of 7.25, 11.76, and 14.96% were recorded for the bricks with 0, 5, and 10% TRW, respectively, after the 28-day curing period. From all of the results obtained from the laboratory investigations, the LKD-TRW bricks produced with up to 10% TRW were within the satisfactory engineering requirements for masonry units. Full article

Quicklime is produced through the thermal processing of limestone in industrial kilns. During quarry operations, fine particulate quarry dust adheres to limestone lump surfaces, increasing the bulk concentration of impurities in limestone products. During thermal processing in a kiln, impurities such as Si, Mg, Al, Fe, and Mn react with Ca, reducing quicklime product quality. Which reactant phases are formed, and the extent to which these result in a reduction in quality, has not been extensively investigated. The present study investigated as-received and manually washed limestone product samples from two operational quarries using elemental compositions and a developed predictive multi-component chemical equilibrium model to obtain global phase diagrams for 1000–1500 °C, corresponding to the high-temperature zone of a lime kiln, identifying phases expected to be formed in quicklime during thermal processing. The results suggest that impurities found on the surface of the lime kiln limestone feed reduce the main quality parameter of the quicklime products, i.e., calcium oxide, CaO (s), content by 0.8–1.5 wt.% for the investigated materials. The results also show that, in addition to the effect of impurities, the quantity of CaO (s) varies greatly with temperature. More impurities result in more variation and a greater need for accurate temperature control of the kiln, where keeping the temperature below approximately 1300 °C, that of Hatrurite formation, is necessary for a product with higher CaO (s). Full article

This paper investigates the effect of subgrade soil stabilization on the performance and life extension of flexible pavements. Several variables affecting soil stabilization were considered, including subgrade soil type (CL or CH), additive type and content (3, 6, and 9% of hydrated lime, 5, 10, and 15% of class C fly ash (CFA), and 5, 10, and 15% of cement kiln dust (CKD)), three stabilization thicknesses (15, 30, and 45 cm), and four pavement sections with varying thicknesses. The effects of these variables were investigated using four different damage mechanisms, including the fatigue life of the asphalt concrete (AC) and stabilized subgrade layers, the crushing life of the stabilized subgrade soil, and the rutting life of the pavement, using a non-linear mechanistic-empirical methodology. The results suggest that the optimum percentage that maximizes the pavement life occurs at 3% of lime for subgrade soil type CL, 6% of lime for subgrade type CH, and 15% of CFA and CKD for both subgrade soil types. The maximum pavement life increase occurred in the section with the lowest thickness and the highest stabilization thickness, which was 1890% for 3% of lime in the CL subgrade and 568% for 6% of lime in the CH subgrade. The maximum increase in the pavement life of subgrade stabilization with 15% of CFA was 2048% in a CL subgrade, and 397% in a CH subgrade, and life extension due to subgrade stabilization with 15% of CKD was 2323% in a CL subgrade and 797% in a CH subgrade. Full article