Method for reducing methylene blue value in fine aggregates
Patent Information
- Authority / Receiving Office
- EP · EP
- Patent Type
- Applications
- Current Assignee / Owner
- AGGRE TECH YESIL & SURDURULEBILIR AGREGA TEKNOLOJILERI LTD STI
- Filing Date
- 2024-08-05
- Publication Date
- 2026-07-08
AI Technical Summary
Existing methods for reducing the methylene blue value in fine aggregates, such as natural and crushed sand, are water-intensive, generate sludge waste, and fail to meet stringent industry standards, leading to increased costs, environmental impact, and reduced construction material quality.
Thermal treatment of fine aggregates at temperatures between 400°C to 800°C for up to 15 minutes in a rotary or stationary kiln, without water, to convert clay and micaceous minerals into stable forms, achieving methylene blue values below 1 g/kg and eliminating the need for washing processes.
The method reduces water consumption, operational costs, and environmental impact while producing high-quality aggregates that meet stringent industry standards, improving construction material performance and reducing cement and bitumen usage.
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Abstract
Description
[0001] DESCRIPTION
[0002] METHOD FOR REDUCING METHYLENE BLUE VALUE IN FINE AGGREGATES
[0003] TECHNICAL FIELD
[0004] The present invention relates to the field of construction materials. Specifically, the invention relates to methods for reducing the methylene blue value in fine aggregates such as natural and crushed sand used in the production of concrete, asphalt, mortar, and other construction chemicals.
[0005] BACKGROUND OF THE INVENTION
[0006] In the construction industry, fine aggregates such as natural and crushed sand are essential components used in the production of concrete, asphalt, and mortar. The quality of these fine aggregates significantly affects the durability and performance of the resulting construction materials. One of the key quality indicators is the methylene blue value, which measures the amount of clay and micaceous minerals and their water absorption in the fine aggregates. The methylene blue value is determined according to the EN 933-9:2022 (Test for geometrical properties of aggregates - Part 9: Assessment of fines-Methylene blue test) Standard. This standard is used to test the reaction of the fine fraction of aggregates with methylene blue. This test is particularly used to determine the clay and / or micaceous mineral content in aggregates and helps assess the cleanliness of the aggregates.
[0007] The methylene blue test is performed by adding a methylene blue solution to a specific volume of aggregate sample and mixing it for a certain period. As a result of the test, a methylene blue value is obtained. This standard is an important method for controlling the quality of construction materials and ensuring their reliability. High methylene blue values (MBV) indicate a higher presence of clay and / or micaceous minerals, which can adversely affect the performance of the aggregate in construction applications. Reducing the MBV enhances concrete mixing and placement, increases compressive strength, and improves resistance to frost, de-icing salts, and other environmental factors. Lower MBV leads to better aggregate cohesion and reduces the risk of shrinkage and cracking, thereby extending the lifespan of concrete structures and ensuring greater structural integrity. Various methods can be used to reduce MBV, including washing, drying, adsorption, chemical processes, sand exchange, and sand blending. Conventionally, the methylene blue value of fine aggregates is reduced through washing and scrubbing processes that use large amounts of water to remove clay and other impurities. These methods, while effective, generate significant wastewater and require proper disposal to avoid environmental contamination. Additionally, the water-intensive nature of said processes makes them less sustainable, especially in regions facing water scarcity. Washing fine aggregates to reduce methylene blue values and remove very fine clay and silt particles results in the following issues:
[0008] - Water consumption and water source contamination;
[0009] Energy requirement for recycling muddy water within the system;
[0010] Risk of muddy water escaping the system and contaminating riverbeds;
[0011] Production of sludge waste, leading to production loss and increased environmental damage; and
[0012] Increased production costs.
[0013] Some fine aggregate samples, even after washing, do not achieve the desired methylene blue values due to residual clays and / or micaceous minerals, which results in the followings:
[0014] Increased cement usage to achieve target strength in produced concrete, raising costs and CO2 emissions;
[0015] Failure to achieve expected target strength in some concrete grades even with increased cement and additive usage;
[0016] Increased use of chemical additives in concrete, with some fine aggregates not responding to these additives;
[0017] Early hardening or poor pumpability of concrete; and
[0018] Increased natural sand usage to improve workability in concrete due to the absence of very fine material in washed sands.
[0019] Furthermore, the undesired elimination of stone dust / fil lers from natural or crushed sand through said washing process necessitates reintroduction of the same in hot mix asphalt, mortar, and construction chemicals production, which are crucial for the quality thereof.
[0020] Recent advances have explored the use of chemical treatments and adsorption techniques to reduce the methylene blue value in aggregates. For example, iron-based nanoparticles and other adsorbents have been tested for their ability to remove methylene blue from aqueous solutions, offering a potential method for aggregate treatment without extensive water usage. However, these methods often require complex equipment and precise control over chemical reactions, necessitating significant investment in infrastructure and expertise, making them less practical for large-scale applications in the construction industry.
[0021] Among prior art teachings, GB2609224A discloses an apparatus for processing aggregate material, particularly for removing clay contaminants and other deleterious materials comprising a chassismounted trough inclined at an angle, with rotatable shafts equipped with angled blades for material transport and attrition. A weir within the trough enhances retention time and scrubbing efficiency by increasing material retention and water levels. The apparatus includes spray bars for adding water, a discharge opening, and a dewatering screen. The design allows for the adjustment of the height angle and of the weir to optimize processing.
[0022] US2020062649A1 discloses a method for controlling clay impurities in construction aggregates and cementitious compositions, comprising the step of treating clay-bearing aggregates with an ion- exchanged polycondensate of dialkylamine and epichlorohydrin that contains anionic groups of both acetate and chloride ions. The acetate content is between 51-99%, preferably 60-95%, based on the molar concentration of the anionic groups, ensuring minimal presence of chloride ionic groups.
[0023] US Patent US10669200B2 discloses a method and device for producing artificial crushed sand through thermal treatment using fine sand or round sand as the starting material. The sand is heated to a melting temperature by either bundling solar rays or using a conventional melting device powered by converted or stored solar energy. The heated sand grains are melted together into a three-dimensional intermediate product, which is then cooled and comminuted to a particle size of less than 2 mm. The end product differs from the starting material in shape and surface roughness, offering a long-term solution for meeting the demand for crushed sand and providing sand for the construction industry. The method achieves necessary temperatures of at least 1700°C, and sometimes up to 1810°C, to form new grain boundaries, though solar methods can exceed 2000°C and lack precise control.
[0024] Priyadharshini P. et al. cites about influence of temperature and duration of thermal treatment on properties of excavated soil as fine aggregate in cement mortar, specifically high plasticity soils from tunnel excavations, heating them between 200-1000°C for durations ranging from 30 to 180 minutes, to assess their suitability for use in cement mortar. This article noted that said soils contain 25-40% clay minerals, predominantly kaolinite, illite, and montmorillonite. (May 2019, Journal of the Construction Division 31(8), D0l:10.1061 / (ASCE)MT.1943-5533.0002759). Consequently, these conventional methods often fail to achieve the desired reduction in methylene blue value to meet stringent industry standards such as those set by the European Union for aggregates, specifically for natural sand or crushed sand, used in concrete production in an effective and industrially applicable approach. There is a need for a more efficient, cost-effective, and environmentally sustainable method to reduce methylene blue value in fine aggregates that can be easily implemented on a large scale.
[0025] BRIEF DESCRIPTION OF THE INVENTION
[0026] The primary object of the present invention is to provide a method for reducing the methylene blue value in fine aggregates without the use of water, while also reducing operational costs and environmental impact associated with traditional washing processes in aggregate processing.
[0027] Another object of the invention is to provide a method that improves the quality and performance of fine aggregates used in the production of concrete, asphalt, and other construction materials, and meets stringent industry standards, such as the European Union Aggregate Standards for Concrete, by achieving methylene blue values below 1 g / kg without producing sludge waste.
[0028] Another object of the invention is to provide a method that eliminates the need for washing and separation of fine clay and silt-sized particles from fine aggregates.
[0029] A further object of the invention is to provide a system that improves the quality and performance of fine aggregates used in the production of concrete, asphalt, and other construction materials.
[0030] Yet, another object of the invention is to provide a method that reduces the cement quantity required in concrete production and the bitumen quantity required in hot mix asphalt production, thus enhancing the sustainability of construction practices.
[0031] In order to meet the aforementioned objectives, the present invention provides a method and a system involving thermally treating aggregates, such as natural or crushed sand with a particle size of less than 5 mm, in a thermal treatment unit such as a rotary or stationary kiln at a temperature range of 400°C to 800°C for a duration of up to 15 minutes based on their mineralogical and thermal properties.
[0032] Without using water or producing sludge waste as in conventional applications, the method according to the invention provides the methylene blue value of fine aggregates to be reduced below 1 g / kg, meeting the European Union Aggregate Standards for Concrete (MB1 category, BS EN 12620, 2013) and allowing for effective production of fine aggregates for concrete, asphalt, and construction chemicals.
[0033] Furthermore, the method according to the invention eliminates the need for washing process, thus avoiding the separation of fine clay and silt particles (less than 63 microns), and prevents the removal of fillers (stone dust) from fine aggregates. By retaining said fillers in natural or crushed sand, the method reduces or eliminates the usage of additional natural sand in concrete, which is crucial for maintaining the quality of hot mix asphalt, mortar, and construction chemicals.
[0034] Consequently, the method effectively and rapidly reduces, compared to the prior art, the undesired clay and / or micaceous mineral content of fine aggregates from various natural sands, gravels, or crushed stone screening plants, enhancing the quality of concrete and asphalt while lowering the quantities of cement and bitumen required. This is especially important for producing high-quality concrete in earthquake-prone areas. The term "reduction" above refers to the conversion of clay and / or micaceous minerals into more stable and non-absorbent forms.
[0035] These and other aspects, structural and characteristic features, advantages, and embodiments of the present invention will become more apparent from, and will be understood more clearly by reference to the following detailed description, examples, and associated figures.
[0036] BRIEF DESCRIPTION OF THE FIGURES
[0037] Figure 1 illustrates a process flow diagram for the method of reducing methylene blue value in fine aggregates.
[0038] Figure 2a-d shows natural sand and methylene blue test results for Example 1, including pre- and post-thermal treatment samples and their corresponding methylene blue tests.
[0039] Figure 3a-d shows crushed sand and methylene blue test results for Example 2.
[0040] The reference numerals in the figures correspond to the following steps / components::
[0041] 1 Fine aggregates fed to the system
[0042] 2 Crushing means for crushing larger stones and gravels
[0043] 4 Screening means for separating finer particles
[0044] 6 Classifiers for consistent particle size distribution
[0045] 8 Fine aggregates meeting MB1 values for industrial use 10 Conveyor
[0046] 20 Thermal treatment unit (rotary or stationary kiln)
[0047] 30 Heating means
[0048] 40 Airflow system
[0049] 50 Control unit
[0050] 60 Cooling unit
[0051] 70 Collection unit
[0052] 100 Acquiring / obtaining step for fine aggregates
[0053] 200 Feeding step for fine aggregates
[0054] 300 Thermal treatment step
[0055] 400 Cooling step
[0056] 500 Collection Step
[0057] DETAILED DESCRIPTION OF THE INVENTION
[0058] The present invention provides a method for reducing the methylene blue value in fine aggregates, specifically natural and crushed sand, used in the production of concrete, asphalt, and other construction materials. The method involves thermal treatment of the aggregates without the use of water, thus eliminating the need for washing process and preventing the production of sludge waste. The treatment reduces the methylene blue value to less than 1 g / kg, meeting the European Union standards for concrete aggregates (MB1 category, BS EN 12620, 2013).
[0059] The fine aggregates refers to materials passing through a 5 mm sieve, including primarily natural and crushed sand, produced from various natural sands, gravels, or crushed stone screening plants. They are fed to the system using a conveyor (10), ensuring a continuous and controlled supply of aggregates into a thermal treatment unit (20), where they are subjected to temperatures ranging from 400°C to 800°C. The specified temperature range is designed to optimize production costs and reduce the methylene blue value to the MB1 category more effectively and rapidly. Higher temperatures, above 800°C, can also reduce methylene blue values but less feasible.
[0060] The duration of the treatment can change depending on the mineralogical and thermal properties of the aggregate and moisture content thereof. The maximum residence time is 15 minutes. If the moisture content of the sand is less than 10% by weight, for instance, the residence time is reduced to a maximum of 5 minutes. This optimal duration minimizes energy costs while still achieving the desired reduction in methylene blue values. For sands with moisture content between 10% and 25%, the residence time is up to 8 minutes. Sands with 25% to 50% moisture content require up to 12 minutes of treatment. For sands with more than 50% moisture, the residence time can be up to 15 minutes to achieve the desired methylene blue value reduction according to the invention.
[0061] The thermal treatment unit (20) can be either rotary or stationary kiln, depending on the specific requirements of the process. Located within the kiln (20), heating means (30) provide the necessary heat for the thermal treatment, ensuring that the aggregates reach the desired temperature. These could be electric or gas-fired, designed to handle high thermal demands while maintaining energy efficiency, ensuring the aggregates reach the pre-determined temperatures efficiently. An airflow system (40) ensures uniform heat distribution within the kiln (20), making sure that all aggregates are evenly treated.
[0062] A control unit (50), comprising a temperature sensor and a timer, adjusts the thermal treatment procedures based on the moisture content, mineralogical, and thermal properties of the aggregates. This precise control optimizes energy consumption and ensures the desired reduction in methylene blue value.
[0063] After the thermal treatment, the aggregates are cooled to a handleable temperature at a cooling unit (60) or may be left to free cooling at the atmosphere. The cooling unit (60) may include air cooling systems, water cooling systems, or free cooling systems, depending on specific requirements and environmental conditions. This step is crucial for safe handling and further processing, and prevents thermal damage to the aggregates. The treated aggregates are collected and stored for subsequent use at a collection unit (70), the cooled aggregates meeting stringent quality standards, with reduced methylene blue values suitable for concrete, asphalt, and other construction applications. The collection unit (70) may comprise storage containers or bins where the aggregates are temporarily held before being transported for use in concrete, asphalt, or other construction materials. The collection mechanism ensures that the aggregates are stored in a controlled environment, maintaining their quality until use.
[0064] According to a preferred arrangement of the invention, the method comprises the following steps without requiring any usage of water (sand-washing process):
[0065] - Acquiring / obtaining step for fine aggregates (100)
[0066] - Feeding step for fine aggregates (200)
[0067] - Thermal treatment step (300) - Cooling step (400)
[0068] - Collection step (500)
[0069] In the acquiring / obtaining step (100), fine aggregates are produced or obtained from various natural sands, gravels, or crushed stone screening plants. These aggregates are essentially less than 5 mm in size according to the invention, ensuring they meet the criteria for fine aggregates used in concrete, asphalt, and other construction applications. To achieve the target particle size of less than 5 mm, the methods may further comprise preparatory steps known from the prior art, such as crushing larger stones and gravels (2), screening to separate finer particles (4), and using classifiers (6) to ensure consistent particle size distribution, specifically selecting and using particles that pass through a 5 mm sieve.
[0070] In the feeding step (200), fine aggregates, i.e. natural or crushed sand passing through a 5 mm sieve, are fed into the system using a conveyor (10).
[0071] In the thermal treatment step (300), the fine aggregates are subjected to thermal treatment in a rotary or stationary kiln (20) preferably in an air atmosphere at temperatures ranging from 400°C to 800°C for an effective duration of up to 15 minutes, depending on their mineralogical and thermal properties. For instance, the duration preferably increases by 2 to 5 minutes for every 10% increase in moisture content of the fine aggregates, with a maximum duration of up to 15 minutes.
[0072] In the cooling step (400), the thermally treated aggregates are cooled to a manageable temperature, ensuring they can be safely handled and used in subsequent processes. In the collection step (500), the cooled and treated fine aggregates are collected and stored for further use in the production of concrete, asphalt, and other construction materials.
[0073] Consequently, said method according to the invention eliminates the need for washing and separation processes, reducing operational costs and environmental impact while improving the quality and performance of the fine aggregates. The method can be implemented without necessarily involving an aggregate-preheating step.
[0074] In order to illustrate the practical application and benefits of this invention, the following examples, performed on a laboratory scale, are provided. These examples are intended to demonstrate specific embodiments of the invention and should not be construed as limiting the scope thereof. EXAMPLE 1: A natural sand sample (1) with an initial methylene blue value greater than 5.5 g / kg (MB5.5 category) is thermally treated at 500°C for up to 5 minutes. After treatment, the methylene blue value drops to less than 1 g / kg (MB1 category). Prolonging the treatment beyond 5 minutes or increasing the temperature further reduces the methylene blue value. If the temperature is below 500°C, the reduction in methylene blue value is negligible.
[0075] The natural sand and methylene blue test results for Example 1 are shown in Figures 2a-d. These figures show: (a) the natural sand sample (1) before thermal treatment, (b) the natural sand sample (8) after thermal treatment, (c) the methylene blue test for natural sand before thermal treatment, and (d) the methylene blue test for natural sand after thermal treatment.
[0076] EXAMPLE 2: A crushed sand sample (1) with an initial methylene blue value greater than 6 g / kg (due to the relatively higher content of muscovite and chlorite minerals therein, as one of the most severe mineralogical conditions), is thermally treated at 800°C for 5 minutes, reducing the methylene blue value to 0.5 g / kg. When the same sample is treated at 650°C, the methylene blue value only reduces to 4 g / kg. Increasing the treatment duration to 15 minutes at 650°C does not reduce the methylene blue value below 4 g / kg. This demonstrates the significance of both temperature and duration in achieving optimal results.
[0077] The crushed sand and methylene blue test results for Example 2 are shown in Figures 3a-d. These figures show: (a) the crushed sand sample (1) before thermal treatment, (b) the crushed sand sample (8) after thermal treatment, (c) the methylene blue test for natural sand before thermal treatment, and (d) the methylene blue test for crushed sand after thermal treatment.
[0078] In conclusion, the invention offers a novel, efficient, and environmentally sustainable method for reducing the methylene blue value in fine aggregates. By eliminating the need for water and preventing sludge waste, the method significantly lowers operational costs and environmental impact while ensuring the production of high-quality construction materials. Specifically, the advantages of this invention include but are not limited to:
[0079] - Reduced Water Consumption: Eliminates the need for water in the aggregate cleaning (washing) process, conserving water resources.
[0080] - Lower Energy Usage: Reduces energy consumption by eliminating the need for recycling muddy water. - Environmental Protection: Prevents the risk of muddy water escaping into natural water bodies and reduces the production of sludge waste.
[0081] - Prevention of Sludge Waste: Avoids the generation of sludge waste, thereby preventing production loss and minimizing environmental damage.
[0082] - Cost Efficiency: Lowers production costs by eliminating water usage and sludge waste management.
[0083] - Improved Aggregate Quality: Ensures the production of high-quality fine aggregates, enhancing the performance of construction materials.
[0084] - Consistency in Cement and Additive Usage: Achieves the desired methylene blue values without the need for excessive cement and additives, thus maintaining consistent quality and reducing CO2 emissions.
[0085] - Enhanced Workability: Retains fine particles and stone dust in the aggregates, improving the workability of concrete and reducing the need for natural sand.
[0086] - Applicability to Various Construction Materials: Beneficial for the production of concrete, hot mix asphalt, mortar, and construction chemicals, especially in earthquake-prone areas where high-quality construction materials are essential.
[0087] While certain examples and embodiments of the present invention have been described so far, it is obvious that various changes, modifications, and adaptations can be made by those skilled in the art without departing from the spirit and scope of the invention. For example, the feeding mechanism comprises a hopper for initial aggregate intake before conveying the fine aggregates into the thermal treatment unit. Injecting inert gases such as nitrogen or argon into the furnace atmosphere during thermal treatment can enhance processes like the reduction of methylene blue value and prevent oxidation. Sensor systems may be integrated to monitor and control the temperature, flow rate, and chemical composition within the furnace. Furthermore, automated control units and advanced algorithms could be incorporated to optimize the process parameters, ensuring high precision and efficiency Therefore, the attached claims ensure that such changes, modifications, and adaptations are included within the scope of protection, maintaining the integrity and intended scope of the invention.
Claims
CLAIMS1. A method for reducing the methylene blue value in fine aggregates to less than 1 g / kg for use in concrete, asphalt, and other construction materials, comprising;- thermally treating the fine aggregates in a thermal treatment unit at a temperature range of 400°C to 800°C for a duration of up to 15 minutes;- wherein the aggregates have a particle size of up to 5 mm;- wherein the aggregates primarily comprise natural sand or crushed sand; and- wherein the method does not involve any aggregate-washing process.
2. The method according to claim 1, wherein the method does not involve use of water, thus eliminating the need for washing process and preventing the production of sludge waste.
3. The method according to claim 1, wherein the moisture content of the fine aggregates is less than 10% by weight, and the thermal treatment duration is up to 5 minutes.
4. The method according to claim 1, wherein the moisture content of the fine aggregates is between 10% and 25% by weight, and the thermal treatment duration is up to 8 minutes.
5. The method according to claim 1, wherein the moisture content of the fine aggregates is between 25% and 50% by weight, and the thermal treatment duration is up to 12 minutes.
6. The method according to claim 1, wherein the moisture content of the fine aggregates is more than 50% by weight, and the thermal treatment duration is up to 15 minutes.
7. The method according to claim 1, further comprising the following steps;- acquiring the fine aggregates from natural sands, gravels, or crushed stone screening plants; or- producing fine aggregates via conventional approaches such as crushing larger stones and gravels, screening to separate finer particles, and using classifiers to ensure consistent particle size distribution, specifically using particles that pass through a 5 mm sieve.
8. The method according to claim 1, comprising the following steps;- feeding fine aggregates passing through a 5 mm sieve from natural sands, gravels, or crushed stone screening plants into a thermal treatment system;- thermally treating the fine aggregates in the thermal treatment unit at a temperature range of 400°C to 800°C; and- maintaining the aggregates in the thermal treatment unit up to 15 minutes;- thereby achieving a methylene blue value of less than 1 g / kg for the thermally treated aggregates, meeting the European Union standards for concrete aggregates (MB1 category, BS EN 12620, 2013) as well as other similar standards for use in concrete, asphalt, and other construction materials.
9. The method according to claim 1, comprising maintaining the aggregates in a rotary or stationary kiln for a duration based on moisture content thereof, where the duration increases by 2 to 5 minutes for every 10% increase in moisture content, with a maximum duration of up to 15 minutes, from 400°C to 800°C.
10. The method according to claim 1, further comprising the following steps;- cooling the thermally treated aggregates to a handleable temperature; and- collecting the cooled aggregates for use in concrete, asphalt, and other construction materials.
11. A system for reducing the methylene blue value in fine aggregates to less than 1 g / kg, without using water or producing sludge waste, for use in concrete, asphalt, and other construction materials, characterized by comprising;- a thermal treatment unit for treating fine aggregates at a temperature range of 400°C to 800°C for a duration of up to 15 minutes;- a feeding mechanism for introducing fine aggregates having a particle size of up to 5 mm obtained from natural sands, gravels, or crushed stone screening plants into the thermal treatment unit; and- a control unit for adjusting the thermal treatment procedures, comprising a temperature sensor and a timer to regulate the thermal treatment duration based on moisture content, mineralogical, and thermal properties of the aggregates.
12. The system according to claim 11, characterized by further comprising cooling means for cooling the thermally treated aggregates to a handleable temperature.
13. The system according to claim 11 or 12, characterized by further comprising a collection mechanism for collecting the cooled aggregates for use in concrete, asphalt, and other construction materials.
14. The system according anyone of the preceding claims 11 to 13, characterized in that the thermal treatment unit is a rotary or stationary kiln.
15. The system according anyone of the preceding claims 11 to 14, characterized in that the control unit comprises means for adjusting the thermal treatment duration and heat supply based on the moisture content of the aggregates, where the duration increases by 2 to 5 minutes for every 10% increase in moisture content, with a maximum duration of up to 15 minutes, from 400°C to 800°C.
16. The system according anyone of the preceding claims 11 to 15, characterized in that the feeding mechanism comprises a conveyor belt.
17. The system according anyone of the preceding claims 11 to 16, characterized in that the collection mechanism comprises a storage container for the cooled and treated aggregates.
18. The system according to any one of the preceding claims 11 to 17, characterized in that the cooling means comprises an air cooling system, a water cooling system or a free cooling system.
19. The system according to any one of the preceding claims 11 to 18, characterized in that the feeding mechanism comprises a hopper for initial aggregate intake before conveying.
20. The system according to any one of the preceding claims 11 to 19, characterized in that the thermal treatment unit comprises means for uniform heat distribution to ensure consistent treatment of the fine aggregates.