Comparison of Physical and Mechanical Properties of Stone Aggregates and Their Use in the Structure of a Flexible Pavement, from Mines in Ecuador

Abstract

One of the reasons that cause premature deterioration of the wearing course is the quality of the materials that make up the flexible pavement structure of the road network in Ecuador. Therefore, there is a need to thoroughly study the stone materials, such as coarse aggregate and fine aggregate, which form the structure of the flexible pavement. The quality of these materials will determine the service life of the wearing course as well as the high or low cost of road construction. The main objective of this research was to determine the highest quality material based on its technical and economic characteristics. For this purpose, three main mines that supply stone materials in the country were selected: “Kumochi”, “Los Muelles”, and “Cantera El Salvador”. Several samples of fine aggregate and coarse aggregate were taken from these mines to conduct laboratory tests, including natural moisture content, Atterberg limits, gradation, modified Proctor, and relative density. The California Bearing Ratio (CBR) test was also performed to determine the load-bearing capacity of the samples. These data will be used in future investigations for the design of sustainable pavement structures. Additionally, physical and mechanical properties were determined through tests including aggregate soundness, resistance to abrasion, and the Los Angeles abrasion test to determine the percentage of fractured faces of the coarse aggregate. In conclusion, it was found that the material from the “El Salvador” mine has the best technical and economic characteristics for the formation of flexible pavement structures. However, the material from the “Kumochi” and “Los Muelles” mines met the standards of the international AASHTO norm. The final recommendation after conducting the research is that the aforementioned materials can be used not only for the formation of the pavement structure but also for the wearing course.

1. Introduction

Aggregates, also known as construction materials, are an important raw material commonly used in the construction of roads, buildings, bridges, and other civil infrastructure projects. They are composed of fine aggregate, known as sand, and coarse aggregate, known as gravel, crushed stone, limestone, and other materials. The production of these materials is of great global importance, with China being the main producer, followed by India and the United States. The aggregates industry is relevant in several countries.

In European countries such as Spain, for instance, the construction of houses requires an average of 150 to 450 tons of aggregates, schools use 3000 tons, a football stadium utilizes 300,000 tons, 1 km of highway requires 30,000 tons, and 1 km of railway requires 10,000 tons. Additionally, recycled materials from construction or demolition waste are also used as primary or secondary raw materials [1]. Furthermore, infrastructure projects such as hospitals, coliseums, bridges, shopping centers, airports, tunnels, skyscrapers, and logistics facilities are carried out to facilitate activities involving the movement of people and goods.

Another study conducted in Spain indicates that aggregates are also used for industrial applications. For example, 80% of limestone is used in cement production, 4% of aggregates are employed in lime and gypsum manufacturing, 3.5% of aggregates are used in basic metallurgy, 4.5% in the ceramic and glass industry, 4% in fuel for thermal power plants, 3% in basic chemical industry, and 1% in molding sands [2].

Globally, one of the main economic indicators of a country’s development is the growth and evolution of the construction sector. This implies that as construction increases, the demand for aggregates will also increase.

In the case of Ecuador, economic and financial indices are compiled and presented by the Central Bank of Ecuador. Among the information provided, the “Gross Value Added by Economic Activity” predicts that the construction sector will grow by 2.9% in 2022 compared to 2021 [3].

An appropriate fine aggregate for construction must meet specific requirements regarding its mineral composition and particle shape, which are typically found in designated mining areas. This is why mining plays a crucial role in obtaining high-quality fine aggregates, with river sand being widely recognized for its suitability in construction [1,2].

The particle shape and mineral composition characteristics also apply to coarse aggregates, which can be used directly after extraction or undergo a crushing process, with the latter being commonly used in construction [3].

The strength of aggregates is directly influenced by their porosity, where aggregates with lower porosity exhibit higher strength. The results of the study revealed that aggregates of basic nature, such as limestone and marble, exhibited superior water resistance compared to aggregates of acidic nature, represented by two types of granite. In particular, marble, despite its chemical similarity to limestone, demonstrated higher water resistance due to its lower porosity [4].

Based on the findings of this research, it can be concluded that aggregate quality plays a significant role in the compressive strength of concrete elements. There was a direct relationship observed between aggregate quality and compressive strength, suggesting that selecting high-quality aggregates can enhance the load-carrying capacity of structural concrete elements.

On the other hand, no significant correlation was found between aggregate quality and the stiffness of concrete beams. This indicates that other factors, such as the water–cement ratio and concrete mix proportioning, may have a more pronounced impact on the structural stiffness of beams.

Additionally, a positive relationship was observed between abrasion resistance and shear strength in concrete elements. This implies that as aggregate abrasion resistance increases, the concrete’s ability to resist shear forces improves, which is particularly important in structures exposed to adverse environmental conditions or subjected to dynamic loads.

In summary, the results of this study demonstrate the importance of considering aggregate quality in the design and construction of concrete elements, especially with regard to compressive and shear strength. These findings contribute to scientific knowledge in the field of structural engineering and can be used to optimize the performance and durability of concrete structures in future construction projects [5].

The same as crushing rock being able to improve the characteristics of coarse aggregate, the process of washing sand can significantly enhance its particle size distribution, directly affecting its physical properties. A rougher and more irregular shape ensures better cohesion between particles, both in individually used aggregates and in bound mixtures [6,7,8].

To obtain sand and gravel as construction aggregates, these materials undergo a process that begins with the extraction of natural resources from riverbeds, coastlines, and other habitats. The extraction process can be carried out using various methods, including dredging, quarrying, and open-pit mining [8,9,10].

Another sustainable mining practice is the use of dredging equipment that minimizes environmental impact. Dredging equipment employing low-impact techniques, such as suction dredging, can reduce the amount of sediment and chemical products released into rivers and other bodies of water [11,12].

The extraction of sand and gravel is a vital economic activity that involves extracting natural resources for use in construction. The mining process can have significant environmental impacts, including habitat destruction, soil erosion, and water pollution. However, these impacts can be mitigated through sustainable mining processes mentioned earlier [13].

The economic impact generated by the quality and volume of aggregate material used in road construction, for example, directly influences the construction budget. The cost of the layers comprising the pavement’s structural package depends mainly on their components and the requirements they must meet. Generally, the wearing course is the most costly layer due to its stricter quality requirements, addition of different additives, and construction demands. However, it is important to note that the cost of each layer can vary according to road conditions and design requirements. Underneath the wearing course, there are intermediate layers, such as the base and subbase, which function to transmit loads to the soil. One of the main functions of the subbase is to reduce costs by providing a firm and reliable foundation for the base layer, thus reducing its thickness and consequently its price. The cost of the base and subbase layers also varies according to factors such as the aggregates used for their production, project location, and specific requirements [14,15].

Sand and gravel are essential components of road construction, primarily forming the base and subbase layers of roads. The quality of the sand and gravel used in road construction is crucial to ensure the durability and longevity of the road. This article will explore the quality control process of sand and gravel used in road construction and examine various techniques employed to ensure that the material meets the required specifications [16].

The quality control process of sand and gravel used in road construction involves several steps, including sampling, testing, and analysis. Sampling is a critical step in the quality control process as it determines the representativeness of the material. It involves collecting representative samples of sand and gravel from the source. Samples are collected using various methods, including grab sampling, core sampling, and mechanical sampling [17].

Testing is the process of determining the physical and mechanical properties of the sand and gravel. It involves various laboratory tests, including sieve analysis, specific gravity, and percentage of absorption. These tests determine the size distribution, particle shape, and material strength. Analysis is the process of evaluating the test results to determine if the material meets the required specifications. It involves comparing the test results with the specifications set by regulatory authorities. If the material meets the specifications, it is considered suitable for use in road construction [18,19].

Quality management systems also involve monitoring the production process to ensure that the material meets the required standards [20,21].

Testing standards are used to ensure that laboratory tests conducted on sand and gravel meet the required specifications. Test standards specify the methods and procedures to be used for laboratory testing, including equipment, sample preparation, and data analysis [22].

The base and subbase layers play a significant role in the pavement structure and construction cost. They need to have high hardness and resistance to applied loads. These layers are typically composed of aggregates, as mentioned earlier. In addition to this, it is important to consider properties that directly affect the mechanical behavior of unbound mixtures and their quality, such as particle distribution, shape, relative density, internal friction, and cohesion, which will be studied in this article [23].

The quality of the aggregate materials plays a fundamental role in the construction of the pavement’s base and subbase, and its impact on the structure’s quality should not be underestimated. Aggregate materials like gravel and sand provide the necessary strength to withstand the applied loads on the pavement. The proper selection of aggregates, considering aspects such as particle size distribution, particle shape, and abrasion resistance, is crucial to ensure durable and stable base and subbase layers. These aggregates act as reinforcement elements in the pavement structure, helping to distribute loads and minimize deterioration caused by loading and traffic. Therefore, it is vital to understand and evaluate the quality of aggregate materials used in the construction of pavement base and subbase layers to ensure the long-term integrity and performance of roads and transportation routes.

Therefore, the purpose of this research is to contribute to innovation by proving updated information on the most suitable material type in terms of mechanical performance and economic efficiency. Thus, the aim was to provide precise data to both public and private entities, enabling them to design practical flexible pavement in the areas influenced by the mines previously mentioned in this study.

2. Materials and Methods

To carry out the present study, a sample of coarse aggregate and a sample of fine aggregate were used from each mine, resulting in a total of six samples for each test. The study was divided into five phases, which include preliminary studies, determination of the index properties of the aggregates, determination of the bearing capacity of the base and subbase mixtures, determination of the physical and mechanical properties, and percentage of fractured faces of the coarse aggregate. It is important to mention that all phases were conducted using experimental laboratory research because it aimed to have a controlled environment where a comprehensive analysis of variables that could alter the results could be obtained.

The first phase consisted of preliminary studies, which were conducted by extracting the samples using manual collection instruments and plastic containers to retain moisture and fine fraction of the material. Subsequently, the aggregates were mixed through sieving processes to meet the particle size distribution established by the Ecuadorian Road Standard (NE-VI-12).

The second phase involved conducting tests to determine the index properties of the aggregates according to the American Society for Testing and Materials (ASTM) and the Ecuadorian Standardization Service (INEN).

In the conducted study, the ASTM D2216-19 test was carried out to determine the natural moisture content of a soil sample in the laboratory. The sample was taken to preserve its natural moisture content, as shown in Figure 1. A minimum sample weight of 100 g was taken for the washed sand and 5 kg for the screened gravel, which were weighed using a Satorius M-Power balance with a precision of 0.001 g for small samples and a Lexus B22T0001 balance with a precision of 0.001 kg, which were used in the development of all tests. The samples were placed in pre-weighed and cleaned oven containers and subjected to a temperature of 105 °C for a sufficient period to ensure complete drying. Once this state was reached, the containers were removed from the oven and weighed again. Water was then added to the minimum test samples, and they were reweighed to obtain the wet weight of the soil. Finally, the sample was placed in the oven again at the same temperature until a constant weight was achieved, indicating that the sample was completely dry, and it was weighed for the final time to obtain the dry weight of the soil. With these values, the moisture percentage was calculated using Equation (1).

In the conducted study, the ASTM D2216-19 test was carried out to determine the natural moisture content of a soil sample in the laboratory. To obtain a representative soil sample, multiple samples were taken at different points in the area of interest and mixed to obtain a homogeneous sample. A minimum sample weight of 100 g for the washed sand and 5 kg for the screened gravel was taken from each mine, which were placed in pre-weighed and cleaned aluminum containers. The containers were subjected to a temperature of 105 °C for a sufficient period to ensure complete drying. Once this state was reached, the containers were removed from the oven and weighed again. With these values, the moisture percentage was calculated using Equation (1).

The percentage was calculated using the following equation:

$$\mathsf{\omega }\mathrm{\%}=\left(\frac{\mathrm{W}\mathrm{w}}{\mathrm{W}\mathrm{s}}\right)\ast 100$$

(1)

where

Ww: Weight of water.

Wm: Wet weight of soil.

Ws: Dry weight of soil.

ω%: Moisture content.

The property of natural moisture content is of great investigative importance in road construction, especially in the formation of the base and subbase, as it has a significant effect on material compaction and strength. The natural moisture content of aggregates used in road construction can affect bearing capacity, wear resistance, durability, and pavement stability. Inadequate moisture content can negatively impact material compaction, resulting in reduced bearing capacity and increased susceptibility to permanent deformation. Therefore, it is essential for civil engineers to understand the relationship between natural moisture content and material strength to ensure the construction of durable and safe roads. Furthermore, research in this area can lead to improved construction practices and the development of new materials and construction techniques that enhance the quality and durability of roads.

In the determination of the Atterberg limits under INEN 691 and 692 standards, the fraction of fine aggregate passing through sieve No. 40 (425 microns) was used. For the liquid limit (INEN 691), the one-point test method was conducted using 200 g of moistened sample. The sample was carefully mixed with water in a mortar using a pestle or spatula. Subsequently, water was added progressively to meet the specified drop ranges, as established by ASTM standards.

In the determination of the plastic limit (INEN 692), 100 g of sample passing through sieve No. 40 (425 microns) was used. Water was arbitrarily added to the sample until a soil paste was formed, which could be molded into a sphere using fingers without sticking. Cylinders were placed in appropriate containers to extract the moisture content.

For the determination of the liquid limit, a representative sample of the soil to be analyzed was prepared. This sample was dried and sieved through sieve No. 40. Water was then added to the sample to obtain a soil paste with an initial moisture content of approximately 20% to 30%. The soil paste was placed in the Casagrande cup and smoothed with a rod. The cup was dropped from a standard height of 10 mm at regular time intervals, and the number of blows required for the groove in the sample to close over a length of 13 mm was recorded, as shown in Figure 2. The process was repeated several times with different moisture levels to obtain a range of results and determine the liquid limit of the soil. The liquid limit was determined as the value at the intersection between the curve and the ordinate 25 rounded to the nearest whole number. Equation (1) was used because the main calculation corresponds to the moisture content.

Atterberg limits are a crucial tool in soil investigation and the formation of base and subbase for road construction and other civil engineering structures. These limits provide valuable information about the plastic and shear strength properties of soils, which assist engineers in selecting suitable materials for construction. The determination of Atterberg limits is of great importance in the formation of road base and subbase and other civil engineering structures. They serve as indicators of the plastic and shear strength properties of soils, enabling the selection of the most appropriate materials for base and subbase construction. Additionally, they are also used in soil classification and in the evaluation of slope and embankment stability, which is crucial for ensuring the safety and durability of constructed structures.

The plasticity index was calculated using the following equation:

$$\mathrm{I}\mathrm{P}=\mathrm{L}\mathrm{L}-\mathrm{L}\mathrm{P}$$

(2)

where

IP: Plasticity index.

LL: Liquid limit.

LP: Plastic limit.

According to the procedure described in ASTM C136/136M-19 standard, 1000 g of previously dried washed sand was taken from an oven with a constant temperature of 110 ± 5 °C, and the sieves were arranged from largest to smallest opening. Then, the sand sample was sieved for 10 min using an electric sieve shaker, as shown in Figure 3, ensuring that the material retained in each sieve was well separated and ready for weighing. The weight retained on each sieve was recorded, and the cumulative percentage passing through each sieve was determined. This process resulted in the grain size distribution curve of the sand sample.

On the other hand, the process for the screened gravel was similar, with the difference being that sieves with a larger frame and correspondingly larger openings were used. Additionally, the sieving was performed manually due to the dimensions of the sieves. In this case, a sample of dried screened gravel from an oven at a constant temperature of 110 ± 5 °C was taken and manually sieved, ensuring that all the material passed through the sieves. Similar to the washed sand test, the weight retained on each sieve was recorded, and the cumulative percentage passing through each sieve was determined. The importance of particle size distribution lies in its ability to determine the distribution of particle sizes present in the material, which affects its water drainage capacity and load-bearing capacity. These parameters are essential for the formation of unbound mixtures used in road construction.

The modified Proctor test allows determining the appropriate amount of water to be added to the soil and aggregate mixture to achieve optimal density and moisture content, thereby avoiding potential compaction issues and reducing the strength of the layer. This ensures greater durability and resistance of the road against traffic loads and weather conditions it will be exposed to. Consequently, it guarantees proper load-bearing capacity of the road structure and prevents future failures in the base and subbase layers that could lead to costly repairs and maintenance.

Regarding the testing procedure for determining the relative density of washed sand, ASTM C127-15 standard was used, which corresponds to the test method for density, relative density, and absorption of coarse aggregate. In this case, approximately 1000 g of pre-dried sample was immersed in a container of water for 24 ± 4 h to achieve the state of surface-dry aggregate (SSD), as shown in Figure 4, where the pores of the aggregate are filled with water, but the outer surfaces are dry. Then, the specific gravity bottle was filled and weighed with water, and subsequently, the content of the bottle was poured into a container to be dried in an oven and obtain its dry weight.

The calculations were performed according to the following equations:

$$SH=\frac{A}{(B+S-C)}$$

(3)

$${SH}_{\left(sss\right)}=\frac{S}{(B+S-C)}$$

(4)

$$Bulkrelativedensity=\frac{A}{(B+A-C)}$$

(5)

where

SH: Apparent relative density.

A: Mass of the oven-dried sample.

B: The pycnometer must be filled with water up to the calibration mark.

C: Mass of the pycnometer filled with the sample and water up to the calibration mark.

S: Mass of the sample in SSD (saturated surface dry) condition.

SH_(sss): Apparent relative density, surface saturated dry.

Regarding the test for screened gravel, ASTM C128-15 standard was used, which corresponds to the test method for density, relative density, and absorption of fine aggregate. In this case, approximately 1000 g of coarse aggregate sample was also submerged for 24 ± 4 h to fill the pores and obtain the SSS state, as shown in Figure 5. The immersed and air-dried basket was weighed. Then, the sample was placed inside the basket and weighed again, both in air and submerged, while shaking the basket from side to side to remove any air bubbles that the aggregate may contain. Finally, the sample was removed from the water and placed in a container to be dried in an oven and determine its mass.

Calculations were performed using the following equations:

$$\mathrm{S}\mathrm{H}=\frac{\mathrm{A}}{(\mathrm{B}-\mathrm{C})}$$

(6)

$${\mathrm{S}\mathrm{H}}_{\left(\mathrm{s}\mathrm{s}\mathrm{s}\right)}=\frac{\mathrm{B}}{(\mathrm{B}-\mathrm{C})}$$

(7)

$$\mathrm{D}\mathrm{e}\mathrm{n}\mathrm{s}\mathrm{i}\mathrm{d}\mathrm{a}\mathrm{d}\mathrm{r}\mathrm{e}\mathrm{l}\mathrm{a}\mathrm{t}\mathrm{i}\mathrm{v}\mathrm{a}\mathrm{a}\mathrm{p}\mathrm{a}\mathrm{r}\mathrm{e}\mathrm{n}\mathrm{t}\mathrm{e}=\frac{\mathrm{A}}{(\mathrm{A}-\mathrm{C})}$$

(8)

where

SH: Relative density.

A: Mass of the oven-dried tested sample.

B: Mass of the sample saturated surface dry.

C: Apparent mass of the saturated sample in water.

SH_(sss): Relative density saturated surface dry.

The relative density of the aggregate is a key parameter in the construction of road bases and subbases, as it directly influences the density of the resulting mixture and, therefore, the load-bearing capacity it provides to the road. An optimally dense mixture has higher resistance to deformation and lower susceptibility to water accumulation, resulting in increased durability and safety on the road. Additionally, a well-compacted mixture has fewer void spaces, making it more resistant to the formation of potholes and cracks due to traffic and weather conditions. Therefore, the relative density of the aggregate is a critical factor in road base and subbase construction, and its accurate determination is essential to ensure the quality and durability of the project.

The third phase consisted of determining the load-bearing capacity of the base and subbase samples using the California Bearing Ratio (CBR) test according to ASTM D1883-16 standard.

The sample used for this test consisted of 6000 g of material passing the ¾-inch (19 mm) sieve, with appropriate correction for the portion of the sample retained in it by removing and replacing it with material passing the ¾-inch sieve and retained on the No. 4 (4.75 mm) sieve.

Next, the mold was immersed, and the deformation meter was placed as shown in Figure 6, and the initial height was recorded to calculate the expansion or swelling of the material.

Then, the mold was immersed, the deformation meter was positioned to touch the rod, and the initial height was recorded to calculate the expansion or swelling of the material.

The material was soaked for 96 ± 2 h while maintaining a constant water level during this period, and the swelling was calculated with a precision of 0.1% as a percentage of the initial height previously recorded.

Subsequently, weights were placed without the rod to conduct the test using the automatic testing machine, Controls model 73V1174.

The specimen was placed in the machine, and the test was conducted.

This process was carried out similarly, with variations in the number of blows during the compaction process, using 25 and 10 blows per layer.

Calculations were performed according to the following equations:

$${\mathsf{\rho }}_{\mathrm{d}}=\frac{{\mathrm{M}}_{\mathrm{s}\mathrm{a}\mathrm{c}}}{{\mathrm{V}}_{\mathrm{m}}}$$

(9)

$${\mathrm{M}}_{\mathrm{s}\mathrm{a}\mathrm{c}}=\frac{{\mathrm{M}}_{\mathrm{m}+\mathrm{w}\mathrm{s}}-{\mathrm{M}}_{\mathrm{m}}}{(1+{\mathrm{w}}_{\mathrm{a}\mathrm{c}})}$$

(10)

where

${\mathrm{M}}_{\mathrm{s}\mathrm{a}\mathrm{c}}$: Compacted soil mass.

${\mathrm{M}}_{\mathrm{m}+\mathrm{w}\mathrm{s}}$: Wet soil mass plus mold mass.

${\mathrm{M}}_{\mathrm{m}}$: Mold mass.

${\mathrm{w}}_{\mathrm{a}\mathrm{c}}$: Moisture content during the compactation process.

${\mathrm{V}}_{\mathrm{m}}$: Compactation mold volume.

The fourth phase corresponded to the determination of the physical and mechanical properties of the samples.

In accordance with ASTM D1557-12 standard, this method was used to determine the relationship between the moisture content in the soil and its compacted dry unit weight using a mold with standardized dimensions and a 10 lb piston dropped from a height of 18 in, resulting in a compaction effort of 27,000 kN-m/m³, as shown in Figure 7.

Method C was used because less than 30% of the aggregate mixture was retained on the ¾-inch sieve, indicating the presence of significantly sized granular material.

During the preparation of the sample for the test, it was necessary to sieve the aggregate sample through a ¾-inch sieve and separate the components by size to ensure that the material to be compacted in the mold was homogeneous.

The appropriate moisture percentage was selected for each aggregate sample by adding water incrementally and thoroughly mixing to achieve a uniform distribution of moisture throughout the sample.

After each piston blow, the thickness of the compacted layer was measured to ensure the correct height was achieved for each layer. Upon completing the compaction of the five layers, the collar was removed, and the total volume of the compacted sample was measured. A sample was then extracted to determine the moisture content of the compacted sample, with samples taken from both the top and bottom parts. This process was repeated for each of the five different and progressive moisture contents.

The calculations were performed using the following formulas:

$${\rho }_m=\mathrm{K}\ast \frac{(M_t-M_{md})}{\mathrm{V}}$$

(11)

where

${\rho }_m$: Wet density.

K: Conversion constant, use 1 for g/cm³ and volume in cm³, 1000 for g/cm³ and volume in m³, 0.001 for kg/cm³, and 1000 for kg/m³ and volume in cm³.

$M_t$: Mass of moist soil in the mold.

$M_{md}$: Mass of the compaction mold.

V: Volume of the compaction mold in cm³ or m³.

$${\rho }_d=\frac{{\rho }_m}{1+\frac{\omega }{100}}$$

(12)

where

${\rho }_d$: Dry density.

${\rho }_m$: Wet density.

ω: Moisture content.

The moisture content was calculated using Equation (1).

The aggregate soundness test, according to ASTM C88-18 standard, was conducted following ASTM C88-18 standard procedures. Firstly, the sample was selected and prepared by washing and oven-drying at a constant temperature of 110 ± 5 °C, followed by separation based on the desired particle size distribution. Subsequently, the sample was immersed in a sodium sulfate solution for 16 h to simulate the moisture conditions to which the aggregates would be exposed in the field.

After this period, the sample was dried for 15 ± 5 min and placed in a drying oven at a constant temperature of 110 ± 5 °C until a constant weight was achieved. This was verified at intervals of 2 to 4 h until the weight loss was less than 0.1% of the sample in 4 h of drying. Once the constant temperature was reached, the samples were cooled to room temperature before being immersed again in the magnesium sulfate solution. This immersion and drying process was repeated three times to ensure sample saturation with the solution.

Upon completion of the immersion and drying cycles, a qualitative analysis was performed on the samples larger than ¾ inch, classifying them based on the damage caused to the aggregate, such as cracking, crumbling, fracturing, or scaling. The number of affected particles was recorded for each type of damage produced. The effect of sulfate on the aggregate can be observed in Figure 8.

The soundness of aggregates influences the material’s ability to withstand traffic loads and its durability against climatic conditions and the passage of time. Therefore, the soundness test is essential to determine the quality of aggregates and ensure their proper performance in pavement construction.

Furthermore, the abrasion resistance test was conducted following ASTM C131/131M-20 standard. The aggregate was sieved to achieve the particle size distribution specified by the standard for Method A, with a load of 5000 g. Subsequently, the sample was washed and oven-dried at a constant temperature of 110 ± 5 °C until a constant mass was obtained. Once the aggregate sample was sieved and oven-dried, it was placed in the Los Angeles abrasion machine along with the steel spheres, as shown in Figure 9. The machine rotated the sample and steel spheres at a specific speed for a determined period, causing wear on the surface of the aggregates.

Afterward, the sample was removed from the machine, and the material was sieved through a No. 12 (1.70 mm) sieve, separating the fine and coarse materials. The mass loss was calculated and expressed as a percentage of the original mass of the sample.

The abrasion resistance of aggregates is important for evaluating the durability and quality of materials used in pavement construction. Pavements must be able to withstand vehicular traffic and adverse environmental conditions without excessive wear. Therefore, this test is used to assess the ability of aggregates to resist abrasion and determine if they are suitable for use in the construction of pavement bases and subbases.

The final phase consisted of determining the percentage of fractured faces according to ASTM D5821-13 standard. Once the sample could be handled by hand, each element was carefully inspected to determine if it met the fractured particle criterion: “A fractured surface constitutes an area of at least 25% of the area projected by the particle when viewed perpendicular to it”.

It was taken into account for this test that each aggregate particle has at least two fractured faces. The ASTM D5821 test was used to determine the percentage of fractured faces in coarse aggregates and was performed on a minimum number of 200 particles. The procedure began with the preparation of the aggregate sample, which must be representative of the material to be used in the project.

Once the sample was prepared, 200 randomly selected aggregate particles were chosen for testing. These particles were washed and dried to remove any contamination, and particles that did not meet the fractured particle criterion, i.e., particles that did not have a fractured surface constituting at least 25% of the area projected by the particle when viewed perpendicular to it, were removed.

Next, each selected particle was placed on a glass plate and carefully inspected to determine if it met the two fractured faces criterion. A particle was considered to have two fractured faces if both opposite faces of the particle have a fractured surface constituting at least 25% of the area projected by the particle when viewed perpendicular to it. The difference between particles that met this criterion and those that did not was noticeable, as shown in Figure 10.

Once the particles that met the particle and two fractured faces criterion were identified, the total number of tested particles and the number of particles that met the mentioned criterion were recorded.

The percentage of fractured faces was calculated by dividing the number of particles that met the two fractured faces criterion by the total number of tested particles and multiplying the result by 100.

The percentage of mass of the particles was calculated according to the following formula:

$$P=\left[\frac{F}{(F+N)}\ast 100\right]$$

(13)

where

P: Percentage of particles with fractured faces.

F: Mass of particles with fractured faces.

N: Mass of particles that do not meet the criterion for fractured particles.

The property of percentage of fractured faces in coarse aggregate is directly related to interparticle friction and shear strength of the material. A greater number of fractured faces in aggregate particles can provide a rough contact surface that increases interparticle friction between the aggregates. This can enhance the material’s capacity to withstand loads and reduce material slippage, which is important for the stability and shear strength of pavement base and subbase.

Furthermore, the percentage of fractured faces also influences the material’s shear strength, as particles with more fractured faces can provide greater resistance to movement and deformation under load. Therefore, it is important to measure the percentage of fractured faces in coarse aggregate to ensure that the requirements for interparticle friction and shear strength necessary for durable and stable base and subbase in pavement construction are met.

3. Results

As a result of mixing aggregates following the limits established by the NEVI standard in phase one, the particle size distribution curves described in Figure 11, Figure 12, Figure 13, Figure 14, Figure 15 and Figure 16 could be identified:

Particle size distribution curves were identified in Figure 11, Figure 12, Figure 13, Figure 14, Figure 15 and Figure 16 that remain within the limits established by the NEVI standard for both Base Class 1 Type B and Subbase Class 2, with minimal variations between materials from each mine depending on the type of unbound mixture.

As a result of the tests carried out in phase two, the results of the natural moisture content test along with the recommended limits for better transportation and storage of the mined material can be identified in

Table 1. Results of moisture content test.

Moisture Content
Mine	Material	Value (%)	Recommended Limits
El Salvador	Washed sand	3.94	<8%
	Screened gravel	1.29	<3%
Kumochi	Washed sand	4.00	<8%
	Screened gravel	1.80	<3%
Los Muelles	Washed sand	4.09	<8%
	Screened gravel	1.85	<3%

.

It can be observed that the obtained moisture content percentages comply with the recommended limits for workability and compliance according to the design requirements (NEVI-12).

Continuing with the tests to determine the index properties in the second phase, the following Atterberg limits results were obtained, as shown in

Table 2. Results of Atterberg limits test.

Mine	El Salvador	Kumochi	Los Muelles	Limits (NEVI)
Material	Washed Sand	Washed Sand	Washed Sand
Atterberg Limits	Value	Value	Value
Liquid limit	17.85	17.85	13.69	≤25
Plastic Limit	23.28	23.28	20.39	-
Plasticity index	−5.43	−5.43	−6.7	<6

, along with the recommended range for each limit according to NEVI.

It can be observed that the liquid limit values are within the range established by the NEVI standard, being less than or equal to 25. The plasticity index, as observed, is negative which complies with the value established by the NEVI standard that stipulates a value less than six for this index.

Regarding the granulometric analysis of the aggregate, the curves are described in Figure 17, Figure 18, Figure 19, Figure 20, Figure 21 and Figure 22, where the upper and lower limits for fine and coarse aggregates determined by the ASTM standard can also be seen.

The results of the modified Proctor test are shown in

Table 3. Results of the modified Proctor test.

Modified Proctor
Mine	Material	Maximum Dry Density (gr/cm3)	Optimum Moisture Content (%)
El Salvador	Base	2.007	10.00
	Subbase	2.187	9.45
Kumochi	Base	1.893	10.45
	Subbase	2.051	8.15
Los Muelles	Base	1.891	8.80
	Subbase	1.996	9.50

.

Consistent data are shown for the granulometric type of Class 1 Type B base and Class 2 subbase. Additionally,

Table 4. Results of the relative density test.

		Relative Density	Typical Values	Absorption	Recommended Values
Mine	Material	Value	Range	Value (%)	Value (%)
El Salvador	Washed sand	2.29	2.5–3.00	0.6	4% max.
	Screened gravel	2.49		3
Kumochi	Washed sand	2.23		1.4
	Screened gravel	2.45		1
Los Muelles	Washed sand	2.36		4
	Screened gravel	2.41		2

displays the results of relative density, as well as typical values for sands and gravels, along with the absorption percentages accompanied by the recommended value for aggregates by the United States Department of Transportation [24,25].

Since the relative density value is not within the typical range of values for aggregates, the analysis of results was compared with data obtained from a study conducted by Veintimilla L. using mine material from the Ambato Canton, which allowed for a more direct comparison [26]. Regarding the absorption percentage, it falls within the range recommended by the Federal Highway Administration (FHWA) in the Standard Specifications for Road and Bridge Construction [25].

Once the results of the index properties tests for aggregates were obtained, phase three continued with the CBR test applied to the base and subbase samples, resulting in the values shown in

Table 5. Results of California Bearing Ratio test.

California Bearing Ratio
Mine	Material	CBR 0,2 plg (%)	Limits (NEVI)
El Salvador	Base	104	≥80%
	Subbase	74	≥30%
Kumochi	Base	100	≥80%
	Subbase	67	≥30%
Los Muelles	Base	101	≥80%
	Subbase	62	≥30%

, which also includes the limits established by the NEVI for each type of material.

The obtained values comply with the NEVI standard, which establishes that the CBR for base must be at least 80% while for subbase it must be at least 30%. Therefore, it was verified that the unbound base and subbase mixes from the three mines comply with Ecuadorian regulations.

CBR values higher than 100% could be identified, which is due to the standard used for this test, namely ASTM D1883 [27].

Continuing with phase four, the results of the aggregate durability test in sodium sulfate are shown in

Table 6. Results of the aggregate durability test in sodium sulfate.

Aggregate Durability in Sodium Sulfate
Mine	Material	Value (%)	Limit (NEVI)
El Salvador	Washed sand	3.2	<10%
	Screened gravel	1.6	<12%
Kumochi	Washed sand	3.9	<10%
	Screened gravel	1.8	<12%
Los Muelles	Washed sand	4.7	<10%
	Screened gravel	2.3	<12%

, along with the limits stipulated by the NEVI for each type of material.

The aggregates from the three mines presented a weighted percentage loss that complies with the NEVI standard, which establishes a maximum value of 10% for sand and 12% for gravel of weighted percentage loss due to sulfate action.

Regarding the mechanical wear resistance or abrasion resistance, the resulting data are shown in

Table 7. Results of the coarse aggregate abrasion resistance test.

Abrasion Resistance
Mine	Material	Value (%)	Limit (NEVI)
El Salvador	Screened gravel	12	<40%
Kumochi	Screened gravel	11	<40%
Los Muelles	Screened gravel	9	<40%

, where the wear percentages obtained for each gravel sample are identified, in addition to the limit established by the NEVI.

The percentage of loss due to mechanical action from the three mines complies with the NEVI standard, as it establishes a maximum value of 40%.

Continuing with phase five, the test to determine the percentage of fractured faces of coarse aggregate resulted in the values shown in

Table 8. Results of fractured faces percentage tests.

Percentage of Fractured Faces
Mine	Material	Value (%)	Limit (NEVI)
El Salvador	Screened gravel	80	≥75%
Kumochi	Screened gravel	76	≥75%
Los Muelles	Screened gravel	77	≥75%

, where the minimum percentage that must be met according to the NEVI can also be identified.

The percentage of fractured faces in the coarse aggregate from the three mines complies with the NEVI standard, which establishes a minimum value of 75% of particles that meet the fractured face criterion.

4. Discussion

After obtaining the results from phase one, particle size distribution curves were identified that meet the requirements stipulated by NEVI for base Class 1 Type B and subbase Class 2.

In phase two, the natural moisture content values for washed sand range from 4% to 3.13%, while for screened gravel, they range from 1.85% to 1.29% at the stockyards of each mine, which is within the recommended limits (3% to 8%) for meeting design requirements (NEVI-12).

As for the Atterberg limits, it was identified that the data obtained from sand for the plasticity index of all three mines fall within the limits of the Ecuadorian Road Standard (<6), with all values being negative, indicating no plasticity, which minimizes deformations that may occur when applying loads on layers and prevents layer expansion in the presence of water, thus reducing volumetric changes in the presence of moisture.

Regarding the particle size analysis, it was identified that for the “El Salvador” mine:

Washed sand: The particle size distribution curve is not within the parameters of ASTM C33 because there were more coarse particles up to sieve No. 16, and from sieve No. 40, there was less fine material resulting in a material with an irregular particle distribution [28].

Screened gravel: The particle size distribution curve for screened gravel showed an increased amount of particles from the ¾-inch sieve, indicating that the gravel from this mine had more particles smaller than 19 mm, resulting in a poor particle size distribution.

For the “Kumochi” mine:

Washed sand: Based on the presented granulometric curve, it was identified that from sieve No. 30 to sieve No. 60, there was a smaller quantity of particles of this size, resulting in this section of the curve approaching the upper limit established by ASTM C33 and slightly exceeding it, making the material less irregular in terms of particle distribution.

Screened gravel: The granulometric curve of this material showed a range that exceeds the upper limit specified by the standard exactly at sieve No. 1, as more particles of this size are needed to give uniformity to the curve.

For the “Los Muelles” mine:

It was determined that both the fine and coarse aggregate granulometric curves fall within the limits established by ASTM C33.

Both granulometric curves are in the middle of the upper and lower limits, indicating a high quality and good particle distribution in terms of the granulometric standard established by the norm.

The modified Proctor test determined that the base material with the highest maximum dry density was obtained from the “El Salvador” mine.

Regarding the moisture required to achieve the maximum dry density, the one that required the least amount of moisture in the compaction process was made from the aggregates from the “Los Muelles” mine.

As for the subbases, the one with the highest maximum dry density was made from the “El Salvador” mine, while the one that required the lowest percentage of moisture to reach its maximum dry density was made from the “Kumochi” mine.

Table 9. CBR Values.

Type	Maximum Density (g/cm3)	Maximum Density (95%) (g/cm3)	Optimum Moisture Content (%)	CBR (%)
Subbase Class 1	1.972	1.873	9.81	77.8
Subbase Class 2	1.988	1.889	9.64	74.5
Subbase Class 3	1.926	1.830	10.9	70.2
Base Class 1 Type A	2.187	2.078	10.06	99.2
Base Class 2	2.131	2.024	9.95	95.2
Base Class 3	2.079	1.975	10.29	89.5
Base Class 4	2.045	1.943	9.64	86.1

Source: Analytical-Technical Correlation between Resilient Modulus and California Bearing Ratio Laboratory Tests of the Copeto Mine, Parra et al.

shows maximum density values from the “Analytical-technical correlation between laboratory tests of resilient modulus and California Bearing Ratio of the Copeto mine” study by Parra et al., which showed that the figures obtained in this study for the “El Salvador”, “Kumochi”, and “Los Muelles” mines are consistent and bear some resemblance to the values obtained in the study conducted in the Santo Domingo province of Ecuador [29].

Regarding specific gravity, the washed sand with the highest density comes from the “Los Muelles” mine, while the lowest density is from the “Kumochi” mine.

As for screened gravel, the one with the highest density comes from the “El Salvador” mine, contrasting with the one from the “Los Muelles” mine, which had the lowest relative density.

As identified, the values obtained in Table 4 do not fall within the range established by author Mishra G., which is from 2.5 to 3.00; however, similar relative density values calculated by Veintimilla L. can be identified in

Table 10. Real Density and Absorption Capacity of Aggregates—Quarries Summary.

Quarries:	KUMOCHI		PUERTA DEL SOL		MINA MORA
FACTOR:	DR (gr/cm3)	CA (%)	DR (gr/cm3)	CA (%)	DR (gr/cm3)	CA (%)
Gravel-PCA	2.25	2.68	2.32	3.75	2.30	5.18
Gravel-STOCK	2.35	3.75	2.41	4.06	2.34	6.13
Sand-PCA	2.56	0.90	2.47	3.70	1.75	2.88
Sand-STOCK	2.69	0.94	2.42	4.74	1.78	3.00

from their study conducted in the Ambato Canton of the Tungurahua province, Ecuador, due to the soil’s origin, components, and characteristics [26,30].

The absorption percentage obtained is within the recommended range of a 4% maximum by the United States Department of Transportation [26].

In phase three, according to the analysis of the results, the CBR obtained by the bases had values higher than 100, meeting the requirement of the Ecuadorian Road Standard which states: “the CBR support value shall be equal to or greater than 80%”. For the subbase, values were also obtained that meet the standards of the standard which states: “The support capacity shall correspond to a CBR equal to or greater than 30%” [31].

Thus, it can be identified that the CBR values obtained far exceed the minimum values recommended by the standard for both the base and subbase. It is worth mentioning that the base and subbase with the best results were those made with material from the “El Salvador” mine. According to Table 9, coherent and similar values were obtained for the base and subbase samples. Later, in phase four, according to the Ecuadorian Road Standard, it was found that the values obtained for resistance to sodium sulfate are within the estimated range because no percentage exceeds 10%, in the case of washed sand, or 12% for screened gravel. Similarly, with regard to mechanical factors, it was noted that the abrasion values of the crushed gravel samples are within the standards indicated by the Ecuadorian Road Standard: “The percentage of aggregate abrasion wear shall be less than 40%” [31].

This indicates that the wear suffered by the aggregate is lower than that established by the standard, thus entering the desired quality standard. Finally, in phase five, the values obtained in the test for the percentage of fractured faces comply with the requirement stipulated by the Ecuadorian Road Standard: “Coarse aggregates retained on the INEN 4.75 mm sieve must have a certain angularity, containing at least 75% by weight of crushed elements containing two or more fractured faces” [31].

This means that the material has faces that, when in contact with the fine aggregate and each other, will achieve good friction and, therefore, a high shear strength.

5. Conclusions

After carrying out the analysis of the index properties of the aggregates from the “El Salvador”, “Kumochi”, and “Los Muelles” mines, it was determined that the values obtained for the Atterberg limits, moisture content, modified Proctor, and relative density meet the requirements established by the Ecuadorian Road Standard and are consistent with the type of material evaluated. However, regarding the particle size distribution, only the fine and coarse aggregates from the “Los Muelles” mine comply with the limits established by ASTM standards.

The unbound mixtures made from the material from the three mines achieved an average of 102% for Class 1 Type B base and 68% for Class 2 subbase, in terms of California Bearing Ratio (CBR). These values comply with the standard set by the Ecuadorian Road Standard, which recommends a CBR greater than 80% and 30%, respectively, for each type of unbound mixture. It is important to highlight that the mixtures made with material from the “El Salvador” mine obtained the highest CBR value.

In the sulfate resistance test, average weighted loss values of 3.93% and 1.90% were obtained for the fine and coarse aggregates, respectively. These values are within the limits established by the Ecuadorian Road Standard, which recommends values below 10% for sand and 12% for gravel. It is noteworthy that the aggregates from the “El Salvador” mine had the lowest weighted loss percentage, indicating that they will be less susceptible to chemical and weathering factors.

These results are consistent with recent similar research, where it has been observed that the selection and quality of aggregates used in unbound mixtures significantly influence the performance and durability of base and subbase layers in pavements. These findings support the importance of carefully considering the origin and properties of aggregates in the construction of roads and transportation routes, with the aim of ensuring long-term strength and stability of pavement structures.

After conducting the abrasion resistance test for coarse aggregate, an average percentage loss value of 10.67% was obtained, which complies with the Ecuadorian Road Standard’s recommendation of a value below 40%. It should be noted that the aggregate with the lowest loss came from the “Los Muelles” mine with 9%, indicating that this aggregate will be less susceptible to mechanical wear.

The average percentage of fractured faces for the coarse aggregate was 77.67%, which falls within the standard of the Ecuadorian Road Standard, recommending values greater than or equal to 75%. Therefore, it can be said that the coarse aggregate from the three mines underwent a proper crushing process. However, the aggregate from the “El Salvador” mine had the highest percentage of fractured faces with 80%.

In conclusion, the material from the “El Salvador” mine presented the best physical and mechanical characteristics, in addition to having the lowest average cost per cubic meter at the plant 6.50 USD). The quality of the materials from the “Kumochi”, “Los Muelles”, and “El Salvador” mines was evaluated through laboratory tests, resulting in the aggregates from all these mines being suitable for the production of base and subbase for road construction.

The relevance of this study extends to public and private entities involved in the planning, design, and construction of road infrastructure. The results of this research provide valuable information for informed decision making in the selection of aggregates, resulting in a significant improvement in pavement quality and the optimization of available resources. This investigation successfully contributed with filling the existing information gap regarding the characterization of coarse and fine aggregates in Ecuador. Through an innovative approach, the aim is to provide public and private entities with up-to-date and reliable data, thus facilitating a practical and efficient flexible pavement design in areas influenced by the studied mines. This is all to enhance the quality of road infrastructure and optimize the use of economic resources available in the country, while providing researchers with updated information on this field in South America.