Validity of Limestone Aggregates for Using in Asphalt Concrete Mixtures for Surface Layer of Roads

Abstract


Introduction
Natural aggregate is considered as a group of rocky particles of the size gravel, sand formed from weathering and erosion of the source rocks, which represent igneous, metamorphic, sedimentary rocks and are formed in their different sedimentary environments (Shareef et al., 2020) , including those resulting from the cracking of different rocks, which is called natural aggregate with gravel and crushed sand (Câmara et al., 2021).As for industrial aggregates, they are obtained from crushing natural rocks, limestone by crushers, which is called limestone in coarse sizes as gravel, fine size as sand) (Atiyeh and Aydin, 2020).Limestone is an important source of coarse and fine aggregate.The limestone crusher is among the important principles in the industrial environment, which represents the largest portion of the materials used in roadworks, construction, and engineering projects that require aggregates as well as the importance of its use in designing an asphalt concrete mix for the surface layer, as it occupies the largest portion of the concrete volume, about 70-75% of the total volume of the concrete block (Arulrajah et al., 2013).The process of selecting the comprehensive aggregate used for all these projects requires a lot of effort and in order to suit all the requirements and the wide and rapid urban developments in the fields of life, and on this basis that the selection process must have special specifications that match the international and Iraqi standards specifications for these materials (Vavrik et al., 2002).
Numerous studies have evaluated the usage of aggregates in asphalt mixtures in various parts of Iraq and also in places nearby Iraq (Jaber et al., 2022).In order to create asphalt mixtures for use in building roads.Nassif (2018) studied the evaluation of the viability of limestone for engineering purposes in northern Iraq .The quaternary age sediments were examined to ascertain their suitability for engineering purposes as well as their suitability for road and concrete works.This was done in order to evaluate the geotechnical evaluation and environmental impacts of the mixed gravel quarries in the Qara Salem region and Kirkuk, Iraq.The qualitative evaluation of coarse aggregates was investigated in a few regions of Salah al-Din in central Iraq, and the results showed that sedimentary rocks (the Injana Formation, Fatah Formation, Muqdadiyah Formation, and Bai Hassan Formation) are the primary sources of other rocks (Al-Haddad, and Abdullah, 2001).However, the geotechnical assessment of the coarse aggregate of the quaternary-age sediments in the Jimen area and the formation of Bai Hassan for the Shurao area in the city of Kirkuk, northern Iraq, has been investigated to determine its validity in engineering uses, including road works and concrete works.On the other hand, the comprehensive aggregate's applicability was used for some structural uses of roads and concrete works in a few Kirkuk Governorate locations (northern Iraq) (Al-Tamimi, 2020).Morover, The Marshall method and the super pave method were tested with limestone aggregates in places other than Iraq.These methods worked better for designing asphalt pavements in the State of Jordan because of the high temperatures and heavy traffic loads (Ibrahim and Yahya, 2007).
The study aims to invistigate the viability of limestone as a comprehensive aggregate, used in road works by studying the geotechnical properties those rocks for designing asphalt concrete for the surface layer and comparing it with the Iraqi specifications for roads and bridges.

The Study Area
The study area is located in the west of the Sulaymaniyah, at latitudes of 35  27' 00 and 35  43' 00 north and longitudes of 44  18' 00 and 44  58' 00 east, in the geological region known as the area of the simple tortuous mountainous region (Hasan et al., 2021), as shown in Fig. 1.

Stratigraphy of the Study Area
The Bazian area has a teartiry geological time and the recent deposits are from the quaternary period.It includes Koloch, Paleocene, which consists successively of mudstone of gray or black color.The Gercus formation, Sinjar formation Paleocene consists of limestone as well as dolomite rocks, and the Belaspi formation middle and upper Eocene ,consists of chalk limestone as well as contains flint (Vieira and Pereira, 2015).

Materials and Methods
The study relied on taking samples from Singar and Pilaspi formations various proposed sites for the purpose of conducting laboratory tests, as well as conducting several reconnaissance tours of the research area to identify and study the exposed formations sediments belonging to the geology of quaternary age sediments, as well as identifying the sites from which the samples were taken and constructing a complete vision.For the region, samples (sampling) were collected according to American Society for Testing and Materials (ASTM D75, 2013), which were taken with two samples from the quarries operating in Bazian district and transferred to the Kirkuk construction laboratory under the appropriate environmental conditions for laboratory tests, including physical tests, durability tests, and asphelet tests.These tests were done using the generl Iraqi standered ( I.Q.S ,1999-2003).

Sieve analysis (gradient)
Fine and coarse aggregate in the asphalt concrete mixture consist of natural and river sand and crushed sand passing through a sieve of 4.75 mm and coarse through a sieve of 63 mm.The proportion of natural sand should not exceed 25% of the fine parts passing through a sieve of size 2.36 mm for the surface layer and the bond.The grains must be strong, durable, sound and dry for the coarse aggregate.As for the fine aggregate, it must consist of clean grains with a rough surface and with angles.The value of the sand equivalent should not be less than 45% according to the required specification.Analysis was carried out on the sifter for fine and coarse aggregate in the Kirkuk structural laboratory according to the required specification for grading (ASTM C136, 2006).

Filler
The filler consists of cement, limestone powder, or slaked lime.A certain weight is taken from the filter and washed on sieve No. 200, then dried and weighed again and compared with the specification (ASTM C117, 2004).The results of the sieve analysis of the models were illisterated in Table .1.

Specific gravity and absorption ratio
The specific gravity is defined as the weight of a specific volume of a substance at a certain temperature to the weight of the same volume of distilled water at the same temperature (ASTMC97-09, 2010).The specific gravity was found based on American specification (ASTM C127, 2004), where the specific weight was calculated.As for the rate of absorption, which means the increase in the weight of the total aggregate as a result of water entering the internal composition of the aggregate and not the amount of water on the outer surface of the granules according to the required specification.The results were illusterated in table 2, and can be calculatedusing the equation 1. Where: A = dry weight of aggregate B = saturated and dry weight of its surface Absorption (%)

Grain shape
The grain shape of the aggregate considers one of the important properties that has a direct impact on the engineering properties of the aggregate .The shape of the granules has a direct impact on road works, and that lies in its endurance to intense passing movements and depends on the mechanical properties and its resistance when exposed to applied loads.The percentage of voids and gaps is reduced by longitudinal shape and elongation (Bell, 2007).The factor of flatness and elongation is as follows: (Jamkar, 2004) has shown that the presence of flat shapes and elongation affects the increase in the ratio of gaps and voids, thus needing a greater amount of water and cement to cover the entire external surface and negatively affect the operability and reduce the resistance of concrete.The tests of elongation and flattening factors were carried out in Kirkuk construction laboratorybased on the Iraqi standard (ASTM D4791, 2005) and the results were given in Table 3, and they thecalculated using equations 2 and 3.

Loss angeles abrasion test
It is a measure of the resistance of coarse aggregates to abrasion and friction by measuring the impact of the outer surface on abrasion and friction.It is a qualitative indicator for the different sources of aggregates similar in chemical composition (Smit & Collis, 2001), for aggregates used in concrete roads and surfaces subject to severe friction as a result of passing and others.The percentage of abrasion (erosion) is determined by the amount of weight loss that occurs on the aggregates.on the otherhand, if the loss is a high percentage, the aggregates are low resistance to erosion.
All the tests were carried out at the national center (Kirkuk construction laboratory) based on the required specification (ASTM C131-C535,2003).The results of the applied tests were illustrated in Table 4, where the weights were taken and the number of balls was determined according to the mentioned specification.A sample weighing (5000 gm) was taken, dried at a temperature of 110 5 degrees celsius for 24hours.The 12 balls were placed according to the volume gradient class (A) of the aggregate with the model in the device, then the device rotated (500) cycles at a speed of (30-33) revolutions per minute.After the cycles ended The form is extracted and sieved on sieve No. 12, then the remaining part is washed on this sieve and dried in an oven at a temperature of (105-110) degrees celsius, and then its dry weight is calculated by applying equation 4 to find ratio ofmechanical corrosion. Where: A = total weight of aggregate used for test B = weight of the remaining portion on sieve No. ( 12)

Soundness test
This test is done by repeatedly immersing the model in a solution of sodium sulfate and magnesium sulfate and periodically drying the model in a drying oven to assess the extent of the aggregate's resistance to weathering processes.The model was soaked in a sodium sulfate and saturated magnesium sulfate solution for 16-18hours, then dried in an oven at 110 C  , and the weight loss was determined according to this specification (ASTM C88-2004) as shown in Table 5.

Crushing test
In this test, the total weight of the materials, medium gravel and fine gravel, is taken and sifted on sieve No. 4, then we take the remainder on sieve No. 4 according to the required specification )ASTM-C-131-01, 2004) as in Table 5 it is unbroken, then we find the crushing percentage through equations 5 and 6.

Harmful substances in the aggregate
A certain weight is taken from the sample, and it is weighed while it is dry, then it is placed in water and left for 24 hours.After that, the sample is weighed while it is wet.We will notice the amount of materials lost in accordance with the required specification (ASTM C124, 2004), as shown in Table 5.

Asphalt Cement Test
The surface asphalt layer consists of asphalt with penetration (40-70) ( 22), asphalt with suitable penetration is used taking into consideration the size of the passage of grains and the prevailing climatic conditions to obtain the stability strength of the asphalt mixture.In roads and airports, where the size of the passage of grains is large and the climate is hot (Igor & Marico, 2020), asphalt with penetration from 40 to 50 is used, but in cold regions where the size of the passage of grains is low, asphalt with penetration range from 50 to 60.As for the percentage of asphalt, it ranges (4-6)% of the total weight of the mixture.The required tests are asphalt cement according to the Iraqi specification (I.Q.S,1999-2003).The results of the test were shown in Table 5.The results of the required tests in Table 5, including: Los angeles, chemical corrosion, cracking rate, sand equivalent, and harmful substances, which were used for design the asphalt mixture for the surface layer according to the Iraqi standard and its amendments (1999)(2000)(2001)(2002)(2003), showed their conformity with the requirements of the required tests, and thus the mixture was designed for limestone aggregate.

Mix Design
The main objective of designing asphalt mixtures is to obtain materials with the correct ratios of the required properties, taking into account such ratios as: sufficient amount of asphalt, obtaining appropriate stability, making the void content high.Grinding, making molds and hammers, stacking samples, testing density, stability, and creep (Marshall), the ratio of air spaces, the total theoretical specific weight of materials, the ratio of voids in the mineral aggregate, and the best percentage of asphalt are all ways to figure out the temperature of the mixture.The following procedures are taken to prepare the mixture : • The percentage of materials is calculated using a trial or error method.
• Conducting sieve analysis for all materials separately.
• Find the percentage of each sieve from table (6).
Test samples with varying asphalt content are prepared to obtain test curves and data with an increase in asphalt content of 0.5% with two asphalt content.The test samples are prepared with percentages of asphalt (3.0, 3.5, 4.0, 4.5, 5.0, 5.5%) as the base layer and the binding layer while surface layer with a percentage of asphalt (4.0, 4.5, 5.0, 5.5, 6.0%)According to the Iraqi specification for roads and bridges for (1999)(2000)(2001)(2002)(2003).The weight of the aggregate and the asphalt binder that fills the core should be 1200 g.       • The specific gravity and absorption ratio of the two samples were found to be in compliance with the requisite parameters, indicating their appropriateness for use in asphalt concrete projects.• The results of the tests on the flatness and elongation factors of the samples revealed that the highest percentage of flat-shaped grains is 20-22% and the highest percentage of longitudinal-shaped grains is 30-26% indicating that they did not exceed the permissible limits according to the British standard, which is in compliance with the requirements.• The stability test for both the coarse and fine aggregates showed that the loss was a small percentage within the limits of the standards, and thus showed its suitability for use in asphalt concrete works.
As for the results of examining each of the sand equivalent and harmful substances, they conform to the required specifications.• The testes of crushing ratio were also reveals that the harmful materials are identical to the specifications required for asphalt mixtures.

Recommendations
The study recommends following up the work of quarries in the region and constantly following it up by the General Authority for Geological Survey and recommending conducting various periodic checks on the rubble to ensure its quality and suitability for the field of engineering use and Using rock crushers in quarries for the purpose of breaking aggregates with a granular size greater than 50 mm for the purpose of benefiting from them and using them in the surface layer of the road as a result of their suitability to the conditions and requirements of the asphalt concrete works of the studied models.

Fig. 8 .
Fig.8.The correlation between the asphalt and void in material aggregate

Table 1 .
Grades of coarse and fine aggregates, crusher sand and filler (for limestone)

Table 2 .
Specific gravity and absorbtion (for limestone)

Table 3 .
The results of the flatness and elongation coefficient of the study area models

Table 4 .
Validity of materials required to design the mixing equation for limestone

Table 5 .
The results of the asphalt cement tests used in the mixing equation

Table 6 .
Percentage of limestone aggregate

Table 7 .
The asphalt mixture's results for limestone

Table 8 .
The results of the mixing equation with the specifications for the surface layer of limestone