Preparation method and applicability evaluation of 3D printing alumina ceramic artificial coarse aggregate

The particle size and morphology of crushed stones impact their macroscopic mechanical and physical properties, which has become a hot topic in the study of road and geotechnical engineering. However, some reported studies fail to control the particle morphology as the only independent variable. This paper presented a new method to print artificial aggregates based on 3D printing technology of particles. The applicability of the new method was verified with uniaxial compression and dynamic modulus tests of asphalt mixtures formed by the printing aggregates. Results showed that the printing aggregates earned similar physical properties to real coarse when sintered at 1400 °C with alumina ceramic powder and CuO: TiO2 a 1:2 additive in mass. Besides, the gross volume density, compressive strength, and shrinkage of the printing aggregates show a similar trend of increasing and then decreasing with the increase of additives. The optimal mass percentage of additives was obtained to be 5%. Mechanical tests indicated that the mechanical indexes of the asphalt mixtures formed with the two types of coarse aggregates were similar, while the results of the specimens formed with artificial coarse aggregates showed less dispersion. The stability of test results was significantly improved for different asphalt mixture specimens prepared with 3D printed coarse aggregate. This provides a basic method for further research on the multi-scale properties of particle material.


Introduction
Crushed stone coarse aggregates such as basalt, granite, and limestone are widely used in pavements, roadbases, and subgrades due to their good strength and stability [1].To improve the overall strength and modulus, the method of controlling the initial particle gradation and sufficient compaction is widely used to form a dense skeleton structure [2,3].However, the mesoscale characteristics of aggregates such as size, geometric feature, and embedded pattern have a significant effect on the skeleton structure [4].The evaluation indexes of particle gradation and compaction degree are macroscopic phenomenological.Moreover, there are infinite possibilities of particle morphology for aggregates of the same gradation, which makes it difficult to truly ensure that particle morphology is the only independent variable to reveal the stacking mechanical properties [5][6][7][8][9][10].To study the effect of aggregate morphological characteristics on its compaction and macroscopic mechanical properties, scholars have prepared regularly shaped aggregates such as square, sphere, cylinder, etc, and combined them with the discrete element method to study the effect of aggregate morphological characteristics on the properties of asphalt mixtures [11].Li [12] prepared glass spheres with different sizes instead of irregular aggregates for forming asphalt mixtures and investigated the effect of particle size difference on the permanent deformation resistance of mixtures by x-ray CT scanning technique.Chen [13]investigated the effect of the aggregate sphericity coefficient on the high-temperature stability of mixtures and found that when the sphericity coefficient of the aggregate is closer to 1, the greater the embedded force and internal friction between the aggregates, and the better the high-temperature stability.
In recent years, with the rise of 3D printing technology, some scholars have begun to explore the use of 3D printing to prepare particles with complex morphology.Such as He [14], Guo [15], Xiao [16], Li [17], et al confirmed the feasibility of 3D printing technology for the preparation of road aggregates.Feng [18] printed the aggregates with resin materials and found that the macroscopic profile of the printing aggregate was the same as that of the natural aggregate.Volumetric indicator deviation is controlled within 5%, but the printing aggregate micro-texture is smoother.Chen [19] prepared aggregates with specific morphology and believed that the use of such artificial aggregates reduces the coefficient of variation of the test values.To solve the problems of low water absorption, small apparent density, local softening, and deformation under high temperatures of 3D printing PLA aggregate, Gong proposed a method of preparing artificial aggregate with target morphological characteristics and particle size [20].Zhang [21] used 3D printing to prepare artificial aggregates with different densities from natural aggregates to track the aggregate stack behavior during compaction.It can be seen that the use of 3D printing technology to prepare aggregates with similar properties to natural aggregates is still in the preliminary exploration stage.Research to evaluate the application of 3D printing aggregate by performing mechanical tests on asphalt mixture specimens formed from 3D printing aggregates is void.
With this background, this paper proposes a batch collection and printing method of real shape particles based on 3D printing technology.The applicability of the printing method was analyzed by comparing the basic mechanical properties of asphalt mixtures prepared with artificially printing aggregates and natural basalt aggregates.It can provide a basic method and useful reference for comprehensively revealing the stacking mechanism and mechanical properties of aggregates.

. Raw material comparison
The raw materials for 3D printing are determined by the printing method.Common raw materials mainly include plastics, photosensitive resins, precoated sand, gypsum, cement-based materials, metal materials, and ceramics [22].The specimens of plastic, resin, and rubber materials after printing and forming have a certain strength, but their apparent density and water absorption are smaller than natural aggregates, and they are prone to local softening or melting under high temperatures [23].The strength of gypsum and precoated sand after printing is only 2∼6 MPa, and the strength is only 12 MPa after special treatment [24].Metal materials print aggregates with smooth surfaces and poor adhesion to asphalt [25].Concrete-based materials print aggregates with less precision [26].Ceramic materials have high strength, rough surface, and high-temperature resistance, which are similar to the properties of natural aggregates.Meanwhile, combined with the three-dimensional printing method (3DP), the size and precision of the printing aggregate can be precisely controlled.Therefore, ceramic powder was finally selected as the initial material for 3D printing coarse aggregates.
However, there is a wide variety of ceramic powders.They can be simply divided into traditional ceramics and special ceramics according to their use [27].Compared with traditional ceramics, special ceramics have a higher strength to meet the strength requirements for the preparation of aggregates.To further clarify the types of ceramics required for 3D printing raw materials, several commonly used special ceramic powders were selected for raw material selection, and the basic sintering properties of raw materials are shown in table 1.
The density of the sintered alumina specimen is similar to that of natural aggregate [27].The sintering process of alumina is mature and simple, the sintering temperature is relatively low, and the compressive strength can reach about 800 MPa after complete densification.Comprehensive consideration of raw material sintering method, sintering temperature, strength after forming, volume stability of the sintering process, and following the principle of forming particles with a density similar to that of natural aggregates, and ultimately determine the alumina ceramic powder as a raw material for 3D printing.

Numericalization of aggregate morphology
Before 3D printing, the morphology data of the aggregate needs to be clarified first.To obtain the real morphology of the aggregate, we used an ATOS Core 135 3D blue light scanner from GOM, Germany, as a data acquisition device (figure 1(a)).The principle of the equipment is to project a precise blue light beam on the object's surface to be measured.Three-dimensional surface points are calculated based on three different light intersections.2∼5 million points are measured simultaneously, with a spacing of less than 0.005 mm between two adjacent points.Each two adjacent points are connected to form a mesh point cloud and realize the accurate portrayal of the real morphology of the aggregates.To ensure the representativeness and diversity of the aggregates, the original aggregates were derived from all coarse aggregates (particle size > 2.36 mm) in a single Marshall specimen.
To scan more aggregates at one time, a self-made fixture that can fix 9 aggregates at the same time was developed, as shown in figure 1(b).When scanning, the marker points are pasted on the fixture, and after scanning, the image of each aggregate is spliced and processed with polygonization and hole patching, and the images are exported one by one to 3Dmax for batch layout (figure 2), to obtain the three-dimensional morphology data of each real particle.Before scanning, the marker points are pasted on the fixture.During scanning, the coordinate axes were established with the marker points as a reference to obtain the 3D data of the aggregate surface points.After scanning, the image of each aggregate is spliced and processed with polygonization and hole filling, and the images are exported one by one to 3Dmax for batch layout (figure 2), to obtain the 3D morphology data of each real aggregate.

Determination of additive content and specimen shrinkage
The sintering temperature of pure alumina ceramics is above 1650 °C, which consumes too much energy.The sintering temperature was reduced and the sintering efficiency was improved by adding additive [27].Liu [27] investigated the effect of four additive systems, CuO-TiO 2 , CuO-TiO 2 /SiO 2 , Nb 2 O 5 and Nb 2 O 5 -SiO 2 , on the sintering properties of alumina ceramics.It was found that CuO-TiO 2 with a mass ratio of 1:2 gave alumina ceramics a relative density of 99% under atmospheric pressure sintering, which was the best among the four additive systems.Therefore, this mass ratio of CuO and TiO 2 is also used for sintering in this paper.Considering the potential influence of the additive content on the quality of 3D printing aggregate and the shrinkage characteristics of the sintered specimens, further test sintering of 3D printing specimens with different additive content was carried out.The square specimens shrink linearly in all dimensions after sintering, and the  shrinkage rate is easy to calculate.Therefore, 50 × 50 × 50 mm square brick specimens were selected for the test sintering specimens.
As shown in table 2, five test groups with different additive content were set up.Four parallel specimens were prepared for each group, and a total of 20 alumina ceramic square brick specimens were prepared,.whereinthe amount of alumina and additives added is determined by mass percent.The parameters of raw materials sa shown in table 3.
To improve the printing quality, the raw material powders were pretreated.First, the Al 2 O 3 , TiO 2 , and CuO powders were preheated in an oven at 110 °C for 4 h to remove the moisture in the materials.Secondly, the powders were mixed and stirred proportionally for 15 min to make them more uniform, and then the powders were poured into the powder supply bin of the 3D printer for printing.The 3D printer work by bonding raw material powders by spraying a binder, the printing accuracy is 0.1 mm, the printing layer thickness is set to 0.07 mm, the ratio of spray thinning is 100%, and the bonding material is furan resin, also produced by Wuhan EASYMFG company.After printing, the specimen is shown in figure 3(a), with the size of 50 × 50 × 50 mm.Put the specimen into the 200 °C oven to keep warm for 3 h, take out the specimen after drying, and remove the excess powder on the surface.
The printed specimens need to be sintered at high temperatures to improve their strength and densification.The sintering equipment is a muffle furnace model SX-8-16 produced by Changsha Kefai Furnace Co.The specimens were neatly placed on the crucible, and the crucible was also placed in the middle of the muffle furnace chamber to ensure that all specimens were heated uniformly.After adding CuO and TiO 2 , the sintering temperature of alumina ceramics was reduced to 1400 °C.To avoid cracking of the specimen caused by too rapid heating, the specimen needs to be sintered in sections.The sintering program is set as follows: warm up to 500 °C at 5 °C/min, hold the temperature for 1 h, then warm up to 1400 °C at 5 °C/min, hold the temperature for 6 h, and the furnace automatically cut off after the end of the heat preservation.The specimen and the furnace   , the sintered bulk density and compressive strength of square brick specimens with different additive content were tested.Figure 4 shows the variation curves of bulk density and compressive strength with the additive content.With the increase of additive content, the bulk density and compressive strength first increased and then decreased, and reached the maximum when the additive content was 5%.When the additive content is 5%, the bulk density is 2.96 g cm −3 , which is similar to that of basalt, and the maximum compressive strength is 53.36 MPa.The optimum additive content was finally determined to be 5%.
Considering that sintering causes shrinkage of the printed specimen, to ensure that the 3D printing coarse aggregate has the same morphological size as the natural aggregate after sintering, the numerical image of the coarse aggregate needs to be enlarged by a corresponding magnification before printing.The magnification is determined by the specimen shrinkage.The shrinkage of the alumina ceramic specimen is calculated using equation (1), and the magnification of the numerical image of the aggregate before printing is calculated using equation (2).
Where S L is the average shrinkage of all specimens at a certain additive content; S Li is the shrinkage of different specimens under the content; L 0 is the average size of length, width, and height of the specimen before sintering; L I is the average size of length, width, and height of the specimen after sintering; n is the number of specimens at that additive content; x is the magnification of the aggregate image.The dimensions of the square brick specimens before and after sintering with 5% additive content are shown in table 4. The shrinkage of the sintered specimen was calculated to be 0.30 and the magnification of the aggregate image to be 1.43 when the additive content was 5%.

Coarse aggregate printing
According to the requirements of uniaxial compression and uniaxial dynamic modulus test on the size of asphalt mixture specimens, two types of real Marshall specimens with the size of j100 × 100 mm and j100 × 150 mm were selected.The printing aggregate comes from the particles contained in the two types of real Marshall specimens.The aggregates with sizes above 2.36 mm were counted one by one by sieving test.As shown in table 5, there are 2095 particles above 2.36 mm in a single j100 × 100 mm specimen and 3090 particles above 2.36 mm in a single j100 × 150 mm specimen.
Obtain the real morphological characteristics of each grade of aggregate in the two types of specimens, and print the coarse aggregate one by one by using the scanning-printing-sintering process mentioned above.To prepare two sizes of asphalt mixture specimens using 3D printing aggregates, a total of 24825 coarse aggregate particles were printed.3 × 2095 particles for j100 × 100 mm specimen and 6 × 3090 particles for j100 × 150 mm specimen.

Specimen preparation
Referring to 'Standard Test Methods of Bitumen and Bituminous Mixtures for Highway Engineering' (JTG E20-2011) [29], the specimens were formed by the rotary compaction method (SGC).The target void ratio of the specimen was 3.5%, and the dimensions were j100 × 100 mm and j100 × 150 mm.Control the compaction work and compaction temperature of each specimen to be the same.
The asphalt mixture is SMA-13, the cellulosic stabilizer is lignocellulose from Langfang Hexiang Building Materials Co., the content is 0.3% of the mass of aggregate, the binder is SBS modified asphalt, the coarse aggregate is 3D printing artificial coarse aggregate, the fine aggregate is basalt, and the mineral powder is limestone mineral powder.The basic performance test of the material was conducted according to 'Standard Test Methods of Bitumen and Bituminous Mixtures for Highway Engineering' (JTG E20-2011).The material technical indexes meet the requirements of 'Technical Code for Construction and Acceptance of Highway Asphalt Pavement' (JTG F40-2004) [30], as shown in table 6.
The specimen gradation was derived from a single Marshall specimen, and the gradation curves are shown in figure 5.The aggregate gradation and morphology of the same-size specimens were identical.The optimum oilstone ratio was determined to be 6.05% by the Marshall test.
Based on the selected gradation, the optimum oil-stone ratio was calculated by Marshall test.A total of 5 oilstone ratios were determined using the specification recommended oil-stone ratio of 5.9% as the median value and 0.3% as the interval.Standard Marshall specimens were made according to the 5 oil-rock ratios, and 4 specimens were molded under each oil-rock ratio, as shown in figure 6.The density of each specimen was determined separately, and volumetric parameters such as void ratio, mineral gap ratio, and asphalt saturation were calculated, while the Marshall stability and flow value of each specimen were determined, as shown in table 7. Taking the oil-stone ratio as the horizontal coordinate and the indexes of the Marshall test as the vertical coordinate, the relationship graph between the oil-stone ratio and the indexes of gross bulk density, void ratio, asphalt saturation, Marshall stability and flow value is plotted as shown in figure 7.
From figure 7, the asphalt content corresponding to the maximum value of the Marshall stability is a 5.9%, 1 = the asphalt content corresponding to the maximum value of the gross bulk density is a 5.6%, 2 = and the asphalt content corresponding to the median value of the range of the specified void ratio is a 6.2%.

=
The optimum asphalt content is obtained by substituting a ,a , a 1 2 3 into equation (3) as the initial value of the optimum asphalt content OAC 1  OAC a a a 3 5.9% 5.6% 6.2% 3 5.9% 3 Take the average of OAC 1 and OAC 2 as the optimal oil-stone ratio OAC 6.05%.= To compare the difference in mechanical properties between the specimens prepared with 3D printing aggregate and those prepared with natural aggregate, the specimens were prepared with basalt coarse aggregate of the same gradation as the control group.The final forming of the specimens is shown in table 8. No. D1-D3 are j100 mm × 100 mm specimens, and No. D4-D9 are j100 mm × 150 mm specimens.No. D1-D9 specimens are the test group, and all the coarse aggregates are 3D printed, with the same gradation and particle morphology.No. A1-A3 are j100 mm × 100mm specimens, and No. B1-B6 are j100mm × 150 mm specimens.No. A1∼A3 and No. B1∼B6 specimens are the control group, and the coarse aggregate is natural basalt.

Experiments
The results of the physical and mechanical properties test of 3D printing coarse aggregate show that the 3D printing artificial coarse aggregate compressive strength, bulk density, and other indicators meet the requirements of the 'Technical Code for Construction and Acceptance of Highway Asphalt Pavement' (JTG F40-2004) [30].
To further evaluate the applicability of 3D printing artificial coarse aggregate, asphalt mixture specimens were prepared using 3D printing artificial coarse aggregate for mechanical property testing.The static compression properties of asphalt mixtures were evaluated by the uniaxial compression test, and the dynamic compression properties were evaluated by the uniaxial compression dynamic modulus test.The uniaxial compression test and the uniaxial compression dynamic modulus test were carried out with reference to 'Standard Test Methods of Bitumen and Bituminous Mixtures for Highway Engineering'(JTG E20-2011) [29].

Uniaxial compression test
To compare the difference between the static compression characteristics of asphalt mixtures prepared with 3D printing artificial coarse aggregate (test group D1-D3) and asphalt mixtures prepared with natural basalt coarse aggregate (control group A1-A3), the uniaxial compression tests were conducted using a universal material testing machine MTS-810 manufatured by MTS Company, USA.Test the compressive strength of asphalt mixtures prepared with different types of coarse aggregates.The loading rate of the universal material testing machine was set at 2 mm min −1 , and the temperature of the specimen was controlled at 20 °C.

Uniaxial compression dynamic modulus test
The uniaxial compression dynamic modulus test was conducted using the Simple Performance Tester SPT from Changsha University of Science and Technology.To ensure the integrity of the 3D printing aggregate, the test group D4-D9 specimens (size j100 × 150 mm) were tested directly.Firstly, the displacement sensors were installed in the middle of the specimen in the vertical direction, with each sensor 120°apart, and a total of three were installed.The specimen with the installed sensors was put into the constant temperature box at the set temperature to keep warm for 4 h, and the specimen was taken out after the temperature stabilized.After calibrating the displacement sensors, the specimens were put into the SPT for testing.The test was carried out with half-sine wave loading, the strain level was 75-125με, the test temperature was 20 °C, 35 °C, 50 °C, and the loading frequency was 25 Hz, 10 Hz, 5 Hz, 1 Hz, 0.5 Hz, 0.1 Hz. the test was carried out one by one with the temperature from low to high, and the frequency from large to small.difference of 1.32 MPa.The compressive strength of the three specimens in the test group is between 3.40 and 3.60 MPa, with a difference of 0.20 MPa, and the average compressive strength of 3.53 MPa.In the control group, the range of the compressive strength is from 4.55 to 5.10 MPa, with a difference of 0.55 MPa and an average compressive strength of 4.84 MPa.The variance of the compressive strength data of the test group was 0.01, and the standard deviation was 0.09.The variance of the compressive strength data of the control group was 0.04, and the standard deviation was 0.21, which was larger than that of the test group.The variation range of compressive strength of different specimens prepared with 3D printing artificial coarse aggregate is smaller, while the dispersion of test results is lower.The reason for the above results is that the coarse aggregates of the test group are all from 3D printing, and the coarse aggregate gradation, morphology, dimensions, and physicomechanical properties of each specimen are the same.At the same time, the forming process is kept consistent, which greatly reduces the factors that make the test results change.The discrete nature of the test results is reduced, which effectively improves the stability of the test data.

Uniaxial compression dynamic modulus test
Existing studies have shown that the dynamic modulus of natural aggregate-based asphalt mixtures increases with increasing temperature or decreasing frequency [31,32].This paper focuses on the factors affecting the dynamic modulus of 3D printed aggregate-based asphalt mixtures.The dynamic modulus of specimens D4-D9 at each temperature and frequency was recorded.The results are shown in figure 9.As can be seen from figure 9, the dynamic modulus of asphalt mixtures also shows obvious temperature and frequency characteristics.Dynamic modulus increases with decreasing temperature, which is because the asphalt mixture is a typical thermo-rheological material.As the temperature decreases, the strength of asphalt increases and its viscosity decreases.Dynamic modulus increases with increasing frequency, this is because the frequency increases, the  load time decreases, the dynamic response time of the mixture decreases, and the dynamic modulus increases.
Although the specimen materials and forming process of the test group remain consistent, the dynamic modulus of different specimens is different.The reason may be that the spatial distribution of aggregates in each specimen is different, resulting in differences in the distribution of the aggregate skeleton.This in turn affects the macroscopic mechanical performance of the asphalt mixture specimens, resulting in differences in the dynamic modulus results.The coefficients of variation of dynamic modulus of six specimens (D4-D9) at each frequency (25 Hz, 10H, 5 Hz, 1 Hz, 0.5 Hz, 0.1 Hz) under each temperature condition (20 °C, 35 °C, 50 °C) were calculated and plotted in figure 10.The specific calculation procedure is to calculate the standard deviation and mean value of the dynamic modulus of six specimens for each frequency at a certain temperature, respectively.Afterwards, the coefficient of variation was obtained by dividing the standard deviation by the mean value.
It can be seen that the coefficient of variation of dynamic modulus of the test group shows obvious temperature dependence and loading frequency dependence.At each frequency, the coefficient of variation of the dynamic modulus increases with the increase of temperature.At 20 °C and 35 °C, the coefficient of variation of dynamic modulus decreases with the increase of frequency.At 50 °C, the coefficient of variation of dynamic modulus increases and then decreases with the increase of frequency.Overall, the coefficient of variation of dynamic modulus is smaller at low temperature and high frequency, and larger at high temperature and low frequency, indicating that the dispersion of uniaxial compression dynamic modulus test results is larger under high temperature and low frequency conditions.This is because the dynamic modulus of asphalt mixtures have temperature and frequency dependence.Under high temperature and low frequency conditions, asphalt mixtures are mainly characterized by viscoplastic properties, producing different degrees of plastic deformation, and the dispersion of dynamic modulus test results increases.Under low-temperature and high-frequency conditions, asphalt mixtures are mainly characterized by viscoelastic properties, producing small elastic deformation under load, and the dispersion of dynamic modulus test results is small.
The coefficient of variation of dynamic modulus was overall larger at 50 °C temperature, and the dispersion of test results was higher.To evaluate the effect of 3D printing coarse aggregate on reducing the dispersion of the dynamic modulus test results, 50 °C was chosen as the test temperature.The control group specimens B1∼B6 were selected for the dynamic modulus test at 50 °C.The loading frequency was kept the same as that of the test group.The coefficient of variation of dynamic modulus under each loading frequency of the control group was calculated and compared with that of the test group, and plotted in figure 11.As shown in figure 11, the CVs of 3D printing coarse aggregate specimens (test group) were smaller than those of basalt coarse aggregate specimens (control group) at each loading frequency under 50 °C.The CV decreases from large to small loading frequency by 25.20, 23.88, 22.61, 19.27, 17.82, and 15.77, with an average decrease of 20.76.The decrease in the CV indicates that the variation of the test group data is smaller than that of the control group, the data of the test group is more stable and reliable.The above data reflect that the use of 3D printing coarse aggregate can effectively reduce the dispersion of the dynamic modulus test results, which is because all the coarse aggregates in the test group were 3D printed, and the aggregate gradation and particle morphology are the same, which weakens the variability of the test results caused by the dispersion of the aggregates.

Conclusion
1) In this paper, a 3D printing method for alumina ceramic coarse aggregates is proposed.The 3D printed aggregate performance is optimized when the additive content reaches 5%.
2) Asphalt mixtures prepared with 3D printed coarse aggregates showed an average decrease in compressive strength of 1.32 MPa compared to asphalt mixtures prepared with natural coarse aggregates, but the compressive strengths of the different specimens prepared from 3D printing artificial coarse aggregate were less discrete.
3) The dynamic modulus test showed that the variability of the test results under high temperature (50 °C) conditions was large.The specimens prepared with 3D printing artificial coarse aggregate can significantly reduce the dispersion of the dynamic modulus test results under high-temperature conditions.The coefficient of variation is reduced by 20.76 on average.4) Using the 3D printing coarse aggregate preparation method proposed in this paper, it is possible to form asphalt mixture specimens with identical aggregate gradation, coarse aggregate physical and mechanical properties, and appearance.Combined with the mechanical properties test results, even if the mixture forming process and materials are the same, there are differences in the mechanical properties of different specimens, and other influencing factors need to be further explored.

Figure 3 .
Figure 3.Comparison of specimens before and after sintering.
chamber were automatically cooled to below 100 °C and then the furnace door was opened to avoid specimen cracking due to the large temperature difference.The sintered square brick specimens are shown in figure 3(b).It can be clearly seen in the figure that the square brick specimens underwent a shrinkage.According to the 'Test Methods of Rock for Highway Engineering' (JTG E41-2005) [28]

Figure 4 .
Figure 4. Physical and mechanical index change curve.

3. 1 .
Uniaxial compression test The test results are shown in figure 8.The test results are shown in figure 8.The average compressive strength of the test group was 3.52 MPa and the average compressive strength of the control group was 4.83 MPa, a

Figure 9 .
Figure 9. Dynamic modulus of testing group.

Figure 10 .
Figure 10.Coefficient of variation of dynamic modulus.

Table 2 .
Test groups with different additive content.

Table 3 .
Parameter of the raw materials.

Table 4 .
Specimen size table before and after sintering.

Table 5 .
Amount of Coarse aggregate.

Table 6 .
Main technical indexes of materials.
to determine the indicators in line with the asphalt mixture technical indicators of asphalt

Table 7 .
Results of marshall test.

Table 8 .
Summary table of specimens.