ASPHALT CONCRETE MIXTURES WITH STEEL SLAG AGGREGATES AND RECLAIMED ASPHALT, METHODS AND USES THEREOF

Abstract

The present disclosure relates to an asphalt concrete mixture comprising: 50% to 75% (w/w) of steel slag aggregates, wherein the size of the steel slag aggregates is up to 20 mm, measured by sieving; 15% to 30% (w/w) of reclaimed asphalt, wherein the size of the of reclaimed asphalt is up to 14 mm, measured by sieving; 10% to 20% (w/w) of natural stone aggregates and/or filler; and 2% to 4% (w/w) of virgin bitumen. Infrastructures comprising the described asphalt concrete mixture are also disclosed.

Claims

1. An asphalt concrete mixture comprising: 50% to 65% (w/w) of steel slag aggregates, wherein the size of the steel slag aggregates is up to 20 mm, measured by sieving; 15% to 30% (w/w) of reclaimed asphalt aggregates, wherein the size of the aggregates of reclaimed asphalt is up to 14 mm, measured by sieving; 10% to 20% (w/w) of natural stone aggregates and/or filler; 2% to 4% % (w/w) of virgin bitumen.

2. The asphalt concrete mixture according to claim 1, wherein the mass ratio between steel slag aggregates and reclaimed asphalt aggregates ranges from 1.6:1 to 4.3:1.

3. The asphalt concrete mixture according to claim 1, wherein the mass ratio between steel slag aggregates and reclaimed asphalt aggregates ranges from 2.5:1 to 4:1.

4. The asphalt concrete mixture according to claim 1, comprising: 50% to 65% (w/w) of steel slag aggregates.

5. The asphalt concrete mixture according to claim 1, comprising: 55% to 60% (w/w) of steel slag aggregates.

6. The asphalt concrete mixture according to claim 1, wherein the size of the steel slag aggregates ranges from 4-16 mm.

7. The asphalt concrete mixture according to claim 1, wherein the size of the steel slag aggregates ranges from 10-14 mm.

8. The asphalt concrete mixture according to claim 1, comprising 15-20% (w/w) of reclaimed asphalt aggregates.

9. The asphalt concrete mixture according to claim 1, wherein the natural stone aggregates and/or filler are selected from the group consisting of: limestone, cement, lime, granite, basalt, and mixtures thereof.

10. The asphalt concrete mixture, according to claim 1, wherein the air void content ranges from 3-5% (v/v).

11. The asphalt concrete mixture according to claim 1, wherein the size of the of reclaimed asphalt aggregates ranges from 4-10 mm.

12. The asphalt concrete mixture according to claim 1, comprising 3.0% (w/w) to 3.5% (w/w) of virgin bitumen.

13. The asphalt concrete mixture according to claim 1, comprising 3% (w/w) to 5% (w/w) of the filler.

14. The asphalt concrete mixture according to claim 1, comprising 11% (w/w) to 13% (w/w) of the natural stone aggregates.

15. The asphalt concrete mixture according to claim 1, wherein the natural stone aggregates are selected from a group consisting of: limestone, granite, basalt, and mixtures thereof.

16. The asphalt concrete mixture according to claim 1 comprising at least one additional additive selected from the group consisting of: acids, polymers, anti-stripping agents, lime, gilsonite and fibers.

17. The asphalt concrete mixture according to claim 1, wherein up to 20% (w/w) of the steel slag aggregates have a size ranging from 14 mm to 20 mm, 31% to 50% (w/w) of the steel slag aggregates have a size ranging from 4 mm to 14 mm, and 11% to 15% (w/w) of the steel slag aggregates have a size up to 4 mm.

18. An infrastructure comprising the asphalt concrete mixture according to claim 1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0046] The following figures provide preferred embodiments for illustrating the disclosure and should not be seen as limiting the scope of the invention.

[0047] FIGS. 1A.sup.1D: Embodiment of a comparison between the cut sections of conventional asphalt mixtures ((a) AC 14 surf/bin/reg with natural aggregates and (c) AC 20 bin/base with natural aggregates) and the disclosed asphalt mixtures ((b) AC 14 surf/bin/reg with SSA and RA and (d) AC 20 bin/base with SSA and RA).

[0048] FIG. 2: Schematic representation of a sample section obtained by digital image overlapping, using AutoCAD and ImageJ, of the AC 14 surf/bin/reg mixture with SSA and RA of the present disclosure. Dark greysteel slag aggregates (coarse aggregates >4 mm); Light greyLimestone aggregates (natural aggregates and from the RA); WhiteBitumen, air voids, filler, and fine aggregates (limestone and SSA).

[0049] FIG. 3: Schematic representation of a sample section obtained by digital image overlapping, using AutoCAD and ImageJ, of the AC 20 bin/base mixture with SSA and RA of the present disclosure. Dark greysteel slag aggregates (coarse aggregates >4 mm); Light greyLimestone aggregates (natural aggregates and from the RA); WhiteBitumen, air voids, filler, and fine aggregates (limestone and SSA).

DETAILED DESCRIPTION

[0050] The present disclosure relates to an asphalt concrete mixture comprising: 50% to 75% (w/w) of steel slag aggregates, wherein the size of the steel slag aggregates is up to 20 mm, measured by sieving; up to 30% (w/w) of reclaimed asphalt, wherein the size of the of reclaimed asphalt is up to 14 mm, measured by sieving; 3% to 25% (w/w) of natural stone aggregates and/or filler; and up to 4% (w/w) of virgin bitumen. Infrastructures comprising the described asphalt concrete mixture are also disclosed.

[0051] In an embodiment, the present disclosure relates to asphalt concrete mixtures for surface, binder, or regulating courses (AC 14 surf/bin/reg) and binder or base courses (AC 20 bin/base), wherein the mixture comprises 50% to 75% (w/w) of SSA, preferably 50% to 65% (w/w) of SSA, up to 30% (w/w) of RA, preferably 15% to 30% (w/w) of RA, 3% to 25% (w/w) of natural aggregates and/or filler, preferably 10% to 20% (w/w) of natural aggregates and/or filler, and up to 4% (w/w) of virgin bitumen, preferably 2% to 4% (w/w) of virgin bitumen. In an embodiment, the resulting mixtures show better mechanical performance using a lower percentage of virgin bitumen incorporation than conventional mixtures with natural aggregates. The percentage of virgin bitumen was reduced by 30%, significantly saving non-renewable resources.

[0052] The collective term aggregates is used for the mineral materials such as sand, gravel, and crushed stone, used with a binding medium (i.e., bitumen) to form compound materials (such as asphalt concrete). The term aggregates is also used for base and subbase courses for flexible and rigid pavements. Natural aggregates are generally extracted from large rock formations through an open excavation. Extracted rock is typically reduced to usable sizes by mechanical crushing.

[0053] In an embodiment, the mechanical performance of the disclosed asphalt concrete mixtures was compared to that of identical conventional mixtures produced with 94% to 96% (w/w) natural aggregates, and 4% to 6% (w/w) virgin bitumen. The results showed that asphalt concrete mixtures of the present disclosure present excellent water sensitivity and rutting resistance, superior to the performance of the conventional asphalt concrete mixtures. The result is even more impressive considering that it was achieved with 80% waste materials and a reduction of 30% in the bitumen added.

[0054] Most works with SSA incorporation in asphalt mixtures showed difficulties obtaining adequate values of air void content (Va), typically higher than expected. Due to the physical characteristics of steel slag, namely its angular shape and rough surface, it is not easy to compact the mixtures with this type of material, maintaining Va values within the specified limits. This problem is solved by the asphalt concrete mixture of the present disclosure, which shows Va values according to the regulatory specifications (3.0% to 5.0% (v/v) for AC 14 surf/bin/reg and 3.0% to 6.0% (v/v) for AC 20 bin/base).

[0055] In an embodiment, the asphalt concrete mixture comprises SSA, RA, natural aggregates (NA) (e.g., limestone, granite, basalt), filler (e.g., limestone, cement, lime, granite, basalt), and bitumen with penetration grade 50/70. The amount of each material for the mix design of AC 14 and AC 20 mixtures is presented in Table 1 in kg/ton. The size of aggregates was obtained by particle size distributionsieving method. In an embodiment, the values given in Table 1 have a tolerance of 10% depending on specific designs to consider the variability of the waste materials.

TABLE-US-00001 TABLE 1 Mix design of the asphalt concrete mixtures developed in kg/ton. Component Aggregates size AC 14*** AC 20**** SSA 14/20 14-20 mm 190 SSA 10/14 10-14 mm 294 190 SSA 4/10 4-10 mm 199 137 SSA 0/4 <4 mm 145 116 NA 0/4 <4 mm 111 127 RA 0/14 <14 mm 172 172 Commercial filler* <0.125 mm 25 Recovered filler** <0.125 mm 20 37 Bitumen 50/70 NA 34 31 *Limestone filler **According to material obtained in the asphalt plant (limestone, granite, basalt, etc) ***64% (w/w) of SSA; 11% (w/w) of NA; and 17% (w/w) of RA ****63% (w/w)of SSA; 13% (w/w) of NA; and 17%(w/w) of RA

[0056] FIGS. 1A.sup.1D show the morphological differences between conventional asphalt mixtures and the disclosed asphalt mixtures. This figure was obtained with a HD digital camera after sawing (with a circular cut-off saw) slabs of asphalt mixtures produced according to the processes presented in this disclosure.

[0057] FIG. 2 and FIG. 3 represent a schematic representation of a sample section of the AC 14 surf/bin/reg mixture and the AC 20 bin/base mixture, respectively, with SSA and RA of the present disclosure. It can be seen that the coarse SSA aggregates (greater than 4 mm), represented in dark grey, account for most of the sample area (approximately 45 to 50% of the total area of the sample for AC 14 surf/bin/reg mixture (FIG. 2) and 48 to 53% of the total area of the sample for the AC 20 bin/base mixture (FIG. 3)). The light grey aggregates in the drawing are coarse limestone aggregates from the RA and virgin aggregates incorporated into the mixture. The remaining white area represents the fine aggregates (SSA, limestone and RA smaller than 4 mm), bitumen and air voids.

[0058] In an embodiment, the volumetric characteristics of the asphalt concrete mixtures were obtained using the maximum theoretical density (MTD) and the bulk density. The bulk density of the samples was obtained by method B of the standard EN 12697-6:2020. The maximum theoretical density (MTD) was determined according to EN 12697-5:2018, using a pycnometer and a disaggregated mixture sample. After determining the bulk density of the specimens and the MTD of each mixture, it is possible to calculate the air voids content (Va) according to Equation 1:

[00001]$\begin{array}{cc}{V}_a=\frac{{}_m-{}_b}{{}_m}100& \left(1\right)\end{array}$ [0059] Where: [0060] V.sub.a is the air voids content of the asphalt specimen, in 0.1 percent (by volume); [0061] .sub.m is the MTD of the mixture, in megagrams per cubic metre (Mg/m.sup.3); [0062] .sub.b is the bulk density of the specimen in megagrams per cubic metre (Mg/m.sup.3).

[0063] The volumetric characteristics of the asphalt concrete mixtures developed can be seen in Table 2, which shows the average values of each asphalt concrete mixture. The values obtained for Va (%) are considerably lower as compared to the 6% to 7% values presented in the state-of-the-art [4,9], showing that the problem of high air void contents observed in asphalt mixtures with high amounts of SSA is solved by the disclosed asphalt concrete mixtures.

TABLE-US-00002 TABLE 2 Volumetric characterisation of the asphalt concrete mixtures with SSA and RA. Mixture MTD (kg/m.sup.3) Bulk density (kg/m.sup.3) Va (%) AC14 2884 2790 3.3% AC20 2885 2793 3.2% AC14 - 64% (w/w) SSA and 17% (w/w) of RA AC20 - 63% (w/w) SSA and 17% (w/w) of RA.

[0064] In an embodiment, the asphalt concrete mixtures' mechanical performance was evaluated through water sensitivity and permanent deformation resistance tests. The water sensitivity test was carried out following EN 12697-12:2018 as the preliminary performance control test. It is necessary to store three specimens at room temperature, without conditioning in water, while a second group is conditioned in water for three days at 40 C. Finally, all the samples are tested by indirect tension at 15 C. (EN 12697-23:2018). The test results are the average indirect tensile strength of the conditioned in water (ITSw) or dry (ITSd) specimens. The indirect tensile strength ratio (ITSR) is the ratio between ITSw and ITSd and is the main parameter used to evaluate water sensitivity. According to current practice, the asphalt mixtures should have ITSR values higher than 70% or, ideally, 80% to ensure adequate performance [20,21].

[0065] A comparison between the results obtained for conventional (AC 14 50/70 surf/bin/reg and AC 20 50/70 bin/base) and the disclosed mixtures is present in Table 3. The conventional AC 14 50/70 surf/bin/reg mixture was produced with 92% (w/w) of natural stone aggregates, 3.2% (w/w) of recovered filler and 4.8% (w/w) of bitumen 50/70. The conventional AC 20 50/70 bin/base was produced with 93% (w/w) of natural stone aggregates, 2.6% (w/w) of recovered filler and 4.4% (w/w) of bitumen 50/70. There was an increase of 7.5% in the ITSR for the AC 14 mixture and 1% for the AC 20 mixture, demonstrating the improved durability of the new mixtures in the presence of water. Surprisingly, even with a reduction of 30% in the amount of binder added, the disclosed asphalt concrete mixtures showed excellent ITSR results

TABLE-US-00003 TABLE 3 Water sensitivity test results of the asphalt concrete mixtures with SSA and RA. Indirect tensile strength (kPa) ITSR Asphalt mixture ITS.sub.d ITS.sub.w (%) Increase AC 14 - conventional 2673 2480 93 7.5% AC 14 - SSA and RA of 3026 3036 100 the present disclosure AC 20 - conventional 2255 2183 97 1.0% AC 20 - SSA and RA of 3063 3014 98 the present disclosure AC14 - 64% (w/w) SSA and 17% (w/w) of RA AC20 - 63% (w/w) SSA and 17% (w/w) of RA.

[0066] In an embodiment, the wheel-tracking test (WTT) was used to evaluate the resistance to permanent deformation according to EN 12697-22:2020. Briefly, the method consists of repeatedly passing a wheel over the asphalt mixture at a high operating temperature (60 C.) while measuring the evolution of the wheel rut depth with the number of cycles (up to 10 000 cycles). As for the results obtained in this test, the main parameter is the wheel tracking slope (WTS.sub.AIR), which indicates the increase in deformation per thousand cycles between the 5000.sup.th and the 10000.sup.th cycles. The other parameters obtained in this test are the mean proportional rut depth (PRD.sub.AIR) and the final rut depth (RD.sub.AIR). The RD.sub.AIR is the total deformation after 10000.sup.th cycles, while the PRD.sub.AIR is the ratio between RD.sub.AIR and sample thickness.

[0067] A comparison between the conventional and the new mixtures is presented in Tables 4 and 5. The disclosed asphalt concrete mixtures showed an improvement (decrease) of 75% to 77% in the permanent deformation rate (WTS.sub.AIR) compared to the conventional asphalt mixtures.

TABLE-US-00004 TABLE 4 Wheel tracking test results of the conventional and disclosed asphalt concrete mixtures, in particular AC 14 mixtures. WTS.sub.AIR PRD.sub.AIR RD.sub.AIR Asphalt mixture (mm/10.sup.3 cycles) (%) (mm) AC 14 - conventional 0.24 14.0 5.4 AC 14 - SSA and RA 0.06 6.1 2.4 Improvement 75% 56% 56%

TABLE-US-00005 TABLE 5 Wheel tracking test results of the conventional and disclosed asphalt concrete mixtures, in particular AC 20 mixtures. WTS.sub.AIR PRD.sub.AIR RD.sub.AIR Asphalt mixture (mm/10.sup.3 cycles) (%) (mm) AC 20 - conventional 0.26 10.8 6.6 AC 20 - SSA and RA 0.06 4.2 2.5 Improvement 77% 61% 62%

[0068] Based on the abovementioned results, the disclosed asphalt concrete mixture differs from previously developed solutions since it shows improved mechanical and environmental performance and volumetric properties that were not previously achieved when using natural, SSA and RA materials. Surprisingly, the asphalt concrete mixtures now disclosed comprise more than 75% (w/w) of waste materials and 30% (w/w) less of added bitumen, which resulted in improved mechanical and environmental performance and volumetric properties. The disclosed mixtures are then the optimum solution after a series of combinations that were not able to meet the expected properties, namely:

[0069] Asphalt concrete mixtures with different compositions did not meet the expected results. Table 6 lists the composition of comparative examples which were not able to meet the expected properties. Several examples presented in Table 6 were not able to meet the maximum air voids content limit of 5% (v/v) for AC14 (7.8% (v/v) for Example 2 and 6.4% (v/v) for Example 4) or 6% (v/v) for AC 20 (7.3% (v/v) for Example 1 and 11.6% (v/v) for Example 5). The water sensitivity of some of these compositions, measured as a percentage of strain retain after conditioning the samples in water, was also below the minimum limit value of 80% (77% for Example 1 and 74% for Example 3).

TABLE-US-00006 TABLE 6 Comparative examples Asphalt SSA % NA % Bitumen % Example mixture (w/w) (w/w) (w/w) 1 AC20 50 45 5 2 AC14 75 20 5 3 AC20 75 20 5 4 AC14 80 15 5 5 AC20 90 5 5

[0070] As used in the specification and claims, the singular forms a, an and the include plural references unless the context clearly dictates otherwise. For example, the term a sample includes a plurality of samples, including mixtures thereof.

[0071] Whenever the term at least, greater than, or greater than or equal to precedes the first numerical value in a series of two or more numerical values, the term at least, greater than or greater than or equal to applies to each of the numerical values in that series of numerical values. For example, greater than or equal to 1, 2, or 3 is equivalent to greater than or equal to 1, greater than or equal to 2, or greater than or equal to 3.

[0072] Furthermore, it is to be understood that the invention encompasses all variations, combinations, and permutations in which one or more limitations, elements, clauses, descriptive terms, etc., from one or more of the claims or from relevant portions of the description is introduced into another claim. For example, any claim that is dependent on another claim can be modified to include one or more limitations found in any other claim that is dependent on the same base claim.

[0073] Furthermore, where the claims recite a composition, it is to be understood that methods of using the composition for any of the purposes disclosed herein are included, and methods of making the composition according to any of the methods of making disclosed herein or other methods known in the art are included, unless otherwise indicated or unless it would be evident to one of ordinary skill in the art that a contradiction or inconsistency would arise.

[0074] Where ranges are given, endpoints are included. Furthermore, it is to be understood that unless otherwise indicated or otherwise evident from the context and/or the understanding of one of ordinary skill in the art, values that are expressed as ranges can assume any specific value within the stated ranges in different embodiments of the invention, to the tenth of the unit of the lower limit of the range, unless the context clearly dictates otherwise. It is also to be understood that unless otherwise indicated or otherwise evident from the context and/or the understanding of one of ordinary skill in the art, values expressed as ranges can assume any subrange within the given range, wherein the endpoints of the subrange are expressed to the same degree of accuracy as the tenth of the unit of the lower limit of the range.

[0075] The term comprising, whenever used in this document is intended to indicate the presence of stated features, integers, steps, or components, but not to preclude the presence or addition of one or more other features, integers, steps, components or groups thereof.

[0076] The disclosure should not be seen in any way restricted to the embodiments described and a person with ordinary skill in the art will foresee many possibilities to modifications thereof. The above described embodiments are combinable.

[0077] The following claims further set out particular embodiments of the disclosure.

[0078] The following citations are incorporated herein by reference: [0079] ADDIN EN.REFLIST 1. Moura, C.; Nascimento, L.; Loureiro, C.; Rodrigues, M.; Oliveira, J.; Silva, H. Viability of Using High Amounts of Steel Slag Aggregates to Improve the Circularity and Performance of Asphalt Mixtures. Applied Sciences 2022, 12, 490. [0080] 2. Chen, Z.; Leng, Z.; Jiao, Y.; Xu, F.; Lin, J.; Wang, H.; Cai, J.; Zhu, L.; Zhang, Y.; Feng, N., et al. Innovative use of industrially produced steel slag powders in asphalt mixture to replace mineral fillers. J. Clean. Prod. 2022, 344, 131124. [0081] 3. Skaf, M.; Manso, J. M.; Aragn, .; Fuente-Alonso, J. A.; Ortega-Lpez, V. EAF slag in asphalt mixes: A brief review of its possible re-use. Resources, Conservation and Recycling 2017, 120, 176-185. [0082] 4. Rodriguez-Fernndez, I.; Lastra-Gonzalez, P.; Indacoechea-Vega, I.; Castro-Fresno, D. Technical feasibility for the replacement of high rates of natural aggregates in asphalt mixtures. Int. J. Pavement Eng. 2021, 22, 940-949. [0083] 5. Revilla-Cuesta, V.; Ortega-Lpez, V.; Skaf, M.; Pasquini, E.; Pasetto, M. Preliminary Validation of Steel Slag-Aggregate Concrete for Rigid Pavements: A Full-Scale Study. Infrastructures 2021, 6, 64. [0084] 6. Hainin, M. R.; Aziz, M. M. A.; Ali, Z.; Jaya, R. P.; El-Sergany, M. M.; Yaacob, H. Steel slag as a road construction material. Jurnal Teknologi 2015, 73. [0085] 7. Maharaj, C.; White, D.; Maharaj, R.; Morin, C. Re-use of steel slag as an aggregate to asphaltic road pavement surface. Cogent Engineering 2017, 4, 1416889. [0086] 8. Pasetto, M.; Baldo, N. Mix design and performance analysis of asphalt concretes with electric arc furnace slag. Construction and Building Materials 2011, 25, 3458-3468. [0087] 9. Sorlini, S.; Sanzeni, A.; Rondi, L. Reuse of steel slag in bituminous paving mixtures. Journal of hazardous materials 2012, 209, 84-91. [0088] 10. Yi, H.; Xu, G.; Cheng, H.; Wang, J.; Wan, Y.; Chen, H. An overview of utilization of steel slag. Procedia Environmental Sciences 2012, 16, 791-801. [0089] 11. Ziaee, S. A.; Behnia, K. Evaluating the effect of electric arc furnace steel slag on dynamic and static mechanical behavior of warm mix asphalt mixtures. J. Clean. Prod. 2020, 274. [0090] 12. Kong, D.; Chen, M.; Xie, J.; Zhao, M.; Yang, C. Geometric characteristics of BOF slag coarse aggregate and its influence on asphalt concrete. Mater. 2019, 12. [0091] 13. Cui, L.; Ling, T.; Zhang, Z.; Xin, J.; Li, R. Development of asphalt mixture density estimation model applicable to wide air void content range using ground penetrating radar. Construction and Building Materials 2021, 293, 123521. [0092] 14. Tarsi, G.; Tataranni, P.; Sangiorgi, C. The challenges of using reclaimed asphalt pavement for new asphalt mixtures: A review. Mater. 2020, 13, 4052. [0093] 15. Enieb, M.; Al-Jumaili, M. A. H.; Al-Jameel, H. A. E.; Eltwati, A. In Sustainability of using reclaimed asphalt pavement: based-reviewed evidence, Journal of Physics: Conference Series, 2021; IOP Publishing: p 012242. [0094] 16. Abdel-Jaber, M. t.; Al-shamayleh, R. A.; Ibrahim, R.; Alkhrissat, T.; Alqatamin, A. Mechanical properties evaluation of asphalt mixtures with variable contents of reclaimed asphalt pavement (RAP). Results in Engineering 2022, 14, 100463. [0095] 17. EAPA. Asphalt the 100% recyclable construction product EAPA. Position paper; European Asphalt Pavement Association: Brussels, Belgium, 2014; p 21. [0096] 18. Zaumanis, M.; Mallick, R. B.; Frank, R. 100% recycled hot mix asphalt: A review and analysis. Resources, Conservation and Recycling 2014, 92, 230-245. [0097] 19. Zaumanis, M.; Mallick, R. B.; Frank, R. 100% hot mix asphalt recycling: Challenges and benefits. Transportation Research Procedia 2016, 14, 3493-3502. [0098] 20. Infraestruturas de Portugal. aderno de Encargos Tipo Obra: 14.03Pavimentao Caracteristicas dos materiais. vol. V; Almada, 2014. [0099] 21. Chomicz-Kowalska, A.; Gardziejczyk, W.; Iwanski, M. M. Moisture resistance and compactibility of asphalt concrete produced in half-warm mix asphalt technology with foamed bitumen. Construction and Building Materials 2016, 126, 108-118.