Mechanical and moisture performance of asphalt concrete containing polyurethane-coated basalt fiber and recycled polyethylene

1. Introduction

Currently, comprehensive measures aimed at designing and constructing high-quality automobile roads are being implemented, resulting in significant achievements. Following the National Strategy defined in Resolution No. PR-307, the Resolution of the President of the Republic of Uzbekistan No. PR-307 dated July 6, 2022, “On organizational measures for the implementation of the Innovation Development Strategy of the Republic of Uzbekistan for 2022-2026”, defines important tasks related to the production of stone mastic asphalt mixtures and the construction of experimental test road sections [1].

The implementation of these tasks requires the development of new types of products and innovative technologies in the road sector, aimed at increasing the service life of road pavements and producing modern composite materials for construction purposes.

This research is related to construction materials and is intended for the preparation of mixtures used in the construction of polymer asphalt concrete pavements for highways, airfields, and urban streets.

Currently, various polymer additives are used in the Republic to ensure the heat resistance and crack resistance of polymer asphalt concrete mixtures, including PKM (Ukraine), RW Elast (France), Butanol 5126 (Germany), PR Plast (France), and others [GOST 9128-2013: Asphalt concrete and polymer asphalt concrete mixtures for roads and airfields. Technical specifications] [2].

However, the disadvantage of these polymer additives is their insufficient resistance to shear deformation under high temperatures and heavy traffic loads when applied in the road and climatic conditions of Uzbekistan. As a result, rutting occurs in polymer asphalt concrete pavements.

A polymer stabilizing additive containing polyethylene polyamine, BND 60/90 paving-grade petroleum bitumen, polyamide fiber, polymer-dispersed additives, and surface-active agents is known (RU 2272795, IPC C04V 26/26) [3].

The closest analogue in terms of technical essence and achieved effect is a material with the following composition, wt.%: crushed plastic household waste – polyethylene (PET) and polypropylene (PP) 20-60; reclaimed asphalt pavement (RAP) 40–80 (RU 2737926 C1) [4].

The disadvantages of the known material include incomplete adaptation of the raw materials to the road and climatic conditions of Uzbekistan, as well as increased plastic deformation under dry and hot climatic conditions, which reduces shear resistance. In addition, the material is not produced domestically, resulting in high costs and logistical difficulties due to importation.

The objective of this study is to develop an asphalt concrete mixture containing a polymer additive based on polyurethane-coated modified basalt fiber, which ensures improved heat resistance of the mixture and increased shear resistance of the pavement due to reduced plastic deformation.

The scientific novelty of this research lies in the dual-phase modification mechanism: where polyurethane-coated basalt fibers provide a 3D reinforcing skeleton, while recycled polyethylene (rPE) serves as a visco-elastic filler. This synergy significantly improves the interfacial adhesion between the mineral aggregate and the bitumen matrix, achieving a 3.7-fold improvement in rutting resistance–a performance metric previously unattained with single-modifier systems in the extreme climatic conditions of Central Asia.

2. Materials and methods

2.4. Experimental design and testing

Numerous experimental compositions were prepared using different component ratios (Table 2). The mixtures were produced using dedicated equipment, and based on test results, the optimal composition of the polymer additive was determined.

Table 2Compositions of the polymer additive, wt.%

Composition	Comp.1	Comp.2	Comp.3	Comp.4	Comp.5
Modified basalt fiber	38	35	32	30	28
recycled polyethylene (rPE)	62	65	68	70	72

To prepare 1000 g of polymer additive:

– 380-420 g of polyurethane-coated modified basalt fiber.

– 580-620 g of recycled polyethylene (rPE) were mixed in a W-70 extruder under heated conditions. The resulting mass was immediately granulated before cooling. The technical properties of the obtained material are presented in Table 2.

Table 3Technical characteristics of the obtained composition

Indicator name	Parameter values, %
	Specified value, %	Proposed value, %
		No. 1	No. 2	No. 3	No. 4	No. 5
Moisture content, by weight	Up to 8.0	0.0	0.0	0.0	0.0	0.0
Heat resistance determined by mass change when heated at 220 °C	Up to 8.0	4.0	6.3	8.0	9.5	10.3
Fibers with a length from 0.1 mm to 2.0 mm	Not less than 80	90	80	65	60	50

To evaluate the physical, mechanical, and performance properties of asphalt concrete mixtures containing the proposed polymer additive, the following materials were used:

– Gabbro-diabase crushed stone (5-10 mm and 10-20 mm) in accordance with GOST 8267-93 [6].

– Crushed gabbro-diabase sand (0-5 mm) in accordance with GOST 31424-2010 [7].

– Non-activated limestone mineral filler grade MP-1 in accordance with GOST 16557-2005 [8].

– Paving-grade petroleum bitumen BND 60/90 in accordance with GOST 22245-90 [9].

– Polymer additive based on basalt fiber.

The asphalt concrete mixture containing the new polymer additive was prepared according to standard production technology (Table 4 and Fig. 1). The suitability of the polymer additive and the optimal mixture composition were determined based on the physical and mechanical properties of the asphalt concrete mixture in accordance with GOST 9128-2013 requirements.

Table 4Asphalt concrete mixture composition, %

Material name	Material	Content, %
Gabbro-diabase crushed stone, 10-20 mm fraction	Coarse aggregate	29.63
Gabbro-diabase crushed stone, 5-10 mm fraction	Medium aggregate	15.25
Gabbro-diabase crushed sand, 0-5 mm fraction	Crushed sand	42.53
Limestone mineral filler	Mineral filler	7.00
Road viscous petroleum bitumen, grade BND 60/90	Binder	5.40
Polymer additive	Modifier	0.19

Fig. 1Nomogram of the selected mix design for dense-graded type B asphalt concrete

3. Results

Test specimens were prepared and tested in accordance with GOST 12801-98 [10] and O‘zDSt 3610:2022 [11]. Five asphalt concrete mixtures with identical aggregate gradation but varying polymer additive compositions were produced. The test results are summarized in Table 5 and Fig. 2-5.

The results demonstrate that increasing the content of polyurethane-coated modified basalt fiber improves compressive strength at 20 °C and 50 °C, shear adhesion, crack resistance, and rutting resistance. The average rut depth was reduced from 10.06 mm in the control mixture to 2.01 mm in the optimized composition.

Fig. 2Compressive strength, at 0 °C, MPa

Fig. 3Shear resistance: internal friction coefficient

Fig. 4Water resistance

Fig. 5Crack resistance

4. Conclusions

The study concludes that the developed polymer additive, based on a 40:60 ratio of polyurethane-coated basalt fiber and recycled polyethylene, provides a superior modification effect for asphalt mixtures.

1) Mechanical synergy: The interaction between the high-tensile basalt fibers and the elastic polyurethane coating creates a reinforcement network that increases shear adhesion by 30-35 % and compressive strength at high temperatures (50 °C) by up to 60 %.

2) Deformation resistance: A critical finding of this research is the 3.7-fold reduction in average rut depth, decreasing from 10.06 mm in conventional mixtures to 2.01 mm in the optimized composition. This is attributed to the 3D reinforcement network created by the polyurethane-coated basalt fibers within the bitumen matrix, which provides superior resistance to plastic deformation under heavy traffic loads and high ambient temperatures.

3) Sustainability: The use of recycled polyethylene demonstrates a viable pathway for “Green Construction”, reducing the carbon footprint of road projects without compromising structural integrity.

4) Practical implication: The additive is fully compatible with standard asphalt mixing plants, requiring no additional infrastructure, which facilitates its rapid adoption in BRT and highway projects.