Effect of encapsulated waste oils and compaction method on the curing and strength of cold mix asphalt

Abstract

Cold Mix Asphalt (CMA) is a sustainable alternative to conventional hot mix asphalt (HMA) due to its lower energy consumption and reduced environmental impact. However, CMAs often suffer from high moisture susceptibility, prolonged curing times, and inadequate mechanical performance. This study investigates the potential of calcium alginate capsules (CA capsules) containing waste sunflower oil (WSO) and waste engine oil (WEO) to improve CMA performance. Unlike previous research focusing on self-healing aspect of rejuvenating capsules, this work evaluates the impact of these CA capsules on curing efficiency, strength development, and mechanical behavior under different curing times and compaction methods: Marshall Compacted Mixture (MCM) and Gyratory Compacted Mixture (GCM). CA capsules were characterized using the Field Emission Scanning Electron Microscopy (FESEM)-EDS-Map and Thermogravimetric Analysis (TGA), and mechanical properties of CMA samples were assessed via indirect tensile strength (ITS), tensile strength ratio (TSR), rutting, and semi-circular bending (SCB) fracture tests.Weight measurements taken over the curing period showed that mixtures containing 0.5% CA capsules experienced greater moisture loss, thereby accelerating the curing process. GCM samples exhibited up to 90% higher ITS values than MCM samples, while samples with CA capsules showed an average 7-15% decrease in dry ITS. TSR values increased by up to 10% with 0.5% CA capsule addition, indicating improved moisture resistance. Fracture energy increased by 18-22% at - 20 °C in samples with 1% WSO, despite a slight reduction in fracture toughness. ANOVA analysis confirmed that compaction method had the greatest influence on ITS, TSR, and fracture energy, while CA capsule type mainly affected rutting depth. CA capsules with WEO led to deeper ruts than WSO, suggesting better compatibility of WSO with the asphalt matrix. These findings highlight that incorporating oil-based CA capsules-especially at 0.5-1% content-not only improves curing efficiency but also enhances the durability and sustainability of CMAs, particularly under low-temperature and high-moisture conditions.

Keywords: Calcium alginate capsule; Cold mix asphalt (CMA); Curing time; Sustainability; Waste oil.

Fig. 1

The three steps of the CA capsule production process: a) Sodium alginate solution being dropped into calcium chloride solution; b) CA capsule formation in the solution; c) Wet CA capsules.

Fig. 2

The FESEM photography outputs, a) Encapsulated WSO, b) Encapsulated WEO.

Fig. 3

a) EDS mapping of the encapsulated WSO, b) EDS mapping of the encapsulated WEO.

Fig. 4

a) EDS map sum spectrum of the encapsulated WSO, b) EDS map sum spectrum of the encapsulated WEO.

Fig. 5

Derivative weight (left) and weight loss (right) versus temperature graphs for different CA capsule types.

Fig. 6

Schematic illustration of the dual function of CA capsules in CMA.

Fig. 7

Impact of different CA capsule and compaction types and quantities on moisture content of CMA over several curing days (Control = CMA without capsules; Ca0.5E = 0.5% CA capsule with WEO; Ca0.5 S = 0.5% CA capsule with WSO; Ca1E = 1.0% CA capsule with WEO; Ca1S = 1.0% CA capsule with WSO).

Fig. 8

Impact of different types and levels of compaction on moisture content and weight loss of the Ca0.5S sample over various curing days.

Fig. 9

Impact of various types and amounts of CA capsules on moisture content and weight loss of GCM65 over different curing days.

Fig. 10

CMA sample after ITS test, a) control mixture, b) CA capsule mixture.

Fig. 11

SCB samples, a) before the fracture test, b) after the fracture test.

Fig. 12

ITS results for different dry samples.

Fig. 13

TSR results for different samples.

Fig. 14

Rut depth for different samples.

Fig. 15

Fracture toughness results of samples at −20 ℃ and 0 ℃.

Fig. 16

Fracture energy results of samples at −20 ℃ and 0 ℃.

Fig. 17

Fracture toughness values of various samples during different curing days at −20 °C.

Fig. 18

Fracture toughness values of various samples during different curing days at 0 °C.

Fig. 19

Fracture energy values of various samples during different curing days at −20 °C.

Fig. 20

Fracture energy values of various samples during different curing days at 0 °C.