Effects of Rediset Additive on the Performance of WMA at Low, Intermediate, and High Temperatures

Abstract

Utilizing polymers with asphalt mixtures is one solution to improving the performance of asphalt mixtures. Warm mixed asphalt (WMA) technology has begun to be widely used; however, hot mixed asphalt (HMA) is the most common paving procedure worldwide. HMA has some side effects, such as increasing emissions of exhaust gases, which lead to environmental pollution and air pollution and increasing energy consumption. Thus, utilizing WMA would help to improve asphalt mixture performance, reduce mixing and paving temperatures, reduce CO₂ emissions, and save energy. In this study, two WMA additives (Sasobit (M1) and Rediset LQ-1200 (M2)) are used with the control HMA to investigate and evaluate the asphalt mixture’s performance and the effects of WMA additives. Rediset LQ-1200 is a new version of materials classified under chemical additives in WMA. The Sasobit and Rediset LQ-1200 dosages were 1.5 and 0.5 percent by binder weight, respectively. Different mixture and binder tests were utilized, such as penetration, DSR, BBR, IDT, CML, HLWT, and APA. To simulate long-term performance, laboratory conditions of single or combined effects were used. The results showed that M2 had more cracking resistance and durable performance with low rutting resistance, while M1 had more rutting resistance and less moisture suitability, with low cracking resistance and durability.

1. Introduction

Warm mix asphalt (WMA) is an asphalt mixture that is made using the principles of a wide range of technologies—such as organic, chemical, and foaming processes—that allow the production of pavement at lower temperatures compared to hot mix asphalt (HMA). WMA technology is one example of a low-energy, low-emission technology that has become more popular as environmental and sustainability awareness has grown [1]. WMA has multiple effects, including environmental and construction engineering benefits such as reducing fuel consumption, decreasing the production of greenhouse gases, and improving pavement compaction. WMA first appeared in Europe in the late 1990s and has grown in popularity over the last decade [2]. However, there are still some challenges and issues to forecasting WMA behaviors, such as the aging of WMA compared to hot mix asphalt (HMA), the relative behavior between WMA technologies, and the cumulative effects of environmental exposures. As a result, more observation and understanding of the distinctions are needed [3].

Most of the highway road networks in the world are made of fixable pavement. For many years, HMA was the most commonly used road construction method that met structural performance requirements. HMA mixing and compacting temperatures range from 150 °C to 190 °C, which has a negative impact on the environment, consumes a lot of energy, produces high carbon emissions, and makes the construction process difficult in cold weather [4].

Recently, a new asphalt pavement technology has been developed, referred to as “warm mix asphalt” (WMA), which requires a decrease in manufacturing temperature. The performance of WMA is relatively wide, while the concept of the WMA methodology is similar (reducing binder viscosity and improving workability) [5]. WMA can be made using different products to decrease the temperature of asphalt pavements by around 14–25 °C [6]. The temperature reduction in WMA technologies depends on many factors, such as WMA additives, binder type, and technical process [7]. WMA began in Europe, and is usually produced at lower temperatures than HMA by about 38 °C (100 °F). The aims of WMA are to reduce temperatures, save energy, and reduce carbon emissions by 30% when compared with HMA [8].

WMA technologies were developed to reduce the temperatures used in the production and placement of asphalt mixes. WMA’s role as a green technology has had a favorable impact on the asphalt industry’s economic and environmental conditions [9]. Overall, WMA has a number of advantages over traditional HMA technologies, such as paving benefits, environmental benefits, energy benefits, etc. Paving with WMA is more workable than HMA, even at reduced temperatures. This situation enables longer compaction and paving times than with HMA. WMA technologies are frequently utilized in cold climates to extend the paving season, permit paving in the evening, or pave at high altitudes without losing workability, as mixtures can be compacted at lower temperatures [10]. WMA technology has environmental benefits such as energy savings and lower carbon production, resulting in less pollution during production [11,12]. When compared to HMA, the production of WMA has energy savings between 20 and 75% [13].

The classification of warm mix asphalt technology depends on the type of technology or degree of temperature reduction. WMA technologies can be categorized in a variety of ways, such as organic, foaming, and chemical additives. Organic indicates a wax additive that is added to the asphalt mixture during the mixing process to increase stiffness and reduce the viscosity of the mixture [14,15]. The most common types of wax are Fischer-Tropsch waxes, Montan waxes, and fatty acid amides [16,17].

The chemical additive WMA process is also utilized to reduce mixing and compacting temperatures [18]. The chemical additive manufacturing procedures do not rely on foaming or viscosity reduction to reduce mixing and compacting temperatures. It is a composite of emulsifiers, surfactants, polymers, and other additives that improve the coating, workability, compaction, and adhesion promoters (anti-stripping agents) of asphalt mixtures. In fact, several manufacturers are beginning to develop their own WMA technologies, focusing on the chemical additive process. Cecabase, RedisetTM WMX, and Evotherm are examples of chemical additives in WMA technologies [18].

Chemical additives and wax additives were found to behave differently with different pavement distresses. For rutting, chemical additives had little effect on or worsened rut resistance for asphalt mixtures [19,20,21]. However, chemicals improved fatigue cracking in asphalt mixtures [2,22,23]. Chemical additives showed an increase in moisture damage or had behavior similar to HMA [19,20,21]. Thermal cracking of chemical additives showed increased resistance to cracking at low temperatures [23,24,25]. Waxes are known to have a negative effect on thermal cracking [23,26,27]. Wax either had no effect on fatigue cracking or had a negative effect compared to HMA [23,28,29]. Wax showed improved rutting resistance in asphalt mixtures [19,23,28].

One of the wax WMA additives is sasobite. Sasobit is produced by the Sasol Wax Company of South Africa. The addition of the Sasobit additive to asphalt mixtures made the mixtures more durable and resistant to cracking, according to Jiaqiu Xu et al. [30]. In addition, Burak Sengoz demonstrated that adding 1 to 3% Sasobit to an asphalt mixture reduced penetration and increased the softening point, while viscosity tests revealed that adding Sasobit to an asphalt mixture reduced its compaction and mixing temperature [31]. The workability of the asphalt mixture increases with the addition of Sasobit. Ke Zhang conducted a study to investigate the effect of the addition of Sasobit to an asphalt mixture using a DSR test [32]. The DSR result rose to varying degrees [32]. Jiaqiu Xu et al.’s research showed that when adding Sasobit additive to binder, the bending beam rheometer (BBR) test results showed that Sasobit has a weakening effect on low-temperature mechanical properties [30].

There is a new version of Rediset materials called Rediset LQ-1200 but there is a lack of information on its effects on the performance of asphalt mixtures and binder.

2. Materials and Methods

2.1. Material Selection

Table 1. Properties of Mixtures Tested.

Mixture ID	M0	M1	M2
PG	64–10	64–10	64–10
Bitumen (%)	5.6	5.6	5.6
WMA	None	Sasobit	Rediset LQ-1200
Dosage	None	1.5 % binder	0.5 % binder
P25mm (%)	100	100	100
P19.0mm (%)	100	100	100
P12.5mm (%)	92.2	92.2	92.2
P9.5mm (%)	86.8	86.8	86.8
P4.75mm (%)	57.2	57.2	57.2
P2.36mm (%)	38.7	38.7	38.7
P1.18mm (%)	24	24	24
P0.60mm (%)	15.6	15.6	15.6
P0.30mm (%)	10	10	10
P1.5mm (%)	7	7	7
P0.075mm (%)	5.4	5.4	5.4
NMAS (mm)	12.5	12.5	12.5
Gb	1.0	1.0	1.0
Gsb	2.7	2.7	2.7
Ps	94.4	94.4	94.4
Gse	2.8	2.8	2.8
DP	1.2	1.2	1.2

PG = performance graded; WMA = warm mix asphalt; P_{25 mm =} percent passing a 25 mm sieve; P_{19.0 mm} = percent passing a 19 mm sieve; P_{12.5 mm} = percent passing a 12.5 mm sieve; P_{9.5 mm} = percent passing a 9.5 mm sieve; P_{4.75 mm} = percent passing a 4.75 mm sieve; P_{2.36 mm} = percent passing a 2.36 mm sieve; P_{1.18 mm} = percent passing a 1.18 mm sieve; P_0.60mm = percent passing a 0.60 mm sieve; P_0.30mm = percent passing a 0.30 mm sieve; P_1.5mm = percent passing a 1.5 mm sieve; P_0.075mm = percent passing a 0.075 mm sieve; NMAS = nominal maximum aggregate size; G_b = specific gravity, asphalt binder; G_sb = bulk specific gravity of aggregate; P_s = percent of aggregate; G_se = effective specific gravity of aggregate; D_P = dust percentage.

shows the gradation of the mix design used in this study. HMA was used as the control mix (donated M0), while two WMA additives were used: Sasobit (M1) and Rediset LQ-1200 (M2). The doses of Sasobit and Rediset LQ-1200 additives were 1.5% and 0.5% by weight of binder, respectively. In mixing procedures, the oven was set to the approximate plant mixing temperatures of 160 °C for the HMA and 140 °C for the two WMAs. Samples were created with target air voids (Va) of 7±1% according to AASHTO T166, with different sizes as required for mixture tests. Different mixture and binder tests were utilized (i.e., penetration, dynamic shear rheometer, bending beam rheometer, indirect tensile strength, Cantabro mass loss, Hamburg loaded wheel-tracking, and asphalt pavement analyzer). In addition, different laboratory conditions were used that included unaged, single, or combined effects of oxidation and moisture, as described in the following section.

2.2. Laboratory Conditions

2.2.1. Oxidation Conditioning

Oven conditions were conducted according to AASHTO R30. After preparing the mixture samples, they were placed in an oven (Figure 1) at 85 °C for 120 ± 0.5 h. After conditioning was complete, the oven was turned off and the samples were allowed to cool to room temperature.

2.2.2. Combination of Oxidation and Moisture Damage Conditioning

According to AASHT T166, specimens were initially vacuum-saturated to approximately 80% of their V_a volume before being temporarily stored in room-temperature water until they were transferred to a pre-heated water bath at 64 °C, as shown in Figure 2. Specimens stayed in the water bath for 14 days and were then allowed to cool to room temperature. Finally, the specimens were transferred to the oven for oxidation conditioning as described in Section 2.2.1.

2.3. Mixture Testing

2.3.1. Cantabro Mass Loss (CML) Testing

The specimen size used for CML was 150 mm in diameter and 115 mm tall. Samples were placed in a Los Angeles (LA) abrasion drum for 300 rotations at 25 °C without sphere bolls (Figure 3). The specimen’s mass was recorded before and after testing. The percent of mass loss was calculated using Equation (1).

$$ML=\frac{m_1-m_2}{m_1}\times 100$$

(1)

where

• ML = percent mass loss;
• m₁ = specimen mass before testing;
• m₂ = specimen mass after testing.

Figure 3. (a) Cantabro testing examples, (b) samples after testing.

Figure 3. (a) Cantabro testing examples, (b) samples after testing.

2.3.2. Indirect Tensile (IDT) Testing

The IDT test was performed on specimens 150 mm in diameter and 95 mm in height. The test processor was set according to AASHTO T283 (Figure 4), where specimens were loaded at 50 mm/min until they failed at 25 °C. Equation (2) was used to determine tensile strength (S_t).

$$S_t=\frac{200\times {\mathrm{P}}_{\max }}{\mathsf{\pi }\times \mathrm{t}\times \mathrm{D}}$$

(2)

where

• P _max = maximum load (N);
• t = specimen thickness (mm);
• D = specimen diameter (mm).

Figure 4. IDT Testing equipment.

Figure 4. IDT Testing equipment.

2.3.3. Asphalt Pavement Analyzer (APA) Testing

The APA test was conducted according to AASHTO T340, as shown in Figure 5. The APA specimen size was 150 mm in diameter by 75 mm in height. Rut depth (RD_APA) measurements were taken at 25, 4000, and 8000 cycles at 64 °C, with RD_APA at 8000 cycles (16,000 passes) serving as the study’s main finding. Two specimens were used to conduct one test, while three sets were used to represent the RD_APA value in the test result.

2.3.4. Hamburg Loaded Wheel-Tracking (HLWT) Testing

The HLWT was conducted according to AASHTO T324 standards (Figure 6). The HLWT specimen size was 150 mm in diameter by 63 mm in height. HLWT was performed to 20,000 passes (or failure at 12.5 mm rut depth). Rut depth (RD_HLWT) measurements were taken at 5000, 10,000, 15,000, and 20,000 passes; the key finding of the current study was RD_HLWT at 20,000 passes or failure. The samples were immersed in water at 50 °C for 30 ± 1 min before and during testing.

2.4. Binder Testing

2.4.1. Dynamic Shear Rheometer (DSR) Testing

DSR testing was conducted at intermediate (DSR_8mm) and high (DSR_25mm) temperatures using an Anton Paar SmartPave 301 as shown in Figure 7. Each binder sample had its complex shear modulus (G*) and phase angle (δ) measured. DSR_8mm was conducted using 8 mm plates with 2 mm spacing and DSR_25mm was conducted with 25 mm plates with 1 mm spacing. Testing was performed according to AASHTO T315. The intermediate and high critical temperatures (T_c) of asphalt binder were calculated using Equation (3).

$${\mathrm{T}}_{\mathrm{c}}={\mathrm{T}}_1+\left(\frac{{\log }_{10}\left({\mathrm{P}}_{\mathrm{s}}\right)-{\log }_{10}\left({\mathrm{P}}_1\right)}{{\log }_{10}\left({\mathrm{P}}_2\right)-{\log }_{10}\left({\mathrm{P}}_1\right)}\right)\left({\mathrm{T}}_2-{\mathrm{T}}_1\right)$$

(3)

where

• T_c = critical temperature, ˚C;
• T₁ = lower of the two test temperatures, ˚C;
• T₂ = higher of the two test temperatures, ˚C;
• P_s = property specification value;
• P₁ = results of the test for the specified value of the property at T₁;
• P₂ = results of the test for the specified value of the property T₂.

Figure 7. DSR equipment.

Figure 7. DSR equipment.

2.4.2. Bending Beam Rheometer (BBR) Testing

The BBR test was performed in an asphalt binder according to AASHTO T313 (Figure 8). Critical temperatures of creep stiffness (T_c-s) and m-value (T_c-m) were utilized based on AASHTO M320. Equation (3) was used to determine T_c-m and T_c-s.

2.4.3. Penetration (Pen.) Testing

A penetrating test was conducted on asphalt binder samples at 25 °C according to ASTM 5, as shown in Figure 9. Asphalt binder samples were conditioned in water at 25 °C before testing for at least one hour. An average of three samples’ values was used to represent the penetration test value.

3. Test Results

Table 2. Binder Test Results.

Mixture	Pen. (dmm)	DSR8mm	DSR25mm	BBR Tc-s	BBR Tc-m
M0	34	26.5	69.8	−10.9	−17.7
M1	30	27.3	74.1	−12.1	−9.9
M2	33	25.6	69.4	−13.9	−18.3

and

Table 3. Mixture Test Results.

Conditions	Mix	CML ML (%)	IDT St (kpa)	HLWT					APA
				5K	10K	15K	20K	P12.5	25	4K	8K
Unaged	M0	6.1	1415	2.55	6.50	10.62	---1	16462	0.256	2.562	3.604
	M1	7.6	1602	2.26	4.12	6.42	---1	19492	0.239	1.480	1.762
	M2	6.4	1757.2	3.85	4.11	8.63	---1	14928	0.272	2.385	2.931
Oxidation	M0	7.3	1711	1.29	2.38	3.39	4.61	---2	0.140	2.241	2.850
	M1	11.1	1835	1.44	4.68	5.6	7.25	---2	0.204	1.145	1.418
	M2	8.1	2114.8	1.45	4.13	7.13	---1	18816	0.058	2.292	2.728
Combination of oxidation and moisture	M0	11.6	1073	6.1	10.4	---1	---1	12693	---3	---3	---3
	M1	13.1	995	2.57	3.23	7.19	---1	17435	---3	---3	---3
	M2	10.4	1174	7.26	---1	---1	---1	9647	---3	---3	---3

---¹ Test reached rut depth of 12.5mm before 20K passes; ---² Test reached 20k passes; ---³ Data were not collected in this condition due to material limitations.

summarize all tests for both binder and mixture testing, respectively. The values for a given test method (CML or IDT) represent the average of three samples. In the HLWT and APA tests, two specimens were used (referred to as a set) to represent one test value, while an average of three sets was used to represent the test value in Table 3. The HLWT was performed to 20,000 passes or failure at 12.5 mm rut depth, where the pass number at which failure was reached is reported. Rut depth of HLWT (RD_HLWT) measurements were made at 5000, 10,000, 15,000, and 20,000 passes, while the rut depth of APA (RD_APA) measurements were taken at 25, 4000, and 8000 cycles (Table 3).

3.1. Binder Testing

Figure 10 shows the penetration test results. M1 had a lower pen. value compared to M0 and M2, while M2’s pen. value was similar or slightly lower than M0’s value. In addition, for the DSR_8mm results displayed in Figure 10, M1 had a slightly higher T_c value compared to M0 and M2. M0 had a higher T_c degree than M2. Both M0 and M2 had T_c values similar to each other, according to DSR_25mm (Figure 10), while M1 had a slightly higher value than the other asphalt binder. In fact, the PG grade difference between M1 and the other asphalt binders was nearly one.

Figure 11 shows BBR test results for stiffness and m-value. M2 showed the lowest T_c-s value, while M0 showed the highest. The temperature difference between M2 and M0 was approximately 3°C. In addition, M0 and M2 showed similar T_c-m value results, while M2 had a slightly lower T_c-m value. The difference between M1 and both M0 and M2 was one PG grade.

3.2. Mixture Testing

Figure 12 shows the CML test results. M0 showed a lower CML value for all conditions. CML values for M2 were slightly higher than M0 in both unaged and oxidation conditions, while the CML value of M2 was lower than M0 in the combined effect condition. The M1 CML test results were higher than M0 and M2.

IDT test results are shown in Figure 13. M0 had a lower S_t value than M1 and M2 in both unaged and oxidation conditions. In the combined effect condition, M0 had an S_t value lower than M2 and higher than M1. As shown in Figure 13, M2 had an S_t value higher than M1 in all conditions.

Figure 14 shows the HLWT test results. M0 had a lower rutting resistance than M1 and a better rutting resistance than M2 in the unaged and combined conditions, while in the oxidation condition M0 had the highest rutting resistance of the other mixtures. It was also observed that M1 showed better rutting resistance than M2 in all cases.

Figure 15 shows the APA test results. M0 had a higher RD_APA rut depth value than M1 and M2 in unaged condition. In oxidation conditioning, M0 had a comparable RD_APA rut depth value to M2 while it had a higher RD_APA rut depth value than M1. In both unaged and oxidation conditions, M1 had a lower RD_APA rut depth value than M2.

3.3. Statistical Assessment of Mixture Testing

Table 4. Statistical Assessment of Mixtures.

Condition	MIX	CML (%)				IDT (kPa)				APA at 8K
		Δ (Mi − M0)	p-Value	t-Test	Sig.D *	Δ (Mi − M0)	p-Value	t-Test	Sig.D *	Δ (Mi − M0)	p-Value	t-Test	Sig.D *
Unaged	M1	1.5	0.012	A	Yes	187.0	0.018	B	Yes	−1.84	0.004	A	Yes
	M2	0.3	0.494	B	No	342.2	0.004	A	Yes	−0.67	0.065	A	No
Oxidation	M1	3.8	0.001	A	Yes	124.0	0.052	B	No	−1.43	0.001	A	Yes
	M2	0.8	0.036	B	Yes	403.8	0.003	A	Yes	−0.12	0.074	A	No
Combination of oxidation and moisture	M1	1.5	0.018	A	Yes	−78.0	0.050	B	Yes	---1	---1	---1	---1
	M2	−1.2	0.037	C	Yes	101.0	0.082	A	No	---1	---1	---1	---1

Sig.D * significant differ to M0. ---¹ Data were not collected in this condition due to material limitations.

shows a statistical assessment of the obtained results mentioned in Table 3 for asphalt mixtures. The values of Δ were calculated by subtracting the results of each mix (M1, M2) from M0. p-values were obtained from the statistical analysis of the t-test, which indicates the significance of the difference between the sample’s means. There is a statistically significant difference between the mean when the p-value is less than 0.05; on the other hand, there is no statistically significant difference if the p-value is higher than 0.05.

Statistical assessment of the CML test showed that there was a significant statistical difference between M1 or M2 and M0 in all cases, except in the case of an unaged condition, where the M2 CML test value was not significantly different from the M0 value. In addition, Table 4 shows that there was a significant statistical difference between M1 or M2 and M0 in most IDT testing cases. There was no significant statistical difference between M1 and M0 in the oxidation condition and M2 and M0 in the combined effect condition. For APA testing, there was a significant statistical difference between M1 and M0 in both the unaged and oxidation conditions. However, there was no significant statistical difference between M2 and M0 in both the unaged and oxidation conditions.

4. Discussion

Many studies have concluded that chemical WMA additives generally improve the cracking resistance of asphalt mixtures, while wax WMA additives generally improve rutting resistance [2,19,22,23,28].

BBR test results showed that the M2 asphalt binder performed better at low temperatures than the other asphalt binder types (M0 and M1). The difference in BBR T_c-s values between the M2 asphalt binder and the other asphalt binders (M0 and M1) was approximately 3 °C, and the difference in BBR T_c-m values was nearly one PG grade, indicating that the M2 asphalt binder improved low-temperature cracking resistance. According to IDT testing, M2 had better cracking resistance than the other asphalt mixtures (M0 and M1), with a statistically significant difference (Table 4). M1 also had better cracking resistance than M0 in both the unaged and oxidation conditions, with a significant statistical difference; however, M1 had lower cracking resistance compared to M0 in the combined effect condition. Bazuhair et al. (2018) illustrated the reason for this observation [12]. According to CML test results, M2 showed a similar or slightly better durability than M0, while M1 has a lower durability compared to other asphalt mixtures, with a significant statistical difference (Table 4).

DSR_8mm results showed similar performance of all mixtures (M0, M1, and M2), which indicates all binders may have similar performance at intermediate temperatures. Overall, DSR_8mm results show that the two asphalt binders would perform similarly to the control asphalt binder.

Penetration testing showed that M1 had a lower pen. value than M0 and M2, which indicated a stiff asphalt binder that helps improve the rutting resistance of the asphalt mixture. M2 and M0 pen. values showed similar binder properties at intermediate temperatures. DSR_25mm test results showed that M1 had a better performance at high temperatures, where the difference between the T_c values of M1 and the other asphalt binders (T_c values of M0 and M1) was nearly one PG grade. M0 and M1 showed similar asphalt binder performance at high temperatures. In addition, the M1 asphalt mixture showed better rutting performance than the other asphalt mixtures (M0 and M2) according to HLWT and APA testing. It was also observed that the M2 asphalt mixture is moisture susceptible, whereas the HLWT showed M0 had better rutting resistance than M2 and the APA showed M2 had better rutting resistance than M0.

Overall, the binder and mixture testing results of M0, M1, and M2 confirm the conclusion of most studies that chemical WMA additives generally improve the cracking resistance of the asphalt mixtures, while wax WMA additives generally improve rutting resistance.

5. Conclusions

This article’s objective was to evaluate the effects of the Rediset additive on the performance of WMA at low, intermediate, and high temperatures. The test results showed that the WMA additives (M1 and M2) performed similar to or better than the control HMA (M0). Laboratory evaluation of the Rediset additive showed that the M2 mixture had high fatigue and thermal cracking resistance, with durable performance. The M2 mixture was also moisture susceptible and had less rutting resistance. With the advantages of utilizing WMA (i.e., paving benefits, environmental benefits, energy benefits, etc.), WMA would be recommended in road paving construction, and the M2 additive is generally suitable for crack resistance and cold-climate regions.