Utilization of bitumen modied with pet bottles as an alternative binder for the production of paving blocks

This study considers the utilization of bitumen modied with polyethylene terephthalate (PET) bottles waste as an alternative binder in paving blocks. The optimum bitumen content of asphalt concrete was modied with 2%, 4%, 6%, 8%, and 10% of PET waste. The compressive strength test, skid resistance, water absorption, and abrasion test were conducted on the paving block samples. Compressive strength test was conducted to verify the samples' compressive strength performance while water absorption and abrasion test were used to ascertain the durability properties of the samples. Results obtained for PET-modied bitumen concrete paving blocks (PMBCB) show an increase in compressive strength, skid resistance, and a decrease in the water absorption and abrasion loss when compared to unmodied bitumen samples. The maximum compressive strength for the PET-modied bitumen concrete was recorded at 10% PET replacement level. This implies that the utilization of PET-modied bitumen as binders in concrete paving blocks will not only help in waste recycling but also contribute signicantly to the protection and preservation of the environment.


Introduction
In recent years there has been an increasing tendency to recycle wastes generated by human activities through different effective solid waste management practices; Polyethylene terephthalate(PET), being one of the most common consumer plastics is used as a raw material for making materials such as bottles, containers for packaging food products and other consumer goods 1 . PET is the chemical name for polyester, it's a clear, strong, and lightweight plastic. Due to these exceptional properties, they have been widely used as high-impact resistant containers for foods and beverage packages, especially convenience-sized soft drinks, juices, and water 2 . Waste from PET bottles is particularly important as it constitutes a signi cant component of total solid waste generated 3 . This has been attributed to the fact that PET bottles are swiftly becoming the world's most preferred packaging material for drinks, foods, and beverages as several millions of them are produced globally 4 and consequently posing a serious disposal problem 5 Bitumen on the other hand is one of the oldest identi ed construction materials especially in road construction 6 . Other areas of bitumen application include roo ng, pipe coating, environmental protection, electrical insulation, soundproo ng, landslip containment, textiles, and medicine 7 . The engineering properties of bitumen to be used in any construction activities is very paramount and highly dependent on bitumen production and processing procedure 8 . It can be inferred that most available bitumen would not provide all the needed engineering characteristics for construction activities, hence, the need to improve it to meet speci c required properties has been achieved by the addition of additives in literature 8 9 . This modi cation has been carried out to obtains softer blends at low service temperatures thereby reducing cracking 10 ; obtain stiffer blends at high temperatures thus reduce rutting, reduce viscosity, increase stability and strength of mixtures 11 ; improve resistance to abrasion and resistance to the fatigue of blends, oxidation and aging 8 ; and to reduce the structural thickness and life costs of pavements 12 .
Several works have improved the properties of bitumen by using different types of additives and modi ers such as polymers, chemical modi ers, extenders, oxidants and antioxidants, hydrocarbons, and anti-stripping additives. Gopinath 13 used modi ers to improve the rheological behaviour of bitumen, and they concluded that Polymer (PET)-modi ed bituminous binders offered better resistance against permanent deformations due to their higher phase angle and a higher softening point when compared to conventional binders. In the work of Ogundipe 11 , PET waste was used as a modi er for asphalt concrete, experimental results obtained using the Marshall test showed that the stability of modi ed asphalt concrete was reduced by 20.4% in comparison with the unmodi ed asphalt concrete; thereby indicating that PET waste could improve the permanent deformation resistance of bitumen. This is a good pointer that PET-modi ed bitumen could be used to obtain structural pavement blocks with good durability properties and at a very economical rate.
As a result of the environmental degradation posed by the disposal of PET bottles, this study intends to determine the applicability of PET-modi ed bitumen as binder in the production of paving blocks thereby providing effective PET bottle recycling measures as well as durable and economical production of paving blocks.

Materials
The following materials were used in this study.

Cement
Ordinary Portland cement (Dangote 3X brand, 42.5R grade) conforming to BS 12:1991 was used for preparing concrete mix.

Aggregate
The aggregate typed used was quarry dust. It is grey ne rock particles with maximum particle passing 4.75 mm sieve. The quarry dust used is dry in condition, thoroughly retained on 150 μm aperture sieve size, and sourced locally at a granite quarry site in Omu-Aran, Kwara State. The physical properties of quarry dust used is presented in Table 1.

Bitumen
Bitumen of grade 50/70 was adopted for this research. It was sourced from a petroleum company. The properties of the bitumen is shown in Table 2   The polymeric materials used for modi cation were waste polyethylene terephthalate (PET) bottles collected within Landmark University campus (see Figure 1). The labels on the bottles were removed and the bottles were then washed and air-dried to enable easy melting

Mix Proportions
The mix proportion used for laboratory work is shown in Table 3. The optimum bitumen content of the bituminous concrete was modi ed with 2%, 4%, 6%, 8%, and 10% of molten PET bottles to determine their effect at different modi cation levels. Remark: Mix ID: C100, is 100% Cement base concrete paving block; B100, is unmodi ed bitumen paving blocks; and PMB-a, PMB = PET modi ed bitumen paving blocks -while 'a' is the percentage replacement of bitumen with PET.

Compressive Strength
The compressive strength of the samples was measured at 7, 14, and 28days according to ASTM C39/C39M-09a, using the Universal Testing Machine (see Figure 2). The compressive strength tests are done in whole units of sample blocks, and the value is taken as the quotient of the maximum test load (until rupture) and the cross-section of the specimen tested 14 .

Water Absorption
Water absorption test was conducted to determine the amount of water absorbed under speci ed conditions in accordance with British Standard 15 . The paving block samples after 28 days were ovendried at a temperature of 105 0 C for 6 hours. The oven-dry weight of the paving block was measured and subsequently wholly immersed in water for 24hours. The weight after water immersion is also measured.

Skid Resistance
The skid resistance of the samples was measured using the Portable Skid Resistance Tester (British Pendulum tester) shown in Figure 3 in accordance with British Standard 16 . The pendulum released from the horizontal position hit the surface and the needle position indicates reading of the pointer to the nearest whole number 17 . This approach focus on the pavement surface microtexture which refers to the small-scale texture of the pavement aggregate component that controls contact between the tire rubber and the pavement surface 18 . Three (3) runs of British pendulum tester (BPT) were conducted over each of the samples produced and the mean value is recorded. Before running the BPT, A 24-hour curing period was taken into account and the surface was properly wet as per wet condition speci cations.

Cantabro loss
The Cantabro abrasion resistance test was carried out on the specimen using Los Angeles abrasion (LAA) testing machine in accordance with ASTM standard 19 . Durability is a vital requirement of any type of pavement surface. Hence, it is imperative that the loss of particles on bitumen pavement surface when subjected to abrasive load be minimum for structural reliability 20 . In this test, each sample of the paving block was placed in LAA machine. The initial weight of each specimen is measured ( ) and recorded before placing it into the machine. The LAA machine was allowed to rotate at a speed of 30-33 revolutions per minute for 300 revolutions. After the revolution, the abraded sample (see Figure 4) was cleaned from any loose rubbles and weigh( ).Equation 1 is used to compute the abrassion loss. Figure 5 presents the compressive strength results of the cement and PET-modi ed bitumen paving blocks. As expected, the compressive strength increases with curing days in the range of 8.18 to 17 Nmm -2 , 11.67 to 20.49 Nmm -2, and 11.78 to 23.64 Nmm -2 for 7, 14, and 28-days curing period respectively.

Compressive Strength
Considering the different mix of paving blocks used in this study, those with cement binder have the highest compressive strength; indicating that bitumen and PET-modi ed bitumen binder do not signi cantly improve the compressive strength. The reduction unmodi ed and PET-modi ed paving block compressive strength compared to cement binder pavement block is attributed to the development of a weaker interfacial transition zone (ITZ) formed at the interface of bitumen binder and aggregates.
However, PET-modi ed paving blocks show increased compressive strength compared to unmodi ed Bitumen paving block samples. According to Udawattha 21 , the minimum strength requirement for 'class 4' for use of pedestrian walkways is 15N/mm 2 , therefore, the pavement block produced with 10% PETmodi ed bitumen with curing period of 28-days is suited for the construction of pedestrian pavement.
A one-way analysis of variances (ANOVA) was performed to determine if the effect of curing age and percentage of PET bottles on the compressive strength is signi cant or not. The results of the ANOVA analysis for the relationship between Compressive strength, curing age and percentage of PET bottles are summarized in Table 4. As seen from Table 4, the statistical p-value computed is 1.0805E-6; hence, it can be concluded that the in uence of curing age and percentage of PET bottles on the compressive strength is signi cant.

Water Absorption
Moisture damage of pavements is a signi cant problem affecting the durability of pavements. The amount of water absorbed for each paving block sample is shown in Figure 6. There is an observed decrease in water absorption with increasing PET contents in paving blocks. The water absorption decreases by about 56 % while considering the value obtained for unmodi ed bitumen paving block (7.2%) to that with 10 % PET modi ed bitumen (3.2%). Hence, PET addition signi cantly reduces the a nity of bitumen paving blocks to water as observed in paving block sample PMB-10 having the lowest water absorption value. This can be attributed to the good water-repellant characteristics of PET due to its hydrophobic properties 22 . The low water absorption characteristics exhibited by the PET-modi ed bitumen is key to ensure that the mixture is protected from moisture damage during the service stage.

Skid Resistance
The skid resistance value measured for samples is shown in Figure 7. Skid resistance is quanti ed using a skid number (SN) which measures the ratio of frictional resistance to motion in plane of interface 'F' to load perpendicular to interface 'L'(the higher the SN, the better). TRRL Road Note 27 23 . Among all samples tested, the 2%PET-modi ed bitumen samples had the lowest skid numberof34 while 6% PETmodi ed bitumen sample has the highest skid number of 85. Also, samples with 4% PET-modi ed bitumen contributed the least skid resistance with only 0.1% increase in skid number when compared to unmodi ed bitumen samples while both 8% and 10% PET-modi ed bitumen contributed 64.71% skid number to the samples. This indicates an improved skid resistance in bitumen pavement blocks modi ed with PET. All tested samples meet the Category C minimum skid resistance value (45) based on TRRL Road Note 27 speci cation 24 , except samples having 2% PET-modi ed bitumen which has a reduced SN of 33.34. However, a lower level of skid resistance offered by the 2% PET-modi ed bitumen may be acceptable in some residential streets depending on its geometry and tra c conditions.

Cantabro Abrasion Loss
The Cantabro test was used to evaluate the particle loss of the specimen and the result obtained is shown in Figure 8. The effect of various binder compositions on the abrasion loss showed a decreasing trend of abrasion value with increasing PET content. The correlation between compressive strength and Cantabro loss of the paving block is presented in Figure 9. The Cantabro loss demonstrated a clear negative linear relationship with compressive strength. This is attributed to enhanced binder characteristics and aggregate packing force of aggregates within PET-modi ed bitumen paving block resulting in enhanced compressive strength and less abrasion loss. This result is also in agreement with 20 and 25 .

Conclusion And Recommendation
One way to reduce the cost of road construction and rendering it more sustainable is by utilization of waste materials. This study considers using bitumen modi ed with polyethylene terephthalate (PET) waste as an alternative binder in paving block. The experimental results have demonstrated signi cant performance in terms of skid resistance, compressive strength, and abrasion loss. Based on the experimental investigation, the following conclusions are drawn: 1. PET-modi ed bitumen is found to have the highest skid number indicating that PET can signi cantly improve the skid resistance of paving blocks. 2. The utilization of unmodi ed bitumen in paving block reduces its compressive strength, however, PET-modi ed paving blocks show increased compressive strength compared to unmodi ed Bitumen paving block samples. The highest compressive strength is obtained at 10% PET modi ed bitumen level. 3. Abrasion loss decreases with increasing PET content. A clear negative correlation is obtained between abrasion loss and compressive strength which further con rms that PET modi ed bitumen pavement block will perform well in term of durability and strength requirement.
4. There was signi cant reduction in water absorption with increasing PET contents. This is important as it will ensure that the paving block is protected from moisture damage during its service stage, hence enhanced durability performance.  Water Absorption for the pavement blocks  Skid resistance for pavement blocks with different binder content Cantabro abrasion loss for different binder composition Relationship between Cantabro loss and Compressive Strength