Authors: Falak Naz, Dr. Hu Kui, Anwar , Zakir
Certificate: View Certificate
Transportation engineering play a vital role in the developing of a society and a country. It’s actually deal with the planning, designing, operating and managing different types of facilities for all modes of transportation to provide safe, convenient, comfortable, efficient and economical movement of people as well as goods. Due to the climatic variations and growth of traffic loading, road infrastructure faces number of serious failures such as rutting, stripping, fatigue cracking, bleeding etc. Maintenance of roads is necessary because roads lose its serviceability with passage of time. A lot of researches have been done to improve the quality of hot mix asphalt and to overcome problems associated with HMA. In current research polypropylene fibers were used as additive in asphalt concrete at different percentages i.e., 1%, 2%, 3% by weight of total mix. The main target of this study was to check the effect of polypropylene fibers on the rutting performance of HMA and also to check the response of fibers modified samples against moisture damage. For mixing of fibers with Hot Mix Asphalt “wet method” of mixing was adopted. For determination of OBC Marshall Mix Design was followed. Same OBC was used for control and fibers modified samples. Wheel tracker test and indirect tensile test were carried out for determination of rutting and moisture susceptibility of different mixes respectively. On the basis of rutting test result, it was revealed that adding 1% polypropylene fibers enhanced the ability of hot mix asphalt to resist rutting up to 14%, while for 2% and 3% fibers decrease in rutting resistance was noted which was 18% and 78% respectively. From the results of indirect tensile strength, it was observed that resistance to moisture damage is increases by increasing the quantity of fibers because it has maximum elongation and modulus as compared to bitumen.
The main objective of transportation engineering is to transfer people and goods from one place to another safely, efficiently, economically and comfortably.
According to NHA report the total length of roads in Pakistan is 463,000 km and mostly hot mix asphalt is used for the construction of wearing course. The top surface faces different type of pavement distresses i.e., rutting, Fatigue cracking etc. because it’s directly receives the variation in climate conditions and traffic loading. The safety and comfortably of roads in Pakistan are mostly disturbed by rutting (Japan International Cooperation Agency, JICA) . To enhance asphalt concrete properties researchers are using different types of fibers, which gives positive results (Airey) .
In current research Polypropylene fibers is used with Aggregates mixed with Hot Mix Asphalt as additive to check the response of pavement against different conditions especially in the case of rutting. Over the centuries, the natural stone aggregate was delivering excellent performance as an aggregate in the road construction. The environmental effects because of the overuse of natural stone aggregate is also in warning rates. These effects needs to connect the researches on alternative construction material and non-conventional aggregates. But while selecting the non-conventional aggregates in road construction for sustainability purpose, quality and durability may not be compromised.
In the last few decades, numerous researchers have explore various types of fibers, including Kevlar, nylon, asbestos, polyester, glass, polypropylene, carbon, aramid synthetic, and recycled/waste fibers for reinforcing asphalt mixtures and accomplish the excellent pavement behavior .
The main aim of using fibers is to decrease the impact of the most regular distresses, it is believed that the incorporation of fibers to asphalt may improve the rutting, fatigue and flexibility characteristics and boost the strength of asphalt content due to their native similarities with asphalt binder and their superior mechanical properties . Furthermore, the researcher found that the incorporation of fibers to control asphalt mixtures significantly increases the fatigue life at peak strain levels, and it enhance rutting resistance at 45 and 55oC .
Moreover, extreme fibers material in correspondence to the asphalt binder content decrease the adhesion of the asphalt and in order to resulting in the reduction of particles .
Addition of fibers in dense graded mixtures to enhance resistance ability towards cracking and rutting is still smaller . The favorable results of this additive on bitumen are becoming greater defense to rutting, shorten temperature sensitivity, adhesive, better flow at extreme temperature and cohesive failure, growing stiffness and etc. .
II. LITERATURE REVIEW
Different researcher investigated the effect of fibers all over the world in Hot Mix Asphalt. In this unit a brief summary of previous studies about the utilization of fibers in Hot Mix Asphalt is discussed. According to previous work, methodology for the mixing of polypropylene fibers in Hot Mix Asphalt was adopted.
Hot Mix Asphalt (HMA) is a common material used for road surfacing. It is a mixture of stone, gravel or sand bounded together by binding material i.e., Bitumen. Conventional HMA is consists of crushed stone, stone dust as filler and bitumen as asphalt binder .As the top surface of the pavement structure is directly exposed to such conditions that can affect the properties of HMA i.e., climate conditions and traffic loading etc. It wills causes different type of failure such as rutting, fatigue cracking, longitudinal cracking, stripping etc. so it is necessary that HMA should have sufficient strength to withstand against such scenarios. Bitumen amendment is a common and valuable method to achieve the concern goal. Mostly the modification of asphalt binder is done with addition of fibers. In the early 1990s polymers were introduce in order to modify and improve the characteristics of Hot Mix Asphalt for worst case scenario. Another researcher Brown and Cross significantly worked for the reinforcement of asphalt binder by using fibers . He identified and concluded that the use of fibers in Hot Mix Asphalt can improve the cohesive and tensile strength of asphaltic concrete when compared to conventional mix.
A. Utilization of Fibers in Asphalt Pavements
Different types of researches have been conducted for the enhancement of rutting performance using various chemical as admixtures. Another researcher uses different percentages of Polyacrylatonitrile fibers (PAN) and PolyolefinParamid (POA) fibers i.e. 0.1wt%, 0.2wt%, 0.3wt% to investigate the behavior of the asphalt concrete at various temperature (-15?C, 0?C, 15?C) . Fraction energy, Indirect Tensile Strength ITS, toughness and post cracking energy were the target parameter for checking the behavior of conventional and fibers modified asphalt mortar. In the accordance of result it was detected that strength was significantly increases at low temperature i.e. -15?C at 0.3% of PAN or PON. It was also investigated that fibers addition enhanced fraction energy properties of asphalt. One of the previous research Stated that the fibers can be used for the enhancement of pavement response against distresses such as rutting, fatigue etc. . With fresh asphalt or in the rehabilitation process of pavement in the form of overlay. In this research they adopted the method of using fibers in the overlay. For the experimental work two set of samples were prepared i.e. fibers mix samples and original samples. 3D move analysis software was used for analysis and it was found that the use of fibers in overlay have maximum design life but have high cost of construction as compared to the conventional asphalt. In old research they Added cellulose fibers with stone mastic asphalt (SMA) to study the response of the asphalt mix having nominal maximum aggregate size (NMAS) i.e., 25mm, 19mm, 12.5mm. The central target of this study was to compare the result of rutting and fatigue for three mixes. For this purpose, flow test and dynamic modulus test were performed. Result indicates that mix with NMAS 25mm has good response against rutting failure and has maximum stiffness as compared to other two samples. Phase angle and dynamic response was used for the determination of fatigue parameter and results show that mix with 12.5mm size aggregate has better response for fatigue. According to previous history and already published research study the influence of the aramid-polyalphaolefin polymers on the cracking performance of asphalt concrete at low and high temperature. Rectangular beam bending test was used for low temperature, while the master curves obtained from dynamic modulus was used for checking high temperature cracking . Result shows that fibers mix asphalt have better result in low temperature cracking. Also, the fracture energy of modified asphalt was higher as compared to the conventional mix. Increment for flexural strength and strain energy, while reduction in stiffness modulus was observed from bending beam test results. In another researches they mixes styrene-butadiene-styrene (SBS) with hot mix asphalt and conducted different types of tests i.e., viscous measurements, frequency sweep tests, and fluorescence microscopy to study the influence of polymers on rheological properties of the hot mix asphalt . They mixes different percentages of SBS with hot mix asphalt i.e. 20%, 30%, 40% and found that SBS-modified asphalt with 30% of SBS have high viscosity which increases the viscoelastic behavior.
The another researches Rehman Investigated the consequence of fibers on the properties of asphaltic material by mixing different percentages of polyvinyl chloride (PVC) and polyethylene.
In previous the researcher Prasad studied the effect of using waste-plastic in flexible pavement and rigid pavement as a modifier at different percentages. Plastic waste are generally composed of cups, carry bags etc. which can be used as a coating material for aggregate . In this study polypropylene, high density polyethylene and low-density polyethylene were mixed with 80/100 grade bitumen and rheological test and performance tests such loss of stability test, Marshall Stability, flow value etc. were conducted on conventional and modified samples. On the basis of results, they concluded that by adding plastic to the conventional mix rheological properties were improved. Also, by coating weak aggregate with plastic can be used for road construction. The optimum PET content and OBC by weight of asphalt was 8% and 5.4% respectively.
III. RESEARCH METHODOLOGY
This unit comprises the detail procedure of tests that were adopted for the material characterization prior to mixing i.e., bitumen ARL 60/70, aggregate (coarse and fine). After material characterization detail procedure of preparing, conditioning and testing the Marshall samples for flow and stability value will be discussed. In last performance test were conducted for different percentages i.e., 1%, 2%, 3% of fibers and results were comparing for conventional and modified samples.
A. Methodology and Experimental Program
Objectives of the project were obtained by using the following plan. Initially the required materials i.e., bitumen ARL 60/70, crushed stone were collected from the respective sources. Polypropylene fibers were used as additive in HMA. Properties of all materials were tested in highway laboratory. Marshall Specimens were prepared for determination of OBC. Using that OBC Performance tests were conducted.
B. Materials Testing and Characterization
C. Selection of Aggregates Gradation
For the gradation of aggregate NHA class-A specifications was selected.
According to NHA guidelines for hot mix asphalt maximum aggregate size was kept 19mm.
Following table show NHA gradation while figure show gradation curve.
D. Polypropylene Fibers
Polypropylene is a type of polymer family with better toughness when compared with other fibers, which can increase adhesion between asphalt and fibers. Polypropylene fibers were used as additive by percentage weight of total mix. Following table shows different physical properties of Monofilament polypropylene fibers. In this research 12 mm lengthy fibers was used.
E. Mixing of Polypropylene Fibers with Asphalt Concrete
As mentioned earlier that bitumen 60/70 grade was used in this research. For mixing of fibers in asphalt concrete there are two methods i.e., wet method and dry method. Wet method was used for mixing of fibers in asphalt concrete because it has better result as compared to dry method for mixing of fibers. Heated bitumen (160°C) was first mixed thoroughly with fibers until uniform mix was obtained. After that this mix was mixed with aggregate until it covers all particles of aggregates. For aging of mix it was then kept for four hours in oven at 120°CThis mixed was then removed from oven and compacted in Marshall Mould having 4-inch diameter with 75 blows for each face per side. The fabricated simples are placed to cool down for 24 h. In addition, although preparation temperature of mixtures was close to the melting temperature of polypropylene fibers as shown in Table 4, it can be said that fibers were not dissembled from this temperature applied during specimen preparation. Figure proved good illustration of this method.
F. Asphalt Mixture Preparation
Different types of hot mix asphalt samples were prepared for testing, one conventional mix and three mixes with different percentage of polypropylene fibers i.e., 1%, 2% and 3%. Fibers were used as admixture in the asphalt concrete.
G. Preparation of Aggregates and Bitumen for Marshal Mix
ASTM D6926 specification were used, Net weight of a Marshall sample is normally 1200g with diameter of 4 inches. Initially gradation of aggregate according to NHA specification was done and after that aggregate were placed in oven at 110 ± 5oC temperature. The maxing temperature was 160oC and compaction temperature was 150oC. Five different percentages i.e., 3.5%, 4%, 4.5%, 5%, 5.5% of ARL 60/70 bitumen were mixed with aggregate to prepared five samples.
H. Mixing of Aggregates and Bitumen (Conventional Mix)
Usually, NHA guidelines are followed in Pakistan to mix aggregates with bitumen for the preparation of asphalt concrete. Temperature of the mix during mixing process was kept in range of 160? C to 165?C and the viscosity is in the range of 0.22-0.45 Pa. sec according to the NHA specifications.
I. Preparation of Fibers Modified Mix
For the preparation of fibers modified mix, Polypropylene fibers were initially mixed with bitumen and then mixed with aggregate according to wet method of mixing. After that this mix was placed in oven for 4 hrs. At temperature of 120?C for ageing. Mix was removed from oven and compacted in Marshall Mould using mechanical compactor. After preparing mixture compaction process was done. For this purpose, mixture was placed in the mould having specified dimensions i.e., 4” internal diameter and 3” height. A baseplate and extension color are also attached to the mould. For compaction, mould along with color and baseplate was then placed in Marshall mechanical compactor. 75 blows on each side were applied (Asphalt institute design criteria for ESALS ≥ 30 million). When 75 blows were completed on either side then mould is removed from compactor and specimen was extracted from the mould using extraction jack. Specimen was then cooled at room temperature.
J. Stability and Flow Testing
K. Bulk Specific Gravity (Gmb) Calculation
For determination of bulk specific gravity standard procedure of ASTM D2726 was followed.
Initially at 25?C the submerged weight of specimen was recorded in water bath. After that specimen was taken out from water bath and the extra surface water of specimen was wiped with towel and again weight of wiped specimen was recorded. Using the formula Gmb was calculated from the recorded values
L. Theoretical Relative Density (Gmm) calculation
ASTM D2041 specification Gmm was calculated for the specimens. Weight of mixture in loose form was recorded and put inside vacuum container at standard temperature 25?C and sample was fully submerged in vessel. For reducing residual pressure to 4kpa vacuum was created. For 15 minutes conditions were held. Vessel contains loose sample was filled with water. Now vessel containing specimen and water put inside water bath up to 10±1 minutes at 25?C. Flask was removed from water bath and extra surface-water was wiped from surface of flask and weight of replaced by asphalt sample is calculated. By dividing mass of loose sample with equal volume of water that was replaced by specimen give us Gmm. Using following formula Gmm was determined.
Gmm = maximum specific gravity of the mixture,
M. Stability and flow testing Marshall Samples
Marshall Samples were tested for stability and flow using standard method of ASTM D6927. At
60?C samples were submerged in water bath for 30 minutes prior to testing. After conditioning, samples were taken out from water bath and immediately tested for Marshall Stability. Up to the point of failure load was applied at the rate of 50mm/min.
N. Asphalt Mixture Volumetric Properties
Volumetric properties i.e., theoretical maximum specific gravity, unit weight, bulk specific gravity, voids in mineral aggregates (VMA), percent air voids, voids filled by asphalt (VFA) were calculated using ASTM standard specifications. Following table shows volumetric properties of mixture.
O. Optimum Binder Content (OBC) Calculation
In this study OBC for Marshall Mix design was calculated 4.42% and it was determined from the graphs of unit weight; stability and 4% air voids vs. bitumen content using following formula. OBC = (BC1+BC2+BC3) / 3
BC1 = Bitumen content at maximum stability,
BC2 = Bitumen content at maximum unit weight and
BC3 = Bitumen content at 4% air voids.
IV. RESULTS AND DISCUSSION
In flexible pavements, most commonly observed failures in Pakistan is rutting. There are many reasons for rutting occurrence but the most dominant factors are rise in traffic loading as well as variation of temperature. Also, highways in cold area of Pakistan are facing stripping failure. Presence of moistness in asphalt concrete is one of the key reasons for stripping failure. In this research Polypropylene fibers were mixed at different percentages in hot mix asphalt and two type of tests were conducted i.e. wheel tracker test and moisture susceptibility test (indirect tensile test) to determine influence of fibers addition on the performance of hot mix asphalt against rutting stripping failure.
A. Indirect Tensile Test (IDT)
Following specifications and guidelines of ASTM D-6931 indirect tensile test was conducted. To performed this test, samples were prepared using different percentages of polypropylene fibers using standard size Marshall Mould having diameter 100mm and height 63.5mm. Mixes were prepared according to procedure of Marshall Mix design. Before testing the samples, they were cooled down at room temperature 25°C. Maximum load for each sample was recorded in Newton and diameter and height in millimeter. Putting all the noted data in the following formula indirect tensile strength was calculated:
“St” represents tensile strength in kPa,
“P” represents maximum load in kN’
“D” represents diameter and “t” thickness of sample in mm.
A. Moisture Susceptibility Test
Bituminous material can loss its serviceability due to the occurrence of moisture and causes stripping failure of pavement. The degree of moisture destruction is known as moisture susceptibility. To conduct moisture susceptibility test according to AASHTO T 283-14, Marshall Samples were prepared following standard Marshall Mix design of sample preparation. A Total of 6 control samples and 18 of polypropylene fibers modified samples were prepared having different percentage of fibers i.e., 1%, 2%, 3% having OBC 4.42%. These samples were divided into two groups i.e., conditioned and unconditioned.
Tensile Strength Ratio (TSR)
Tensile strength ratio was used for finding out the extent of moisture damage of bituminous mixes. TSR is actually the ratio between the tensile strength of conditioned samples and unconditioned samples.
Where “S1” and “S2” represent tensile strength of unconditioned and conditioned samples respectively. Following table show TSR for control and fibers modified samples.
C. Indirect Tensile Strength Comparison for Different Mixes
Following table and graph show comparison of average indirect tensile strength of conditioned and unconditioned samples.
D. Comparison of TSR Value for Different Mixes
Following table show comparison of tensile strength ratio for control and fibers modified samples.
E. Rutting Test Results
To check the rutting performance of control and modified samples wheel tracker machine was used for this purpose. In most cases rutting accrue due to the high temperature because of the visco-elastic behavior of bitumen so in this study test temperature was kept 60°C during rutting test and the number of passes for all samples was ten thousand. After the completion of required passes rutting depth was recorded.
Wheel tracker apparatus was use for conducting rutting test. Same OBC was used for control and fibers modified samples and OBC was calculated by following the guidelines of Marshall Mix Design. Different percentages of polypropylene fibers i.e., 1%, 2% and 3% were added to hot mix asphalt. Conducting indirect tensile strength, resistance to moisture damage was determined from tensile strength ratio. On the basis of analyzing results following conclusions were made. According to susceptibility test results of indirect tensile strength test it was observed that the tensile strength of unconditioned samples was maximum compared to the tensile strength of conditioned samples for control and modified samples. It was also determined that by increasing the percentage of fibers, tensile strength also increases because tensile strength is associated with the stiffness of mix and fibers provide more stiffness to the mix. Up to 3% addition of fibers by weight of mix it was noted that resistance to moisture damage is increases because fibers have maximum elongation and modulus than bitumen but reduction in tensile strength may occurred at high percentages due to induction of coagulation. On the basis of rutting test result, it was revealed that adding 1% polypropylene fibers enhanced the ability of hot mix asphalt to resist rutting up to 14%. For 2% and 3% fibers decrease in rutting resistance was noted which was 18% and 78% respectively. This decrease is may be due to the use of same OBC for all percentages of polypropylene fibers because bitumen may not be able to lubricant all aggregate particles and fibers to developed affective interlocking force. On the basis rutting test result 1% fibers by weight of mix is optimum fiber content because it gives better result as compared to other percentages.
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Copyright © 2022 Falak Naz, Dr. Hu Kui, Anwar , Zakir . This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.