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Shear strength evaluation of composite pavement with geotextile as reinforcement at the interface
Geotextiles and Geomembranes xxx (xxxx) xxx–xxx
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Technical note
Shear strength evaluation of composite pavement with geotextile as reinforcement at the interface Shyue Leong Lee∗, Mohammad Abdul Mannan, Wan Hashim Wan Ibrahim Department of Civil Engineering, Faculty of Engineering, Universiti Malaysia Sarawak, 94300, Kota Samarahan, Sarawak, Malaysia
A R T I C LE I N FO
A B S T R A C T
Keywords: Geosynthetics Polymer concrete Asphalt concrete Surface condition Curing types Temperature
This research was conducted to investigate the shear strength at the interface between polymer concrete and asphalt concrete with geotextile as reinforcement at the interface of these two types of concrete. The samples were tested for the parameters of different surface conditions [rough and smooth], curing types [room and thermal curing], temperature effect and the impact of geotextile as reinforcement. To investigate the correlation between these parameters, four different testing conditions were implemented. The results showed a significant improvement of shear strength for rough surface sample as compared to smooth surface sample. Moreover, samples cured in oven had lower shear strength as compared to samples cured in room condition. Besides that, high temperature has an adverse impact on the shear strength at the interface between polymer concrete and asphalt concrete due to the weakening of asphalt concrete at high temperature. As for samples reinforced with geotextile, the shear strength resistance was better as compared to unreinforced samples. Through visual observation, the types of failure under all testing conditions were mixed failure mode.
1. Introduction Pavement can be divided into flexible pavement, rigid pavement and composite pavement. In general, flexible pavement is a mixture of asphalt and aggregates, rigid pavement is a mixture of cement, water and aggregates, and composite pavement is a combination of flexible pavement laid on top of rigid pavement or vice versa. In this research, a mixture of orthophthalic unsaturated polyester resin [OUPR] and limestone are proposed as polymer concrete [PC] for rigid pavement. This PC is proposed to be placed on top of asphalt concrete [AC] to form composite pavement [CP] with geotextile as reinforcement at the interface between these two types of concrete. Moreover, PC has the potential as rehabilitation material for road maintenance. Hence, investigating the shear strength behavior at the interface of this CP is important. Shear strength comes from the interlocking of aggregate, adhesive strength of tack coat and friction at the interface between the two layers of pavement structure (Li et al., 2016) and is measured through shear test which is the most commonly used method (Raposeiras et al., 2013; Zhao et al., 2017). The shear strength at the interface between two layers of pavement structure affects pavement performance such as its mechanical properties, durability and maintenance regime (Rasmussen and Rozycki, 2004; Sprinkel, 2009; Kim et al., 2011; Ge et al., 2015; Li
∗
et al., 2016; Hu et al., 2017; Zhao et al., 2017). This is to ensure the pavement layers acts monolithic and functions normally (Raposeiras et al., 2013; Li et al., 2016; Isailović and Wistuba, 2018). Debonding of interface between two layers of pavement structure led to weak interlaminar strength. It can be caused by one of the three different stress conditions, namely, pure tension, pure shear and mixed condition which is a combination of shear and compressive or tensile stresses (Carreño et al., 2017). Other associated factors are stress caused by shrinkage, traffic load, temperature change, moisture, cycles of freezing and thawing, inappropriate construction techniques or inadequate choice of tack coat and others (Sprinkel, 2009; Ge et al., 2015). Pavement failure due to debonding can be categorised into delamination, slippage, top-down cracking, fatigue cracking, longitudinal cracks, and deformation (Sprinkel, 2009; Li et al., 2013; Ge et al., 2015; Hu et al., 2017; Zhang, 2017; Nithin et al., 2018). All these pavement failures led to adverse impact on traffic safety (Hu et al., 2017) and shorten the service life of pavement (Zhang, 2017). Moreover, these pavement failures are an indicator of shear strength failure (Sprinkel, 2009; Ge et al., 2015). There are many factors influencing the shear strength between two layers of pavement structure. The factors can be tack coat, geosynthetic [such as woven and non-woven geotextiles, biaxial and multiaxial geogrids], temperature, interface condition, load and other.
Corresponding author. E-mail addresses: [email protected] (S.L. Lee), [email protected] (M.A. Mannan), [email protected] (W.H. Wan Ibrahim).
https://doi.org/10.1016/j.geotexmem.2019.11.002 Received 27 May 2019; Received in revised form 23 October 2019; Accepted 15 November 2019 0266-1144/ © 2019 Elsevier Ltd. All rights reserved.
Please cite this article as: Shyue Leong Lee, Mohammad Abdul Mannan and Wan Hashim Wan Ibrahim, Geotextiles and Geomembranes, https://doi.org/10.1016/j.geotexmem.2019.11.002
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Temperature affects the tack coat in which it either increase or decrease the shear strength owing to the change of characteristic of tack coat (Raposeiras et al., 2013; White, 2016; Zhang, 2017; Nithin et al., 2018). The decrease of shear strength is directly proportional to the increase of temperature. This is because the increase of temperature decreases the viscosity of the asphalt and led to a decrease of shear strength (Hu et al., 2017; Zhao et al., 2017; Nithin et al., 2018). On the other hand, a decrease of temperature increases the shear strength due to an increase of stiffness of the tack coat and the interlocking of aggregate (Kim et al., 2011; Hu et al., 2017). As for the weather in Malaysia, the weather consists of sunny day and raining day. Besides that, the temperature during day time and night time is different. Therefore, the change of shear strength due to the different of temperature is very crucial and needs to be investigated. Geosynthetic as reinforcement at the interface between two layers of pavement structure has a negative impact on bond and shear strengths. Besides that, the characteristic of geosynthetic such as types, weight, and thickness, affect the shear strength (Nithin et al., 2018; Sagnol et al., 2018). However, Barraza et al. (2010) mentioned that the increase of tack coat increased the shear strength at the interface of pavement structure. Besides that, research conducted by Li et al. (2013) found that an increase of shear strength was observed when geotextile was used as reinforcement. Since scant literatures are available, there is a need for investigation using geotextile as reinforcement at the interface of PC laid on top of AC. As for surface condition, either smooth or rough surfaces affects the shear strength at the interface of pavement structure (Collop et al., 2009; Li et al., 2013; White, 2016; Nithin et al., 2018). One of the factors which affect the shear strength at the interface of pavement structure was the aggregate grading of the mixture for upper and lower layers of the pavement structure (Collop et al., 2009; Zhao et al., 2017; Nithin et al., 2018). Variation of aggregate gradation for the mixture can produce such as dense graded asphalt concrete, porous asphalt concrete or stone mastic asphalt concrete. So, different surface textures produced from these mixtures will result in different shear strength at the interface of pavement structure (Raposeiras et al., 2013; Zhang, 2017; Zhao et al., 2017). Besides that, shear strength for milled surface is higher than non-milled surface (Zhang, 2017). Therefore, surface condition has effect on the shear strength at the interface of pavement structure and the correlation between the different surface conditions with geotextile is needed to be investigated for this research. Thus, the objective of this research is to investigate the shear strength behaviour at the interface of CP caused by the correlation between the parameters of surface conditions [rough and smooth], curing types [room and thermal curing], temperature effect and geotextile as reinforcement. Besides that, the correlation between geotextile as reinforcement at the interface of CP with different surface conditions and curing types were investigated. Moreover, for this research, the PC was laid on top of AC to form CP and this combination is different than other researches. The PC of this research is applicable for rigid pavement and rehabilitation material for road maintenance. As such, there is a need of research on shear strength at the interface of CP with geotextile as reinforcement at the interface of CP.
Fig. 1. [a]. CS – smooth surface; [b]. MS – rough surface.
shrinkage of 8% and gel time of 18–23 min for 1% MEKP under 25 °C. 2.2. Sample preparation 2.2.1. Asphalt concrete Dense graded asphalt concrete [DGAC], known as AC 14, was prepared in accordance to the standard specification of Public Work Department Malaysia (Public Work Department, 2008). In this research, two types of AC surfaces from the surface of DGAC were prepared, known as control surface [CS] and modified surface [MS]. CS sample is known as normal DGAC. As for the MS sample, it was prepared by immersing one of the surfaces of DGAC into lacquer thinner to a depth of 2 ± 1 mm for 3 ± 1 min, followed by brushing of the immersed surface using painting brush to remove the asphalt until the aggregate was exposed. Fig. 1 is a typical sample of CS and MS of prepared AC sample, in which CS has a smooth surface while MS has a rough surface. Then, the perimeter of prepared AC was covered and sealed properly using half-cut PVC pipe for both CS and MS of AC in order to mould the upper layer of PC. The duration from the preparation of DGAC up until MS sample required only 3 days. 2.2.2. Polymer concrete For PC preparation, aggregates with 60% of 5.00–10.00 mm size and 40% of 1.18–3.35 mm size were mixed thoroughly. The required amount of MEKP was added to OUPR and mixed homogeneously. The fresh PC was prepared according to ratio of 1:3, with one part of binder to three parts of aggregate. It was then poured on top of the AC and the end product is known as CP as shown in Fig. 2. 2.3. Test procedure Shear strength at the interface between PC and AC of CP was tested. To test the shear strength, shear apparatus was fabricated in accordance to Federal Highway Administration (2007) and was conducted by using California bearing ratio machine with the loading rate of 1 mm per minute. Fig. 3 shows the fabricated shear apparatus with the sample of CP. For this research, there were four testing conditions to be evaluated. The testing parameters and the testing conditions are shown in Table 1, with code assigned to respective condition. There are four conditions with ten codes assigned. The prepared samples for Condition 1 were cured under room temperature, 25 ± 2 °C, with the annual humidity of 70%–89% (WW, 2018). The samples were CP control surface [C-1CS] and CP modified surface [C-1-MS]. Both C-1-CS and C-1-MS were not geotextile reinforced at the interface between PC and AC. For Condition 2, geotextile was used as reinforcement at the interface between PC and AC control surface [C-2-CS] and modified surface [C-2MS]. Geotextile was placed before the pouring of PC on top of AC. Accordingly, the prepared samples for Conditions 1 and 2 were cured under room temperature and tested at the designated age as shown in Table 1.
2. Research methodology 2.1. Materials The materials used in this research are geotextile as reinforcement, limestone as aggregate and orthophthalic unsaturated polyester resin [OUPR] as binder. The geotextile is a non-woven type geotextile with tensile strength of 9 kN/m, modulus of elasticity (tension test) of 12000 MPa and melting point of 165 °C. Limestone with sizes of 1.18–3.35 mm and 5.00–10.00 mm had a specific gravity of 2.65 and 2.68, respectively. For OUPR, the catalyst is Methyl ethyl ketone peroxide [MEKP]. This resin has a specific gravity of 1.12, volume 2
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preheated to 60 °C for 2 ± 0.5 h before the samples were placed inside the oven. Then, the samples were tested on the designated age without cooling as shown in Table 1. Temperature of 60 °C was selected because before AC was tested for its performance, the sample is required to be either immersed in the water for 30–40 min or placed in the oven for 2 h according to ASTM D 1559 (1989). Accordingly, the removal of the sample from oven until the determination of maximum load was not more than 30 s (ASTM D 1559, 1989). Condition 4 was divided into two testing procedures. For procedure 1, the CP control surface [C-4-CS-1] and CP modified surface [C-4-MS1] were cured under room condition for 7 days to ensure the full curing of PC even though Torgal et al. (2013) mentioned that PC can achieve more than 80% of its final strength in a day. After that, the samples were oven cured at 60 °C for 4 h and directly tested for shear strength without cooling down. For procedure 2, the CP control surface [C-4-CS2] and CP modified surface [C-4-MS-2] samples were allowed to cool down for another 24 h in room temperature before their shear strength were tested. The samples were cool down for 24 h to ensure the samples were back to room temperature. For Condition 4, 4 h of oven curing at 60 °C was chosen because the minimum amount of sunshine in Kuching, Malaysia, is only 3.7 h per day (Malaysia Meteorological Department, 2015). The performance of CP was determined and through testing conditions the following information and analysis can be obtained:
Fig. 2. Sample of composite pavement.
I. The effect of surface conditions for CP control surface and CP modified surface can be investigated by comparing C-1-CS to C-1MS and C-2-CS to C-2-MS, respectively. II. The performance of geotextile as reinforcement at the interface between PC and AC can be determined by comparing C-1-CS to C-2CS and C-1-MS to C-2-MS, respectively. III. The analysis for samples cured under room and oven at 60 °C can be performed by comparing Condition 2 to Condition 3. The effect of room temperature and thermal [60 °C] towards shear strength development of the CP during the construction can be determine by comparing C-2-CS to C-3-CS and C-2-MS to C-3-MS, respectively. IV. The effect of temperature is determined through samples cured under Condition 4. C-4-CS-1 and C-4-MS-1 are directly tested for shear strength after taken out from oven at 60 °C. While C-4-CS-2 and C-4-MS-2 are allowed to cool for 24 h under room temperature. Fig. 3. Illustration of CP in shear apparatus for shear test.
Under Condition 3, the CP control surface [C-3-CS] and CP modified surface [C-3-MS] were oven cured at 60 °C. The oven was first Table 1 Sample testing conditions. Test Condition
Code
Testing Parameters Geotextile
1 2 3 4
C-1-CS C-1-MS C-2-CS C-2-MS C-3-CS C-3-MS C-4-CS-1 C-4-MS-1 C-4-CS-2 C-4-MS-2
– – ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓
Age of Test, Hour Curing Types
Asphalt Concrete Sample
Room, ± 25 °C
Oven, ± 60 °C
Control Surface
Modified Surface
✓ ✓ ✓ ✓ – – ✓ ✓ ✓ ✓
– – – – ✓ ✓ – – – –
✓ – ✓ – ✓ – ✓ – ✓ –
– ✓ – ✓ – ✓ – ✓ – ✓
2, 4, 6, 24, 48
168
For Conditions 1, 2 and 3, the first letter “C” means” test condition” and followed by a dash. The second digit “1” mean “Condition 1”, “2” means “Condition 2”, “3” means “Condition 3” and followed by a dash. The third letter “CS” means control surface and “MS” means modified surface. For Condition 4, the first letter “C” means “test condition” and followed by a dash. The second digit “4” means “Condition 4” and followed by a dash. The third letter “CS” means “control surface”, “MS” means “modified surface” and followed by a dash. The fourth digit “1” means “procedure 1” and “2” means “procedure 2”. 3
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the shear strength of C-2-MS was 1.70 times more than C-2-CS at the testing age of 48 h as shown in Fig. 4 due to the change of surface roughness on AC. This is because the exposed aggregate for MS sample was higher than CS sample and the fabric of the non-woven geotextile gripped on the microtexture of aggregate from MS of AC while CS was a smooth surface. Besides that, research conducted by Zhang (2017) showed that the shear strength for milled surface is higher than nonmilled surface. The milled surface produced higher shear strength because it is rougher as compared to non-milled surface. 3.3. Effect of geotextile as reinforcement at the interface between PC and AC Through the comparison of C-1-CS and C-2-CS as well as C-1-MS and C-2-MS, the shear strength of sample with geotextile was higher than that without geotextile. For instance, at 2-day, the shear strength of C-2CS [geotextile reinforcement] was 2.86 times more than C-1-CS [without geotextile reinforcement]. As for C-2-MS [geotextile reinforcement], its shear strength was 1.34 times more than C-1-MS [without geotextile reinforcement] at the testing age of 48 h. Besides that, the shear strength of C-2-MS was 1.70 times more than C-2-CS. From the analysis, it showed that geotextile has the ability to improve the shear strength at the interface between PC and AC. With geotextile as reinforcement in CP, the bond between the aggregate from PC and geotextile, and the bond between geotextile and the aggregate from MS sample were improved. This led to the increase of shear strength at the interface of CP. This is because the gripped on microtexture of aggregate from AC by fabric from the non-woven geotextile was higher for MS sample as compared to CS sample due to the difference in surface conditions. Moreover, the non-woven geotextile also gripped on the aggregate from the PC. In addition, the resin can penetrate or be absorbed into the geotextile and coated on the surface of AC. Therefore, due to these reasons, CP contained non-woven geotextile as reinforcement had higher shear strength as compared to CP which contained no non-woven geotextile.
Fig. 4. Shear strength comparison between Conditions 1, 2, and 3 of CP.
3. Results and discussion 3.1. Shear strength results Fig. 4 shows the comparison of shear strength for CS and MS of CP between Conditions 1, 2, and 3. The comparison of shear strength for CS and MS of CP between testing procedures 1 and 2 is illustrated in Fig. 5.
3.4. Effect of curing types [room and thermal temperature] on shear strength
3.2. Effect of surface conditions [rough and smooth] on shear strength
From Fig. 4, it can be observed that the increase of shear strength for C-3-CS [geotextile reinforcement, oven cured] was stable, unlike C1-CS [without geotextile reinforcement, room temperature curing] and C-2-CS [geotextile reinforcement, room temperature curing]. The same behavior was also shown by C-3-MS [geotextile reinforcement, oven cured] as compared to C-1-MS [without geotextile reinforcement, room temperature curing] and C-2-MS [geotextile reinforcement, room temperature curing]. This can be attributed to the different curing types of sample C-3-CS and C-3-MS as compared to C-1-CS, C-2-CS, C-1-MS and C-2-MS. Samples from Condition 3 were cured in oven at 60 °C while samples from Condition 1 and Condition 2 were cured under room temperature. Moreover, as can be observed from Fig. 4, although geotextile can improve the shear strength of CP, it is noted that the shear strength was lower for C-3-CS and C-3-MS as compared to the samples from Conditions 1 and 2. This showed that when the parameters of temperature, surface conditions and geotextile were considered for Condition 3, the effect of temperature is more dominant and followed by the effect of surface conditions and geotextile as reinforcement at the interface of CP. When the sample was cured under room temperature, the PC became harden with the passing of time while there was no change of the AC. As for the oven cured sample at 60 °C, the PC hardened with the increase of time and the AC also became weak. This is due to the change of viscosity of the asphalt that bond the aggregate together and led to a change of strength of AC. As such, for samples C-3-CS and C-3-MS, the factor that needed to be considered was not only the interface
In this research, surface conditions of CS and MS were used to investigate the shear strength of these two surface conditions. The shear strength of C-1-MS was 3.61 times more than C-1-CS at the testing age of 48 h as shown in Fig. 4. The shear strength of C-1-MS was higher because the surface of C-1-CS was smooth while the surface of C-1-MS was rough. The coated surface of aggregate by PC was higher for MS sample as compared to CS sample due to the exposed aggregate for MS sample which was found to be higher than CS sample. Therefore, the shear strength was higher for C-1-MS as compared to C-1-CS. Moreover,
Fig. 5. Shear strength comparison of testing procedures 1 and 2 of CP for Condition 4. 4
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conditions [smooth and rough] and geotextile as reinforcement but also the effect of temperature towards the strength of AC as compared to C2-CS and C-2-MS because C-3-CS and C-3-MS were directly tested after taken out from oven at 60 °C. 3.5. Effect of temperature on shear strength For Condition 4, the effect of temperature can be observed and is shown in Fig. 5. For Procedure 1 [C-4-CS-1 and C-4-MS-1], the determined shear strength obtained was lower than the samples from Procedure 2 [C-4-CS-2 and C-4-MS-2]. This is due to the different of testing methods. Samples from Procedure 1 were directly tested for shear strength after oven cured for 4 h at 60 °C as compared to samples from Procedure 2 which were allowed to cool down for 24 h in room temperature before being tested. Besides that, the shear strength obtained from MS samples (C-4-MS-1 and C-4-MS-2) was higher than CS samples (C-4-CS-1 and C-4-CS-2) for both Procedure 1 and Procedure 2. This is due to the non-woven geotextile gripped on the microtexture of aggregate from the MS sample and the exposed microtexture of aggregate was higher for MS sample as compared to CS sample. The shear strength of C-4-MS-2 was found to be 14.43 times more than C-4-MS-1 and the shear strength of C-4-CS-2 was 24 times more than C-4-CS-1. Samples from C-4-CS-1 and C-4-MS-1 were directly tested for shear strength without cooling down. The viscosity of asphalt was reduced due to high temperature, weakened the bond between the aggregates in AC and led to the decrease of shear strength. As for the sample from C-4-CS-2 and C-4-MS-2, the samples were allowed to cool down and the AC returned to its original stage. Therefore, this showed that high temperature can reduce the shear strength of CP due to the change of the properties of AC. However, the negative effect of high temperature can be reversed by allowing the CP cool down to room temperature.
Fig. 7. Surface appearance of AC from the tested CP using MS with geotextile as reinforcement, [a] directly tested after oven cured, C-4-MS-1; [b] allowed to cool for 24 h before being tested for shear strength, C-4-MS-2.
MS and C-1-MS. While C-3-MS was higher than C-2-MS and C-1-MS. III. The amount of AC attached on PC for the surface of the interface between PC and AC after testing was higher for C-3-MS as compared to C-3-CS. IV. The attached of AC on PC for C-4-CS-1 after being tested was higher than C-4-CS-2. As for C-4-MS-1 and C-4-MS-2, the attached AC on PC for C-4-MS-1 was higher than C-4-MS-2. The surface of the AC was uneven in C-3-CS as compared to C-1-CS and C-2-CS, as well as in C-3-MS as compared to C-1-MS and C-2-MS. This was because C-3-CS and C-3-MS were directly tested for shear strength after taken out from oven conditioning. As for C-2-CS and C-2MS, the geotextile was used as reinforcement but not for C-1-CS and C1-MS. It is believed that the non-woven fabric provides gripping on the microtexture of aggregate which caused the surface condition of AC was more uneven for C-2-CS and C-2-MS as compared to C-1-CS and C-1-MS. It can also be observed that the surface condition of AC in C-4-CS-1 and C-4-MS-1 was more uneven as compared to C-4-CS-2 and C-4-MS-2 after they were tested. This was because the samples of C-4-CS-1 and C-4-MS1 were directly tested after being cured for 4 h in oven at 60 °C as compared to C-4-CS-2 and C-4-MS-2. From these observations, it can be concluded that the type of failure for all the testing Conditions fall under mixed failure mode which was a combination of cohesive and adhesive failure modes. It means that a part of the failure occurs at the interface and another part of the failure occurs at the substrate (Gillespie and Pepper, 1998; Carreño et al., 2017). The mixed failure mode is stronger than adhesive failure mode but weaker than cohesive failure mode. This is because adhesive failure mode means the failure would occur at the interface between PC and AC, while cohesive failure mode means the failure would occur at the AC which indicates that the shear strength at the interface of CP is greater than the shear that would occur at AC.
3.6. Failure mode of tested CP The surface conditions of AC from the tested samples of CP using control and modified surfaces were observed. Fig. 6 shows the surface appearance of AC from tested CP using CS and MS with geotextile as reinforcement for Condition 2. The surface appearance of AC from tested CP using MS with geotextile as reinforcement for Procedure 1 and Procedure 2 under Condition 4 is shown in Fig. 7. The images of AC were from the CP tested for shear strength at 2-day age and was captured from the side. For CP using control and modified surfaces, the observations are summarized as followed: I. The amount of AC attached on PC for the surface of the interface between PC and AC after testing was higher in sample C-3-CS as compared to C-2-CS, and in sample C-2-CS was higher than C-1-CS. II. The amount of AC attached on PC for the surface of the interface between PC and AC after testing was almost the same for both C-2-
4. Conclusion This research was conducted to investigate the shear strength at the interface between PC and AC with geotextile as reinforcement between their interface. The behavior of shear strength was investigated through the correlation between the parameters of different surface conditions [smooth and rough], curing types [room and thermal temperature], temperature effect and the impact of geotextile within sample. It can be concluded that: I. Surface conditions affected the shear strength due to the effect of surface roughness at the interface of CP. For Condition 1, without geotextile reinforcement, the shear strength of CP using MS [C-1MS] was 3.61 times more than CS [C-1-CS]. For Condition 2 reinforced with geotextile, the shear strength of CP using MS [C-2-
Fig. 6. Surface appearance of AC from the tested CP using CS and MS with geotextile as reinforcement. 5
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Acknowledgements
MS] was 1.70 times more than CS [C-2-CS]. II. The interface between PC and AC reinforced with geotextile improved its shear strength. The shear strength of C-2-CS was higher than C-1-CS (without geotextile reinforcement). The shear strength of C-2-MS was 1.34 times more than C-1-MS and the shear strength of C-2-CS was 2.86 times more than C-1-CS. It was observed that the improvement of shear strength for CS samples was higher than MS samples. However, the shear strength of C-2-MS (geotextile reinforcement) was higher than C-1-MS (without geotextile reinforcement) and the shear strength of C-1-MS was higher than C-2CS (geotextile reinforcement). This can be due to the use of MS sample and geotextile as reinforcement. From the tested CP, the uneven surface condition of tested AC for C-2-CS was higher than C1-CS due to the effect of geotextile. As for C-2-MS, the uneven surface condition of AC was slightly higher than C-1-MS. Therefore, the shear strength improvement was higher for CS as compared to MS. III. The shear strength of oven cured samples decreased as compared to room temperature cured samples. The shear strength of room temperature cured CP with CS [C-2-CS] was 15.51 times more than oven cured sample [C-3-CS]. Also, the shear strength of room temperature cured CP with MS [C-2-MS] was 8.83 times more than oven cured sample [C-3-MS]. During the curing, PC became harden with the passing of time. As for oven cured sample at 60 °C, the PC was harden with the passing of time and the AC also became weak at the same time due to the change of the viscosity of asphalt. The change of the viscosity of asphalt affected the bond between the aggregates in AC and reduced the strength of AC. Therefore, the shear strength of oven cured CP was lower as compared to room temperature cured CP. IV. Shear strength of CP was affected by the change of temperature. Sample tested at the high temperature had lower shear strength as compared to sample tested at room temperature. For CP using CS with geotextile as reinforcement, the shear strength of C-4-CS-2 was 24 times more than C-4-CS-1. Besides that, for MS using geotextile as reinforcement, the shear strength of C-4-MS-2 was 14.43 times more than C-4-MS-1. The difference in shear strength was due to the samples from C-4-CS-1 and C-4-MS-1 was directly tested for shear strength without cooling down at the temperature of 60 °C. The samples from C-4-CS-2 and C-4-MS-2 were allowed to cool down until room temperature before tested for shear strength. The viscosity of asphalt was reduced due to high temperature, weakened the bond of aggregates in AC and led to the decrease of shear strength. Therefore, shear strength is reduced due to high temperature and can be reversed by allowing the sample cool down to room temperature. V. The surface condition of AC from the tested samples of CP using control and modified surfaces was affected by the temperature and geotextile. When the samples were tested at 60 °C, the uneven of AC was higher as compared to the samples which were tested at room temperature. Also, the surface of AC was more uneven for C-4-CS-1 and C-4-MS-1 as compared to C-4-CS-2 and C-4-MS-2. The surface of AC was also more uneven for C-3-CS and C-3-MS as compared to the AC from Conditions 1 and 2 for both samples of CS and MS. Moreover, CP with geotextile as reinforcement had a more uneven surface of AC as compared to CP without geotextile as reinforcement. This is due to the effect of the non-woven geotextile gripped on the surface of aggregates from AC. Therefore, through visual observation, the type of failure for all the testing Conditions 1, 2, 3 and 4 was mixed failure mode which is a combination of cohesive and adhesive failure modes.
This work was supported by University of Malaysia Sarawak (UNIMAS) Research Grant number F02(DPP31)/1246/2015(06). Appendix A. Supplementary data Supplementary data to this article can be found online at https:// doi.org/10.1016/j.geotexmem.2019.11.002. References Isailović, I., Wistuba, M.P., 2018. Asphalt mixture layers' interface bonding properties under monotonic and cyclic loading. Constr. Build. Mater. 168, 590–597. ASTM D 1559, 1989. Resistance to Plastic Flow of Bitumen Mixture Using Marshall Apparatus. Barraza, D.Z., Peréz, M.C., Fresno, D.C., Zamanillo, A.V., 2010. New procedure for measuring adherence between a geosynthetic material and a bituminous mixture. Geotext. Geomembranes 28, 483–489. Carreño, R.D.L., Pujadas, P., Cavalaro, S.H.P., Aguado, A., 2017. Bond strength of whitetoppings and bonded overlays constructed with self-compacting high-performance concrete. Constr. Build. Mater. 153, 835–845. Collop, A.C., Sutanto, M.H., Airey, G.D., Elliott, R.C., 2009. Shear bond strength between asphalt layers for laboratory prepared samples and field cores. Constr. Build. Mater. 23, 2251–2258. Ge, Z.S., Wang, H., Zhang, Q.S., Xiong, C.L., 2015. Glass fiber reinforced asphalt membrane for interlayer bonding between asphalt overlay and concrete pavement. Constr. Build. Mater. 101, 918–925. Gillespie, H.A., Pepper, L., et al., 1998. Use of epoxy compounds with concrete. ACI 70, 28 503R-93. Federal Highway Administration, 2007. Protocol P67 test method for determination of the shear strength at the interface of bonded layers of concrete (Pc07). Retrieved August, 2018, from. https://www.fhwa.dot.gov/publications/research/ infrastructure/pavements/ltpp/07052/pro67.cfm. Hu, X.D., Lei, Y., Wang, H.N., Jiang, P., Yang, X., You, Z.P., 2017. Effect of tack coat dosage and temperature on the interface shear properties of asphalt layers bonded with emulsified asphalt binders. Constr. Build. Mater. 141, 86–93. Kim, H.W., Arraigada, M., Raab, C., Partl, M.N., 2011. Numerical and experimental analysis for the interlayer behavior of double-layered asphalt pavement specimens. J. Mater. Civ. Eng. 23, 12–20. Li, S., Li, Y.Z., Liu, Z.H., Sun, Z.L., 2013. Interlaminar shear stress and structure of continuously reinforced concrete composite asphalt pavements. J. Highw. Transp. Res. Dev. 7 (4), 9–16. Li, S., Huang, Y., Liu, Z.H., 2016. Experimental evaluation of asphalt material for interlayer in rigid–flexible composite pavement. Constr. Build. Mater. 102, 699–705. Malaysian Meteorological Department, 2015. General climate of Malaysia. Retrieved, August, 2017, from. http://www.met.gov.my/index.php. Nithin, S., Rajagopal, K., Veeraragavan, A., 2018. An investigation on the interface bond strength of geosynthetic reinforced asphalt concrete using Leutner shear test. Constr. Build. Mater. 186, 423–437. Public Work Department, 2008. Standard Specification for Road Works-Section 4: Flexible Pavement. JKR/SPJ/2008-S4. Kuala Lumpur, Malaysia. Raposeiras, A.C., Fresno, D.C., Zamanillo, A.V., Hernandez, J.R., 2013. Test methods and influential factors for analysis of bonding between bituminous pavement layers. Constr. Build. Mater. 43, 372–381. Rasmussen, R.O., Rozycki, D.K., 2004. Thin and ultra-thin whitetopping. In: National Cooperatve Highway Research Program (NCHRP) Synthesis, vol. 338 (Washington, United States). Sagnol, L., Quezada, J.C., Chazallon, C., Stöckner, M., 2018. Effect of glass fibre grids on the bonding strength between two asphalt layers and its contact dynamics method modeling. Road Mater. Pavement Des. 26, 1–18. Sprinkel, M.M., 2009. Condition of Concrete Overlays on Route 60 over Lynnhaven Inlet after 10 Years. Virginia Transportation Research Council FHWA/VTRC 09-R13. Torgal, F.P., Jalali, S., Labrincha, J., John, V.M., 2013. Concrete with Polymers. (Cambridge, England). White, G., 2016. State of the art: interface shear resistance of asphalt surface layers. Int. J. Pavement Eng. https://doi.org/10.1080/10298436.2015.1126270. World Weather [WW], 2018. In: Kuching Monthly Climate Averages. Retrieved December, 2018, from. https://www.worldweatheronline.com/kuching-weatheraverages/sarawak/my.aspx. Zhang, W.G., 2017. Effect of tack coat application on interlayer shear strength of asphalt pavement: a state-of-the-art review based on application in the United States. Int. J. Pavement Res. Technol. 10, 434–445. Zhao, H.D., Cao, J.F., Zheng, Y., 2017. Investigation of the interface bonding between concrete slab and asphalt overlay. Road Mater. Pavement Des. https://doi.org/10. 1080/14680629.2017.1329866.
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Technical note
Shear strength evaluation of composite pavement with geotextile as reinforcement at the interface Shyue Leong Lee∗, Mohammad Abdul Mannan, Wan Hashim Wan Ibrahim Department of Civil Engineering, Faculty of Engineering, Universiti Malaysia Sarawak, 94300, Kota Samarahan, Sarawak, Malaysia
A R T I C LE I N FO
A B S T R A C T
Keywords: Geosynthetics Polymer concrete Asphalt concrete Surface condition Curing types Temperature
This research was conducted to investigate the shear strength at the interface between polymer concrete and asphalt concrete with geotextile as reinforcement at the interface of these two types of concrete. The samples were tested for the parameters of different surface conditions [rough and smooth], curing types [room and thermal curing], temperature effect and the impact of geotextile as reinforcement. To investigate the correlation between these parameters, four different testing conditions were implemented. The results showed a significant improvement of shear strength for rough surface sample as compared to smooth surface sample. Moreover, samples cured in oven had lower shear strength as compared to samples cured in room condition. Besides that, high temperature has an adverse impact on the shear strength at the interface between polymer concrete and asphalt concrete due to the weakening of asphalt concrete at high temperature. As for samples reinforced with geotextile, the shear strength resistance was better as compared to unreinforced samples. Through visual observation, the types of failure under all testing conditions were mixed failure mode.
1. Introduction Pavement can be divided into flexible pavement, rigid pavement and composite pavement. In general, flexible pavement is a mixture of asphalt and aggregates, rigid pavement is a mixture of cement, water and aggregates, and composite pavement is a combination of flexible pavement laid on top of rigid pavement or vice versa. In this research, a mixture of orthophthalic unsaturated polyester resin [OUPR] and limestone are proposed as polymer concrete [PC] for rigid pavement. This PC is proposed to be placed on top of asphalt concrete [AC] to form composite pavement [CP] with geotextile as reinforcement at the interface between these two types of concrete. Moreover, PC has the potential as rehabilitation material for road maintenance. Hence, investigating the shear strength behavior at the interface of this CP is important. Shear strength comes from the interlocking of aggregate, adhesive strength of tack coat and friction at the interface between the two layers of pavement structure (Li et al., 2016) and is measured through shear test which is the most commonly used method (Raposeiras et al., 2013; Zhao et al., 2017). The shear strength at the interface between two layers of pavement structure affects pavement performance such as its mechanical properties, durability and maintenance regime (Rasmussen and Rozycki, 2004; Sprinkel, 2009; Kim et al., 2011; Ge et al., 2015; Li
∗
et al., 2016; Hu et al., 2017; Zhao et al., 2017). This is to ensure the pavement layers acts monolithic and functions normally (Raposeiras et al., 2013; Li et al., 2016; Isailović and Wistuba, 2018). Debonding of interface between two layers of pavement structure led to weak interlaminar strength. It can be caused by one of the three different stress conditions, namely, pure tension, pure shear and mixed condition which is a combination of shear and compressive or tensile stresses (Carreño et al., 2017). Other associated factors are stress caused by shrinkage, traffic load, temperature change, moisture, cycles of freezing and thawing, inappropriate construction techniques or inadequate choice of tack coat and others (Sprinkel, 2009; Ge et al., 2015). Pavement failure due to debonding can be categorised into delamination, slippage, top-down cracking, fatigue cracking, longitudinal cracks, and deformation (Sprinkel, 2009; Li et al., 2013; Ge et al., 2015; Hu et al., 2017; Zhang, 2017; Nithin et al., 2018). All these pavement failures led to adverse impact on traffic safety (Hu et al., 2017) and shorten the service life of pavement (Zhang, 2017). Moreover, these pavement failures are an indicator of shear strength failure (Sprinkel, 2009; Ge et al., 2015). There are many factors influencing the shear strength between two layers of pavement structure. The factors can be tack coat, geosynthetic [such as woven and non-woven geotextiles, biaxial and multiaxial geogrids], temperature, interface condition, load and other.
Corresponding author. E-mail addresses: [email protected] (S.L. Lee), [email protected] (M.A. Mannan), [email protected] (W.H. Wan Ibrahim).
https://doi.org/10.1016/j.geotexmem.2019.11.002 Received 27 May 2019; Received in revised form 23 October 2019; Accepted 15 November 2019 0266-1144/ © 2019 Elsevier Ltd. All rights reserved.
Please cite this article as: Shyue Leong Lee, Mohammad Abdul Mannan and Wan Hashim Wan Ibrahim, Geotextiles and Geomembranes, https://doi.org/10.1016/j.geotexmem.2019.11.002
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Temperature affects the tack coat in which it either increase or decrease the shear strength owing to the change of characteristic of tack coat (Raposeiras et al., 2013; White, 2016; Zhang, 2017; Nithin et al., 2018). The decrease of shear strength is directly proportional to the increase of temperature. This is because the increase of temperature decreases the viscosity of the asphalt and led to a decrease of shear strength (Hu et al., 2017; Zhao et al., 2017; Nithin et al., 2018). On the other hand, a decrease of temperature increases the shear strength due to an increase of stiffness of the tack coat and the interlocking of aggregate (Kim et al., 2011; Hu et al., 2017). As for the weather in Malaysia, the weather consists of sunny day and raining day. Besides that, the temperature during day time and night time is different. Therefore, the change of shear strength due to the different of temperature is very crucial and needs to be investigated. Geosynthetic as reinforcement at the interface between two layers of pavement structure has a negative impact on bond and shear strengths. Besides that, the characteristic of geosynthetic such as types, weight, and thickness, affect the shear strength (Nithin et al., 2018; Sagnol et al., 2018). However, Barraza et al. (2010) mentioned that the increase of tack coat increased the shear strength at the interface of pavement structure. Besides that, research conducted by Li et al. (2013) found that an increase of shear strength was observed when geotextile was used as reinforcement. Since scant literatures are available, there is a need for investigation using geotextile as reinforcement at the interface of PC laid on top of AC. As for surface condition, either smooth or rough surfaces affects the shear strength at the interface of pavement structure (Collop et al., 2009; Li et al., 2013; White, 2016; Nithin et al., 2018). One of the factors which affect the shear strength at the interface of pavement structure was the aggregate grading of the mixture for upper and lower layers of the pavement structure (Collop et al., 2009; Zhao et al., 2017; Nithin et al., 2018). Variation of aggregate gradation for the mixture can produce such as dense graded asphalt concrete, porous asphalt concrete or stone mastic asphalt concrete. So, different surface textures produced from these mixtures will result in different shear strength at the interface of pavement structure (Raposeiras et al., 2013; Zhang, 2017; Zhao et al., 2017). Besides that, shear strength for milled surface is higher than non-milled surface (Zhang, 2017). Therefore, surface condition has effect on the shear strength at the interface of pavement structure and the correlation between the different surface conditions with geotextile is needed to be investigated for this research. Thus, the objective of this research is to investigate the shear strength behaviour at the interface of CP caused by the correlation between the parameters of surface conditions [rough and smooth], curing types [room and thermal curing], temperature effect and geotextile as reinforcement. Besides that, the correlation between geotextile as reinforcement at the interface of CP with different surface conditions and curing types were investigated. Moreover, for this research, the PC was laid on top of AC to form CP and this combination is different than other researches. The PC of this research is applicable for rigid pavement and rehabilitation material for road maintenance. As such, there is a need of research on shear strength at the interface of CP with geotextile as reinforcement at the interface of CP.
Fig. 1. [a]. CS – smooth surface; [b]. MS – rough surface.
shrinkage of 8% and gel time of 18–23 min for 1% MEKP under 25 °C. 2.2. Sample preparation 2.2.1. Asphalt concrete Dense graded asphalt concrete [DGAC], known as AC 14, was prepared in accordance to the standard specification of Public Work Department Malaysia (Public Work Department, 2008). In this research, two types of AC surfaces from the surface of DGAC were prepared, known as control surface [CS] and modified surface [MS]. CS sample is known as normal DGAC. As for the MS sample, it was prepared by immersing one of the surfaces of DGAC into lacquer thinner to a depth of 2 ± 1 mm for 3 ± 1 min, followed by brushing of the immersed surface using painting brush to remove the asphalt until the aggregate was exposed. Fig. 1 is a typical sample of CS and MS of prepared AC sample, in which CS has a smooth surface while MS has a rough surface. Then, the perimeter of prepared AC was covered and sealed properly using half-cut PVC pipe for both CS and MS of AC in order to mould the upper layer of PC. The duration from the preparation of DGAC up until MS sample required only 3 days. 2.2.2. Polymer concrete For PC preparation, aggregates with 60% of 5.00–10.00 mm size and 40% of 1.18–3.35 mm size were mixed thoroughly. The required amount of MEKP was added to OUPR and mixed homogeneously. The fresh PC was prepared according to ratio of 1:3, with one part of binder to three parts of aggregate. It was then poured on top of the AC and the end product is known as CP as shown in Fig. 2. 2.3. Test procedure Shear strength at the interface between PC and AC of CP was tested. To test the shear strength, shear apparatus was fabricated in accordance to Federal Highway Administration (2007) and was conducted by using California bearing ratio machine with the loading rate of 1 mm per minute. Fig. 3 shows the fabricated shear apparatus with the sample of CP. For this research, there were four testing conditions to be evaluated. The testing parameters and the testing conditions are shown in Table 1, with code assigned to respective condition. There are four conditions with ten codes assigned. The prepared samples for Condition 1 were cured under room temperature, 25 ± 2 °C, with the annual humidity of 70%–89% (WW, 2018). The samples were CP control surface [C-1CS] and CP modified surface [C-1-MS]. Both C-1-CS and C-1-MS were not geotextile reinforced at the interface between PC and AC. For Condition 2, geotextile was used as reinforcement at the interface between PC and AC control surface [C-2-CS] and modified surface [C-2MS]. Geotextile was placed before the pouring of PC on top of AC. Accordingly, the prepared samples for Conditions 1 and 2 were cured under room temperature and tested at the designated age as shown in Table 1.
2. Research methodology 2.1. Materials The materials used in this research are geotextile as reinforcement, limestone as aggregate and orthophthalic unsaturated polyester resin [OUPR] as binder. The geotextile is a non-woven type geotextile with tensile strength of 9 kN/m, modulus of elasticity (tension test) of 12000 MPa and melting point of 165 °C. Limestone with sizes of 1.18–3.35 mm and 5.00–10.00 mm had a specific gravity of 2.65 and 2.68, respectively. For OUPR, the catalyst is Methyl ethyl ketone peroxide [MEKP]. This resin has a specific gravity of 1.12, volume 2
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preheated to 60 °C for 2 ± 0.5 h before the samples were placed inside the oven. Then, the samples were tested on the designated age without cooling as shown in Table 1. Temperature of 60 °C was selected because before AC was tested for its performance, the sample is required to be either immersed in the water for 30–40 min or placed in the oven for 2 h according to ASTM D 1559 (1989). Accordingly, the removal of the sample from oven until the determination of maximum load was not more than 30 s (ASTM D 1559, 1989). Condition 4 was divided into two testing procedures. For procedure 1, the CP control surface [C-4-CS-1] and CP modified surface [C-4-MS1] were cured under room condition for 7 days to ensure the full curing of PC even though Torgal et al. (2013) mentioned that PC can achieve more than 80% of its final strength in a day. After that, the samples were oven cured at 60 °C for 4 h and directly tested for shear strength without cooling down. For procedure 2, the CP control surface [C-4-CS2] and CP modified surface [C-4-MS-2] samples were allowed to cool down for another 24 h in room temperature before their shear strength were tested. The samples were cool down for 24 h to ensure the samples were back to room temperature. For Condition 4, 4 h of oven curing at 60 °C was chosen because the minimum amount of sunshine in Kuching, Malaysia, is only 3.7 h per day (Malaysia Meteorological Department, 2015). The performance of CP was determined and through testing conditions the following information and analysis can be obtained:
Fig. 2. Sample of composite pavement.
I. The effect of surface conditions for CP control surface and CP modified surface can be investigated by comparing C-1-CS to C-1MS and C-2-CS to C-2-MS, respectively. II. The performance of geotextile as reinforcement at the interface between PC and AC can be determined by comparing C-1-CS to C-2CS and C-1-MS to C-2-MS, respectively. III. The analysis for samples cured under room and oven at 60 °C can be performed by comparing Condition 2 to Condition 3. The effect of room temperature and thermal [60 °C] towards shear strength development of the CP during the construction can be determine by comparing C-2-CS to C-3-CS and C-2-MS to C-3-MS, respectively. IV. The effect of temperature is determined through samples cured under Condition 4. C-4-CS-1 and C-4-MS-1 are directly tested for shear strength after taken out from oven at 60 °C. While C-4-CS-2 and C-4-MS-2 are allowed to cool for 24 h under room temperature. Fig. 3. Illustration of CP in shear apparatus for shear test.
Under Condition 3, the CP control surface [C-3-CS] and CP modified surface [C-3-MS] were oven cured at 60 °C. The oven was first Table 1 Sample testing conditions. Test Condition
Code
Testing Parameters Geotextile
1 2 3 4
C-1-CS C-1-MS C-2-CS C-2-MS C-3-CS C-3-MS C-4-CS-1 C-4-MS-1 C-4-CS-2 C-4-MS-2
– – ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓
Age of Test, Hour Curing Types
Asphalt Concrete Sample
Room, ± 25 °C
Oven, ± 60 °C
Control Surface
Modified Surface
✓ ✓ ✓ ✓ – – ✓ ✓ ✓ ✓
– – – – ✓ ✓ – – – –
✓ – ✓ – ✓ – ✓ – ✓ –
– ✓ – ✓ – ✓ – ✓ – ✓
2, 4, 6, 24, 48
168
For Conditions 1, 2 and 3, the first letter “C” means” test condition” and followed by a dash. The second digit “1” mean “Condition 1”, “2” means “Condition 2”, “3” means “Condition 3” and followed by a dash. The third letter “CS” means control surface and “MS” means modified surface. For Condition 4, the first letter “C” means “test condition” and followed by a dash. The second digit “4” means “Condition 4” and followed by a dash. The third letter “CS” means “control surface”, “MS” means “modified surface” and followed by a dash. The fourth digit “1” means “procedure 1” and “2” means “procedure 2”. 3
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the shear strength of C-2-MS was 1.70 times more than C-2-CS at the testing age of 48 h as shown in Fig. 4 due to the change of surface roughness on AC. This is because the exposed aggregate for MS sample was higher than CS sample and the fabric of the non-woven geotextile gripped on the microtexture of aggregate from MS of AC while CS was a smooth surface. Besides that, research conducted by Zhang (2017) showed that the shear strength for milled surface is higher than nonmilled surface. The milled surface produced higher shear strength because it is rougher as compared to non-milled surface. 3.3. Effect of geotextile as reinforcement at the interface between PC and AC Through the comparison of C-1-CS and C-2-CS as well as C-1-MS and C-2-MS, the shear strength of sample with geotextile was higher than that without geotextile. For instance, at 2-day, the shear strength of C-2CS [geotextile reinforcement] was 2.86 times more than C-1-CS [without geotextile reinforcement]. As for C-2-MS [geotextile reinforcement], its shear strength was 1.34 times more than C-1-MS [without geotextile reinforcement] at the testing age of 48 h. Besides that, the shear strength of C-2-MS was 1.70 times more than C-2-CS. From the analysis, it showed that geotextile has the ability to improve the shear strength at the interface between PC and AC. With geotextile as reinforcement in CP, the bond between the aggregate from PC and geotextile, and the bond between geotextile and the aggregate from MS sample were improved. This led to the increase of shear strength at the interface of CP. This is because the gripped on microtexture of aggregate from AC by fabric from the non-woven geotextile was higher for MS sample as compared to CS sample due to the difference in surface conditions. Moreover, the non-woven geotextile also gripped on the aggregate from the PC. In addition, the resin can penetrate or be absorbed into the geotextile and coated on the surface of AC. Therefore, due to these reasons, CP contained non-woven geotextile as reinforcement had higher shear strength as compared to CP which contained no non-woven geotextile.
Fig. 4. Shear strength comparison between Conditions 1, 2, and 3 of CP.
3. Results and discussion 3.1. Shear strength results Fig. 4 shows the comparison of shear strength for CS and MS of CP between Conditions 1, 2, and 3. The comparison of shear strength for CS and MS of CP between testing procedures 1 and 2 is illustrated in Fig. 5.
3.4. Effect of curing types [room and thermal temperature] on shear strength
3.2. Effect of surface conditions [rough and smooth] on shear strength
From Fig. 4, it can be observed that the increase of shear strength for C-3-CS [geotextile reinforcement, oven cured] was stable, unlike C1-CS [without geotextile reinforcement, room temperature curing] and C-2-CS [geotextile reinforcement, room temperature curing]. The same behavior was also shown by C-3-MS [geotextile reinforcement, oven cured] as compared to C-1-MS [without geotextile reinforcement, room temperature curing] and C-2-MS [geotextile reinforcement, room temperature curing]. This can be attributed to the different curing types of sample C-3-CS and C-3-MS as compared to C-1-CS, C-2-CS, C-1-MS and C-2-MS. Samples from Condition 3 were cured in oven at 60 °C while samples from Condition 1 and Condition 2 were cured under room temperature. Moreover, as can be observed from Fig. 4, although geotextile can improve the shear strength of CP, it is noted that the shear strength was lower for C-3-CS and C-3-MS as compared to the samples from Conditions 1 and 2. This showed that when the parameters of temperature, surface conditions and geotextile were considered for Condition 3, the effect of temperature is more dominant and followed by the effect of surface conditions and geotextile as reinforcement at the interface of CP. When the sample was cured under room temperature, the PC became harden with the passing of time while there was no change of the AC. As for the oven cured sample at 60 °C, the PC hardened with the increase of time and the AC also became weak. This is due to the change of viscosity of the asphalt that bond the aggregate together and led to a change of strength of AC. As such, for samples C-3-CS and C-3-MS, the factor that needed to be considered was not only the interface
In this research, surface conditions of CS and MS were used to investigate the shear strength of these two surface conditions. The shear strength of C-1-MS was 3.61 times more than C-1-CS at the testing age of 48 h as shown in Fig. 4. The shear strength of C-1-MS was higher because the surface of C-1-CS was smooth while the surface of C-1-MS was rough. The coated surface of aggregate by PC was higher for MS sample as compared to CS sample due to the exposed aggregate for MS sample which was found to be higher than CS sample. Therefore, the shear strength was higher for C-1-MS as compared to C-1-CS. Moreover,
Fig. 5. Shear strength comparison of testing procedures 1 and 2 of CP for Condition 4. 4
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conditions [smooth and rough] and geotextile as reinforcement but also the effect of temperature towards the strength of AC as compared to C2-CS and C-2-MS because C-3-CS and C-3-MS were directly tested after taken out from oven at 60 °C. 3.5. Effect of temperature on shear strength For Condition 4, the effect of temperature can be observed and is shown in Fig. 5. For Procedure 1 [C-4-CS-1 and C-4-MS-1], the determined shear strength obtained was lower than the samples from Procedure 2 [C-4-CS-2 and C-4-MS-2]. This is due to the different of testing methods. Samples from Procedure 1 were directly tested for shear strength after oven cured for 4 h at 60 °C as compared to samples from Procedure 2 which were allowed to cool down for 24 h in room temperature before being tested. Besides that, the shear strength obtained from MS samples (C-4-MS-1 and C-4-MS-2) was higher than CS samples (C-4-CS-1 and C-4-CS-2) for both Procedure 1 and Procedure 2. This is due to the non-woven geotextile gripped on the microtexture of aggregate from the MS sample and the exposed microtexture of aggregate was higher for MS sample as compared to CS sample. The shear strength of C-4-MS-2 was found to be 14.43 times more than C-4-MS-1 and the shear strength of C-4-CS-2 was 24 times more than C-4-CS-1. Samples from C-4-CS-1 and C-4-MS-1 were directly tested for shear strength without cooling down. The viscosity of asphalt was reduced due to high temperature, weakened the bond between the aggregates in AC and led to the decrease of shear strength. As for the sample from C-4-CS-2 and C-4-MS-2, the samples were allowed to cool down and the AC returned to its original stage. Therefore, this showed that high temperature can reduce the shear strength of CP due to the change of the properties of AC. However, the negative effect of high temperature can be reversed by allowing the CP cool down to room temperature.
Fig. 7. Surface appearance of AC from the tested CP using MS with geotextile as reinforcement, [a] directly tested after oven cured, C-4-MS-1; [b] allowed to cool for 24 h before being tested for shear strength, C-4-MS-2.
MS and C-1-MS. While C-3-MS was higher than C-2-MS and C-1-MS. III. The amount of AC attached on PC for the surface of the interface between PC and AC after testing was higher for C-3-MS as compared to C-3-CS. IV. The attached of AC on PC for C-4-CS-1 after being tested was higher than C-4-CS-2. As for C-4-MS-1 and C-4-MS-2, the attached AC on PC for C-4-MS-1 was higher than C-4-MS-2. The surface of the AC was uneven in C-3-CS as compared to C-1-CS and C-2-CS, as well as in C-3-MS as compared to C-1-MS and C-2-MS. This was because C-3-CS and C-3-MS were directly tested for shear strength after taken out from oven conditioning. As for C-2-CS and C-2MS, the geotextile was used as reinforcement but not for C-1-CS and C1-MS. It is believed that the non-woven fabric provides gripping on the microtexture of aggregate which caused the surface condition of AC was more uneven for C-2-CS and C-2-MS as compared to C-1-CS and C-1-MS. It can also be observed that the surface condition of AC in C-4-CS-1 and C-4-MS-1 was more uneven as compared to C-4-CS-2 and C-4-MS-2 after they were tested. This was because the samples of C-4-CS-1 and C-4-MS1 were directly tested after being cured for 4 h in oven at 60 °C as compared to C-4-CS-2 and C-4-MS-2. From these observations, it can be concluded that the type of failure for all the testing Conditions fall under mixed failure mode which was a combination of cohesive and adhesive failure modes. It means that a part of the failure occurs at the interface and another part of the failure occurs at the substrate (Gillespie and Pepper, 1998; Carreño et al., 2017). The mixed failure mode is stronger than adhesive failure mode but weaker than cohesive failure mode. This is because adhesive failure mode means the failure would occur at the interface between PC and AC, while cohesive failure mode means the failure would occur at the AC which indicates that the shear strength at the interface of CP is greater than the shear that would occur at AC.
3.6. Failure mode of tested CP The surface conditions of AC from the tested samples of CP using control and modified surfaces were observed. Fig. 6 shows the surface appearance of AC from tested CP using CS and MS with geotextile as reinforcement for Condition 2. The surface appearance of AC from tested CP using MS with geotextile as reinforcement for Procedure 1 and Procedure 2 under Condition 4 is shown in Fig. 7. The images of AC were from the CP tested for shear strength at 2-day age and was captured from the side. For CP using control and modified surfaces, the observations are summarized as followed: I. The amount of AC attached on PC for the surface of the interface between PC and AC after testing was higher in sample C-3-CS as compared to C-2-CS, and in sample C-2-CS was higher than C-1-CS. II. The amount of AC attached on PC for the surface of the interface between PC and AC after testing was almost the same for both C-2-
4. Conclusion This research was conducted to investigate the shear strength at the interface between PC and AC with geotextile as reinforcement between their interface. The behavior of shear strength was investigated through the correlation between the parameters of different surface conditions [smooth and rough], curing types [room and thermal temperature], temperature effect and the impact of geotextile within sample. It can be concluded that: I. Surface conditions affected the shear strength due to the effect of surface roughness at the interface of CP. For Condition 1, without geotextile reinforcement, the shear strength of CP using MS [C-1MS] was 3.61 times more than CS [C-1-CS]. For Condition 2 reinforced with geotextile, the shear strength of CP using MS [C-2-
Fig. 6. Surface appearance of AC from the tested CP using CS and MS with geotextile as reinforcement. 5
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Acknowledgements
MS] was 1.70 times more than CS [C-2-CS]. II. The interface between PC and AC reinforced with geotextile improved its shear strength. The shear strength of C-2-CS was higher than C-1-CS (without geotextile reinforcement). The shear strength of C-2-MS was 1.34 times more than C-1-MS and the shear strength of C-2-CS was 2.86 times more than C-1-CS. It was observed that the improvement of shear strength for CS samples was higher than MS samples. However, the shear strength of C-2-MS (geotextile reinforcement) was higher than C-1-MS (without geotextile reinforcement) and the shear strength of C-1-MS was higher than C-2CS (geotextile reinforcement). This can be due to the use of MS sample and geotextile as reinforcement. From the tested CP, the uneven surface condition of tested AC for C-2-CS was higher than C1-CS due to the effect of geotextile. As for C-2-MS, the uneven surface condition of AC was slightly higher than C-1-MS. Therefore, the shear strength improvement was higher for CS as compared to MS. III. The shear strength of oven cured samples decreased as compared to room temperature cured samples. The shear strength of room temperature cured CP with CS [C-2-CS] was 15.51 times more than oven cured sample [C-3-CS]. Also, the shear strength of room temperature cured CP with MS [C-2-MS] was 8.83 times more than oven cured sample [C-3-MS]. During the curing, PC became harden with the passing of time. As for oven cured sample at 60 °C, the PC was harden with the passing of time and the AC also became weak at the same time due to the change of the viscosity of asphalt. The change of the viscosity of asphalt affected the bond between the aggregates in AC and reduced the strength of AC. Therefore, the shear strength of oven cured CP was lower as compared to room temperature cured CP. IV. Shear strength of CP was affected by the change of temperature. Sample tested at the high temperature had lower shear strength as compared to sample tested at room temperature. For CP using CS with geotextile as reinforcement, the shear strength of C-4-CS-2 was 24 times more than C-4-CS-1. Besides that, for MS using geotextile as reinforcement, the shear strength of C-4-MS-2 was 14.43 times more than C-4-MS-1. The difference in shear strength was due to the samples from C-4-CS-1 and C-4-MS-1 was directly tested for shear strength without cooling down at the temperature of 60 °C. The samples from C-4-CS-2 and C-4-MS-2 were allowed to cool down until room temperature before tested for shear strength. The viscosity of asphalt was reduced due to high temperature, weakened the bond of aggregates in AC and led to the decrease of shear strength. Therefore, shear strength is reduced due to high temperature and can be reversed by allowing the sample cool down to room temperature. V. The surface condition of AC from the tested samples of CP using control and modified surfaces was affected by the temperature and geotextile. When the samples were tested at 60 °C, the uneven of AC was higher as compared to the samples which were tested at room temperature. Also, the surface of AC was more uneven for C-4-CS-1 and C-4-MS-1 as compared to C-4-CS-2 and C-4-MS-2. The surface of AC was also more uneven for C-3-CS and C-3-MS as compared to the AC from Conditions 1 and 2 for both samples of CS and MS. Moreover, CP with geotextile as reinforcement had a more uneven surface of AC as compared to CP without geotextile as reinforcement. This is due to the effect of the non-woven geotextile gripped on the surface of aggregates from AC. Therefore, through visual observation, the type of failure for all the testing Conditions 1, 2, 3 and 4 was mixed failure mode which is a combination of cohesive and adhesive failure modes.
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