Experimental evaluation of the effects of partial replacement of coarse
aggregate with Graded Palm Kernel Shell in Asphaltic Wearing Course Adewale Olutaiwo, Abah, Uwakwe Raymond
Department of Civil & Environmental Engineering, University of Lagos, Nigeria [email protected]
doi:10.6088/ijcser.6009
ABSTRACT This research looked at the evaluation of the effect of partial replacement of coarse aggregate (4-8mm crushed stone) with graded palm kernel shell in asphaltic wearing course. The volumetric and physical properties of the asphalt mixtures were evaluated in order to determine the performance characteristics of PKS in the mass production of wearing course asphalt concrete for medium traffic road. Percentages of PKS used were 0%, 30%, 50%, 70% and 100%. Specifically, 15 samples for control mix and 60 samples for the PKS proportions of compacted asphalt mixtures were prepared by using Marshall mixing procedure. The samples were prepared by varying bitumen contents from 5.0% to 7.0% in an increment of 0.5% and tested using the Marshall method. In summary, at 30% replacement of coarse aggregate (4-8mm crushed stone) with the graded palm kernel shell at 5.8% bitumen content, the Marshall stability was 12.800KN, Flow was 2.920mm, Va was 3.0%, VFB was 83.100% . The results indicated that the mixture at 30% PKS meets the criteria provided in the Asphalt Institute Standard Specification. It was observed that for medium trafficked roads, graded palm kernel shells between 10%-30% by weight of coarse aggregate (4-8mm crushed stone) can be used for the replacement while even 100% replacement is possible for lightly trafficked rural roads.
Keyword: Palm Kernel Shell, Coarse Aggregate, Mix Design, Air Voids, and Marshall Stability and Flow.
1. Introduction The road construction industry depends majorly on conventional materials such as asphalt cement, granite, sand and filler materials for the production of asphalt concrete. The high and increasing cost of these materials has greatly hindered the development of road pavement facilities in developing countries. There arises the need for engineering consideration of the use of cheaper and locally available materials to reduce the construction cost for sustainable development. Researchers, although very few have studied the effects and performance of palm kernel shell (PKS) in bituminous mixture as a partial replacement with both coarse and fine aggregates majorly on dense graded asphalt but analyses were much on the physical properties (stability and flow) with little or no consideration on the volumetric properties. Presented below are few research works conducted on the utilization of the PKS in the production of asphalt concrete. For example, (Falad,1999) investigated the sustainability of palm kernel shells as aggregate in light and dense concrete for structural and non-structural purposes. He concluded that, palm kernel shell could be used as an aggregate up to 45% in the production of light and dense concrete. As palm kernel shells perform creditably when partially replaced in concrete production, it is anticipated that it could be fully used as light weight coarse aggregate in concrete production. (Mohammed et al., 2014) presented a paper on the preliminary assessment of some properties of asphaltic concrete, with partial
Experimental evaluation of the effects of partial replacement of coarse aggregate with Graded Palm Kernel
Shell in Asphaltic Wearing Course
Adewale Olutaiwo, Abah, Uwakwe Raymond
International Journal of Civil and Structural Engineering 91
Volume 6 Issue 1 2015
replacement of fine aggregate (sand) with crushed palm kernel shell. It was concluded that their preliminary investigations have shown that replacement of some proportions of fine aggregate (sand) with crushed palm kernel shells is capable of imparting positively on some properties of asphaltic concrete. In addition, the study has been able to establish that not only is uniform grain size distribution achievable from crushed palm kernel shell, the 10 and 50 % by weight replacement of fine aggregate with crushed palm kernel, satisfactorily supports the requirements for asphaltic concrete. (Ndoke,2006) looked at the potentials of palm kernel shells as coarse aggregates in road binder course with emphasis on strength of the asphalt concrete as given by the Marshal Stability and flow values. He observed that Palm kernel shells can be used as partial replacement for coarse aggregate up to 10% for heavily trafficked roads and 50% for light trafficked roads. (Olanipekun, 2006) investigated the properties of coconut shells and palm kernel shells as coarse aggregates in concrete. The coconut shells were crushed and substituted for conventional coarse aggregates in gradations of 0%, 25%, 50%, 75% and 100%. Two mix ratios (1:1:2) and (1:2:4) were used respectively. He noted that the compressive strength of the concrete decreased as the percentage of the shells increased in the two mix ratios. However, concrete obtained from coconut shells exhibited a higher compressive strength than palm kernel shell concrete in the two proportions. His results also indicated a 30% and 42% cost reduction for concrete produced from coconut shells and palm kernel shells respectively. He concluded that coconut shells were more suitable than palm kernel shells when used as substitute for conventional aggregates in concrete production. (Olutoge, 1995) in his investigations into the physical properties of rice husk ash, sawdust and palm kernel shell found their bulk densities to be 530kg/m3, 614kg/m3and 740kg/m3 respectively. He concluded that these materials had properties which resembled those of light weight concrete materials. In his findings, it was clearly indicated that palm kernel shells could be used as light weight coarse aggregate as its bulk density affirms its viability.
2. Materials used
The survey on the materials to be used was first embarked prior to the laboratory test. The constituent materials which formed the asphalt concrete tested were: mineral filler, stone dust, river sand and crushed stone of sizes 4-8mm and 8-16mm. They were obtained from Julius Berger Construction Company at Apapa Lagos, Nigeria. The bitumen (60/70 pen.) was also obtained from Julius Berger Construction Company laboratory. The palm kernel shells were obtained from a local market at Ikole-Ekiti south west of Nigeria (Coordinates: 7.7833°N, 5.5167°E).
3. Materials and methods
The experimental equipment included centrifuge extraction, vibratory Sieves, laboratory oven, asphalt mixer, quartering trail, weighing scale and compaction machine.
3.1 Sample preparation
Specified proportions for the samples,i.e.5% filler of size 0.075mm, 57% stone dust of maximum size 5mm, 8.3% river sand of maximum size 4mm , 20% crushed stone of size 8-16mm and 9.7% crushed stone of size 4-8mm with 5%,5.5%, 6%,6.5% and 7% bitumen of penetration grade 60-70 were mixed together at 145˚C and compacted at both ends (50 blows) to produce compacted cylindrical samples for Marshall stability tests. The graded Palm kernel shells were added at 30, 50, 70% and 100% by weight of coarse aggregate (4-8mm) still
Experimental evaluation of the effects of partial replacement of coarse aggregate with Graded Palm Kernel
Shell in Asphaltic Wearing Course
Adewale Olutaiwo, Abah, Uwakwe Raymond
International Journal of Civil and Structural Engineering 92
Volume 6 Issue 1 2015
maintaining the percentage so that the palm kernel shell acts as partial replacement for the coarse aggregate and mixtures gotten. Five samples were prepared for each proportion of palm kernel shells and for each asphalt binder contents. Marshall tests were carried out on the produced samples and the average of the results for each mix proportion determined. This research was based on medium traffic roads and the number of compaction applied to the both sides of the specimen samples were 50 blows. The required specifications for medium traffic roads are given in the table below.
Table 1: Standard design specifications for medium traffic roads
Stability(KN) 13.500 Not less than 7.5 Satisfactory
Flow(mm) 3.560 2-4 ''
Va(%) 4.805 3 - 5 ''
VFB(%) 71.900 75 - 85 Less
OBC(%) 5.3 5-8 ok
Experimental evaluation of the effects of partial replacement of coarse aggregate with Graded Palm Kernel
Shell in Asphaltic Wearing Course
Adewale Olutaiwo, Abah, Uwakwe Raymond
International Journal of Civil and Structural Engineering 95
Volume 6 Issue 1 2015
4.2 Analysis of effect of using PKS as partial replacement
Table 6-13 below, give the properties of the asphalt mixtures using 30% ,50%,70% and 100% PKS to replace coarse aggregate of size 4-8mm. Table 6: Properties of the mixture with replacement of coarse aggregate (4-8mm) with 30%
PKS.
4.2.1 Results
The numerical average of the BC% = the Optimum binder content (5.8%)
Table 7:Results at 5.8% OBC for 30% pks replacement
Stability(KN) 10.195 Not less than 7.5 satisfactory
Flow(mm) 3.000 2-4 ''
Va(%) 2.890 3 - 5 less
VFB(%) 81.900 75 - 85 ok
OBC(%) 6.0 5-8 ok
It indicated that the mix at 100% meets the criteria at 6.0% OBC hence , it is satisfactory.
4.3 Comparison of Optimum Bitumen Content at percentage mix proportion of pks
replacement
The percentages of PKS used were 0%, 30%, 50%, 70% and 100%. Specifically, 15 samples of compacted asphalt mixtures were prepared for each proportion by using Marshall mixing procedure. The samples were prepared by varying bitumen contents from 5.0% to 7.0% in an increment of 0.5% and tested using the Marshall Method. The optimum bitumen content for each PKS percentage in the mixture was found and the corresponding parameters obtained are shown in the Table 14 below.
Table 14: Comparison of OBC at percentage mix proportion of PKS replacement
Properties 0% 30% 50% 70% 100% Specifications
Stability(KN) 13.5 12.8 11.9 10.6 10.2 Not less than 7.5
Flow(mm) 3.6 2.9 3.3 3.2 3.0 2-4
Va(%) 4.8 3.0 4.3 6.1 2.9 3-5
VFB(%) 71.9 83.1 74.0 65.0 81.9 75-85
OBC(%) 5.3 5.8 5.8 5.6 6.0 5.0-8.0
4.4 Discussion
On the basis of Marshall Stability and flow value, the suitability of mix for paving is decided, but some other parameters like unit weight of mix, percent air voids and voids in mineral aggregates are important to take into consideration durability criteria. From table 14 above,all the OBC fell within the specifications. All the PKS mix proportions except at 70% are within the specifications including the control mix. At 70% PKS replacement, the percent air void was high about 6.1%, adopting this value could result in decreased density and increased permeability of the pavement because the mixture will become permeable to water leading to reduced durability.
4.5 The analysis of the parameter trends from 0%-100% PKS replacement in the
bituminous mixtures properties
Experimental evaluation of the effects of partial replacement of coarse aggregate with Graded Palm Kernel
Shell in Asphaltic Wearing Course
Adewale Olutaiwo, Abah, Uwakwe Raymond
International Journal of Civil and Structural Engineering 99
Volume 6 Issue 1 2015
Table 15: Unit weight trend
Bitumen content (%) 0% 30% 50% 70% 100%
Specifications
5.0 2.346 2.240 2.202 2.160 2.100 Not less than
1.5g/ml
5.5 2.380 2.265 2.210 2.154 2.142 ''
6.0 2.408 2.293 2.234 2.199 2.174 ''
6.5 2.381 2.306 2.265 2.212 2.173 ''
7.0 2.368 2.307 2.273 2.226 2.189 ''
Figure 7: Graph of unit weight trend from 0% to 100% PKS replacement
Unit weight was observed to have decreased with increased PKS proportions from 0% to 100%, this should however be expected since PKS is a lighter weight aggregate. One of the key elements in the durability and moisture susceptibility of an asphalt mixture is asphalt film thickness otherwise called density or unit weight. Asphalt film thickness describes the dimension of the asphalt binder coating of the aggregate particles. A thin asphalt coating on aggregate particles is one of the primary causes of premature aging of the asphalt binder, and is one definition of lack of durability. Inadequate film thickness can create a lack of cohesion between aggregate particles and create a "dry" mix. Also, if the asphalt film is too thin, air which enters the compacted HMA can more rapidly oxidize the asphalt, causing the pavement to become brittle. It is specified by AI, that the density of the asphaltic wearing course should not be less than 1.5g/ml.
Table 16: Voids in mix (Va %) trend
Bitumen content (%) 0% 30% 50% 70% 100%
Specifications
5.0 4.900 6.200 7.100 7.700 9.400 3-5%
5.5 4.800 6.300 4.100 6.400 6.400 ''
6 4.500 1.800 4.300 5.500 2.800 ''
6.5 4.400 2.600 1.300 3.100 4.400 ''
7.0 4.000 3.400 3.100 4.100 4.900 ''
Experimental evaluation of the effects of partial replacement of coarse aggregate with Graded Palm Kernel
Shell in Asphaltic Wearing Course
Adewale Olutaiwo, Abah, Uwakwe Raymond
International Journal of Civil and Structural Engineering 100
Volume 6 Issue 1 2015
Figure 8: Graph of percent air voids trend from 0% to 100% PKS replacement
It was observed that percent air void decreases with increasing asphalt binder content. The durability of an asphalt pavement is a function of the air-void content. This is because the lower the air-voids, the less permeable the mixture becomes. Too high an air-void content provides passage ways through the mix for the entrance of damaging air and water. A low air-void content, on the other hand, can lead to flushing, a condition in which excess asphalt squeezes out of the mix to the surface. The allowable percentage of air voids (in laboratory specimens) is between 3.0 percent and 5.0 percent for most surface course mixes.
Table 17: Percent voids filled with bitumen (VFB %) trend
Bitumen content (%) 0% 30% 50% 70% 100%
Specifications
5.0 69.900 63.700 60.100 57.700 52.000 75-85 %
5.5 72.600 65.800 74.200 64.200 64.000 ''
6.0 75.700 88.200 75.100 69.900 81.900 ''
6.5 77.300 84.900 91.700 81.900 75.700 ''
7.0 80.100 82.200 83.300 80.200 75.300 ''
Figure 9: Graph of voids filled with bitumen trend from 0% to 100% PKS replacement
Experimental evaluation of the effects of partial replacement of coarse aggregate with Graded Palm Kernel
Shell in Asphaltic Wearing Course
Adewale Olutaiwo, Abah, Uwakwe Raymond
International Journal of Civil and Structural Engineering 101
Volume 6 Issue 1 2015
It was observed that VFB increases with increasing asphalt content. The VFB property is important not only as a measure of relative durability, but also because there is an excellent correlation between it and percent density. If the VFB is too low, there is not enough asphalt to provide durability and to over-densify under traffic and bleed. Thus, the VFB is a very important design property. The AI specifications require 75-85% during the design phase; this requirement is intended for the mix during the design phase only and is typically not a production requirement.
Table 18: Percent voids in mineral aggregate (VMA %) trend
BC (%) 0% 30% 50% 70% 100% Specifications
5.0 16.300 17.100 17.800 18.200 19.600 Not less than 13%
5.5 17.500 18.400 15.900 17.900 17.800 ''
6.0 18.500 15.200 17.300 18.300 15.500 ''
6.5 19.400 17.200 15.600 17.100 18.100 ''
7.0 20.100 19.100 18.500 19.200 19.800 ''
Figure10: Graph of voids in mineral aggregate trend from 0% to 100% PKS replacement
It was observed that VMA decreases with increasing asphalt binder content,reached a minimum, then increases. Asphalt durability is often linked to the thickness of the asphalt coating on the aggregate particles.
Table 19: Marshall stability (KN) trend
Bitumen content (%) 0% 30% 50% 70% 100%
Specifications
5.0 12.721 13.519 11.622 11.343 9.413 Not Less than
7.5KN
5.5 14.076 11.727 11.360 9.969 5.709 ''
6.0 16.166 13.576 12.198 14.294 10.195 ''
6.5 13.826 13.672 13.463 12.901 14.289 ''
7.0 12.373 12.707 12.906 11.712 14.659 ''
In order for a pavement to have adequate film thickness, there must be sufficient space between the aggregate particles in the compacted pavement. This void space is referred to as
Experimental evaluation of the effects of partial replacement of coarse aggregate with Graded Palm Kernel
Shell in Asphaltic Wearing Course
Adewale Olutaiwo, Abah, Uwakwe Raymond
International Journal of Civil and Structural Engineering 102
Volume 6 Issue 1 2015
Voids in the Mineral Aggregate (VMA). It must be sufficient to allow adequate effective asphalt (that which is not absorbed into the aggregate particles) and air voids. The Asphalt Institute specified VMA not to be less than 8% for asphaltic wearing course.
Figure 11: Graph of stability trend from 0% to 100% PKS replacement
It was observed that stability of the mixtures decreases from 0% to 100% proportions of PKS replacement. Maximum stability was achieved at 6.0 BC% at 0% PKS replacement, while minimum value was achieved at 100% mix proportion of PKS replacement at 5.5% BC.
Table 20: Marshall flow trend
Bitumen content (%) 0% 30% 50% 70% 100%
Specifications
5.0 3.2 3.2 3.3 3.3 3.1 2.0 – 4.0mm
5.5 3.7 3.0 3.3 3.2 3.8 ''
6.0 3.5 2.9 3.3 3.0 3.0 ''
6.5 3.9 3.5 3.3 3.5 3.0 ''
7.0 4.1 3.6 3.4 3.4 3.0 ''
Figure 12: Graph of flow trend from 0% to 100% PKS replacement
The PKS mix proportions meet the specification except for the mix at 5.5% BC and 100% PKS replacement which fall below 7KN. The stability of the asphalt mix is an important
Experimental evaluation of the effects of partial replacement of coarse aggregate with Graded Palm Kernel
Shell in Asphaltic Wearing Course
Adewale Olutaiwo, Abah, Uwakwe Raymond
International Journal of Civil and Structural Engineering 103
Volume 6 Issue 1 2015
element in its ability to resist rutting and thus a key factor to evaluate. Rutting refers to permanent deformation of the asphalt surface that accumulates in the wheel paths. It is primarily the result of repeated traffic loading cycles. Rutting may be accompanied by fatigue cracking and other distresses, making it a serious concern and potential indicator of pavement failure. The American Asphalt Institute specifies stability for asphaltic wearing course not to be less than 7.5kN.It was observed that flow increases from 0% to 100% mix proportion of PKS replacement. Marshall Flow is the degree of deformation of the compacted asphalt sample when subjected to load. Flow is directly related to the amount of bitumen in mixture. The durability of pavement and its performance is a function of the quantity of asphalt content in the mixture. High bitumen content causes pavement bleeding leading to rutting and low bitumen content causes stripping and raveling which leads to pavement deformation. The AI flow range for asphaltic wearing course is 2-4mm.
5. Conclusion and recommendations
From the results obtained in this experiment, it can be concluded that graded Palm kernel shells can be used as partial replacement for coarse aggregate in wearing course up to 10% for heavily trafficked roads, 30-50% for medium trafficked roads, and full replacement-100% for very lightly trafficked rural roads. From the above study, I recommend that graded palm kernel shell can be used for asphalt concrete production for low to medium traffic roads and through the use of palm kernel shells in road construction materials, the environmental hazards associated with complete dependence on conventional materials can be minimized. In addition, the cost of road construction and maintenance can be greatly minimized through the use of alternative agricultural waste products (palm kernel shell) for road construction materials.
6. References
1. British Standards Institution (BS 598, 1985), Methods of determination of index properties of pitch-bitumen Binder, 1995, pp 2-16.
2. British Standards Institution (BS 812, 1975), Methods of determination of mechanical properties of aggregate, 1995, Part 3, p 4-8.
3. Falad, (1999), Sustainability of palm kernel shells as aggregate in light and dense concrete for structural and non-structural purposes.
4. Mohammed et al., (2014), Paper presented on the preliminary assessment of some properties of asphaltic concrete, with partial replacement of fine aggregate (sand) with crushed palm kernel shell.
5. Ndoke P. Ndoke, (2006),Performance of Palm Kernel Shells as a Partial replacement for Coarse Aggregate in Asphalt Concrete, Leonardo Electronic Journal of Practices and Technologies, 9, pp 145-152.
6. Olutoge, (1995), The physical properties of rice husk ash, sawdust and palm kernel shell, ARPN Journal of Engineering and Applied Sciences, 5(4), pp 7-13.
7. Neville A. M., (2008), Properties of concrete, Pearson Education, Asia Pte ltd, Edingburg, Scotland, pp 108-176.
Experimental evaluation of the effects of partial replacement of coarse aggregate with Graded Palm Kernel
Shell in Asphaltic Wearing Course
Adewale Olutaiwo, Abah, Uwakwe Raymond
International Journal of Civil and Structural Engineering 104
Volume 6 Issue 1 2015
8. Nuhu-Koko M. K.,(1990), The use of Palm kernel shells as aggregates for concrete, Paper presented at 21st Annual Conference of Materials Testing, Control and Research, FMW, Lagos, Nigeria, pp 20,
9. Oglesby C. H., Hicks R. G, (1982), Highway engineering, 4th Edition, John Wiley and Sons, New York, pp 683-685.
10. Omange G. N., (2001), Palm kernel shells as road building materials, Technical Transactions of the Nigerian Society of Engineers.
11. Olanipekun, (2006), Investigation of the properties of coconut shells and palm kernel shells as coarse aggregates in concrete
12. Uviasah M. O, (1976), Properties of Palm kernel shells and Fibre as aggregates for making concrete, Unpublished Bachelor of Engineering Thesis, Department of Civil Engineering, University of Benin, Benin, Nigeria.
13. Yusuf and Jimoh, (2011), Worked on the appropriateness of the various nominal mixes of the ‘palm kernel shell concrete’ as rigid pavement.
