Abstract

Semi-flexible pavement consists of selected porous asphalt mixture filled with cementitious slurry. This new type of

pavement has prospects to be designed as a high deformation resistant pavement (Setyawan et al, 2001). Porous asphalt,

as the skeleton of the composite has been de-signed to have a porosity of 30% by selected the aggregates gradation,

type of bitumen, bitumen content and fibre content. This investigation concerned with the design and properties of

porous asphalt to be used as the skeleton for grouted macadam. The ranges of mixtures were evalu-ated by using different

type of bitumen, bitumen content, filler addition and aggregate gradation. This investigation concluded that porous

as-phalt manufactured by using specified gradation utilising 50-pen bitu-men is appropriate to be used as skeleton for

grouted macadam.

Keywords:

cellulose filler, grouted macadam, polymer modified, porous asphalt, semi-flexible pavement

Setyawan, Ary

English

Sebelas Maret Institutional Repository

 MEDIA TEKNIK SIPIL/Juli 2005/41   DESIGN AND PROPERTIES  OF HOT MIXTURE POROUS ASPHALT  FOR SEMI-FLEXIBLE PAVEMENT APPLICATIONS  Ary Setyawan  Fakultas Teknik Jurusan Teknik Sipil UNS, Jln. Ir. Sutami No.36A Surakarta 57126 Email : cenase@yahoo.co.uk  Abstract Semi-flexible pavement consists of selected porous asphalt mixture filled with cementitious slurry. This new type of pavement has prospects to be designed as a high deformation resistant pavement (Setyawan et al, 2001). Porous as-phalt, as the skeleton of the composite has been de-signed to have a porosity of 30% by selected the aggregates grada-tion, type of bitumen, bitumen content and fibre content. This investigation concerned with the design and properties of porous asphalt to be used as the skeleton for grouted macadam. The ranges of mixtures were evalu-ated by using differ-ent type of bitumen, bitumen content, filler addition and aggregate gradation. This investigation concluded that porous as-phalt manufactured by using specified gradation utilising 50-pen bitu-men is appropriate to be used as skeleton for grouted macadam.  Keywords:  cellulose filler, grouted macadam, polymer modified, porous asphalt, semi-flexible pavement.   LITERATURE REVIEW Even though this type of pavement has already been constructed in 1960’s, there is a lack of guidance available for designing the porous asphalt for semi-flexible pavement. The first recommendations for porous asphalt skeleton gradations were presented in the report of Salviacim process evaluation con-ducted at WES for the U.S. Army (Rone 1976, An-derton 2000). The recommended gradation resulted in a porous asphalt skeleton with air voids content in the range of 15% to 25%, which is generally 10% less than the air voids recommended for current gradations. The lower air voids was believed to be the major reason for test section failures since the cementitious grouts failed to fully penetrate the po-rous asphalt skeleton.   Further guidance was authored by Roffe in two marketing publications for Jean Lafebvre Enter-prises (Roffe 1989a & Roffe 1989b), which offered general description of the Salviacim process. These publications contained fundamental mix design guidance, such as recommended open graded ag-gregate gradations for asphalt mixtures and grout formulations, but offered limited information on thickness design and engineering properties. The guidance recommended the use of even more open aggregate grading, resulting in air void contents in the range of 25% to 35%.    POROUS ASPHALT MIXTURE DESIGN AND PROPERTIES The design of aggregate gradations The porous asphalt aggregate gradations used in this investigation were based on a non-standard UK gradation adopted in Blackwater Valley Route pro-ject (Child 1998). The original gradation used in this investigation was gradation A, whilst the modi-fied gradations B and C were investigated to assess the effects of increasing the proportion of finer ag-gregate fractions on the properties of the mixture. The porous asphalt gradations are presented in Ta-ble 1 and in Figure 1.   Compared to gradation A, gradation B contained 3% more of aggregate size B (10-6mm), 7% more of aggregate size D (4.75-2.36mm) whilst omitting aggregates size A (14-10mm) and maintaining the proportion of aggregate size C (6.3-4.75mm).  Table 1.  Aggregate sizes and gradations. Bin desig-nation Size (mm) Gradation A %  Gradation B %  Grada-tion C %  A 14-10 10 0 0 B 10-6 52 55 45 C 6.3-4.75 30 30 30 D 4.75-2.36 3 10 20 E 2.36-0.075 2 2 2 F <0.075 3 3 3  42/ MEDIA TEKNIK SIPIL/Juli 2005 0204060801001200.01 0.1 1 10 100Particle size (mm)% PassingGradat ion AGradat ion BGradat ion C Figure 1. Porous asphalt aggregate gradations.  Gradation C utilised an even finer gradation. Com-pared to gradation A, it incorporated 7 % less of ag-gregate size B (10-6mm), 17% more aggregate size D (4.75-2.36mm) whilst omitting aggregate size A (14-10mm).  Three types of porous asphalt mixtures were pro-duced utilising gradations A, B and C and their mix compositions are shown in Table 2.        Table 2.  Initial porous asphalt mix compositions. Mixture Code Type of bi-tumen Gradation Bitumen Content 7SBSAL5 7%SBS A 5% 7SBSBL5 7%SBS B 5% 7SBSCL5 7%SBS C 5%  The compacted mixtures were then characterised according their volumetric properties and water permeability. The results, are presented in Table 3, each value in the table was an average result from four test specimens.   Table 3. Properties of porous asphalts made with different aggregates gradations. Speci-mens code Density (g/cm3) Specific Gravity Porosity (%) Water Perme-ability 10-3 (m/s) 7SBSAL5 1.83 2.46 25.57 1.34 7SBSBL5 1.85 2.46 24.85 1.11 7SBSCL5 1.87 2.46 23.78 0.94  The essential characteristics of the porous asphalts selected were porosity and water permeability. Mix-ture porosity is related to water permeability but it is not the only controlling factor. The pore size and hence interconnectivity of these voids is what dic-tates the magnitude of hydraulic conductivity.  A larger value of water permeability would imply a mix that is easier to impregnate with cementitious grout.    From the results in Table 3, it could be seen that the porous asphalt gradations B and C have about 1% and 3% lower porosities respectively compared to gradation A.   However gradation A has approximately 30% and 60% higher permeability value compared to grada-tions B and C respectively. For the remainder of the investigation, gradation A was thus adopted as the primary gradation for designing porous asphalt skeletons.   The selection of optimum bitumen contents and bi-tumen types Theoretically, when designing hot mix porous as-phalts, the optimum bitumen content can be calcu-lated using an empirical equation based on previ-ously determined aggregate properties (Roffee 1989) as follows: OBC = 3.25 (α) Σ0.2……………………..[1] α       = 2.65/SGagg Σ       = 0.21C + 5.4S + 7.2s + 135f where: OBC  = optimum bitumen content, SGagg = apparent specific gravity of aggregate blend, Σ = specific surface area, C = percentage of material re-tained on 4.75mm sieve,   S  = percentage of material passing 4.75mm sieve and retained on 600µm sieve,  s  = percentage of material passing 600µm sieve and retained on 75µm sieve,  f  = percentage of material passing 75µm sieve.  Substituting the appropriate gradation and proper-ties of the selected aggregates, the Optimum Bitu-men Content (OBC) was calculated as 4.2% by mass of the combined aggregates. For practical con-siderations, the three bitumen contents selected for the remainder of the investigation were 4.0%, 4.5% and 5.0%.   Three bitumen types were also incorporated in pro-ducing porous asphalt skeletons; 100 pen straight run bitumen, 50pen straight run bitumen and 7% SBS (Styrene butadiene Styrene) Modified bitumen. The proposed mix designs are presented in Table 4.  Table 4. Porous asphalt mixture compositions.  Mixture  code Bitumen types Aggregates types Grada-tion Bitumen content 100AL4 100 pen Limestone A 4.0% 100AL4.5 100 pen Limestone A 4.5% 100AL5 100 pen Limestone A 5.0% 50AL4 50 pen Limestone A 4.0% 50AL4.5 50 pen Limestone A 4.5% 50AL5 50 pen Limestone A 5.0% 7SBSAL4 7% SBS Limestone A 4.0% 7SBSAL4.5 7% SBS Limestone A 4.5% 7SBSAL5 7% SBS Limestone A 5.0%   MEDIA TEKNIK SIPIL/Juli 2005/43 The mixtures were characterised according their volumetric properties and water permeability, the results are presented in Table 5.   Table 5. Properties of porous asphalt skeletons at different bitumen types and contents. Mixture Code Density (g/cm3) Specific Gravity Porosity  (%) Water Perme-ability 10-3 (m/s) 100AL4 1.81 2.50 27.74 1.55 100AL4.5 1.80 2.48 27.51 1.48 100AL5 1.79 2.46 27.45 1.45 50AL4 1.82 2.51 27.44 1.57 50AL4.5 1.82 2.49 26.99 1.25 50AL5 1.83 2.47 25.94 1.22 7SBSAL4 1.82 2.50 27.20 1.61 7SBSAL4.5 1.82 2.48 26.53 1.47 7SBSAL5 1.83 2.46 25.57 1.34  The result clearly shows that for all types of porous asphalt mixtures, increasing the bitumen content had resulted in a reduction in the measured porosity and hence water permeability. It was also observed that at bitumen contents higher than 4%, binder drainage was evident for all the bitumen types used. For the remainder of this investigation, 4% bitumen content was selected as the optimum bitumen con-tent (OBC) for producing porous asphalt skeletons.    The addition of loose cellulose fibres into the hot-mix porous asphalt mixes was also investigated. Two types of specimens were produced incorporat-ing 50pen. and 100pen. bitumen as presented in Ta-ble 6. The fibres are added to allow the use of more bitumen, whilst reducing the risk of binder drainage during hot mix storage and transportation (Wood-side et al 1997a).  The volumetric properties and water permeability of all the porous asphalt types investigated at optimum bitumen content are presented in Table 7 and the mechanical properties are presented in Table 8.  The average bulk densities of the compacted porous asphalt specimens, manufactured with different binders reflected no significant differences as shown in Table 7. The porosity of the compacted samples is also shown in Table 7 and the range of porosity values were all within the expected range of 27 to 30%.  Table 6. Porous asphalt mixtures to evaluate the ef-fect of additional cellulose fibre.  Mix Code Type of bitumen Grada-tion Aggregates Type Bitumen Content % Fibre 100AL4f 100pen A Limestone 5% 0.3 50AL4f 50pen A Limestone 4.36% 0.3   Table 7. Properties of porous asphalt at optimum bitumen content. Mix Code Density (g/cm3) Specific Gravity Porosity (%) Water Per-meability 10-3 (m/s) 100AL4 1.81 2.50 27.74 1.55 50AL4 1.82 2.51 27.44 1.57 7SBSAL4 1.80 2.50 27.20 1.61 100AL4f 1.80 2.49 27.68 1.44 50AL4f 1.81 2.49 27.11 1.52  Table 8. Mechanical properties of porous asphalt mixtures at optimum bitumen contents. Mix Code ITSM  (MPa) ITS  (kPa) Unconfined Comp. Strength (kPa) Cantabro loss (%) 100AL4 548.68 125.26 760.64 34.3 50AL4 953.71 259.65 1691.59 18.7 7SBSAL4 331.44 155.82 906.56 10.1 100AL4f 926.37 138.78 840.96 67.2 50AL4f 1063.42 267.70 1687.64 41.7  In this investigation, water permeability was the most important property since it indicated the ease and extent to which the cementitious grout can penetrate the interconnected voids of the porous as-phalt skeleton. All the porous asphalt skeletons showed quite similar water permeability in the range of 1.44×10-3 m/s to 1.61×10-3 m/s.  The usual range of porous asphalt permeability values is be-tween 0.5×10-3 m/s to 3.5×10-3 m/s (CEN 1998). The permeability values obtained from this investi-gation were close to the mid-point of the range. In-corporation of cellulose fibres into the 100-pen and 50-pen porous asphalts slightly lowered the mixture permeability.  The results of modulus and strength properties as shown in Table 8 indicate that the type of binder used in a porous asphalt mixture has a significant influence on its properties. The 50-pen fibre rein-forced bituminous mixture gave the highest values of tensile strength as well as stiffness modulus fol-lowed by the straight run 50-pen bituminous mix-ture. The SBS modified bituminous mixture exhib-ited the lowest stiffness value.  The results of the Cantabro test as shown in Table 8 indicated that 7% SBS Polymer modified porous asphalt, with its enhanced elastic properties, pro-vided excellent resistance to disintegration with an average abrasion loss value of 10.1% followed by 50-pen porous asphalt with average abrasion loss value of 18.7%. The 100pen mixture produced un-acceptably high values of disintegration. Therefore a 100pen mixture may not be suitable for trafficking prior to filling with the cementitious grout. The lower abrasion loss value of SBS modified bitumi-nous mix could be attributed to the improved cohe-44/ MEDIA TEKNIK SIPIL/Juli 2005 sion in the compacted mixture. In another investiga-tion, the use of 7% SBS modified binder reduced the abrasion loss of porous asphalts by approxi-mately half compared to the straight run bitumen (Zoorob et al 1999).  The results in this investigation showed that the in-troduction of loose cellulose fibres lowered the abrasion resistance capabilities of 100-pen and 50-pen mixtures. The reason for this increase in Can-tabro loss was not clear. One possibility is that the fibres absorbed some of the binder thus reducing the binder film thickness, although this was anticipated in the mix design and was offset to some extent by the increased bitumen content of the fibre mixtures as shown in Table 6. It is also possible that the fibre modified binders were less workable at the same mixing and compaction temperatures. This would have generated mixtures with greater, and thus weaker binder film thicknesses at the aggregate to aggregate contact points. Research conducted at Ul-ster University to investigate the effect of fibre types as modifiers in Stone Mastic Asphalts con-cluded that the addition of loose fibres lowered the ability of the mixtures to withstand the Cantabro test and may have resulted in durability problems (Woodside et al 1997b).   The recommended maximum allowable value of abrasion loss is 20% (Khalid & Perez-Jimenez 1996), therefore, in this investigation 7% SBS modified mix and 50-pen mix could be classified as mixtures suitable for porous asphalt surfacings. For the remainder of the investigation only 50-pen bi-tuminous mixture was selected as skeleton for semi-flexible, grouted macadam. Figure 1 shows the hot mix hot laid porous asphalt ready for grouting proc-ess during the full scale trial after 24 hours of com-paction.   Figure 2. Cementitious slurry grouting on the hot mix hot laid porous asphalt.  CONCLUSION 1. Selecting the porous asphalt gradation was mainly controlled by the need to provide ade-quate porosity and void interconnectivity to fa-cilitate rapid impregnation with highly flowable cementitious grouts. The use of finer aggregate gradations indicated slightly lower porosities but accompanied by much lower water permeability. It was clear that mixture porosity is related to water permeability but was not the only control-ling factor. The pore size and hence the inter-connectivity of these voids dictated the magni-tude of hydraulic conductivity. 2. The mechanical properties of the porous asphalt skeleton were crucial factors during the process of selecting the optimum bitumen content and bitumen type. It was decided early on the inves-tigation that the porous asphalt skeleton should be designed to withstand limited site traffic as would be expected during the construction phase. The optimum bitumen content and bitu-men type for the porous asphalt skeleton were thus selected based on a range of mix perform-ance parameters including: hydraulic conductiv-ity, indirect tensile strength, indirect tensile stiffness modulus, unconfined compressive strength and resistance to abrasion tests. A 14mm maximum aggregate size porous asphalt skeleton was finally adopted which having a de-sign aggregate gradation with 4% bitumen con-tent using a 50-pen grade straight run bitumen.  REFERENCES Anderton G.L., 2000, “Engineering Properties of Resin Modified Pavement (RMP) for Mecha-nistic Design”, US Army Engineer Research and Development Centre ERDC/GL TR-00-2, Vicksburg, MS-USA. Child, S.M. 1998, “Porous Asphalt on the Blackwa-ter Valley”.  In JG. Cabrera (ed.), Proceeding of the second European Symposium on per-formance and durability of bituminous mate-rials, Leeds, April 1997: 427-438, Zurich: AEDIFICATIO Publisher, ISBN 3 931681 14 9. CEN, 1995, “CEN TC 227: Permeability Test for Porous Asphalt, Draft European Standard.” Roffe, J.C, 1989a, “Salviacim – Introducing the Pavement”, Jean Lafebvre  Enterprise, Paris, France. Roffe, J.C, 1989b,  “Salviacim – The Paving Proc-ess,” Jean Lafebvre Enterprise, Paris, France. Rone, C.L., 1976, “Evaluation of Salviacim”, Mis-cellaneous Paper S-76-20, US Army Corps of Engineer Waterways Experiment Station, Vicsburg, MS-USA.   MEDIA TEKNIK SIPIL/Juli 2005/45 Setyawan A., Zoorob, S.E., Hassan, K.E., 2001, “Design and Investigation of The Properties of High Deformation Resistance Slurry Filled Porous Asphalt Mixes (SFPA)”, Jurnal Penelitian Media Teknik Sipil, Edisi Juli 2001 Tahun ke 1, No 2, pp.30 Woodside, A.R. and Woodward, W.D.H., 1997a, “Use of The Cantabro Test to Rapidly Predict The Performance of Bituminous Mixes”, In JG. Cabrera (ed.), Proceeding of the second European Symposium on performance and durability of bituminous materials, Leeds, April 1997: 427-438, Zurich: AEDIFICATIO Publisher, ISBN 3 931681 14 9. Woodside, A.R., Woodward, W.D.H, Akay, M. and Akbulut, H., 1997b, “The enhancement of stone mastic asphalt by the use of cellulose fibre”, In JG. Cabrera (ed.), Proceeding of the second European Symposium on performance and durability of bituminous materials, Leeds, April 1997: 427-438, Zurich: AEDIFICATIO Publisher, ISBN 3 931681 14 9. Zoorob S.E., Cabrera J.G. and Shigeki T., 1999, “Effect of Aggregate Gradation and Binder Type on the Properties of Porous Asphalt”, In J.G. Cabrera & S.E Zoorob (eds), Proceed-ings of the Third European Symposium on Performance and Durability of Bituminous Materials and Hydraulic Stabilized Compos-ites, Leeds April 1999: 59-82,  Zurich: AEDIFICATIO Publishers, ISBN 3 931681 31 9.                                         46/ MEDIA TEKNIK SIPIL/Juli 2005   

1997b, “The enhancement of stone mastic asphalt by the use of cellulose fibre”,

Design and Investigation of The Properties of High Deformation Resistance Slurry Filled Porous Asphalt Mixes (SFPA)”, Jurnal Penelitian Media Teknik Sipil,

Engineering Properties of Resin Modified Pavement (RMP) for Mechanistic Design”,

Evaluation of Salviacim”, Miscellaneous Paper S-76-20, US Army Corps of Engineer Waterways Experiment Station,

Porous Asphalt on the Blackwater Valley”.

DESIGN AND PROPERTIES

OF HOT MIXTURE POROUS ASPHALT

FOR SEMI-FLEXIBLE PAVEMENT APPLICATIONS

http://eprints.uns.ac.id/1052/1/1%2D4%2D1%2DPB.pdf

DESIGN AND PROPERTIES OF HOT MIXTURE POROUS ASPHALT FOR SEMI-FLEXIBLE PAVEMENT APPLICATIONS

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