Utilisation of Natural Fibers in Stone Matrix Asphalt
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The technology of asphalt materials and mixtures evolved in the last three decades in Europe and North America. The SMA (stone matrix asphalt) mixture is a gap-graded mix. The comparison of strength and drain down of pavement wearing coat made with SMA mix with fibre and without fibre is done. This research is done to evaluate the use of sisal fibres in the mixture by laboratory tests in which a flow parameter is analyzed, as well as the mechanical properties of the mixture. For the SMA mix the aggregate gradation is taken as per the MoRTH specification and the binder content is 4%, 4.5%. 5%, 5.5%, 6%, 6.5%, 7% by weight of aggregate and fibre used is 0.3% by weight of aggregate. Natural fibres (sisal fibres) are used to meet the flow requirement of the SMA mix and also it doesn't affect the mechanical properties.
KEY WORDS: Asphalt mixtures, SMA (Stone Matrix Asphalt), sisal fibres and mechanical properties.
Stone Matrix Asphalt (SMA) is a gap-graded mixture that relies on stone to stone contact to provide strength and a rich mortar binder to provide durability. The fibers are normally used to prevent draindown of the binder during transport and placement of the bituminous mixture. The fibers commonly used are polypropylene, polyester, mineral, cellulose and natural fibers (sisal,coconut,bamboo). Cellulose fibers are extensively used in SMA in Europe and USA. These fibers are patented. The fibers improve the service properties of the mix by forming micromesh in the asphalt mix to prevent the draindown of the asphalt so as to increase the stability and durability of the mix. Here we are using the natural fibers(sisal fiber) which is more economic than cellulose fibers which doin same work as cellulose fiber.
The SMA has been very used in the Europe, in countries as Germany, Belgium, among others, and in North America. Its application has been carried through mainly in high volume traffic roads and/or weighed and airports, either as layer of high resistance and high durability, to assist in the tack in wet track, in the reduction of water spray from tires, in the reduction of the reflection of light of lighthouses in rainy nights, and the reduction of noise. The SMA mixture consists basically of two fractions: coarse aggregate and one raised text of mastic, that it is formed typically by small aggregate, to filer mineral, asphalt and staple fibers. The composed mineral skeleton of coarse aggregate supplies to the mixture one high involve between the grains, of form that the mixture earns in resistance (the ratio of coarse aggregates is superior to the ratio of the same ones in the dense and continuous mixtures), while the raised text of mastic supplies to the mixture higher durability .
SMA is rich in asphalt due to its particular grain sized constitution, with a consumption of between 6% and 7%. After compacting it is an impermeable, with less than 4% of volume of voids. Generally it is applied in thicknesses varying from 1.5 to 7.0 cm, depending of the grain size. Due to gradation that presents and high coarse aggregate concentration, the mixtures SMA have a rough macro texture, forming small "channels" between coarse aggregate, responsible aggregates for efficient a superficial draining .
Fibers are added to mixtures SMA can be organic, inorganic origin or material mineral, with intention to prevent the flow parameter of the asphalt during the construction process (production, transport and application of the mixture). The fibers, generally, do not have influence on the performance of the mixture after the compacting, even so make possible a bigger text of asphalt, what it around generates a thicker film of the aggregate, being late the oxidation, the penetration of humidity and the separation of aggregates. These advantages serve to increase the resistance to the consuming of the produced asphalt concrete .
Some fibers already had been studied in asphalt mixtures, as the fiber of cellulose, glass and mineral, each one with a variation of different percentage, as it can be observed in Table 1.
Vale et al. (2006) the coconut fiber had carried through studies in asphalt mixtures type SMA using, following the assay of flow parameter of AASHTO T 305/97 to determine the percentage of fiber used in the mixture that must be in maximum 0.3%. In this research the percentage of fibers of coconut used during the flow parameter assay varied enters 0.1 and 0.7% of the weight of the mixture.
The results had shown that for mixtures of type SMA the incorporated percentage of sisal fibers, to a temperature of 70Â°C, varied between 0.5 and 0.7%. The sisal fiber 3 presented good efficiency with regard to the flow parameter, being also, satisfactory the results of the mechanical assays (tensile strength, module of resilience and fatigue) .
The paving bitumen 60/70 grade was used in this study. The bitumen was tested for physical properties before and after Thin Film Oven test (ASTM D 1754 2002). The CRMB was also used as one of the stabilizers in the SMA mixes. The particle size of the crumb rubber for preparation of modified binder was passing 0.600mm sieve and retained on 0.075mm sieve with 5 per cent passing through 0.150 mm sieve. The percentage of crumb rubber was 12 by weight of asphalt cement. This percentage of CR was added in neat bitumen to prepare grade of modified bitumen as per Indian specifications. The purpose of using CR in SMAwas to explore the feasibility of using waste in SMA, as Government of India is emphasizing on use of wastes like plastic and rubber in the bituminous pavement on high-density corridors. The properties of virgin and modified binders are given in table.
The aggregates were procured from a jaw type stone crusher with vertical shaft impactor in Delhi derived from igneous rock. The properties of the coarse aggregates are given in table 1. The percentage of combined flakiness and elongation indices was less than 30%, which is the requirement for dense graded bituminous mixes. The crusher dust was used as fine aggregates and it was non plastic in nature. The aggregates of different sizes were used in suitable proportions by trial and error method to obtain the average proportions of the grading as specified by NAPA (Designing and Constructing of SMA mixtures-State of the Practice, Quality Improvement Programme 122 1999) for SMA and MORTH (Ministry of Road Transport & Highways, Specifications for Road and Bridge Works 2001) for dense graded asphalt concrete (AC) mix. These gradings are shown in table 2. The coated jute fibers were used in cellulose form.
The fiber as stabilizer was added in the SMA mixture to prevent the draindown and improving the performance related properties of the mix. The natural fibers are constituted of cellulose materials, gotten of the thick part. The process of shred of the thick part for attainment of the natural fiber can be made by maceration in water or mechanical processes. Compared with other vegetal staple fibers, the coconut fiber has percentile minor of cellulose (36 to 43%), however the amount of lignin (41 to 45%) is about two times the existing values for jute and the sisal, conferring to it, a bigger resistance and hardness front to other staple fibers (Esmeraldo, 2006). The used staple fibers of coconut in the research had been yielded by the Embrapa in the state of the Ceara.
Design of experiments
The following tests were carried out on mixtures:
1. Marshall mix design at 600C, using 50 blows per side
Resistance to rutting by Hamburg wheel loaded device at 500C
Resistance to aging:
Short-term oven aging with diametral modulus at 250C
The two projects set up by Georgia Department of transportation (GDOT)(1991) to evaluate the performance of SMA versus that of conventional mixes as (i) an immediate and wearing course under heavy truck loads. And (ii) an overlay for Portland cement concrete pavements are
a) the first SMA project no 9102 in 1991, various combinations of SMA and standard mixes were placed in a 2.5 mile, high traffic volume test section on Interstate 85 northeast of Atlanta in Georgia. 50 blows Marshall Mix design procedure was chosen as the design standard following European design of SMA. Granite Gneiss with an abrasion value of 35%and gneiss-amphibolites with an abrasion value of 20%, an AC-30 Asphalt Cement modified with a low-density polyethylene thermoplastic to stiffen the binder, Mineral filler, Mineral Fiber and Hydrated lime were also added to the mixers to reinforce the matrix and stabilize the thicker asphalt film.
(b) A second research project in 1992, SMA was used as an overlay for Portland cement concrete pavements in the test section on Interstate 75 south of Atlanta in Henry County. 50 blow Marshall Design method, Granite gneiss-amphibolites with abrasion value of 37 %, Styrene butadiene (SB) as an asphalt modifier, cellulose fiber, hydrated lime and mineral filler was used.
SMA has proven to have the following intrinsic benefits:
- 30-40% less rutting than standard mixes.
- 3 to 5 times greater fatigue life in laboratory experiments.
- 30-40% longer service life. (In Europe)
- Overlay for Portland cement concrete pavements.
WisDOT conducted research study in 1991 choosing six projects, two in each Hardness regions
Region 1: Igneous gravels with LA abrasion wear values between 15 to 30
With Cellulose Fiber and Mineral fiber stabilizer
Region 2: softer, more absorptive dolomitic crushed stone or gravels with hardness value between 30 and 60
With Polymer (Thermoplastic) stabilizer (Lo %) and Polymer (Thermoplastic) stabilizer (Hi %)
Region 3: lime stone/dolomite stone or gravels with hardness value between 20 and 40 Polymer (Elastomeric) stabilizer (Lo %) and Polymer (Elastomeric) stabilizer (Hi %)
And found that
SMA's are providing cracks 30 to 40% less than for the standard DGAP's in most instances.
The larger maximum size aggregate SMA's seem to have impeded crack development more than the smaller sized aggregate SMA's.
The SMA's in the region with the aggregates most resistant to abrasion and impact retard cracks 52% better than the standard AC pavements while in the region with aggregates least resistant to abrasion and impact retard cracks only 14% better than the standard AC control.
After five years, the SMA pavements are providing less friction but better speed gradients than the standard asphalt pavement .No one SMA type is better than the other in this regard.
Considering all types of distresses, the different types of SMA's are almost performing same and better performers than the standard AC pavements over five years, although the SMA modified with the inorganic fiber seems to be the worst performing SMA.
The analysis of ride values indicates that an SMA is generally rougher when compared with a standard AC pavement.
Bradely et.al. (2004) conducted feasibility study of use waste fibers i.e. carpet and tire fibers with respect to conventional fibers such as cellulose and mineral fibers by conducting mix designs followed by drain down, moisture susceptibility, and permanent deformation testing of each mixture and found that waste tire and carpet fibers can be viable options for use as stabilizing additives in SMA mixtures.
Kamaraj C., G. Kumar, G. Sharma, P.K. Jain and K.V. Babu (2004) carried laboratory study using natural rubber powder (wet process) with 80/100 bitumen in SMA as well as dense graded bituminous mix with cellulose fiber and stone dust and lime stone as filler and found its suitability as SMA mix through various tests.
Punith V.S., Sridhar R., Bose Sunil, Kumar K.K., Veeraragavan A (2004) did a comparative study of SMA with asphalt concrete mix utilizing reclaimed polythene in the form of LDPE carry bags as stabilizing agent (3 mm size and 0.4%) .The test results indicated that the mix properties of both SMA and AC mixture are getting enhanced by the addition of reclaimed polythene as stabilizer showing better rut resistance, resistance to moisture damage, rutting, creep and aging.
Muniandy R., Huat, B.B.K. (2006) used Cellulose oil palm fiber (COPF) and found fiber-modified binder showed improved rheological properties when cellulose fibers were preblended in PG64-22 binder with fiber proportions of 0.2%,0.4%,0.6%,0.8 %and 1.0% by weight of aggregates. It showed that the PG64-22 binder can be modified and raised to PG70-22 grade. The Cellulose oil palm fiber (COPF) was found to improve the diameteral fatigue performance of SMA deign mix. The fatigue life increased to a maximum at a fiber content of about 0.6%, whilst the tensile stress and stiffness also showed a similar trend in performance. The initial strains of the mix were lowest at a fiber content of 0.6%.
Kumar Pawan, Chandra Satish and Bose Sunil (2007) tried to use an indigenous fiber in SMA Mix by taking low viscosity binder coated jute fiber instead of the traditionally used fibers and compared the result with the imported cellulose fiber, using 60/70 grade bitumen and found optimum fiber percentage as 0.3% of the mixture. Jute fiber showed equivalent results to imported patented fibers as indicated by Marshall stability test, permanent deformation test and fatigue life test. Aging index of the mix prepared with jute fiber showed better result than patented fiber.
Shaopeng Wu et al. (2007) used slag after 3 year of ageing with PG76-22 modified binder, lime stone filler, short chopped polyester fiber (3%) for the SMA mix in Marshall method and found it to be suitable for use.
Chui-Te Chiu, Li-Cheng Lu, (2007) used asphalt rubber (AR),produced by blending ground tire rubber (GTR) (i) 30% of a coarse GTR with a maximum size of #20 sieve and (ii)20% of a fine with a maximum size of #30 sieve with an asphalt, as a binder for SMA and found AR-SMA mixtures were not significantly different from conventional SMA in terms of moisture susceptibility and showed better rutting resistance than that of conventional dense graded mixture.
Yongjie Xue, Haobo Hou, Shujing Zhu, Jin Zha (2008) used municipal solid waste incinerator (MSWI) fly ash as a partial replacement of fine aggregate or mineral filler and BOF Slag as part of coarse aggregate with polyester fiber of 6.35 mm in length obtained from recycled raw materials, PG76-22 binder in the SMA mix and performed Marshall and superpave method of design and found it's suitability for use in the SMA mix.
Gradation of Aggregates with Fibre:
Total weight of sample= 1200gm
Test conducted for aggregates
Impact Value Test
The ratio of the weight of fines formed to the total sample weight in each test shall he expressed as a percentage, the result being recorded to the first decimal place:
Aggregate impact value = (B/A) x 100
B=weight of fraction passing 2.36-mm IS Sieve, and
A =weight of oven-dried sample.
Wt. Of oven dried sample (in gm)
Wt. of aggregate retained through 2.36mm IS sieve (in gm)
Wt. of passing aggregate (in gm)
According to MoRTH the aggregate impact value should be
The standard aggregate crushing test shall be made on aggregate passing a 12.5-mm IS Sieve and retained on a 10-mm IS Sieve.
Ratio of the weight of fines formed to the total sample weight in each test shall be expressed as a percentage, the result being recorded to the first decimal place:
Aggregate crushing value = (B/A) x 100
B = weight of fraction passing the appropriate sieve, and
A = weight of surface-dry sample.
Wt. Of oven dried sample (in gm)
According to MoRTH the aggregate crushing value should be
Los Angel's Abrasion Value
The test sample and the abrasive charge shall be placed in the Los Angeles abrasion testing machine and the machine rotated at a speed of 20 to 33 rev/min. The machine shall be rotated for 500 revolutions.
difference between the original weight and the final weight of the test sample shall be expressed as a percentage of the original weight of the test sample. This value shall be reported as the percentage of wear/abrasion value.
Wt. Of oven dried sample (in gm)
Wt. of aggregate retained through 2.36mm IS sieve (in gm)
Wt. of passing aggregate (in gm)
According to MoRTH the Los Angle's Abrasion value should be
Flakiness and Elongation Index
The elongation index is the total weight of the material retained on the various length gauges, expressed as a percentage of the total weight of the sample gauged.
The flakiness index is the total weight of the material passing the various thickness gauges or sieves, expressed as a percentage of the total weight of the sample gauged.
Wt. of sample taken in gm.
Aggregate passing in the gauge in gm.
Average flakiness index
Aggregate retained in the elongation gauge in gm.
Average elongation index
Marshall method of mix design was used to find out the OBC as per ASTM procedure (ASTM D 1559 1989) in all the mixes. Specimens of 100mm diameter and 63.5mm height were prepared by applying 50 blows on each face. The mixing and compaction temperatures were obtained from viscosity-temperature relationships developed for neat and CRMB binders corresponding to mixing and compaction viscosities of 0.17 and 0.28 Pa.s, respectively. The mixing and compaction temperature from figure 1 was observed to be 160 and 1508C for unmodified binder and slightly higher for CRMB binder respectively. OBC was calculated as per Asphalt Institute MS-2 series (Sixth edition) by taking the bitumen corresponding to 4.5 percent air voids (mid value of the range) and checked for other parameters. The air voids in the design were kept at 4.5% as per the requirements of MoRTH specifications (Ministry of Road Transport & Highways, Specifications for Road and Bridge Works 2001), although it is slightly higher than generally used value of 4% in USA, Europe and other countries. Moreover, the pavement temperature in India is normally more than 608C during extreme summer in northern part of the country, a condition not realised in the Europe or the USA. This also demands higher percentage of air voids in the mix. The OBC obtained corresponding to designed air voids was checked for minimum voids in mineral aggregate (17%) and stone to stone contact in the SMA mixes.
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