Cheap Flexible Waterproofing Treatments for Rural Roads

7/28/2019 Cheap Flexible Waterproofing Treatments for Rural Roads

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CHEAP FLEXIBLE WATERPROOFING TREATMENTS FOR RURAL ROADSR. S. Shukla, Scientist and V. K. Jaitly, Scientist

Central Road Research Institute, New DelhiABSTRACT

This paper deals with the development of bituminous primers and cut-backs for water-proofing of ruralroads. The efficacy of the water proofing treatments has successfully been tried on a communitydevelopment road near Delhi constructed with locally available soil, stabilized with brick-bats, lime,cement and molasses. Depending on the traffic intensity specific recommendation are made for their use.1. Introduction1.1 Rural roads may be defined as roads with lowtraffic volume in predominantly agricultural areaswhere type of traffic is mainly slow moving animaldrawn carts. These roads differ from urban roads inthe sense that while in construction of urban roads,

the conventional specifications like soling, water-bound macadam base courses and bituminouswearing course are provided, in rural roadsgenerally locally available materials such as soil,moorum, kanka, gravel, etc., are used.

1.2 The general concept of rural road today is tolevel the ground, to provide a shallow embankmentof one half to one metre height, to allow it to getcompacted by one or two rains and then open it fortraffic. On such roads deep ruts are formed due tochannelized bullock cart traffic. Formation of muddue to accumulated rain water in these channels

makes the road impassable.

1.3 In early fifties efforts were made in Punjab to-wards stabilization of locally available soil byblending with sand and grafting with brick bats. Thismethod known as Mehras method opened newavenues for the improvement of rural roads. Laterthe methods of soil stabilization with other materialssuch as cement2, lime3 and molasses were alsodeveloped.

In order to improve the service value of thestabilised soil road by Mehras method, the Central

Road Research Institute constructed a 2.5 km longtest-track in 1959 under community developmentprogramme for connecting village Rajokri nearDelhi with Delhi-Gurgaon road (NH 8). In all, 21specifications were laid using locally available soil,mixed with brick-bats, cement, lime and molasses.On some of the specifications

water proofing treatments were given by use offlexible bituminous binders. Development ofsuitable primers and cut-back bitumens for waterproofing treatments and their performanceevaluation from the basic theme of this paper.

Relevance of Mehras Method for Constructionof Rural Roads2.1 Special features of Mehras method of soilstabilization are:

2.1.1 The road crust consists of two courses, thebase and the upper course. Thee base course soilhas less clay and more sands and the upper coursehas more clay and less sand. The base courseconsisting of graded soil rich in sand is designed toprotect the upper course from the capillary rise ofsubgrade moisure during wet season.

In the upper 35-60 per cent of broken brickaggregates or other soft local aggregates likekankar, laterite, moorum or soft stones areincorporated into the graded soil. This proportion ofcoarse aggregates increases shear strength andbearing values of the soil aggregate mass andensures that aggregates do not cause self crushingwithin the road crust under load and vibrations.

The soil subilized layers are prone to damage byabrasion action by the traffic. For the prevention ofthis phenomenon the Mehras method stipulatesthat the wearing course should be covered with thin

premix carpet to protect it from abrasion by bullockcart traffic as well as from infiltration of rain waterfrom top.


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3. Development of Cut-Backs and Primers forWater Proofing Treatment3.1 The test track was constructed in the month ofDecember when atmospheric temperatures andpavement temperature were around 20C and 27Crespectively. The fluxing charts prepared for

surface dressing indicated a minimum flux of 10 percent kerosene oil to impart a viscosity of 80000centistokes for good wetting of fine aggregates tobe used. This amount of flux was consideredadequate for pneumatic tyred traffic. Over a periodof one or two months the flux will evaporate awayleaving behind bitumen 80/100 as a binder.3.2 Since the road was to be used mainly bybullock cart traffic where surface deformation wouldbe of much larger magnitude, the binder is requiredto be more pliable to accommodate suchdeformation without cracking with this view in mind

the bitumen/kerosene oil blend was further cut with15 to 20 per cent furnace oil. Two cut-backs withthe following compositions were finally adopted forwater proofing purposes:

Type of material Compositioncut-backNo. 1

Percentagecut-backNo. 2

Bitumen 80/100 75 70Furnace oil 15 20Kerosene oil 10 10

These cut-back were to be slightly warmed beforeusing them for surface dressing work.

3.3 In addition to cut-backs two primers were alsoprepared for cold application as dust palliatives.The composition of the primers was as givenbelow:

Type of material Primer No.1 Primer No.2

Bitumen 80/100 30 50Furnace oil 70 -Diesel oil - 50

4.1 The basic objective for laying the test-track wasto improve the service value of the stabilized soilroad (Mehras method) without the use ofconventional premix carpet black top surface forlight traffic. In all, 21 specifications were laid on an

grafting as such or in combination with a thinsurface dressing and priming treatment was alsostudied.4.2 The soil sub-grade was mainly silty with liquidlimit of about 28 per cent and PI of 8. The optimum

moisture content as determined by Proctor methodwas around 12-13 per cent. The CBR value of thesub-grade soil at optimum moisture and Proctordensity was about 10 per cent. For intensity oftraffic of about 15-20 bullock carts per day thethickness required was worked out as 12.5 cms5.For all specifications a thickness consisting 7.5 cmof base course and 7.5 cm of surface course wasadopted.

4.3 For preparation of sub-grade the existing un-even surface was leveled and trenches of 3.5 mwide and 15 cm deep were cut. The subgrade soil

was scarified to a depth of 15 cm and aftercorrecting the moisture content to optimum, wascompacted by a 8-10 tonne roller to 100 per centProctor density (1.8 gm/cc).

4.4 The base course was constructed withmechanically stabilized soil. For base courseconstruction the soil was excavated from borrowpits, clods were broken to 10-12 mm size andspread on prepared sub-grade to loose thickness of12.5 cm. Jamuna sand was added to control thesend content to minimum of 40 per cent and PI of 4to 6 per cent. The moisture content slightly higher

than the optimum was added and whole mass wascompacted to 100 per cent of Proctor density by a8-10 tonne roller. The surface was finished toproper grade and profile. For comparison purposes,on three sections only local soil was used as basecourse.

4.5 Construction of Surface Course4.5.1 For surface couse 16 sections wereconstructed with mechanically stabilized soil withcement, lime and lime/molasses mix. One sectionwas laid with local soil and in two sections brickballast grafting was done over the compacted layer

of local soil. In remaining two sections the stonegrafting was done over the mechanically stabilizedsoil.

4.5.2 Mechanically stabilized soil with brickaggregates. In the construction of mechanicallystabilized soil (graded soil) with brick aggregates,the plasticity index was controlled to 9 to 12 percent and the proportion of brick aggregates was


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approach road to village Rajokri connecting Delhi-Gurgaon road Fig. 1 gives the details of differentspecifications each about 120 m long. The effect ofbinder such as cement, lime and molasses eithersingly or in combination in varying degree ofconcentration was studied. The effect of brick or

stone

controlled to 35 per cent by weight of total mix. Onthe prepared base a layer of mechanicallystabilized soil was placed and brick aggregates of30-40 mm size were added. The resulting mix wasspaded, mixed, watered, wet mixed and compactedto Proctor density. The soil subilized layers are

prone to damage by abrasion action by the traffic.For the prevention of this phenomenon the Mehrasmethod stipulates that the wearing course shouldbe covered with thin premix carpet to protect it fromabrasion by bullock cart traffic as well as frominfiltration of rain water from top.

4.5.3 Mechanically stabilized soil with brickaggregates and stone grafting. On the preparedbase the stabilized soil mix with brick aggregateswas spread loose to proper grade and profile. Thestone aggregates of 25 mm size were spread tosingle layer thickness uniformly at the rate of 0.20to 0.23 cu.m per 10 sq. m. The layer of stabilizedsoil along with superimposed layer of stone graftingwas rolled. For effective grafting relatively lightrolling was done on the first day. The hungry spotswere made up with 25 mm aggregates and waterwas sprinkled on the surface. The rolling wasresumed on the following day for proper

embedment of stone layer.4.5.4 Cement stabilized soil: The soil wasexcavated from borrow pits and was pulverized.Clay was added to control the plasticity to 9 to 12.The graded soil was stabilized with cement contentof 2.5 per cent and 5 per cent by weight of soil. Forone cu. M. of soil 75 kg cement was added to makeup the cement content to 5 per cent. The mix wasbrought to proper moisture content. The mix wasbrought to proper moisture content. The materialwas spread on the prepared base and the laidmaterial was remixed by a rotavator till uniform

distribution of cement was obtained. The wholemass was compacted by a 8-10 tonne roller to finalfinish. The surface was cured for 2-3 days bysprinkling water over the surface.

4.5.5 Lime/molasses stabilization: Molasses is abye-product of sugar industry. For preparing themix the pulverized soil with sand was spread on thebase. The lime and molasses were added in

and grated with stone aggregates and local soilgrafted on the top with brick aggregates. The cut-back treatment was given on four sections andremaining eight sections were given primertreatment. On two sections one half was treatedwith cut-back and the other half was primed. Thecut-back sections were covered with a coarse sandamuna sand and roiled where as in primed sectionswhere the primer was not completely absorbedwere sanded lightly the following day.5.2.2 Both primer and cut-backs were applied byperforated tins. The primer was applied at the rateof 7-10 kg per 10 sq. metre area and was allowedto cure for 24 hours before opening the road totraffic. The cut-back bitumen was applied at therate of 10-12 kg per 10 sq. metre area. The surfacewas immediately covered with either coarseBadarpur sand or river Jammuna sand at the rateof 0.06-0.09 cu. M. per 10 sq. m area and rolled tofinal finish. The traffic was allowed as soon as thebinder attained the ambient temperature.

6 Performance Evaluation6.1 For performance evaluation the road sectionswere inspected occasionally and performance of

each section was monitored visually. In the firstnine months the performance of primed sectionsand sections covered with surface dressing withcut-backs were superior to section left uncovered.The addition of small added advantage, ratherdeformation on these sections was more than onsections with cement. The sections was more thanon sections with cement. The sections treated withline molasses gave good performance. During rainy


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different combinations of 1 to 5 per cent for limeand 1.5 per cent to 5 per cent for molasses. Overthe graded soil the lime was added and mixed witha rotavator. After through mixing the molasses wasadded and mixed with a rotavator to ensure uniformdispersion of molasses. After adjusting the moisture

content the laid material was compacted and rolledto compacted thickness of 7.5 cm. With limemolasses stabilization five sections were laid.

5 Preparation of Cut-Back/Primer5.1 The cut-backs and primers were prepared atsite. Bitumen 80/100 was heated in a tar boiler.When bitumen attained a temperature of 100C, therequired quantity of furnace oil was added andwhole mass was stirred by a wooden rod for 20-30minutes till a uniform homogeneous mix wasobtained. After through mixing the kerosene wasadded and stirred for another half an hour for

uniformity. Similar procedure was adopted for thepreparation of primers.

Construction of Bituminous Surfacings Thebituminous treatment was given over 12specifications consisting of graded soil with brickaggregates, graded soil with cement and brickaggregates, graded soil with brick aggregates

season these sections gave some rutting markswhich were ironed out during dry weather. Theperformance of the sections with stone grafting wasbetter then those having no stone grafting.

6.2 After one and half years of service most of the

sections showed signs of distress in varying degreeexcept sections 17 and 18 constructed with stonegrafting and covered with primer and surfacedressing. The sections covered with primer showedmore abrasion 2,4,5,8,14,15,16,17 and 20 thanthose constructed with surface dressing 3,7 and 18.Among the section which stood without bituminoustreatment was with 2.5 per cent lime and 5 per centmolasses. In general the behaviour of cut-back wasbetter than primer. The role of primer was only tosuppress the dust but the cut-back treatment gavean added advantage of carrying the traffic withoutmuch abrasion. Among the two cut-back the cut-

back with 20% furnace oil behaved better than theone with 15 per cent furnace oil. Similarly theprimer with furnace oil gave better performancethan with diesel oil although the overall bitumencontent in both of them was almost the same.

Cost Analysis7.1 The cut-back and primer treatments work out cheaper than conventional premix carpet with seal coat

generally recommended for soil stabilized roads. The cut-back treatment cost works out approximatelyhalf of the premix carpet whereas the cost of primer treatment is only one third of the premix carpet.

Conclusions8.1 The durability of soil stabilized roads can be enhanced by applying water-proofing treatments with aprimer or cut-back.

8.2 The application of primer helps only to the extent of filling up of the surface voids and suppression ofdust. It does not prevent abrasion.

8.3 A light application of suitably designed cut-back and flushed with coarse send prevents abrasion aswell as helps in carrying the bullock cart traffic effectively.

8.4 The additional cost of primer or cut-back treatment is off-set by enhanced life of the stabilized soilroad pavements.

8.5 The rural roads constructed with stabilized soil should be covered with primer. The traffic should beallowed till the weather is dry.

8.6 Before the on-set of monsoon the road surface should be covered with a suitably designed cut-backand flushed with coarse sand or fine grit. This treatment will carry a traffic intensity of upto 45 vehicles perday.


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8.7 When traffic intensity goes above 45 vehicles a day, the road should be given a treatment of premixwith seal coat.

AcknowledgementsThe authors wish to thank Dr. M. P. Dhir, the Director, Central Road Research Institute, New Delhi for hiskind permission to publish this paper. They are also greateful to Shri Y. C. Gokhale, Deputy Director and

Head of Flexible Pavements Division for reviewing the paper and offering valuable suggestions.

References

1. Mehra S.R. Cheap all weather roads from soil and soft aggregates Fourth InternationalConference on Soil Mehcanics and Foundation Engineering, London, August 1957.

2. Bhatia H. S. Cement stabilized base in highway Construction Indian Concrete Journal Vol. XXX-10. 1957.

3. Mehra S. R. And Chaddha L.R. Use of line in soil stabilization Indian Roads Congress Gol. XIV-3, 1995.

4. Dogra R N and Uppal I S Stabilization of soil with molasses and lime Indian National Society ofSoil Mechanics and Foundation Engineering, No. 5, June 1959.

5. Mohan Rao Design of Roads for bullock cart traffic Road Research Bulletin No. 6, Indian Roads

Congress, New Delhi-1959.

Cheap Flexible Waterproofing Treatments for Rural Roads

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