A Open Discussion on IRC 37_SG

8/18/2019 A Open Discussion on IRC 37_SG

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Sanjay Garg, SE(B)-S&R 1

A open discussion

on

IRC:37-2012By

Sanjay Garg

S.E(B), MORT&H


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Characterization of Materials

For a successful and effective pavementdesign, characterization should be based on

material properties that accurately capture the

material response which influenced by

construction quality, applied traffic loading andenvironmental conditions varies over design life.

At present, no such consideration in material

characterization is taken care of.


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• What is the correct modulus for the

different materials?• Is computation of effective subgrade

strength based on empirical procedure is

justified and in order?

• How E-value is same for DBM and BC?

• What is the validity of table 7.1 in IRC 37?

• Why effect of environmental influences on

material properties is not considered?


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Mathematical Modeling

• Details of mathematical modeling need tobe furnished. It need to be refined after

considering adequate nos. of

layers/sublayers as per their damagemechanics and behaviour under loading.


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Characterization of Traffic

•Axle load spectra approach need to beadopted after considering axle multiplicity,

change in axle loading and configurations;

change in tire type and tire pressure; and change

in pavement failure modes.

• Lateral traffic wander effect need to be

considered.


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Location of critical pavement responses

•Currently - 2 locations - directly beneath thecenter of the tire and at the centre of dual tire for

a single axle with dual tires.

• To evaluate the maximum principal (design)

strains/stress under single or multi-axle

loadings, pavement response should be evaluated

at several locations and corresponding pavement

damages (distresses) will be calculated for eachlocation. Location of maximum damage will be

the critical location and should be made part of

design process.


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Distress Prediction & Failure Criterion

•Flexibility to choose a failure criteriashould be given,

• Rutting in bituminous layers as well as in

base/sub-base layers need to be taken,• Top-down fatigue (longitudinal) cracking and

thermal fatigue (transverse) cracking will also

be considered in design process.

• Functional distresses like surface roughness

and friction may also be included as failure

criterion.


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Transfer functions

•Transfer functions need to redefined as percurrent practices of materials and their quality,

varied conditions of traffic, climate, mix designs,

pavement constructions, reliability and

maintenance practices etc. as per actual field

conditions found in India.

• Calibration is also essential.

• Weakest part of entire design process.


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Reliability concept

•Reliability concept need to defined properly afteraccounting adequately for traffic prediction,

material characterization and behavior modeling,

environmental conditions, construction quality,

and maintenance practices etc.

• It is kept as an input variable in order to have a

choice for the desired degree of certainty into the

design process and to ensure that the variousdesign alternatives will survive for the analysis

period without reaching to unacceptable condition

of pavement performance.


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Incremental DamageAccumulation Procedure

• Accumulation of damage as a function of

time, traffic and climate need to be

defined properly after accounting properly

the changes in all input data occurring

over the design period.


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Pavement Performance & its Prediction

• Pavement Performance in terms of functionalperformance, structural performance, and

safety need to defined and should be made

part of design process.


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Design Period

• Why only 15 years or 20 years?


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Thickness & Gradation of GSB

•

Cl. 7.2.1.3 - composed of two layers -separation/filter (lower) layer and drainage layer,

• What are the minimum thickness of these two

layers for satisfying their intended purposes?

• Drainage layer – cl. 11.8/Annex-V of IRC:37 &

Ministry’s “Specifications for Roads and Bridges

(2013))” .

• Gradation of both layers.


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Stabilised base and sub-base layer

• Reference to relevant IRC codes fordesigning/constructing the respective

bound sub-base and base layer should be

specified in IRC:37 as there is lot ofconfusion among the use of IRC:60,

IRC:74, IRC:88, IRC:SP:89 and

IRC:SP:49.


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Design with stabilized base course

• Pavement design with stabilized basecourse along with material properties,

failure criterion, damage accumlation,

transfer function need to reviewed andrefined in view of changes occurring

AustRoad 2012 & current developments

therein in 2015.


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Mix Design issues

Fatigue resistant and durable bituminous mix

• Adoption of 3% air void may cause failure due to their

tendering nature or rutting. Adoption of bitumen

content in excess of 0.50-0.60% will further aggrieved

the problem.

• For flexible pavements having bituminous layer

thickness more than 200 mm, What are special

requirement for bituminous layers? Desired properties

like NMAS, ratio of fine aggregates to bitumen, layer

thickness, bitumen content, air void, bitumen

modulus, VFB & VMA requirements need to be

mentioned.


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Rutting resistant Mix

•

What is the criterion for governing mix design toobtain a Rutting resistant bituminous layer?

• Mix Design guidelines or manual for dense graded

bituminous layers need to developed for Indian

conditions of traffic and climate.


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Other Bituminous Mix issues

•

If RAP (Recycled asphalt) content is less than15%, then its properties including modulus value

is almost similar to that of neat bituminous mix

and need to be accordingly incorporated in

IRC:37. Further, adoption of a modulus value of

600 MPa for any mix having RAP is too less and

strongly need to be revised in order to evolve an

economical pavement design.


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Other Bituminous Mix issues

•

Para I.2 (page 50) of Annex-I of IRC:37-2012states

“…….unacceptable rutting in the bituminous layer is

observed probably due to use of softer bitumen for

the climate, higher temperatures and heavy axle

loads. This problem is now addressed by the

selection of high viscosity binder for the bituminous

mix in line with the European practice.”

• However, details of high viscosity binder need to

be furnished.


20/25


•

Tack coat with modified bitumen must beprovided at the interface of all bituminous layers

to enhance the interface friction.

• Type, content and relative effectiveness of the

bitumen modifier need to be mentioned so that a

highway engineer may obtain a fatigue resistant

and durable bituminous mix at his site.


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Wearing Surface

•

For regions of truck volumes > 3000 CVPD perdesign lane, a wearing coat having adequate rutting

resistance, durability, impermeability and wear

resistance, like Stone Mastic (Matrix) Asphalt (SMA)

as per IRC:SP:79 should be used. Thickness maybe 50 mm to 100 m. High bitumen content (6-7 %

or more) and low in-place air voids (< 6%) should

be used to ensure mix impermeability and durability

for SMA. Use of BC should be limited for the

highway stretches having truck traffic volumes per

design lane less than 3000 CVPD.


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Design of Perpetual Pavements

•

Design details furnished for the design ofperpetual pavement in IRC:37 are totally wrong

and inadequate. It should be revised thoroughly

either in view of the paper titled as “Perpetual

Flexible Pavements: Pavements of Future”

published in the Journal of the Indian Road

Congress, Vol.73-2, 2012 or else.


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Preventive Maintenance

• A program employing a network level, long term

strategy that enhances functional pavement

performance by using an integrated, cost effective set

of practices that extend pavement life, improve safety

and meet motorist expectations.

• Pavement preservation is applying the right

treatment …at the right time…on the right

pavement in order to provide a sustainable

pavement condition, prolong the life of a pavement,

used funds most efficiently, reduces the frequency of

costly and time consuming rehabilitation/

reconstruction projects and the associated traffic

disruptions.


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Pavement Management System

Need for the development ofcomprehensive pavement management

system to obtain an effective pavement

maintenance approach for ensuringcost optimized pavement performance

and longevity.


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Thanks

Documents

A Open Discussion on IRC 37_SG