a paradigm shift on permeability of thin asphalt evaluation by means of averages, mean or median can

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  • A PARADIGM SHIFT ON PERMEABILITY OF THIN ASPHALT SURFACINGS Presenter: Dr Emile Horak

    co-authors Wim Hofsink, Herman Marais, Joanne Muller and Ane’ Cromhout

  • Paradigm: The concept and meaning

    Thinking patterns, rules to look at the world, data, information, skewed by confirmation and hindsight biases

    Kuhn (1962)- biases in scientific research

  • Pervasive nature of paradigms

    Rules, standards, guidelines, culture, religion, how we look at information

  • Rules can make us blind to all available information

    The thinking rule : “If it is not square,… it is not there! …” It is round, does

    not fit the rule. Result: It is

    subconsciously ignored.

    We literally become ignorant

    to this

  • Paradigm shift is often to look at all the information or from a different perspective : It exposes our ignorance!

  • Our ignorance are forced to be challenged- versus previously just confirmation what we already know!

    Agnotology: The study field of ignorance or doubt, particularly the publication of inaccurate or misleading scientific data.

    The study of culturally induced ignorance or doubt. Robert N Proctor and Londa Schiebinger

    https://www.yourdictionary.com/ignorance

  • Agnotology is in the other direction of “knowledge” …Agnotology, the study of ignorance. Agnotology is seldom discussed, because studying the absence of something — in this case knowledge — is incredibly difficult.

    Epistemology, or the study of knowledge. This field helps define what we know and why we know it. (Confirmation and hindsight biases)

    The difficulty of studying something we don’t know

    ResearchSearch

    http://www.sup.org/books/title/?id=11232 http://www.iep.utm.edu/epistemo/

  • Ignorance is bliss! Modern effect of the internet! Everyone is an instant expert!

    The ten thousand hour rule applies: Gladwell

    Do not express this image in the Afrikaans language!

  • Broad based information gathering • As-built information • Quality control and quality assurance information • Surveys (eg visual, rutting, Falling Weight

    Deflectometer (FWD), riding quality, macro texture, Dynamic Cone Penetrometer (DCP)

    • Ground Penetration Radar (GPR) • Test pits and material sampling • Laboratory tests

    Climbing the slope of enlightenment: FORENSIC INVESTIGATIONS

  • More detailed and specialised investigation phase • X-Ray Diffraction (XRD), or X-Ray Florescence (XRF), • Bending Beam Rheometer (BBR), • Multiple Stress Creep Recovery (MSCR) Test, • Dynamic Shear Rheometer (DSR), • Multiple-Stress Creep-Recovery (MSCR) test, • Asphalt Mix Performance Test (AMPT), • Computed Thomography (CT) scans and modelling, etc

    Climbing the slope of enlightenment: FORENSIC INVESTIGATIONS

  • Reason’s “Swiss cheese” model -distress development – multiple factors contribution on a random basis

    Other holes due to latent conditions

    Some holes due to normal variation

    Distress Development in a road is

    never just a single factor. The complexity can lead to confusion! Fact and fiction must be separated

    Layers of cheese slices - random outlier type defects - the holes through which effects can permeate to the next ‘cheese’ layer

  • Water from the top as main cause of distress

    Distress observation on surface therefore misleading

    Open surface allowing water into asphalt and lower layers

    Horizontal permeability being higher than vertical

    Water entering base at weak spot away from original surface entrance

    Distress development in base and away from original water entrance

    Distress development – often due to the confusing contribution of the whole pavement system

  • The density precipice

    0

    10 0

    20 0

    30 0

    40 0

    50 0

    60 0

    70 0

    80 0

    90 0

    10 00

    De ns

    ity %

    te r p

    er m

    ea bi

    lit y

    (l/

    hr /m

    2 )

    89 90 91 92 93 94 95 96 97 0

    100

    200

    300

    400

    500

    Density %

    Water permeability (l/hr/m2)

    The proverbial edge of the cliff

    Typical correlation of density of asphalt versus measured permeability

    PERMEABILITY OF THIN ASPHALT LAYERS

  • McDaniel R (2019) Through thick and thin. Asphalt Pavement Magazine Volume 24,

    PERMEABILITY OF THIN ASPHALT LAYERS

    Typical HMA zone where

    permeability may increase exponentially

    Permeability is the flow of water through interconnect ed voids

    Variability due to: Influence of stone size on voids and therefore permeability

  • 0

    0.2

    0.4

    0.6

    0.8

    1

    2.5 3.5 4.5 5.5 6.5 7.5 Voids in the Mix (%)

    Probability Density Functions Voids in the Mix

    90th percentile Project B 6.65

    90th percentile Project A 4.86

    Median Project A 4.33

    Median Project B 5.53

    Voids specification 3% to 6%

    Cromhout et al CAPSA 2019

    Variability in the air voids demonstrated with Probability Density Functions (PDFn)

    PERMEABILITY OF THIN ASPHALT LAYERS

    Evaluation by means of

    averages, mean or median can be totally misleading regarding actual

    variability

  • a) Micro cracks during paving operation

    WAYS THAT WATER ENTER THE ASPHALT SURFACING

    Shear cracks - compaction rolling . Become visible only after rain. Fines pumped to line the lips of the transverse fine cracks

  • b) Rolled in chips (RIC) provides openings in asphalt layers

    WAYS THAT WATER ENTER THE ASPHALT SURFACING

    Side view Top view

  • Cracked or crushed RiC can cause a dramatic increase in surface permeability

    WAYS THAT WATER ENTER THE ASPHALT SURFACING

    (Grobbelaar, 2014)

  • Once the water is inside it will go sideways! Water appearing away from Marvil

    indicating horizontal flow in the asphalt layer.

    The Marvil has several short comings and should be improved to allow better

    permeability measurement of either vertical or horizontal flow

    Maree and Viljoen (1983) MARVIL criteria for bases and surfacings

    Layer Percentile permeability limits (l/hr)

    Mod-dry regions

    Wet regions

    Surfacings

  • Horizontal =up to 10 times vertical permeability

    The Marvil test in ‘no man’s land’ Therefore more prone to measure horizontal permeability !

    Diameter of Marvil is 175mm

    Work done by Harris: Based on approximately 180mm thickness of asphalt. Indications that thinner asphalt layers may be more permeable horizontally than vertically

    Horizontal flow

    Vertical flow

  • Permeability measurement

    Vertical permeability - not done regularly, horizontal virtually never

  • Permeability predictions using permeability equations and Rational Bailey Method Ratios can help benchmark asphalt mixes permeability propensity

    𝒌𝒌 = 𝟒𝟒𝟒𝟒 𝟏𝟏𝟏𝟏𝟏𝟏

    𝟐𝟐 𝟑𝟑 ∗ 𝑨𝑨𝑨𝑨 𝟏𝟏𝟏𝟏𝟏𝟏

    ∗ 𝐷𝐷75 3.70

    k= coefficient of permeability(mm/s) AV = total air voids (%) D75= Sieve size through which 75% of the aggregate is passing (mm)

    Improved air void and flow path simulation method , Vardanega and Waters (2011)

  • Summary and conclusions

    • Collective experience regarding permeability have characteristics of a paradigm shift. Implying a new look at existing information

    • It is recognized as significant as experience shows that asphalt surfacings fail due to the outliers and not the average values

  • Summary and conclusions (Cont) • Statistical procedures should therefore be re-

    examined to reflect the probability density function of as built results to give a better appreciation of variability outside the specified ranges.

    • Permeability is a measure of the interconnectedness of voids. Therefore the need for accurate determination of voids in the laboratory is recognized. –CoreLok method

  • Summary and conclusions (Cont)

    • Construction and mix design factors may contribute significantly towards vertical permeability of asphalt layers. Micro-cracks (rolling technique or cold compaction) and the continued use of Rolled in Chips (RIC)

    • It is recommended that various obvious alternatives to RIC be considered and evaluated.

  • Summary and conclusions (Cont)

    • Recognition that horizontal permeability in asphalt layers is between 3 to 10 times higher than vertical permeability

    • Vertical and horizontal permeability are seldom measured separately in the laboratory.

  • Summary and conclusions (Cont)

    • The Marvil field permeameter- prone to tester capability - may actually measure horizontal permeability more than vertical permeability (diameter size)

    • Improvements needed for better field permeameter as well as laboratory permeameters to measure both