Pervious Concrete Pavement Strength-Marks

8/18/2019 Pervious Concrete Pavement Strength-Marks

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Design of Pervious Portland Cement Concrete Pavement – How important is Strength?

By Andrew E. Marks, PE

Managing Director, Puget Sound Concrete Specification Council; 2222 !

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A#e. S., Des Moines,$A %&'%&; P"one 2( (%) *%!; e+ail andrew.+arksco+cast.net

Abstract

-"is article ea+ines t"e relati#e i+portance of /uantifying co+pressi#e and fleural strengt"s

in t"e construction and structural design of per#ious pa#e+ents. -"e "ypot"esis put forward is

t"at conser#ati#e design procedure is cost effecti#e and relia0le wit"out strengt" data as a controlor acceptance para+eter, and ad#ocates use of AC1 (22 specification.

Paper

Per#ious Portland Ce+ent Concrete per#ious concrete3 pa#e+ent presents uni/ue c"allenges for

t"e pa#e+ent designer. -"ere are yet no appro#ed AS-M procedures for /uantifying strengt"

c"aracteristics of per#ious concrete. 1f t"e designer desires to 4ignore5 t"at fact, as +anydesigners atte+pt to do, and apply con#entional strengt" +easure+ent procedures to per#ious

concrete as a control or acceptance test, t"ere are also no #alues put forward against w"ic" to

co+pare or e#aluate t"e +aterial. -"is situation presents a 0arrier to greater acceptance and useof per#ious concrete as a +ain strea+ pa#e+ent +aterial of c"oice.

1n t"e de#elop+ent of t"is article, t"ere are so+e funda+ental facts and assu+ptions identifiedw"ic" for+ t"e 0asis of 0ot" o0ser#ations and t"e proposed procedure reco++ended "erein.

A+ong t"ose are t"e following6

'. -"e function of a pa#e+ent is to distri0ute an applied load o#er an area sufficient to pre#ent failure of t"e underlying soil.

2. -"e utility of a rigid concrete3 pa#e+ent is to ac"ie#e t"is function wit"in t"e structure

of t"e pa#e+ent itself, wit" little or no 0enefit deri#ed fro+ en"anced 0ase layers, and todo so o#er t"e entire design life wit"out 0enefit of structural +odification o#erlays,

sealcoats, etc.3

. 7igid pa#e+ents fail in one or 0ot" of two +odes6a. 8atigue 9 fatigue is t"e progressi#e, locali:ed, and per+anent structural da+age

t"at occurs w"en a +aterial is su0ected to cyclic strains at no+inal stresses t"at

"a#e +ai+u+ #alues less t"an t"e static yield strengt" of t"e +aterial. 0. Erosion 9 Erosion da+age in pa#e+ents is t"e loss of su0grade support caused 0y

t"e +o#e+ent of discrete sla0s effecting t"e +o#e+ent of water, causing

+o0ili:ation and loss of fine grained +aterials in t"e :one i++ediately 0eneat"

t"e sla0. -"ree necessary co+ponents of erosion da+age are +o#e+ent of t"esla0, water in t"e :one 0eneat" t"e sla0, and an erodi0le su0strate.

c. -"e design para+eter t"at c"anges as load and su0grade /uality assu+ptions #ary

is t"ickness.

mailto:[email protected]:[email protected]


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design li#es and design loadings. -"is is a result of t"e fact t"at low cost re+edial strategies for

failed concrete pa#e+ents do not eist. 1f a rigid pa#e+ent fails, t"e likely outco+e is t"at it will

0e re+o#ed and replaced. During construction of utilities, lane additions, and ot"er proectsw"ic" allow us to o0ser#e current loading and actual t"icknesses of old concrete pa#e+ents, we

find al+ost wit"out eception t"at concrete pa#e+ents continue to function a0o#e epectation

well 0eyond t"eir anticipated design life, and also 0eyond w"at pa#e+ent design procedureswould lead us to epect. -"ese o0ser#ations illustrate t"at rigid pa#e+ent design procedures in

place today are conser#ati#e. As an ea+ple, t"e StreetPa#e software, w"ic" uses t"e algorit"+s

fro+ PCA@s PCAPA? progra+ copyrig"ted in '%&(, defaults to an &( pro0a0ility, w"ic" is tosay t"at under t"e defined conditions, t"e pa#e+ent can 0e epected to last 0eyond its design life

&( of t"e ti+e.

-"e "ypot"esis ea+ined in t"is discussion is t"at conser#ati#e design procedure is cost effecti#eand relia0le wit"out strengt" data as a control or acceptance para+eter for t"e design of per#ious

pa#e+ent structures. ne additional fact fa#ors t"is "ypot"esis. $e know t"at t"e strengt" of

t"e pa#e+ent section is proportionate to t"e s/uare of t"e section t"ickness, 0ut is linear wit"

respect to t"e strengt" of t"e +aterial. -"e result is t"at a large c"ange in +aterials strengt" can 0e offset or co+pensated 0y a relati#ely s+all c"ange in t"ickness.

$"en we ea+ine per#ious pa#e+ents constructed in t"e region, we find t"at t"ese pa#e+ents

"a#e e"i0ited structural ade/uacy under anticipated loading, and under etre+e loading. -"ese

o0ser#ations "a#e 0een +ade on well constructed pa#e+ents as well as t"ose constructedcontrary to w"at we now 0elie#e to 0e accepta0le procedures. 1n addition, we "a#e anecdotal

e#idence of poorly and inconsistently consolidated pa#e+ents t"at "a#e 0een ground to restore

surface integrity, t"us reducing t"e net section dept", yet carrying truck loadings in ecess of

design ale weig"ts wit"out structural failure. As stated earlier, t"is speaks not only to t"estructural integrity of per#ious concrete as a pa#ing +aterial; it also speaks to t"e conser#ati#e

nature of rigid pa#e+ent design procedures.

StreetPa#e is a software produced and distri0uted 0y t"e A+erican Concrete Pa#e+ent

Association ACPA3. -"ere are a nu+0er of pieces of software t"at will c"aracteri:e rigid

pa#e+ents, and w"ic" also +ay 0e ade/uately applied. 1 a+ fa+iliar wit" StreetPa#e and itsantecedent progra+, PCAPA?, w"ic" 1 "a#e found t"at to 0e accurate and conser#ati#e. 1t "as

t"e c"aracteristic of 0eing a0le to perfor+ calculations using lower M7 #alues anticipated wit"

per#ious concrete to design rigid pa#e+ent t"icknesses. 1 feel co+forta0le reco++ending its

use, and StreetPa#e is w"at 1 use to design per#ious pa#e+ent t"icknesses, and is also w"at 1"a#e used to generate t"e #alues referenced in t"is discussion.

-o use StreetPa#e, 1 +ake t"e following general assu+ptions6

• MAA-


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• M7 !( 9 t"is is lower t"an +easured #alues, and conser#ati#e.

• E 2.( +illion calculated 0ased on M73

• o dowels

$"en per#ious concrete designs 0ased on t"ese #alues are co+pared to designs for con#entional

concrete pa#e+ents under t"e sa+e traffic, we o0ser#e t"ickness reco++endations typically int"e range of '5 to 'F'=25 t"icker t"an for con#entional pa#e+ents. 0ser#ations of perfor+anceof t"ese per#ious pa#e+ents designed under t"ese para+eters in use today recogni:ing t"at

t"ere is a li+ited perfor+ance "istory on w"ic" to co+pare3, confir+ t"at t"ese pa#e+ents are

perfor+ing, and do not e"i0it early distress associated wit" structural co+pro+ise. $e "a#e"ad t"e opportunity to o0ser#e pa#e+ents t"at were intentionally or unintentionally constructed

t"inner t"an design t"at "a#e recei#ed "ea#ier t"an anticipated loading trucks, construction

traffic3 and "a#e also o0ser#ed no early structural failures.

-"e assu+ption of M7 !( psi is a critical assu+ption. Alt"oug" it is recogni:ed t"at t"ere are

no accepted AS-M procedures to c"aracteri:e t"e fleural strengt" of per#ious concrete, t"ere

"a#e 0een 0ea+s +olded and 0roken using con#entional concrete procedures. 1 do not "a#eaccess to la0oratory data, and lack t"e a0ility to create +y own, so 1 "a#e soug"t out t"is data

fro+ sources t"at 1 0elie#e to 0e credi0le, including ACPA. 1 "a#e found, and 0een told t"at t"e

#alues of +odulus of rupture fleural strengt"3 on co+petent per#ious concrete speci+ensper+ea0ility@s fro+ 2)) to ',))) in="r3 in t"e Puget Sound area range fro+ t"e lowF to +idF


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ne of t"e attri0utes of per#ious concrete construction is t"at t"e use of +ec"anical +et"ods to

consolidate t"e concrete gi#es t"e inspector t"e a0ility to see w"at t"e finis"ed product will looklike and "ow it will likely perfor+, at t"e ti+e of construction. Per 7MCA per#ious contractor

certification and AC1 (22, any concrete of /uestiona0le /uality s"ould 0e corrected at t"e ti+e of

construction. -"us t"ere is little reason t"at inco+petent +aterial s"ould 0e placed. 1t "as 0eeno0ser#ed t"at concrete w"ic" is insufficiently co+pacted, or allowed to dry is readily apparent on

#isual o0ser#ation. Gikewise, concrete t"at is plugged, and of low per+ea0ility due to

construction is also readily apparent, and su0ect to correction at t"e ti+e of construction. 8ro+t"is, it follows t"at co+petent concrete is +ore t"an an assu+ption F co+petency can 0e #erified

0y #isual o0ser#ation of construction, and ensured 0y ad"erence to accepted construction and

/uality assurance procedures.

-"e goal of a per#ious pa#e+ent and t"e nature of a per#ious concrete construction +aterial

dictate a different approac" t"an co++only applied for con#entional Portland ce+ent concrete in

structural or pa#ing applications. -"e designer is una0le to test for strengt" perfor+ance of t"e

ready +ied concrete +aterials 0eing placed. He can, "owe#er, ensure t"at specifiedconstruction procedures are ad"ered to. He can ensure t"at +i design su0+ittal para+eters are

likewise +et. He can perfor+ critical o0ser#ations during construction. He can use engineering udg+ent. -"ere are ways to create a per#ious pa#e+ent w"ic" +eets t"e necessary criterion of

passing stor+ water w"ile also +eeting t"e necessary criterion of carrying load wit"out

co+pro+ising eit"er attri0ute. $"en typical acceptance test procedures are followed in t"edesign and construction of per#ious concrete pa#e+ents, it is o0ser#ed t"at t"e +easure+ent of

strengt" acceptance criteria o#errides, and results in lower per+ea0ility, and t"e desira0le

attri0ute, porosity, is lost. 1n order to +eet 0ot" criteria, t"e pa#e+ent attri0utes +ust 0e

designed conser#ati#ely and construction +et"ods followed.

-"is lesson "as 0een learned on ot"er lowFstrengt" and=or low ce+ent content applications using

Portland ce+ent. 8or Ea+ple, strengt" of ce+ent treated roadway 0ase C-B3 or soil ce+ent#aries widely, and it "as 0een found t"at perfor+ance issues arise w"en strengt" is too great.

Control of soil ce+ent or C-B is 0y #erification of ce+ent content, and field co+paction relati#e

to la0oratory tests. Control of per#ious concrete, per AC1 (22, is 0y #oids of plastic concrete,t"ickness and unit weig"t, w"ic" in co+0ination will result in /uality per#ious concrete

pa#e+ents.

-"e conse/uences of not +eeting +ini+u+ strengt"s of con#entional concrete in a 0uildingstructure, 0ridge or e#en "ig"way pa#e+ent can 0e large; t"e conse/uences of not +eeting

strengt" in a low speed pa#e+ent t"at is intentionally o#erdesigned to acco++odate strengt"

#ariance is low. $"ile t"is approac" to design of per#ious pa#e+ents is re+arka0le in its lack of sop"istication, it is elegant in its si+plicity, yet still returns econo+ical, costFeffecti#e

t"icknesses. 1t gi#es t"e designer freedo+ to acco++odate a wide range of perfor+ance and

construction conditions, and still "a#e a "ig" confidence inter#al for s"ort and long ter+ perfor+ance of t"e pa#e+ent structure.

nce t"e per#ious pa#e+ent structure is designed and decided, t"e "ydrologic re/uire+ents of

t"e proect can t"en 0e acco++odated using t"e #oid syste+ of t"e per#ious pa#e+ent and 0ase


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as storage #olu+e, and a greatly increased soil interface area as infiltration 4trenc"5, at t"e

designer@s election. -"e surface area of t"e pa#ed area creates a great storage #olu+e in a

relati#ely t"in section, and t"e large soil interface surface +akes soils of e#en low per+ea0ilitysignificant in ter+s of net infiltration #olu+e during a stor+ or runoff e#ent. >se of per#ious

pa#e+ents not only replicates a preFde#elop+ent condition, it affords t"e designer great latitude

in selection of stor+water solutions. >se of per#ious concrete affords t"e "ig" confidenceinter#al of #ery conser#ati#e design assu+ptions, and a construction +et"od t"at +akes

#erification of long ter+ perfor+ance +ore apparent t"an for con#entional concrete place+ent

+et"ods, and does so cost effecti#ely. 1nstallations in t"e Ireater Seattle and Puget Sound area"a#e confir+ed t"is approac" and t"ese assu+ptions.

Documents

Pervious Concrete Pavement Strength-Marks