El Sayad, H

Northwood, D

Poh, K

Roy, S

Shaaban, IG

University of Liverpool Repository

21st Conference on Our World in 'Concrete & Structures: 2.6· 28 August 1996, Sill8apore Pore Size Distribution of Mortar in Near Surface Concrete Its Measurement and Delineation with Carbonation S K Roy, National University of Singapore, Singapore H El-Sayad, Cairo University,-Egypt I G Shaaban, Zagzin University, Egypt D 0 Northwood, University of Windsor, Canada K B Poh, Public Works Department, Singapore ABSTRACf Ingress of deleterious agents from the environment causes deterioration ofconcrete and loss of its durability. Since the ingress takes place through the surface, characteristics of the near surface concrete has become an important issue in recent years. The permeation characteristics of near surface concrete are greatly responsible for concrete dutability. Tests available for assessment of permeation characteristics such as Initial Surface Absorption, Figg Permeation and Covercrete Absorption arc discussed in the introductory part of this paper. The pore size distribution of the mortar in the near surface concrete is considered an important parameter governing the durability of the concrete. Simultaneous measurement of pore size distribution by mercury porosimetry and carbonation-rate by phenolphthalein test was made on samples exposed outside in the tropical marine environment of Singapore. The carbonation rate is then delineated with pore size distribution. Results of this pore size distribution and carbonation rate measurements in near surface aortars ofseveral concretes are reported in this paper. 1.0 	 INTRODUCTION 1.1 	 GENERAL The deterioration of concrete usually involves movement of aggressive gases and/or liquids from the surrounding environment into concrete, followed by physical andlor chemical actions within its internal structure possibly leading to irreversible damage (Basheer et al. 1993). Hence, the surface and near surf~ce permeation characteristics, rather than the mechanical properties are the important factors for concrete durability . The permeatH3n characteristics can be assessed using tests such as Initial Surface Absorption (ISA T) (Levitt, 1969), Figg Permeation Methods (Figg, 1972) and Cover concrete (Covercrete) Absorption test (CAT) (Ohir, 1987). . Dhir et al (1989) showed that the potential depth of carbonation may be predicted from the Figg Air Index. Moreover, Dhir et al (1991) demonstrated that even mechanical properties such as the abrasion resistance of concrete correlated to the ISAT ·results as both tests assess the quality of cover concrete. 1.2 	 INITIAL SURFACE AI3S0RPTION TEST (IS AT) ISAT was developed by Levitt (1969) as a quality control test for precast concrete tiles and kerbs. It is described in detail in BS 1881': Part 5: 1970. The revised version issued in 1983 (BS 1881: Part 122) has only minor changes. The ISA T apparatus is shown in figure I. It consists of a U-tube type structure with an opening at the bottom in the form of a circular cap (diameter 90mm) with surface area greater than 5000 mm2• The cap is capable of being sealed to the concrete surface to withstand a small pressure of 202 N/m1 (200mm head of water) by means of a clamp. Chan (1986) modified the ISAT apparatus to make it more compact, portable and easier to use. Ohir et a! (1987) used a 'model air craft engine elastic' similar to an elastic band to provide better seal for the cap on the concrete surface. The ISAT cap was further modified by Byars (1991) by introducing a slope to the roof in order to flush the air bubbles rapidly prior to testing. One of the open ends of the U-tube is fitted with a reservoir which can be isolated from the system. The other is attached to a calibrated capillary tube supported horizontally by a frame 200mm above the concrete surface. The system is filled with water expelling any air bubbles. The amount of water absorbed by the concrete surface per minute (ISA value) is measured at 10, 30,60 and 120 minutes. 1.3 	 FIGG AIR PERMEATION INDEX (API) Figg (1973) described the development of a test for air and water permeability of the cover concrete. Cather et al (1984) modified the test technique in order to make it more applicable on site. Dhir et al (1987) reported a problem in using the Figg water test due to possi.ble inconsistency in the manual injection of wate~ in concrete . .It was concluded that the test is unreliable. In the same publication, the Figg Air Test was modified to give more repeatable results. In the API test apparatus a hole of 0 30 x 50 mm is drilled in the concrete surface. A polythene disc bridge and silicon rubber are inserted to block off the top 20 mm of the hole. During the test air is evacuated from the test cavity using a hypodermic needle connected to a hand vacuum pump (55 KPA below atmospheric pressure). The elapsed time for the pressure to . increase from 55 to 45 KPA below atmospheric pressure is considered an index of the air permeability of concrete. 1.4 	 COYER CONCRETE "COYERCRETE" ABSORPTION TEST (CAT) Ohir et al (1987) developed CAT in order to test the first 50 mm of the concrete cover to the reinforcement. A hole similar to that drilled in the API is used. A basic ISA T set-up is used but with a 13 mm internal diameter cap. An inlet tube located inside the sealed hole is used to supply water to the hole as shown in figure 2. The procedure for CAT is similar to that for ISAT. 1.5 	 APPLICATION OF THE PREMEATION TESTS IN SITU The effect of the moisture content of concrete on the permeation test results is considerable. For example a concrete sample with a strength ·of 30 N/mm2 when tested after water soaking for 2 days gave an ISA value of 0.25mllm2/s. This is classified as low sorptivity concrete in accordance with the concrete society recommendations (1986). If, however, the same sample is tested after a long period of air drying, the measured ISA value was 50 mllm2/s which is classified as high sorptivity (Ohir et al 1987). Despite this, there is no standard preconditioning method which is suitable for both laboratory and in situ applications. BS 1881: parts: 1970 recommends two days air drying as a preconditioning method for . in situ concrete. The obvious variations in exposure to sun. wind and rain makes this approach unviable.Ohir et al (1993) presented a technique for preconditioning concrete prior to the application of ISA T. The technique is based on drying the concrete surface by withdrawing moisture using a vacuum pump. The vacuum is applied to a modified ISA T cap containing silica gel granules which tum from pink to blue as the drying process proceeds. After drying is completed, the ISAT may be carried out in situ by fixing the cap to the structural member using suction cups. The measurements must be taken within 1'0 minutes from the release of vacuum pilot. In situ trials have shown that the test procedures reproducibl.e results, is rwn destructive and simple.to operate. Shaaban and EI Sayad (1994) applied the same vacuum technique to precondition samples for the API and CAT tests. It was reported that applyin~the vacuum directly to the hypodermic needle or the cap in Art and CAT respectively, leads to better reproducibility in the results. However, the vacuum technique was 214 I lind to ; sensit h API &,Tth8.1 ISAT. Ie auth( .buted t le natUl e fonne which int drill lies II' :rete "lereror he 1eity 01 vity 111, ;tthe IT ments. Theq\ If near: conere :rs wid th( lded « e in c with )rk) ar mouldl en sur r conci urtaces. 'e Size .tributi f mort near ~ concr· Id the carL ~ ~ -"'!,un UCp..L- -* ....1lt.:: 11lUl"t..l-,f "''1.1\.1 UI\" nft_""i.u....~ ,:)\.'...f'"'~AC" of JS con' expose two y( the tl p.n· .•• _•••.)en! of ____~,- ore afc ~d in tt :r. :RIME ,DETJ Coner' els 'of v grades ast and water :~ :mys. f' leiS we: .\ - expOSf ~ ;-- .:~ years two si :iingap( nely (iftop at : ational UPtu"~1ti v~ ~;,nO'~n~r(. ,., '-J~~,Awhir;~ ..... ;.l'. inlantl ~ .... ,-, .... ~~~tn Anti (ii: lSt Coa which )rderin. e ocear co 	 p8.l1el~ lered 1 5, 8, and 11 posed t: . as( em I where .!Isnum' 3,4,6•. 12 and ire exp( the Nt top. After' :ars eXI the par re retur :.'.: laoOl:.:.::" imu lITe ....L" '.auoll u·,;,·r c -uel1:>ur,-j ?,~ ruU! me '::;)Ulded Lice al e unn. d SUr! The ,,:!p.nolnhc;,~...,l test, .. ed to ,__ T;;ine the ·,·Jnation . de 	 he pher alein (e ~ simpl, 8.l110ng Ite: ,ilable I }SUring lation It als( tmedia: :cation an lIT> n' of tt'ul life 'mainin;' . jsting sLs. Phei 'lalein i,:ourless ac' ,n - e mOrc,'- '--'1lcnlur )le WllC' .L- '}h is a'- .. · - ~ va the raJ 8.4 to at is, \! le con< ~Il__, ••• _. Tril'l r ... _.._.,\hth;][ci ........ t:!);]rl".rl ___ • % ,nlll .._..... "1"10 ethy ."o\. Th, on is sp )nto at· broken rface ",." as been :d of cit loose ( s. The ffii nent is out im ely aftc . roken: ha 1 expo~ (aline ,f conc rning , 'Irple c 11 no ron ocr lrbonat . s t8.lCen I.ace an the dep Ie carb surfaet can be w se loea Jrface ( ~ and tl thod pr or indicati he extc lrbonat iIr piee< extrac . _m the t ions of e2 crete p, porc si 'ibution :rement a ry pOSt :r (Mic tics Po 9320) C( - - (ne pc- ":-'Il<;;l<;;' ,---- ",Ulll ar--''''l1atcIY .,,.,, ..J 0. ,m. It s be cmp ! that it 1ly the Ih__ .. _ used fl_ ,lorosil\ poresiz lsures I IUme d tion oj materi mcrcul sion or tOn. Ivp' P' etry i~ d on .ry lal erning ~netrall small I I IllS la, e ease ( . welting quid Ii 'cury a 'ndrical is exp by the yl~C"hhllJ " l ~., ...111 t".OII',-~~:~ .. ' ,'. VI 	 d valent, er of th ded pOI y __._.u:e.en~._ .. _. merc.l\.~ angl mtact t 1 the n 'and t pore P sure a h a gi increm of :ury inl nto the ystem volum mercur penetT pores a que chization 'e pres~ )ores a :Iy c cal, he! above m cons a speci . leI ,hich rr •.... . best re pores ,al mate Howey,S use i rally at f as the cal me-): . treath· \I herwis d be a I lInplex m. ~~ .L:;:;e:OlUl'i-- '; ":iIll.IplC (- !-. '-Slec IS r-' i: )Ken m: . mailer and th~d in ar for at!4 hoUi 'Nhp.n l'.(.,,,, __ , ,he ~nec,..,';_..•$Ihen n~. ""~ Ihl'! I\I'!I\,--~. v ....,tpr In Iv _ I! into on epressl s. As n ' is nor Ilg t, . mater will n ~trate i pores luI 'Iydrostc.: ssure. Jroperti, ... se a me., urface .ontact solid lme thl".num Ski area 8.1 1: radius 'vature Ie at a pressl \.n il ; in pre In the y shift: al8.l1ce en ~UUUI,;C le::"i,,\: 11I1U :ou:f:;,:·:, ~Fc:u C<:\u~;::g :hc fUOIUS :~f ,'C :-va~ure .-J . he mer .)ntactir: solid tc c :me sma :.Jlhen f : adius i5c to that t rAe entra;,:_~, ;:.ercurv L._ ,il~ vnlnr.,~ v the por JS after ating t1 pIe, pr is a 10 fo[( nercur: .he POf! le sam I he 'olumecury pe.' 19 the p.' 15 measc" irectly ,functil. ::iJp!ied r ':. As tt ';ure inc' mercu If-··.. ~·:: Into sn·_ I1 -- -nd sma"-" . ·'es. ihr 1es are 1 . ier I high! e 10 en: .I intru~ mercur ce f ..._ ... "•• I1c.;inn c ....._ ••1f".rC'.l1ry ..._ ...... ,,~f',n r:.rnl ......"' ......_. thf": r:n_o.I."'........ ic:.: releasee rude th ury frol : lores. The ; tensio e merCI ) taken 85 .nd the cing co ngle is ed to t ,0° lYYjJ. compie the pro le tollo' :u-amet( Nere de' ed: i) .rusion ii) re area ned ian iametel werage liamete . v) It and t lsily IIn Il Its see : prese the n for T..__._.. nore d._..._.J ~.O )ULTS inset Figu shows JIIS oft iandia for 'JOmmc Ulooo a Jlooo Sl l'lgun ;nows' ,espect bo.ti<hs ofb unmOl ayers 2 15 IJmm Fi <).2. Schematic arrangement of CAT 216 median pore diameter m) 60 .-~ 50 40 30 20 10 0 2 :s ' 4 5 10 118 9 Fig.3(a) Median pore diameter vs concrete samples (moulded and unmoulded layers) carbonation depth (rnm) 12r-------~------------------------------------------~ 10 8 6 4 2 O~· ---L---L~~~~--~~~L---L---L-~~~~--J-~~ 1 2 3 4 5 7 12 138  9 10 11 Fig.3(b) Carbonation depth vs concrete samples (moulded and unmoulded l ayers ) 217 lr 1 : the _- sam i, th edia ore I letel Ir th UI ,uld< lffipl with ~er ( )nal :Jepl re gl :r 'Ian t' : Olf' _nou!' . san . s (sn .. ~r ca: laUCl ~ :pm; ~ b~ rl.~_.J_<: !i:hL _... in·tl._ C.vn fi c _ ..'" c:fl •.••• ,'ll th.:....!~ ur.... _)llde'_ rc 1S, \\ : laq _ arbc on C IS w' QUnl lye I :r ore s . 'as WI Figu (a), i n be . 1 tha. : me, par, ai- -- ;ler -.<' "he r:- -"·ucu '-"crs _C 'wu ---l!IC~ ---; ~1I_L"'y I'L_. .:r th:_. __ lat 0 ___ ~ un!._ Idee ers. is co be d 0 -Ie fr 'lhat pore f tht -rboll I CO! te h__ beel rc ed a esul the j latio . son ilciu arbe " ')n UI<'" ...... h~ 1.::-':"":;'\ lUl fl...... II .;:>I.........hJl~:) ... l"''';.l~U)' thA, uu,;.rI;"""" ..,V"~ mou ;:\ COl te is ater I the ulde, Cl 'ete, ; ca m ( onat ,rodl la y arbo,_ ,:d UI o1de., lncr may t be gh t. c; nate, mid, mcn It is j"est l lat a ragr:. c Kam' ,lion dar in I unCI wi the rcur; p' imel ~st tl nfin is h; lIesi At " L ,'en h idity: 'es c. ;pee size fille. W Nate I a c( letel: y co :te II' is nl Iter i e ·.ores '.,.J he!. earb, ,Hox!- :ann ,eact. : a C(.I ete I' p .vate .ffuse )Ugh por 'cae! : cor e be d me ca,latio )nt, ~h~11 ,ct; t lisa slow lceS~ A :esul len I , are satt: d bu ye.0 a la) If ~"r'Vl~,'L!:~ vu thej~ "~n~, ,",u,r\.f~·~ ".uvv~r1p. ~,,,,- f?pn....'-f 0\uu~P, > ."lrout:h me pc; and I t on moi! re W» urfa,- Thi e: .ins por 1:e 0: lrtar near face ,cret n lfltlUC': ,C' carb'H:;ction>,-' :er a en a' "phe' ,;ond::;,l. 4 NCl 101' e SI mt 110rt ot t' :nou" 1 an, e ~gio.n '.ve k-car' "aHor ,'es 0'" : mo .' , :0 ar,,' "le,llI Uloe' ~urfll'__ , '.1fll_,,:i:cr~tl'. ",'::; dif._._n! ~ ... nnuL __ r~{>l_.:~ hllY_ h :r ca latio pths j ;ner ')ona rat' Inert 's as 'ared n I:....,_r nOl_~.ifthl .. _.iliar ._ ..he c,_ .. _:ete 5 'KNI LEI s The l.,_"hon I"ra __ ..J to . _. rnfL __ ,'I C:~--"o Lilt., [ of I :acu ,f Ar eetl: nct r ling NF n .anm,d 0', Ie ~ 101 Buil ar, ::stat 1\1_-'"1gelc-_4- U1. lL- ..... ,(111U-- 1 uri! --:ny (r' C"I'tnga - - -~ lor '"-t_ -'If -:nem .-- .::cmcc • -10 Sl j', -,n RE tEN s eer, A.M lontl cry .. al .ong E." Ie IUtO( pc abili syst for casu th n-sit eati( rope or ( rete- :onf ce P :ectil If 'Tilt; ll·~:·'Cl!iU IfLi Pool. . 23~ 9, I·; Ap 993, E ~81: 5: I "tv lds ( . sting dene- Iller< )r ther 1 stn h". ish ~ lard: ;titul Lor E '~81: 122 183 " (·for :rmi .; tlie iaJ SI. ,_."'" bsor n of cret( _ 3riti tand : Ins' ion, don. U.YdJ:J' C'~. l-1"'A:ia...cu·:" .... VI (li'....~,.,alu.) 1'". .. iw..... a."·· ..-iucu' -.C tllll1f~ urfa. bsor. n of leret, Inte Re~ Uni :itv <.. I: .ee, I 5, I. """<:lthF",, ,~ ,aoE t 'ft', ~tfq'4Y""'"' ~ ... " ?!"1u n'p\j"ll "T't-. rove Its t he I Met for termg tf ir erm lity oncr Ma ne 0 mcn I..ese , Yo 3- ':0. 1'- - :>p."' - 245, - -14. :han ~. "I gn, I ifica and elop It of aratl ft leasl lent n sit efme n pi rties cone, lten . -~epo JniYI • Y 01'- Idee 21, 6. C R.A .tHo P.C, 1.!reur 'orsir: ,- {y of ,Ient-,:d later and ;oci, con on j )rs" Istru n an E :dmg: enal "01.7, A, p n 1-2·5 1993 )hir <., vlett C. Ch Y.)\ Nea Jrfa( e'{cteri ;of ( ,', rete: :ssmand :lopli of j, ;,tu :st rr )ds". - . igaz' lfC, :te R U'ch, .. 1.39 . 14 ...,n 1,'v•.,-.o,'" l;U! )hif K. vlett C! Chi Y.N Nea: Jrfac cl,ii'_cterliii -;otc- rete: 1CI~dictL' ·)fCli:;iinatkri {:Sistflik,". ~'fU5~'"7;np~ vi rnn"":';'c,l,P I)p,::';"'ur",h \. iJi. ill 'r'tv. lifO', pp. 1'1~'_i4.'l 989 -)11[[ - K.., .. .viet -.C . CIl Y.!" "Nea Jrfa( S lure: 01. 2 'p. I: 28, 1,,' K." ::ina . 1 L~ I.,.;la; 1'.':, ami D 'ars "\. u~- .. _,.;nnrl.~.",~lino- ... jIll (v .. ~r~t~ l,.." f'prlT-~:':";j,:;lln t'"'~~~~'''O t='J;~ I: nitia face orpt " M, ine ( :mcr ~ese, V c 4 '0. 1(' lp. 1 118, 3. _:iQI! _.... "tv. ____ octs __ .. leas!. .... .! air _ .. _ wat._....~rm ....__ .litv '_. c, rete' Igaz )f C 'etel:arer )1. 210. 8 p.i ~ 13-: 197 .. ;1 M. .~on'_c_~ruc!:. _ testi ..c .'If ,,_ .. _;1"'" _; thl'....... ,,) urfal )5011 I me P :edir )f S) JsiUl 'Noln. ['ucti resti :>f C 'ete Tirr ,Ins e of ,'i! r:.ng1f~~-~S~ L(- .... ~)n, p- .... '..)-jO tt"\07'. ;haa I.G : EI-~ d H. 'rece ,ioni 11 sit ocre erm! ,n te (, F . Inte iona I'.... U1lc .... ·~:·~HtI \ ....... r\..H.... t ... t .... lit 'u ........luVlJr~ /""lounc~-- f VOl :air( _~ypt, 116 180, Jalll. 199 Nasi nW 'Not I a II' lct 01 erm '. ,:3, L 5-\] 921 

Pore Size Distribution of Mortar in Near Surface Concrete. Its measurement and delineation with carbonation

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