PARAMETERS INFLUENCING THE QUALITY OF GROUT IN HOLLOW CLAY MASONRY

Transcription

1 PARAMETERS INFLUENCING THE QUALITY OF GROUT IN HOLLOW CLAY MASONRY G.R. KINGSLEY, Former Reserch Assistnt University of Colordo, Boulder, USA L. G. TULIN, Professor of Civil Engineering University of Colordo, Boulder, USA J.L. NOLAND, Principl Atkinson-Nolnd & Assocites, Inc., Boulder, Colordo, USA ABSTRACT Even though grout is n essentil component of reinforced hollow msonry, little systemtic reserch hs been performed to ssess the influence of grout plcement procedures, grout constituents, or msonry unit bsorption properties on the qulity of grout. Good qulity grout is defined here to be tht which is well bonded to msonry units nd free of interni flws, e.g., rches nd voids. The objective of this project ws to define how vrious prmeters influence grout qulity in grouted msonry. Prmeters considered were consolidtion type, consolidtion time, dmixture type, initil wter-cement rtio, nd msonry bsorption properties. In ddition, n evlution of the UBC Stndrd No "Field Compressive Test Specimen for Grout" will be presented. 1. INTRODUCTION A number of fctors my ffect the qulity of grout in reinforced msonry construction (1,3,4,5,6). Some of these, such s unit bsorption properties, vry rndomly from job to job. Others, such s wter-cement rtio nd consolidtion technique, vry s result of poor definition in the codes. It ws the objective of this work to determine how these vrious prmeters influence the strength nd integrity of grout in hollow cly msonry structures. In order to ccomplish this tsk, n experimentl progrm ws crried out in two phses. In Phse 1, the procedure for mixing, pouring nd consolidting grout ws vried until grout plcement procedure ws developed tht resulted in grout free of flws nd shrinkge crcks. In this phse, grout qulity ws evluted visully by cutting verticlly through grouted cells of hollow bricks. In Phse 2, the grout plcement procedure ws held constnt, nd the effect of vrying grout wter-cement rtio nd msonry bsorption properties on grout compressive strength nd brickjgrout bond strength ws observed. This pper will be concerned primrily with the results of Phse 1, with the exception of discussion of results from compression tests on grout specimens constructed ccording to UBC Stndrd No (7). 1085

2 2. PROGRAM SCOPE Ech series of tests in this investigtion involved the vrition of grout constituents, msonry unit properties, or construction procedures. The grout constituents vried were ggregte type, wter content, nd dmixture. Unit property vribles were bsorption nd size, nd construction procedures were vried by ltering the method nd time of consolidtion. Ech of these vribles will be discussed briefly below. ~~1-M~~º~~Y~Q~orEtiºn ProEer!l~~ Due to the porous nture of cly, bricks hve tendency to bsorb wter from the mortr or grout in contct with them. The mgnitude of this effect depends on the bsorption properties of the prticulr unit, nd the properties of the mortr or grout. The result of this migrtion of wter from grout is reduction in the wter-cement rtio of the grout, s well s significnt reduction of grout volume. The units in this study were chosen to represent wide rnge of bsorption properties in order to determine the effect of bsorption on grout properties. The bsorption chrcteristics of ech brick used re listed in Tble 1. TABLE 1 BRICK ABSORPTION PROPERTIES Brick Type Width IRA mm in -~g!!!_- ~m m (min) 30in (min) Buckskin / Buckskin / Copper Nugget / Copper Nugget / Copper Nugget / Mission Autumn / Gold Wlnut / Buff / Unit Size Hollow cly units with nominl widths of 102, 152, nd 203 mm were chosen to represent the rnge of brick sizes used in construction. 2.3 Grout Wter Content The compressive strength of concrete nd cement mortrs depends on the quntity of wter vilble for hydrtion of the cement. It is firly esy to control this quntity in concrete. In grouted msonry, however, the bsorbent units decrese the wter 1086

3 content of the grout, leving n unknown quntity of wter for hydrtion. Since different bricks bsorb differing mounts of wter, the grout wter content t the time the cement tkes its initil set remins unknown even if the initil wter content is tightly controlled. One of the primry objectives of this project ws to determine the effect of vrying initil wter content on the properties of grout. The initil wter content of grout controls its pourbility. In generl, wter is dded to grout to ttin pourble consistency. A slump of 203 mm, (8 inches), represents resonble lower bound for the desired consistency. The upper bound cnnot be mesured dequtely by the slump test, but is recognized s the point just before the constituents begin to segregte. For the purposes of this study the initil wter contents for the grout were chosen to represent these upper nd lower bounds plus n dditionl intermedite point. The mount of wter required for ech btch ws vried s required by the presence of dmixture nd corse ggregte. ~-=-.L~gregª!~ Both fine nd corse ggregtes were used in this investigtion in order to determine the influence of corse ggregte on grout shrinkge nd strength Admixtures Grout dmixtures were considered s possible mens to eliminte flws nd shrinkge crcks (4). Severl dmixtures were investigted nd judged purely qulittively by visul exmintion of the grouted cvities. Since wter loss is the source of grout shrinkge, ech dmixture hd some effect on the wter in the grout. The dmixtures chosen for investigtion were lime, bentonite, super-plsticizer, fly sh, nd combintion of luminum powder, plsticizer, nd wter retention gent clled grout id _ Consolidtion -- A gret del of emphsis is plced on the importnce of proper consolidtion in the field, with prticulr ttention pid to the prctice of "reconsolidtion", (i.e. second consolidtion performed fter bsorption hs cesed but before workbility is lost). Since the purpose of reconsolidtion is to eliminte shrinkge crcks (4), consolidtion technique ws n importnt prmeter during Phse 1. Consolidtion methods tried were roddi ng nd mechnicl vibrtion. Also vried ws the time of the second consolidtion, (from 30 seconds to 60 minutes fter pouring), nd the totl number of consolidtions, (from O to 5 times in 30 minute period). 3. TEST PROCEDURE Specimens for visul evlution of grout were obtined by grouting four-unit high stcks of hollow cly units, nd then swcutting verticlly through the grouted cells. Specimens for unixil compression tests of grout were removed from identicl 1087

4 four-unit stcks with mm (2 1/8 inch), dimeter core drill. In ddition, compression test specimens were constructed in ccordnce with UBe stndrd "Field eompressive Test Specimens for Grout". 4. TEST RESULTS The results were recorded in the form of photogrphs nd descriptive notes indicting the effect of ech vrible on the qulity of the grout cores (i.e. freedom from flws nd shri nkge crcks). Figure 1 shows exmple specimens. Unfortuntely, i n no combintion of brick- type, grout initil wter content, nd consol idtion technique ws it possible to eliminte shrinkge crcks consistently. However, some importnt observtions were mde concerning the effect of reconsolidtion on grout. Specimens tht were reconsolidted soon fter pouring, while grout ws still fluid, invribly developed shrinkge crcks. Figure 1 Erly c ons ol i dtion did eliminte ir bubbles, nd yielded n otic ebly denser g r out t hn in unconsolidted specimens, but c ontinuing mi g r tion o f wter fter vibrtion cused significnt g r out shrin kge. Specimens tht were reconsolidted t lter times showed vriety of results depending on the bsorption chrcterist i cs of the brick nd the initil wter content o f t he g rout. For bricks with low IRA's or grouts with high i niti l wter contents, reconsolidtion t ny time up to bout f i fteen minutes hd no more beneficii effect thn i n i til consolidtion. After this time, consolidtion of the continully stiffening mi x served only to disrupt the body of the grout, leving voids where the vibrtor hd been. In the cse of high IRA bricks or grouts with low initil wter contents, the grout becme too stiff to consolidte s erly s two minutes fter pouring. In mny cses, shrinkge crcks still ppered when grout ws vibrted in stiff condition. The use of grout dmixtures to eliminte shrinkge crcks ws more encourging. While lime nd fly sh improved the workbility of the wet mix, they did not help to decrese shrinkge. Bentonite cused n undesirbie stiffening of the grout, nd s resuit of the dditionl wter required, cused n increse in the mount of shrinkge. The ddition of super-plsticizer permitted drmtic decrese in the initil wter content of the grout, nd resulted in grout cores tht contined fewer 1088

5 shrinkge crcks thn in stndrd grout. Grout id consistently reduced shrinkge crcks to minimum, usully eliminting them entirely. Bsed on the results of Phse 1, grout for Phse 2 lwys contined Grout id, nd ws consolidted only once by mechnicl vibrtion. An interesting result of the compression tests done in Phse 2 ws comprison of grout strength s shown by the use Stndrd grout specimens nd specimens drilled from n ctul grout cvity, s shown in Figure 2. In every cse, the use Stndrd test showed significntly less strength thn grout from the sme btch poured in brick cvity. There re five differences between these two tests tht re possible sources of the disgreement in strengths: 1. The surfce-to-volume rtio of the UBe specimen is lrger thn for the ctul hollow units. 2. use specimens re cst ginst the exterior fces of bricks rther thn ginst the die-skin of the grout cvity. 3. UBC specimens re cured wet rther thn dry. (USC specimens were llowed 48 hours to dry before testing in this project.) 4. USC specimens re rodded rther thn vibrted. 5. Pper towel "bond-breks" seprte the grout from the brick surfce in UBC tests. Chnges in brick properties nd the geometry of the grout spce re not likely to cuse such drmtic chnges in strength. Ssed on experience with concrete, the humid curing conditions should cuse n increse rther thn decrese in strength. Therefore, it cn be concluded tht either the consolidtion technique or the bond- brek re detrimentl to strength. The ppe r towel my significntly inhibit the migrtion of wter from grout to brick, thus incresing the finl wter- cement rtio. 5. CONCLUSIONS Some conclusions regrding the prmeters studied re listed below. Conclusions re bsed only on the dt collected in this project, nd pply only to grouted hollow cly unit msonry. 1. Mechnicl vibrtion produces more thoroughly consolidted core thn rodding. 2. There ppers to be no optimum time for reconsolidtion, becuse grout shrinkge continues fter grout ceses to be fluid enough to vibrte. For hollow cly units with high rtes of bsorption or grouts with low wter contents, the grout cn become too stiff to vibrte s soon s two minutes fter pouring. Thus, 1089

6 45 1 :::E --- :::E I d 38 ~ ~ tf1 '-.,. :z:! Cb '-' i I :::r:: l- L.:l I :z: w n:: 31 ~ l- tf1 w... >- tf1 tf1 w n:: CL 24 1 :::E CJ U l- => CJ n:: ~ L:) >- 17 I-... >- -< u ~ Li n e o f e qu l s trength 1 O IL L _ ~ L.L.J UBe STO eompressive STRENGTH (N/S Q. MM) Figure 2 tended purpose of e1iminting grout shrinkge crcks, it cou1d potenti11y destroy the integrity of grout core if performed t the wrong time. 3. Admixtures which most successfu11y decresed grout shrinkge either () e1iminted its source by permitting decrese in initil wter content without 10ss of pourbi1ity, or (b) counterc ted it by cusing slight expnsive ction in the grout. Super-plsticizers were modertely successful, nd Grout id ws extremely successful in minimizing shrinkge crcks. Admixtures tht improved the wter retentivity or workbility of grout hd little effect on grout shrinkge. 4. Hol1ow c1y unit size nd bsorption properties hd litt1e effect on the size nd number of shrinkge 1090

7 crcks in grout, however, bricks with very high IRAls cused shrinkge to occur t quick rte, thus ffecting the mount of time vilble for consolidtion. 5. The mount of wter bsorbed from grout by prticulr unit seems to be function of the initil wter content of the grout rther thn the bsorption properties of the bricks. The higher the initil wter content of the grout, the more wter will be bsorbed from it by the surrounding msonry, nd thus more shrinkge occurred. 6. Grouts with corse ggregtes showed less shrinkge thn grouts with fine ggregtes. 7. The UBC Stndrd No method for constructing field test specimens for grout results in significnt underestimtion of ctul grout strength. More relistic vlues of compressive strength cn be obtined removing grout cores from the ctul wlls in question or from prisms built identiclly to the wlls. In generl, it seems tht the common prctices for grouting of msonry structures hve not been subjected to serious scrutiny, but hve developed empiriclly. In prticulr, the prctice of reconsolidtion, required in the Uniform Building Code, does not perform its intended service nd my seriously dmge the integrity of msonry wll. The UBC Stndrd No field test specimen lso does not perform its intended function of representing the properties of grout in msonry wll. In light of these results, further testing needs to be done on different msonry types to determine their generlity, nd chnges in the current codes my be in order. 6. REFERENCES (1) HAMID, A.A., nd R.G. DRYSDALE, ~!!ec! 2! rou!i~g 2D ~tr~~g!h ºh~~~E!~ri~!iE~ 2f Co~cr~!~ ~~~2~rY, Proceedings of the North Americn Msonry Conference, Boulder, CO, August (2) HAMID, A. A. nd R. G. DRYSDALE, ~:!:!gg~~!:~9 E~il:Yr~ ºri.!.~r _i~ for ~2:!:!!~9 º2~c~~!~ ~~so~~y Q~9~r Axi~l º2~2r~~~i2D, ACI Journl, October (3) HARRINGTON, R. W., Ç2~~!~:!:!.~!ion ~~9 º:!:!~li!y Ç2~!~ol 2.f!!igh ~i!! ~2:!:!!~9 ~~info~e~9 ~~~Q~ry, Proceedings of the North Americn Msonry Conference, Boulder, CO August, (4) MILLER, M. E., R.O. NUNN, nd G.A. HEGEMIER, ~he 1~!lg~~E~ Q! ~l~~~l º2~2~E!i2~L ~~9 ~9mi~!:!:!~~ on ~tr~~g!h El~st i~ ~Q9gli 2! º2~cr~!~ ~~~.2~rY, Ntionl Science Foundtion Report No. UCSD/AMES / TR- 78-2, August, (5) NUNN, R. O., M. E., MILLER, nd G. A. HEGEMIER, ro :!:!!= ~!1qf~ ª2~9 St~~~g!h i~ Conc~~!~ ~so~ry, Ntionl Science Foundtion Report No. UCSD / AMES / TR-78 / 001, Mrch

8 (6) PERSON, OSCAR F., ªº~!h~ tligh ~ift ºrout ~~tem ws Dey~l º2~3, Proceedings of the North Americn Msonry Conference, Boulder, CO, August (7) Uniform ªgildi~g ºº3~, Chpter 24,