LABORATORY MEASUREMENTS OF WATER INFILTRATION THROUGH CONCRETE BLOCK PAVEMENTS

Transcription

1 LABORATORY MEASUREMENTS OF WATER NFLTRATON THROUGH CONCRETE BLOCK PAVEMENTS Prfessr Brian Shackel, Schl f Civil Engineering. University f New Suth Wales, Sydney, Australia. Sid Yamin, Cncrete Cnstructins (New Suth Wales), Sydney, Australia. SUMMARY. This paper reprts a limited experimental study f the infiltratin f simulated rainfall int newly laid cncrete blck paving. The tests were cnducted at a single rainfall intensity f apprximately 45 mm per hur. Factrs studied included the pavement crssfall, the paver shllpe and thickness and the area f the jints. The experiments shwed that upt abut 65% f the rainfall pentrated the jints f the pavement. The amunt f infiltratin culd be reduced by abut 5% by sealing the jints with a water-based acrylic sealant. NTRODUCTON Relatively little is knwn abut the mvement f water int cncrete blck paving, CBP (1). Mst wrk s far reprted has cncentrated n field measurements f infiltratin (eg. 2,3). Typically, such measurements mvlve applying water t just a small area f the pavement and arc cnsequently f dubius value because it is nrmally nt pssible t distinguish between water radiating hrizntally frm the measurement pint alng the jints and bedding sand frm vertical infiltratin. Cntrlled full-scale tests are s far rare, whether in the labratry (4) r in the field (5). Such trials, hwever, indicate that significant infiltratin f rainwater thrugh CBP may ccur. Fr example, in the Netherlands upt 45% f the annual rainfall has been reprted t penetrate CBP (5) EQUPMENT This paper reprts preliminary results frm an n-ging study f water infiltratin int CBP. This study was initiated at the University f New Suth Wales (UNSW) in The prcedures adpted in the UNSW trials invlved cnstructing 1.5 m square areas f CBP in a steel bx which culd then be placed at any required crssfall beneath a rainfall simulatr. The equipment is illustrated schematically in Figure 1. T simulate rainfall a series f clsely spaced water jets fed frm a cnstant head water tank discharged nt a fine nyln mesh placed sme.6 m abve the pavement t be evaluated. This system gave a unifrmly distributed simulatin f rainfall acrss the CBP surface. The steel bx cntaining the CBP was arranged s that water draining thrugh the bedding sand and runff frm the pavement surface culd be cllected and measured separately. Cnstant Head Water Tank Dispersin - Mesh Bx Drainage Figure ). Schematic layut f the Experimental Apparatus.

2 The simulatr was adjusted t apply a nminal rainfall intensity f 45 mmlhr. This lay midway in the range frainfull intensities encuntered in Australia (35 t 55mmlhr). Measurements made using a tipping bucket rain gauge at 2 randmly selected lcatins beneath the simulatr shwed that the mean rainfall intensity was 43 mmlhr with a standard deviatin (pint t pint) f7.7 l1un/hr. This simulated rainfall intensity was used thrughut all the tests described herei n. EXPERMENTAL PROCEDURES The factrs selected fr study cmprised: 1. Pavement Crssfall - Crssfalls f 1%, 2% and 5% were investigated 2. Paver Shape - Bth rectangular and shaped (Unipave) cl1crete pavers were used. 3. Paver Thickness - Bth 6 mm and 8 mm thick pavers were studied. 4. Jint Sealing - The effects f applying a water-based acrylic sealant t the jints was examined TABLE 1. Sand Grading Sieve Size Cumulative (mm) Percentage Passing The sand used in the experiments had the grading given in Table 1. The fractin passing a 2.36 mm sieve was used as the bedding sand whilst the fractin passing 1.25 mm served as the jinting sand. The sand was ven dried at 15 C befre use. The bedding sand was placed in a lse thickness f 3 mm in the steel bx. The pavers were then Jayed by hand in herringbne bnd rientated s that the paver axes lay parallel t the sides f the bx. The pavers were guilltined t fit t the edge f the bx. Gaps arund the periphery f the pavement were filled with mrtar. The pavers were cmpacted with three passes f a vibrating plate cmpactr and jinting sand was then brushed int the jints. A further three passes f the plate cmpactr were then applied. The weights f dry sand used t bth bed and jint each pavement were recrded and are given in Table 2. Difficulty was experienced in bedding the 6 mm thick rectangular pavers firmly int place. Here a Significant prprtin f the jinting sand migrated int the bedding curse. After cmpactin the jint widths were measured at 2 r mre randmly selected lcatins using a calibrated steel mandrel which was pushed int the jints. The ttal lengths f the jints in each pavement were als measured. These data are summarised in Table 3. TABLE 2. Weights f Bedding and jinting Sand used in the Experiment Paver Thickness (mm) Weight f Bedding Weight f Jinting Sand & Shape Sand (Kg) (Kg) 8 lulu Rectangular lum Rectangular lulu Unipave Shape

3 The bx cntaining the cmpacted paving was placed under the rainfall simulatr and was set t the required crssfall. This crssf.111 was applied in nly ne directin acrss the bx. Simulated rainfall was then allwed t fau nt the pavement and measurements f the water draining thrugh the CBP and acrss the pavement surface were btained as functins f time. Generally, the experiments cntinued until these water flws achieved equilibrium values. Typically. this required test duratins f up t abut 25 minutes at the particular rainfall intensity used TABLE3. J' illt W'dl 1 t S an da reas L Paver Shape Paver f Average \ Average Jint Plan Area Thickness lint Width lint Length (sq mm) (mm) (mm) (mm) Rectangular Rectangular Unipllve Shape RESULTS OF THE EXPERMENTS Effects f the Pavement Crss fall Typically, fr CBP a minimum slpe arund 2% is recmmended (1). n the experiments described here crssfalls f 1%, 2% and 5% were studied. As shwn in Figure 2 the percentage f rainfall draining frm the tp f the paved area increased almst linearly with increase in the crssfall. Hwever, it may be seen that between apprximately 3% and 35% fthe incident rainfall penetrated the CBP. 73, _, _; U , ,----,, , :;;t U. Z 68 :::e '-''',, '.-.--.' : L CROSSFALL (%) Figure 2. Effects f Changes in Crssfall n Runff ay be seen frm Figure 3 that the water held in the jints and bedding sand, measured as a functin f decreased as the pavement crssfall increased. Here the beneficial effects f increasing the crssfall were prnunced \vhen the grade was increased frm 1% t 2%. Further increase t 5% nly marginally the amunt f water penetrating the CBP. Changes in the pavement crssfall had relatively little n the water draining frm the bedding sand. This is shwn in Figure 4. the experimental results indicated that. at least fr the particular heavy rainfall intensity studied here, crssfall f CBP shuld be abut 2%. This cnfirms the recmmendatins in practice nted

4 ::::. - ld ()...J W ::t: W L r.; 4/ ", -L:::...../ 5 /' -- 1% - 2% 5% TME (min) -- Figure 3. Effects f Crss fall n the Water held in the Jints and Bedding Curse (8 mm rectangular pavers laid in herringbne bnd). _ 35 c: W 2 Z / <t.; 15 r w / ;* 1% 2% 3% 15 TME (min) Figure 4. Effects f Crss fall n the Water Drained frm the Bedding Curse (8 mm rectangular pavers laid in herringbne bnd). Effects f Jint Width and Area Frm Table 3 it may be seen that, fr the pavements installed with rectangular pavers, the average jint spacing fr the 6 mm thick pavers was greater than fr the 8 mm thick pavers. This meant that the area f the jints available fr water infiltratin was greater fr the 6 mm pavers than fr the 8 mm pavers. Test measurements shwed that the 3vement having the greater jint area was assciated with greater average...!bsrptin f water int the jintsana1jectdmg sand. At tfie same time the average run water frm the CBP surface was slightly :ln ther wrds, as might be expected intuitively, an increase in the area f the jints led t mre water entering the pavement. n this respect it is nted, hwever, that the bedding and jinting sands were dry at the cmmencement f the test. Further research is needed t determine whether jint area significantly affects infiltratin and runff where the bedding and jinting sands are initially saturated.

5 shaped pavers are used the practical cnsequences affecting pavement drainage are that: a} the length f jints in unit area f CBP tends t increase (eg, vide Table 3). b) the average gradient fthe jints will be less than the crssfall fthe pavement (because all r a prprtin f the jints will lie in plan acrss the directin f the maximum crssfall)..j\ Bth f these factrs wuld be likely t aid water penetratin f the pavement. - ==- D EO... W :x: w ;: 5 4 L -- L L 3 V6 L 2 1 r L 5 8mm 8mm Rectangular Shaped 1 15 TME (min) 2 25 Figure 5. Effects f Paver Shape n Water Held in Jints and Bedding Sand (Crssfall=2%) Figures 5 and 6 shw a cmparisn between the water penetratin data btained fr 8 mm thick shaped and rectangular pavers. t may be seen that, whilst the lng-term r equilibrium values were little affected by shape, the initial build-up in bth the amunts f water held in the jints and bedding sand and the amunts f water draining frm the bedding curse was much mre rapid fr the shaped pavers than fr the rectangular pavers. Thus the test measurements tcndcd t supprt the cntentin that, prir t saturatin, CBP incrprating shaped pavers may facilitate water penetratin. Hwever, as shwn in Figures 5 and 6, there was little difference in pavement drainage nce the sand had been wetted-up. n ther wrds, the effects f paver shape n water infiltratin int CBP are nly likely t be evident in initially dry pavements... _ 35. S...,! i W 2 Z < w ;:, 1. L.. / / V 5 A ; j l r mm 8mmm 1 Rectangular Shaped 15 TME (min) Figure 6. Effects f Paver Shape n Water Draining frm the Bedding Sand (Crsslhll=2%)

6 Effects f Paver Thickness n the tests described here it was nt pssible t prperly islate the effects f paver thickness frm ther factrs affecting water infiltratin. Accrdingly research is still needed int the pssible effects f paver thickness n the drainage f CBP. The Effects f Jint Sealing Fllwing the cmpletin f the measurements dcscribed abve, several f the pavements were sealed using a water-based acrylic sealer. This was applied by spraying the sealant nt the pavements at a nminal rate f l. /sq m s as t fld the jints. Nrmally sealing is best achieved when the jinting sand is dry. Fr this reasn attempts were made t dry ut the pavements befre sealing by the use f heaters directed at the paver surface. Hwever, it is unlikely that the jinting sand was cmpfutcly dry at the time f sealing. Accrdingly, the results reprted here may nt represent the ptimal perfrmance f the sealant. The effects f scaling the jints are summarised in Figure 7 fr the pavements laid in bth 8 mm shaped pavers and 6 mm rectangular pavers. This figure is pltted in terms f the measured water flws in the pavements expressed as percentages f thse in the unsealed pavements. Frm Figure 7 it may be seen that sealing the jints reduced by 5% r mre the amunts f waler penetrating the pavement (ie. water held in the jints and bedding curse and water drained frm the bedding sand). At the same time, the surface runff increased t a maximum f abut 14% f that bserved fr the unsealed pavements mmshaped Drained Water ; mm Rect. -"C Drained Water 12 ell 6 mm Rect. C/? 1 Held Water s:: :::l 8 ---:--- 8 mm Shaped Runff -"C 6 ell 6 mm Rect. Runff en 4 <> * 8 mmm Shaped 2 :l( Held Water TME (min) Figure 7. Effects f Sealing the Jints fr bth 8 mm Shaped and 6 mm Rectangular Pavers laid in Herringbne bnd (Crssfall=2%) Overall, the use f a sealant was fund t reduce but nt ttally eliminate the penetratin f water int the pavements. Hwever, it is imprtant t recgnise thal the sealant may have been installed in a less than ptimal way. Further study f sealants is warranted. CONCLUSONS Althugh the wrk described in this paper is nly the first stage in a lng-term study it is, nevertheless, pssible t draw a number f useful cnclusins. These can be stated as fllws: 1.Between 3% and 35% f the simulated rainfall penctrated newly laid, un trafficked and unsealed cncrete blck pavements

7 ,Tn,rease in the pavement crssfall was beneficial in increasing surface runff and, fr initially dry CBP, in the amunt f water held in the jints and bedding sand. n the case f water held in the pavements, in the crssfall beynd 2% was nly f marginal benefit. This tends t cnfirm that 2% is the inirrlmum practical crssfall fr CBP. ncrease in the pavement crssfall frm 1% t 5% had little effect n the rate with which water drained frm the bedding sand. 4. Water penetratin terided t increase and runff t decrease with increase in the surface area f the jints in initially dry CBP. 5. The use f shaped pavers prmted mre rapid initial drainage f water int the pavement than fr rectangular pavers. Hwever, there was litlle difference in the lng-term drainage perfrmance f blck pavements incrprating shaped and rectangular pavers nce the jinting and bedding sands had becme saturated. 6. The applicatin f a water-based acrylic sealant t CBP cntaining mist sand in the jints reduced the water penetratin int the pavement by 5% r mre but did nt ttally seal the pavements. 1. t was nt pssible t discern any effect f paver thickness n the drainage f CBP. Further study f this effect is warranted. t is cautined that the wrk described in this paper was limited in scpe and is nly reprted fr a single high but representative rainfall intensity. t is als nted that the pavements were initially dry in many f the tests. Further wrk is needed t study the effects f different rainfall intensities, the influence f the initial saturatins f the jinting and bedding sands and the use f jint sealants. Nevertheless, the wrk reprted here shws that significant water penetratin can ccur in newly laid untrafficked blck pavements. The cnsequences and cntrl f this water penetratin deserve further study and it is intended t cntinue this research at the University f New Suth Wales. REFERENCES l. SHACKEL B The Design and Cnstructin f nterlcking Cncrete Blck Pavements. Elsevier Applied Science Publishers, Lndn, 229 pp CLFFORD J M Evaluatin f Tests t Determine Waterprf Characteristics f Segmented Blck Pavements. NTRR, CSR. Pretria, Teeh Rpt TP/39/ HADE J D and SMTH D R Permeability f Cncrete Blck Pavements. Pre 3rd nt. Cnf. n Cnc. Blck Pavements, Rme pp CLARK A J Water Penetratin Thrugh Newly Laid Cncrete Blck Paving. Cement and Cncrete Assn. Tech Rpt. 529, Nvember, LEENDERS P The Water Prsity f a Cncrete Blck Pavement and the Use f Waste Materials in Paving Blcks. Prc 3rd nt. Cnf. n Cnc. Blck Pavements, Rme pp Authr's Address: Prfessr Brian Shackel, Schl f Civil Engineering, University f New Suth Wales, POBx, Kensingtn, NSW 233, AUSTRALA Fax: