Interpretation of Accelerated Test Method ASTM P214 Test Results

Transcription

1 TRANSPORTATION RESEARCH RECORD Interpretation of Aelerated Test Method.. ASTM P214 Test Results DANIEL P. JOHNSTON In South Dakota during the lt deade, alkali-silia reativity (ASR) h hanged from a loalized ourrene to a stateide problem. ASTM P214 hosen the preferred test for determining potential reativity of sands used for onrete in the state. The test modified to use different NaOH onentrations to explore the feibility of using to different be strengths to better predit reativity. Of 3 sands tested, over 4 perent gave results that ere inonlusive (expansion values in the.1 to.2 perent range), and only 1 perent of the sands ere nonreative. A modified interpretation of the test results to inlude a ~est fit for expansion at 3, 7, 11, and 14 days, using the general equation Y = X2 + A 1 X + A (X = Time 112 ) gave a muh learer pattern of projeted reativity hen the A 1 oeffiients ere plotted against the A2 oeffiients for all 3 sands. The sands break out into to linear "families" of oeffiients: one reative and one nonreative. It appears the method also an be used to determine the effetiveness of pozzolans at reduing ASR. During the pt deade in South Dakota, alkali-silia reativity (ASR) h hanged from a loalized ourrene to a stateide problem, ith a tremendous potential impat on the durability and expeted servie life of the state's PCC pavements. The first signifiant manifestation of ASR ourred in the late 197s on a setion of I-9 built in A loal sand used in the onrete mix proved to be highly reative. Mineralogial analysis of the sand onfirmed it ontained 44 perent hert. To address this problem, the ement speifiation for onrete paving mixes hanged to a lo alkali ement (Na 2 equivalent :5.6 perent) in Sine 198, several other onrete pavements have exhibited varying degrees of ASR-related distress involving onrete sands. In addition, the premiere oarse aggregate for onrete in the etern part of the state, a quartzite, found to be slo, lateexpanding alkali-silia reative (1). Exhaustion of existing sand pits during the pt 2 years, oupled ith the unknon reativity of potential ne sand soures and onern about the long-term effetiveness of lo alkali ement in reduing ASR, prompted an evaluation of all onrete sands being u.sed in South Dakota. ASTMP214 The primary test hosen for determining the ASR potential of various sands ASTM P214 Aelerated Detetion of Potentially Deleterious Expansion of Mortar Bars Due to Alkali-Silia Reation (2,3). The test is rapid and reproduible, but interpretation of the test results an be diffiult ithout additional testing. Table 1 lists the test results for 3 sands, and Figure 1 indiates the 95 perent onfidene limits (dhed lines). Of the 3 sands, only three an be lsified nonreative using the.1 perent expansion ri- S?uth Dakota Department of Transportation, 7 Et Broaday Ave., Pierre, S.D terion (4). Fourteen sands have expansion values that lie in the inonlusive range and thirteen sands are definitely alkali-silia reative. Using upper values for 95 perent onfidene limits adds to more sands (Sands 92 and 12) to the reative list. Field performane onfirms that these sands are indeed reative; 4 perent of the sands remain in the inonlusive ategory. ASTM C289 Potential Reativity of Aggregates (Chemial Method) also used a sreening method for some of these sands but, unfortunately, a omparison of the to test results ith atual field performane ompliates interpretation. In an attempt to determine the effet of be strength on the P214 test, a series of different onentrations of sodium hydroxide (NaOH) substituted for ln NaOH. Sand 57, one of the most reative of the 3 sands, used in these tests. A ontrol series of mortar bars made ith Ottaa sand run in parallel to determine hether any other fator involved. Results are listed in Table 2 and presented graphially in Figure 2. Readings ere taken up to 3 days after fabriation of the bars to indiate possible long-term trends. Control samples did not undergo expansion at any time regardless of onentration. The major effet of OH- onentration is on the rate of expansion. With.25N NaOH, the final expansion at 28 days only.8 perent ompared ith.449 perent for ln solutions. The.5N solution ahieved an expansion of.228 perent at 28 days, roughly half that of the ln solution. Both stronger NaOH onentrations had expansion urves that fit the general equation: Expansion(%)= Time +A 1 Time 112 +A (1) here R 2 values are.9992 (ln) and.9912(.5n), even though the ln urve is onvex and the.5 urve is onave. The data for the.25n urve also fit the equation, but only for expansion values beyond 17 days (R 2 =.946). In all es, the zero value exluded from the urve-fitting data. A omparison of response to onentration at 14 and 28 days (Figure 3) shos an almost linear relationship at I4 days but a definite urvilinear one at 28 days. The expansion reation is. subjet to a diffusion-ontrolled delay during the first 2 days and to a signifiant redution in reation rate at later ages oing, no doubt, to get formation and reation rims interfering ith the alkali-silia reations. A modifiation of P2I4 to inlude expansion testing at more than IN NaOH onentration, somehere beteen.5 and IN, ould probably improve the reliability of the test in prediting potential ASR. The same equation type an be used to analyze the expansion of the 3 sands using the standard ln onentration. Figures 4, 5, and 6 illustrate three typial urve types obtained from the analyses. Sand 57 is highly reative and gives a onvex urve. The other line in the figure is a regression fit using the same type of equation but

2 13 TRANSPORTATION RESEARCH RECORD 1458 TABLE 1 ASTM P214 Test Results FIELD SAND %EXPANSION s 95% CONFIDENCE ASTMC289 PERFORMANCE O.Ql ().()() ()() ()() Average Innouous Nonreative.193 Innouous Reative.285 Innouous Reative.16. Deleterious Reative'!?.253 Pot. Delet. Reative.34 Deleterious NIA.322 Deleterious Reative.246 Deleterious Reative.231 Pot. Delet. Reative.198 Deleterious Reative.159 Deleterious Reative.149 Innouous Nonreative.11 Innouous Nonreative.19 Innouous Nonreative.169 Deleterious Reative O.Q?l Pot. Delet. Nonreative.118 NIA NIA.13 NIA NIA.186 Innouous Reative.43 Innouous Nonreative.23 Innouous Reative.16 Pot. Delet. Nonreative.18 Deleterious Reative.115 Innouous Reative.57 Innouous NIA.12 NIA NIA.8 NIA ~IA.275 NIA NIA.345 NIA NIA.171 NIA NIA inluding zero. Sand 169 is inonlusive and fits a onave urve. Sand 183 is Slear quartzite and does not orrespond in its behavior to any other sand tested. All of the sands fit the general equation ell exept for the three sands ith expansion values belo.1 perent Table 3 lists seond degree polynomial oeffiients for the various sands..4 The major problem ith using the 14-day expansion value a primary indiator of reativity is that it is an isolated point and does not reflet the ay a ertain sand or oarse aggregate expands during the test. ASTM P214 is a very severe test and auses expansion to our even hen the aggregate tested is nonreative in its field performane. By examining the oeffiients for the general expansion urve and ombining these ith the 14-day test results, it may be possible to larify the "inonlusive" range. The manner in hih a sand e~pands an be onsidered an index of the sand's reativity, regardless of the final expansion value ahieved. Coeffiients for eah sand represent ho the expansion develops, they.3 ;; Q..2 'ti..1. o.oo % Expansion FIGURE 1 95 perent onfidene intervals for 3 sands. TABLE 2 Perentage Expansion at Different NaOH Conentrations DAY % EXPANSION.25 N.5 N ()38 14.()()4 ().() N

3 Johnston ;;.3 a..2 '# N.6 N T.25 N.4.3 ;; a a..2 '# Time {days) FIGURE 2 Perentage expansion versus time for Sand 57. FIGURE 5 Typial ASTM P214 test result (Sand 169)..6.4 'ii.3 a Q )(.2 14 Daye 28 Days.4.3 'iii a..2 'ti..1 '# NaOH Conentration (N) FIGURE 3 Perentage expansion versus NaOH onentration FIGURE 6 ASTM P214 test results (Sand 183, quartzite) 'iii a..2 '# FIGURE 4 Typial ASTM P214 test result (Sand 57). are proportional to the intrinsi properties of eah individual urve, suh urvature and displaement from the vertial and horizontal axes. At first glane, these oeffiients do not appear to ontain any more information than the 14-day expansion values. When the oeffiients are plotted against eah other, hoever, they separate into to distint groups, one reative and the other nonreative. Figure 7 is a plot of A 1 (the first order oeffiient) versus (the seond order oeffiient) for the general equation for all 3 sands. Both groups form a linear relationship ith respet to the oeffiients to a high degree of signifiane. A omparison of the 14-day expansion riteria ith the linear lses of sands indiates an upard trend along the bottom unreative line until Sand 169 is reahed at a.164 perent expansion. All sands more expansive than this lie on the reative line ith the degree of expansion generally trending upard from right to left. Figure 8 is an expansion of Figure 7 in the region here most sands are plotted. It shos a lear differentiation beteen reative and unreative sands. Only three sands are somehat "inonlusive" (Sands 99, 183, and 225). Sand 183 is quartzite and lies beteen the reative and unreative zones, presumably in a reg;ion here a slo, late expanding ASR aggregate belongs. Sand 99 is not quite on the nonreative line but is onsiderably loser to the nonreative sands than to the reative ones. Sand 225 is muh loser to the reative sands and probably ould be lsified reative. A omparison of projeted reativity ith knon field performane indiates striking auray of the oeffiient plots at prediting potential reativity. Of the sands ith 2 or more years of use in South Dakota onrete pavements, the projeted reativity mathed the knon field performane in all but to es. Sand 43 used in a pavement that shoed signs of severe ASR approximately 15 years after onstrution. Unfortunately, the oarse aggregate use in the pavement ame from the same supplier and may be the atual soure of the deterioration reation. The mineralogial omposition of Sand 43 is primarily dolomiti, and the estimated hert ontent by polarized light mirosopy is under 5 perent; both fats argue in favor of its not being alkali-silia reative. Sand 99 is also a dolomiti sand and omes from the same region of the state Sand 43. There is a possibility that both aggregate are alkaliarbonate reative, disussed by Mather et al. (5).

4 132 TRANSPORTATION RESEARCH RECORD 1458 TABLE3 Coeffiients for Equation 1 SAND % EXPANSION A o.i Al AO PROJECTED REACTIVITY Nonreative Reative Reative Nonreative Reative Reative Reative Reative Reative Reative Reative Nonreative Nonreative Nonreative Reative Nonreative Nonreative Nonreative Reative Nonra..:tiv Ra..:tiv -().() Nonreative Reative Reative Nonreative Nonreative Nonreative Reative Reative Reative Gab bro G+4.5% Opal Harzburgite H+4.5% Opal.276 -O.Cl Nonreative Reative Nonreative Reative Further onfirmation of the status of an aggregate an be obtained by plotting the zero order oeffiient, A, against, shon in Figure 9. Again, to straight lines are obtained ith the points on one.representing reative sands and those on the other nonreative. The relationship is not quite lear the previous one, but using the ombination of the to plots allos some refinement of the projeted reativity. For instane, if A is negative, then the sand is reative. The quartzite sample is off by itself, but it does have a negative A Sand 225 is reative, and hether Sand 99 is remains inonlusive G.l o.2 :;: -Cl).1 o.oo (.1. Cl) o.5 :;: -Cl).1 (.15.2~ Coeffiient Coeffiient FIGURE 7 Plot of Ai versus A 1 for 3 sands. FIGURE 8 Plot of Ai versus A 1 for 3 sands.

5 Johnston :ii ~--:::;;;ooo~= :;;?------i '(3 ;.;::::: -.1 ~ -.2 t> <o :.3 ;; :.2 Q. )( '# i,, ~ Coeffiient FIGURE 9 Plot of A versus for 3 sands FIGURE 1 opal (6). Expansion results for gabbro and 4.5 perent 14 The use of oeffiients to larify potential ASR is possibly of great benefit. The unusual linearity in the oeffiient plots an be attributed to the existene of to separate mehanisms for expansion. Coeffiient is diretly proportional to the urvature of the expansion urve. Ai is diretly proportional to the horizontal displaement of the urve from zero, and A is related to the vertial displaement. The existene of "families" of urves indiates systemati reations. The preliminary let square fits for reative sands are Q) '(3.2 ;.;::::: ~.1 (.). < -.1 Ai = Az A = and for the nonreative sands are Coeffiient FIGURE 11 Plot of Ai versus for gabbro and 4.5 perent opal ( 6)..4 A 1 = A = Az +.2 The true appliability of the method for determining potential reativity annot be determined ithout using data on other aggregates obtained by other laboratories. An initial attempt to do so involved data on to oarse aggregates, a gabbro and an harzburgite, tested by Daoud (6). Both aggregates are nonreative, so Daoud added the pessimum amount of opal to eah and retested them. He also took daily readings of expansion up to 12 days after the zero reading. Figure 1 presents a plot of his data for the gabbro perent opal. The general equation fitted to his Daoud' s data in to ays. The first relatively poor fit inluded the zero reading and readings at days 1 and 2, here the muh more exat fit used only data from days 3 to 12. Figure 11 is a plot of Ai versus for the gabbro, and for the gabbro perent opal. Results support the ide appliation of the method. Determining Pozzolans Effetiveness for Reduing ASR A promising appliation of the proposed method of interpreting ASTM P214 test results ould be an aelerated replaement for ASTM C441 Effetiveness of Mineral Admixtures or Ground Blt-Furnae Slag in Preventing Exessive Expansion of Conrete Due to the Alkali-Silia Reation. Figure 12 illustrates the effet of Q).3 '(3 ;.;:::::.2 -Q).1 t> ( Coeffiient.4 FIGURE 12 Plot of Ai versus for Sand 57 ith four fly hes (1 perent). 1 perent addition of three Cls C fly hes and one Cls F fly h on the expansion behavior of Sand 57. Figure 13 is bed on data from Ramakrishnan and Ramahandran (7) and demonstrates the effet of inreing addition of a Cls F fly h on the reativity of Sand 57. Several items of note from the graphs follo: At a 1 perent addition rate, the fly hes do not mitigate the potential reativity of Sand 57, although they deree the rate of reativity.

6 134 TRANSPORTATION RESEARCH RECORD :.3 Q) ; ;;:.2 -Q).1. ( A 1 Coeffiient FIGURE 13 Plot of Ai versus for Sand 57 ith various perentages of Cls F fly h (FA). Ramakrishnan (7) and Ramahandran obtained a somehat loer 14-day expansion for Sand 57 (.2755 perent versus.315 perent), but the oeffiient plot still indiates reativity. perent addition of the fly h redues the 14-day expansion belo.2 perent, bu.t the oeffiient plot still indiates reativity. A 3 perent addition eliminates potential ASR, and the oeffiient plot onfirms this. CONCLUSIONS ASTM P214 is a good test for determining potential ASR. Using to different NaOH onentrations for the test, one at ln and the other somehere beteen.5 and ln, may help minimize inonlusive results. Using a urve-fitting equation of the form Y = X 2 + A 1 X + A (X = Time 112 ) and plotting the polynomial oeffiients against eah other appears to inree the preditive value of test results in the.1 to.2 perent expansion range. ASTM P214 an also be used to determine the effetiveness of various pozzolans at reduing potential ASR. Further ork in analyzing data for different aggregates subjeted to ASTM P214 by various laboratories is needed before the validity and limitations of the proposed method of interpreting ASTM P214 an be properly evaluated. It may be neessary for eah laboratory to develop its on orrelations to ensure proper interpretation. REFERENCES 1. Buk, A. D. Alkali Reativity of Strained Quartz a Constituent of Conrete Aggregate. Cement, Conrete and Aggregates, CCAGDP, Vol. 5. No. 2, Winter 1983, pp Oberholster, R. E., and G. Davies. An Aelerated Method for Testing the Potential Alkali Reativity of Silieous Aggregates. Cement and Conrete Researh, Vol. 16, 1986, pp Davies, G., and R. E. Oberholster. Use of the NBRI Aelerated Test to Evaluate the Effetiveness of Mineral Admixtures in Preventing the Alkali-silia Reation. Cement and Conrete Researh, Vol. 17, 1987, pp Hooton, R. D., and C. A. Rogers. Evaluation of Rapid Test Methods for Deteting Alkali-Reative Aggregates. Pro., 8th International Conferene on Alkali-Aggregate Reation, Kyoto, Japan, 1989, pp Mather, K., A. D. Buk, and W. I. Luke. Alkali-Silia and Alkali Carbonate Reativity of Some Aggregates from South Dakota, Kans, and Missouri: In Highay Researh Reord 45, HRB, National Researh Counil, Whington, D.C., 1964, pp Daoud,. E. K. Properties and Reativity of Gabbro and Harzburgite Gravels Used in Conrete Work in Kuait. AC/ Materials Journal, Vol. 87, No. 5, Sept-Ot., 199, pp. 44~ Ramakrishnan, V., and S. Ramahandran. Alkali Reativity of Conrete Aggregates. SDDOT Report, SD9--1-F, Pierre, June Publiation of this paper sponsored by Committee on Chemial Additions and Admixtures for Conrete.