A Durability Test for Aggregates

A Durability Test for Aggregates F N HVEEM and TRAVIS W SMITH Respectively, Materials and Research Engineer and Supervising Highway Engineer, Materials and Research Department, California Division of Highways, Sacramento The routine tests used in California to control the quality of aggregates, particularly bases and subbases, are grading, specific gravity, unit weight, absorption, soundness, Los Angeles rattler, R-value, cleanness and sand equivalent A new test in which aggregates are degraded in the laboratory has been developed to measure the m echanical durability of aggregates in terms of a "durability index." The test was developed largely as a result of the need for a measure of the breakdown occurring to aggregates during construction and normal use under traffic conditions Equipment and procedures used in performing the test are for the most part those used in the sand equivalent and cleanness value tests Test values on many aggregates from the coast ranges of California, which are abundant in sandstone, serpentine and shale, are low However, the aggregates from Southern California show consistently high durability indices There is little or no correlation between the Los Angeles rattler and the durability index for the majority of materials tested This is not surprising because the two tests measure the results of different abrasion processes Results of the durability tests are correlated with behavior based on test results from control and record sampling during the last two years Correlation of the test results and the known behavior of aggregates in use for many years looks very promising •STONES, large and small, have been used for construction purposes for many thousands of years In more modern times, engineers refer to the smaller sizes under the general term of mineral aggregates Presumably, this sounds more scientific as it indicates that crushed stone, gravel or sand particles all consist of one or more minerals Other phrases such as "the enduring stone" convey the idea that solid rock is unchanged by the vicissitudes of time, but both engineers and geologists know that rocky materials vary greatly in their ability to withstand the elements or to resist abrasive forces The money spent for mineral aggregates represents a large portion of the total money spent for construction, whether for buildings, dams or highway pavements and structures Records indicate that between one-fifth and one-third of the funds expended for construction of highways in California is for the procurement and placement of aggregates; hence , with a budget of approximately $ 300 million for major construction during the fiscal year , this would result in $ 60 to $100 million for aggregates on State highway projects alone Production, processing, testing and control of aggregate s are ever-present considerations in providing better highways for the traveling public The complexity of the problems connected with aggregate production is increased by the depletion of the best and most convenient sources, by the necessity for considering beneficiation processes in aggregate production, and by the ever-present desire to secure good quality aggregates and at the same time keep the cost within reasonable limits Paper sponsored by Committee on Construction 119 Practi ces ~R igid Pavements 120 On the whole the producer prefers an aggregate that is easily and economically produce(.!; the engineer lLl;:es for it to have ideal properties anrl strnr.tural r,haraderistks; and the one who pays the bill wants it to be cheap and last forever The usual tests to control the quality of aggregates in California are grading, specific gravity , unit weight, absorption, soundness, Los Angeles rattler, R-value, cleanness, and sand equivalent Generally, not all of these tests are applied to any one aggregate product These tests are used on the premise that they will control the quality, suitability, and usefulness of the aggregate as well as these same attributes of the finished product that is produced from the aggregates Both the producer and the user are concerned with a characteristic of the aggregate that may be best described as "durability." Durability means, in the broad sense, the ability of the aggregate to remain unchanged over a fairly long period of time in spite of adverse natural processes or forces to which it is subjected Specifically, the term durability as used here means resistance to breaking down or grinding up into finer particles At; au i11dicatio11 of the concern over durability of aggregates, Washington, Oregon and Idaho have in recent years started using specific tests to measure this property Many other public and private agencies are concerned with this problem and have considered or taken steps to assure more durable aggregates Considerable work has been done throughout the world in an attempt to develop a test method to evaluate resistance of aggregates to mechanical degradation One of the earliest devices was the Deval Abrasion Test developed in France and, incidentally, a Deval tumbler was the first piece of testing equipment set up in the laboratory of the California Division of Highways in 1912 Probably the most widely used today is the Los Angeles rattler, developed about 1925 There have been various types of impact tests such as use of laboratory rollers, and piston-type crushing tests However, whereas these various test methods will break down or tend to pulverize rock particles under test, the fine material produced generally differs markedly in character from the fines resulting from normal degradation on a roadbed A fairly successful method of reproducing characteristic types of fines and aggregate breakdown in the laboratory has been accomplished through the use of a kneading compactor on samples containing considerable amounts of water However, this type of laboratory determination requires considerable time and rather expensive equipment There have been a few clear-cut examples of failure or serious distress in California highways that could be attributed to deterioration or lack of durability of the aggregates There have been other cases where breakdown of the aggregates was suspected as the cause of trouble but convincing proof is difficult to secure Unless the entire operation is subjected to close control and frequent tests, a question always arises whe n excess fines are found; that is, were the fines introduced at the time of construction or did the aggregate lack the ability to withstand abrasive action and the subsequent weathering? Probably most highway engineers can cite an example of aggregates that met specifications when placed in a stockpile but when these aggregates were incorporated in construction weeks or months later they would not meet the specifications Again suspicions always arise as to whether the aggregates really met the specifications initially and subsequently degraded, that is , if the aggregate lacked the necessary durability to withstand the weathering and handling involved Figures 1, 2, and illustrate degradation or breakdown that can take place in the production and handling of aggregate Figure shows 11/2- by %-in stone as it left the plant where it met the cleanness specifications for concrete aggregate The next three figures show changes in cleanness after successive steps in handling the aggregate It would not meet the cleanness specifications in the condition shown in Figure These pictures, which record one of California's first major encounters with the problem of aggregate degradation, were taken shortly after the cleanness value was introduced as a specification requirement The question of durability of aggregates has been emphasized in recent years in highway construction by the progress that has been made toward completion of the Interstate System As a result of inquiries or investigations by various committees and agencies into highway construction practices, the question of durability or breakdown of aggre- 121 Figure Degradation of 11/a- by% - in pee aggregate Figure Degradation of l1/2-by%-in pee aggregate gates has been increasingly emphasized The activities of these committees and other similar studies have generally evolved around the question of aggregates complying with specifications There have been numerous investigations concerning the quality or thicknesses of aggregate layers in place If an investigation indicates a certain grading or other test characteristic for an aggregate in place and previous tests indi- 122 :(.: ' Figure Degradat ion of l1/z- by 3/t.-in pee aggregate Figure Degradation of l1/a- by'% - in pee aggregate cate different characteristics before placing, a logical question is "What changes would normally take place as an aggregate is incorporated into a completed roadway?" To answer this question and at the same time move toward a more thorough knowledge of the characteristics of suitable aggregates, a durability test was developed by the California Division of Highways that will be incorporated in their new standard specifications 123 TABLE AVERAGE TEST RESULTS OF CONTROL AND RECORD SAMPLES ON AGGREGATE BASES Contract No No Locations Contr ol or Rec ord c 61-3Tl3Cl5-F R c 61-7X13C15-P R 61-6Xl3C54-F c 61-3T13C3 l c R R c 61-6X13C52-P R 61-11VJ3C7-F c 61-10X13C32-P c 62-2T13C2 c R R R c 62-JOT13Cl R 61-4X13C38-P c R c 61-3TC3 R 62-6Y24C3 c R 61-9Xl3Cl2-P 60-6TC13-FP , c R c R 61-1TC6 c R 60-1DDC15-P c 61-4Xl3C35-P c R R Avg Passing Sieve ( %) J'/, in %in No 94 93 100 100 100 100 97 98 99 100 96 97 91 93 96 98 100 100 100 100 97 97 96 97 100 100 100 100 96 98 88 97 99 99 68 72 98 99 94 96 80 81 67 69 75 73 77 78 77 84 95 94 63 81 67 34 38 50 56 44 51 37 38 40 42 47 46 52 53 52 57 49 48 24 37 38 41 67 74 51 55 58 56 38 48 25 39 39 45 71 86 91 96 96 96 96 73 81 60 74 81 85 No 30 20 22 22 26 23 28 15 16 24 25 22 21 24 25 22 25 25 26 11 17 20 22 30 31 30 30 31 31 15 22 15 24 20 25 No 200 " 4 10 8 10 7 10 13 14 12 11 Q 10 10 Avg Avg Sand R- Equiv, Value 50 50 66 59 47 54 47 39 66 58 31 33 48 49 44 40 31 31 28 32 40 40 31 33 37 44 32 30 35 26 24 25 38 27 80 82 79 82 76 82 80 82 80 79 80 79 79 80 81 82 79 79 81 80 79 81 79 80 81 79 80 80 81 74 78 79 78 82 Durability Index Coar se Fine De Df 87 86 80 80 87 78 78 74 85 70 66 68 67 66 63 69 59 65 67 57 62 57 54 51 59 48 59 44 52 40 40 43 35 28 Tables and show grading, sand equivalent, R-value and other data secured in California's durability study One set of data was secured from construction control samples as the various components of the roadway section were constructed The other set of data was secured from final record samples after the roadway had been completed Perhaps a third evaluation that is needed and may be secured to a limited extent would be from tests after these roads have been in service for many years The above data are not always conclusive because the frequency of sampling is too limited to get good statistical values Generally the final record samples show a breakdown of the aggregate, that is, finer gradation and lower R-value and sand equivalent The data also show that this breakdown can be related to results of this new durability test It may be noted that some inconsistencies exist in the attached tables, particularly in the average grading analys es between the control and record samples for aggregate subbases This can probably be best explained by the fact that most subbase control samples were obtained from a windrow, and it could not be established with any degree of certainty where the material represented by the control sample would be placed and compacted on the roadbed This coupled with the probability of segregation during placing and grading variations in each load of material, may account for those data showing a coarser grading in the record sample than was found in the control sample Because most of the base control samples were obtained immediately after being deposited on the roadbed from a spreader box, a better determination of the actual location of the material represented by the control sample was obtained One of the early phases of this durability study was the compaction of aggregate samples and subsequent testing to determine the changes in test characteristics Aggregates were compacted using efforts far in excess of that required for normal compaction in order to accelerate the normal breakdown and then the resulting materials were tested to compare the new characteristics with the former characteristics 124 TABLE AVERAGE TEST RESULTS OF CONTROL AND RF:CORD SAMPLES ON AGGREGATE SUBBASES No Locations Control or Re cord 60-3TC37-F 61-3T13Cl8 c R c R c R c R c R c R c R c R c R c R c R c R c R c R c R c R c R c R c R c Contract No 62-10Y24C01 61- 1Tl3C16 61 - 3T13C 5- F 62-2T13C2 60-3TC38 60- 3TC24 - FIPD 61- 4Xl3C 39-P 60- 5VC11-F 62-10T13Cl 62-11V l 3C4-F 61 - 6X 13C51-F 60- 5TC1 61-5X13C26-P 61 10T l3C l 61- 4MBC1 61- 4Xl3C3 8-P 61-4T l 3C26-P 10 fi2-2Y24C05-P R Avg Pa ssing Sieve ( %) 1% in % in No No 30 94 92 100 100 75 72 92 94 82 88 63 52 B5 95 92 90 96 96 100 100 62 69 54 34 69 77 64 GG 79 73 82 86 42 39 76 76 100 100 35 40 44 27 44 51 42 3S 57 52 38 48 99 100 100 100 92 93 98 100 100 100 76 80 99 100 JOO 99 6B 90 56 BO BB 92 77 89 68 66 85 97 96 97 50 52 93 94 100 98 27 52 34 56 51 58 45 66 28 23 62 65 88 88 14 16 28 18 20 27 30 2S 39 34 18 21 100 100 36 36 34 46 49 50 22 24 46 46 48 51 14 27 26 44 23 29 30 50 100 100 100 100 100 100 100 100 89 97 100 100 90 98 No 200 4 12 15 8 7 B 10 12 13 6 11 16 12 14 B 12 14 15 16 B 14 16 10 12 16 27 Avg Sand Equiv 68 60 75 68 39 34 42 37 29 24 45 39 37 2a 48 54 38 36 29 27 38 35 54 39 46 40 32 30 50 39 58 44 22 23 40 2B 36 33 32 18 Avg RValue 77 82 69 74 70 70 80 83 80 80 81 83 81 77 81 76 BO B2 70 72 75 68 77 74 71 68 76 79 75 75 69 68 80 71 81 76 78 77 59 50 Durability Index Coarse De Fine Df 86 85 90 81 73 67 74 66 79 63 69 78 62 61 74 66 52 46 63 49 45 40 38 5B 35 30 36 2B 13 21 12 26 18 In addition to routine sieve analyses and sand equivalent tests, the R-values of these materials were determined before and after laboratory compaction The California resistance (R) value test measures the internal resistance to plastic deformation of a laboratory-fabricated saturated specimen subjected to a vertical load The saturated test specimen is placed in a Hveem stabilometer and a load of 160 psi is applied vertically The resultant lateral pressure transmitted through the specimen, read from the stabilometer gage, is used in determining the resistance or R-value of the material The R-value may range from 100 for a nonyielding specimen such as ste el to for a material having no internal resistance Some of the results of this phase of t e st research are summarized in Table a nd illustrated by Figures through 15 Figure shows a summary of the changes in Rvalue that r esults from excessive compaction of certain aggregates, whereas Figures through 15 show test data comparing actual degradation occurring between control and record samplings with the same material degraded in the laboratory compactor It should be noted that, although a somewhat higher degree of particle breakdown was achieved in compacting the material in the laboratory, particularly in the finer sizes, the general shape of the grading curves compares favorably with those of the field sample An interesting relationship is indicated by examining the sand equivalent values of the control samples compared to those values on the same materials sampled from the road after compaction, that is, final record samples Examination indicates that those materials having low e r values in the durability test are most likely to show the greatest reduction in the sand equival ent values as a result of handling and processing 125 TABLE SUMMARY OF LABORATORY DEGRADATION TESTS USING KNEADING COMPACTOR" (1, 000 applications at 290 psi) Sample No SE 60-2668 Base T D 60-2666 Subbase T 3/4 In No No 30 No 200 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 86 86 100 100 56 52 61 61 99 99 45 48 51 55 54 58 97 97 60 63 58 66 56 62 56 57 49 50 100 41 100 100 100 100 100 48 97 98 46 56 58 68 100 100 51 71 48 92 34 51 67 79 72 76 45 78 36 17 31 61 43 86 5J 80 37 44 60 65 70 87 30 33 29 29 90 88 22 27 20 25 27 33 56 60 24 3J 29 40 36 46 36 39 28 31 19 29 49 59 16 24 15 29 77 84 24 49 24 70 J6 30 39 55 49 50 22 54 J6 32 11 35 10 54 22 54 21 26 28 35 42 64 100 100 39 48 21 29 21 29 18 37 19 26 50 56 24 36 28 30 54 56 16 25 21 60 27 61 46 80 25 41 36 69 11 D 61-4238 Subbase 62-3177 Bas e 61-1400 Bas e 61-4332 Base 61-4116 Base 61-3819 Subbase 62-3228 Base 61-3567 Base 60-3358 Subbase 61-4335 Base 62-3284 Base 61-1245 Subbase 60-2799 Bas e 62-2933 Subbase 62-4171 Ba se 62-1003 Bas e 61-1044 Base 61-2861 Subbas e 61-2431 Subbas e 62-3064 Subbase 62-1691 Subbase 61-5058 Base 61-5445 Subbase 61-3963 Subbas e 61 - 843 Subbase 61-624 Base 61-3101 Bas e 62-4144 Subbase 61-1199 Subbase 61-4459 Subbase 61-1231 Base 62-1679 Bas e 61-3851 Base 60-2919 Base 61-1365 Subbas e 61- 300'1 Base 60-3408 Subbasc 61-506 Subbase 62-1685 Base 61-2788 Subbas e 61-5444 SUbbase 61-1483 Subbase 60-3950 Subbase 61-4154 Subbase 61-5123 Subbas e Durability Passing Sieve ( %) Type of Material T D T D T D T D T D T D T D T D T D T D T D T D T D T D T D T D T D T D T D T D T D T D T D T D T D T D T D T D T D T D T D T D T D T D T D T D T D T D T D T D T D T D T D T D T D 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 80 86 100 100 100 100 100 100 100 JOO 100 100 JOO JOO 86 92 100 100 100 JOO 100 JOO 100 100 100 100 100 100 100 JOO 90 95 100 100 JOO 100 97 99 46 55 42 5J 5J 67 48 54 JOO 100 38 53 66 89 78 79 52 58 43 87 45 74 60 93 62 69 55 83 33 72 44 ~ith 1, 000 appHCfttions at 290 psi T, values as usad; D, values after laboratory compaction R- 68 37 82 75 73 78 66 49 37 43 30 67 59 29 26 46 28 37 23 40 27 42 26 25 23 34 22 44 26 34 22 52 32 35 15 30 15 39 17 32 28 24 19 19 16 22 13 24 17 30 17 33 16 25 13 37 28 29 22 34 17 28 26 47 43 34 27 79 58 73 83 83 79 77 80 81 74 71 5 a 19 21 21 10 20 13 19 13 10 13 10 17 15 22 14 14 31 53 28 35 15 20 32 25 27 12 36 16 21 34 36 11 13 18 18 40 12 14 11 15 11 10 16 10 13 14 24 11 15 10 26 32 10 31 14 37 16 33 21 21 50 24 26 42 20 37 23 43 23 27 23 35 32 22 16 62 31 31 20 19 11 39 19 53 21 29 14 28 Index Value 84 83 68 81 84 82 80 81 79 84 80 71 64 79 79 81 80 78 87 80 22 84 27 82 66 56 26 57 47 82 11 79 53 81 25 80 46 48 81 81 83 81 61 52 65 65 77 79 76 60 80 70 82 73 71 48 8J 80 73 76 71 42 82 83 78 30 58 30 79 43 79 54 68 13 76 56 De De 67 86 88 85 8J 67 78 78 74 76 74 73 67 73 67 73 65 78 76 62 76 62 67 57 40 33 38 33 40 31 29 29 35 28 26 27 27 26 35 43 25 23 24 22 28 20 25 19 26 16 16 62 57 57 62 52 50 49 45 59 44 48 43 48 41 52 40 40 40 43 38 58 42 38 36 47 15 22 14 24 13 21 12 26 10 26 126 90 ao • I I LEGEND I - - - - ~ @ A-Value of "As Received" material R-Value of material compacted 1000 tamps using Hydraulic Compactor o - I CONTRACT 62-3TC3 crass Agg Base - Locations Dc=62, Dl=57 eo- AVG CON TROL AVG RECORD Q t LAB AS USED L AB DEGRADED S.E R-VALUE 40 79 Bl Bl Bl 40 37 2B ,; J GRADING LEGEND I r I f /10 ) J - : b- I I o {J / I) D / 0 v' / 'jl J U' , ./ ~~ / r - 20 ·' , _:::: ~ ·~~ 10 v Figure 100 9D- o- -~== ~ Q t(/) (/) ~ po.:::- 200 100 50 30 16 U.S STANDARD SIEVE SIZES ' Comparison of changes in aggregate test values between construction place ment and laboratory degradaL.luu CONTRACT 61- ITC6 Class A11g Base -4 Locations Dc=52 , Dl=40 S.E R-VALUE B (.!) ,, -"''# v AVG CONTROL AVG RECORD LAB AS USED LAB DEGRADED ct 60 35 26 37 23 81 74 82 73 / h" h )/ l' I GRADING LEGEND I /Y/ J b- """" o {J I I;, 1- z / ~ 50 VI I I/// /, a: w a _ /' / r/ I 11/ / ,,-' k7 [/ ;: _) 30 I- V/ ~v v - :::::.: 20 10 v Figure 10 -5 ·-"' ~ -.,;,: i - 200 too 50 30 16 US STANDARD SIEVE SIZES e Compari son of changes in aggregate test values between cons truction place ment and l aboratory degradat ion 129 100 90 t- BO ~ - I!) ~ en en ~ 70 AVG AVG, LAB LAB CONTRACT 60-IDDCI S-P Class AQQ, Base - Locations Dc=40, Df =43 GRADING S.E R-VALUE LEGEND CONTROL 78 24 RECORO 79 25 [!, A AS USEC 27 Bl DEGRADEO 23 o o 80 • ' // f1 VI I vv) I 60 I 1- '/ z ~ 50 / a:: w a_ 40 , ~ / _,,,,, L/ 10 - I Figure 11 100 90 I 80 I I!) ~ en en ~ ==:: - 70 I - ~ 1./ ~ v- ~,, i. :- / 20 ,, ~ / ~ , .- 200 100 50 30 16 US STANDARD SIEVE SIZES - " CONTRACT 60-STCIO Class Agg Subbase - Locations Dc=38, Df=58 GRADING S.E R -VALUE LEGEND 76 AVG CONTROL 32 AVG, RECORD 79 30 [!, -A LAB AS USEC 73 35 o o LAB DEGRADED 32 78 • I (I / • // tf/ / a:: w ~/ ,~I/, a_ 40 // _J //, ~ 20 - -5 ~ // ;) I~ /; v '/ (J ~ -?' "~ ~ _, v / v ·' ' / / I/ 30 I- ' u ~ 50 Figure 12 v z I I Comparison of changes in aggregate tes t values between cons truction place ment and laboratory degradation 1- I / / _ I v:? J - 60 10 /1 , Ir' I i tI j !1 'I' ) ,/ 30 I- I t I I • _J v II ~ 200 100 50 30 16 B U.S STANDARD SIEVE SIZES Comparison of changes in aggregate test values between constr uction pl ace ment and laboratory degradation 130 100 90 80 (!) ~ 70 I - CJ) CJ) ~ CONTRACT 61-5X l3C26- P Class Aaa Subbase - Locations Df=35 GRADING S.E R-VALUE LEGEND AVG CONTROL C> 50 75 AVG RECORD 39 75 LAB, AS USED -6 44 71 -0 LAB DEGRADED 26 64 • 60 ~ //, I I - ~ I~/ /' 20 / V lJ; Cl:: 10 J~ ~f / I 30 I- , - ~- _,y" :. -~ / I vJ / ~ I ,,/ / z 40 - /~ • t! 50 -' ~ ~ I 1- w ~ ,/ ~, //.,,/ 200 100 50 30 16 " U S STANDARD SIEVE SIZES Figure l3 Comparison of changes in aggre gate te st values between construction pl acement and laboratory degradation -, JO0 CONTRAC T 61-4X 13C 38-P Class Ann Subbase - Local'\ons 9OtDc =l3, 01=21 GRADING S.E R-VALUE LEGEND Ba AVG CONTROL ~ 40 81 AVG RECORD 28 76 (!) Z Q t - LAB AS USED -6 39 79 iii -0 LAB DEGRAD ED 43 CJ) • if 60 z ~ 50 0: w II I 40 ~ 'I 03 I- / 20 _ "' / ~ ,/ ~ - ~ - Figure l4 I ,/ ~ I , .// / ~ -· vv _ 17 I I // "'/ v / v I I 1/ / / I '"' II I I / i -' • 1/ 1- / I I v J I v / ,_ - v 2.00 100 50 30 16 US STANDARD SIEVE SIZES Comparison of changes in aggregate test values between cons truction place ment and laboratory degradation 131 100 90 , _ 80 (!) z iii , _ 70 (/) ~ 1, CONTRACT 61·4Tl3C26-P A.gg Subbase - 10 Locations 12, Of= 26 GRADING S.E R-VALUE LEGEND Q 78 AVG- CONTROL 36 n AVG RECORD 33 ~ LAB AS USED 79 53 """"' o a LAB DEGRADED 21 54 ,/ ~ oc • 'iJ • / ,/' 60 z , ~ 50 a:: / w If/ n 40 _J ~-/' ~ 30 I- 20 _ 10 I - Figure 15 ~- "" ,,,.""' ,,"' 1· ~~ dv / I/ / v v / J / '/ ,, ~/; '/ tv // 1- /t'/ / /,, 200 100 50 30 16 U.S STANDARD SIEVE SIZES B - Comparis on of changes in a ggregate t est v alues be t ween construction p l ace ment and laboratory degradati on ~~~~~~~~~~~~~~~ 00 ~~~., ~~~ ~~ ,. ~-. -,c-r~~ 100 Ll Cf) _J c:: f- ~ 40 (.) IL f- ~ 60 _J :g: ::::> w 80 z