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Transcript of REPORT ON DUNAGAN'S BUOYANCY APPARATUSdigital.lib.lehigh.edu/fritz/pdf/151_1.pdf · REPORT ON...
fRITZ fNGfNEER'~~G LABORATORY'LEHIGH UNIVERSITY
BETHLEHEM, PENNSYLVANIA
REPORT ON DUNAGAN'S BUOYANCY APPARATUS
By: J. M. Holme
lSI. f.
,;::
REPORT ON DUNAGAN'S BUOYANCY APPARATUS,
I - GENERAL PURPOSE OF APPARATUS,AND SHORT DTSCUSSIONOF OTHER tffiTHODS
The Dunagan Buoyancy Apparatus is designed for
the purpose of determining the constituents of fresh con
crete.-'';rhe;: industry has long felt the need ,of an efficient
appara tus for maldng thi s determination as it would un- ~
, dOUbt~y reduce' the time element in our present cylinder
strength tests. Several engineers have advanced methods
but without exception they lack practicability.
R. L. Bertin of the Vfuite Construction Company
described a method for segregating fresh concrete in the
April issue of the A;C.I. Journal, as have W. I. Freel,
G. J. Griesenauer, H. C. Ross and C. A. 'Huges. While I
have not attempted to apply any of these methods, I am of
the opinion they all fall short of their purpose. Bertin's
method is the one most ~orthy of.~ote, but should be placed(!.v,;(:. ......... .h.> Y;-~~ .... ~ , .
2nd to Dunagan's. ~fundamental suggestion is to eliminate
the use of previously established apparent specific gravities
thruout a series of tests. He states that different samples
of aggregate will give great variations in specific gravities
determinations~ This point he stresses but passes over the
subjects of silt content and the cement retained on the
/'
/Ij .V!;lOO'sieve by sayingtha t the final results should be cor-
rected'for these items. From my experience t4is past
semester, I would say that he has stressed too highly the
point which involves least error and slighted .the sources
of greatest error.
II - DESCRIPTION OF DUNAGAN APPARATUS A1ID DISCUSSION OF ITS USE
2
Conslanf WQ~r/~,..e,.((Jrert!ow .s;pouf ,.~ _
. 1-' ~;;""";;;;:;:';:--I
lit- -J-
10
0\
~ 1t'/~=1))1~(~11~ ~=-~ =~\'\\ ~""'''''=~''I''''~\'i\,\'/~'''1''""""",,,.'\ ~= k ~::::7-' ....-:::,. -_."\ =,- --- .,Cross section of apparat1.1.s - Balanced v:rithout'load asshovm
.when Q is filled to overflow. containeft"C" is. immersed· and
\ pan B is in position.''''v:;J
:#;Weighing of samples.'-J. -',. , :.
(a) In air~
Sample is'weighed in pan B to an even kilogram<"(
by placing' slotted,. Kgwg~. o~r~eft-hand side of balance...?:;'. .\
Cb') 0eighing SamPl~) '~l1llnersed.,
Container C is removed. and 'partly filled with water ..
3
The sample is poured into C and stirred to remove entrained
air. C is then filled with water, the sample allowed to
settle for I minute and then replaced on beam and Q filled
to overflowing. The weight iwnersed is then obtained by1-
placing wgs in pap B and sliding the rider "R II• The beam
is graduated from zero to ten grams and the weight is
accurate to the nearest one half gram.
III - 'NECESSARY PRELIMINARY TESTS
Before beginning any series of tests certain pre-
liminary tests must be made. A - Apparent Specific Gravi ties.
The fir st of these is for the.apparent specific gravi ties
of the aggregates and of cement. Representative samples of
the aggregates should be secured, soaked in water for 24
hours'and allowed to surface dry. Using either surfaceCi--
dried coprse aggregate, surface dried fine aggregate, or
cement the sample is weighed in air and its weight recorded
= 1000 gms.
= 1000 gms.
2000 gms.
x·and its (Vfg; recorded as
---'
(}-(C'o]irse aggrega te =((Fine aggregate((Cement(
The sample is then weiShed iwnersed
·w~..J._-=Then.app. Sp. Gr. =(WI - w~
A - Consistency of Results
In our work we made a series of determinations for
the specific gravities of the aggregates and of the cement.
For the cement we obtained a consistent result of 3.1. For
the aggregates results were averaged in both cases and varia-~ ..
tions from the mean.noticed~~ The largest variation from the
mean was in no case greater than 2 parts in 260. This is
certainly a striking contrast to figures Bertin cities vlhere-
in he notes variations from the mean as large as 9 parts in
260. I am inclined to believe with Dunagan that sampies
taken from the same stock pile will give a resulting apparent
specific· gravity that will not cause any appreciable error
in the results. At any time results are in doubt tb~ ag-
gregates can be checked for the specific gravity by weigh-
ing immersed, surface drying and weighing in air.
B - IVioisture Determination
The determination for free moisture or absorption
is based on the previously determined ~pparent specific
-gravity.
is positive. If the result is a negative vilue it indicate~
the amount of moisture the aggregate ,is capable of absorbing.
These tests should be made before actual working tests and
should be checked from time to time during the work. cor,:,
rections can readily be made and resulting errors are
negligible.
C - Silt Determination
The remaining preliminary tests are for the purpose
of determining the percentage of silt in the aggregates and. 'I
the percentage of cement retained on the(l)lOO sieve. Silt·!.,,~I c'\.
is considered to be any of the aggregate passing the'@lOO
sieve. I shall outline the method Dunagan suggests for
these determinations.
A representative sample of aggregate is secured and
is weighed immersed.. Recorded Wl . The 'sample is then trans-. n -"
ferred to the ne sted sieve s {(1J4 on &rioo) and wasl:-ed until
free of silt. It is then weighed immersed again - Recorded
The percentage of silt = Wl - W2
Wl
C - Determination of Cement Correction
In his manual Dunagan. makes mention of the cement
retained on #100 sieve but fails to state a method for
determining its percentage. It may be obtained in two ways.
1 - weigh a' sample immersed - record Wl . Transfer to #100
and wash. Weigh immersed the cement that does not pass the
sieve and record W2 •
percent retained W2
2 - Use a mix of fi ne aggregate (wi th si 1 t previously re-
moved by washing) and cement in the proportions they occur
in the working mix.
Weigh the washed sand immersedjrecord Wl .. rt
.Add cement and recordtotolweight im.11lersedf\W2 •
Transfer tO~lOO sie~eand wash until all cement has passed
that will pass and then weigh immersed'/ record W3
./ (foJ retained = W3 - Wi J~t ~ W2 - Wl
These last determinations;(% silt passing the #100
and %cement retained on the #100) are the sources of error
that make determinations of the constituents of concre~e
obtained by this method of douQtful value .. I shall discuss
them after giving an example of an actual test run ..
IV - PROCEDURE FOR ACTUAL TEST
The preliminary tests described above are assumed
to have been run. A sample of concrete is secured.
aggregate)f~
\/1100 (fine..1
w~· immersed = W2 ./
It is washed on the nested 'Sieves(#~ and ~OO until free of\.j, f1..
cement and silt. The aggregate retained on (#7'4 (coJirsef/.J J.
is weighed im.11l~rsedtrecord w3~f~~e aggregate on
aggrega te) is added and total V>lJ W4 obtai ned •.
/f:sp gr j
W3 = Wj of C.A. immersed - W3 Sp gr- QJ, = wg of
C A in air. /
~jW4 ~ :- VI]3 = wfJ of FA immersed (W4-W3 sp gr- FA= Vl9
of FA in ai r. vi'
(fP gr )W2 - Vi = wg of cement immersed (W2- VV4 ) sp gr-l cel7?enl;:='4
QOEont =wg of cement in air.
v - DISCUSSION OF RESULTS AND PROBABLE ERRORS
The wg of the original sample in air minus the sum
of these last 3 wgs in air = the wg of the water. If no cor-
rections be made any silt that ·was present in the aggregates-'
in recorded as cement. Secondly any cement retained on the
#lOO is recorded as aggregate. These two factors do not
cancel each other and the result is the w/c is incorrect.
Corrections can be made for both of the se factors but the
corrections are of uncertain value.
In one series .of tests which we made to determine
the percentage of silt in fine aggregate the mean equaled
0.8% silt. The greatest variation from the mean was 1.0%.
This variation would cause an error in the w/c ratio of
0.2 gals,. per sack. For 2000# concrete this error (if it
were the only error) might not be serious. In another series
of tests on different sand we found a mean of 4.83% silt
with the greatest variations from the mean = 2.1%. This
variation would cause an error in the w/c ratios of 0.4 galsl
sack. An error of this magnitude would probably render the
7
concret@ 'que,'s'ti·onabJe~Errors 0 f thi s nature fallon the wrong
side of safety, since they give a W/C ratio of a lower value
than the actual W/C. Consequently a strength determination
based on this method would indicate too high strength concr'ete.
The question of cement retained on the #100 sieve
is dependent on several factors. 'More cement is retained
when washed mixed with sand than when washed alone. The time
washed with sand in proportions of the mix the
These second washings were done as nearly as
done in actual test.
and thoroughness of washing ,also have
In tests ,:we made (When washedr ~0.8~. WhenV.I, Q .(l. --~ %re t '= 1.6%.
,,/-- ._~
possible to the way they would be
a decide.-. d ~ffec~~ ,oP", ,~'i~__.J.J
alone) the ~\retained =-' : ,-,1 1\ '
.' ..... 1
How-
, ever" Mr. Nettles determined that by continued washing he
could grea tly reduce the percentage retained. lr~ashing a
sample without the addition of sand he obtained 0.9% ret., '
Washing a second sample together,with sand and continuing
washing long after'the lait trace of cement passing could. ,',..
be detec ted he obtained a figure 0 f 0.9,3% retained whi'ch is
in close aggreement with his first figure. I am of the firm
opinion and our tests bear witness that with oIdnary washing
the percentage of cement retained on the #100, s~e isa
function of the sand (both quantity and kind).
'VI - EXAMPLES Al\lJ) DISCUSSION OF RESEARCH AND FIELD TEST RESULTS
, In handling the apparatus during the coursel of a
test (that is weighing and vlashing) considerable care must
aggregate will cause an increase
An error in weighing againin
this may be/either direction.
//
l~S of
';}: ,
~J,.6'--
'V'
I\
).I
be exerCised.; Any, !' I,
in the .cementJ determinat ion.- { ~--)
I\;ffects tbe ~llc }but. ..;-~-+"...",
On the accompanying sheets, 1,2,3 are the results
of five tests we made on one batch of concrete. It may be
seen in each case the water cement ratio is somewhat less
than the actual, water cementra tio used in preparing the mix.
The largest vai~iation amounts to 0.31 gals. per sack, while
th~ average variation is 0.17 g~ls/sack.
On sheet 4, I have ·li sted .several of the results
taken from actual test done for the Clinton Conveyor by Mr.
Dunagan. These samples \vere'in each case, taken from a mixer
and in each run the samples received approximately the same, . ' ~
amount of mixing. The results show great i~consistenc~s.
. r ,In two case s the\ W/¢) is approximately 1 gal. low. In an-
. '---.._/ ..
other case it is 1.72 ga1./~ack too high. 'A third value is
0.28 ga1s/s~ck low and two 'additional values 0.08'ga1s. per'
sack high.
,From the comparision of these few figures )'Nhieh are
symbolic of both sets 'of te sts in general) I f e'e1 that our
results are by far the more' consistent and show that they
are the result of extreme laboratory care. The second set
of figures (sheet 4) are such as might be expected from
field tests made with the apparatus. It is decid,ed1y im-
Corrections t:; I .rO ~ - U1 • .r-! . °,rO Weight Submerged Q).p H P lQ ~ 'J1 • • r.:: r-1 .ptU) Z• 0'
Q) +' ..c:rd Q) rl ° .p • I:) r.:: +' rlrl 0 ° H·r-!..- •0 +' tU) I:) bfIl) .r-! • I +'H .r-! ..c: oe:- ro ° ..c: o A .r-! :> OHX CHZ ..c: H <I) 'r-!b.O rl H . '¢.r-! .p tU) .r-! X [;J .r-! b.O :>U1 +' • AO.r-! Q)S b.O <I)' .... Per Silt Cement H <l)H A b.D H bJJm !.is .r-! .p lQ .......... .p .r-! 'r-! H 0: ° .~ 0::<I) <I) .r-! S H~ ..-l .b.D .r-! 0:: <I) ai • 0 H <I) ord ° p HCH ..
rl ~ <l)p Cent -No. +No. Total 0 s .p A . a>r.:: :s: 0:: rl rl 0 ~ en A <It p-!o U1A H :s:: ~ 0 P rl W A :s:: .r-! I:) X m A p Q 0 <I)8 * en 100 100 ::J ::J CJi ---.. ~ I:) ·bJJ ° ~ ~.p H ~ by by' +'m * u: ~** ~ p ---..+' H .0 ::;. p-! p 0U) '* **
~.
wt. ~.V.s: s: II p-! ....... Z.- _. .-
j 1 "'/f93.1l :;.27&,,0 1/38"£t. ;I2 3039.() ..
3 ,z39.? 239.0 /?,Zh /7,28'~-_.
G.1C/() --4 */6/t?-5" /h, O'6'~5 'J<t76£.3 :'J<~3
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7 .;l. f~,5' ·.~,6 -4,7-~,tg f ~~ -6,9 k?$~ ~~"'76 Aj~~() /.tJt/tl 11317.4 9,4,z ,/, t?t?O ~~3
8 ~,j'ft' tt,~ '3 6,7£~---
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3 'z33/1 .:l.3'j/1 /7,7tJ J',2.'64 *J.5:2tJ,5 t£ ..3f'
* 8'~Z. 7 ~*t'.2 ~*~6~3-
5 f~.~ -+2,{, '?'8s.~ /4-1£? '3,694 5tO,1W.2,4! 3,CJtJ5 44.'1r 6.37. g' it'*/'Z +7.7 ,-4.E 1-3,4 G4/,2. **./- ~..2..f' :;~-1Z.~ 2,~b2- 40(J.r ::10,33 ;),5'iS" 2i',787 ,27/, :;l. l<~0 -2.(,;-7,7 -1-4-3 -~.O .;:Lr;~-. ~ 'i<~476 39/,"1 /,t/lJtJ /;lb, z. '1,55 J, df)O 9,2-3
, 8 I !0.59'! G.7.3 : I ~,7-1
****
Test DataKey: - 1. Total Sample
2. Cement + Sand +3. Water4. Stone and Sand
** Preliminary
'stone
Test Data5. Stone6. Sand7. Cement8. Water-Cement
OperatorSample) (1Taken ) (2
Corrections t) I .rd >.. -- Ul • 'M . 0rd Weight Submerged Q).p ~ .,olQ ~ fJ} . • s::: ..--1 .p~ Z• .,
Q) .. -P ..Qd Q) ,-j 0 -P • 0 s::: .p ,-\..--1 0 0 H'M •0 -P QD otu:Q.> 'M • I -PH 'M ..G ot- co 0 ..G o Pi 'M :> OH>< tt-lZ ..G ~ Q) 'M~ .-I H . ..G 'M -P ~ 'M >< OJ 'M QD :> Cf.l -P • Pi 0 'M illS QDQ)Per Silt Cement H Q)H Pi till H ~co co 'M
-P lQ __-P 'M 'M ~ 1J2 0 ~ 0::Q) Q) 'M S ~~ 'M • till 'M 0:: Q) co • . H Q) .rcj 0 ,0 ~tt-l .,
.-l !A Q)p bent -No. +No. Total 0 s .p Pi • <J>S::: ~ 0::.-1 .-l 0 ~ UJ . Pi <r\ P-lo Cf.lPi H ~ ;:j D ,0 ,-\ uJ PI ~'M 0 >< co Pi ,0 • 0 Q)8 * . if, 100 100 ~ ~ CfJ --.. >.. 0 · QD 0 >.. -:t:.p H >.. by by' .pco * u: ~** ;?: P -..-P H .0 ~. P-l P <:I~/) *~.
** ES:i§: II P-l .....- wt. ~.V. z-- -1 I'" :.2. tJ3'6' !/.;..1a?3 7691,5" -2 127.28:.< -_.3 ,?~q.·8 :J-09',8' /6,9/ 17,2~ d4 */"(1'z.r5 r·~53.5 '*tJ,~ -/",2,& +'z,~ gS{;,/ 1'f'-1"j, ~J3 1/.JfK,~ a. g"(),j. 15#/,9~J.h~ 3.9tJS l4~i6.~>.--.--6 5'!r,J :*/.Z of ?,I -4./ 1-~{) .s-9,g, 3 /l<~•.~.a5' 9~,.! .e,r;/7 371/,2-12q,~ 2.5"f5" b~,?f
7 ',254.; /.6 -.2.6-?-1 -1-4./ -5:;; ,,21'9./ Pi'~..f7~ 3617.7 /.~tl{) 11/8,IP 9,5;; /,0lnJ Q,:J..38 0,57/ (;.-1$ -- .---- . -
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! 8 I 1 it),5¥;J... b,5"5'
9tJ6/3, '.
* Test Data*** Key: - 1. Total Sample
2. Cement + Sand +3. Water4. Stone and Sand
** Preliminary Test Data5. stone
stone 6~ Sand7. Cement8. Water-Cement
OperatorSample) (1Taken ) (2
.........
Corrections 8 I 0
to ~ - U2 • •...i . 0to Weight Submerged (J)~
~ ~~.0 l!J ~ 'il . 0 5=: ....-1 ~till :z;
• a.> -P .Qd 0 -P . 0 l=: -P r-Irl 0 0.. -. H·...i .0 -P QD ot:uW .r-;l • I -PH .,-1 .s:: ot-- ~ 0 11 0 A ''-; :> OHX (j.-fZ ..s:::: H a.> .,-;t-J) r-I H • ..s:::: .,-1 .p QD ....i X rJl .,-4 :> U2 -P . PiO •...i Q)
S t<o a.> Per Silt Cement H a.>H A till H QDctl as .,-1.p l!J __ .p •...i •...i H t:r: o ~ 0:a.> a.> •...i E H ;:s:a.> .,-1 • till .,-1 ll:: Q) aj • 0 H Q) otO 0 .0 H(j.-f ..
.-l !A a.>.o Jent -No. +No. Total 0 s ~ . IV5=: ~ ll:: rl r-I 0 ;s 8] A <!j P10 IJ)A H is: ::s 0 .0 r-I rrl A ~'...i Q X as A .0 • 0 ())s * if, 100 100 ::s ::l UJ
---- ~Q . b.O 0 ~ <:t: +-=> H ~
,--. .p
ctl * U). ~** ~ .0____-P
H P 3': P1 .0 by by 1.0U) * ** ~ ~ II P1 --- wt. i\.,V. \Zl
17FCJ.~-l' '-' -
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5 * 1<* **....~- ; ~ -- -' -., . /
C "* **.7 :'1' **
8 I.. , !
****
Test DataKey: - 1. Total Sample
2. Cement + Sand +3. Water4. Stone and Sand
** Preliminary
'Stone
Test Data5. Stone6. Sand7. Cement8. Water-Cement
Gperator3ample) (1Tak-en ) (2
/ ~) 7,0
,/brCenl- A.6.so/ure Yo/u.I77e II//x bv WeIQ.h;: "
,
Wafer Cemenl Sand Ii'ocK Cemenf .jf,,.,d '/?ock S'fR ~9a~KSltrndard /R..34 9.s"e ~S:t64 4~.S-O I ..z.~3 4./' ~,49 'hOt)
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1.I:f
possible to use the care and take th~ time necessary in field
tests that can be used in laboratory research work.
Therefore operating the apparatus under the present
suggested method results such as those on sheet 4 are to be
expected.
VII - TECHNIQUE A1~ ADEQUATE SIEVES
I feel that some errors may be eliminated if a more
rigid code for operation is set forth. It is my stiggestion
that the sieves used be changed and a time element be intro-
duced into the washins. The accompanying figure sho'V1Ts theI
screens as I. think tb.ey might be arr'snged.
i'o",.p fils confa/ner waler'/-I9hl.
t}//ndriCa/conla/ner
~;%.s"pQce beTween sieYt:?S'/ anolconfa/ner .
f---!'------!
Both sieves fit tightly against sides of container
If an arrangement of sieve of this type could be
devised Rcleanu water could be used in washing; the sieves
could be shaken violently and no losses could occur ~~th
-
reasonable cars being exercised. If the pr eliminary tests
were made using these sieves the percentage of cement re-
tained on #100 could, I believe be somewhat controlled by
f .
using .the 2nd method I .have suggested for its determination
and by washing and shaking the sieves in as a consistent
manner for a certain established length of time.
VIII - CONCLUSION
I do not feel that the apparatus is without pos-
sibilities. It's greatest fault comes from the lack of ~
i' ~
check on the two most important iiems cement and water. ,AJ~~'1 f~¢J
As it stands therefore I do not think the apparatus serves /Ji1,. M""~"I ........\ ~.
its purpose to an appreciable extent. However since the \
sources of error are well known a study devoted to their
elimination should certainly bring about results that will
tend to increase the efficiency of the apparatus to a con-
siderable extent.
/.5