Compatibility of admixture with cement

1. Title MINIMUM AND MAXIMUM DOSAGEOF ADMIXTURES
Basic Information
Learning relatedto
function
QualityManagement
Discipline Civil Construction
Package Civil Quality
Learning Details
Description To facilitate approval of admixture inconcrete mix, the typical dosage
and possible detrimental effectsof underandoverdosage isrequired.
The minimumandmaximumdosage shouldbe knownpriortocarry
out concrete mix designsatsite.
Root Cause GenerallyinDatasheetsof admixture the minimumandmaximum
value isgivenas1.0 % to 2.0 %.But it mayvarieswiththe Grade and
Brand of cementand shouldbe determinedpriortoconcrete trials.
SolutionAdopted Testthe consistencyof cementadmixture slurrywithMarshcone isas
follows:
-Mix the cementmortar withw/c0.32 to .035
-Watershouldmixedinsteps70% of watershall be mixedincement
inbeginningandrest30% wateris mixedalongwithadmixture.
-Cementadmixture slurrythenpouredthroughMarshCone andtime
will be measuredinseconds.
-The procedure isrepeatedwithincrementof admixture havingsame
w/c ratio.
-Graph isplottedwithtime (Yaxis) vsdosage of admixture ( Xaxis).
-Saturationpointandlimitsof mixingdosage of admixtureinconcrete
isdeterminedfromthistest.
Learning Recommendedoptimal dosage isnottoexceedthe saturationpoint
foundfromthe Marsh Flow TestData. Excessive dosage beyond
saturationpointmayleadto segregationproblem.
Impact These valuesare beneficial indesignof everygrade of concrete mix
and limitsthe hitandtrial methodtofindoptimumdosage of
admixture in concrete, Hence savestime.
RecommendedPractices
Do’s Mix the cementmortarwithw/c 0.32 to .035
Don’t Don’tmix 100 % of waterwhile mixingincementin beginning
Attachment And References :Site Civil QualityManual,Docno.LTPQ-S-MNL-C-001,Revno.01

2. Attachment Brand of Cement:Ultratech
Brand of Admixture :FosrocSP 500
Observations
Sr No W/C
Wt of
Admixture
Wt of
cement
%
Admixture
of cement
Time of
flow
gms. gms sec.
1. 0.33 4.0 600.0 0.67 162
2. 0.33 5.0 600.0 0.83 132
3. 0.33 6.0 600.0 1.00 110
4. 0.33 7.0 600.0 1.17 106
5. 0.33 8.0 600.0 1.33 111
6. 0.33 9.0 600.0 1.50 124
7. 0.33 10.0 600.0 1.67 145
8. 0.33 11.0 600.0 1.83 170
0
20
40
60
80
100
120
140
160
180
0.00 0.50 1.00 1.50 2.00
% age admixture of cement
Timetakeninseconds

3. Saturation Point:Here the saturationpointisfoundat1.1 %. Hence
the dosage of admixture cannotbe increasedabove than1.1% insite
concrete.Compare the marshcone dosage withdesignmix dosage.If
the difference ismore than0.15-0.2%,call/checkwiththe
manufacturer.