Date post: | 13-Apr-2017 |
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DETERMINATION OF ADMIXTURE DOSAGE BY – MARSH CONE TEST
ByMiss Vrushali PatilMiss Amal Pandhre
AdmixtureWhat is an admixture ?
A material other than cement water aggregate
HISTORY History of admixtures is as old as the history of
concrete it embraces a very vast field . Specially developed in Japan and Germany
around 1970 Later on they were made popular in USA and
Europe Unfortunately the use of plasticizer and super
plasticizer have not become popular in India till recently (1985)
Recent advances and challenges in concrete technology High quality concrete : HSC and HPC
chemical admixture : Super plasticizer to provide the desired properties.
However, variations in the characteristics of Cement and type and dosage of admixture compromises benefits of super plasticizer due to incompatibility problems.
TYPES OF ADMIXTURES
Admixture
Chemical admixture
Plasticizer
Super plasticizer
Accelerators
Set retarders
Mineral admixture
Blast furnace slag
Flyash
Silica fume
Rice husk
OUR INTERSET OF STUDY
Super plasticizer
STUDY OF THE COMPATIBALITY
OPTIMUM SUPERPLASTICIZER DOSAGE
COST-BENEFIT CONSIDERATION
SELECTION OF THE SUPER PLASTICIZER
Factors affecting cement -superplasticizer intereaction
Direct effect :Rate of hydration reactionSolubility of calcium sulphateAbsorption of superplasticizer
HOW MUCH QUANTITY OF SUPER PLASTICIZER TO USE
?
MARSH CONE TEST :EVALUATION OF THE OPTIMUM DOSAGE
i. 70% of mixing water is
added with cement
ii. Superplactisizer and
remaining water added after
one minute
iii. Mix for two minutes at same
speed
iv. Then pass cement slurry
through the funnel
simultaneously note time
MIXING SEQUENCE
CASE STUDY Different types of cement
OPC PPC
Super plasticizer - POLYTANCRETE
Different dosage 0.1 to 0.5
Procedure i. As per IS code 2kg of cement- Marsh cone test
and w/c ratio is 0.4 i.e Cement = 2kgWater quantity = 2000X 0.4 = 800 g = 800ml
ii. Super plasticizer dosage is varied from 0.1 to 0.5
iii. Slurry is prepared iv. The prepared slurry is passed by the marsh
cone test and the time passing the cone is noted as t sec.
v. A graph is plotted dosage in % versus Marsh time (sec)
LAB TRIALS
OBSERVATION TABLE 1TYPE OF CEMENT
W/C RATIO
QTY. OFCEMENT
DOSAGE OFSUPERPLASTICIZERIN “ %”
MARSH TIME
OPC 0.4 2 KG 0.2 3’46”OPC 0.4 2 KG 0.25 3’10”OPC 0.4 2 KG 0.3 1’ 39”OPC 0.4 2 KG 0.35 1’ 30”OPC 0.4 2 KG 0.4 1’ 16”OPC 0.4 2 KG 0.425 1’1”OPC 0.4 2 KG 0.45 1’0”
OBSERVATION TABLE 2TYPE OF CEMENT
W/C RATIO
QTY. OFCEMENT
DOSAGE OF
SUPERPLASTICIZERIN “ %”
MARSH TIME
PPC 0.4 2 KG 0.2 2’ 16”
PPC 0.4 2 KG 0.25 1’ 48”
PPC 0.4 2 KG 0.3 1’09”
PPC 0.4 2 KG 0.35 1’ 09”
PPC 0.4 2 KG 0.4 14”
PPC 0.4 2KG 0.425 8”
OBSERVATIONFrom Graph - zone of
saturation dosage of 0.425%and 0.35% for OPC and PPC respectively.
After a sudden change in the time and the constant value of time shows optimum dosage of super- plasticizer
0.15 0.2 0.25 0.3 0.35 0.4 0.450
20
40
60
80
100
120
140
160
180
200
220
240
OPC
PPC
DOSAGE in %
TIM
E IN
SEC
RESULTi. The optimum dosage of
polytancrete SPR Superplasticizer for OPC cement is between 0.425 to 0.45%
ii. The dosage of polytancrete for PPC cement is between 0.3 to 0.35%
CONCLUSIONFrom this case study it is concluded that the % of dosage of same plasticizer for different type of cement having same w/c ratio is DIFFERENT.
%dosage
MARSH TIME OPC
MARSH TIME PPC
0.2 3’46” 2’ 16”0.25 3’10” 1’ 48”0.3 1’39” 1’ 09” 0.35 1’25” 1’ 09”0.4 1’16” 14”
0.425 1’01” 8”