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”