Rajan singh rawat

INTRODUCTION Admixtures are ingredients other than basic ingredients cement, water and aggregates that are added to concrete batch immediately before or during mixing to modify one or more of the specific properties of concrete in fresh and hardened state. Added in small quantity either in powder or liquid form Combination is used when more than one property to be altered.

PURPOSE 1.To modify fresh property Increase the workability without increasing the water cement ratio or decrease the water content at the same workability. Retard or accelerate the time of initial setting. Reduce or prevent the settlement or create slight expansion. Modify the rate or capacity of bleeding. 2.To modify harden property Reduce the heat of evolution. Accelerate the rate of strength development at early stages. Increase the durability Decrease the permeability of concrete.

Classification of admixtures 1. Accelerating admixtures 2. Water reducing admixtures 3. Retarding admixtures 4. Air entraining admixtures 5. Mineral 6. Super plasticizers

Super plasticizers These are the modern type of water reducing admixtures, basically a chemical or a mixture of chemicals that impart higher workability to concrete. Three different purposes or a combination of these to increase workability without changing the mix proportion. to reduce the mix water and W/C ratio in order to increase the strength and improve the durability. to reduce both water and cement in order to reduce creep shrinkage and thermal strains caused by heat of cement hydration.

Super plasticizers (SP) are basically classified in the following categories: 1.sulphonated melamine formaldehyde condensate (SMF) 2.sulphonated naphthalene formaldehyde condensate (SNF) 3.modified ligno-sulphonates (MLF) 4.other organic compounds ( sulphuric acid ester and carbohydrate ester) There are three possible ways in which super plasticized concrete can be produced : 1.High workability concrete, 2.Concrete with low water/ cement ratio, 3.Concrete with reduced cement content.

Material Cement: Ordinary Portland Type-1 cement was used. Fine Aggregates: Fine aggregates confirming to the gradation of ASTM-136 were used. Coarse Aggregates: Lime stone crushed stones of size1/2 in and below were used.

Review Two types of super plasticizers (Rheobuild 1100, Rheobuild 561M) Three nominal ratios of 1:1:2, 1:1.5:3 and 1:2:4 The water cement ratio as 0.50, 0.55 and 0.60 Experiments have been divided into three series namely a) Series No 1: workability series, b) Series No 2: water reduction series, c) Series No 3: cement saving series

Series No 1 (workability series) A.EFFECT ON WORKABILITY AND COMPRESSIVE STRENGTH Slump tests were carried out Cubes [6*6*6] were tested at the ages of 3,7,28 days. a.Mix proportion 1:2:4 Test results showing effect of super plasticizers on compressive strength and workability at constant w/c ratio.

Effect of SP on Compressive strength at constant W/C ratio Rheobuild 561M gives better results than Rheobuild 1100.

b: Mix proportion 1:1.5:3 Test results showing effect of super plasticizers on compressive strength and workability at constant w/c ratio

Effect of SP on Compressive strength at constant W/C ratio 7 day compressive strength increase was commendable when compared to mix proportion of 1:2:4.

c: Mix proportion 1:1:2 Test results showing effect of super plasticizers on compressive strength and workability at constant w/c ratio

Effect of SP on Compressive strength at constant W/C ratio The increase in 3 day compressive strength was great as compared to other two mix proportions.

B.EFFECT ON SPLITTING TENSILE STRENGTH Cylinders (6*12”) was tested by splitting tests at the age of 28days a: Mix proportion 1:2:4 Test results showing effect of super plasticizers on splitting tensile strength of concrete at constant w/c ratio

b: Mix proportion 1:1.5:3 Test results showing effect of super plasticizers on splitting tensile strength of concrete at constant w/c ratio

c: Mix proportion 1:1:2 Test results showing effect of super plasticizers on splitting tensile strength of concrete at constant w/c ratio Increases in splitting tensile strength at a constant W/C ratio. Slump values for the same w/c ratio are slightly different from the case of compressive strength and workability.

C.EFFECT ON (MODULUS OF RUPTURE) FLEXURAL STRENGTH Standard plain concrete beams were tested at third point load after 28days of pouring. a: Mix proportion 1:2:4 Test results showing effect of super plasticizers on modulus of rupture (flexural strength) of concrete at constant w/c ratio (series-1) Mix proportion 1:2:4

b: Mix proportion 1:1.5:3 Test results showing effect of super plasticizers on modulus of rupture (flexural strength) of concrete at constant w/c ratio (series-1) Mix proportion 1:1.5:3

c: Mix proportion 1:1:2 Test results showing effect of super plasticizers on modulus of rupture (flexural strength) of concrete at constant w/c ratio (series-1) Mix proportion 1:1.5:3

Series No 2 The water content was gradually increased, at constant workability. Keeping all other ingredients of the mix constant, increasing the dosages of the SP to compensate for the loss in workability. SURAJ Test results showing effect of super plasticizer on water reduction and compressive strength at constant workability (series-2) mix ratio (1:1.5:3)

Effects of super plasticizer on compressive strength at constant workability

Test results showing effect of super plasticizers on water reduction and compressive strength at constant workability (series-2) mix ratio (1:1.5:3)

Effects of super plasticizer on compressive strength at constant workability

Series No 3 Cement content and water content were reduced keeping water/cement ratio and workability as constant SURAJ Test results showing effect of super plasticizer on cement saving at constant work ability and constant w/c ratio (series 3) mix ratio (1:1.5:3

Test results showing effect of super plasticizer on cement saving at constant work ability and constant w/c ratio (series 3) mix ratio (1:1.5:3)