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CONCRETE CHEMICALS (HRWR & VMA)Report by:JAYDIP JADIA (080284106101)RAMESH MORI (090283106001]WONJANBENI ODYUO(080280106306)Report for Repair and Rehabilitation of Structure

Applied Mechanics department, L.D. COLLEGE OF ENGINEERING, Ahmedabad.11. HIGH RANGE WATER REDUCERADMIXTURES:

Admixtures are chemicals, added to mortar at time of mixing to modify properties either in the wet state or after mix has hardened.

Main Admixtures are available in market like plasticizers , super plasticizers and hyper plasticizers.

It can be single chemical or blend.

Usually it is in solution with typically 35-40% active chemicals.

Amount added generally less than 5% of cement content.Other types of admixtures are accelerators and retarders.Mechanism of action:

1) Chemical integration in hydration: (accelerators and retarders)

2) Surface acting type on cement surface causing better particle dispersion(all plasticizers)

3) Increases viscosity of water (viscosity modifier used)History:Plasticizers - 1932Air entraining admixtures - 1941Super Plasticizers -1953Hyper Plasticizers -1995 Types of Admixtures:

Plasticizers: Reduces water content up to 5% to 12% Dosage: Requirement of admixture 0.2% to 0.6% of cementMaterials: Ligno sulphonate , natural polymer from wood after removals of sugarUse: For low to medium slump concrete

Dispersing plasticizers:60% of admixtures used are dispersing admixtures like plasticizers , super plasticizers , hyper plasticizers.

Causes reduction in viscosity and fluidity of the concrete paste improved, therefore workability increases2) Super plasticizers:

Reduces water content up to 12% to 30%

Dosage: Requirement of admixture 0.6% to 2% of cement.

Materials: sulphonate polymer of naphthalene or melamine formaldehyde condensates and poly carboxylate3) Hyper plasticizers:

Mainly based on poly carboxylic ether

All this are long chain poly carbonic molecules and they get absorbed surfaces causes surface charges.Mechanism of direction:1)Plasticizers , Super plasticizers and Hyper plasticizers are water reducers.

[They are surface acting agents and absorbed on the cement and giving them negative charges leading to repulsion. In earlier by adding water we do dispersion but now adding less water we get dispersion because they are negative charges with less water content.]

2) Negative charges also creates development of sheath of oriented water molecules around cement particles.

3) Now , water is free from restraining mechanism and available for lubrication. Earlier not available without plasticizers.Water reducing agents:

With plasticizersWithout plasticizersWRASuper plasticizers (HRWR) chemicals:Ligno sulphonate

Sulphonate melamine formaldehyde

Sulphonate naphthalene formaldehydeHow to use dispersing admixtures: Without plasticizers With plasticizers8Potential advantages of HRWR:Significant water reduction;

Reduced cement contents;

Increased workability;

Reduced effort required for placement;

More effective use of cement;

More rapid rate of early strength development;Increased long-term strength.Potential disadvantages of HRWR:Additional admixture cost (the concrete in-place cost may be reduced);

Slump loss greater than conventional concrete;

Modification of air-entraining admixture dosage;

Less responsive with some cement;

Mild discoloration of light-coloured concrete.

EFFECTS OF OVERDOSE OF WRA ON THE COMPRESSIVE STRENGTH OF CONCRETE:

If percentage of admixtures is increases 5% of cement content than compressive strength decreases after 28 day CONCRETE ADMIXTURES MANUFACTURED, INDIANAME AND ADDRESSBRAND NAMEDISCRIPTIONFUNCTIONFosroc ChemicalsDrive in road,Ahmedabada) cobplast 211b) conplast 337c) conplast NCWater reducerSuper plasticizerPlasticizerIncrease workabilityGives high workabilityRetards setting timeMc-Bauchemie Pvt. Ltd.Sector 17, VashiMumbaia) Emce plast BVb) Zentrameny F BVc) Centriplact T5 BVWater reducerSuper plasticizerPlasticizerIncrease workabilityHigh early strengthExcellent compatibilitySika Oualcrete Pvt. Ltd.Park street, Calcuttaa) platiment BV 40b) sikamant FFPlasticizerSuper plasticizerWater reducerHRWRRoffe Chemicals Pvt.S.V. Road, SantacruzMumbaia) roff plast 330b) roff super plast 321c) roff super plast 840PlasticizerSuper plasticizerSuper plasticizerWater reducerHigh early strengthHigh performance retarder2. VISCOSITY MODIFYING AGENTOne of the latest innovation, also referred to as Stabilizers.

To produce concrete with better robustness against the impact of variations in the concrete constituents and in site conditions

VMA's build up a three dimensional structure in the liquid phase of the mix to increase the viscosity and yield point of the paste.

Improves the uniform distribution and suspension of the aggregate particles & reducing tendency to bleeding, segregation and settlement.

Supplied as a powder blend or are dispersed in a liquid.

Ranges from 0.1% to 1.5% by weight of cement Function of a VMA:To modify the rheological properties of the cement paste.

1) yield point : force needed to start the concrete moving.

2) plastic viscosity : resistance of a concrete to flow under external stress.

reduce segregation in highly flow able self compacting concrete

reduce washout in underwater concrete

reduce friction and pressure in pumped concrete

compensating for poor aggregate grading, especially a lack of fines in the sand

reducing powder content in self compacting concrete

reduce bleeding in concrete

improve green strength in semi-dry concrete APPLICATIONS OF VMA:Self-compacting concrete is a concrete that is able to flow and consolidate under its own weight, completely fill the formwork even in the presence of dense reinforcement, whilst maintaining homogeneity and without the need for any additional compaction.

When VMA is added, it makes the concrete more tolerant to variations in the water content of the mix so that plastic viscosity is maintained and segregation prevented. 1) In Self Compacting Concrete2) For Under Water Concrete:The major effect of a VMA for underwater concrete is to increase the cohesiveness of the fresh concrete to such a level that during and after placing the fresh concrete is not washed out.

In this way it gives the concrete structure the required strength and durability.

With VMA admixture Without VMA admixture 3) For pumping concrete: The most common problem with pumping concrete occurs when the coarse aggregate particles start to lock at a pipe bend & constrictions.

When VMA is added, it prevents this segregating effect by making the concrete more cohesive without the need to change the mix design.

Other VMA applications: Sprayed concrete and repair mortar

In sprayed concrete rebound occurs while spraying, to reduce rebound VMA is added.Thick layers of sprayed repair mortar may suffer from sagging on vertical surfaces, to avoid this VMA is added.

2) Lightweight concrete

The low density of lightweight aggregates causes floatation problems in high workability concretes, VMA will increase the paste viscosity helping to prevent floatation and keeping the mix homogeneous.

Products of viscosity modifying agent.Rheomac UW 450 - anti-washout admixture , ready-to-use, liquid cellulose-based admixture developed for underwater concrete applications. Functions:

Reduction in washout of cement and fines. Reduction in segregation.

Rheomac VMA 362 Functions:

Controls bleeding.Provides flexibility in mixture proportioning and batching.Provides concrete stability during transport and placement.

Conclusion The purpose of the addition of a VMA is to replace or limit the addition of fines, thus making a fresh concrete more cohesive.

Different types of fines (cement types, fillers, fly ash, micro silica etc. etc.) have different effects on the rheology of the fresh mix, for this reason there are several types of VMA that influence the rheology of the mix in a different ways.

Depending on the application or required effect, the addition of a VMA might need an adjustment of the mix composition to obtain the optimum effect.

The choice for a certain type of VMA therefore depends on both the application that it is used for and the concrete mix constituents. References: Guidelines for Viscosity Modifying Admixtures For Concrete ,European Federation of Concrete Admixture Associations, September 2006 .

Concrete technology by M.S. SHETTY

CONCRETE Microstructure, Properties, and Materials by P. Kumar Mehta & Paulo J.M. Monteiro

CHEMICAL ADMIXTURES FOR CONCRETE by ACI Education Bulletin E4-03.

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