BLD62003 Building Materials

Tutorial 3 Presentation

Thun Shao Xun 0315919Muhd. Hasif 0316413Clement Lim 0321702Shane Sim 0321288

Compacting Factor Test

- To determine the workability of freshly mixed concrete.

What?

1. Concrete and water cement is mixed into upper hopper. Concrete excess must be levelled accordingly.

2. The trap door of upper hopper is opened in order for the concrete to fall into the lower hopper.

3. The trap door of lower hopper is opened for the concrete to fall into the cylinder

4. The remaining concrete which remains above the top level of cylinder is cut off by plane blades.

How?

5. The concrete in the cylinder is weighed and labeled as partially compacted concrete.

6. Fresh sample of concrete is filled into the cylinder and vibrated until it is fully compacted.

7. It is then weighed and labeled as fully compacted concrete.

Method of calculation

Consistency Compacting Factor

Very Dry 0.70

Very Hard 0.78

Hard 0.85

Plastic Hard 0.89

Plastic 0.92

Liquid 0.95

High Liquid 1.00

THE FACTORS AFFECTING WORKABILITY 

AND STRENGTH OF CONCRETE

First Factor: Aggregate / Cement Ratio

If the volume remains the same and the proportion of cement in relation to that of sand is increased the

surface area of the solid will increase.

If the surface area of the solids has increased, the water demand will stay the same for the constant workability.

Assuming an increase in cement content for no increase in water demand, the water cement ratio will decrease.

If the water cement ratio reduces, the strength of the concrete will increase.

The influence of cement content on workability and strength is an important one to remember and can be summarized as follows:

1. For a given workability an increase in the proportion of cement in a mix has little effect on the water demand and results in a reduction in the water/cement ratio.

2. The reduction in water/cement ratio leads to an increase in strength of concrete.

3. Therefore, for a given workability an increase in the cement content results in an increase in strength of concrete.

Second Factor: Relative Humidity

If the concrete is allowed to dry out, the hydration reaction will stop. The hydration reaction cannot proceed without moisture. The three curves shows the strength development of similar concretes exposed to different conditions.

Third Factor: Compaction of Concrete

• elimination of voids from the concrete.

• the process - compaction - increases strength of concrete by 30%

• Manually - Rodding

• Mechanically - Vibration

How?

Result?

• Less Compaction - Honey Comb Concrete

• Over Compaction - Segregation of Concrete

Admixtures of Concrete

Shrinkage Reducing

Super Plasticizer

Corrosion Inhibitor

SHRINKAGE REDUCING

reduced drying shrinkage in water.

Function?

How?

PROBLEM

- Excess water begin to evaporate.- Capillary pores formed.- Water within have high surface tensions.- Force tends to close the pores.- Volume reduced and let to shrinkage.

IF USE ADMIXTURE

- Reduce water surface tension effect - Reduce shrinkage as water evaporates

Capillary Pores

Significantly reduces drying shrinkage by as much as 80% at 28 days, and up to 50% at one year or beyond when 2% MasterLife SRA 20 admixture

by mass of cement is used in the concrete mixture.

Reduces stresses induced from one-dimensional surface drying in concrete slabs and floors.

Reduces carbonation.

Advantages?

Reduces drying shrinkage cracking and microcracking thereby improving aesthetics,

watertightness and durability.

Reduction in drying shrinkage minimizes pre-stress loss.

Minimizes curling.

Increase permeability.

Advantages?(Continued)

Super Plasticizer

a type of linear polymer chemical additive

used in cement and concrete manufacturing as high-range water reducer.

What?

make high strength concrete (compressive strength up to 22,000

psi).

can be utilized in producing flowing concrete used in a heavy reinforced structure with inaccessible areas.

Advantages?

Concrete early strength enhancement (50 to 75%).

Does not significantly affect surface tension of water and does not entrain a significant amount

of air.

Advantages?(Continued)

loss of workability as a result of rapid slump loss and incompatibility of cement and super

plasticizers.

Disadvantages?

Sulfonated melamine

Sulfonated Napthalene

Modified Lignosulfonates

A combination of high dosages of water reducing and accelerating admixtures

Types?

Corrosion Inhibitor

Chemical compound.

Usually react with metallic surface.

Layer to protect the material such as reinforcing steel.

What?

Reduces the rate at which chlorides and moisture enter the material.

Reduces maintenance cost.

Forms a strong and durable material.

Decreases the corrosion rate.

Advantages?

Rheocrete 222+ (a combined waterproofer and organic corrosion inhibitor)

Extended service life of reinforced concrete structures

Reduces the corrosive effect of moisture and chlorides

Easily used in elevated temperatures

Examples?

Bridge Corrosion

Corrosion Inhibitor