Slump Test for Workability of Concrete

Introduction: 

Workability of concrete is defined as the ease with which concrete is mixed; placed, compacted etc.

Slump test is most basic test which is used to measure workability of freshly prepared concrete.

Concrete is poured in a cone; then cone is lifted up, the concrete collapses.

The reduction in the height of heap of concrete is called SLUMP VALUE. Slump value is proportional to workability of concrete.

Equipment

Slump cone of standard dimensions i.e. top diameter 10cm, base diameter 20cm, height 30cm.

Standard tamping rod of 60cm length 1.5 cm diameter.

Trowel, scoop, scale etc. 

Slump Cone (Image Source)

Procedure

1. All ingredients of concrete are weighed and mixed in dry state.
2. Required amount of water is added in mixed concrete sample. Concrete is again mixed manually.
3. Freshly prepared concrete is poured in slump cone. Concrete is poured in four layers
4.  Each layer is compacted by giving 25 uniform blows by using standard compaction rod.
5. Then the slump cone is lifted up gently in vertical position.
6. Let the concrete mass take its natural position. Measure slump value of concrete by using a scale.
7. Slump value defines the workability of concrete. 

Conclusion:

1. Slump test is good and fast to be used at site.
2. No much technical skills are required to conduct this test.
3. The test is less reliable as compared to compaction factor test.
4. Not good to be use in case of stiff concrete.

Types of Slump Cones (Image)

Determining Dry Density Of Soil By Core Cutter Mrthod

Intrduction:

Cylindrical core cutter is a seamless tube which is pressed into soil so that it gets filled with soil sample. The volume of tube is known; the mass of soil is calculated. Dry density of soil is obtained as

                    ρ= α/1+w

                    α=M/V

         M= mass of soil

         V =volume of soil sample=volume of core cutter

        W= water content in soil

Equipment:

Cylindrical core cutter of 100 mm diameter and 130 mm long

Steel rammer of about 9 kg.

Steel dolly, 25 mm high and 100mm internal diameter.

Weighing balance of accuracy up to 1g.

Palatte knife, straight edge etc

Procedure

Measure internal diameter of core cutter and calculate its volume.

Determine the mass of cutter (M₁) up to nearest gram.

Expose small area on ground up to 300mm.

Place the dolley over core cutter and press the cutter in ground by hitting it by rammer.

Stop pressing when about 15 mm of dolley protrudes over the soil surface.

Remove the soil around the cutter; trim the top of soil projecting sample from cutter.

weight the cutter  with soil sample (M₂) up to nearest gram.

Remove the sample from cutter; take out small amount of sample for water content determination.

Observations:

ρ= α/1+w

α=M/V

α=wet density of soil

V =volume of soil sample=volume of core cutter

W= water content in soil

Mass of empty core cutter=M₁

Mass of core cutter + soil sample =M₂

M= mass of soil = M₂- M₁

Conclusion:

Core cutter method is good enough to finding out the dry density of soil direct at site.

This is more practical and does not need much equipments

It’s fast and reliable.

Soil water Content Determination (By Oven Drying)

Introduction: 

Soil contains some amount of water in its pores. The water content of soil (w) may be defined as ratio of mass of water to the mass of solids in soil.

W= M₂-M₁/M₃-M₁

M₁=mass of container with lid

M₂ = mass of container with wet soil and lid.

M₃= mass of container with dry soil and lid.

Equipment:

 Thermostatically controlled oven, Weighing balance with accuracy of 0.04% accuracy of weight, desiccators, airtight containers, Tongs.

Soil specimen: 90% of soil sample should pass through 425 micron sieve; the minimum quantity should be taken equal to 25 g.

Procedure:

Clean and dry the container, then weight it (M₁).

Take the require quantity of wet specimen in container and weight it (M₂)

Place the container in oven for 24 hours at temperature of 110±5o c.

When soil has dried remove the sample from oven with help of tongs.

Replace the lid on container cool it; weight the container (M₃).

Observations:

M₁=mass of container with lid

M₂ = mass of container with wet soil and lid.

M₃= mass of container with dry soil and lid.

W=M₂-M₁/M₃-M₁

W= water content of soil.

Units= expressed in form of % age

Conclusion:

Moisture content in soil determines most of properties of soil, like shear strength, bearing capacity of soil etc. like in case of clay, clay do not have a good intimacy with water. But if it mixed with optimum moisture content (OMC) it provides maximum dry density, it behaves like strong cement stones. In case of construction of water bound macadam roads, making subgrades of roads or making cores of dams clay has to be compacted at optimum moisture content. So a soil engineer must have knowledge about calculation of soil moisture content.

Determination of Dry Density by Sand Replacement Method

Introduction:
A hole of specific dimensions is excavated in soil. The mass of soil excavated is calculated out.  The volume of hole is determined by filling the hole with sand of known dry density. The volume of hole is equal to the mass of sand in hole divided by its dry density. Dry density of excavated soil is calculated as

Equipment:

1. Sand pouring cylinder
2. Calibrating container of 100 mm diameter and 150 mm height
3. Soil cutting and excavation tool.
4. Glass plate of 450mm square and 9mm thickness.
5. Metal container to collect excavated soil.
6. Metal tray, 300 mm square and 40mm deep with a hole of 100 mm diameter at its center.
7. Weighing balance, moisture content cans, oven and desiccators.
8. Clean uniform sand passing from 1mm diameter sieve and retaining on 600 micron sieve.

Procedure Part -1 (Calibration)

1. Determine the internal volume of calibrating cylinder by filling it with water and mass of water required to fill. Volume may also be calculated from measuring internal dimensions of container.
2. Fill the sand pouring cylinder with sand up to 10 mm of its top. Determine mass of cylinder to nearest gram (M1).
3. Place sand pouring cylinder on calibrating container. Open the shutter and allow sand to fall in to calibrating cylinder up to the time when there is no movement of sand is noticed; then close the shutter.
4. Lift the pouring cylinder and weigh it up to nearest gram (M3)              
5.  Now again fill the cylinder up to 10mm.
6. Open the shutter and allow again the sand to run out of cylinder. When volume of sand let out equal to calibrating cylinder; close the shutter.
7. Place the cylinder over a plane glass plate .open the shutter; sand will fill the internal cone of cylinder.
8. Close the shutter when there is no movement of sand is noticed.                
9. Remove the cylinder from glass plate; collect sand; weight the sand (M2)
10. Determine dry density of sand as shown in table. 

 
Procedure part-2 (Dry Density)

1. Expose 450 mm square area on ground. Trim surface down to level earth by scrapping tool.
2. Place metal tray on leveled surface.
3. Excavate the hole in soil through central hole in the tray as a pattern. Depth of hole should be about 150 mm.
4. Collect soil and determine mass of it (M).
5. Remove metal tray from excavated hole.
6. Fill the sand pouring cylinder with sand up to 10 mm of its top. Determine mass of cylinder to nearest gram (M1).
7. Place cylinder over the hole and let the soil fall from hole by opening shutter. Close the shutter when there is no movement of sand is noticed.
8. Remove the cylinder from hole and find out its mass (M4).    
9. Take soil sample to calculate water content in soil.
10. Determine dry density of sample as explained in observation part-2.

Observation Part-1

1. Volume of calibrating cylinder=V_C
2. Mass of pouring cylinder filled with sand=M₂
3. Mass of pouring cylinder after pouring sand in to calibrating cylinder= M₃
4. Mass of sand in calibrating cone=M₂
5. Mass of sand in calibrating container Mc=M₂-M₁-M₃
6. Dry density of sand=M_c/V_c

Observation Part-2

1. Mass of excavated soil =M
2. Mass of cylinder filled with sand=M₁
3. Mass of pouring cylinder after pouring sand in hole=M₄
4. Mass of sand in hole Ms =M₁-M₄-M₂
5. Volume of sand in hole= Ms/ρ_s
6. Bulk density, ρ =M/V
7. Water content = w
8. Dry Density of Soil = ρ /(1+w)

Conclusion:

The test is precise soil testing method which gives reliable results.
This method is laborious and time consuming than core cutter method.