Concrete Workability Test Methods
Workability means the physical characters of concrete which impact the strength and stability along with the cost of labor and presence of the finished product. Concrete becomes functional when it is simply set and compacted evenly that means devoid of bleeding or Segregation.
The following factors impact the workability:
- Water content in the concrete mix
- Amount of cement & its Properties
- Aggregate Grading (Size Distribution)
- Type of Aggregate Particles (Shape, Surface Texture, Porosity etc.)
- Temperature of the concrete mix
- Humidity of the environment
- Mode of compaction
- Method of placement of concrete
- Method of dispatching of concrete
Also read : HOW CONCRETE BECOMES STRONGER WITH ADDITION OF REBAR
Some useful guidelines to enhance the workability of concrete.
- Raise water/cement ratio
- Raise the size of aggregate
- Utilize well-rounded and smooth aggregate in place of uneven shape
- Enhance the mixing time
- Enhance the mixing temperature
- Apply non-porous and saturated aggregate
- Include air-entraining mixtures
Workability tests
Generally, 4 types of tests are conducted to check workability which range from slump test, compacting factor test, flow test, and vee bee test.
Slump test
The slump test result belongs to a slump of the behavior of a consolidated inverted cone of concrete under the action of gravity. It works out the uniformity or the wetness of concrete. Metal mould, in the form of the frustum of a cone, open at both ends, and arranged with the handle, top internal diameter 4 in (102 mm), and bottom internal diameter 8 in (203 mm) with a height of 1 ft (305 mm). A 2 ft (610 mm) long bullet nosed metal rod, (16 mm) in diameter.
Necessary Apparatus
Compacting Factor apparatus, Trowels, Graduated cylinder, Balance and Tamping rod and iron bucket.
This test is generally executed in laboratory and finds out the workability of fresh concrete if size is about 40 mm maximum. The test is conducted according to the specification of IS: 1199-1959.
Compacting factor test
This test includes the following steps:
- Retain the apparatus on the ground and provide grease on the inside surface of the cylinders.
- Calculate the mass as w1 kg by weighing the cylinder precisely and set the cylinder on the base so that the central points of hoppers and cylinder rest on one vertical line and wrap the cylinder with a plate.
- For each 5 kg of aggregate, mixes should be arranged with water-cement ratio with 2.5 kg sand and 1.25 kg of cement and then include necessary amount of water comprehensively unless the concrete becomes uniform.
- By applying hand scoop devoid of compacting, fill the freshly mixed concrete in upper hopper section slowly and cautiously and within two minutes discharge the trap door in order that the concrete goes into the lower hopper to fetch the concrete into standard compaction.
- Drop the concrete into the cylinder by inletting the concrete into standard compaction instantly once the concrete has come to rest and open the trap door of lower hopper and then detach the extra concrete over the top of the cylinder with a pair of trowels, one in each hand will blades horizontal slide from the opposite edges of the mould inside to the center with a sawing motion.
- Cleanse the perfectly from all sides. Detect the mass of partially compacted concrete and filled in the cylinder. Suppose it is W2 kg. Then, fill the cylinder again with the similar sample of concrete in roughly 50 mm layers; by vibrating every layer greatly in order to drive out all the air and procure full compaction of the concrete.
- Struck off level the concrete and weigh and cylinder is filled with fully compacted concrete. Suppose, the mass is W3 kg.
- Work out the compaction factor with the following formula
C.F = W2-W1 / W3 – W1
Flow Table Test
The purpose of the flow table test is to find out the stability of fresh concrete. A cone is arranged in the center of the flow table and filled in two equivalent layers with fresh concrete. With the help of a tamping rod, every layer is tamped 10 times. Wait 30 seconds prior to upraise the cone. The cone is upraised facilitating the concrete to flow. The flow table is then upraised to 40mm and then dropped 15 times, resulting the concrete to flow. Then, the diameter of the concrete is calculated.
Vee-Bee Test
This test is conducted for concrete with very low workability. Under this test, the concrete is moulded into a cone in a cylinder container and the total set up is arranged on a vibrating table. As soon as the vibrator turns on, concrete provided on the cone starts to capture the cylindrical container being remoulded. Remoulding is finished once the concrete surface remains in horizontal direction. The time necessary for end of remoulding while starting of vibrator is calculated and indicated as vee-bee seconds. It offers a measure for workability. The workability is increased if the vee-bee seconds is reduced.
