Setting Time Of Concrete| Brief Explanation
Setting Cement Time Under laboratory conditions are detected by a standard WICAT tool. Setting time, both initial and final, indicates the quality of the cement.
The setting time of concrete varies widely from the setting time of the cement. The setting time of the concrete does not coincide with the setting time of the cement from which the concrete is made.
The timing of setting concrete depends on the w / c ratio, temperature conditions, type of cement, the use of the mineral mixture, the use of plasticizers — specifically the retarding plasticizer. The setting parameter of concrete is of more practical importance to site engineers than the setting time of cement.
When retarding plasticizers are used, increasing the setting time, the length of time the concrete stays in the plastic state is of particular interest.
The setting time of the concrete is determined by the penetrometer test. This test method is covered by 1976 IS 8142 and ASTM C – 403. The following procedure can be applied to prepared mortar and grout.
The tool contains a container that must have a minimum lateral dimension
150mm and minimum depth 150mm. There are six penetration needles with bearing areas of 645, 323, 161, 65, 32, and 16mm. Each needle stem is written in circumference at a distance of 25 mm from the bearing area.
A device is provided to measure the force leading to the needle penetration. The test method involves the collection of a representative sample of a sufficient amount of concrete through a sieve of 4.75 mm and the resulting mortar is filled into a container.
Compact the mortar by rodding, tapping, rocking, or vibrating. Floor the surface and cover it to prevent moisture loss. Remove the bleeding water, if any, using a pipette.
Add the appropriate size needle depending on the stucco setting level as follows.
Bring the needle bearing surface in contact with the mortar surface. Gradually and
Uniformly apply vertical force on the tool until the needle penetrates to a depth of 25 ± 1.5 mm as indicated by the scribe mark.
The time it takes to penetrate a depth of 25mm can be about 10 seconds. Record the amount of force required to produce a penetration of 25 mm and the time required to add water to the cement. Calculate the penetration resistance by dividing the force recorded by the bearing area of the needle.
It is the penetration resistance. Avoid the mortar-affected area for subsequent penetration. The clear spacing should be twice the diameter of the bearing area.
The needle is inserted at least 25 mm away from the wall of the container. Form the graph of the penetration resistance as the coordinate and the time spent as the abscissa. The resolution of the six penetration resistance cannot be reduced.
Continue testing until a penetration resistance of at least 27.6 MPa is reached. Connect the various points through the smooth curve.
Also, Watch This For A Better Understanding of setting time of concrete:
With a penetration resistance equal to 3.5 MPa, draw a horizontal line. Its point of intersection with the smooth curve is read on the x-axis giving the initial setting time.
Similarly, the horizontal line is drawn by the impedance of 27.6 MPa that reads on the x-axis giving the final set the point at which the smooth curve is cut. A typical graph is shown in Figure 6.11
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