Experiment No: 07
Determination of Time of Setting of Hydraulic Cement by
Vicat Needle
Introduction
The determination of the setting time of hydraulic cement is a critical procedure in the construction industry. Setting time refers to the period required for cement to transition from a fluid or plastic state to a solid state. This characteristic influences the handling, finishing, and curing processes in concrete construction.
The term setting refers to the
solidification of the plastic cement paste. The beginning of solidification,
called the initial set, marks the point in time when the paste
has become unworkable. Accordingly, concrete placement, compaction, and
finishing operations are difficult beyond this stage. The paste does not solidify
suddenly; it requires considerable time to become fully rigid. The time taken
to solidify completely marks the final set, which should not be
too long in order to avoid delays in the construction process. Almost
universally, the initial and the final setting times are determined by the
Vicat apparatus, which measures the resistance of a cement paste of a standard
consistency to the penetration of a needle under a total load of 300 g. The initial
set can be described as the time in the setting process when the needle
penetrates a 40-mm-deep cement paste until a 25 mm of
penetration is achieved.
The final set is said to be reached when the needle makes an
impression on the surface of the paste but does not penetrate. ASTM C 150, Standard
Specification for Portland Cement, requires the initial setting time to
be not less than 45 min, and the final setting time to be not more than 375
min, as determined by the Vicat Needle (ASTM C 191).
ASTM C191 outlines the standard test method using the Vicat
Needle apparatus, ensuring consistency and reliability in assessing the time of
setting for hydraulic cement.
Scope
These test methods determine the time of setting of hydraulic
cement by means of the Vicat needle. This test method is applicable to all
types of hydraulic cements, including Portland cement, blended cements, and
other cementitious materials used in concrete. The method determines both the
initial and final setting times using the Vicat Needle apparatus, ensuring
compliance with industry standards.
Purpose
The primary purpose of this test is to determine the initial
and final setting times of hydraulic cement. This information is essential for
understanding the workability and timing requirements of cement in construction
applications. The setting time can impact the timing of formwork removal, the
application of subsequent layers, and the overall construction schedule.
ASTM Designation
ASTM C191— Standard Test Methods for Time of Setting of Hydraulic Cement by Vicat Needle.
Terminology
Hydration
The chemical reaction between hydraulic cement and water
forming new compounds most of which have strength-producing properties.
Hydraulic cement
A
cement that sets and hardens by chemical reaction with water and is capable of
doing so under water.
Portland cement
A hydraulic cement produced by pulverizing clinker, consisting
essentially of crystalline hydraulic calcium silicates, and usually containing
one or more of the following: water, calcium sulfate, up to 5 % limestone, and
processing additions.
Normal
consistency
A degree of plasticity
of a hydraulic cement paste that is appropriate for testing as measured by a
stipulated method.
Initial
and Final setting time
The time at which the
cement paste loses its plasticity is termed initial setting time. The time
taken to reach the stage when the paste becomes a hard mass is known as final
setting time.
Significance and Use
This test method determines compliance with a specified
limit for Vicat time of setting. It should be used in mixture with the
appropriate cement specification. However, this procedure may not provide the
same results as other methods for hydraulic cement paste or mortar or concrete
setting.
Determining the setting time of hydraulic cement is vital
for ensuring the material meets the required performance criteria in
construction. The setting time affects the scheduling of construction
activities, such as the removal of formwork, the application of finishes, and
the timing of curing processes. Accurate determination of setting time ensures
that the cement performs as expected under specific environmental conditions
and helps in preventing issues related to premature cracking, insufficient curing,
or delayed construction activities.
Apparatus
Reference Masses:
The
physical testing methods for hydraulic cement and related materials must
conform to Class 6 reference masses in Specification ASTM E617. Values from
Table 1 of Specification ASTM E617 for Class 6 metric reference masses:
TABLE 1 Tolerances for Reference Masses
|
Mass, g |
Acceptance Tolerance, ±mg |
Maintenance Tolerance, ±mg |
|
10000 |
1000 |
2000 |
|
5000 |
500 |
1000 |
|
3000 |
300 |
600 |
|
2000 |
200 |
400 |
|
1000 |
100 |
200 |
|
500 |
50 |
100 |
|
300 |
30 |
60 |
|
200 |
20 |
40 |
|
100 |
10 |
20 |
|
50 |
7 |
14 |
|
30 |
5 |
10 |
|
20 |
3 |
6 |
|
10 |
2 |
4 |
|
5 |
2 |
4 |
|
3 |
2 |
4 |
|
2 |
2 |
4 |
|
1 |
2 |
4 |
Scales and
Balances:
The
maintenance tolerance for a mass determination device should not exceed 0.05%
of the test load throughout the test load range. The mass determination devices
with a capacity that exceeds 1000 g must have a readability of no more than 0.1
g. The index scale of a mass determination device with a capacity of 1000 g or
less must be readable up to 0.01 g.
Glass Graduates:
200 mL or 250 mL capacity, and conforming
to the Specification ASTM C1005.
Flat
Trowel:
Having a sharpened
straight-edged steel blade 100 mm to 150 mm in length.
Plane
Non-Adsorptive Plate:
100 ± 5 mm square of similar
planeness, corrosivity, and absorptivity to that of glass (Fig.1, H).
Conical
Ring:
Made of a rigid, non-corroding,
nonabsorbent material and having a height of 40 ± 1 mm, an inside diameter at
the bottom of 70 ± 3 mm, and an inside diameter at the top of 60 ± 3 mm (Fig.1,
G).
Vicat Apparatus:
The Vicat apparatus for this test method shall have a movable rod, B, of mass 300 ± 0.5 g. The end of the rod used for measuring penetration shall have a straight steel removable needle with a diameter of 1.00 ± 0.05 mm and length no less than 50 mm. The needle end that contacts the specimen shall be flat, plane, and at right angles to the axis of the rod.
Figure
1: Vicat
Apparatus
Temperature and
Humidity
·
The temperature of the
air in the vicinity of the mixing slab, molds, and base plates shall be
maintained at 23.0 ± 4.0 °C and at a relative humidity of not less than 50 %.
·
The temperature of the
mixing water used to prepare cement paste and mortar specimens shall be 23.0 ± 2.0
°C.
·
Except during those
times when specimens are being placed into or removed from storage, maintain
the atmosphere in a moist cabinet or moist room at a temperature of 23.0 ± 2.0
°C and a relative humidity of not less than 95 %.
Procedure: Manual
Vicat Apparatus
Preparation of
Cement Paste
·
Mix 650 g of cement with a measured
quantity of water.
·
Measure the water required based on the
percentage of mixing water required for normal consistency.
·
Place the weighed cement in a mixing
bowl.
·
Add the measured amount of water and
mix thoroughly to form a uniform paste. Ensure the mixing time is sufficient to
achieve a homogeneous mixture.
v
For mechanical mixing follow ASTM C305.
v For using reagent water
follow specification ASTM D1193.
Molding Test
Specimen
I.
Quickly form the cement paste into
the approximate shape of a ball with gloved hands.
II.
Then toss six times through a free
path of about 150 mm from one hand to another so as to produce a nearly
spherical mass that may be easily inserted into the Vicat ring with a minimum
amount of additional manipulation.
III.
Press the ball, resting in the palm
of one hand, into the larger end of the conical ring G, Fig. 1, held in
the other hand, completely filling the ring with paste.
IV.
Remove the excess at the larger end
by a single movement of the palm of the hand.
V.
Place the ring on its larger end on
the base plate H, and slice off the excess paste at the smaller end at
the top of the ring by a single oblique stroke of a sharp-edged trowel held at
a slight angle with the top of the ring, and smooth the top, if necessary, with
a few light touches of the pointed end of the trowel.
VI.
During these operations of cutting
and smoothing, take care not to compress the paste.
VII.
Immediately after molding, place the
test specimen in the moist cabinet or moist room and allow it to remain there
except when penetration measurements are being made.
VIII.
The specimen shall remain in the
conical mold, supported by the non-absorptive plate throughout the test period.
Time
of Setting Determination:
i. Allow the time of setting specimen to remain in the moist cabinet or moist room for 30 min after molding without being disturbed.
ii. Determine the penetration of the 1 mm needle at this time and every 15 min thereafter (every 10 min for Type III cements) until a penetration of 25 mm or less is obtained.
iii. Perform the penetration test by lowering the needle D of the rod B until it rests on the surface of the cement paste.
iv. Tighten the setscrew, E, and set the indicator, F, at the upper end of the scale, or take an initial reading. Release the rod quickly by releasing the set screw, E, and allow the needle to settle for 30 s; then take the reading to determine the penetration.
v. At the option of the tester, if the paste is obviously quite soft on the early readings, retard the fall of the rod to avoid bending the 1 mm needle, but when actual penetration measurements to determine the time of setting are made, release the rod only by the setscrew.
vi. Make each penetration test at least 5 mm away from any previous penetration and at least 10 mm away from the inner side of the mold. Record the results of all penetration tests and, by interpolation, determine the time when a penetration of 25 mm is obtained.
vii. The elapsed time between the initial contact of cement and water and the penetration of 25 mm is the Vicat time of setting or Vicat initial time of setting.
viii. Determine the Vicat final time of setting end point to be the first penetration measurement that does not mark the specimen surface with a complete circular impression. [By the needle with an annular attachment]
ix. Verify final set by performing two additional penetration measurements on different areas of the specimen surface.
x. Obtain verification measurements within 90 s of the first “final set” measurement.
xi.
The
elapsed time between the initial contact of cement and water and the end point
determination above is the Vicat final time of setting.
Precautions
·
Keep
all the apparatus free from vibration during the penetration test.
·
Keep
the 1 mm needle straight and clean.
·
The
needle must be kept clean to prevent cement from adhering to the sides of the
needle and decreasing penetration, and to prevent cement from adhering to the
point and increasing penetration.
Calculation
Calculate the Vicat
time of setting to the nearest 1 min as follows:
where:
E = time in minutes of last penetration greater than 25 mm,
H = time in minutes of first penetration less than 25 mm,
C = penetration reading at time E, and
D = penetration reading at time H.
·
Calculate
the Vicat final time of setting by determining the elapsed time
between the time of the initial contact between cement and water and the time
when the Vicat final time of setting end-point is determined, rounded to the
nearest 5 min.
Report
Report the time of
setting using Manual Vicat Needle Apparatus method as follows:
Vicat time of setting (A or B) ______ min
Vicat final time of setting (A or B) ______ min
LAB Assignment Questions:
Basic Understanding
1. What
is the significance of determining the setting time of hydraulic cement?
2. What
is the difference between the initial and final setting time of cement?
3. Why
is the Vicat apparatus used for determining the setting time of cement?
Procedure and Equipment
4. Can
you describe the procedure for determining the initial and final setting time
using the Vicat needle?
5. What
are the components of the Vicat apparatus?
6. How
do you prepare the cement paste for the setting time test?
7. What
is the importance of maintaining a constant temperature and humidity during the
test?
8. What
is the purpose of using the initial and final setting time needles in the Vicat
apparatus?
Calculation and Interpretation
9. How
do you determine the initial setting time using the Vicat needle?
10. How
do you determine the final setting time using the Vicat needle?
11. What
is the significance of the penetration depth in determining the setting time?
12. What
would you infer if the cement paste sets too quickly or too slowly?
13. How
does the water-cement ratio affect the setting time?
Standards and Specifications
14. Which
standards (e.g., ASTM, IS) are followed for determining the setting time of
hydraulic cement?
15. What
are the standard values for the initial and final setting times of Ordinary
Portland Cement (OPC)?
16. Why
is it important to conduct the test at a standard temperature (e.g., 27°C or
20°C)?
17. What
are the acceptable limits of initial and final setting times for different
types of cement?
Application and Practical Considerations
18. How
does the setting time of cement influence the construction process?
19. What
could be the reasons for abnormal setting times, and how can they be corrected?
20. How
does the setting time affect the workability and strength of concrete?
21. What
precautions should be taken while conducting the setting time test with the
Vicat needle?
22. How
can the setting time of cement be controlled in practical applications?
References
ASTM C191 Standard Test
Methods for Time of Setting of Hydraulic Cement by Vicat Needle.