Experiment No: 06
Determination of Normal
Consistency of
Hydraulic Cement Paste
Introduction
This test estimates the amount of water needed to create a regular consistency cement paste. The paste's viscosity should allow the Vicat's plunger to penetrate up to 10±1 mm from the bottom of the mold. Each time the cement is mixed with water varying from 22 to 30% of the weight of cement.
The determination of normal consistency is crucial for several reasons:
1. Water-Cement Ratio: The water-cement ratio is a key
factor in determining the strength and durability of concrete. Knowing the
normal consistency helps in accurately calculating the amount of water required
for concrete mix designs.
2. Uniformity in Testing: For subsequent tests such as
setting time (ASTM C191) and soundness (ASTM C151), it is essential to have a
paste of normal consistency. This ensures that the results are consistent and
comparable across different batches of cement.
3. Workability: Normal consistency is directly
related to the workability of cement paste. A paste with the right amount of
water will be easier to mix, handle, and apply, leading to better construction
quality.
4. Hydration Process: The amount of water required for
normal consistency affects the hydration process of cement. Too much or too
little water can alter the hydration reactions, leading to either incomplete
hydration or excess porosity, which can weaken the final product.
Several factors can influence the normal consistency of cement, including:
- Fineness
of Cement:
Finer cement particles have a larger surface area, which requires more
water to achieve the desired consistency.
- Cement
Composition:
The chemical composition of cement, particularly the amount of gypsum and
other additives, can affect the water demand.
- Ambient
Conditions:
Temperature and humidity can influence the amount of water needed to
achieve normal consistency.
Typical Water Content for Normal Consistency
The amount of water required to achieve normal consistency
typically ranges between 22% and 30% of the weight of the cement. However, this
can vary depending on the type of cement and its specific characteristics. For
instance, rapid-hardening cement may require less water, while blended cements
with supplementary cementitious materials may require more.
Scope
This test method encompasses the
determination of the normal consistency of hydraulic cement.
Purpose
To determine the amount of water required to produce a hydraulic cement paste of standard consistency.
ASTM Designation
ASTM C187— Amount of Water Required for Normal Consistency of Hydraulic
Cement Paste.
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.
Significance and Use
This test method is intended to be used to determine the
amount of water required to prepare hydraulic cement pastes with normal
consistency, as required for certain standard tests. The determination of
normal consistency is significant because it directly affects the water-cement
ratio, which in turn influences the strength, workability, and durability of
the cement paste. Accurate determination of normal consistency is essential for
conducting further tests on cement, such as setting time (ASTM C191) and
soundness (ASTM C151). The consistency test ensures that the paste has a
standard flowability, leading to uniform results in subsequent tests.
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.
Vicat Apparatus:
The Vicat apparatus consists
of a frame A (Fig. 1) supporting a moving rod B, weighing 300 g, with a
plunger end C measuring 10 mm in diameter for a minimum distance of 50 mm, and
a removable needle D measuring 1 mm in diameter and 50 mm in length. Reversible,
rod B may be locked in any desired position using a set screw E and is equipped
with an adjustable indication F that travels along a scale (graduated in
millimeters) connected to frame A. The paste is kept in a rigid conical ring G,
sitting on a planar non absorptive square base plate H, about 100 mm on each
side. The rod B should be made of stainless steel having a hardness of not less
than 35 HRC, and shall be straight with the plunger end which is perpendicular
to the rod axis. The ring should be made of a noncorroding, nonabsorbent
material, and shall have an internal diameter of 70 mm at the base and 60 mm at
the top, and a height of 40 mm.
Figure
1: Vicat
Apparatus
In addition, the Vicat apparatus shall conform to the following requirements:
|
Weight of movable rod
|
300 g ± 0.5 g
|
|
Diameter of plunger end of rod
|
10 mm ± 0.05 mm
|
|
Diameter of needle
|
1 mm ± 0.05 mm
|
|
Inside diameter of ring at bottom
|
70 mm ± 3 mm
|
|
Inside diameter of ring at top
|
60 mm ± 3 mm
|
|
Height of ring
|
40 mm ± 1 mm
|
|
Graduated scale
|
The graduated scale, when compared
with a standard scale accurate to within 0.1 mm at all points, shall not show
a deviation at any point greater than 0.25 mm. |
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.
Procedure:
Preparation of Cement Paste
I.
Mix 650 g of cement with a measured
quantity of water.
II.
Measure the water required based on
initial trials, typically around 22% to 30% of the weight of the cement,
depending on the type of cement used.
III.
Place the weighed cement in a mixing
bowl.
IV.
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. 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.
Consistency Determination:
I.
Center
the paste confined in the ring, resting on the plate, under the rod B, Fig. 1,
the plunger end C of which shall be brought in contact with the surface of the
paste, and tighten the set-screw E.
II.
Then
set the movable indicator F to the upper zero mark of the scale, or take an
initial reading, and release the rod immediately.
III.
Release
the rod at a time not exceeding 30 s after completion of mixing.
IV.
The
apparatus shall be free of all vibrations during the test.
V.
The
paste shall be of normal consistency when the rod settles to a point 10 mm ± 1
mm below the original surface in 30 s after being released.
VI.
Make
trial pastes with varying percentages of water until the normal consistency is
obtained. Make each trial with fresh cement.
Calculation
Calculate the amount of water
required for normal consistency as the mass of water divided by the mass of dry
cement, expressed as a percentage. Calculate the mass ratio to the nearest 0.1
% and report the mass ratio to the nearest 0.5 %.
Graphs
Draw a normal graph paper
(Penetration, mm vs. Percentages of Water). For 10mm penetration (From Graph), calculate
the Percentage of Water required for Normal Consistency.
Figure
2: Typical graph for determining the normal consistency of cement
Report
Percentage of Water required for Normal Consistency.
LAB Assignment Questions:
Basic Understanding
1.
What is the normal consistency of
hydraulic cement paste?
2.
Why is it important to determine the
normal consistency of cement paste?
3.
What does normal consistency indicate
about the cement paste?
Procedure and Equipment
4.
What apparatus is used to determine the
normal consistency of cement paste?
5.
Can you describe the procedure for
determining the normal consistency of cement paste?
6.
What is the significance of the Vicat
apparatus in this test?
7.
How is the initial setting time related
to the normal consistency of cement?
8.
Why is it important to use fresh water
while preparing the cement paste for this test?
Calculation and
Interpretation
9.
How do you determine the normal
consistency from the test data?
10. What
is the standard penetration depth of the Vicat plunger for normal consistency?
11. What
would you conclude if the Vicat plunger does not penetrate to the specified
depth?
12. How
do different types of cement affect the normal consistency?
Standards and
Specifications
13. Which
standards (e.g., ASTM, IS) are followed for determining the normal consistency
of cement paste?
14. What
is the typical range of water-cement ratio for achieving normal consistency?
15. Why
is it important to standardize the water content when determining normal
consistency?
Application and
Practical Considerations
16. How
does the normal consistency of cement affect the workability of concrete?
17. What
are the factors that can influence the normal consistency of cement paste?
18. How
does the normal consistency relate to the setting time and strength of the
cement?
19. What
are the practical implications of having a cement paste that is too thick or
too thin?
20. What
precautions should be taken while performing the normal consistency test?
Reference:
ASTM C187: Standard
Test Method for Amount of Water Required for Normal Consistency of Hydraulic
Cement Paste.