5-Compressive Strength of Cement Mortar PDF

College of Engineering Concrete Tech.
/Practical
Civil Department 2017-2018
Concrete Lab. 2nd year
__________________________________________________________________________________
TEST# 5 standard test method for
Compressive Strength of Hydraulic Cement Mortar

5-1 References:
1. ASTM C109-07
2. ASTM C305-99
5-2 Purpose:
This test method provides a means of determining the compressive strength of hydraulic
cement mortars and results may be used to determine compliance with specifications.
5-3 Materials:
1. Potable water.
2. OPC.
3. Local sand [similar to Ottawa sand, sized between sieves No.20 (850 micron) and
sieve No.30 (600 micron) ]
5-4 Equipment:
1. Sensitive balance,
2. Graduate cylinder,
3. Standard molds of (5×5) cm (2”×2”) dimension,
4. Mechanical Mixer,
5. Testing machine,
6. Small trowel,
7. Rubber or Wooden Tamper,
8. Brush,
9. Coating release agents (oils, or greases),
10. Sieves No.20 and No.30, and
11. Hand covers (plastic gloves).
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College of Engineering Concrete Tech. /Practical
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5-5 Procedures:
1. The proportions of materials for the standard mortar shall be one part of cement to 2.75
parts of graded standard sand by weight. Use a water-cement ratio of 0.485 for all
Portland cements. Thus, the amount of materials required to produce one set of three
cubes are (400 grams of Portland cement), (1100 grams of Ottawa Sand) and (194 cc of
water).
2. Place the 194 cc of water in the mixing bowl, add the 500 grams of cement, and mix at a
slow speed for 30 seconds.
3. Add the 1100 grams of Ottawa Sand over a 30-second period while continuing to mix at a
slow speed.
4. Stop the mixing, change the mixer setting to medium speed (285 ± 5 rpm), and mix for 30
seconds.
5. Stop the mixer and let the mortar stand for 90 sec. During the first 15 seconds, scrape
down into the batch any mortar that may have collected on the sides of the bowl. Cover
the bowl for the remainder of the interval.
6. Finish preparing the mortar by mixing for 60 seconds at medium speed.
7. Immediately upon completion of mixing, start molding the specimens by placing a 25 ±
mm (1 ± in.) layer of mortar in all of the three cube compartments. Tamp the mortar layer
in each cube compartment with the hard rubber tamper 32 times within about 10 seconds
in accordance with Figure (1) in four rounds. Each round to be at right angles to the other
and consisting of eight adjacent strokes over the surface of the specimen. Use sufficient
tamping pressure to ensure uniform filling of the molds. Complete the lift in each mold in
turn before moving on to the next one.
8. Complete the filling of the molds by adding another layer and duplicate the tamping
procedure. At this point the mortar should be slightly above the top of the molds.
Carefully cut the excess mortar flush with the edge of a steel trowel.
9. Place the completed mortar cubes in a moist closet, protected from dripping water for 20
to 24 hours after which the cubes are to be stripped from the molds.
10. Insert the mortar cubes in a water bath until ready for testing.
11. All specimens should be tested within a specified time period:
Test Age Permissible Time Tolerance
24 hours ± 1/2 hour
3 days ± 1 hour
7 days ± 3 hours
28 days ± 12 hours
Figure (1)
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College of Engineering Concrete Tech. /Practical
__________________________________________________________________________________
5.6 Testing Specimens:

Prior to testing, the specimens should be wiped clean. Apply the loads only to the true
surfaces of the cubes. Use a straightedge to check the cube surfaces. Any loose grains of
sand or other extraneous material should be removed from the surfaces in contact with the
testing machine.
The specimen should be placed under the center of the upper bearing block of the
testing machine. A light coating of oil should be applied to the upper platen. The rate of
load application is 1.4 kN/sec or (35 MPa/ min.). Compressive strength is computed as
follows:
𝐹𝑎𝑖𝑙𝑢𝑟𝑒 𝐿𝑜𝑎𝑑 (𝑁)

Compressive strength =
𝐶𝑢𝑏𝑒 𝐿𝑜𝑎𝑑𝑒𝑑 𝐴𝑟𝑒𝑎 (𝑚𝑚2)
5-7 Notes and Specification:

Iraqi Specifications for type-I 41 N Cement
Age (days) Compressive Strength (MPa)

3 16
7 24
28 41
 The engineer should recognize the different types of cements in field from the
symbols wrote on bags, then use this test procedure for compliance with specification.
For example:
 Cement Type-I 32 N: refers to a cement of type-1 normal hardening having
compressive strength of 32 MPa at 28 days.
 Cement Type-I 42 N: refers to a cement of type-1 normal hardening having
compressive strength of 42 MPa at 28 days.
 Cement Type-I 42 R: refers to a cement of type-1 rapid hardening having compressive
strength of 42 MPa at 28 days.
 Cement Type-I 52 R: refers to a cement of type-1 rapid hardening having compressive
strength of 52 MPa at 28 days.
5-8 Questions:
1. What does it mean by standard OTTAWA sand, explain its characters and uses?
2. Did your test results comply with specification?
3. What are the main factors that may affect the test results?
4. What are the factors that the strength of cement depend on?
5. Why strength tests are not based on using neat cement paste?
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College of Engineering Concrete Tech.

TEST# 5 standard test method for

Compressive Strength of Hydraulic Cement Mortar

5.6 Testing Specimens:

𝐹𝑎𝑖𝑙𝑢𝑟𝑒 𝐿𝑜𝑎𝑑 (𝑁)

5-7 Notes and Specification:

Age (days) Compressive Strength (MPa)

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