## Introduction

Cement is the most important material in structural works, and this is seen by the wide spread of using it in different structural works. Therefore, compressive test of mortar is one of very important tests that determine whether the cement is good and capable to be used as structural material or not, by comparing the result of this test with the standard specifications.

 Cracks in concrete

## Objectives

The aim of the compressive strength test is to find the compressive strength of standard cement sand mortar cubes, and of the tensile test is to find the tensile strength also of standard cement sand mortar cubes.

## Theory

#### Compressive Strength

Using 7.07 cm x 7.07 cm x 7.07 cm mortar cubes with sand to cement proportion of 1:3 where the sand should be standard as specified in IS:650 as fine aggregate, compressive strength of cement could be indicated after 28 days curing.

The following formula was used to determine the compressive strength for cement:

Stress=P/A

Where,

A= Surface area

#### Tension Strength

Tensile strength test is similar to the compressive strength test but it’s an optional test because tensile strength equal about (0.1 to 0.15) from the compressive strength.

## Equipments

1. Cement sample, standard sand and water as well
2. Cube mold  7.07 x 7.07 x 7.07 cm and base plates
3. Weighting balance up to 0.1 gm accurate
4. Motored cube vibration machine
5. Measuring cylinder
6. Trowel and tray
7. Tenile testing mashine: Cement Tensile Testing Machine
8. Compression testing machine: compression testing machine
9. three infinity (∞) shaped molds

## Procedure

#### Part A (Compression test)

For each cube, the quantities of materials taken were as follows:
Cement = 180gm
Standard sand = 523gm
Water = 108 gm ( for

** Note that these are just sample quantities and it could be changed
1. The cement and sand were mixed with trowel on non-porous plate for one minute. Then water was added to the mixture of cement and sand, and was mixed for 3 minutes until the mixture of uniform color was obtained.
2. Thin layer of oil was applied to the interior faces of the molds. Molds were placed on the table of the vibration machine, and firmly held in position by means of suitable clamps.
3. The entire quantity of mortar was placed in the hopper of the cube mold and compacted by vibrations for period of about 2 minutes.
4. At the end of vibration, the mold was removed together with the base plate from the machine, and the top surface of cube in the mould was finished by smoothing the surface with the blade of trowel. Identification marks were graved on cubes.
5. The filled molds were kept in the atmosphere of at least 90% relative humidity for 24 hours in the humidity chamber, after completion of vibration. Also temperature was maintained at 27± 2°C.
6. At end of this period. Cubes were removed from the molds and immediately submerged in clean fresh water and kept there until taken out just prior to breaking. After they are taken out and until they are broken, the cubes should not allow to become dry.
7. The test cube was placed on the platform of compression testing machine without any packing between the cube and the steel platens of the testing machine.
8. The load was applied on smooth surface on the cube steadily and uniformly starting from zero at a rate of 35 N / mm/minute till the cubes failed.

#### Part B (Tension test)

1. From the same sample of mortar that is made in compression test, three molds are filled with mortar.
2. First half of the mold is filled then its hit 25 times with a specific hitter, the its filled to the top and again its being hit another 25 times with the same hitter
3. Three molds are filled and are left for one day to solidify
4. Then they are removed and put in water for one week.
5. After that the samples have been put in the tensile machine one by one , and records are taken.

## Data and Calculations

#### Part A (Compression test)

Table (1) below shows the data collected to determine the compressive strength of three cement cubes.

Table (1): Data collected for compressive strength
 Sample No. Area (mm2) Maximum force it crash on (kN) Maximum stress it crash on (MPa) 1 65.1 × 64.7 76.9 18.257 2 62.5 × 64.8 72.8 17.975 3 66.5 × 66.1 80.2 18.245

#### Sample Calculation

Chosen Sample: Sample No.1

$stress=\frac{P}{A}$

$stress=\frac{76.9&space;kN}{65.1&space;\ast&space;64.7mm^2}=18.257&space;MPa$

#### Part B (Tension test)

Table (1) below shows the data collected to determine the compressive strength of three cement cubes.

Table (2): Data collected for tension strength

 Sample No. Area (cm) Maximum force it crash on (kN) Maximum stress it crash on (MPa) 1 2.5 × 2.5 1.08 1.728 2 2.5 × 2.5 0.8 1.28 3 2.5 × 2.5 0.8 1.28

## Results and Conclusion

It is noticed from this experiment that the tension stress values of mortar are not large. These values give an impression about the type and properties of mortar cement, and then the concrete that make of it using a standard values for concrete design, so the cement bears compressive forces more than tensile forces.

Sources of errors in this experiment are due to:

1. Fallibility in preparing the standard portions of cement, sand, and water.
2. Presence of air bubbles while placing the mix in molds.

## Engineering use

This experiment is very important for civil engineering work, because it gives an impression about the type and properties of cement and the concrete that is prepared from it, and so the results of this experiment is used basically in concrete design calculation, for building construction works and other works, It also determines the failure force and failure stress that a cement block can stand before complete failure. There's a lot of construction works requires adequate compressive strength to durability.

So it is important for engineers to know how cement behaves under compression and tension in order to know how and where to use it appropriately and this test provides us with information about the behavior of cement under stress and compression forces.