Compressive Strength of Hardened Concrete

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Introduction to Engineering and Computing

NGN 110 – Recitation 01

Spring 2015

Department of Civil Engineering

Title: Compressive Strength of Hardened Concrete

Lab Instructor: Professor Arshi Faridi

Experiment Date: 23/03/2015

Submission date: 30/03/2015

Abstract

The main objective of this lab experiment is to obtain and determine the compressive strength of concrete based on the American Standards for Testing using and Materials (ASTM) and the British Standard (BS) through non-destructive and destructive methods respectively. This enabled us to compare between the destructive and non-destructive methods to observe its accuracy and precision. Based on the final results, the compression strength recorded from the non-destructive method was 38.0 MPa while the destructive method was 48.7 MPa. Therefore, we have concluded that both methods classified the concrete as moderate-strength concrete and that the destructive method was more accurate and precise while the non-destructive method lacked consistency and precision.

List of Figures & Tables

Figure 1: Schmidt hammer  …………………………………………………………...………3

Figure 2: Abrasive stone ...………………………………...………..…………………………3

Figure 3: Concrete cube ……………………………………………………..………………..3

Figure 4: Electronic Vernier caliper ……………………………….………………………….3

Figure 5: Digital Balance  ………………………………………………….…………………3

Figure 6: Compression machine……………………………………….…….………………...4

Table  1: Compressive strength floor 1 ……………………………………………….……....5

Table  2: Compressive strength cube 1………………………………………………….…….5

Contents

Introduction        

Theory        2

Experimental set up        3

Procedure        4

Results        5

Discussion of Results        6

Conclusion        7

Recommendations…………………………………………………………………………………………………………………….………7

References        7

Introduction

Concrete is an important material used for construction purposes. Concrete is a mixture of crushed stones, sand, cement and water. All of these materials are mixed in a specific ratio. Almost all buildings are made of concrete and the building's beams are reinforced with steel to make them stronger. It is important to know the compressive strength of the concrete as it varies from one mixture to another; and certain value must be met to make sure the concrete can withstand the load of the building. In this lab experiment, there were two different methods of testing the compressive strength, American Standards for Testing (ASTM) though a non-destructive method and Materials and the British Standard (BS) through a destructive method. For the non-destructive method Schmidt hammer and electronic Vernier caliper was used; for the destructive method compression machine was used. A hardened concrete cube was tested against both methods.

Objectives of the experiment are:

• To understand the concept of destructive method of testing compressive strength.
• To understand the concept of non-destructive method of testing for compressive strength.

Theory

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• ; This  equation will tell us its compressive strength, which is the maximum compressive stress a material can sustain under crushing loading, that will enable us to classify the concrete in terms of its strength.[pic 8]

Experimental set up

Apparatus:

• Schmidt hammer

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• Abrasive (grinding) stone [pic 11]

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• Concrete cube

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• Electronic Vernier Caliper

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• Digital balance

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• Compression machine [pic 19]

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Procedure

Non-Destructive method:

1. The surface to be tested is rubbed with the abrasive (grinding) stone.
2. The Schmidt hammer is placed perpendicular to the surface and then it is pressed against the surface until it is triggered.
3. The number of rebounds is recorded as the Schmidt hammer is pressed against the surface of the sample
4. The value (Rebound Number) that is provided on the Schmidt hammer is then recorded.
5. The procedure is repeated ten times and 10 values are recorded; this step will insure accuracy and precision.
6. The average value of the ten readings is calculated.
7. Using the calibration chart, the average rebound number is then converted to the value of the compressive strength of the surface.

Destructive method:

1. The dimensions of the concrete cube are measured using an electronic Vernier Caliper.
2. The cross sectional area of the concrete cube is calculated as the product of the average depth and width.
3. The concrete cube is weighed using the digital balance.
4. Using the values obtained for the Volume and Mass, the density is calculated by dividing the Mass over the Volume.
5. The concrete cube is then placed in the compression machine and the compressive load is applied until cracks starts to show on the surface, the compression failure load is then recorded.
6. Using the values of the compression failure load and the cross sectional area, the compressive strength of the concrete cube is calculated by dividing the compression failure load over the cross sectional area.

Results

Our results consists of the values of the compressive strength of floor 1 and cube 1 using a Schmidt hammer (non-destructive method) and a Compression machine (destructive method) respectively.

From the Schmidt hammer (non-destructive method):

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