Shmidt Hammer Method Statement

Method Statement for Rebound Hammer of Hardened Concrete (ASTM C-805)_ (Report Ref: MS/101/Rev. A)

Project: Engineering, Procurement, Construction, and Commissioning of Debottlenecking of Coker Unit 9U-20) MAB

TABLE OF CONTENT

 Introduction  Principle of Rebound Hammer Test  Test Procedure  Appendix A: Chart of Compressive strength Vs. Rebound Number

Introduction: Rebound hammer test (Schmidt Hammer) is used to provide a convenient and rapid indication of the compressive strength of concrete. It consists of a spring controlled mass that slides on a plunger within a tubular housing. The operation of rebound hammer is shown in the fig.1. When the plunger of rebound hammer is pressed against the surface of concrete, a spring controlled mass with a constant energy is made to hit concrete surface to rebound back. The extent of rebound, which is a measure of surface hardness, is measured on a graduated scale. This measured value is designated as Rebound Number (rebound index). A concrete with low strength and low stiffness will absorb more energy to yield in a lower rebound value.

Fig 1: Operation of the rebound hammer

The rebound hammer test method is used for the following purposes: a) To find out the likely compressive strength of concrete with the help of suitable corelations between rebound index and compressive strength. b) To assess the uniformity of concrete. c) To assess the quality of concrete in relation to standard requirements. d) To assess the quality of one element of concrete in relation to another.

Principle of Rebound Hammer Test: Rebound hammer test method is based on the principle that the rebound of an elastic mass depends on the hardness of the concrete surface against which the mass strikes. The operation of the rebound hammer is shown in figure above. When the plunger of rebound hammer is pressed against the concrete surface, the spring controlled mass in the hammer rebounds. The amount of rebound of the mass depends on the hardness of concrete surface. Thus, the hardness of concrete and rebound hammer reading can be correlated with compressive strength of concrete. The rebound value is read off along a graduated scale and is designated as the rebound number or rebound index. The compressive strength can be read directly from the graph provided on the body of the hammer.

Test Procedure 1. 2. 3. 4. 5. 6. 7. 8. 9.

Selected the test location. Test area should be at least 150mm in diameter. Ground the test area till becomes smooth. Hold the instrument firmly so that the plunger is perpendicular to the test surface Gradually push the instrument toward the test surface until the hammer impacts After impact, maintain pressure on the instrument and, if necessary, depress the button on the side of the instrument to lock the plunger in its retracted position Record the rebound number on the scale to the nearest whole number. Take ten readings from each test area Discard readings differing from the average of 10 readings by more than 6 units and determine the average of the remaining readings Read the compressive strength directly from the graph provided on the body of the hammer Taking into consideration the test direction (Upward, or downward, or horizontal direction)

Appendix A Chart of Compressive strength Vs. Rebound Number

Umwertungskurven für Betonprüfhammer Modell L/LR Würfeldruckfestigkeit des Betons nach 14 - 56 Tagen

Fig. 2.5

Fig. 2.6

Deutsch

Umwertungskurven für Betonprüfhammer Modell N/NR Würfeldruckfestigkeit des Betons nach 14 - 56 Tagen

Modell N/NR: Umwertungskurven in Abhängigkeit von der mittleren Würfeldruckfestigkeit und des Rückprallwerts R

fckcubem: Mittlere Würfeldruckfestigkeit (wahrscheinlichster Wert)

Modell L/LR: Umwertungskurven in Abhängigkeit von der mittleren Würfeldruckfestigkeit und des Rückprallwerts R

Streugrenzen fckcube: Max. und min. sind so bestimmt, dass 80 % aller Versuchsergebnisse eingeschlossen sind.

Die in Fig. 2.5 und Fig. 2.6 abgebildeten Betonprüfhämmer zeigen die Schlagrichtung an.

© 2017 Proceq SA

Messung

7

Date:

Kuwait International Industrial Laboratory Inspection & Radiation Services Co.

Test Ref:

Standard Test Method for Rebound Number of Hardened Concrete - ASTM C805 Project Information

Test Information

Project :

Location: Concrete Grade:

Owner:

Test Orientation:

Consultant:

Casting date:

Contractor:

Testing Date:

Rebound Number Reading SR.

Test Element

Test direction

1

2

3

4

5

6

7

8

9

10

Average Rebound Number

Estimated Strength MPa

Remarks:

Tested by:

Sr. Technician

Approved by:

QA/QC Engineer

kg/cm

2