Schmidt Rebound hammer: 2013

Factors Influencing the Results
Type of cement
Concrete made of high alumina cement can give strengths up to 100% higher, whereas super sulphated cement concrete can give 50% lower strength compared to a calibration obtained on Portland cement cubes. It is necessary to recalibrate the hammer for different types of cement.

Type of aggregate

Gravel and most crushed rocks give similar correlations, but lightweight aggregates and aggregates with unusual properties require special calibration.

Surface and internal moisture condition of the concrete.

This method of testing is applied only on close textured concrete. Open texture concrete typical of masonry blocks, `honeycombed’ concrete, or no fines concrete cannot be tested using this method.

Trowelled and floated surfaces as in floors, are harder than moulded surfaces and in most cases will tend to overestimate the strength.

A wet surface will give rise to under-estimated of the strength of concrete calibrated under dry conditions. This influence can be considerable and in structural concrete it is about 10% lower on wet surfaces than on an equivalent dry surface.

Age of concrete
In a very old and dry concrete the surface will be harder than the interior, giving rebound values somewhat higher than normal. New concrete with moist surface generally has a relatively softer surface, resulting in lower than normal rebound.

OVER VIEW OF THE CONCRETE HAMMER

Non-destructive Testing Of Concrete via Rebound Hammer - Overview

INTRODUCTION
The standard method of determining strength of hardened concrete consists of testing concrete cubes in compression. The quality of entire concrete of a structure cannot be fully assessed by testing a few concrete cubes. The results obtained in testing cubes do not always reflect the actual strength of concrete in construction. In a whole day, concreting work cubes are cast in a few batches, the differences (unintentional and intentional) in the composition are not uncommon, their compaction and their hardening conditions always differ more or less from those of the structure. In addition, the number of test cubes is generally so small that they can only be considered as random tests. Sometimes, in case of failure of cubes, doubtful concrete, cracks, deterioration of concrete, etc. it becomes necessary to assess the quality and strength of concrete of the structure. As far back as early thirties, the necessity was felt to develop instruments by which in-situ strength of concrete may be obtained. Various non-destructive methods of testing concrete have been developed, which include, Firing method, Skramtayev’s method, Polakov’s method, Magnitostroy method, Fizdel ball hammer, Einbeck pendulum hammer, Ball indentation hammer, Rebound hammer, Pull out techniques, Windsor probe, Ultrasonic pulse velocity methods, Radioactive and nuclear methods, Magnetic and electrical methods. In all these methods of tests, due to simplicity, rebound hammer test based on surface hardness became most popular in the world for non-destructive testing of in-situ concrete.

ONLY ENGINEERS

TEST BETTER – BUILD STRONGER

FOR:

-CONSTRUCTION/BUILDING ENGINEERS

-CIVIL ENGINEERS

-STRUCTURAL/HIGHWAY ROAD ENGINEERS

-MECHANICAL ENGINEERS

FEATURES OF SCHMIDT CONCRETE HAMMER

Features of the HT-225 Concrete Rebound Test Hammer

1. The Concrete Rebound Test Hammer is used to test the Surface Hardness and Penetration Resistance of concrete.

2. It works by measuring the rebound of the spring-loaded hammer, when impacting against the surface of the concrete sample.

3. It is a non-destructive test which can help to estimate the compressive strength of concrete.

4. It is used to test the compressive strength of building structures, floors, bridges, dams, highway Roads and rocks, pavements, Slab, beam, Truss and Column etc

5. It is an easy-to-use instrument that provides a quick and on-the-spot test for obtaining an immediate indication of concrete strength in various parts of structures.

6. It is portable and Handy.

7. It is used in assessing the likely compressive strength of concrete with help of suitable co-relations between rebound index and compressive strength.

8. It is used in assessing the uniformity of concrete

9. It is used in assessing the quality of the concrete in relation to standard requirements

10. It is used in assessing the quality of one element of concrete in relation to another

11. It is most commonly used due to its simplicity and low cost.

Note: The Rebound Hammer method can be used with greater confidence for differentiating between the questionable and acceptable parts of a structure or for relative comparison between two different structures.

CONTACT US:

No. 18 Addis Ababa Crescent wuse zone

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schmidt Hammer - Introduction.

SCHMIDT CONCRETE REBOUND TEST HAMMER

BRIEF INTRODUCTION

Concrete is susceptible to a variety of environmental degrading factors which tend to limit its service life. This therefore has brought about the need for test methods to measure the in-place properties of concrete for quality assurance and for evaluation of existing conditions. Since such test are expected not to impair the function of the structure and allow for re-testing at the same location to evaluate the changes in property at some other point in time, these methods should be non-destructive. Hence the Concrete Test Hammer.

Concrete structures as many other engineering structures, are subjected to deterioration that affects their integrity, stability and safety. Faced with the importance of the damages noted on the structures, the current choices are directed towards the repair of the existing structures rather than towards the demolition and construction of new ones. But before any repair work being done, it is common practice to determine the causes of the deterioration so that successful repair can be done.

Many repair work such as Road Highways fail because the exact causes of the deterioration was not adequately identified. This identification process comprises many methods including non-destructive testing methods. Non-Destructive Testing (NDT) is usually undertaken as part of the detailed investigation to complement the other methods. The conclusions of the investigation are based essentially on these tests. A correct assessment of a deteriorated concrete structure is a crucial basis for the success of a repair system.

Experience has shown that in many cases repairs fail much earlier than expected due to improper diagnosis of the actual situation of the structure, either because the cause of the degradation was not properly understood, or the extent of the damage was under-stated. The strength of the concrete structure will vary by age but its rate may depend on various factors such as the type of concrete, type of aggregate, surface and internal moisture condition of the concrete etc. Since, the use of Schmidt hammer is commonly accepted for the preliminary assessment of concrete surface hardness as the non-destructive test, this will provide useful estimation of the uniformity of concrete and measure the strength of existing surface concrete and to detect weak spots.

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The procedure for testing a concrete structure is given below:

• All members and points of a concrete structure selected for testing should be marked for identification; they should also be in dry condition.

• Testing should be conducted on surfaces that are smooth and uniform, preferably surfaces created by casting against a form. Avoid rough spots, hony-comb or porous areas. Free or trowelled surface may also be satisfactory if appropriate corrections are applied or a special calibration is prepared. If loosely adhering scale, plaster work or coating is present, this should be rubbed off with a grinding wheel or stone.

• For concrete section less than 100 mm thick, the rebound of the hammer will be affected by the elastic deformation of the section, and it should be backed up by a heavy mass placed on the back side.

• At each of selected points, made smooth and clean, take six rebound readings. For each reading shift the hammer 25 mm and take care not to rebound the same spot twice. The point of impact should be at least 20 mm away from any edge or sharp discontinuity. Small air pockets near the surface under the point of impact cause low rebound, on the other hand, immediately over a hard aggregate the impact will result in a high rebound.

Note: Manufacturer of Concrete hammer recommends at selected points 5 or better 10 impact reading. It is recommended at least 9 valid reading and not more than 25. It is normally better to confine the readings of a test (9 to 25 readings) to an area not exceeding about 300 mm x 300 mm rather than to carry out random testing extending over the whole structure or unit.

• The usual directions of test are either horizontal or vertically down, but any direction of test can be used as long as it is consistent. Calibration or corrections for a given direction of test are supplied with the hammer or can be derived.

• The rebound values usually are considered reliable when at least six readings deviate not more than +2.5 to 3.5 on the impact scale. The compressive strength is then determined by taking average of rebound reading.

• Compressive strength of the concrete can be determined from the relationship between the rebound number and the strength given by the curve. For reliable results the calibration curve will be derived from the given set of materials and conditions.

IMGAGES OF THE CONCRETE REBOUND HAMMER

ENGINEERS ONLY! TEST BETTER - BUILD STRONGER!

ENGINEERS ONLY

Introduction of HT-225 Concrete Rebound Test Hammer

Features of the HT-225 Concrete Rebound Test Hammer

1. The Concrete Rebound Test Hammer is used to test the Surface Hardness and Penetration Resistance of concrete.

2. It works by measuring the rebound of the spring-loaded hammer, when impacting against the surface of the concrete sample.

3. It is a non-destructive test which can help to estimate the compressive strength of concrete.

4. It is used to test the compressive strength of building structures, floors, bridges, dams, highway Roads and rocks.

5. It is an easy-to-use instrument that provides a quick and on-the-spot test for obtaining an immediate indication of concrete strength in various parts of structures.

6. It is portable and Handy.

7. It is used in assessing the likely compressive strength of concrete with help of suitable co-relations between rebound index and compressive strength.

8. It is used in assessing the uniformity of concrete

9. It is used in assessing the quality of the concrete in relation to standard requirements

10. It is used in assessing the quality of one element of concrete in relation to another

11. It is most commonly used due to its simplicity and low cost.

Specification

1. Test Range: 10-60 mpa

2. Impact Energy: 2.207J (0.225 kgf.m)

3. Impact Stroke: 75 mm

4. Friction of Slider: 0.5-0.8 N

5. Spherical radius of impact pole: 25+/-1 mm

6. Dimension: 278*D54 mm

7. Weight: 1kg

schmidt concrete Rebound Hammer

TEST BETTER - BUILD STRONGER.

ENGINEERS ONLY!

Concrete is susceptible to a variety of environmental degrading factors which tend to limit its service life. This therefore has brought about the need for test methods to measure the un-place properties of concrete for quality assurance and for evaluation of existing conditions. Since such test are expected not to impair the function of the structure and allow for re-testing at the same location to evaluate the changes in property at some other point in time, these methods should be non-destructive. Hence the importance of the Concrete Test Hammer.

With the incessant building collapse in the Nigeria, especially in Lagos, the Lagos state government is taking the problem very seriously through its agencies to curb the menace of building collapse in the state.

The Nigeria National Emergency Management Agency (NEMA) has being on rescue mission each time there is a collapse but the government is asking questions about the kind of jobs Engineers in the country are doing. Most of the times the collapse are as a result of inadequate building materials, incompetence of the contracting engineer, low quality building materials, etc.

The Nigerian Society of Engineers (NSE) and Council for the regulation of Engineering in Nigeria (COREN) should ensure that only qualified Engineers are registered and also Development Control Abuja to approve and monitor the kind of structure design contractors bring to them.