EXPERIMENT of Rebound Hammer Test

Purpose

The rebound hammer test is one of the non-destructive tests used to check the compressive strength of concrete. 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.

Standard Designation

ASTM C805

Scope

• This test method covers the determination of a rebound number of hardened concrete using a spring-driven steel hammer.
• The values stated in inch-pound units are to be regarded as the standard.
• This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.

Apparatus

Rebound Hammer

Procedure

• Should be tested against the test anvil.
• Apply light pressure on the plunger and allow it to extend to the read position for the test.
• Apply a gradual increase in pressure until the hammer impacts.
• Take the average of about 15 readings.

Interpretation of Results

The rebound reading on the indicator scale has been calibrated by the manufacturer of their bound hammer for horizontal impact.

Average Rebound Number	Quality of concrete
>40	Very good hard layer
30-40	Good layer
20-30	Fair
<20	Poor concrete
0	Delaminated

Conclusion

1.    The rebound value can be measured discretionary, whereas the number of crushed specimens is limited.

2.    The combination of both methods is the best and most reliable procedure to determine the compressive strength of concrete structures.

3.    The method does not damage the structure like the classical method, where cores must be taken for the evaluation of the compressive strength.

4.    It is a fast, inexpensive and easy to perform method using light and portable test equipment.

Business Letter Templates in docx

1.Business-Letter-About-Dissolving-Partnership

Company, Inc.

123 Alphabet Drive

Los Angeles, California 90002

15 December 2012

Dr. Kris Johnson

Marketing Representative

Creativity Plus, Inc.

824 Imagination Lane

Miami, Florida 33111

Dear Kris,

Working with Creativity Plus, Inc. for the past four months has been a wonderful experience. Regrettably, Company, Inc. no longer has need of your services. We have decided to move our company in a different direction, and that decision requires that we make a number of changes to our infrastructure. To that end, we have decided to keep all of our current marketing efforts in-house, so we can no longer make use of your marketing consultation services.

Thank you for the excellent work you have done for us. I hope to remain on good terms with you and Creativity Plus, Inc., and if we require services similar to what you have provided for us in the past, we would certainly like to consider you again.

Warm regards,

Sam Brown

Vice President of Company, Inc.

555-555-5555

s.brown@companyinc.com

2.Business-Letter-About-Meeting

Company, Inc.

123 Alphabet Drive

Los Angeles, California 90002

15 November 2012

Ms. Susan Smith

Supervisor of Product Development

Pet Supply Provider, Inc.

472 Canine Road

Los Angeles, California 90002

Dear Ms. Smith:

It was a pleasure meeting you at the conference last week. As we discussed, I sincerely believe that the widget gizmo produced by Company, Inc. can greatly streamline your production process. If you are still willing, I would like to bring some of the key members of my team along with me to meet with you at Pet Supply Provider, Inc. We would like to give you an overview of our services and discuss with you the best plan to suit your needs.

Meeting in person would allow us to fully evaluate your wants and needs. Our team is available to meet any time this week or next. Please let me know, at your earliest convenience, when you would be available.

Cordially,

Sam Brown

Vice President of Company, Inc.

555-555-5555

s.brown@companyinc.com

Determine the percentage of different grain sizes contained within a soil (Particle Size Analysis)

Particle Size Analysis

Purpose:

This test is performed to determine the percentage of different grain sizes contained within a soil. The mechanical or sieve analysis is performed to determine the distribution of the coarser, larger-sized particles, and the hydrometer method is used to determine the distribution of the finer particles.

Standard Reference:

ASTM D 422 - Standard Test Method for Particle-Size Analysis of Soils

Significance:

The distribution of different grain sizes affects the engineering properties of soil. Grain size analysis provides the grain size distribution, and it is required in classifying the soil.

Equipment:

Balance, Set of sieves, Cleaning brush, Sieve shaker, Mixer (blender), 152H Hydrometer, Sedimentation cylinder, Control cylinder, Thermometer, Beaker, Timing device.

Test Procedure:

Sieve Analysis:

1.     Write down the weight of each sieve as well as the bottom pan to be used in the analysis.

2.     Record the weight of the given dry soil sample.

3.     Make sure that all the sieves are clean, and assemble them in the ascending order of sieve numbers (#4 sieve at top and #200 sieve at bottom). Place the pan below #200 sieve. Carefully pour the soil sample into the top sieve and place the cap over it.

4.     Place the sieve stack in the mechanical shaker and shake for 10 minutes.

5.     Remove the stack from the shaker and carefully weigh and record the weight of each sieve with its retained soil. In addition, remember to weigh and record the weight of the bottom pan with its retained fine soil.

Data Analysis:

Sieve Analysis:

1.     Obtain the mass of soil retained on each sieve by subtracting the weight of the empty sieve from the mass of the sieve + retained soil, and record this mass as the weight retained on the data sheet. The sum of these retained masses should be approximately equals the initial mass of the soil sample. A loss of more than two percent is unsatisfactory.

2.      Calculate the percent retained on each sieve by dividing the weight retained on each sieve by the original sample mass.

3.     Calculate the percent passing (or percent finer) by starting with 100 percent and subtracting the percent retained on each sieve as a cumulative procedure.

For example:

Total mass = 500 g

Mass retained on No. 4 sieve = 9.7 g

Mass retained on No. 10 sieve = 39.5 g

For the No.4 sieve:

Quantity passing = Total mass - Mass retained

= 500 - 9.7 = 490.3 g

The percent retained is calculated as;

% retained = Mass retained/Total mass

= (9.7/500) X 100 = 1.9 %

From this, the % passing = 100 - 1.9 = 98.1 %

For the No. 10 sieve:

Quantity passing = Mass arriving - Mass retained

= 490.3 - 39.5 = 450.8 g

% Retained = (39.5/500) X 100 = 7.9 %

% Passing = 100 - 1.9 - 7.9 = 90.2 %

(Alternatively, use % passing = % Arriving - % Retained

For No. 10 sieve = 98.1 - 7.9 = 90.2 %)

        4. Make a semilogarithmic plot of grain size vs. percent finer.

        5. Compute Cc and Cu for the soil.

Observation And Calculation

Total Weight of soil sample = 500

Group No.	Sieve No.	Dia (mm)	WT. Defined (gm)	%age Retained %	Commulative % age WT. Retained	% Passing
G R O U P No 1	4	4.75	30	6	6	94
	8	2.36	60	12	18	82
	10	2.00	28	5.6	23.6	76.4
	16	1.18	46	9.2	32.8	67.2
	30	0.6	44	8.8	41.6	58.4
	40	0.425	20	4	45.6	54.4
	50	0.3	64	12.8	58.4	41.6
	80	0.18	104	20.8	79.2	20.8
	100	0.15	0	0	79.2	20.8
	200	0.075	100	20	99.2	0.8
	Pan	0	0	0	0	0

Concrete Durability and factor affecting of durability

Definition The ability of concrete to withstand the conditions for which it is designed without deterioration for a long period of years is known as durability. OR Durability of concrete may be defined as the ability of concrete to resist weathering action, chemical attack, and abrasion while maintaining its desired engineering properties. Durability is defined as the capability of concrete to resist weathering action, chemical attack and abrasion while maintaining its desired engineering properties. It normally refers to the duration or life span of trouble-free performance. Different concretes require different degrees of durability depending on the exposure environment and properties desired. For example, concrete exposed to tidal seawater will have different requirements than indoor concrete.

Concrete will remain durable if:

• The cement paste structure is dense and of low permeability
• Under extreme condition, it has en-trained air to resist freeze-thaw cycle.
• It is made with graded aggregate that are strong and inert
• The ingredients in the mix contain minimum impurities such as alkalies, Chlorides, sulfates and silt

Factors Affecting Durability of Concrete

Durability of Concrete depends upon the following factors:

Cement content

Mix must be designed to ensure cohesion and prevent segregation and bleeding. If cement is reduced, then at fixed w/c ratio the work ability will be reduced leading to inadequate compaction. However, if water is added to improve work ability, water / cement ratio increases and resulting in highly permeable material.

Compaction

The concrete as a whole contain voids can be caused by inadequate compaction. Usually it is being governed by the compaction equipment's used, type of form works, and density of the steelworks

Curing

It is very important to permit proper strength development aid moisture retention and to ensure hydration process occur completely

Cover

Thickness of concrete cover must follow the limits set in codes

Permeability

It is considered the most important factor for durability. It can be noticed that higher permeability is usually caused by higher porosity .Therefore, a proper curing, sufficient cement, proper compaction and suitable concrete cover could provide a low permeability concrete

Types of Durability of Concrete

There are many types but the major Concrete Durability types are:

1. Physical durability
2. Chemical durability

Physical Durability

Physical durability is against the following actions

1. Freezing and thawing action
2. Percolation / Permeability of water
3. Temperature stresses i.e. high heat of hydration

Chemical Durability

Chemical durability is against the following actions

1. Alkali Aggregate Reaction
2. Sulfate Attack
3. Chloride Ingress
4. Delay Ettringite Formation
5. Corrosion of reinforcement

Causes for the Lack of Durability in Concrete

1. External Causes:

1. Extreme Weathering Conditions
2. Extreme Temperature
3. Extreme Humidity
4. Abrasion
5. Electrolytic Action
6. Attack by a natural or industrial liquids or gases

2. Internal Causes

a) Physical

• Volume change due to difference in thermal properties of aggregates and cement paste

• Frost Action

b) Chemical

• Alkali Aggregate Reactions

i. Alkali Silica Reaction

ii. Alkali Silicate Reaction

iii. Alkali Carbonate Reaction

• Corrosion of Steel