Dr. Sophia Hassiotis

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Strength Testing

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Compressive Testing Tensile Testing

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Beam Split Cylinder Durability Testing

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Chemical Attack Freeze-Thaw

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Concrete is most often known for its compressive strength Flexural strength is of importance when used in rigid pavements. Most often, 28-day strength is specified although other strengths such as 1-day, 7-day, 56-day and 90-day strength can be used as well. Concrete continues to gain strength over time Curing methods can pay a major role in Concrete strength gain and a standard curing method has to be observed for repeatable test results.

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Compressive Strength of Cylindrical Concrete Specimens (ASTM C39 )

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Apparatus: Forney Hydraulic Universal Testing Machine 200,000 lbs Tension, 400,000 lbs Compression Accuracy is approximately 10% of the maximum load.

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Maintain the specimen in a water storage tanks and controlled temperature of 73.5 + 3.5 °F [23.0 +- 2.0 °C] up to the time of compression testing.

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Carefully align the axis of the specimen with the center of thrust of the spherically seated upper platen.

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Bring the upper platen to bear on the specimen, adjusting the load to obtain uniform seating of the specimen, no more than 50% of the ultimate load.

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Center the specimen on the lower platen of the testing machine.

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Apply the load at a loading rate of 35 psi/s (within a range of 28 to 42 psi/s). Maintain this loading rate at least for the last half of the anticipated loading phase.

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Make no adjustment in the rate of movement till the end of the test

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Apply the compressive load until the load indicator shows that the load is decreasing steadily and the specimen displays a well-defined cracking pattern. Record the maximum load (lb)

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Concrete is not nearly as strong in tension as it is in compression.

Concrete flexural strength is important in some applications. For example, flexural strength is typically used as a Concrete performance measure for pavements because it best simulates flexural stresses at the bottom of the Concrete surface course as it is subjected to loading.

The standard flexural strength test is:

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AASHTO T 97 and ASTM C 78: Flexural Strength of Concrete (Using Simple Beam with Third-Point Loading)

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AASHTO T 177 and ASTM C 293: Flexural Strength of Concrete (Using Simple Beam with Center-Point Loading)

The standard split tension test is: AASHTO T 198 and ASTM C 496: Splitting Tensile Strength of Cylindrical Concrete Specimens

In absence of flexural or tensile testing, the ACI Concrete Code gives some rough rules-of-thumb for converting compressive strength:

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Durability is a measure of how Concrete performs over time.

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Two major factors that affect Concrete durability are freeze-thaw cycles and chemical attack.

Some standard tests for chemical attack are:

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AASHTO T 259: Resistance of Concrete to Chloride Ion Penetration

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AASHTO T 277 and ASTM C 1202: Electrical Indication of Concrete's Ability to Resist Chloride Ion Penetration

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AASHTO T 303 and ASTM C 227: Accelerated Detection of Potentially Deleterious Expansion of Mortar Bars Due to Alkali-Silica Reaction

Standard freeze-thaw tests are:

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AASHTO T 161 and ASTM C 666: Resistance of Concrete to Rapid Freezing and Thawing

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AASHTO T 121: Mass Per Cubic Meter (Cubic Foot), Yield, and Air Content (Gravimetric) of Concrete

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ASTM C 671: Critical Dilation of Concrete Specimens Subjected to Freezing

Each one of you will write and submit his/her own lab report (no group reports) Your lab report should be typed and all figures should be professional looking. A big percentage of your grade will be dedicated to the degree of professionalism of your report.

DUE: One week after cylinder breaking Report the following information:

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Cover page with Name, Lab group, Group members, Date

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Calculations for concrete mixing,

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Procedure for mixing concrete in the lab. ASTM test number Procedure for Slump Testing, ASTM test number Procedure for setting cylinders, size of cylinders, ASTM test number When do you remove the cylinders, how do you cure and for how long Compression testing. Record testing machine and procedure for compression testing Record Compressive strength ,type of fracture, Defects in specimen and, Age of specimen.