3Strength 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 timeCuring methods can pay a majorrole in Concrete strength gain anda standard curing method has to beobserved for repeatable test results.
4Compressive StrengthCompressive Strength of Cylindrical Concrete Specimens (ASTM C39)Apparatus: Forney Hydraulic Universal Testing Machine200,000 lbs Tension,400,000 lbs CompressionAccuracy is approximately 10% of the maximum load.
5Compressive Strength — Testing Procedure Maintain the specimen in a water storage tanks and controlled temperature of °F [ °C] up to the time of compression testing.
6Testing Procedure (cont) Carefully align the axis of the specimen with the center of thrust of the spherically seated upper platen.Bring the upper platen tobear on the specimen, adjustingthe load to obtain uniformseating of the specimen, no morethan 50% of the ultimate load.Center the specimen on thelower platen of the testing machine.
7Testing Procedure (cont) 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.Make no adjustment in the rate of movement till the end of the testApply 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)
9Tensile StrengthConcrete 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.
10Tensile Strength Testing — Flexural strength The standard flexural strength test is:AASHTO T 97 and ASTM C 78: Flexural Strength of Concrete (Using Simple Beam with Third-Point Loading)AASHTO T 177 and ASTM C 293: Flexural Strength of Concrete (Using Simple Beam with Center-Point Loading)
11Tensile Strength Tesing — Split Tension Test The standard split tension test is:AASHTO T 198 and ASTM C 496: Splitting Tensile Strength ofCylindrical Concrete Specimens
12Compressive to Tensile Strength Relationships In absence of flexural or tensile testing,the ACI Concrete Code gives some rough rules-of-thumbfor converting compressive strength:
13Durability of Concrete Durability is a measure of how Concrete performs over time. Two major factors that affect Concrete durability are freeze-thaw cycles and chemical attack.
14Durability Testing —Chemical Attack Some standard tests for chemical attack are:AASHTO T 259: Resistance of Concrete to Chloride Ion PenetrationAASHTO T 277 and ASTM C 1202: Electrical Indication of Concrete's Ability to Resist Chloride Ion PenetrationAASHTO T 303 and ASTM C 227: Accelerated Detection of Potentially Deleterious Expansion of Mortar Bars Due to Alkali-Silica Reaction
15Durability Testing — Freeze/Thaw Standard freeze-thaw tests are:AASHTO T 161 and ASTM C 666: Resistance of Concrete to Rapid Freezing and ThawingAASHTO T 121: Mass Per Cubic Meter (Cubic Foot), Yield, and Air Content (Gravimetric) of ConcreteASTM C 671: Critical Dilation of Concrete Specimens Subjected to Freezing
16LAB REPORTEach 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 breakingReport the following information:Cover page with Name, Lab group, Group members, DateCalculations for concrete mixing,Procedure for mixing concrete in the lab. ASTM test numberProcedure for Slump Testing, ASTM test numberProcedure for setting cylinders, size of cylinders, ASTM test numberWhen do you remove the cylinders, how do you cure and for how longCompression testing. Record testing machine and procedure for compression testingRecord Compressive strength ,type of fracture, Defects in specimen and,Age of specimen.