Workability, fractural strength, and compressive strength testing of concreate

Workability of concrete

workability is one of the physical parameters of concrete which affects the strength and durability, as well as the cost of labor and appearance of the finished product, workability of concrete is defined as the ease with which concrete can be mixed placed compacted and finished, concrete is said to be workable when it is easily placed and compacted homogeneously that is without bleeding or segregation, 

Technically speaking workability of concrete is the amount of useful internal work necessary to produce 100 compactions it is said that wet concrete is more workable than dry concrete workability is described as very low, medium, high, and variable  types of workability 

 There are three types number one is unworkable concrete also called harsh concrete, it is concrete with very less amount of water content, hand mixing of this type of concrete is not so easy, these types of concrete have high segregation of aggregates as cement paste is not lubricated properly we stick to aggregates in this type of concrete, it is very difficult to maintain homogeneity of concrete mix and compaction requires more effort water-cement ratio for this type of concrete is below 0.4 unworkable concrete needs more work or effort to be compacted  

 Second is medium workable, this type of concrete is used in most of the construction work this type of concrete is comparatively easy to mix transport pour, and compact without any segregation and loss of homogeneity, the water-cement ratio of medium workable concrete is 0.42 0.55, this type of concrete is used in construction with light reinforcement, generally, a spacing of reinforcement allows concrete to compact effectively  

 Third one is highly workable this type of concrete is relatively very easy to mix transport or this type of concrete is used where effective compaction is not possible or in mass highly workable concrete flow easily and settle down without any effort but there are very higher chances of segregation and loss of homogeneity in this case such concrete is used where heavy reinforcement is used and where the vibration of concrete is not possible highly workable concrete is self-compacting water symmetry issue for this type of concrete is more than 0.5 

Fractural strength concrete

The fracture strength of the concrete, is the ability of an unreinforced beam or slab to resist failure in bending, that is bending moment flexible strength is one measure of the tensile strength of concrete, the ideal method for determination of the tensile occurs in bending when the tensile strength at the bottom of the beam exceeds the tensile capacity of the concrete, which is called the modulus of rupture that is extreme fiber stress in bending, the stress can be calculated as modulus of rupture 

Compressive streangth of concrete

compressive strength of concrete  is a measure of the concrete’s ability to resist loads that tend to compress heat a force is applied to the top and bottom of a test sample until the sample fractures or is deformed, the compressive strength is determined by loading the molded concrete specimen

specimens either cubes or cylinders in uniaxial compression until ultimate failure, normally a strength of cylinder specimen is taken as 0.8 times the strength of q,

 compressive strength depends on several factors like water symmetry, cement contained, characteristics of cement, type and properties of aggregate, degree of compaction, curing aid at the time of testing, testing conditions, ambient conditions, specimen geometry rate of loading, etc

Determining compressive streangth of concrete and testing procedure

the compressive strength of concrete is given in terms of the characteristic, compressive strength of 150 mm size cubes tested at 28 days, as per Indian standards, the correct characteristic compressive strength is defined as the strength of the concrete below which not more than five percent of the test results are expected to fail 

 

The dry proportion of ingredients that is cement sand and coarse aggregate, as per the design requirement shall be measured and thoroughly mixed with the information designed quantity of water to the dry proportion, that is water sedimentation shall be mixed well to obtain a uniform concrete mixture the concrete in the cube mode of size 150 into 150 mm shall be filled the concrete shall be filled into the mold in layers approximately 5 centimeters deep, each layer shall be compacted either by hand or by vibration each layer with not less than 35 strokes per layer, using a damping rod shall be compacted the top of the concrete shall be finished by travel and tapped well till this cement slurry comes to the top of the cubes

At least three specimens prefer barely from different batches shall be made for testing at each selected, now curing the test specimen shall be stored in a place free from vibration in the moist air of at least 90 percent relative humidity and at a temperature of 27 degrees plus-minus 2 degrees centigrade for 24 hours, plus-minus half hour from the time of addition of water to the dry ingredients, 

 The specimens from the mold shall be removed after 24 hours, the specimen shall be kept submerged under fresh water at 27 degrees plus-minus 2 degrees centigrade the specimen shall be kept for 7 or 28 days every 7 days the water shall be removed the specimen shall be removed from the water 30 minutes before the testing the specimen shall be in dry condition, before conducting the testing the q weight should not be less than 8.18 now testing 

 The specimens shall now be placed into the compressive testing machine the specimen shall be placed in the machine in such a manner that the load shall be applied to the opposite sides of the cube as the cast that is not to the top and bottom of the axis of the specimen shall be carefully aligned the load shall be applied to the specimen axially, no packing shall be used between the faces of the test specimen, and the steel pattern of the interesting machine the load shall be applied without short and increase continuously at a rate of approximately 140 kg per centimeter square per minute,

 Till the view collapses the maximum load applied to the specimen shall then be recorded the maximum load at which the specimen breaks is taken as a competitive load 

now calculation compressive strength of concrete is equal to maximum compressive load divided by cross-sectional area cross-sectional area is equal to 150 to 150 mm that is 22 500 millimeter square or 225-centimeter square assuming the compression load is 450 k kilo newton compressive strength will be 4 lakh 50 000 newton divided by 225 under bracket then divided by 9.81 it equals 204 kg per centimeter square note 1 kg is equal to 9.81 compressive strength of concrete shall be expressed to the nearest kg per centimeter square average of three values shall be taken as the representative of the patch provided the individual variation is not more than plus-minus 15 percent of the average