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Why is the 28-days compressive strength of concrete generally specified?
It is attributed to two reasons: 1. Strength of concrete grows faster in initial days and this process of gaining strength slow down with time. This can be said as stabilization in value of gained strength of concrete. After approximately 20 or some more days, strength value get stabilize and does not change too much with time. Therefore, compressive strength is taken after approximatley 3 weeks time. 2. These tests have to performed practically and date record is needed to be maintained. Therefore, if test duration is a multiple of 7 (7 weekdays) then it is more easy to remind. It is the reason we have 28=7x4 days to note down compressive strength of concrete. for ex: if we start test on monday then we know that after 4 weeks on same time on monday we can finish the compressive strength test.
How do you calculate the compressive strength of concrete cubes?
Concrete specimens are tested using the ASTM39 Test Standard Test Methodfor Compressive Strengthof Cylindrical Concrete Specimens by using two samples made from the same test at the same age, usually at strength of 28 days old.Design engineers use the specified strength ƒ´c to design structural elements. This specified strength is incorporated in the job contract documents. The concrete mixture is designed to produce an average strength (ƒ´cr) higher than the specified strength, such that the risk of not complying with the strength specification is minimized.Cylindrical specimensfor acceptance testing should be 6 x 12 inch (150 x 300 mm) size or 4 x 8 inch (100 x 200 mm) when specified. The Concrete strength is calculated by dividing the maximum load at failure by the average cross sectional area.Concrete compressive strength requirements can vary from 2500 psi (17 MPa) for residential concrete to 4000 psi (28 MPa) and higher in commercial structures. Higher strengths up to and exceeding 10,000 psi (70 MPa) are specified for certain applications.Cylinders are placed in a Compression testing machine and loaded to failure from 20 to 50psi. The type of break should be recorded by a Certified Technician.Example 1:For a concrete sample that is broken after 28 daysThe cylinder is 6” diameter, so it has an area of 3.14 x Diameter squared /4A = 3.14 x 6 x 6/4A = 28.26 square inchesIf the force required to break the cylinder was 97,500 poundsThen the compressive strength is 97,500 pounds / 28.26 square inches = 3,450 psi.3,450psi needs to be compared to the Design strength determined by the Design Strength determined by the Design Engineer.Example 2:Given: f 'c = 3000 psiConcrete test cylinders averaged 2800 psi.PSICore 1 =2900Core 2 =2850Core 3 =2450Average compressive strength of 3 cores = 2730 psi.Find: Is the concrete in the structure adequate under CDOT specifications?Solution:Test Evaluation:f 'c = 3000 psiAverage compressive strength of 3 cores - 2730 psiDo any compressive strengths differ from the average by more than 10%?10% of Average compressive strength = 273 psiCore 1: 2900 - 2730 = 170 psi, < 273 therefore OKCore 2: 2850 - 2730 = 120 psi, < 273 therefore OKCore 3: 2730 - 2450 = 280 psi, > 273 therefore -discard core and re-compute average compressive strength using two remaining cores.New average compressive strength = 2875 psi
What is mean by good grading?
The word "grading" refers to the diversity in size of the aggregates. Aggregates that have "good grading" or are "well graded" have the same % of each size stone. The goal is to get the maximum aggregate packing density within a mix that still allows the cement to bond to the aggregates and cure properly, since its the aggregates that give concrete its high compressive strength.
What is the conrete mixing ratio in M25concrete?
The Concrete mixing ratio for M35 grade concrete as per IS Mix design is1:1.6:2.907 (cement:Fineaggregate:Coarse aggregate)The ratio obtained is as per design calculations by considering the grade of aggregates and the type of cement used.The Water/cement ration is 0.43
Are iron weights heavier than concrete weights?
No a lb of bricks and a pound of feathers is still a pound same with concrete and iron
Why is the 28-days compressive strength of concrete generally specified?
It is attributed to two reasons: 1. Strength of concrete grows faster in initial days and this process of gaining strength slow down with time. This can be said as stabilization in value of gained strength of concrete. After approximately 20 or some more days, strength value get stabilize and does not change too much with time. Therefore, compressive strength is taken after approximatley 3 weeks time. 2. These tests have to performed practically and date record is needed to be maintained. Therefore, if test duration is a multiple of 7 (7 weekdays) then it is more easy to remind. It is the reason we have 28=7x4 days to note down compressive strength of concrete. for ex: if we start test on monday then we know that after 4 weeks on same time on monday we can finish the compressive strength test.
Formula for calculating compressive strength of cylindrical body of concrete?
If the concrete sample has been tested in a uniaxial compressive test machine (which would be the normal destructive method of testing a cylindrical sample), then you would use the failure load divided by the cross sectional area of the cylinder to find the strength of the material. Failure Stress = Uniaxial Compressive Strength = Force / Area It should also be noted that concrete strength is more normally found by measuring "cube strength", that is where the concrete is pored into cube shaped moulds of 100 mm x 100 mm x 100 mm and is then allowed to cure for a period of time (typically 28 days). The concrete cube is then tested in a uniaxial test rig. The formula for calculating the strength is the same, however the major difference is in the preparation of the sample as described above.
Why concrete cube has high strength than cylinder?
Reasons for concrete cube to have greater compressive strength as compared to cylinder iscontact area of a standard cube mould with the upper platen in the testing machine is more which results in more confinement .more confinement resist against specimen expansion resulting in more compressive strength
Why is steel good in tension?
It depends on its strength. Usually, concrete is 6.7 to 9 times stronger in compression.To be exact, tensile strength of concrete is equal to 0.7 times square root of its compressive strength. For common concretes with compressive strength of 20 to 40 MPa, it is about 3 to 4.4 MPa of tensile strength respectively.
How do you calculate the compressive strength of concrete cubes?
Concrete specimens are tested using the ASTM39 Test Standard Test Methodfor Compressive Strengthof Cylindrical Concrete Specimens by using two samples made from the same test at the same age, usually at strength of 28 days old.Design engineers use the specified strength ƒ´c to design structural elements. This specified strength is incorporated in the job contract documents. The concrete mixture is designed to produce an average strength (ƒ´cr) higher than the specified strength, such that the risk of not complying with the strength specification is minimized.Cylindrical specimensfor acceptance testing should be 6 x 12 inch (150 x 300 mm) size or 4 x 8 inch (100 x 200 mm) when specified. The Concrete strength is calculated by dividing the maximum load at failure by the average cross sectional area.Concrete compressive strength requirements can vary from 2500 psi (17 MPa) for residential concrete to 4000 psi (28 MPa) and higher in commercial structures. Higher strengths up to and exceeding 10,000 psi (70 MPa) are specified for certain applications.Cylinders are placed in a Compression testing machine and loaded to failure from 20 to 50psi. The type of break should be recorded by a Certified Technician.Example 1:For a concrete sample that is broken after 28 daysThe cylinder is 6” diameter, so it has an area of 3.14 x Diameter squared /4A = 3.14 x 6 x 6/4A = 28.26 square inchesIf the force required to break the cylinder was 97,500 poundsThen the compressive strength is 97,500 pounds / 28.26 square inches = 3,450 psi.3,450psi needs to be compared to the Design strength determined by the Design Strength determined by the Design Engineer.Example 2:Given: f 'c = 3000 psiConcrete test cylinders averaged 2800 psi.PSICore 1 =2900Core 2 =2850Core 3 =2450Average compressive strength of 3 cores = 2730 psi.Find: Is the concrete in the structure adequate under CDOT specifications?Solution:Test Evaluation:f 'c = 3000 psiAverage compressive strength of 3 cores - 2730 psiDo any compressive strengths differ from the average by more than 10%?10% of Average compressive strength = 273 psiCore 1: 2900 - 2730 = 170 psi, < 273 therefore OKCore 2: 2850 - 2730 = 120 psi, < 273 therefore OKCore 3: 2730 - 2450 = 280 psi, > 273 therefore -discard core and re-compute average compressive strength using two remaining cores.New average compressive strength = 2875 psi
Which is weaker shear strength or tensile strength or compressive strength?
That all depends on the material For most all metals, tensile strength is stronger by about factor of 1.7 For most metals tensile strength is equal to compression strength For concrete, both comppression strength and shear strength are higher than tensile strength For many composites, tensile strenght is higherthan compression strength
What is the compressive strength of cement mortar?
Compressive strength measures the largest compression force the material can withstand before it loses its shape or fails.
How silica fume helps in increasing properties of concrete?
Silica Fume(Microsilica),They used in concrete. It can improve concrete's properties such as compressive strength, bond strength, and abrasion resistance; reduces permeability; and therefore helps in protecting reinforcing steel from corrosion. At the same time, ,silica fume can still be used in the production of refractory and porcelain; to raise intensity and durability, it also can be used in paint, coating, resin, rubber and other high molecular as a filler material to improve the material overall performance.
Is aggregate the same thing as concrete?
Aggregate is the gravel or stone in the concrete. It is what gives concrete it's strength. Think of the aggregate as the bricks of a wall and the concrete and sand as the mortar.
What is the fck of concrete?
Concrete The concrete used in structures is characterized by its resistance, the fck. This resistance is measured through the breaking of specimens, and it means to say that a case has a certain fck, the probability of obtaining a lower resistance than that indicated only 5%. It is good to note that the fck, which is the concrete strength is measured by a unit of voltage, ie, a load (force) per unit area. This measure can be given in MPa or kg/cm2. We can say, for example, that a case has fck = 18 MPa. This means that the resistance (fck) of concrete is equal to 18MPa or 180 kgf/cm2. For specification of concrete for the slab lattice, one must distinguish the concrete used in the manufacture of concrete beams cast in situ to form the ribs of the slab. The second has an important structural function, as it forms the table compression of the slab, while the first does not always have. The concrete to be released on the spot will be provided by the manufacturer, but its strength should be reported to the engineer responsible for the design of the slab, allowing it to conduct the calculations correctly. The concrete for casting the beams does not, in most cases, the same structural importance doconcreto to be cast on the spot, except in some cases, such as the continuous slab or sheet, when we squeeze the lower fiber the slab, where the concrete s.apata. Where no such structural importance, the concrete beams do not need a high compressive strength, but should not miss the purpose of protection of armor that are within the s.apata. Therefore, attention should be paid to asua compactness and avoid the use of beams with poor concreting (maggots). The concrete that makes up the slabs and concrete lattice supplement must meet the specifications of NBR-12655 and NBR 6118 and NBR 8953 and respecting the provisions of NBR 12,654. The compressive strength will be specified by the structural design, and required a minimum Class C20 to C20 beams and Class of acordocom NBR 6118 for concrete cast on site. In the case of concurrent execution of specific complementary edo concrete structure, the prevailing higher value of resistance characteristic (fck) specified in the project. The concrete Class C20 corresponds to the characteristic compressive strength at 28 days of 20 MPa. Beams boom and the combination of the lattice frame, the additional hardware and s.apata concrete. It is the end product quedeverá be delivered by the manufacturer to the customer, along with the filler material and a project demontagem.Deve be designed to carry structural strain after the concreting of the slab, but must also have the stiffness needed to withstand the transport and assembly.
Why the size of concrete cubes are 150mm?
Basically, the force supplied by a concrete compression machine is a definite value. For normal concrete strength application, say below 50MPa, the stress produced by a 150mmx150mmx150mm cube is sufficient for the machine to crush the concrete sample. However, if the designed concrete strength is 100MPa, under the same force (about 2,000kN) supplied by the machine, the stress under a 150mmx150mmx150mm cube is not sufficient to crush the concrete cube. Therefore, 100mmx100mmx100mm concrete cubes are used instead to increase the applied stress to crush the concrete cubes. For normal concrete strength, the cube size of 150mmx150mmx150mm is already sufficient for the crushing strength of the machine.
Is volume stress and compressive stress same?
yes
