concrete strength? ,compressive strength of concrete cube, increase the strength of the concrete

Concrete strength

 water, aggregates and cement and  some times admixtures is one of the ingredient of concrete. mixing all materials in right proportions produces concrete. Accordingly only cement  is not a building material, it is the concrete which is a  good building material. find a good concrete strength these point is consider.

a) Ratio of cement to mixing water
b) Ratio of cement, aggregates and sand properly.
c) shape, strength, and  grading, surface texture ,stiffness of aggregate particles.
d) Maximum size of aggregate use.

 concrete Strength is directly respective to the structure of the hydrated cement paste. Air in concrete produces voids so use vibrator always. Excess of water in concrete evaporate leave the voids in the concrete so always consider water cement ratio. 

hence, as the water cement ratio increases, the porosity of the cement paste in the concrete also increases. As the porosity increases, the compressive strength of the concrete always decreases.

compressive strength of concrete

 compressive strength of the concrete cube test provides  the characteristics strength of concrete.  Concrete compressive strength for nornal construction  work vary from 15 MPa (2200 psi) to 30 MPa (4400 psi) and higher in  industrial structures.and commerical.

compressive testing machine 
(standerd test)

The compression testing machine(ctm) is used to determine the compressive strength of cube and cylinder in concrete.

Compressive Strength Formula

Compressive Strength = Load / Cross-sectional Area

test method of compressive strength

Calculations of Compressive Strength of concrete

Size of the concrete cube =15x15x15cm

Area of the specimen =225 cm2

Characteristic compressive strength of concrete (f ck)at 7 days =

Expected maximum load =fck x area x factor of safety 

Range to be selected is …………………..

Similar calculation done in 28 day compressive strength

Maximum load applied =……….tones = ………….N

Compressive strength of concrete = (Load in N/ Area in mm2)=……………N/mm2

=……………………….N/mm2

Reports of Cube Test

1. Identification mark
2. Date of test
3. Age of specimen
4. Curing conditions, including date of manufacture all mentioned 

Curing of Cubes

The test specimens are stored in moist air for 24 hours and after this period the specimens are marked and removed from the molds and kept submerged in clear freshwater until taken out prior to the test.

Test result-compressive  test result given below.

Compressive Strength of Concrete table

(average strength of concrete mix)

Age	Strength percent
1 day	16%
3 days	40%
7 days	65%
14 days	90%
28 days	99%

Compressive Strength of Different Grades in Concrete cube table at 7 and 28 Days. 

 strength of concrete after 7 days and strength of concrete after 28 days

Grade of Concrete	Minimum compressive strength of concrete N/mm2 at 7 days	Specified characteristic compressive strength of concrete (N/mm2) at 28 days
M15	10	15
M20	13.5	20
M25	17	25
M30	20	30
M35	23.5	35
M40	27	40
M45	30	45

 quality control

  quality control for concrete cube

Table-1: tolerance,dimension ,materials list of 150 mm cube mould. 

S.No.	Description	Requirements
1	Distance between opposite faces, mm	150 ± 0.2
2	Height of mould, mm	150 ± 0.2
3	Thickness of wall plate, mm	8
4	Angle between adjacent interior faces and between interior faces and top and bottom plates of mould.	90 ± 0.50
5	Length of base plate, mm	280
6	Width of base plate, mm	215
7	Thickness of base plate, mm	8
8	Permissible variation in the planeness of interior faces: for new moulds, mm for moulds in use, mm	0.03 0.05
9	Permissible variation in the planeness of base plate, mm	0.03
10	materials a) Side plate b) Base plate	Cast iron Cast iron

increase the strength of the concrete mixture

The strength of concrete can be increased, keeping in mind this factor on which the strength of concrete depend.

Strength of concrete depends upon the these factors:

 1. Mixing time– Strength of concrete increases with increase in mixing time up to 2 minutes above which no significant increase in the strength is observed. .

2.Type and age of cement– The variant of strength of concrete with type of cement is shown below –

With age, the strength of cement decreases due to more moisture soaking from the atmosphere.

The quality of cement also depends upon the storage conditions of the cement and here upon the strength of concrete is also dependent on the storage conditions of the cement as shown-

 3.Type and size of the aggregate– Degree of packing is the main factor to be considered here. Greater the degree of packing, lesser is the void content and more is the strength it is good for concrete.

circular or rounded aggregates provide much more degree of compaction than the irregular shaped ones. This is the reason as to why they provide more strength.

There is a common disbelief that greater the maximum size of the aggregate, smaller will be it’s surface area, lower will be the w/c ratio and consequently greater will be the strength. But this is not so, the smaller surface area will lead to smaller surface area for gel bonds, which results in less strength.

4.Curing– Effect of curing can be understood with the following figure-

Curing is compulsory for optimum strength gain and durability. It is necessary for maintaining the required moisture content as well as the temperature conditions.

5.Water-cement ratio – With increase in water-cement ratio, the strength of concrete decreases, .so curing and testing is always important

so these are some important point depends  concrete strength, compressive strength.

Qus-si unit of concrete strength?
the si unit of concrete is mega pascal.

Qus- compressive strength  of concrete cube after 7 days and 14 days?

Compressive strength of concrete cube achieved by concrete at 7 days is about 64 to 65%% and at 14 days is about 90 to 91%% of the target strength.