Laboratoare beton engleză

Laboratory no.1

Compressive Strength of Concrete

Purpose

The aim of this paper is to analyze the way the concrete acts under compressive stresses. Different samples will be used and we will experimentally determine the values of the compressive strength.

Theoretical specifications

Concrete’s class is defined based on the characteristic resistance which is the resistance at compression in N/mm² determined on cylinders of 150/300 mm.

The samples are kept until they are ready for the experiment can be done:

- in a room having the temperature 20±4ºC and humidity of 65±5% ;

- near the structural element, in an identical conditions of humidity and temperature;

Strength in compression can be computed with the fallowing relations:

= [N/mm²]

In order to evaluate the strength in compression there are two conformity criteria:

1. applicable for 6 or more samples

- the strength in compression must fulfill the following conditions:

( 2.2)

where:

-the medium value of the resultant strengths

-minimum value of resultant strengths

-standard offset,

-characteristic strength in compression of 20-days old concrete determined on cylindrical or cubical samples

, -constants depending on sample’s number and the required insurance degree

n- number of samples

2. applicable for 3 samples

- the strength in compression must fulfill the following conditions:

(2.3)

where:

-is considered the medium value of the results

Cubical strength

Can be determined on cubes with l=200mm.

The compressive strength will be experimentally determined and the breaking pattern will be analyzed for cubes with friction between plates of the hydraulic press and the sample’s surface and without friction.

Prism’s strength

Samples are of 100x100x550mm, they must be perfectly centered and the friction must be taken into consideration. The compressive strength is determined with the relation:

(2.7)

The strength is inferior to the cubical samples’ and breaking pattern of prismatic samples clearly shows the transversal tension stress and of a crucial importance in the appearance of micro cracks in the vicinity of structural flaws. The strength of the sample is directly linked to the ration between b and h and to the quality of the concrete.

1.

Ab=200 x 200 mm

45º-60º

2.

3.

4.

100 x 100 x 550 mm