The principle of the test is to measure the secant modulus of the sample by applying a controlled axial compression force to a prism with ratio of 4: 1 and the ratio of the longitudinal compression deformation to the compression stress. The standard specifies two procedures: in the case of a product containing cement binders you need to use the method 2. The equipment used for this test, consists of two instruments:

  • deformation measuring instruments, gages having measuring length of 50 mm and a maximum sensitivity of 50 microns/m capable of providing continuous indications about variation along the measuring section;
  • automatic hydraulic press with a capacity of 300 kN and 20 kN used to determine the compressive strength.

For each test three samples with dimensions 40 mm x 40 mm x 160 mm are required. The test begins after the samples have been cured for 28 days under standard conditions (20°C, RH 95%). The secant modulus is determined by the variation of deformation in the sample when it is loaded so as to produce a stress between 0.5 N/mm 2 (σ2) and 1/3 of the compressive strength (σc) of the sample.

Pre-loading: place the sample, with the deformation measuring instruments axially connected and positioned centrally in the machine. Apply a base stress of 0.5 N/mm2 (σ2) and record the deformation. Increase uniformly the stress at a constant speed within the range (0.6 ± 0.4) N/mm2/s up to the attainment stress of 1/3 of the sample compressive strength (σc) (σ1 = σc / 3). The preferred speed for the application of the stress is 0.6 N/mm2/s. Maintain stress for 60 s and record the strain readings that occur during the next 30 s. If the individual deformation readings are not within a range of ± 10% of their mean value (σ1), center the sample and repeat the preload cycle. Where it is not possible to reduce the differences in a range of ± 10% of their mean value σ1, not to proceed with the load test. Carry out further preload cycles, using the same rate of loading and unloading, keeping the stresses (σ1 and σ2) at a constant speed for a period of 60 s.

Load test: after completing the last cycle and preload for a time of 60 seconds under stress (σ2), measure the variation of the compressive deformation (Δε) as the stress increases from σ1 to σ2, calculating ( Δσ) as the difference between the two levels of stress applied. Measurements of (σ1) and (Δε) should be completed within 30 s. Once all measurements have been completed, remove the deformation measuring instruments, if possible, increase the load at the specified speed until the break occurs in the sample and calculate the stress at break (σf). If the compressive strength of the break sample (σf) differs from (σc) more than 20%, this must be noted in the test report. Calculate the secant modulus for each sample as the ratio of (Δσ) and (Δε). Calculate the mean secant modulus of the three samples, expressing the mean value to the nearest 100 N / mm2. This test procedure is used to test repair mortars.

 

Material type Standard Test method
screeds EN 13813
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self-levelings EN 13813
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restoring EN 1504-3 EN 13412
surface protection mortars EN 1504-2
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Instruments used to perform the test: strainmeters length 50 mm and sensitivity 50 μm/m, Press for cements

 

The test consists to measure the secant modulus of the sample by applying an axial compressive force controlled to a prism and relating the longitudinal compressive deformation to the compressive stress.The purpose of the test consists to measure the secant modulus of the sample by applying an axial compressive force controlled to a prism and relating the longitudinal compressive deformation to the compressive stress.