KS_Emod_opt

Besides the mass per unit area, the material stiffness determines the sound insulation of masonry. In the current DIN 4109 - "Sound insulation in building construction" the sound insulation is calculated on the basis of the mass per unit area. The aim of this research project is to increase the sound insulation of sand-lime masonry by increasing the stiffness of the bricks, while maintaining the same mass per unit area. The stiffness increase is achieved through targeted and cost-effective optimisation of the manufacturing parameters.

Can the modulus of elasticity of the sand-lime brick be increased, for instance by the selection of appropriate raw material, a reduction of the cavity volume, an increase of packing density and/or compaction?

The project is divided into a total of five work steps:

In investigation section A, measurement data of the acoustically relevant parameters (dynamic modulus of elasticity, longitudinal wave velocity cL, dissipation factor η and bulk density ρ) of sand-lime bricks are collected and a correlation with the production parameters is determined.

Subsequently, in investigation section B, bricks are produced in small series with traditional and theoretically optimised formulae and examined in the laboratory with regard to packing density, chemico-mineralogically characterised and the acoustically relevant parameters determined.

In investigation section C, production trials of the optimised bricks are carried out in two sand-lime brick plants. The sand-lime brick samples are also examined acoustically and in terms of building materials.

For investigation section D, walls are installed in the wall test rig of the HFT and measurements of sound insulation and other acoustic investigations are carried out.

Finally, a practical engineering model for the prediction of the sound insulation from the raw material parameters will be developed in investigation section E.

In this research project, the sound insulation of masonry walls was to be improved by increasing the E-modulus of sand-lime bricks, yet without increasing the mass per area. From a production standpoint this meant investigating the correlation between production parameters and E-modulus for a large number of sand-lime brick samples. In the process, samples with a considerably higher E-modulus were able to be produced without changing the mass per area. Upon these results, a sufficient number of test bricks were produced in various sand-lime brick factories to support the measurement of the sound insulation of eight masonry walls with different E-modulus in the HFT laboratory. On the one hand, this showed that some of the bricks produced in large scale at the sand-lime brick factories did not achieve the same desired stiffnesses (or E-modulus) as the samples bricks, and on the other hand that the stiffness of the total wall is significantly reduced due to the un-mortared butt joints. Even though the anticipated improvements in sound insulation were not quite achieved with the examined walls, some important insights into the sound insulation of sand-lime bricks could be gained:

- the stiffness in horizontal and vertical direction in sand-lime brick masonry wall are different due to the mortaring and thus two coincidence frequencies exist, leading to an overall wider yet flatter insulation dip in the sound insulation curve

- the measurements in the wall test stand showed a very high reproducibility

- the moisture content of the brick has little influence on the E-modulus and thus on the sound insulation