This project won First Place out of 36 entries at the Dutch FORM-WORKS edition of the 2020 Concrete Design Competition with the posters below.
The jury made the following comment :
"The winner was unanimously chosen by the jury for the brilliant way of applying interlocking modules to create a sound barrier. The jury appreciated the fact that the students had researched shapes that influence sound and thus shaped their module. The mold was very complicated and tested by the students. Although, from the perspective of experts, there were some difficulties in being able to manufacture an all-sided shuttered element in industrial production. According to the jury, the theme of FORM-WORKS was well fulfilled in this project: both in the choice of the shape of the module itself, the aesthetic whole of the wall and the technical elaboration of the mould." Translated from Dutch from here.
A thorough design and testing process led us to develop a proposal for an industrial scale concrete sound-barrier. The design seeks to maximise the potential of sound absorption and reflection, as well as gapless-modularity. The result it an engaging urban feature.
Early on, we reflected on how to harness the versatility of concrete by altering its density, colour, shape and finish. By amending the basic concrete recipe, such as reducing in sand, increasing aggregate size, introduction of air and not vibrating the mix, concrete's density decreases, improving its acoustic performance. Additionally, the surface of the cast concrete influences its acoustic performance: porous and rough surfaces enable sound absorption while smooth and dense surfaces enable sound reflection.
The wall is composed of a single leaf of stacked, interlocking modules, held in place by their own mass. Each module is composed of two casted elements of identical geometry, but of different external finishes and concrete mixes. Splitting the module into two casted elements simplifies mould making and casting processes, while enabling us to offset the joins thus reducing acoustic gaps in the wall. It also offers more opportunities regarding finishes on each side of the module. This nesting of different casted elements does however require a high level of precision.
The face of the wall closest to the noise source is composed of a porous concrete with a textured surface which absorbs the sound waves. The outer leaf of the wall is composed of a denser concrete mix that reflects the sound that wasn’t absorbed and prevents it from travelling through. The face furthest to the source does not have an acoustic purpose, and its design is solely aesthetic, with a pigment and smooth finish.
The testing process required 8 moulds of two types that were filled with various hand-mixed concrete whose density ranged, providing a range of acoustically absorptive or reflective casts. The casts were left to cure for 48 hours and were de-moulded. We succeeded in creating a concrete with a range of densities, and we are satisfied with their appearance. However, we wished to explore a design solution whereby the sounds absorbing geometry was more prominent and designed into the modular system.
The new design ambition led us to research anechoic chambers whose wedge breaks up sound waves, causing sound waves to bounce back and forth in the gap between the wedge above or below. A detailed study of anechoic geometries enabled us to identify the geometric variables of the anechoic designs.
We selected key design features from the previous DIY design such as the varying concrete mix densities, dry-stack interlocking system and modular approach. The module's base geometry, shown below, can be altered to accommodate for various site conditions and aesthetic requirements. The tongue-in-groove detail provides a gapless, sound-proof solution.
In this design iteration, the assembly of the wall is improved as the casted elements only need to be stacked vertically, rather than being assembled laterally and then vertically. The symmetry visible in both plan and section is vital to the structural equilibrium of the system. The result is an engaging wall with a significant variety, who's form contributes to acoustic performance.
The final design iteration features a ribbed foundation gutter which supports different base block positions enabling for the wall profile to undulate in the X and Y axes. Sufficient undulations can brace the wall as a whole.
Making scale models provided the opportunity to test the geometry and dry-assembly stacking.
The form-work we suggest is in steel to optimise its lifespan. The form-work is composed of modular sections enabling each part of the mould (wedges or undulating core) to be mixed and matched. The pour direction and mould orientation minimises the distance air needs to travel to escape out of the mould through the auxiliary holes.
Final design proposal
Acute acoustics is an industrial scale modular concrete sound-barrier. The gap-less interlocking system with offset module rows prevents noise from travelling through and the dense concrete reflects noise. The negative effects observed when noise is reflected are counteracted by the wall geometry which, by mimicking anechoic chambers, breaks up sound waves. The wall is self-supporting and braced thanks to its undulated plan. It achieves this with a dry assembly method and no reinforcement, which enables it to be taken apart and assembled elsewhere. The modular nature of the wall enables it to adapt to a variety of site conditions and its appearance can be tailored by combining concrete colour and finish texture, and module size. This kit-of-parts approach provides an engaging urban canvas on both sides, on which text and graphics can be drawn.
'Unbridled experiments with concrete at student competition' : article published on the 8th December 2020 in the Cobouw, a major daily paper for the building industry .