Hi Pippin - I flicked through Bambachs thesis looking for clues for dampness and weight loss. He spent a huge amount of time testing and analysing various methods. He did use Portland with an Aluminium expanding agent. CSA will be much better then Portland. Probably not known much 20 years ago when he did his thesis. In the damping tests the concrete did much better than expected and he comments that this was probably because they didn't use any damping factor for it in their calculations. So concrete has considerable damping within itself, which is expected as it is not a homogenous material. I looked at the constrained layer stuff and he comments that the thinner the interleave the better, The commercial damping materials where around 1mm thick and he calculates that 0.15mm would be ideal. I have discussed this elsewhere I think but at this thickness laminated metal with epoxy resin fits his commentary perfectly. So you can layer up metals then mill or cut metals to shape leaving internal holes for light weighting then glue up and finish machine. I would use a glass tissue between layers to control bondline thickness. Typical tissue is 0.2mm thick... you could use paper tissue as well.
Aircraft use laminated metals to counter fatigue cracking in some applications and to get damp structures. natural and acoustic vibrations drive airframe fatigue so damp crack tolerant materials are used. . Airbus use tonnages of aluminium laminated metal in the airframes like the A380. look up a material called GLARE, https://www.compositesworld.com/arti...-the-spotlight and other fibre metal laminates FML's
It also gives the possibility of using steel outers with aluminium inners for light weighting taking advantage of steels stiffness on the outside like a sandwich structure.
A note on some concrete expanding agents. They use fine aluminium powder. Concrete and water being alkaline attack the aluminum resulting in outgassing of hydrogen countering the initial shrinkage. But H2 also attacks high strength steels used for reinforcing or inserts and can result in steel embrittlement. I'd like to use aluminium inserts in the CSA but again its alkaline so would get attacked by the concrete. So I will epoxy coat the aluminium if I do this.... Time to do some yard work.. Peter