Thanks guidance mechanical etc. - preoccupied lime mortar'ing

I at least somewhat see now how in Roman "hydraulic mortars" - mortars which have a self-setting reaction "within themselves" after hydration, not solely relying on drying and/or reaction with carbon-dioxide in the atmosphere (as lime tries to revert to limestone) - are "clever". Roman mortar on quays / harbours in seawater have lasted 2 millennia and remain sound. It was thought unreacted quicklime was "careless" hot-mixing. I can now at least kind-of see what has recently been realised - that feature is deliberate. It gives a self-healing mechanism, by having a reservoir of quicklime to chemically react and self-heal if there is structural settlement etc.

----------------------------------- The Romans were fortunate to have this volcanic ash nearby:

In Germany I saw concrete from the rushed construction of the 1930's and

So the answer to the long lasting Roman concrete is its self healing?

So the answer to the long lasting Roman concrete is its self healing? Bob La Londe

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Elsewhere I've read that we still aren't certain, we have the final product but are unsure of the raw materials or mixing process. For instance the properties of modern concrete vary with the amount of water in the mix.

Vitruvius described What the Romans accomplished but rarely How, it reads like boring ad copy. The Hows passed by example from master to illiterate young apprentice, and were valuable trade secrets. The oldest how-to books that I have copies of are less than a thousand years old. Besides Roman concrete some remaining uncertainties are Hindu Wootz sword steel, Egyptian granite obelisk carving, exquisite Etruscan gold jewelry and Roman catapult torsion windings, though I may have solved the last.

That's what I heard, and what I was getting at. I wondered if you were aware of some newer information on the subject.

"self-repairing" - seems yes. For natural stone buildings, there are several reasons cited for using lime-mortar, of which "self-repairing" is but one, albeit crucial.

Zooming to a big context - stone buildings have been reliable for centuries into millenia... Then we have the "panacea" of Portland cement mortar - and in a very few decades we are seeing a rash of problems. Mysterious absent before. Okay there wasn't Portland cement mortar before the second industrial revolution - essentially the 1880's and strongly into the 1890's (?) - but the overall view is builders of old knew what they were doing; funnily enough, now we care to look back and consider the matter.

Some key characteristics of a mortar for natural stone, as I have gathered:

• must not be harder / stronger than the stone it is joining - else the stones will crack with {thermal cycling, fluctuating moisture levels, settlement of the building, etc.} (all dimensional changes)
• must do the right thing with moisture - not let too much in, and let what shouldn't be there out
• must self-heal with settlement and flexure of the building - given a stone building is flexible and historic foundations despite being sound not being the stiff almost immutable hard raft of modern poured concrete foundations (the "modern" building is almost floating free of the dynamics of the ground it is on (?)).

What I am seeing is that a natural stone building with Portland cement mortar pointing will develop a number of long cracks rising or zig-zagging across extents of wall. Contributing to moisture / water problems with the building. It is my impression (I am at at early stage of learning) that a natural stone building on a natural good but somewhat dynamic foundation will have distributed flexure and the lime-mortar will self-heal, not showing "failure of the pointing".

I am at such an early stage of learning. There is not basis by which I can express strong opinions.

Regards, Rich Smith

old knew what they were doing; funnily enough, now we care to look back and consider the matter.

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My own perception:

there is a "Darwinian selection" in engineering; in that you cannot fully anticipate the intersection and interaction of all variables. So you must accept that something like maybe 10% of ambitious structures will need early replacement - and there is no way of getting around that, given a world of conservatisim will make your economy and society uncompetitive.