Geoff, if you are gonna use a hammer icon for production and Mystiqq, you are gonna use a wrench icon for construction, well it could get confusing. If two of the icons are tools, you think "now I know nothing about tools, and I could be damned if I remember whether this tool represents construction or production".
I think we'll have confusion no matter what, given the names of the categories... But I'm not really using a "hammer icon", and I'm not really using the icon in question to represent "production". The icon itself is a tiiiiiiny little thing with, of which a few pixels are in a roughly hammerlike shape, in addition to a step-ladder shape that I intended to be an incomplete building. And the icon is representing incomplete buildings, not a tech category... Whether incomplete buildings are "construction" or "production" or "buildings in progress" or some combination thereof is debatable... but there's not likely to be any confusion with my icon with the icons for tech categories, which are presented rather differently. So really I suppose I've just shot down my own theory of how to make things similar... oh well.
Mistiqq, you might want to consider making the tech icons resemble the resource icons as seen at the top of the screen in any screenshots. Food is wheat, industry (= production) is a gear, mining is a blocky mineral shape, and science is a test tube.