Presumably no one involved with the exception of at least someone associated with the Strata Mgr’s. has any understanding of Strata law so you may be able to buy time i.e. if the EGM doesn’t get a quorum or more likely they fail to make the item a Special Resolution thus rendering any vote invalid. Your view of whether replacing a grassed area with concrete (probably soon to have oil stains) enhances the block is worth whatever your unit entitlements add up to but legally those approving of concrete require 75% agreement of those who attend (including proxies) a properly convened meeting.
It would appear from what you have stated that there are grounds for the Owners Corp. to explore litigation against whoever authorized the destruction of common property thus far which presumably also included mis-appropriation of money i.e. legal appropriation=approval by special resolution anything else=mis-appropriation.
You might also politely ask the Strata Mgr. whether anything in the contract states or implies that they provide advice as to the legality of any action prior to it’s commencement. Or maybe you can leverage some of all this to get the OC to pay for screening.