There is another way around it which is probably easier. The EC has to have a meeting and make a decision to proceed with the work. To have an EC meeting they are obliged to give notice of the meeting to all owners and include the proposal in the agenda.
Schedule 3 of the Strata Schemes Management Act (refer below, para 2) provides that if owners holding 1/3 of the aggregate unit entitlements give notice in writing to the secretary of the EC that they object to the making of a specific decision then that decision has no force or effect.
Assuming that you have at least 1/3 of the aggregate unit entitlements then you can serve notice to that effect. Note that if they don’t give proper notice of the meeting with an agenda etc., then you could probably challenge the decision on those grounds anyway.
If you are concerned in relation to the admin fund and financial management generally you may want to consider putting up a motion at your next AGM limiting the decisions that the EC can make, i.e. to a certain amount of money.
11 Decisions of executive committee
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(2) A decision of an executive committee has no force or effect if, before that decision is made, notice in writing is given to the secretary of the executive committee by one or more owners, the sum of whose unit entitlements exceeds one-third of the aggregate unit entitlement, that the making of the decision is opposed by those owners.