The closure of steelmaker Arrium would cause Australia's construction industry to collapse within six weeks, its administrator says.

"The impact would be felt far and wide. Arrium long-form structural steel makes up 70 per cent of Australian steel making in infrastructure and construction," KordaMentha's Mark Mentha said on Tuesday.

Arrium is among the industry group clubbing together to buy power.

"When you're talking about billion-dollar projects, delivery for steel would be 18 months or more in advance. The impact of not having steel - you'd have to find alternatives in the global market place."

But peak industry body Master Builders South Australia said Mr Mentha's claim was overblown as the industry had access to other domestic steel providers including BlueScope.