Does economic growth always implies investments in infrastructure?
In economics, we commonly use the formula for GDP as a Indicator of "economic growth"

The GDP formula is: GDP=C+G+I+NX 

Where C is equal to all private consumption, or consumer spending, in a nation's economy, G is the sum of government spending, I is the sum of all the country's investment, including businesses capital expenditures and NX is the nation's total net exports, calculated as total exports minus total imports (NX = Exports - Imports).

Notice how we can have an increase in GDP by increased consumption or government spending. So technically we can see economic growth without any  investment in structure (which would be represented by an increase in I) from a mathematical perspective.

Note how this is a static measurement of economic activity, which we cannot make any predictions regarding the future. However you may want to look at the Solow-Swan Model regarding economic growth with capital accumulation and technological change.

Hope this helps.