Overall, the economy will expand, and productivity per worker will increase.
However, according to some economic models, such as the Solow model, economic expansion will not continue indefinitely through capital deepening alone.
This is partly due to diminishing returns and wear & tear (depreciation).
Investment is also required to increase the amount of capital available to each worker in the system and thus increase the ratio of capital to labour.
The economy will expand in terms of aggregate output, but productivity per worker will remain constant.