Martin Marietta Materials' (MLM) planned $13.5 billion acquisition of Lhoist North America should be seen by investors as the "addition of unique, high quality assets," UBS Securities said in a note emailed Wednesday.

UBS attributed some weakness in Martin Marietta Materials' share price after the proposed acquisition was announced to the "surprise factor of a large non-aggregates deal that leaves [Martin Marietta Materials] with financial leverage of more than 3x."

However, the deal likely "both diversifies end markets/reduces cyclicality, and generates steady cash flow that can be used to delever and fund aggregates deals," the investment firm said.

Some investors see the multiple as high, but the "potential for upside to synergies could reduce the multiple if they execute well," the note said.

Meanwhile, the main risks are "market concentration, execution, and fit/strategic goals of the family that owned Lhoist and will now own 15%" of Martin Marietta Materials, the investment firm said.

UBS reiterated Martin Marietta Materials' buy rating and has kept its $739 price target on the stock.

Price: 571.11, Change: -5.59, Percent Change: -0.97