We expect the momentum we generated in the first half of the year to carry through the second half, and we reiterate our full year 2021 adjusted EBITDA guidance range of $1.38 billion to $1.46 billion.
For the first half of the year, our adjusted EBITDA increased by 7% and our aggregates cash gross profit per ton expanded by 5% through a combination of volume growth, higher pricing and improved operating efficiencies.
Adjusted EBITDA for the second quarter was $406 million, essentially unchanged versus the same quarter last year.
We achieved this result despite a $25 million headwind from much higher diesel and liquid asphalt costs.
Diesel costs rose by $15 million in the quarter.
Liquid asphalt costs were $10 million higher than the same period last year.
Even after considering the energy headwind, our aggregates cash gross profit per ton grew by 2% in the quarter due to our team's consistent execution of our four strategic disciplines.
With a 4% increase in aggregates volume in the second quarter and the market's current visibility to demand, the pricing environment continues to improve.
Freight-adjusted aggregates pricing increased 3% in the quarter, and the rate of growth improved sequentially throughout the quarter.
Adjusted for mix, freight-adjusted price improved 2.6%, twice the growth rate realized in the first quarter.
Our total cash cost of sales increased by 4% in the quarter versus the prior year.
Excluding the diesel headwinds, cash cost of sales grew by less than 1%.
For the trailing 12 months, cash gross profit per ton was $7.26, and for the quarter, it was $7.83 per ton, moving ever closer to our current goal of $9 per ton.
And on a trailing 12-month basis, return on invested capital was 14.8%, an increase of 60 basis points compared to the prior year period.
This improvement was comprised of an essentially unchanged invested capital base and a 4% increase in trailing 12-month adjusted EBITDA.
At June 30, our net debt-to-EBITDA was 1.3 times, reflecting $968 million of cash on hand.
Our debt has a weighted average maturity of 15 years with no significant maturities in the near term.
Subsequently, we executed a $1.6 billion delayed draw term loan which will be used to fund the acquisition along with cash on hand.
As a result, financing cost of $9 million for the bridge commitment was recognized as expense in the second quarter.
And as a reminder, at the end of first quarter, we increased our expectation of the full year rate to between 23% and 24%.

Summary:
We expect the momentum we generated in the first half of the year to carry through the second half, and we reiterate our full year 2021 adjusted EBITDA guidance range of $1.38 billion to $1.46 billion.