Elaine Chao, U.S. secretary of transportation, speaks during the Milken Institute Global Conference in Beverly Hills, California.

Transportation Secretary Elaine Chao has held onto her shares of Vulcan Materials, a construction company she promised to divest from more than a year ago, The Wall Street Journal reported Tuesday.

Vulcan, the U.S.' largest supplier of sand and gravel used in paving and building, has seen its stock price rise more than 12% since April 2018, when Chao said she would cash out her shares, according to a 2017 government ethics agreement.

Chao's shares have risen in value by more than $40,000 since the month she said she would divest them, the Journal reported, citing corporate and government filings.

Chao did receive a payout on the shares, now valued at nearly $400,000, in April 2018, as deferred compensation for the time she spent on the company's board of directors before being confirmed to President Donald Trump's Cabinet, Vulcan told the newspaper.

"I will receive a cash payout for all of my vested deferred stock units in April of the year following the year of my separation from service," Chao said in her January 2017 ethics agreement.