President Donald Trump's proposed border wall along the United States-Mexico border may become an even larger project than previously expected, and if the wall is built, some materials companies could stand to benefit.

The Trump administration is reportedly asking Congress for nearly $18 billion to fund the border wall expansion. The request also calls for the construction of more than 700 miles of new and replacement barriers along the border, according to the Wall Street Journal, citing a document prepared by the Department of Homeland Security.

If granted, the request would bring the total miles of the barrier to nearly 1,000, significantly surpassing the 654 miles of barrier now. Overall, the administration is seeking "about $33 billion in desired new border-security spending, including funding for technology, personnel, and roads," the Journal reported.

President Trump made a campaign promise to build a "big, beautiful" wall to help prevent illegal immigration. He also promised that Mexico would pay for it -- Mexico has repeatedly refused to fund it. The president is now attempting to tie border wall funding to a deal to fix DACA, or Deferred Action for Childhood Arrivals program, which shields adults who were brought to the country illegally as children from deportation.

Still, the administration moved forward in April, selecting four companies to build concrete prototypes. Trump has said that the wall would be made of hardened concrete, rebar, and steel.

While most of the prototype builders, Caddell Construction, Fisher Sand & Gravel/DBA Fisher Industries and W.G. Yates & Sons Construction, are private companies, investors could eye Texas Sterling Construction Co., a prototype builder that is a subsidiary of Sterling Construction Co. Inc. (STRL) - Get Sterling Construction Company, Inc. Report

Investors could also look toward some of the public companies that could provide the materials, such as Martin Marietta Materials Inc. (MLM) - Get Martin Marietta Materials, Inc. (MLM) Report , Vulcan Materials Co. (VMC) - Get Vulcan Materials Company Report or Eagle Materials Inc. (EXP) - Get Eagle Materials Inc. Report . U.S. Concrete Inc. (USCR) - Get U.S. Concrete, Inc. Report could also be in the mix given that CEO William Sandbrook told TheStreet in November 2016 that the company is well positioned to bid on any border wall opportunities.

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Meanwhile, U.S. Steel Corp. X, Nucor Corp. (NUE) - Get Nucor Corporation Report and Steel Dynamics Inc. (STLD) - Get Steel Dynamics, Inc. Report could provide steel for the wall.

But a dark horse could enter the mix if Trump can re-open negotiations with Mexico-- and that's a big if. Mexican cement producer Cemex (CX) - Get Cemex SAB de CV Sponsored ADR Report could be the supplier of choice for concrete.

"Cemex is the perfect example of the kind of company that gets hurt if Trump wins the White House, except for one thing -- the wall," Cramer said on CNBC on Nov.7, 2016, a day before the election. "If Trump actually builds the border wall, and gets Mexico to pay for it, who do you think they will use to supply all that concrete -- Cemex."

To be sure, Congressional support is tepid. According to a September 2017 USA Today survey, less than 25% of Republicans in Congress endorse border wall funding.

-- This story has been updated to reflect that Texas Sterling Construction Co. is a subsidiary of Sterling Construction Co. Inc. 

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