Hi manhhiep2509,
Now that you've provided the entire quote, I can tell you what this grammar rule is modeled on.
Normally, a comparison uses the word "than" and follows parallelism rules:
eg. This team score more points than that team.
The example that you provided is an alternative, but is more in line with the phrase "as....as." Here we're told that 3 things (cost of concrete/steel, time to fabricate, distance of project site to production site) are essentially of equal importance. This idea can be communicated in a number of ways. The one that's written here is sophisticated, but grammatically correct.
Another way to write it would be: "The time needed to fabricate the elements and the distance of the project from the production site are each as important as the relative costs of concrete and steel....."
Ultimately, there's nothing grammatically incorrect about the given sentence. It's a rarer style than typical, mid-level GMAT prompts, but it is "fair game" on the GMAT. Since the Test will adapt to you, if you're doing well, then you can expect to see more higher-level content (including style/wording of the prompt, the logic behind a question, types of questions, grammar tested, etc.).
GMAT assassins aren't born, they're made,
Rich
