ATLANTIC CITY - A city building inspector was at the Tropicana Casino Resort's parking-garage construction site just 40 minutes before the five top floors collapsed on the morning of Oct. 30, killing four workers, city records show.
From his spot on the eighth floor, where workers were about to pour another load of concrete, Anthony Cox, 38, found during his 90-minute routine inspection what he had found during most of his visits: nothing out of the ordinary.
But more than a year earlier, Atlantic City building inspectors had raised concerns with project contractors about batches of concrete that repeatedly failed in tests to reach desired strength within the standard 28 days.
In addition, city records show instances of the concrete's slump - another measure of its strength - being out of range.
Instead of changing the concrete mix, contractors and project engineers extended the test period to 90 days - an allowable practice, city officials said, but one that two independent civil engineers described yesterday as troubling.
As recently as one month before the collapse, some batches of concrete were still more than 500 pounds per square inch short of the desired strength even after 90 days, city records show.
The design specifications contained in city records released this week state that the concrete strength level cannot be considered satisfactory if one test batch falls more than 500 pounds per square inch below the design strength.
Geoff Hichborn, a California-based civil engineer and consultant in the installation of concrete, said he found the switch to a 90-day standard alarming.
"Virtually every engineer in every country uses a 28-day standard unless there's something extraordinary," he said in a telephone interview.
"If there is even one sample in a construction property that is more than 500 [pounds per square inch] less than the specified strength, it raises everybody's attention and everybody gets concerned the instant such a discrepancy is found."
In a statement, general contractor Keating Building Corp. of Philadelphia said the Tropicana garage project, part of a $245 million casino expansion, had been "done by the book. Every precaution was taken, and every required procedure was followed... . As with any project in Atlantic City, the pouring and curing of concrete at the garage was a very closely watched process with multiple test points and checks."
The federal Occupational Safety and Health Administration, whose mission is to safeguard worker safety, is investigating the collapse and is expected to issue its findings within six months.
Immediately after the collapse, construction workers at the site questioned whether enough time had been allowed for the concrete to dry and contended that supports used to hold up the concrete decks while they strengthened were being removed too quickly.
Some workers reported that in the days before the collapse, the pole supports were bending under the weight.
Some said there appeared to be too few of the poles, and a wrongful-death lawsuit filed by the widows of two of the workers alleges that Fabi Construction of Egg Harbor Township, the concrete subcontractor on the project, was shuttling the supports between the Tropicana and the Resorts Casino Hotel, where the company was doing work simultaneously.
The city does not keep records on the poles, including whether they were left in to accommodate the longer time the concrete was taking to strengthen.
But Steve Frame, who as the city's construction official oversees all building inspectors, said his staff had not noted any bent poles or any shortage of poles, sometimes called formwork.
"It was never brought to my attention or any of the inspectors' attention," he said in an interview. "If anything, it was the opposite. I was told the formwork was there for a long time."
It was Frame's department that raised concerns in the summer of 2002 about the time it was taking for the concrete to strengthen. On at least 37 occasions, batches of the concrete that were tested at seven- and 28-day intervals for their compressive strength came up more than 500 pounds per square inch short.
Once his staff raises such a concern, Frame said, it is up to the structural engineer - in this case, DeSimone Engineering Consultants of New York - to come up with a remedy. That remedy could be as drastic as ripping the concrete out, he said. In the Tropicana case, the testing period was lengthened.
"Our requirement is that [the remedy] meets the building code, and it does," Frame said.
He added that as a general rule, concrete is designed "exceedingly" stronger than what is required, so that it is safe even if not at full strength.
Of the switch to a 90-day standard, he said: "It's not the norm, but it certainly happens on other jobs."
But Hichborn said the high slump levels in the inspection reports were another indication that the concrete may have been too weak. He said engineers in California would have insisted on new concrete that met design strength within 28 days as well as lower slump levels.

Another civil engineer interviewed yesterday, Avi Mor of California, said that if the 90-day standard were used, the support system would have to be left in longer.
"If they don't leave them [the poles] in place, then they're really in trouble," he said.
Officials at Fabi Construction declined to comment yesterday. Mario Marra, an engineer with Site Blauvelt, which conducted the concrete strength testing, also declined to comment yesterday.
Stephen DeSimone, a partner at DeSimone Consulting Engineers, did not return a message left at his office.
City inspectors, for their part, said they had seen nothing alarming in the weeks before the collapse.
Frame said the job of the six building inspectors under him, all former construction workers, was to enforce the uniform construction code, not to enforce safety, per se.
But, he added, "certainly if an inspector sees something unsafe, he will report it... and it will make its way to the appropriate authority with that jurisdiction."
Frame said Cox, the building inspector at the Tropicana site the day of the collapse, was an "astute" and "seasoned" inspector who had worked with the city about seven years. Cox had visited the building almost daily in the weeks before Oct. 30 and noted no red flags.
Including on that fateful Thursday morning.
"If he had noticed something, he wouldn't have gone up there," Frame said. "He went up and conducted the inspection, and it passed."
Cox had two other concrete inspections scheduled for later that day on the eighth parking level to check steel reinforcements and other preparations for concrete pours. He couldn't go back. At 10:40 a.m., 40 minutes after he left, the top five decks of what was to become a 10-floor garage crumpled, taking dozens of workers down in a cascade of concrete and rebar.