WASHINGTON, Aug 22 (Reuters) - U.S. investigators trying to find out what caused a Minneapolis bridge collapse that killed 13 people are examining whether de-icing chemicals had corrosive properties, officials said on Tuesday.

The National Transportation Safety Board also said it had received records from the Interstate 35W bridge designer and will assess weight calculations to see whether a construction project played a role in the Aug. 1 collapse into the Mississippi River.

Safety board investigators have detected a possible design flaw that may have been exacerbated by weight. Investigators have focused on steel plates that helped connect support beams underneath the bridge decking.

Construction materials and related vehicles delivered earlier in the day for a resurfacing project on the eight-lane bridge weighed 287 tons, investigators said. It was not clear immediately if that amount alone was a factor.

But authorities said they have a better idea of where equipment was placed, which was crucial for determining the impact of weight.

Investigators are reviewing the history of projects on the bridge after its construction in 1967 and are interested in finding out whether the de-icing system installed 10 years ago to reduce accidents in winter would have caused any corrosion.

The computerized system sprayed potassium acetate to reduce hard-to-see ice caused by extreme cold and moisture from a nearby waterfall.

According to the Minnesota Transportation Department, the de-icing chemical is less toxic and less corrosive than sodium chloride, which had been used previously.

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