Iowa added 3,100 construction workers to payrolls last year, ranking the state No. 9 in the country for employment gains in the industry, the Associated General Contractors of America said. The state added 300 jobs in January. Construction employment rose in 28 states and the District of Columbia between January 2011 and January 2012, while 20 states lost construction jobs and two held steady, the best net positive showing for state construction employment since 2007, the association said.