Construction materials supplier Martin Marietta Materials Inc MLM.N said it would buy HeidelbergCement AG's HEIG.DE assets in California and Arizona for $2.3 billion. By Medha Singh and Shashank Nayar May 24 (Reuters) - Wall Street's main indexes gained on Monday, with the Nasdaq up about 1%, as investors flocked to lagging technology shares, while gearing up for key inflation readings later this week. Risk sentiment also improved with cryptocurrencies clawing back ground after a bout of weekend selling fueled by further signs of a gathering Chinese crackdown on the emerging sector.