As Japan's construction firms are squeezed by the tightest labor market since the 1970s and a rapidly aging population, they are pouring investment into technology -- and providing unexpected support to an economy reeling from the bitter U.S.-China trade war. The industry sees artificial intelligence and robots -- which can scurry around building sites day and night, preparing equipment and moving materials for the next day's construction -- as a way to future-proof and close the labor gap. But a side effect is that one of the country's least-productive sectors is bolstering capital expenditures even as the world's third-largest economy flirts with recession amid a global growth slowdown. Construction company Shimizu Corp., which spent about ¥3 billion ($27.7 million) on robots over three years, is a case in point. Equipped with state-of-the-art AI, cameras and sensors, the machines handle everything from transporting building materials and welding steel to installing ceilings.