JAKARTA - A joint venture between Japanese construction firm Kajima Corp and Indonesian state builder PT Waskita Karya Tbk has been forced to delay the completion of a road to Jakarta’s main port due to flaws in the building material. The Tanjung Priok port in North Jakarta, which handles the bulk of international shipments in Southeast Asia’s biggest economy, is plagued with bottlenecks and long handling times due to years of underinvestment. The contractors were working on a highway designed to improve access to the port, but they will have to rebuild as many as 69 supporting columns due to signs of cracking, Indonesian media reported, quoting public ministry official Hediyanto Husaini. A Kajima spokesman said they had to redo the work as the concrete they used was not strong enough. He gave no details on how long the delay would be or how much costs might increase. Waskita did not respond to requests for comment. Indonesia is grappling with its weakest economic growth in six years, partly because President Joko Widodo’s administration has failed to push through badly needed infrastructure projects due to a lack of coordination among ministries. The dwell time at the Tanjong Priok port is up to eight days, compared to five days in Thailand, four days in Malaysia and slightly more than one day in Singapore, according to Jakarta-based infrastructure consultancy firm Tusk Advisory. In June, during a visit to the port, Widodo threatened to sack officials responsible for the lengthy handling time there.