The pronunciation tab there is paywalled, but in the OED app on my phone, they list /əˌsəʊsiˈeɪʃn/, followed by /əˌsəʊʃiˈeɪʃn/ in the pronunciation section. I honestly can’t recall ever hearing a single person in the US pronounce it /əˌsəʊʃiˈeɪʃn/, and though I won’t say nobody does, the other pronunciation is far and away more common, where the ‘c’ and ‘t’ make entirely distinct sounds.
The pronunciation tab there is paywalled, but in the OED app on my phone, they list /əˌsəʊsiˈeɪʃn/, followed by /əˌsəʊʃiˈeɪʃn/ in the pronunciation section. I honestly can’t recall ever hearing a single person in the US pronounce it /əˌsəʊʃiˈeɪʃn/, and though I won’t say nobody does, the other pronunciation is far and away more common, where the ‘c’ and ‘t’ make entirely distinct sounds.