The lithium aluminate layer is insoluble in cement pore water and protects the underlying aluminium oxide covering the metallic aluminium from dissolution at high pH. It is also a pore filler.
ðə lˈɪθiəm ɐlˈuːmᵻnˌeɪt lˈeɪɚɹ ɪz ɪnsˈɑːljuːbəl ɪn sᵻmˈɛnt pˈoːɹ wˈɔːɾɚ ænd pɹətˈɛkts ðɪ ˌʌndɚlˈaɪɪŋ ˌæljʊmˈɪniəm ˈɑːksaɪd kˈʌvɚɹɪŋ ðə mətˈælɪk ˌæljʊmˈɪniəm fɹʌm dˌɪsəlˈuːʃən æt hˈaɪ pˈiː ˈeɪtʃ. ɪɾ ɪz ˈɔːlsoʊ ɐ pˈoːɹ fˈɪlɚ.