How do I perform a gravimetric analysis of Portland cement? To determine the silica ($\ce{SiO2}$) content in Portland cement by gravimetric analysis it is digested in $\ce{HCl}$ and the silica residue is eventually measured.

The chief constituents are $\ce{Ca2SiO4}$ (or $\ce{2CaO.SiO2}$), $\ce{4CaO.Al2O3.Fe2O3}$, $\ce{Ca3(AlO3)2}$ (or $\ce{3CaO.Al2O3}$), and $\ce{CaSiO3}$ (or $\ce{CaO.SiO2}$). Gypsum is also present. What species are present in solution after the $\ce{HCl}$ has reacted with the cement? I assume $\ce{CaCl2}$ and $\ce{H2O}$ would be present, but would $\ce{AlCl3}$ also form? How would I approach this problem?
http://books.google.com/books?id=VeXQAAAAMAAJ&amp;pg=PA2&amp;lpg=PA2&amp;dq=Gravimetric+Analysis+of+Portland+Cement+%22aluminum 
Copy whole URL. Page 2 for clickable index, then page 18. 
DOI: 10.1039/AN9709500051

Digest it in "strong" HCl (tough lab for employment, worse if you service the fume hoods).  Everything except silica comes out as soluble chlorides (hydrated complex ions).  That says something about Portland cement in acid environments and, unless modified, in seawater.