The present invention is related to the process and composition for the
manufacture of cement expansion additive. The process comprises a
blending step, a reaction step, and a calcination step. The blending step
is to incorporate soluble calcium sulfate, soluble calcium oxide, and
soluble aluminum compounds such as aluminum dross. The addition of water
with the above incorporated materials to from ettringite is so-called
reaction step. The calcination step is to calcine the products which are
produced from reaction step at a temperature range between 60.degree. C.
and 900.degree. C. by transforming ettringite from amorphous to calcium
sulfoaluminate respectively. After calcinations, the final products can
be used as expansive additives for cement or concrete. Further, this
manufacturing method can effectively decrease raw material cost and
production cost due to the raw material coming from recycling and no need
to calcine at high temperature than other relative arts.
