Reactive magnesium oxide cements

Abstract

Novel hydraulic cements are disclosed that include reactive magnesium oxide prepared by low temperature calcination. The cements can be formulated to suit a large number of applications with various setting times, strength and levels of sustainability either by adding iron salts such as ferrous sulfate or blending with other compatible faster setting hydraulic cements such as Portland cement or by using both methods. The compositions are able to incorporate relatively large amounts of low cost pozzolans such as fly ash to advantage as well as wastes. Many excellent properties are exhibited and in particular good comprehensive strength and resistance to sulfates is able to be achieved.

1 . A hydraulic cement composition that includes reactive magnesium oxide at a level of at least 5% w/w of hydraulic cementitious components in the composition excluding pozzolans wherein the hydraulic cementitious components exclude the magnesium oxychlorides and magnesium oxysulfates and wherein the magnesium oxide is prepared by low temperature calcination and fine grinding.  
     
     
         2 . A hydraulic cement composition as defined in  claim 1  that includes Portland cement.  
     
     
         3 . A hydraulic cement composition as defined in any one of  claims 1  to  2  which includes calcium aluminate cements.  
     
     
         4 . A hydraulic cement composition as defined in any one of  claims 1  to  3  which includes geopolymer cements.  
     
     
         5 . A hydraulic cement composition as defined in any one of  claims 1  to  4  which includes a pozzolanic material.  
     
     
         6 . A hydraulic cement composition as defined in  claim 5  wherein the pozzolanic material includes fly ash.  
     
     
         7 . A hydraulic cement composition as defined in  claim 5  wherein the pozzolanic material includes ground blast furnace slag.  
     
     
         8 . A hydraulic cement composition as defined in  claim 2  wherein the weight ratio of reactive magnesium oxide to Portland cement is in the range 1:3 to 2.5:1.  
     
     
         9 . A hydraulic cement composition as defined in any one of  claims 5  to  8  wherein the pozzolan material is at least 80% w/w of the total composition.  
     
     
         10 . A hydraulic cement composition as defined in any one of  claims 1  to  9  wherein an accelerator being an acid or the salt of an acid is flirter included.  
     
     
         11 . A hydraulic cement as defined in any one of the  claims 1  to  10  where an iron salt is included as an accelerator.  
     
     
         12 . A hydraulic cement composition as defined in  claim 11  wherein the iron salt is ferrous sulfate.  
     
     
         13 . A hydraulic cement composition as defined in any one of  claims 1  to  12  wherein sodium or potassium silicate or aluminate is included as an accelerator.  
     
     
         14 . A hydraulic cement composition as defined in any one of  claims 1  to  13  wherein sodium or potassium sulfate is included as an accelerator.  
     
     
         15 . A hydraulic cement as defined in any one of  claims 1  to  14  which is heated or steamed at temperatures in the range 20-1000° C.  
     
     
         16 . A hydraulic cement composition as defined in any one of  claims 1  to  15  wherein the composition further includes soluble phosphates.  
     
     
         17 . A hydraulic cement composition as defined in  claim 16  wherein the soluble phosphate is phosphoric acid or phosphoric acid salts.