RESOURCES RECYCLING AND ITS UTILIZATION OF CONCRETE AND GYPSUM BOARD WASTE

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The reports were made to investigate preparations of reclaimed cement and reclaimed gypsum from concrete and gypsum board waste.It was needed to adjust closely to the chemical composition of normal cement by adding required amount of Fe_2O_3 and Al_2O_3 besides CaO.The compressive strength of the improved reclaimed cement was much increased to 370kgf/cm^2 after for 28 days which was almost the same to that of normal cement. A the above, it was apparent that the preparation of reclaimed cement from concrete waste was a useful process for recycling calcium resource.The cement fine powder in artificial sea water was dissolved 4.1g CaCO_3/dm^3 under CO_2 pressure of 10kgf/cm^2 for 60 min.. The dissolved calcium ion was deposited as calcium carbonate at pH 7 by adding Ca(OH)_2 in calcium hydrogencarbonate solution which formed by dissolving cement fine powder into sea water with an excess of CO_2. The magnesium ion in residual solution after depositing calcium carbonate was recovered as magnesium hydrate by controlling above pH 8.The present work was made to investigate preparation of hardened body from reclaimed gypsum hemihydrate obtained by dry or wet process of water board for resources recycling of waste gypsum board. The gypsum dihydrate powder which was separated as much as possible lining. The dry process was performed by heating the gypsum powder at 200ﾟC for 10min., reclaimed gypsum hemihydrate after dry process was aged the powder for 60 min. in 12% H_2SO_4 solution. The use of reclaimed gypsum hemihydrate after dry process was effective by mixing it in calcined gypsum. For example, the strength of hardened body prepared with equal quantities of reclaimed hemihydrate and calcined gypsum was almost the same that of independently calcined gypsum. By controlling water carrying capacity abdparticle size of the reclaimed hemihydrate containing alpha type of about 25% after wet process, the compressive strength of the hardened body was increased till 110kgf/cm^2.