A method for separating hydrated concrete paste from aggregate includes the steps of providing a feedstock comprising waste concrete with a D10?0.1 mm and a D90?100 mm, passing the feedstock, a water containing liquid and carbon dioxide into a fragmentation vessel, where the wet feedstock is subjected to electric-pulse fragmentation, withdrawing fragmented solid material from the fragmentation vessel, separating the fragmented solid material from admixed liquid phase, separating the fragmented solid material into a fine fraction with a maximum particle size of 250 ?m to provide the carbonated recycled concrete paste and a coarse fraction, recycling the coarse fraction into the fragmentation vessel and/or discharging the coarse fraction as clean aggregate, use of the recycled concrete paste obtained thereby as supplementary cementitious material or filler.

A process is disclosed for the combined manufacture of steel and cement clinker. Steel scrap is loaded in an electric arc furnace for forming molten steel. Cement paste derived from construction and demolition waste is loaded in the electric arc furnace to act as a flux for the steel to assist in the removal of impurities from the molten steel and forming an electric are furnace slag. The heat of the molten steel promotes clinkering of the electric are furnace slag to form clinkered electric arc furnace slag. The clinkered electric arc furnace slag is removed from the electric arc furnace.

A method for producing a supplementary cementitious material from concrete waste and similar materials includes the steps of i) providing a starting material comprising hydrated cement and aggregate comprising silicate and/or alumino-silicate, ii) hydrothermal treatment of the starting material provided in step i) to obtain a hydrothermally activated material, and iii) carbonation of the hydrothermally activated material of step ii) to provide the supplementary cementitious material, as well as supplementary cementitious material obtainable by the method, hydraulic binder comprising the supplementary cementitious material and use of the supplementary cementitious material and of the hydraulic binder for making hydraulic building materials.

Aspects of the invention include a method of producing a cement material comprising step of: first reacting a calcium-bearing starting material with a first acid to produce an aqueous first calcium salt; second reacting the aqueous first calcium salt with a second acid to produce a solid second calcium salt; wherein the second acid is different from the first acid and the second calcium salt is different from the first calcium salt; and thermally treating the second calcium salt to produce a first cement material. Preferably, but not necessarily, during the second reacting step, reaction between the first calcium salt and the second acid regenerates the first acid.

Fiber cement material, which contains organic fibers, is used as an additional raw material for the production of cement clinker. The cement clinker is produced in a system which comprises a cyclone tower (11) and a rotating drum kiln (15). The cyclone tower (11) comprises cyclones (1-5) and a pre-calciner unit (10) wherein fuel is combusted to feed the cyclone tower with heat. The raw clinker meal is passed through the cyclone tower to preheat it. By the combustion of the fuel in the pre-calciner unit (10) a hot zone is produced in the cyclone tower wherein the raw clinker meal is calcined. In order to be able to add larger amounts of the fiber cement material without causing a too high total organic carbon content of the exhaust gasses and/or without causing depositions of organic matter onto the inner walls of the cyclone tower (11), the organic fiber cement material is added in a dry powdered form in said hot zone, in particular in the pre-calciner unit (10) to be heated in less than 5 seconds to a temperature of at least 800 C.

Devices and methods of recycling cement waste. A cement waste recycling device (1) comprising a heater (2) with an inlet (3) for cement waste and an outlet (4) for processed cement waste, wherein the heater (2) is configured for transporting cement waste in a cement waste transportation direction from the inlet (3) to the outlet (4) while transporting heated gas in countercurrent with the cement waste transportation direction.

Method for producing a supplementary cementitious material from concrete waste and similar materials, supplementary cementitious material obtainable by the method, use of the supplementary cementitious material for making hydraulic building materials and alkali activated binders, method for manufacturing alkali activated binders, composite binders and alkali activated binders comprising the supplementary cementitious material, and use of the composite binder for making hydraulic building materials.

Methods and systems are provided for processing post-consumer waste concrete into a usable recycled aggregate and supplementary cementitious material. The concrete is crushed and tumbled under heat and optional watering to liberate unreacted hardened cement paste. The aggregate is then screened for size for application, and the hardened cement paste is milled into a supplementary cementitious material, which can be used alone or blended with other supplementary cementitious materials such as ground glass pozzolan.