Preparation And Performances Of Permeable Brick Of Sintering With Sludge And Straw Powder As Pore Former

With the acceleration of urbanization in our country,the discharge of sewage is increasing day by day,and the sludge production also increases.Sludge contains a large number of pathogenic bacteria,harmful substances such as heavy metals,and the traditional disposal methods have the possibility of secondary pollution,so to find a way of environmental sludge settlement is particularly important.At the same time,the permeable brick(PB)as a new kind of paving material,has the good permeability,water retention,and air permeability,can effectively improve urban waterlogging due to road sclerosis,heat island effect,and other urban problems.In this paper,sludge and straw powder were used as pore former agents to prepare both the sintered PB specimens with sludge and sintered PB with blast furnace slag(BFS),respectively.On the basis of the mentioned above,the sintered PB specimens with double layer composite structure were prepared.In this paper,the physical and chemical properties of sludge were characterized,and it was found that the sludge contained a lot of water,and the adding of 10% fly ash as conditioning agent could significantly speed up the dewatering during the natural drying process of sludge.Sludge had a chemical composition similar to that of clay and it could be used to make sintered PB.The sludge sintered PB specimens were prepared using sludge,fly ash,engineering waste soil and straw powder as raw materials.The results showed that the water permeability coefficient of PB specimen was increased with the increase of sludge dosage,and its flexural strength was decreased with the increase of sludge dosage.When the sintering temperature was lower than 1125 ?,the flexural strength and water permeability coefficient of the as prepared brick specimens were increased with the elevation of sintering temperature.As the sintering temperature was increased above 1125 ?,the water permeability coefficients of the prepared brick specimens were decreased and their flexural strengths were increased with the elevation of sintering temperature,respectively.With the both increases of soaking time at sintering temperature and the molding pressure,the flexural strengths were increased and the water permeability coefficients were decreased gradually for the as prepared PB specimens.Under the conditions of volume amount of sludge being 25% in the batching,the sintering temperature being 1150 ?,soaking time at sintering temperature being 2 h,and the molding pressure being 10 MPa,the flexural strength and water permeability coefficient of the resulting PB specimens were respective 9.1 MPa and 2.8×10-2 cm/s,and the heavy metal dissolution of them was in line with the national standards.The specimens of sintered PB were prepared using BFS as aggregate,engineering residue as binder and straw powder as pore former,respectively.As the sintering temperature being lower than 1175 ?,the flexural strength and water permeability coefficient of the as prepared specimens of sintered PB were increased with the increase of sintering temperature.As the sintering temperature being above 1175 ?,the water permeability were decreased and the flexural strength were increased with the elevation of sintering temperature for the as prepared sintered PB specimens,respectively.At the molding pressure being 15 MPa,the sintering temperature being 1175 ? and the soaking time at sintering temperature being 2 h,the flexural strength and water permeability were respective11 MPa and 5.6×10-2 cm/s for the as prepared specimens of sintered PB with 60 wt% BFS content.Using the sludge sintered PB as the surface layer,and the slag sintered PB as the bottom layer,the specimens of PB with bilayer structure were prepared by semi-dry pressing method.With the increase of the thickness of the surface layer,the water permeability coefficient and flexural strength were gradually decreased,and the porosity and water absorption rate were increased for the as prepared specimens of PB with bilayer structure.The flexural strength was 8.7 MPa,the water permeability coefficient was 4.1×10-2 cm/s,the porosity was 25.6%,and the water absorption rate was 19.3% for the as prepared specimens of PB with bilayer structure,and with surface layer thickness of 1.5 cm.The as prepared specimens of PB with bilayer structure had the apparent anti-clogging performance.