Study On Activation Of Phosphorus Slag Concrete By Chemical Additives

Phosphorus slag is a product of phosphorus ore,silica and coke which is quenched by water in the process of producing yellow phosphorus by electric furnace.The comprehensive utilization of phosphorus slag involves many fields,but the overall utilization rate is not high.There is still a large amount of phosphorus slag accumulation,which has a great impact on the environment.Phosphorus slag as concrete admixture will have some adverse effects,one is long setting time,the other is low early strength,which restricts the application of phosphorus slag in concrete.In order to improve the content of phosphorus slag in concrete,its activity must be fully stimulated.In this paper,a phosphorus slag in Guizhou Province was taken as the research object.The physical and chemical properties of phosphorus slag,the activation of phosphorus slag by chemical additives and its effect on concrete properties,and the activation mechanism of phosphorus slag by chemical additives were studied.The research results can better stimulate the activity of phosphorus slag,improve the comprehensive utilization of phosphorus slag,and reduce the pollution of phosphorus slag to the environment.?1?The physical and chemical properties of phosphorus slag in Guizhou province show that there are many honeycomb-like micro-pore on the surface and inside of phosphorus slag particles.The total content of CaO and SiO₂ in phosphorus slag is 82.08%.It is CaO-rich alkali slag.The phosphorus slag is mainly glass phase and contains a small amount of calcite,quartz,calcium silicate,calcium silicate mineral,CaO/SiO₂ ratio 1.17,mass coefficient K?1.26?>1.10,P₂O₅<3.5%,loss of combustion less than 3.0%.At the same time,it contains a small amount of harmful elements such as P and F.Among them,the existing forms of P and F which lead to the prolongation of setting time of phosphorus slag cement are PO₄^3-,F^-.The contact heat of phosphorus slag and water?3875.05 J/g?is more than twice as much as that of cement and water?1794.71 J/g?,which leads to the release of reaction heat ahead of time and reduces the hydration heat in hydration process,so it can reduce the internal and external temperature differential heat of mass concrete.?2?According to the orthogonal test and test adjustment,the basic mix ratio of C50 phosphorus slag concrete is determined as follows:water consumption 215 kg/m³,water reducing agent dosage 6 kg/m³,water-binder ratio 0.43,sand ratio 37%,polypropylene fiber length 9 mm,dosage 0.9 kg/m³,Q2 superplasticizer dosage 0.5kg/m³,phosphorus slag dosage 20%.At this time,the compressive strength of phosphorus slag concrete cured for 3 d,7 d and 28 d is 28.5 MPa,34.5 MPa,respectively.41.8 MPa.The chemical additives of CaCl₂,NaOH,Al₂?SO₄?₃,Na₂SiO₃and Na₂CO₃ have been screened out to improve the setting time of phosphorus slag cement.Among them,Al₂?SO₄?₃ has better effect on phosphorus slag concrete,and can reach 30.2 MPa,36.5 MPa and 45.6 MPa after 3 d,7 d and 28 d of curing.When CaCl₂,CaO and NaOH are mixed with Al₂?SO₄?₃ respectively,CaCl₂ and CaO and Al₂?SO₄?₃can activate the activity of phosphorus slag concrete very well.The mass ratio of CaO to Al₂?SO₄?₃ is 1:1,the compressive strength of 28 days is 59.4 MPa,and the compressive strength of CaCl₂ and Al₂?SO₄?₃ is 56.1 MPa,and the mass ratio of CaCl₂to Al₂?SO₄?₃ is 2:3.?3?Phosphorus slag cement has sulfate corrosion resistance.Al₂?SO₄?₃ additive can form more hydroxyapatite and Ettringite?AFt?.The ettringite generated is filled in the cementing pore of mortar,forming a dense network structure system.The flocculent hydration products are stacked by smaller flocculent products,which can effectively improve the internal microstructure and porosity of mortar,and the phosphorus slag water.The shrinkage property of the slurry has been improved to a certain extent,which makes the whole microstructure more compact.