Study On Setting Properties Of Phosphorus Slag To Ordinary Portland Cement

Phosphorus slag is the Industrial waste residue from the production of yellow phosphorus by electric furnace method,It will not only occupy a large amount of land,but also pollute water and land.Phosphorus slag has potential activity,It can be used as a mixture instead of part of cement,However,phosphorus slag can prolong the setting time of cement and reduce the early strength,Therefore,the study of phosphorus slag has great significance.On the basis of summing up the experience of predecessors,this paper studies the retarding characteristics of phosphorus slag on ordinary Portland cement and the activation of phosphorus slag activity.The chemical composition,phase composition and structure of phosphorous slag were analyzed,The results show that CaO and SiO₂ is the main component;the effects of phosphorus slag content,phosphate content and fluoride content on setting time and strength of ordinary Portland cement were studied,The results show that with the increasing of PS content,the setting time of PS cement increased gradually,In the blank group without phosphorous slag,the initial setting time was 239 min and the final setting time was 300 min.The initial setting time of the group with only 20%phosphorous slag was 342 min and 414 min.The initial setting time of the group with45%phosphorous slag was 502 min and 574 min;the flexural strength and compressive strength are decreasing gradually,at 3 d,the strength of blank group is31 MPa,the strength of 20%phosphorus slag is 25.2 MPa,the strength of 45%phosphorus slag is 14.7 MPa,but the later stage strength develops rapidly.soluble and insoluble phosphate and fluoride all can delay the setting of cement with low content,With the increasing of phosphate and fluoride,the setting time of cement was significantly prolonged by soluble NaH₂PO₄ and insoluble CaF₂?Ca?H₂PO₄?₂,while the setting time of soluble NaF was not retarded,even can rapid setting,so the main reason for the retarding of PS is related to the form and amount of phosphorus and fluorine in PS.Physical and chemical excitation of phosphorus slag were carried out.Physical activation mainly uses mechanical activation method to grind phosphorus slag particles to a certain fineness,Physical activation test showed that with the increase of specific surface area of phosphorous slag,the setting time of PS cement increased gradually,and the flexural strength and compressive strength increased slightly;Chemical activation mainly studies the effect of the type and content of activator on the setting time and strength of phosphorus slag cement,The results show when the content of phosphorus slag is 30%,NaOH,Na₂CO₃ and Ca?HCOO?₂ can all achieve remarkable stimulation effect.They can not only eliminate the retarding effect of phosphorus slag,but also can improve the strength of PS cement,The optimum dosage is 3%,2%and 3%,the initial and final setting time were 264 min and 317 min,148 min and 200 min,205 min and 266 min;the 3 d compressive strength was 19.7MPa,18.2 MPa,17.6 MPa,the 3 d flexural strength was 7.3 MPa,7.7 MPa,6.4 MPa;the 28 d compressive strength was 44.1 MPa,42.3 MPa,45.8 MPa,and the 28 d flexural strength was 14.5 MPa,12.64 MPa,13.1 MPa,It meets the requirements of the national standard for setting time and strength of P·O 42.5 ordinary Portland cement.The hydration products,hydration process and hydration mechanism of cementitious materials were studied by means of SEM,XRD,TG-DSC,FT-IR and other modern testing methods.The results show that the main hydration products of phosphorus slag cement are Ca?OH?₂ and ettringite?AFt?.The addition of phosphorus slag and phosphate can reduce the hydration rate of cement.Sodium hydroxide,sodium carbonate and calcium formate can stimulate the activity of phosphorus slag.The reason is to promote the hydration of C₃S and C₂S,and accelerate the formation of hydration products.