Study On The Properties Of Calcined Phosphogypsum-slagalkaline Activator Cementitious Material

At present,a large number of calcined phosphogypsum piles up,there are problems such as occupying land resources,low utilization rate and affecting people's health,so the application of phosphogypsum reduction is an urgent problem to be solved.Calcined phosphogypsum as cementing material not only consumes a lot of calcined phosphogypsum but also has low energy consumption and high benefit,but also has the problems of low strength and poor water resistance.This paper takes calcined phosphogypsum as raw material,slag as active admixture,NaOH,Na2CO3 and Mg O as activators,respectively,to prepare calcined phosphogypsum-slag-alkali binder.The compressive strength,softening coefficient,water resistance and durability of the material were tested and analyzed.The main research contents and conclusions are as follows:?1?Study on the basic mechanical properties of calcined phosphogypsum-slag-alkali binderUsing NaOH as alkaline excitation agent,the compressive strength and softening coefficient of sample with increase with the increase of the slag content,with the increase of dosage of NaOH increases after the first drop,the dosage of slag was 30%,1%NaOH,CPG30NH1 binder sample of 28 air-dried compressive strength,wet compression strength and softening coefficient were 30.3 MPa,28.6 MPa and 0.94respectively;Using Na2CO3 as alkaline excitation agent,the compressive strength and softening coefficient of sample with increase with the increase of dosage of slag and,with the increase of Na2CO3 content increased after the first drop,the slag content was 30%,the dosage of Na2CO3 is 1%,CPG30NC1 binder sample 28 air-dried compressive strength,wet compression strength and softening coefficient are 25.7 MPa,24.9 MPa and 0.97 respectively;Using Mg O as alkaline excitation agent,the compressive strength and softening coefficient of sample with increase with the increase of the dosage of slag,with the increase of dosage of Mg O style to increase after the first drop,the dosage of slag was 30%,3%Mg O,CPG30M3 binder sample of28 d compressive strength and dry wet compression strength and softening coefficient were 31.4 MPa,27.3 MPa and 0.87 respectively;All of them meet the requirements of28-day compressive strength?20.0mpa and softening coefficient?0.85.?2?Theoretical analysis of alkali excitation of calcined phosphogypsum-slag-alkali binderBased on solidification body X-ray diffraction analysis,scanning electron microscopy?sem?and thermogravimetric analysis and so on microscopic analysis,it is found that the calcined phosphogypsum slag-alkali binder solidified body,is the main hydration products of dihydrate gypsum?Ca SO₄·2H₂O?crystal,ettringite?AFt?and hydrated calcium silicate gel?C-S-H?,form the relatively dense network skeleton structure,make the material macro performance is good.However,with the increase of the content of alkaline activator,too many expansive hydration products were produced in the system,and micro-cracks appeared in the solidified body,and the macroscopic properties of the material decreased.?3?Study on durability of calcined phosphogypsum-slag-alkali binderThrough the study on the durability of calcined phosphogypsum-slag-alkali binder,it was found that when NaOH was used as an alkaline initiator,CPG30NH1binder had good long-term water resistance and carbonation resistance,but poor antifreeze resistance.When Na₂CO₃ and Mg O were used as aikaline initiators,CPG30NC1 and CPG30M3 binder showed poor long-term water resistance,carbonation resistance and antifreeze resistance.At the same time,the volumes of CPG30NH1,CPG30NC1 and CPG30M3 binder showed the characteristics of expansion before contraction,and their 112-day volume expansion rates were stable at-0.19%,-0.18% and-0.08% respectively.