Study On Properties Of Phosphogypsum Modified Cement Mortar

Phosphogypsum（PG）contains phosphorus,fluorine,some heavy metals,radioactive trace elements and many other impurities that are harmful to the ecological environment.The main component is gypsum dihydrate（CaSO₄·2H₂O）.In this paper,by adding five different amounts（1%,2%,3%,4%and 5%）of quicklime calcined modified phosphogypsum（MPG）cement mortar,a blank cement mortar was used as a control group for comparative analysis.Its working performance,combined with scanning electron microscope（SEM）,used to characterize the change of voids in the mortar before and after modification;X-ray diffraction（XRD）test was used to analyze the phase of PG and hydration products;and Fourier transform infrared spectrum of MPG was used（FT-IR）test was used for qualitative analysis;the hydration and heat release mechanism of MPG cement mortar was analyzed and analyzed.Finally,the durability（freeze resistance,impermeability,and sulfate resistance）of MPG cement mortar was studied to solve the problem.The rationality and economic utilization of PG engineering applications provide new ideas for its resource utilization.The main research results are as follows:（1）The main component of PG is CaSO₄·2H₂O,which does not have the activity of gelling material itself.After using the pre-treatment process of aging and rapid burning（800℃）,PG can replace part of the cement to prepare MPG cement mortar;（2）There are many kinds of impurities in PG.After the addition of quicklime,the activation index of PG powder increases first and then decreases;The water consumption for standard consistency of MPG cement mortar increases with the increase of MPG content and fluidity.With the increase of MPG content,the setting time increases with the increase of MPG content,and it acts as a retarder for hydration and hardening;adding MPG to the mortar system reduces the water loss of cement mortar,and MPG The water retention of cement mortar showed an increasing trend with the increase of PG content.The physical and mechanical tests concluded that the MPG cement mortar R2 experimental group had the best compressive strength and flexural strength;（3）The addition of MPG reduces the hydration heat of cement hydration,and also reduces the rate of cement hydration;（4）Combining hydration degree experiments with XRD and FT-IR micro-tests,it can be seen that the incorporation of MPG inhibits the hydration and hardening process of cement,but the incorporation of MPG does not change the type of hydration products and no new substances are produced,but MPG Incorporation delays the hydration reaction time and has a significant retarding effect.（5）The durability test of MPG cement mortar shows that both the mass loss rate and the compressive strength loss rate of MPG increase gradually with the increase of the amount of MPG added;the maximum water penetration pressure and sulfuric acid resistance of MPG cement mortar With the increase of PG content,salt erosion first increased and then decreased,and the MPG cement mortar with the mass fraction of 2% was the best impermeability.