Study Of The Effect Of Waste Streams Of Tannic Acid Modified Recycled Aggregates On The Properties Of Cementitious Materials

The use of acid soaks can effectively improve the performance of recycled aggre-gates,which have the disadvantages of high water absorption,micro-cracks and poor ro-bustness.In particular,low concentration tannic acid soaking of recycled aggregates can not only improve the surface microstructure of recycled aggregates,but also the organic functional groups complexed on the surface of recycled aggregates can effectively im-prove the bonding properties with the cement interface,significantly improving the strength and durability of concrete/mortar.In fact,most of the methods for modifying recycled aggregates by acid immersion have neglected the treatment of process waste streams.Therefore,in this paper,the process waste stream of tannic acid-modified recy-cled aggregates is used as mixing water to analyse the process of hydration and hardening of cementitious materials and to investigate the mechanism of the effect on mortar per-formance,in order to improve the theoretical basis for the use of process waste stream of tannic acid-modified recycled aggregates as mixing water.The main findings are as fol-lows.（1）The tannic acid-modified recycled aggregate waste solution has a certain retard-ing effect and can inhibit early cement hydration,and the effect of this retarding effect increases with the increase of tannic acid concentration.When the solubility of tannic acid is 0.1%,the inhibition of cement hydration is not obvious;when the solubility of tannic acid is 0.3%,the inhibition of cement hydration is obvious;when the concentration of tannic acid increases to 0.5%and 1.0%,the inhibition of cement hydration is strong.The tannic acid modified recycled aggregate waste solution as mixing water can improve the initial and final setting time of the net cement slurry,and the higher the tannic acid concentration,the more obvious the enhancement effect.Meanwhile,tannic acid modi-fied recycled aggregate waste solution as mixing water could improve the flow of cement mortar,and the flow size of each group of mortar increased with the increase of tannic acid concentration.（2）The results of FTIR,XRD and TGA-DSC showed that the addition of tannic acid modified recycled aggregate waste solution did not generate new hydration products in the system,inhibited the early hydration reaction of C₂S/C₃S,promoted the formation of later hydrated calcium silicate,effectively filled the capillary pores and micro-pores in the mortar,improved the pore structure of the mortar,and thus improved the compressive strength of the mortar.This improves the pore structure of the mortar,thereby increasing the compressive strength of the mortar.Therefore,tannic acid modified recycled aggre-gate waste as mixing water can reduce the early compressive strength of cement mortar,but to a certain extent improve the later compressive strength of cement mortar,when the tannic acid concentration is 0.3%,its 28-day compressive strength increased by 14.34%.（3）The tannic acid-modified recycled aggregate waste solution as mixing water has a certain optimising effect on the pore distribution of mortar,and the effect of capillary water absorption shows a trend of first decreasing and then increasing,when the tannic acid concentration is lower than 0.5%,the capillary water absorption of mortar can be reduced,and when the tannic acid concentration is 0.3%the capillary water absorption of mortar is reduced by 28.08%.The tannic acid-modified recycled aggregate waste can im-prove the mortar’s resistance to chloride ion penetration,and the higher the tannic acid concentration,the more significant the improvement effect.When the concentration of tannic acid was 0.3%,it could effectively improve the resistance to rust and corrosion of reinforcement in mortar.The results of this paper show that selecting a suitable concentration of waste liquid as mixing water can improve the strength and durability of mortar,and the results of the study have some theoretical and practical value for the process waste liquid utilisation of modified recycled aggregates.Figure 46 Table 9 Reference 86...