Study On Properties And Related Mechanism Of Nano-SiO₂ Geopolymer Penetration Reinforced Coral Aggregate

In view of the shortage of resources,transportation difficulties and high production costs caused by the large use of ordinary concrete in the construction process of the island and reef,a large number of scholars considered using the rich coral resources around the island and reef to carry out research on the preparation of coral aggregate concrete by replacing natural aggregate with coral aggregate.However,the high porosity and high chloride content of the coral aggregate itself seriously restrict the strength and durability of coral aggregate concrete.On the other hand,fly ash-kaolin soil polymer raw materials are abundant,the production process is low energy consumption,low pollution,and geological polymers have the advantages of dense structure,acid resistance,strong adhesion and low shrinkage.By incorporating highly active nano-Si O₂in the geopolymer,it is expected to further improve the multi-scale pore structure of coral aggregates.To this end,the nano-Si O₂-fly ash-kaolin base polymer material was prepared with metakaolin,fly ash and nano-Si O₂as the main raw materials,and the physical composition,chemical bond composition and microstructure of the sample were characterized by XRD,XRF,SEM,FTIR,etc.,and the material was used to modify the pore structure of coral aggregate,and the basic physical properties,mechanical properties,microstructure and anti-chloride permeability of coral aggregate after modification were tested.The main conclusions are as follows:（1）Orthogonal experiments were designed to study the effects of nano-Si O₂doping,alkali equivalent,liquid-solid ratio,alkali excitant modulus and curing temperature on the compressive strength,fluidity and coagulation time of geological polymers,and the optimal mix ratios were selected by comprehensive comparison as nano Si O₂doping,alkali equivalent,liquid-solid ratio,water glass modulus,and maintenance temperature of1%,24%,0.84,1.4,40°C,respectively.According to this mix ratio,the fly ash-metakaolin base polymer with the optimal mix ratio was prepared,and the compressive strength at the 3d,7d and 28d ages was 62.30MPa,78.50MPa and 97.80MPa,respectively,with a flow rate of 195mm,and the initial coagulation time and final coagulation time were 148min and 186min,respectively;（2）The methods of direct immersion and vacuum extraction of two modified aggregates were compared and analyzed,and the vacuum pumping method with better effect combined with nano-Si O₂modified geopolymers was selected to enhance the penetration of coral aggregates.The results show that the average 24h water absorption rate of coral aggregate modified by the ground polymer was greatly reduced,from 37.18%to 3.46%,the average compressive strength of coral aggregate after modification was significantly improved,from 19.18MPa to 73.73MPa,and the porosity before and after modification was 10.37%and 2.54%,respectively,and the average pore size was 0.49mm and 0.18mm,respectively,and the pore structure was significantly improved;（3）Under the erosion of chloride ions,the compressive strength of coral aggregate and the diffusion of chloride ions were studied,and under the erosion of chloride ions,the compressive strength of coral aggregate decreased with time,but the geopolymer material inside the pores of coral aggregate after modification physically absorbed chloride ions,which reduced the spread and diffusion of free chloride ions in pores,which had an inhibitory effect compared with the decline of original coral aggregates,and the anti-chloride permeability of coral aggregate after modification was significantly improved,and the content of free chloride ions inside was reduced.The ability to bind chloride ions is greatly improved.