Characterizing the influencing factors in a novel repairing material for concrete structures by AC impedance spectroscopy

This research systematically characterizes the working mechanism of the influencing factors, e.g., magnesia to phosphate (M/P) ratio, borax, sodium tripolyphosphate (STP), fly ash (FA), and silica fume (SF), in magnesium phosphate cement (MPC) from the initial 1 h hydration age by a non-destructive testing method-AC impedance spectroscopy (ACIS). The results show that the M/P ratio significantly affects MPC, and its influencing mechanism is changed during the whole hydration period. At the initial period (within 6 h), a higher M/P ratio causes a quicker hydration rate. During the later stage, a higher M/P ratio relates to a lower strength growth potential. The resistance values collaborate with the compressive strength well. The commonly used borax and STP have different influences in MPC. Borax retards the acid-based reaction, while STP has little retarding effect. STP improves the hydration process and microstructure formation from the initial age. Both the mineral admixtures: FA and SF, reduce the early age properties of MPC. As the hydration continues, they continuously decrease the porosity and optimize the pore size distribution. SF has a smaller particle size and a more significant improvement effect than FA. As ACIS detects, MPC has higher early strength, faster strength increasing rate, and finer pore size distribution than other cement-based materials, e.g., AAM and UHPC. The results are helpful to improve the performances of this novel repairing material for hydraulic concrete structures.

Automated summary

This research systematically characterizes the working mechanism of various influencing factors in magnesium phosphate cement (MPC) using AC impedance spectroscopy (ACIS) for non-destructive testing. The results show that the M/P ratio significantly affects the hydration of MPC, with a higher ratio resulting in a faster hydration rate initially but a lower strength growth potential later on. The commonly used borax and STP have different influences in MPC, with borax retarding the acid-based reaction and STP improving the hydration process. The mineral admixtures, fly ash (FA) and silica fume (SF), reduce the early age properties of MPC but decrease porosity and optimize pore size distribution as hydration continues. ACIS detects that MPC has higher early strength, faster strength increasing rate, and finer pore size distribution compared to other cement-based materials. These findings are important for improving the performance of this novel repairing material for hydraulic concrete structures.