Evolution law of microporous structure in cement asphalt (CA) mortar under the action of polyurethane polycarboxylates.

In this paper, Cement Asphalt (CA) mortar specimens mixed with polyurethane polycarboxylate and ordinary commercial polycarboxylate water-reducing agents have been prepared. The pore structure has been determined by scanning electron microscopy (SEM) and nuclear magneti2c resonance (NMR) characterization. In accordance with the concept of fractal dimension, the fractal model has been engaged to quantify the pore volume of Cement Asphalt (CA) mortar, Through the application of the Pearson correlation coefficient coupled with regression analysis, the relationship between fractal dimension and compressive and flexural performance has been analyzed. The results have shown that when the content of polyurethane polycarboxylate is 0.8%, compared to ordinary polycarboxylate, its 28-day compressive and flexural strength is increased by 35.29% and 39.13%, respectively, and the total porosity is reduced by 31.19%, and the proportion of harmful macropores is reduced by 76.02%. The influence of polyurethane polycarboxylates on the pore structure and uniformity of Cement Asphalt (CA) mortar is due to the longer molecular chains of cellulose ether and associated polyurethane. These chains possess the capability to elongate, intertwine, and fuse with a myriad of Cement Asphalt (CA) mortar particles, thereby constructing an intricate three-dimensional network. According to the analysis of fractal dimension and nuclear magnetic resonance test data, the Cement Asphalt (CA) mortar 's pore volume fractal dimension is greater than 3, indicating that the pore structure has fractal characteristics. In addition, as the fractal dimension increases, the correlation coefficients are 0.9113 and 0.9074, respectively, proving that the fractal dimension of pore structure is significantly positively correlated with flexural and compressive strength, This suggests that the fractal dimension of the pore volume acts as a pivotal link, correlating the mechanical properties with the microscale characteristics of Cement Asphalt (CA) mortar .