Mechanisms of whisker-toughened hybrid fiber concrete based on fractal dimension and radar model

The inadequate resistance of concrete to flexural and bending forces results in cracking and other forms of damage in harsh natural environments. These cracks significantly reduce the lifespan of concrete structures. To address this issue, the incorporation of fibers is considered an effective method for enhancing the performance and durability of concrete in extreme conditions. This study aims to investigate the properties of different types of fibers, namely basalt fibers (BF), reticulated polypropylene fibers (RP), and hybrid fiber (BF-RP), in ordinary concrete (OC). Additionally, CaCO3 whiskers (CW) were added to form the CW-BF-RP fiber system. The mechanical properties and microstructure of the hybrid fiber concrete with CW were thoroughly examined. The results indicated that the inclusion of BF, RP and BF-RP resulted in an improvement in flexural strength. Moreover, the performance of the concrete exhibited an increasing trend followed by a decreasing trend as varying amounts of CW were added to the hybrid fibers. The best performance was achieved with a CW dosage of 2.5 %, which led to a 9.22 % increase in compressive strength, a 42.80 % increase in flexural strength, and a 15.28 % increase in relative dynamic elastic modulus compared to OC. The addition of CW effectively enhanced the hydration process during the initial reaction stage. Of those, a small portion of CW had limited chemical activity during the hydration process. The enhanced hydration products strengthened the bond between BF, RP, and the matrix, resulting in a multi-stage crack-resistant fiber system of CW-BF-RP. The presence of CW also improved the composition of pores in the hybrid fiber concrete, reducing the proportion of capillary and harmful pores to 83.69 % and 7.61 % respectively, with favorable pore characteristic values. The quality of the pore composition in the concrete was accurately assessed by the maximum pore fractal dimension (Dmax), while the overall performance of the concrete was evaluated using the geometric mean value (fn) of the radar chart model, both of which reached its optimal value at a 2.5 % CW content, with values of 2.9521 for Dmax and 0.01728 for fn.