“…The average compressive strength of PE0.0%, PE0.5%, PE1.0%, and PE1.5% was 140.9 MPa, 140.8 MPa, 137.7 MPa, and 131.7 MPa, respectively (Figure 4); all these values fulfill the requirement of the minimum characteristic strength ø 120 MPa as per the Chinese standard for UHPC (T/CBMF37, 2018). Adding steel fibers (Larsen and Thorstensen, 2020;Liu et al, 2020) or replacing polymer fibers by steel fibers (Yu et al, 2019) in concrete generally increase its compressive strength, while the overall influence of polymer fibers on the compressive strength of concrete is delicate: the fibers can lower the matrix compactness (negative effect) but can also bridge the micro-cracks (positive effect) (Bentur and Mindess, 2007). Figure 4 also summarizes the effect of polymer fiber volume content on the compressive strength based on the data from the literature reporting concrete with fiber over 0.5 vol.% (Al-mashhadani et al, 2018;C xavdar, 2014;Choi et al, 2017;Kakooei et al, 2012;Wang et al, 2019Wang et al, , 2020Yu et al, 2020b).…”