Pore structure reconstruction in waste ceramic powder pervious concrete: Rheological and pozzolanic mechanisms

Abstract

Simultaneously optimizing mechanical performance and carbon footprint remains a central challenge in the design of pervious concrete (PC). Waste Ceramic Powder (WCP) provides a promising low-carbon supplementary cementitious material (SCM); however, the micro-mechanisms governing its non-linear strength evolution—characterized by early-age loss and late-age recovery—remain insufficiently understood due to a lack of dynamic, multi-scale evidence. This study elucidates a dual-stage pore structure reconstruction mechanism in WCP-modified PC using rheological testing, non-destructive Low-Field Nuclear Magnetic Resonance (LF NMR), and micro-morphological characterization (SEM, XRD, TGA). Results reveal a counter-intuitive "low porosity–low strength" anomaly at early ages (28 d). This is mechanistically governed by rheology-mediated paste redistribution, where increased yield stress creates "thick coatings but starved bonding bridges," compromising effective load-bearing areas despite reduced porosity. At later ages (56–90 d), active pozzolanic reactions between WCP and portlandite (CH) generate secondary C–S–H gels and drive a distinct “one-increase, three-decrease” transformation (i.e., increasing harmless gel pores while simultaneously reducing all harmful pore categories), markedly densifying the matrix. An optimal WCP replacement level of 20% achieves a 90-day compressive strength 15.34% higher than the control while maintaining excellent permeability (>8 mm/s). This work bridges paste rheology, nanoscale pore evolution, and macroscopic structural response, providing a robust scientific paradigm for the design of high-performance, low-carbon PC.