Pervious concrete pavers are built to do two jobs at once, carry loads and let stormwater drain through. A research team recently tested how far manufacturers can push cement replacement using fly ash, an industrial byproduct from coal-fired power plants, while still producing pavement blocks that perform in the field.

The study evaluated pervious concrete pavement blocks made with Portland Composite Cement and Class C fly ash from the Amurang power plant in North Sulawesi. Researchers compared two production-style approaches. “Type A” mixes used a 1:2:1 binder-to-coarse-to-fine aggregate ratio with 10-millimeter maximum coarse aggregate and 80-millimeter-thick blocks. “Type B” mixes eliminated fine aggregate and used a 1:3 binder-to-coarse aggregate ratio with coarse aggregate up to 20 millimeters and 60-millimeter-thick blocks. Both held a 0.3 water-to-binder ratio and used a Type F superplasticizer for casting on paving block machinery.

For mason contractors and producers who install or supply concrete pavers, the takeaway is clear: gradation matters. In the Type A mixes, compressive strengths for higher fly ash replacement levels were described as relatively stable, and one mix reached 23 MPa at 28 days, meeting Indonesia’s SNI 03-0691-1996 Quality B criteria for parking lot paving blocks. The coarser, no-fines Type B approach topped out around 9 MPa at 28 days, which the researchers said limits those blocks to pedestrian paths, gardens, and other light-duty uses.

Water infiltration also shifted with mix design. In one comparison, infiltration dropped from 5.37 millimeters per hour for a 100 percent cement control block to 2.71 millimeters per hour at 60 percent fly ash replacement, showing how added paste and densification can pinch off pore channels. On the sustainability side, the study framed high-volume fly ash blocks as a path to lower carbon intensity, but flagged a real-world hurdle contractors see all the time: fly ash chemistry varies by source, so up-front testing and screening is essential before scaling production.

Read the full, original article from Bioengineer.org here.