Comparison of rheology and durability of geopolymer and Portland cement concrete at the same strength levels

Geopolymer concrete (GC) is more low-carbon and environmentally friendly than ordinary Portland cement concrete (OPCC). However, there is still a lack of comparative studies on the differences between these two in terms of rheology and long-term durability, when the design strengths are at the same levels to guide engineers. In this study, a comparative study between GC and OPCC of three strength levels (C20, C30, and C40) was carried out in terms of rheological, mechanical, and durability properties. It was found that the compressive strength of GC could be adjusted more substantially by adjusting slag content compared to OPCC without significantly deteriorating the flowability, and three strengths of concrete ranging from C20, C30, and C40 were prepared. A combined analysis of mass loss rate, dynamic elastic modulus loss rate, and ultrasonic velocity change showed that the higher strength level (C40) GC had better freeze-thaw cycle resistance than OPCC. The compressive strength of C40 level GC after more than 140 days of sulfate attack is also superior to that of OPCC. However, there is no significant advantage in the sulfate erosion resistance of GC under short-time sulfate erosion. In addition, compared with OPCC, the variation of rheological parameters has a greater impact on the freeze-thaw cycle resistance and sulfate erosion resistance of GC, saying that reasonable control of the workability of GC is more important than OPCC to ensure durability. The research findings can be a valuable reference for GC's performance-optimized design and facilitate its potential exploitation in concrete engineering applications with various strength requirements.