Anti-cracking and shrinkage performance of sustainable concrete incorporating high-volume natural pozzolans: A case design for high-speed railway concrete slab tracks

This investigation was conducted to examine the effect of the designed composite agent (DCA) on the shrinkage performance of the concrete high-volume natural pozzolans (PHVNC). Based on an economic-cost analysis, it was determined that natural pozzolans (NP) were a suitable replacement for fly ash (FA) in the production of sustainable concrete for high-speed railway concrete slab track design. The results confirmed that the inclusion of DCA effectively improved the earlyage shrinkage performance of PHVNC with 30% or 50% NP content. As a result, the concrete containing high-volume NP and DCA (PHVNDC) exhibited a smaller crack density compared to PHVNC, and even outperformed concrete with a high volume of FA (PHVFC). In terms of the effect of DCA on the drying shrinkage performance of mixes containing NP, a similar trend was observed, where the mixes that included both NP and DCA exhibited lower levels of dry shrinkage and mass loss at 28 days compared to mixes with either NP or FA. The results from phase transformation and microstructure analysis further indicated that adding DCA can enhance the mechanical and shrinkage performance of the mixes containing high-volume NP. This enhancement is attributed to the optimization of the hydration reaction rate, increased production of hydration products, and an overall improvement in the microstructure performance of the mixes with NP. Hence, DCA can serve as a valuable support in preserving the characteristics of NP-based mixtures, making it a valuable discovery for implementing high-volume NP in practical engineering projects with abundant NP resources.