Mortar with Internal Curing Bottom Ash for Sand Shortage and Proper Curing

Using industrial waste such as bottom ash (BA) is a potential alternative to using sand for tackling the current shortage of natural resources in the construction industry. This, along with the internal curing concept, enables proper curing inside and out, especially for low water-to-cement (w/c) ratio concrete, which has low permeability. The current work investigated the flow, compressive strength, heat flow, and microstructure characteristics (using an electron microprobe analysis, EPMA) to evaluate the use of internal curing BA as a sand-replacing material. Partial replacements of fine aggregate with BA were prepared in five different mortars (0, 20%, and 45%), with a fixed water-to-cement (w/c) ratio of 0.35. Consequently, the heat peak increased when using BA compared to the control mortar, indicating a higher hydration rate. The compressive strength of mortar with BA exceeded 50–60 MPa by 28 days. On the microstructural level, BA showed an increase in the volume fraction of small pores from 3 to 50 mm. Moreover, the content of Ca(OH)2 in the mortar with BA increased from 3 to 28 d by enhancing the hydration. This study shows the possibility of valorizing BA as a sand replacement in the internal curing of concrete with a low w/c ratio.

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