Influence of ultrafine slag and sulfate activation on the strength, durability and microstructural performance of high‐volume fly ash concrete containing recycled plastic waste aggregate

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Abstract The present research aims to explore a more reliable way of utilizing a high volume of fly ash in concrete to meet global needs without causing any adverse effect on the environment. In the initial stage of the study, the engineering performance of concrete containing binary systems of high‐volume fly ash (HVFA) and ternary systems of HVFA and alccofine (AL) was examined. In the later stage, the effect of plastic waste aggregate addition and sulfate activation on the strength, durability, and morphology of concrete was determined for both binary and ternary systems of HVFA and AL. The laboratory experimental program involved heat of hydration, compressive strength, flexural strength, water absorption, rapid chloride penetration, TGA, XRD, and SEM analysis. Experimental investigations revealed that the mechanical properties of the HVFA concrete decreased with an increase in fly ash content. The 28‐day compressive strength reduced up to 41.6% for the mix containing 50% FA when compared with normal concrete. However, the addition of reactive AL increased the pozzolanic reaction and formed denser hydration products that densified the matrix, resulting in improved mechanical properties. The addition of 10% AL reduced the chloride permeation to about 26% for the mix containing 50% FA. The denser particle packing reduced the capillary pores near the surface, lowering the water and chloride permeation. The inclusion of plastic aggregate reduced the early age strength properties; however, in the later ages, denser hydration products formed around the boundary of aggregates, which was evident from the morphology analysis. At 28 days, both the control mix and the mix containing 40%FA:10% AL:20% plastic aggregate exhibited the highest compressive strength, ~47 and 42 MPa compared with the other mixtures. In the HVFA mixes, the FA particles were merely acting as pore fillers and remained dormant in the early ages. The addition of AL along with sulfate activation produced more nucleation sites, which then formed C‐S‐H and C‐A‐S‐H. Consequently, the improvement in the microstructure resulted in better mechanical and durability properties.