Optimizing Fresh and Hydration Properties of Concrete with Supplementary Cementitious Materials: A Critical Review on Silica Fume and Rice Husk Ash

Abstract Due to their pozzolanic activities and sustainability advantages, the addition of supplementary cementitious materials such as rice husk ash (RHA) and silica fume (SF) in concrete has received considerable attention. Interestingly, the present review integrates and compares the impact of RHA and SF on fresh as well as hydration properties, with a particular focus on underpinning mechanisms and dosage-sensitive responses, alongside processing-related impacts that are fragmented or marginalized in existing literature. This review, therefore, thoroughly summarizes the effect of RHA and SF on the fresh properties such as workability, setting time, and consistency, as well as hydration properties such as heat of hydration, reaction kinetics, and calcium silicate hydrate (CSH) formation. Applying a structured methodology, studies investigating the effect of particle size, replacement levels, and processing techniques were reviewed. The results show that SF, owing to lower particle size (0.1–0.3 μm) and high amorphous silica content ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" alttext="greater than 85 percent sign" display="inline" overflow="scroll"> <mml:mtext>&gt;</mml:mtext> <mml:mn>85</mml:mn> <mml:mo>%</mml:mo> </mml:math> ), decreased slump by 20–30% at 10% replacement and needed superplasticizers for slump retention. RHA, especially when ground to <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" alttext="less than 10 mu normal m" display="inline" overflow="scroll"> <mml:mtext>&lt;</mml:mtext> <mml:mn>10</mml:mn> <mml:mtext> </mml:mtext> <mml:mi>μ</mml:mi> <mml:mi mathvariant="normal">m</mml:mi> </mml:math> , has higher water demand, but results in workable mixture at 5%–10% replacement when combined with admixtures. SF can accelerate the hydration reaction in early stages and promote the peak heat release temperature to advance 5°C–10°C, while RHA can enhance the later-age hydration through a secondary pozzolanic effect. SF lowers calcium hydroxide content by 4.4% with 5% replacement leading to better long-term stability, while RHA reduces pore size and promotes CSH formation.