Rice husk ash (RHA) effectiveness in cement and concrete as a function of reactive silica and fineness

• Published in: Cement and concrete research Vol. 61-62; pp. 20 - 27
• Main Authors: Antiohos, S.K., Papadakis, V.G., Tsimas, S.
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier Ltd 01.07.2014; Elsevier
• Subjects: Amorphous material (B); Applied sciences; Ashes; Blended; Blended cement (D); Buildings. Public works; Byproducts; Cement concrete constituents; Cements; Concretes; Concretes. Mortars. Grouts; Exact sciences and technology; Fineness; Fineness (A); General (composition, classification, performance, standards, patents, etc.); Materials; Mechanical properties (C); Properties and test methods; Properties of anhydrous and hydrated cement, test methods; Rice husk ash; Silicon dioxide; Specific surface; Strength of materials (elasticity, plasticity, buckling, etc.); Structural analysis. Stresses; Rice husk ash; Mechanical properties (C); Blended cement (D); Amorphous material (B); Fineness (A); Amorphous material; Mortar; Construction materials; Concrete mix design; Concrete workability; Mechanical properties; Compressive strength; Experimental study; Silica; Corrosion resistance; Fineness modulus; Reactivity; Pozzolanic reaction; Chlorides; Cement; Husk (fruit); Rice
• ISSN: 0008-8846; 1873-3948
• DOI: 10.1016/j.cemconres.2014.04.001

Research on ash from burning of rice husks (RHA) has already demonstrated that it is one of the most promising supplementary cementing materials (SCM), given its high specific surface and great amount of silica soluble in alkaline conditions. Indeed, RHA could be a product of added value if it wasn't for its limited availability and periodically high residual carbon content, factors inhibiting its wider use in building materials. Most of the published work has exploited the effectiveness of RHA of very high specific surface and reactive silica, without really investigating the effect of these factors with respect to mechanical and durability characteristics of the derived cement and concrete. This is of crucial importance since someone could falsely rate RHA of moderate fineness and chemical reactivity as potentially reject, constituting thus a significant portion of this by-product unutilised. Reactive silica and fineness effect was assessed in this study by examining two different RHAs, both in blended cement and concrete level. It was found out that RHA is a material extremely “sensitive” to fineness changes; the higher being the fineness the more positive is the effect of RHA inclusion in the mix. Not surprisingly, active silica holds a key role especially for later-age strength gain, indicating that pozzolanic effect takes over from the “physical” effect of the pozzolan as hydration evolves. Pozzolanic potential, strength development of mortars and concrete, efficiency factors (k-values) estimation and resistance against chloride penetration are part of the testing performed and reveal the importance of the binary action of RHA in producing competitive blended cement and concrete.