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This study assesses the viability of using an agro-industrial by-product, rice husk ash (RHA) from a Colombian rice company's combustion facility, as a total replacement for the commercial sodium silicate ordinarily used in alkaliactivated binders. Fly ash (FA), granulated blast furnace slag (GBFS) and binary 50FA:50GBFS blended pastes were activated with a mix of sodium hydroxide and either sodium silicate or one of two types of RHA. The pastes were characterised for strength, mineralogy and microstructure. The findings showed that the agro-industrial by-product can be used to yield alkali-activated materials with 7-day mechanical strengths on the order of 42 MPa. The study confirmed that both amorphous silica and part of the crystalline silica present in RHA participate in the alkaline activation process, providing the alkalinity is suitably adjusted.

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Manuscript Code: 0291 Date of reception/acceptation: 01jan2014/01aug2014Resumen Este estudio se propuso la producción de un material cementicio alternativo de bajo impacto ambiental a partir de la evaluación de dos subproductos de la combustión del carbón. Se elaboraron dos cementos híbridos basados en la activación alcalina de una ceniza volante (FA) y una escoria de parrilla (BS) y adicionados con cemento portland (OPC) hasta en un 30%. FA y BS contienen hasta un 16% de inquemados. Para la optimización de la resistencia a la compresión se utilizó la Metodología de Superficie de Respuesta (MSR). El geopolímero BS alcanzo alta resistencia a la compresión (>100 MPa a 28 días) y el geopolímero FA reporto 30 MPa al aplicar curado térmico. La adición de OPC contribuyo a modificar el método de curado. En el caso del hibrido basado en FA (HFA), se observó un incremento significativo en la resistencia a niveles hasta de 65 MPa a 28 días sin aplicar el curado térmico. AbstractThis study focuses on the production of an alternative cementitious material with low environmental impact through the evaluation of two-coal combustion by-products. Hybrid cements based on the alkali activation of fly ash, (FA) and boiler slag (BS) blend with a proportion of Portland cement (OPC) up to 30% were produced. FA and BS contain an unburned material up to 16%. Response Surface Methodology (RSM) was used to optimize the compressive strength. BS geopolymer achieved high compressive strength (>100 MPa at 28 days) and FA geopolymer reached 30 MPa with thermal curing. The addition of OPC helped modify the curing method. In the case of hybrid based on FA (HFA), there was a significant increase in the compressive strength with levels ranging up to 65 MPa at 28 days without requiring a thermal curing.Palabras claves: Cemento híbrido, ceniza volante, escoria de parrilla, materiales activados alcalinamente, baja huella de carbono.