Use of bioethanol byproduct for supplementary cementitious material production

Corn stover has the potential for use as a supplementary cementitious material (SCM) for concrete. The impact of distilled water and dilute acid pretreatments and post-treatments on the pozzolanic reactivity of corn stover ash (CSA) was studied. Additionally, the potential use of a bioethanol byproduct called high lignin residue (HLR) for SCM production was examined. Pretreated CSA and high lignin residue ash (HLRA) increased the early reactivity of cement paste when used as 20% replacement of cement in the system whereas unpretreated CSA was found to severely suppress the hydration reaction. The highest compressive strength was obtained from samples containing HLRA

Influence of Cementitious System Composition on the Retarding Effects of Borax and Zinc Oxide

This research investigated the retarding impact of zinc oxide (ZnO) and borax (Na2[B4O5(OH)4]·8H2O) on hydration of Portland cement, calcium aluminate cement (CAC), and calcium sulfoaluminate cement (CSA). Heat of hydration of cement paste samples with and without ZnO and borax was used to measure the influence of ZnO and borax on the set time of these cementitious systems. It was found that both ZnO and borax can retard the set time of Portland cement systems; however, ZnO was shown to be a stronger set time retarder than borax for these systems. ZnO did not show any retarding impact on CAC and CSA systems while addition of borax in these systems prolonged the set time. It was concluded that ZnO does not poison the nucleation and/or growth of CSA and CAC hydration products. We suggest that borax retards the cement set time by suppressing the dissolution of cement phases

Utilization of Treated Agricultural Residue Ash as Sodium Silicate in Alkali Activated Slag Systems

This study investigated the influence of rice straw ash (RSA), rice husk ash (RHA), and silica fume (SF) on alkali activated slag (AAS) systems. RSA, RHA, and SF were treated with sodium hydroxide to improve their reactivity in AAS systems. Although addition of SF in AAS systems increased compressive strength, samples containing RSA or RHA had higher compressive strength than those having SF. Treated RSA or RHA further increased compressive strength of AAS samples. It was shown that samples containing treated ash samples had similar compressive strength to those made with sodium silica activator. Therefore, it is suggested that treated ash samples could be used as alternative sources of silica for AAS. Drying shrinkage of AAS samples increased considerably when treated RSA or RHA were used as partial replacement of slag. This could be attributed to higher silica modulus (SiO2/Na2O) ratio of samples containing treated ash, which in turn would lead to a finer pore size structure compared to control samples. However, SF significantly reduced drying shrinkage of AAS. This could be because SF reduces the permeability and porosity of AAS samples

Thermochemical pretreatments for agricultural residue ash production for concrete

Agricultural residue ash is known to be a very reactive source of supplementary cementitious material (SCM) for use in concrete. The influence of thermochemical pretreatments on the reactivity of agricultural residue ash (ARA) for use as an SCM was studied. It was shown that pretreatments are effective in partial removal of alkali metals and other impurities out of both wheat straw and rice straw leading to ARA with lower loss on ignition (LOI), higher internal surface area, and higher amorphous silica content than that of unpretreated ARA. It was shown that the ash alkali content correlated with the ash LOI and amorphous silica content. When used at a cement replacement rate of 20% by mass, pretreated ARA accelerated the hydration of cement paste samples while unpretreated ARA retarded the cement hydration. Pretreatments were found to increase ARA reactivity as measured by calcium hydroxide content reduction with time. ARA increased compressive strength of mortar samples by 25% when used as 20% replacement of cement in the samples. It was found that the calcium hydroxide content of paste samples and mortar compressive strength were correlated to the amorphous silica content of the ash