Abstract
Substitute Ordinary Portland Cement (OPC) by biomass fly ash (BFA) reduce the environmental impact produced by cement-based materials, and at the same time, decreased the economic and environmental burden associated with the landfilling of this waste. This study aims to evaluate the recycling of BFA as supplementary cementitious materials (SCMs) in a commercial screed mortar formulation. Two BFA varieties, both resulting from fluidized bed combustion of forest residues, were used to replace 17, 50, and 67 wt.% of OPC. The influence of simple pre-treatment processes of the BFA, such as sieving and grinding, in the fresh and hardened state properties of the mortars, was evaluated. The BFAs were characterized in terms of chemical (XRF) and mineralogical (XRD) composition, particle size distribution (laser diffraction-COULTER) and morphology (SEM). The prepared formulations were characterized in terms of workability, mass loss upon curing, bulk density, sorptivity (by immersion and capillary), flexural and compressive strength and durability to 25 freeze–thaw cycles. Both of the BFAs are potential SCMs. Substitution of 17 wt.% OPC with BFA complied with the product technical requirements for compressive and flexural strength (10 and 3 MPa, respectively), with the ground and sieved and just sieved BFAs perform slightly better than the as-received BFA.
Highlights
BFA2 is mainly composed by the same oxides but the amounts are different: 32.34 wt.% CaO, 21.79 wt.% SiO2, 9.28 wt.% K2O and 8.74 wt.% Al2O3
The SO3 amount is slightly higher for BFA1 and slightly smaller for BFA2
The larger particles existing in biomass fly ash (BFA) result, essentially, from the contamination with bottom sand, which explains the smaller SiO2 amount in the sieved fraction (
Summary
The production of Ordinary Portland Cement (OPC) involves: (i) very high temperatures, usually above 1450 ◦C, an enormous energy consumption [1,2,3]; (ii) the utilization of large quantities of non-renewable natural raw materials [1,3], mostly limestone and dolomite (as calcium sources) and marls, clays or shale (as silica and alumina sources) [1]; (iii) generation of particulate material [1,3], starting in mining process [1]; and (iv) significant CO2 emissions [1,2,3,4,5,6]. Being mostly generated on the calcination (decomposition of limestone) [1,2,6] and from the consumption of electricity (air coolers and ball mills) [1,2] and fossil fuels (preheater, calciner and kiln) [1,2,6]. Worldwide those emissions are around 8 to 10% of the anthropogenic global CO2 emissions, and it is expected to grow [5]. Producers are being confronted to reduce their environmental impact, which has led to many studies aimed at reducing the environmental footprint of cement-based materials
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