Abstract
Amorphous silica and alumina of metakaolin are used to adjust the bulk composition of black (BSS) and white (WSS) steel slag to prepare alkali-activated (AAS) mortars consolidated at room temperature. The mix-design also includes also the addition of semi-crystalline matrix of river sand to the metakaolin/steel powders. The results showed that high strength of the steel slag/metakaolin mortars can be achieved with the geopolymerization process which was particularly affected by the metallic iron present into the steel slag. The corrosion of the Fe particles was found to be responsible for porosity in the range between 0.1 and 10 µm. This class of porosity dominated (~31 vol %) the pore network of B compared to W samples (~16 vol %). However, W series remained with the higher cumulative pore volume (0.18 mL/g) compared to B series, with 0.12 mL/g. The maximum flexural strength was 6.89 and 8.51 MPa for the W and B series, respectively. The fracture surface ESEM observations of AAS showed large grains covered with the matrix assuming the good adhesion bonds between the gel-like geopolymer structure mixed with alkali activated steel slag and the residual unreacted portion. The correlation between the metallic iron/Fe oxides content, the pore network development, the strength and microstructure suggested the steel slag's significant action into the strengthening mechanism of consolidated products. These products also showed an interesting adsorption/desorption behavior that suggested their use as coating material to maintain the stability of the indoor relative humidity.
Highlights
Due to their industrial scale of production, fly ash and slag are presented as low life cycleCO2 emissions, environmentally-friendly and sustainable solid precursors for alkali-activated cement, mortar and concrete [1,2]
Aluminum cations incorporated in C–S–H gel were found to improve the resistance to carbonation
Myers et al [1] identified in granulated blast furnace slag three distinct tetrahedral Al sites: Q3 (1Al), Q4 (3Al) and Q4 (4Al) which are indicative on the cross-linking degree in the calcium aluminosilicate hydrate (C–(N–)A–S–H) gels and the presence of additional highly polymerized aluminosilicate products
Summary
Due to their industrial scale of production, fly ash and slag are presented as low life cycleCO2 emissions, environmentally-friendly and sustainable solid precursors for alkali-activated cement, mortar and concrete [1,2]. In the present study two different steel slags were used with metakaolin and sand to generate an aluminosilicatic matrix via alkali activation. This aluminosilicatic matrix was designed to attain a good chemical stability taking into account the existing models on mixed C–S–H (CaO–SiO2 –H2 O) structure. Low value of SiO2 /Na2 O is consistent with the increasing number of NBO sites where SiQ2 and SiQ1 structural units were preferentially formed from silicate chains, dimers and monomers. High SiO2 /Na2 O molar ratio generates a decreasing number of NBO sites with structures consisting principally of SiQ3 and SiQ4 structural units which form silicate 3D frameworks and sheets [7]. When CaO is present, C–S–H is the principal hydration product and primary binding phase; it can be described as a single chain structure that faces polymerization decreasing with the increase of Ca content [8]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
