Improving the carbonation resistance of Na2CO3-activated slag mixes via the use of reactive MgO and nucleation seeding

Abstract

When exposed to carbonation, Na2CO3-activated slag (SCAS) concrete demonstrated 53% mass loss and 57% reduction in compressive strength due to the decalcification of C-(A)-S-H.Improvements in the carbonation resistance of SCAS mixes via the inclusion of hydromagnesite seeds (S) and reactive MgO (M) were reported in this study. The conversion of MgO into hydrated magnesium carbonates (HMCs) and the additional formation of hydrotalcite were observed in the presence of these additives. HMCs contributed to the binding network and limited the diffusion of CO2 into the sample. The decalcification of C-(A)-S-H was retarded via the absorption of CO2 in hydrotalcite, producing huntite. These changes in the reaction kinetics of samples involving M and S enabled the retention of hydration products and formation of additional carbonation products, leading to denser microstructures and ~40% increase in compressive strength after carbonation, which was ~10 times higher than the control sample (58 vs. 6 MPa).

Advances in the hydration of reactive MgO cement blends incorporating different magnesium carbonates

“…BSE imaging was also performed to investigate the sample microstructure and the formed phases within the prepared samples. The details of sample preparation for BSE analysis were presented in [43].…”

Mechanical and microstructural changes in reactive magnesium oxide cement-based concrete mixes subjected to high temperatures

“…The incorporation of microfibres is also postulated to enhance the structural stability by delaying the cracking initiation within the carbonation products. These topics have been completed [25,90] or are being investigated by the co-authors.…”

Enhancing the performance of MgO-activated slag-fly ash mixes by accelerated carbonation

“…The 29 Si MAS NMR spectra of the 0FA, 12 FA and 24FA precursor mixes are presented in Fig. [34,46,47,51], the 0FA precursor material presented two broad amorphous resonances at δiso of -75±2 and 110±3 ppm, relating to the Q 0 /Q 1 units in the glass-like unhydrated slag and the Q 4 environments in amorphous silica (SiO2), respectively. The 29 Si NMR spectra of the 12FA and 24FA precursor materials revealed two additional broad resonances at δiso of -90±2 and -109±2 ppm, which together represented a distribution of Q 4 moieties in FA [49,52].…”

“…Further improvements in the performance of the developed RM activated-GGBS-FA samples were achieved via the conversion of the unhydrated MgO into hydrated magnesium carbonates (HMCs) such as rosette-like hydromagnesite (4MgCO3•Mg(OH)2•4H2O), needlelike nesquehonite (MgCO3•3H2O), and acicular artinite (MgCO3•Mg(OH)2•3H2O) [31,32]. This was enabled by subjecting the samples to elevated concentrations of CO2 during curing [33,34]. The utilization of high concentrations of CO2 in the carbonation process not only led to a reduction in porosity and provided a binding network facilitated by the formation of HMCs, thereby improving sample performance [21,30,31,35,36], but also shed light on the feasibility of reducing CO2 emissions asscociated with cement production.…”