Physical, Compressive Strength, and Microstructural Characteristics of Alkali-Activated Engineered Composites Incorporating MgO, MWCNTs, and rGO
Abstract
:Featured Application
Abstract
1. Introduction
2. Experimental Program, Materials, Mix Designs, Mix Preparation, and Test Methods
2.1. Materials
2.2. Mix Proportions
2.3. Mixing, Dispersion of MWCNT/rGO, Casting, and Curing of Specimens
2.4. Test Methods
3. Results and Discussion
3.1. Physical Characteristics: Slump Flow, Flow Time, Flow Velocity and Density
3.2. Hardened Characteristics: Compressive Strength and UPV
3.2.1. Influence of MgO, MWCNT and rGO on Compressive Strength Development
3.2.2. Influence of MgO, MWCNT, and rGO on 28-Day UPV
3.3. Microstructural Characteristics
3.3.1. SEM/EDS Analyses
3.3.2. XRD Analysis
3.3.3. Fourier Transform Infrared Spectroscopy (FTIR) Analysis
4. Conclusions
- The AAEC mixes satisfied the EFNARC [77] criteria for self-consolidating ability. The initial and final setting times ranged from 190 min to 311 min and from 230 min to 369 min, respectively;
- The ternary (fly ash C ‘FA-C’ + FA-F + ground granulated blast furnace slag ‘GGBFS’) mixes exhibited higher slump flows than their binary (FA-C + GGBFS) counterparts due to having a lower FA-C/GGBFS content, while the activator/reagent 2 (calcium hydroxide: sodium sulfate = 2.5:1) mixes resulted in higher slump flows due to having lower silica ratio than the mixes that used reagent 1 (calcium hydroxide: sodium metasilicate = 1:2.5);
- The slump flow of the AAECs decreased with an increase in the MWCNT/rGO content, with a few exceptions depending on mix/reagent types, while the addition of MgO showed a less significant decrease. The higher surface area or water affinity of MgO/MWCNTs and higher agglomeration tendency of MWCNTs/rGO were considered contributing factors;
- All AAECs achieved a 28-day compressive strength ranging from 26.0 MPa to 48.5 MPa > 18 MPa and satisfied the criteria for structural concrete. Control binary AAECs obtained higher 28-day compressive strengths than their ternary counterparts, due to the dominant formation of C-A-S-H/C-S-H compared to the dominant formation of amorphous N-C-A-S-H/N-A-S-H in their ternary counterparts. Binary mix B2 with reagent 2 exhibited a 22% higher 28-day compressive strength than its ternary counterpart T2 due to having higher FA-C and GGBFS contents;
- The AAECs with reagent 2 generally produced a higher compressive strength compared to their reagent 1 counterparts due to the formation of additional C-S-H gel (in addition to C-A-S-H/N-C-A-S-H or C-A-S-H/C-S-H) and more compact microstructures, as per XRD-SEM analysis, which showed the presence of sharper crystalline peaks of quartz and calcite;
- The addition of 5% MgO increased the 28-day compressive strength (by 19~25%), and UPV exhibited potential self-healing capability due to the formation of well-dispersed fine Mg(OH)2, hydrotalcite, and M-S-H, which compensated for volume shrinkage and refined the matrix pore size, as confirmed from XRD-SEM/EDS;
- The 28-day compressive strength increased with the increase in MWCNT/rGO content up to 0.3%, indicating it as an optimum dosage. The decrease in strength at higher dosages (>0.3% wt) of MWCNTs/rGO can be compensated for/reversed by using MgO-MWCNT/rGO combinations that show beneficial effects of MgO addition;
- The addition of 0.3% MWCNTs and rGO increased the compressive strength by 9% and 14.8%, respectively, showing a higher effectiveness of rGO in improving strength. The increase in compressive strength and UPV was attributed to the uniform dispersion and good MWCNT-matrix bond bridging cracks (with no newly formed MWCNT-induced reaction products), while the formation of additional zeolites caused matrix densification with the addition of rGO, as confirmed from the SEM/EDS analysis. Proper dispersion of the MWCNTs/rGO is important to avoid agglomeration and negative effects on the workability, mechanical, and micro-structural properties;
- Fourier transform infrared spectrometer (FTIR) analysis suggested the formation of an aluminosilicate network in AAECs with a higher concentration of Si-O-Si bonds, indicating a more stable structure. A lower % of transmittance at 3380 cm−1 in binary AAECs with reagent 2 and 0.6% MWCNTs (B2C6), compared to their counterpart with 5% MgO (B2M5), confirmed a weaker bond and lower compressive strength even though MWCNTs can act as nucleation sites and accelerate polymerization;
- The UPV values ranged from 3067 m/s to 4068 m/s, showing an increase with the addition MWCNTs/rGO/MgO, with the highest values (19% higher) being observed for MWCNT-incorporated AAECs. This is an indication of a higher capacity to transmit ultrasonic waves, better conductivity, and a better self-sensing ability. A linear correlation revealed an increase in compressive strength with an increase in the UPV content of AAEC mixes at 28 days;
- This research demonstrated the viability of producing ambient-cured powder-based AAECs, as more green and sustainable alternatives to conventional ECCs, that incorporate carbon-nano materials and MgO additives, as they have satisfactory workability, mechanical, and microstructural characteristics. The developed multi-functional AAECs have the potential to be used for structural applications and to produce high-performance resilient durable bridge-building infrastructures with self-healing/sensing and 3-D printing potentials.
Author Contributions
Funding
Institutional Review Board Statement
Informed Consent Statement
Data Availability Statement
Acknowledgments
Conflicts of Interest
References
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Chemical Composition (%) | Fly Ash Type C (FA-C) | Fly Ash Type F (FA-F) | Ground Granulated Blast Furnace Slag (GGBFS) | Silica Sand | HRWRA | Magnesium Oxide (MgO) |
---|---|---|---|---|---|---|
SiO2 | 36.53 | 55.66 | 35.97 | 99.70 | 2.02 | |
Al2O3 | 18.26 | 22.09 | 9.18 | 0.14 | 6.124 | |
Fe2O3 | 5.66 | 4.26 | 0.50 | 0.016 | 0.94 | |
CaO | 20.97 | 7.97 | 38.61 | 0.01 | 2.40 | |
MgO | 5.08 | 1.16 | 10.99 | 0.01 | 92.26 | |
K2O | 0.68 | 1.49 | 0.36 | 0.04 | - | |
Na2O | 4.04 | 4.10 | 0.28 | 0.01 | - | |
MnO | 0.03 | 0.03 | 0.25 | 0.00 | - | |
TiO2 | 1.26 | 0.61 | 0.39 | 0.00 | - | |
P2O5 | 0.96 | 0.43 | 0.01 | 0.00 | - | |
L.O.I. | 2.18 | 1.05 | 0.74 | 0.00 | 1.14 | |
pH | 6.00 | |||||
Density (g/cm3) | 2.61 | 2.02 | 2.87 | 2.65 | 1.06 | 3.58 |
Retained on 45µ, % | - | 18.00 | - | 3.00 | ||
Blaine fineness (m2/kg) | 315.00 | 306.00 | 489.30 | - |
AAECs Mix ID. | Total SCMs (Binder *) | MgO/MWCNT/rGO | SCMs | Reagent Component Ratio | R./B | Chemical Ratios (SCMs + Reagent) | |||||
---|---|---|---|---|---|---|---|---|---|---|---|
FA-C | FA-F | GGBFS | SiO2/ Al2O3 | Na2O/ SiO2 | CaO/ SiO2 | Na2O/ Al2O3 | |||||
Four basic AAEC mixes (with 0% MgO/MWCNT/rGO) | |||||||||||
B1 | 1 | 0 | 0.55 | 0 | 0.45 | 1:2.5 | 0.09 | 2.62 | 0.09 | 0.84 | 0.23 |
B2 | 1 | 0 | 0.55 | 0 | 0.45 | 2.5:1 | 0.12 | 2.56 | 0.14 | 1.02 | 0.35 |
T1 | 1 | 0 | 0.25 | 0.35 | 0.40 | 1:2.5 | 0.09 | 2.75 | 0.08 | 0.59 | 0.22 |
T2 | 1 | 0 | 0.25 | 0.35 | 0.40 | 2.5:1 | 0.12 | 2.69 | 0.12 | 0.73 | 0.32 |
Four AAEC mixes with 5% MgO | |||||||||||
B1M5 | 1 | 0.05 | 0.52 | 0 | 0.43 | 1:2.5 | 0.09 | 2.58 | 0.09 | 0.85 | 0.23 |
B2M5 | 1 | 0.05 | 0.52 | 0 | 0.43 | 2.5:1 | 0.12 | 2.51 | 0.14 | 1.03 | 0.35 |
T1M5 | 1 | 0.05 | 0.24 | 0.33 | 0.38 | 1:2.5 | 0.09 | 2.97 | 0.05 | 0.54 | 0.14 |
T2M5 | 1 | 0.05 | 0.24 | 0.33 | 0.38 | 2.5:1 | 0.12 | 2.97 | 0.05 | 0.54 | 0.14 |
Eight AAEC mixes with 0.3% and 0.6% MWCNT | |||||||||||
B1C3 | 1 | 0.003 | 0.55 | 0 | 0.45 | 1:2.5 | 0.09 | 2.62 | 0.09 | 0.84 | 0.23 |
B2C3 | 1 | 0.003 | 0.55 | 0 | 0.45 | 2.5:1 | 0.12 | 2.56 | 0.14 | 1.02 | 0.35 |
T1C3 | 1 | 0.003 | 0.25 | 0.35 | 0.40 | 1:2.5 | 0.09 | 2.75 | 0.08 | 0.59 | 0.22 |
T2C3 | 1 | 0.003 | 0.25 | 0.35 | 0.40 | 2.5:1 | 0.12 | 2.69 | 0.12 | 0.73 | 0.32 |
B1C6 | 1 | 0.006 | 0.55 | 0 | 0.45 | 1:2.5 | 0.09 | 2.62 | 0.09 | 0.84 | 0.23 |
B2C6 | 1 | 0.006 | 0.55 | 0 | 0.45 | 2.5:1 | 0.12 | 2.56 | 0.14 | 1.02 | 0.35 |
T1C6 | 1 | 0.006 | 0.25 | 0.35 | 0.40 | 1:2.5 | 0.09 | 2.75 | 0.08 | 0.59 | 0.22 |
T2C6 | 1 | 0.006 | 0.25 | 0.35 | 0.40 | 2.5:1 | 0.12 | 2.69 | 0.12 | 0.73 | 0.32 |
Eight AAEC mixes with 0.3% and 0.6% rGO | |||||||||||
B1R3 | 1 | 0.003 | 0.55 | 0 | 0.45 | 1:2.5 | 0.09 | 2.62 | 0.09 | 0.84 | 0.23 |
B2R3 | 1 | 0.003 | 0.55 | 0 | 0.45 | 2.5:1 | 0.12 | 2.56 | 0.14 | 1.02 | 0.35 |
T1R3 | 1 | 0.003 | 0.25 | 0.35 | 0.40 | 1:2.5 | 0.09 | 2.75 | 0.08 | 0.59 | 0.22 |
T2R3 | 1 | 0.003 | 0.25 | 0.35 | 0.40 | 2.5:1 | 0.12 | 2.69 | 0.12 | 0.73 | 0.32 |
B1R6 | 1 | 0.006 | 0.55 | 0 | 0.45 | 1:2.5 | 0.09 | 2.62 | 0.09 | 0.84 | 0.23 |
B2R6 | 1 | 0.006 | 0.55 | 0 | 0.45 | 2.5:1 | 0.12 | 2.56 | 0.14 | 1.02 | 0.35 |
T1R6 | 1 | 0.006 | 0.25 | 0.35 | 0.40 | 1:2.5 | 0.09 | 2.75 | 0.08 | 0.59 | 0.22 |
T2R6 | 1 | 0.006 | 0.25 | 0.35 | 0.40 | 2.5:1 | 0.12 | 2.69 | 0.12 | 0.73 | 0.32 |
Eight AAEC with 5%MgO and MWCNT or rGO (0.3% or 0.6%)) | |||||||||||
B2M5C3 | 1 | 0.05/0.003 | 0.52 | 0 | 0.43 | 2.5:1 | 0.12 | 2.56 | 0.14 | 1.02 | 0.35 |
T2M5C3 | 1 | 0.05/0.003 | 0.24 | 0.33 | 0.38 | 2.5:1 | 0.12 | 2.97 | 0.05 | 0.54 | 0.14 |
B2M5C6 | 1 | 0.05/0.003 | 0.52 | 0 | 0.43 | 2.5:1 | 0.12 | 2.56 | 0.14 | 1.02 | 0.35 |
T2M5C6 | 1 | 0.05/0.003 | 0.24 | 0.33 | 0.38 | 2.5:1 | 0.12 | 2.97 | 0.05 | 0.54 | 0.14 |
B2M5R3 | 1 | 0.05/0.006 | 0.52 | 0 | 0.43 | 2.5:1 | 0.12 | 2.56 | 0.14 | 1.02 | 0.35 |
T2M5R3 | 1 | 0.05/0.006 | 0.24 | 0.33 | 0.38 | 2.5:1 | 0.12 | 2.97 | 0.05 | 0.54 | 0.14 |
B2M5R6 | 1 | 0.05/0.006 | 0.52 | 0 | 0.43 | 2.5:1 | 0.12 | 2.56 | 0.14 | 1.02 | 0.35 |
T2M5R6 | 1 | 0.05/0.006 | 0.24 | 0.33 | 0.38 | 2.5:1 | 0.12 | 2.97 | 0.05 | 0.54 | 0.14 |
AAECMix ID | Fresh Density (kg/m3) | Slump Flow (mm) | Slump Flow Time (s) | Slump Flow Velocity (mm/s) | * Hard/Dry Density kg/m3 | * 28-Day UPV (m/s) | * 28-Day Compressive Strength (MPa) |
---|---|---|---|---|---|---|---|
B1 | 1921 | 700 | 4 | 175.0 | 2000 | 3432 | 38.5 |
B2 | 1924 | 705 | 5 | 141.0 | 2032 | 3067 | 40.8 |
T1 | 1930 | 710 | 3 | 236.7 | 2120 | 3231 | 30.5 |
T2 | 1914 | 750 | 3 | 250.0 | 2064 | 3717 | 33.4 |
B1M5 | 1924 | 690 | 5 | 138.0 | 2016 | 3845 | 46.2 |
B2M5 | 1923 | 685 | 5 | 137.0 | 2072 | 3896 | 48.5 |
T1M5 | 1927 | 700 | 4 | 175.0 | 1984 | 3762 | 38.2 |
T2M5 | 1933 | 705 | 4 | 176.3 | 2056 | 3954 | 41.1 |
B1C3 | 1930 | 720 | 4 | 180.0 | 2008 | 3566 | 41.5 |
B2C3 | 1930 | 660 | 4 | 165.0 | 2080 | 3436 | 44.6 |
T1C3 | 1903 | 710 | 3 | 236.7 | 2016 | 3605 | 33.2 |
T2C3 | 1928 | 725 | 3 | 241.7 | 2096 | 4068 | 36.4 |
B1C6 | 1950 | 700 | 5 | 140.0 | 2044 | 3582 | 35.5 |
B2C6 | 1950 | 670 | 5 | 134.0 | 2036 | 3659 | 36.4 |
T1C6 | 1935 | 630 | 4 | 157.5 | 1960 | 3634 | 26.0 |
T2C6 | 1938 | 710 | 4 | 177.5 | 2168 | 3785 | 28.6 |
B1R3 | 1939 | 650 | 4 | 162.5 | 2032 | 3738 | 43.0 |
B2R3 | 1978 | 620 | 4 | 155.0 | 2152 | 3582 | 45.3 |
T1R3 | 1882 | 625 | 3 | 200.0 | 2060 | 3450 | 35.0 |
T2R3 | 1911 | 720 | 3 | 240.0 | 2096 | 3943 | 37.9 |
B1R6 | 1945 | 620 | 4 | 155.0 | 2060 | 3282 | 40.5 |
B2R6 | 1954 | 660 | 4 | 165.0 | 2060 | 3122 | 42.8 |
T1R6 | 1953 | 735 | 3 | 245.0 | 2068 | 3278 | 32.5 |
T2R6 | 1953 | 780 | 2 | 260.0 | 2176 | 3823 | 35.4 |
AAEC Mix ID | Compressive Strength (MPa) * | Strength Change with Respect to Control (%) (+ve: Increase, −ve: Decrease) | ||||||||
---|---|---|---|---|---|---|---|---|---|---|
7 Days | 14 Days | 28 Days | 56 Days | 180 Days | 7 Days | 14 Days | 28 Days | 56 Days | 180 Days | |
Control AAECs | ||||||||||
B1 | 14.3 | 28.5 | 38.5 | 45.8 | 50.3 | 0 | 0 | 0 | 0 | 0 |
B2 | 15.6 | 30.8 | 40.8 | 48.1 | 52.6 | 0 | 0 | 0 | 0 | 0 |
T1 | 14.9 | 22.5 | 30.5 | 37.8 | 42.3 | 0 | 0 | 0 | 0 | 0 |
T2 | 15 | 25.4 | 33.4 | 40.7 | 45.2 | 0 | 0 | 0 | 0 | 0 |
5% MgO Incorporated AAECs | ||||||||||
B1M5 | 20.1 | 35.5 | 46.2 | 52.6 | 56.8 | 40.4 | 24.6 | 20 | 14.8 | 12.9 |
B2M5 | 21.4 | 37.8 | 48.5 | 54.9 | 59.1 | 37.1 | 22.7 | 18.9 | 14.1 | 12.4 |
T1M5 | 20.7 | 29.5 | 38.2 | 44.6 | 48.8 | 38.9 | 31.1 | 25.2 | 18 | 15.4 |
T2M5 | 20.7 | 32.4 | 41.1 | 47.5 | 51.7 | 38.6 | 27.6 | 23.1 | 16.7 | 14.4 |
MWCNT (0.3% and 0.6%) incorporated AAEC | ||||||||||
B1C3 | 17.9 | 30.5 | 41.5 | 49.4 | 53.9 | 25.1 | 7 | 7.8 | 7.8 | 7.1 |
B2C3 | 19.4 | 34.6 | 44.6 | 51.9 | 56.4 | 24 | 12.2 | 9.2 | 7.8 | 7.1 |
T1C3 | 18.4 | 26 | 33.2 | 41.3 | 45.8 | 23.5 | 15.6 | 8.9 | 9.3 | 8.3 |
T2C3 | 18.5 | 28.9 | 36.4 | 44.2 | 48.7 | 23.4 | 13.8 | 9 | 8.6 | 7.7 |
B1C6 | 15.3 | 29.5 | 35.5 | 44.2 | 48.4 | 7 | 3.5 | −7.8 | −3.5 | −3.8 |
B2C6 | 16.6 | 31.8 | 36.4 | 45.3 | 50.3 | 6.4 | 3.2 | −10.8 | −5.8 | −4.4 |
T1C6 | 15.9 | 20.2 | 26 | 36.2 | 40.4 | 6.7 | −10.2 | −14.8 | −4.2 | −4.5 |
T2C6 | 16 | 21.1 | 28.6 | 39.1 | 42.7 | 6.7 | −16.9 | −14.4 | −3.9 | −5.5 |
rGO (0.3% and 0.6%) incorporated AAEC | ||||||||||
B1R3 | 18.8 | 33 | 43 | 50.3 | 54.8 | 31.5 | 15.8 | 11.7 | 9.8 | 8.9 |
B2R3 | 20.1 | 35.3 | 45.3 | 52.6 | 57.1 | 28.8 | 14.6 | 11 | 9.4 | 8.6 |
T1R3 | 19.4 | 27 | 35 | 42.3 | 46.8 | 30.3 | 20 | 14.8 | 11.9 | 10.6 |
T2R3 | 19.5 | 29.9 | 37.9 | 45.2 | 49.7 | 30.1 | 17.7 | 13.5 | 11.1 | 10 |
B1R6 | 16.3 | 30.5 | 40.5 | 47.8 | 52.3 | 14 | 7 | 5.2 | 4.4 | 4 |
B2R6 | 17.6 | 32.8 | 42.8 | 50.1 | 54.6 | 12.8 | 6.5 | 4.9 | 4.2 | 3.8 |
T1R6 | 16.9 | 24.5 | 32.5 | 39.8 | 44.3 | 13.4 | 8.9 | 6.6 | 5.3 | 4.7 |
T2R6 | 17 | 27.4 | 35.4 | 42.7 | 47.2 | 13.4 | 7.9 | 6 | 4.9 | 4.4 |
5% MgO and MWCNT or rGO (0.3% and 0.6%) incorporated AAECs | ||||||||||
B2M5C3 | 23.8 | 40.2 | 50.9 | 57.3 | 61.5 | 52.4 | 30.5 | 24.8 | 19.1 | 16.9 |
T2M5C3 | 23.1 | 34.8 | 43.5 | 49.9 | 54.1 | 54.3 | 36.8 | 30.1 | 22.5 | 19.6 |
B2M5C6 | 21.6 | 38 | 48.9 | 55.1 | 59.3 | 38.6 | 23.5 | 20 | 14.6 | 12.8 |
T2M5C6 | 21 | 32.7 | 41.4 | 47.8 | 52 | 40.4 | 28.6 | 23.8 | 17.3 | 15 |
B2M5R3 | 25.18 | 41.6 | 52.3 | 58.7 | 62.9 | 61.4 | 35.1 | 28.2 | 22 | 19.6 |
T2M5R3 | 24.61 | 36.27 | 44.97 | 51.37 | 55.57 | 64.5 | 42.8 | 34.6 | 26.2 | 22.9 |
B2M5R6 | 22.18 | 38.6 | 49.3 | 55.7 | 59.9 | 42.2 | 25.3 | 20.8 | 15.8 | 13.9 |
T2M5R6 | 21.7 | 33.4 | 42.1 | 48.5 | 52.7 | 45.3 | 31.5 | 26 | 19.2 | 16.6 |
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Hossain, M.A.; Hossain, K.M.A. Physical, Compressive Strength, and Microstructural Characteristics of Alkali-Activated Engineered Composites Incorporating MgO, MWCNTs, and rGO. Appl. Sci. 2025, 15, 1712. https://doi.org/10.3390/app15041712
Hossain MA, Hossain KMA. Physical, Compressive Strength, and Microstructural Characteristics of Alkali-Activated Engineered Composites Incorporating MgO, MWCNTs, and rGO. Applied Sciences. 2025; 15(4):1712. https://doi.org/10.3390/app15041712
Chicago/Turabian StyleHossain, Mohammad Ali, and Khandaker M. A. Hossain. 2025. "Physical, Compressive Strength, and Microstructural Characteristics of Alkali-Activated Engineered Composites Incorporating MgO, MWCNTs, and rGO" Applied Sciences 15, no. 4: 1712. https://doi.org/10.3390/app15041712
APA StyleHossain, M. A., & Hossain, K. M. A. (2025). Physical, Compressive Strength, and Microstructural Characteristics of Alkali-Activated Engineered Composites Incorporating MgO, MWCNTs, and rGO. Applied Sciences, 15(4), 1712. https://doi.org/10.3390/app15041712