Introduction
Experimental
Raw materials
Material | Properties | Values |
---|---|---|
MCC (Avicel® PH-101)a | Particle size, Sauter diameter, shape | 2 to 260 µm, 49 µm, larger fibrous rods to smaller irregular cuboids |
Moisture content and solid density | ~ 3 wt%, 1.54 g/cm3 | |
Sisal fibres | Size | 20 mm and 20 cm |
Ordinary Portland Cement (CEM I 42.5 R)b | Product composition | 95-100% clinker + 0-5% additional components |
Loss on ignition | ≤ 5.0% | |
Insoluble residue | ≤ 5.0% | |
Sulphur trioxide (SO3) | ≤ 4.0% | |
Chloride (Cl−) | ≤ 0.1% | |
Initial setting time | ≥ 60 min | |
Soundness | ≤ 10 mm | |
2 days compressive strength | ≥ 20.0 MPa | |
28 days compressive strength | ≥ 42.5 MPa and ≤ 62.5 MPa | |
Sand (CEN-EN 196-1)c | Moisture and SiO2 content | ≤ 0.2%, ≥ 95% |
Particle size distribution | ||
Square mesh size (mm) | Cumulative sieve residue | |
2.00 | 0 | |
1.60 | 7 ± 5 | |
1.00 | 33 ± 5 | |
0.50 | 67 ± 5 | |
0.16 | 87 ± 5 | |
0.08 | 99 ± 1 | |
CTABa | Type | Cationic surfactant |
Average molecular weight, Critical micelle concentration (CMC), pH | 364.5 g/mol, 0.92 to 1.0 mM, 6.0-7.5 | |
Pluronic® F-127a | Type, molecular weight, CMC | Non-ionic, 12500 g/mol, 950-1000 ppm |
Experimental methods
Preparation of aqueous MCC suspensions
Characterization of quality of MCC suspensions
Optical microscopy
UV–Vis spectroscopy
Fabrication of plain and hierarchical cementitious composites
Characterization of processability of mortar paste
Characterization of mechanical performance
Flexural and compressive strength
Fiber-matrix interfacial bonding
Fracture behavior through digital image correlation
Characterization of microstructure of cementitious composites
Characterization of density and pore structure
Characterization of hydration products through DTG and XRD analyses
Characterization of durability of cementitious composites
Measurement of water absorption
Measurement of carbonation resistance
Accelerated ageing test
Results and discussion
Dispersion state of microcrystalline cellulose
Quality of freshly prepared mortar pastes
Mechanical properties of cementitious composites
Compressive and flexural strengths
Samples | Compressive strength (MPa) | Increase (%) | Flexural strength (MPa) | Increase (%) |
---|---|---|---|---|
Plain mortar | 42.3 ± 0.8 | – | 6.6 ± 0.1 | – |
0.1% MCC | 51.0 ± 0.9 | 20.6 | 6.5 ± 0.1 | − 1.5 |
1% MCC | 49.5 ± 0.7 | 17.0 | 6.1 ± 0.2 | − 7.6 |
0.25% sisal | 40.8 ± 1.4 | − 3.5 | 6.3 ± 0.7 | − 4.5 |
0.5% sisal | 39.4 ± 0.8 | − 6.9 | 6.1 ± 0.5 | − 7.5 |
0.1% MCC + 0.25% sisal | 51.9 ± 1.6 | 22.6 | 6.8 ± 0.1 | 2.2 |
0.2% MCC + 0.25% sisal | 40.3 ± 3.6 | − 4.8 | 5.9 ± 0.2 | − 11.9 |
0.4% MCC + 0.25% sisal | 34.7 ± 3.3 | − 18.1 | 5.2 ± 0.2 | − 22.3 |
0.6% MCC + 0.25% sisal | 33.7 ± 1.6 | − 20.5 | 5.9 ± 0.7 | − 10.8 |
0.8% MCC + 0.25% sisal | 11.9 ± 1.5 | − 71.8 | 3.1 ± 0.1 | − 53.4 |
1.0% MCC + 0.25% sisal | 41.2 ± 0.9 | − 2.55 | 6.5 ± 0.1 | − 2.3 |
1.5% MCC + 0.25% sisal | 40.4 ± 3.7 | − 4.6 | 6.5 ± 1.0 | − 2.7 |
0.1% MCC + 0.50% sisal | 52.5 ± 0.9 | 24.2 | 7.8 ± 0.4 | 18.2 |
0.2% MCC + 0.50% sisal | 38.1 ± 3.1 | − 9.9 | 7.0 ± 0.3 | 4.7 |
0.4% MCC + 0.50% sisal | 32.9 ± 2.1 | − 22.3 | 5.7 ± 0.6 | − 14.9 |
0.6% MCC + 0.50% sisal | 36.6 ± 2.5 | − 13.6 | 6.6 ± 0.2 | − 1.1 |
0.8% MCC + 0.50% sisal | 42.7 ± 4.7 | 1.0 | 6.4 ± 1.1 | − 3.5 |
1.0% MCC + 0.50% sisal | 41.8 ± 1.2 | − 1.1 | 6.1 ± 0.3 | − 7.9 |
1.5% MCC + 0.50% sisal | 39.5 ± 1.6 | − 6.8 | 6.0 ± 0.2 | − 8.9 |
Samples | Strain (%) | Increase (%) | Fracture energy (J) | % Increase |
---|---|---|---|---|
Plain mortar | 0.0057 ± 0.0002 | – | 0.27 ± 0.02 | – |
0.1% MCC | 0.0056 ± 0.0002 | − 1.7 | 0.16 ± 0.02 | − 40.7 |
1% MCC | 0.0052 ± 0.0003 | − 8.8 | 0.16 ± 0.03 | − 40.7 |
0.25% sisal | 0.0055 ± 0.0004 | − 3.5 | 0.23 ± 0.02 | − 14.8 |
0.5% sisal | 0.0053 ± 0.0006 | − 7.0 | 0.26 ± 0.04 | − 3.7 |
0.1% MCC + 0.25% Sisal | 0.0066 ± 0.0017 | 15.8 | 0.22 ± 0.05 | − 15.4 |
0.2% MCC + 0.25% Sisal | 0.0035 ± 0.0003 | − 38.5 | 0.18 ± 0.02 | − 32.7 |
0.4% MCC + 0.25% Sisal | 0.0035 ± 0.0002 | − 38.5 | 0.16 ± 0.01 | − 40.6 |
0.6% MCC + 0.25% Sisal | 0.0041 ± 0.0004 | − 28.1 | 0.21 ± 0.04 | − 22.9 |
0.8% MCC + 0.25% Sisal | 0.0036 ± 0.0003 | − 36.5 | 0.09 ± 0.01 | − 67.7 |
1.0% MCC + 0.25% Sisal | 0.0054 ± 0.0003 | − 5.8 | 0.26 ± 0.01 | − 1.1 |
1.5% MCC + 0.25% Sisal | 0.0058 ± 0.0004 | 2.2 | 0.27 ± 0.06 | 2.9 |
0.1% MCC + 0.50% Sisal | 0.0073 ± 0.0005 | 27.8 | 0.37 ± 0.04 | 40.3 |
0.2% MCC + 0.50% Sisal | 0.0057 ± 0.0003 | – | 0.29 ± 0.01 | 8.2 |
0.4% MCC + 0.50% Sisal | 0.0046 ± 0.0004 | − 18.7 | 0.22 ± 0.04 | − 16.0 |
0.6% MCC + 0.50% Sisal | 0.0071 ± 0.0010 | 24.8 | 0.29 ± 0.02 | 10.1 |
0.8% MCC + 0.50% Sisal | 0.0060 ± 0.0004 | 5.8 | 0.28 ± 0.06 | 5.1 |
1.0% MCC + 0.50% Sisal | 0.0052 ± 0.0004 | − 8.9 | 0.23 ± 0.02 | − 11.7 |
1.5% MCC + 0.50% Sisal | 0.0048 ± 0.0003 | − 15.9 | 0.23 ± 0.02 | − 14.6 |
Fracture behavior and interfacial bonding
Samples | Time | ||
---|---|---|---|
Fracture initiation | At the peak load | End of the test | |
Plain mortar | 2 min 20 s | 2 min 20 s | 8 min 22 s |
0.5% sisal | 2 min | 4 min 24 s | 12 min 18 s |
0.1% MCC + 0.5% sisal | 2 min 30 s | 4 min 6 s | 24 min 44 s |
Hydration behavior of plain mortar and cementitious composites
Density and porosity of plain mortar and hierarchical composites
Samples | Density (g/cm3) | Average Pore Diameter (nm) | Porosity (%) | Coefficient of water absorption kg/(m2 min0.5) |
---|---|---|---|---|
Plain mortar | 2.39 | 44.1 | 13.7 | 0.065 |
0.1% MCC + 0.5% sisal + CTAB | 2.46 | 34.7 | 12.3 | 0.057 |
Carbonation resistance of cementitious composites
Degradation of cementitious composites
Conclusions
-
MCC aqueous suspensions showed increased agglomeration and reduced stability with increase in MCC concentration. The optimum MCC dispersion was achieved with 40% CTAB (on the weight of MCC), which was used for the fabrication of cementitious composites.
-
Among MCC and sisal fibers, MCC showed higher influence on the flow properties of mortar paste due to their higher surface area and moisture absorption property. At the same sisal fiber content flow properties of fresh mortar first decreased up to 0.2% MCC due to rapid water absorption by MCC, then increased up to 0.8% MCC mainly due to increased amount of CTAB used and after that it started to decrease again due to severe MCC agglomeration. Also, a CTAB: TBP ratio of 1:1 was found to be optimum to suppress foam formation and reduce porosity in cementitious composites.
-
In hierarchical composites, compressive and flexural strengths improved significantly at 0.1 wt% MCC and further increase in MCC concentration reduced mechanical strengths drastically due to MCC agglomeration. Although the effect of sisal fibers on compressive strength was not positive, an increase in sisal fiber content in hierarchical composites from 0.25 to 0.5 wt% resulted in an improved flexural strength mainly due to crack-bridging effect of sisal fibers. Hierarchical composites containing 0.1% MCC with 0.5% sisal fibers showed ~ 24% and 18% higher flexural and compressive strengths, respectively as compared to plain mortar.
-
Hierarchical scale composites showed a synergistic effect on the fracture behavior resulting in a slower crack initiation and propagation as compared to both sisal fiber-reinforced and plain mortar composites. The fracture energy of hierarchical composites improved by 40% as compared to plain mortar composites. Hierarchical composites also demonstrated superior sisal fiber-matrix bonding due to positive influence of MCC on composite’s interface.
-
Hierarchical composites showed formation of a higher amount of hydration products as confirmed from the DTG and XRD analyses. As a result, a decrease in porosity and average pore size accompanied by an increase in density was observed in hierarchical composites. The lower porosity of hierarchical composites reduced the water absorption and penetration of CO2, resulting in an increase in the carbonation resistance. The hierarchical composites were also durable without any noticeable damage to the sisal fibers up to 90 accelerated ageing cycles.