1 Introduction
2 Materials and Methods
2.1 Materials and Preparation of CNTs Suspension
Outer diameter (nm) | Length (μm) | Aspect ratio | Purity | Specific surface area (m2/g) |
---|---|---|---|---|
40–60 | > 5 | 100–300 | > 97% | 40–70 |
Compositions | SiO2 | CaO | Al2O3 | Fe2O3 | SO3 |
---|---|---|---|---|---|
Content/wt% | 22.73 | 66.68 | 5.84 | 2.23 | 2.30 |
Compositions | C3S | C2S | C3A | C4AF | Ignition loss |
---|---|---|---|---|---|
Content/wt% | 49.86 | 26.87 | 10.84 | 9.68 | 2.57 |
Physical properties | Specific surface area/m2/kg | Standard consistency water consumption/% | Initial setting time/min | Final setting time/min |
---|---|---|---|---|
Measured values | 377 | 27.4 | 146 | 201 |
Physical properties | Stability (boiling method) | Compressive strength/MPa | Flexural strength/MPa | ||
---|---|---|---|---|---|
3 days | 28 days | 3 days | 28 days | ||
Measured values | Qualified | 37 | 62.8 | 6.5 | 9.4 |
2.2 Autogenous Shrinkage Test
Sample number | Water to cement ratio | Water reducing agent (%) | CNTs content (wt%) |
---|---|---|---|
AS-A-1 | 0.3/0.35/0.4 | 0.2 | 0.00 |
AS-A-2 | 0.2 | 0.05 | |
AS-A-3 | 0.2 | 0.10 | |
AS-A-4 | 0.2 | 0.15 |
2.3 Ring Test
Specimen number | Water to cement ratio | Sand to cement ratio | Water reducing agent (wt%) | CNTs content (wt%) |
---|---|---|---|---|
AC-A-1 | 0.3/0.35/0.4 | 1.5 | 0.2 | 0.00 |
AC-A-2 | 1.5 | 0.2 | 0.05 | |
AC-A-3 | 1.5 | 0.2 | 0.10 | |
AC-A-4 | 1.5 | 0.2 | 0.15 |
3 Results and Discussion
3.1 Linear Shrinkage
3.1.1 Water-Cement Ratio and Shrinkage of Cement Paste
Water to cement ratio | CNTs content (wt%) | |||
---|---|---|---|---|
0.00 | 0.05 | 0.10 | 0.15 | |
0.30 | − 1397 | − 1178 | − 1119 | − 1318 |
0.35 | − 1178 | − 884 | − 780 | − 990 |
0.40 | − 1132 | − 728 | − 638 | − 981 |
3.1.2 CNTs Content and Shrinkage of Cement Paste
3.2 Ring Strain
3.2.1 CNTs Content and Crack Resistance of Cement Mortar
CNTs content/wt% | Semi-closed experiment | Closed | ||
---|---|---|---|---|
Cracking time/h | Cracking strain/10−6 | Cracking time/h | Cracking strain/10−6 | |
0.00 | 101.3 | − 150 | 212.2 | − 142 |
0.05 | 98.3 | − 110 | 223.2 | − 133 |
0.10 | 102.3 | − 115 | 310.2 | − 138 |
0.15 | 99.8 | − 107 | 248.5 | − 121 |
CNTs content/wt% | Autogenous shrinkage strain \(\upvarepsilon_{1}\) | Total shrinkage strain ε | \({\raise0.7ex\hbox{${\upvarepsilon_{1} }$} \!\mathord{\left/ {\vphantom {{\upvarepsilon_{1} }\upvarepsilon}}\right.\kern-0pt} \!\lower0.7ex\hbox{$\upvarepsilon$}} \times 100\%\) |
---|---|---|---|
0.00 | − 106 | − 150 | 70.7 |
0.05 | − 94 | − 110 | 85.5 |
0.10 | − 92 | − 115 | 80.0 |
0.15 | − 84 | − 107 | 78.5 |
3.2.2 Water-Cement Ratio and Crack Resistance of Cement Mortar
Water to cement ratio | Semi-closed experiment | Closed experiment | ||
---|---|---|---|---|
Cracking time/h | Cracking strain/10−6 | Cracking time/h | Cracking strain/10−6 | |
0.30 | 98.3 | − 120 | 310.2 | − 145 |
0.35 | 104.6 | − 117 | 329.5 | − 124 |
0.40 | 111.5 | − 107 | 340.3 | − 114 |
Water-cement ratio | Autogenous shrinkage strain \(\upvarepsilon_{1}\) | Total shrinkage strain ε | \({\raise0.7ex\hbox{${\upvarepsilon_{1} }$} \!\mathord{\left/ {\vphantom {{\upvarepsilon_{1} }\upvarepsilon}}\right.\kern-0pt} \!\lower0.7ex\hbox{$\upvarepsilon$}} \times 100\%\) |
---|---|---|---|
0.30 | 92 | 110 | 83.6 |
0.35 | 86 | 110 | 78.1 |
0.40 | 58 | 107 | 53.8 |