2.1 Materials, Preparations, and Experimental Procedures
A
\( C\overline{S} A \) cement is manufactured by CTS Cement Manufacturing Corporation, and a commercial cement, Type II/V portland cement, is provided from Riverside Cement Company. An oxide analysis of both types of cement was obtained via X-ray fluorescence (XRF) and summarized in Table
1.
Table 1
Chemical compositional analysis by XDF (mass %).
SiO2
| 11.47 | 20.92 |
AI2O3
| 11.40 | 3.23 |
Fe2O3
| 0.98 | 3.85 |
CaO | 36.71 | 55.18 |
MgO | 2.67 | 2.48 |
SO3
| 9.99 | 8.67 |
Na2O | 0.04 | 0.04 |
K2O | 0.31 | 0.27 |
\( {\text{C}}_{ 4}^{{}} {\text{A}}_{ 3}^{{}} \overline{\text{S}} \)
| 21.69 | 5.36 |
CS | 4.74 | – |
The
\( C\overline{S} A \) and portland cements were employed with a Blanine fineness (ASTM C204) of approximately 6400 and 4100 cm
2/g, respectively. According to the ASTM C109 procedures, the compressive strength of the
\( C\overline{S} A \) and portland cement mortar was measured at 1 h, 3 h, 1 day, 3 days, 7 days, and 28 days and the experimental results are given in Table
2.
Table 2
Compressive strength of calcium sulfoaluminate and portland cement mortar, MPa.
\( C\overline{S} A \) cement | 38.3 | 41.1 | 56.9 | 58.1 | 60.2 | 62.1 |
Portland cement | – | – | 8.9 | 21.5 | 28.4 | 40.0 |
The \( C\overline{S} A \) and portland cement paste specimens were conducted with w/c of 0.40, 0.50, and 0.60. An iced water with a temperature of 0.6 °C was used for the \( C\overline{S} A \) cement paste because the \( C\overline{S} A \) cement paste has a tendency to hydrate very quickly. Each paste specimen had a diameter of 5.08 cm and a length of 1.27 cm. The molds were covered with a plastic sheet and left to cure under laboratory conditions for 3 days, at which time the specimens were stripped from the molds and cured in lime saturated water for 28 days. After curing, the samples were weighed and placed in a sealed plastic container with approximately 1 kg of anhydrous silica gel. The weight of each specimen was periodically measured to determine the degree of desiccation. All of the specimens were stored in the desiccation box for 56 days, at which point the weight change per day was less than 0.02 % because an appropriate level of desiccation for cement pastes was required for nitrogen pore analysis.
For the mercury intrusion analysis, the samples were broken into pieces less than 2 cm in diameter, which is the largest the mercury intrusion device could accommodate. For portland cement, grinding the sample to smaller sizes showed an additional porosity in the 1 μm range that was not present in larger samples. Therefore, the specimens were not ground in the same manner as for the nitrogen sorption test so that surface effects and microcracking of the cement matrix could be avoided. Analysis was conducted in a PMI Instruments Mercury Intrusion Porosimeter at PMI, Inc., Ithaca, NY.
For the nitrogen sorption analysis, the specimens were broken into small pieces and then ground using a mortar and pestle to pass a #16 sieve (1190 μm spacing). The materials were then screened on a #30 sieve (595 μm spacing) and the retained materials were used for the analysis. The ground and screened material samples were analyzed in a Micromertitics ASAP 2010. Surface area calculations were performed according to the Brunauer–Emmett–Teller (BET) theory (Brunauer et al.
1938) and t-plot by Harkins–Jura (Harkins and Jura
1944), and pore size distribution was determined by the Barrent-Joyner-Halenda (BJH) theory (Barrett et al.
1951).
For the concrete freeze–thaw tests, two types of limestone obtained from the state of Missouri were selected based on supplier reports of freeze–thaw performance. One limestone (Limestone G) was reported to have very good performance in a freezing and thawing environment, while the other (Limestone B) was reported to have very poor performance in a freezing and thawing condition. Both types of limestone were tested for their porosity characteristics using the same procedure as the hardened cement pastes. These two types of limestone were combined with
\( C\overline{S} A \) or portland cement, sand, water, and an air-entraining admixture to create concretes typical of early strength designs. Each batch was mixed and specimens molded according to the procedures in the ASTM C192. The specific mix designs and resulting plastic concrete properties are summarized in Table
3.
Table 3
Proportions and properties of concrete mixture for freeze–thaw tests.
Cement (kg) | 420.8 | 420.8 | 477.5 | 477.5 |
Fine aggregate (kg) | 764.0 | 764.0 | 764.0 | 764.0 |
Coarse aggregate (kg) | 1021.2 | 1091.0 | 1021.2 | 1091.0 |
Water (kg) | 198.2 | 198.2 | 225.0 | 225.0 |
Air entraining admixture (kg) | 0.4102 | 0.4102 | 0.4999 | 0.4999 |
Slump (cm) | 15 | 15 | 18 | 17 |
Air content (%) | 6.0 | 6.5 | 5.5 | 6.0 |
Three concrete beams were cast for each mix design for freeze–thaw testing. The dimension of each beam was 7.6 cm × 7.6 cm × 29.2 cm. They were cured in the molds under a polyethylene sheet for 24 h, then stripped and cured in lime saturated water for 14 days, in accordance with the standard ASTM C666. After curing in water, the beams were transferred to individual rigid sheet metal containers which were then filled with water to just above the specimen surface, and placed in a freeze–thaw chamber. The chamber was temperature controlled and automated to cycle between −18 and 4 °C. The temperature was recorded in the middle of a dummy concrete specimen by an embedded thermocouple. During the course of the test, the machine was automatically able to cycle about 5 to 6 times per day. The specimens were periodically removed from the chamber, patted dry with a towel, weighed, and measured fundamental transverse frequency using the impact method as described in ASTM C215 and Olson Instruments RT-1 resonance tester. The relative dynamic modulus (RDM) for each specimen was calculated from the fundamental transverse frequency using the following equation supplied by Olson Instruments:
$$ {\text{RDM}}\,= \,\frac{{f_{n}^{2} }}{{f_{0}^{2} }} \times 100\;\% $$
(1)
where
\( f_{0}^{{}} \) is the fundamental transverse frequency measured at zero cycles and
\( f_{n}^{{}} \) is the fundamental transverse frequency measured at
n cycles.
After measuring the frequency, the specimens were returned to the rigid containers which were refilled with fresh water. The containers were then returned to the freeze–thaw chamber. If any specimen was damaged from freeze–thaw to the point where a fundamental transverse frequency could not be measured, the set was declared to have failed and removed from further testing.