- freely available
Materials 2018, 11(5), 825; https://doi.org/10.3390/ma11050825
2. Experimental Program
2.2. Mix Proportions
2.3. Sample Preparation
2.4. Test Methods
2.4.1. Compression Test
2.4.2. XRD and XRF
3. Results and Discussion
3.1. Characterization of Raw Materials
3.2. Compressive Strength
3.4. Hydration Phase Evolution
3.5. Morphological Transition
- The XRD and SEM results show that the growth of the hydrated phases (for example, ettringite, monosulfate, C-S-Hs) was substantially restrained with the retarders at the very early age (that is, 2–3 h). This likely occurred because the retarders formed hydrophobic barrier layers surrounding anhydrous mineral phases (for example, anhydrite, ye’elimite, C3S, C2S, C3A) in the finely dispersed cement grains. Moreover, the delaying effect of the retarders cumulatively added to the delaying effect of the polymer.
- The use of the retarders increased the ultimate strength of the cement blend systems at the long-term age. Even with a polymer ratio up to 6%, the mortars with the retarders showed higher compressive strengths than the mortar without both retarders and polymers after 28 days of curing. This was likely to happen because the retarders created a finer and denser hydrated cementitious matrix as observed in the MIP results, by increasing the dispersibility of cement grains, their specific surface areas, and the accessibility of water to them.
- Despite variations in the polymer ratio, the compressive strengths of all the mortars with retarders tended to converge at the age of 90 days. This reflects the formation of a more refined pore structure with a higher polymer ratio that compensated the inherited weak strength of the polymer powder itself, as well as the formation of a monolithic co-matrix between the cement hydrates and polymer phases. The authors will examine the combined effects of the set retarders and polymer powder on the ITZs in the near future.
- At the age after 60 days, the sample with retarders and 10% polymer exhibited both the smallest porosity and average pore diameter among all the HCP samples. This highlights that the combined use of retarders and polymer had a synergetic effect to refine the pore structures of the cement blend systems.
- According to the EDS spot analyses, the paste with the retarders at 60 days of curing had a slightly more Al uptake on average than the paste with no retarders. This supports the compression test results that the mortar with the retarders showed higher strengths than the mortar without retarders after 28 days of curing.
Conflicts of Interest
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|Mixture Label||Mortar (Unit: kg/m3)|
|Water||Cement||Sand||Polymer||Retarder A||Retarder B|
|Mixture Label||Cement Paste (Unit: kg/m3)|
|Water||Cement||Polymer||Retarder A||Retarder B|
|Oxide in Cement Blend (wt.%)|
|Oxide Composition (wt.%)||CaO||SO3||SiO2||Others|
|Element Composition (wt.%)||Carbon||Hydrogen||Sulfur||Nitrogen|
|Age||2 h||1 Day||7 Days||28 Days||60 Days||90 Days|
|Mixture Label||Compressive Strength (MPa)|
|M-0-N||25.8 (0.14)||35.8 (2.65)||44.1 (1.72)||49.8 (4.21)||62.0 (3.84)||62.0 (4.17)|
|M-0-Y||16.3 (0.60)||35.7 (1.05)||45.3 (2.20)||54.8 (5.91)||67.2 (4.34)||63.7 (0.75)|
|M-2-Y||13.0 (0.07)||32.6 (1.38)||38.4 (0.90)||53.4 (2.40)||64.4 (4.92)||63.8 (5.65)|
|M-6-Y||11.3 (0.35)||30.9 (1.40)||36.1 (1.54)||52.6 (2.14)||61.1 (5.39)||61.7 (1.94)|
|M-10-Y||8.0 (0.08)||28.1 (1.00)||32.2 (0.15)||41.4 (1.64)||53.2 (2.18)||56.6 (4.26)|
|Mixture Label||Age (day)||Total Porosity (%)||Average Pore Diameter (nm)|
|Mixture Label||Curing Age||Average Ca/Si Ratio||Average Al/Ca Ratio|
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