Replacement of Portland cement (PC) by fly ash (FA) is currently limited to 15–30% by mass, mainly due to low early age strength development of concrete. This research uses calcium formate (Ca(HCO₂)₂; CF) as an admixture to high-volume FA (HVFA) composites to improve its strength properties. HVFA represents 60–70% of cement replaced by FA and dosage of CF varies from 0.5% up to high dosage of 9% of cement content. Compressive strength, isothermal calorimetry, thermogravimetric analysis, X-ray diffraction and scanning electron microscopy were conducted to investigate the effects of CF on hydration and microstructural aspects. The results show that both HVFA pastes with 60% and 70% FA achieved the highest strength at the CF dosage of 3%. At the age of 28 days, adding 3% CF to HVFA mixes led to higher consumption of FA as well as higher formation of calcium hydroxide (Ca(OH)₂), calcium silicate hydrates, calcium carbonate (CaCO₃) and ettringite, which contribute to the increase of strength. The addition of very high dosages of CF at 9% increased the hydration of tricalcium aluminate but could hinder the hydration of tricalcium silicate in both PC and HVFA pastes with 60% and 70% FA.

中文翻译：

---

甲酸钙对高掺量粉煤灰水泥体系早期强度和微观结构的影响

用粉煤灰 (FA) 替代波特兰水泥 (PC) 目前仅限于 15-30% 的质量，主要是由于混凝土的早期强度发展较低。本研究使用甲酸钙 (Ca(HCO ₂ ) ₂; CF) 作为高容量 FA (HVFA) 复合材料的混合物，以提高其强度性能。HVFA 代表 60-70% 的水泥被 FA 取代，CF 的用量从 0.5% 到水泥含量的 9% 的高用量不等。进行了抗压强度、等温量热法、热重分析、X 射线衍射和扫描电子显微镜检查，以研究 CF 对水合和微观结构方面的影响。结果表明，含 60% 和 70% FA 的 HVFA 糊剂在 3% 的 CF 剂量下都达到了最高强度。在 28 天龄时，向 HVFA 混合物中添加 3% CF 导致更高的 FA 消耗以及更多的氢氧化钙 (Ca(OH) ₂ )、硅酸钙水合物、碳酸钙 (CaCO ₃) 和钙矾石，有助于提高强度。添加 9% 的非常高剂量的 CF 会增加铝酸三钙的水合，但会阻碍 60% 和 70% FA 的 PC 和 HVFA 糊中硅酸三钙的水合。