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Low-temperature curing strength enhancement in cement-based materials containing limestone powder

机译：含石灰石粉的水泥基材料的低温固化强度提高

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With the ongoing sustainability movement, the incorporation of limestone powder in cementitious binders for concrete in the U.S. has become a subject of renewed interest. In addition to accelerating the early age hydration reactions of cementitious systems by providing additional surfaces for nucleation and growth of products, limestone powder is also intriguing based on its influence on low-temperature curing. For example, previous results have indicated that the utilization of limestone powder to replace one quarter of the fly ash in a high volume fly ash mixture (40-60% cement replacement) produces a reduction in the apparent activation energy for setting for temperatures below 25 degrees C. In the present study, the relationship between heat release and compressive strength of mortars at batching/curing temperatures of 10 and 23 degrees C is investigated. For Portland-limestone cements (PLC) with limestone additions on the order of 10%, a higher strength per unit heat release is obtained after only 7 d of curing in lime water. Surprisingly, in some cases, the absolute strength of these mortar cubes measured at 7 d is higher when cured at 10 degrees C than at 23 degrees C. Solubilities vs. temperature, reaction stoichiometries and enthalpies, and projected phase distributions based on thermodynamic modeling for the cementitious phases are examined to provide some theoretical insight into this strength enhancement. For a subset of the investigated cements, thermogravimetric analysis, quantitative X-ray diffraction, and scanning electron microscopy are conducted on 7-d paste specimens produced at the two temperatures to examine differences in their reaction rates and the phases produced. The strength enhancement observed in the PLC cements is related to the cement hydration products formed in the presence of carbonates as a function of temperature.
机译：随着持续的可持续发展运动，在美国将石灰石粉掺入混凝土的水泥粘合剂中已成为引起人们关注的主题。除了通过提供用于产品成核和生长的附加表面来加速水泥体系的早期水合反应之外，石灰石粉还因其对低温固化的影响而引人入胜。例如，以前的结果表明，使用石灰石粉代替高容量粉煤灰混合物中的四分之一粉煤灰（水泥替代量为40-60％），在温度低于25时设定的表观活化能降低。在本研究中，研究了在10和23摄氏度的配料/固化温度下砂浆的放热和抗压强度之间的关系。对于石灰石添加量约为10％的波特兰石灰石水泥（PLC），在石灰水中固化7天后，每单位热量释放的强度更高。出乎意料的是，在某些情况下，在10摄氏度下固化时，在7 d时测得的砂浆立方体的绝对强度比在23摄氏度下更高。溶解度与温度，反应化学计量和焓以及基于热力学模型的投影相分布检查了胶凝相，以提供有关这种强度增强的一些理论见解。对于所研究的水泥的子集，对在两种温度下生产的7维糊状样品进行热重分析，定量X射线衍射和扫描电子显微镜检查，以检查其反应速率和所产生的相的差异。在PLC水泥中观察到的强度增强与在温度下碳酸盐存在下形成的水泥水合产物有关。

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