Mechanical Performance and Microstructure of Single Component Geopolymer Mortar
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摘要: 为了研究不同NaOH浓度、胶砂比及溶胶比在多种固化温度下粉煤灰地聚物砂浆的强度发展规律及其微观机理，进行了力学性能试验，并用扫描电镜（SEM）和压汞试验（MIP）分析了其微观形貌、孔径分布. 分析结果表明： 对浓度为10%的NaOH溶液制备的地聚物砂浆试件，即使在很高的温度下固化也没有观察到明显的强度发展；随着NaOH浓度增加或固化温度上升，单组分地聚物砂浆的抗压和抗弯强度均可获得最佳值，该值出现位置由热固化温度和NaOH浓度的共同决定；地聚物的孔径分布微分曲线为单峰分布，控制NaOH的浓度可以大幅减小孔径微分曲线的峰值，显著降低地聚物的孔隙率；粉煤灰颗粒在NaOH的作用下逐渐溶解，并在其表面形成胶凝物质，当Na+ 浓度较低时，地聚物较少，通过控制NaOH浓度可以使得地聚物变得密实，提高其抗压强度；基于热力学关系的分形模型描述地聚物孔结构形态的效果最好，其次为孔轴线模型，空间填充模型和海绵体模型只能较好地描述胶凝孔隙和过渡孔隙的孔结构分形维数；基于热力学关系与基于海绵模型分形维数计算值均在2.0～3.0之间，与一般水泥基材料的结果相近；适当调整NaOH的浓度可以改善地聚物的孔隙结构.Abstract: In order to investigate the strength development rule and microscopic mechanism of fly ash based geopolymer mortar with different NaOH concentrations, cement-sand ratios and solution-cement ratios at various curing temperatures, the mechanical properties test were carried out. The microscopic morphology and pore size distribution were analyzed by scanning electron microscope (SEM) and mercury intrusion porosimetry (MIP), respectively. The results show as follows: For geopolymer mortar specimens prepared using NaOH solution with a concentration of 10%, no significant strength development was observed even at very high curing temperatures. With the increase of NaOH concentration or curing temperature, the compressive strength and flexural strength of single component geopolymer mortar can obtain their best value, and the location of the value is determined by both curing temperature and NaOH concentration. The pore size distribution differential curve of the geopolymer is a unimodal distribution. Controlling the concentration of can greatly reduce the peak value of the pore diameter differential curve and significantly reduce the porosity of the geopolymer. Fly ash particles dissolve gradually under the action of NaOH and form cementitious material on its surface. When the concentration of Na+ is low, the geopolymer polymerization is less; controlling the concentration of NaOH can make the geopolymer become dense and improve their compressive strength. The fractal model based on thermodynamic relation is the best one to describe the structure of the geopolymer pore, followed by the pore axis model, while the spatial filling model and the sponge model can only describe the fractal dimension of the pore structure of gel pores and transition pores. The calculated values of fractal dimension based on thermodynamic relationship and sponge model are between 2.0 and 3.0, which is similar to the results of general cement-based materials. Proper adjustment of the concentration of NaOH can improve the pore structure of the geopolymer.
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图 1 温度-抗压强度-NaOH浓度的关系
Figure 1. Relationship among temperature，compressive strength，and NaOH concentration
图 2 温度-抗弯强度-NaOH浓度的关系
Figure 2. Relationship among temperature，flexural strength，and NaOH concentration
图 3 温度-抗压强度-胶砂比的关系
Figure 3. Relationship among temperature，compressive strength，and cement sand ratio
图 4 温度-抗弯强度-胶砂比的关系
Figure 4. Relationship among temperature，flexural strength，and cement sand ratio
图 5 温度-抗压强度-溶胶比的关系
Figure 5. Relationship among temperature，compressive strength，and solution cement ratio
图 6 温度-抗弯强度-溶胶比的关系
Figure 6. Relationship among temperature，flexural strength，and solution cement ratio
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