牡蛎煅制过程中的微观结构及CaCO3含量分析

目的:研究煅制牡蛎的微观结构变化,考察温度和时间对煅牡蛎质量的影响。方法:采用热重/差示扫描量热法(TG/DSC)分析牡蛎生品。取净牡蛎置于瓷坩埚中,在不同温度条件下,采用烘箱对样品进行煅制,每隔不同时间取出牡蛎,研磨后过200目筛备用。采用扫描电子显微镜(SEM)对煅制后的牡蛎表面进行分析。以BET氮气吸附分析煅制后的牡蛎的孔结构特征。采用电感耦合等离子体发射光谱法(ICP-OES)测定样品中CaCO_3的含量。结果:约500℃煅制,会导致生石灰的含量显著升高。300℃以下煅制3~4 h后取出,牡蛎表面形成的孔道明显。在300℃以下煅制形成的样品比表面积较大。300~350℃煅制的牡蛎中CaCO_3含量较高。结论:在煅制牡蛎时,应以300℃左右为宜,煅制时间3~4 h,这样有利于形成孔道结构,保证较大的比表面积和较高的CaCO_3含量,有利于煎煮和药效的发挥。     

Investigation of Concrete Shrinkage Reducing Additives

This paper analyzes the efficiency of shrinkage reducing additives for the shrinkage deformations of ordinary Portland cement (OPC) concrete and its mechanical properties. OPC concrete was modified with an organic compound-based shrinkage reducing additive (SRA), quicklime, polypropylene fiber, and hemp fiber. It was found that a combination of 2.5% quicklime and 1.5% SRA led to the highest reduction in shrinkage deformations in concrete, and the values of shrinkage reached up to 40.0%. On the contrary, compositions with 1.5% SRA were found to have a significant reduction in compressive strength after 100 freeze-thaw cycles. Hemp fiber did not show a significant shrinkage reduction, but it is an environmentally friendly additive, which can improve OPC concrete flexural strength. Polypropylene fiber can be used in conjunction with shrinkage reducing additives to improve other mechanical properties of concrete. It was observed that 3.0 kg/m³ of polypropylene fiber in concrete could increase flexural strength by 11.7%. Moreover, before degradation, concrete with polypropylene fiber shows high fracture energy and decent residual strength of 1.9 MPa when a 3.5 mm crack appears. The tests showed a compressive strength decrease in all compositions with shrinkage reducing additives and its combinations after 28 days of hardening.