废弃混凝土的水热固化与力学强度

Hydrothermal solidification of discarded concrete and its mechanical strength

为实现废弃混凝土的资源化规模利用,将废弃混凝土回收、粉碎后,掺入适量氢氧化钙(Ca(OH)_2)、碱性激发剂(NaOH)和水,经均匀混合、模压成型后,在高温饱和水蒸气环境中转化为具有较高机械强度的块状制品。实验系统考察了原料配比以及反应温度和时间等因素对水热固化样品劈裂抗拉强度(简称劈拉强度)和微观结构的影响。研究结果表明:Ca(OH)_2掺量为20%时对于结晶性水化硅酸钙(托勃莫来石相)的形成最为有利,水化产物彼此交织成密实结构,实现了最高的样品力学强度;NaOH的引入可激发废弃混凝土的水热反应活性,但掺量不宜过高;水热反应条件下,样品的劈拉强度随环境温度的升高或反应时间的延长而明显增大,但温度过高、时间过长,会因晶型转变及内部结晶应力等原因而导致样品力学强度降低。

Discarded concrete（ DC） was collected,finely ground,and subsequently mixed with Ca（ OH）_2,NaOH,and water in designed proportions to explore the resource utilization of building discards. After a moldcompressing process,cylindrical specimens of the evenly-dispersed mixture were hydrothermally solidified under a moisture-saturated hot atmosphere to yield a material of appreciable mechanical strength. Systematic investigations were performed to determine the dependence of the measured strength（ splitting tensile strength） on the proportion of raw materials and their hydrothermal treatments,i. e.,time and temperature. The results suggested that a weight proportion of 20% Ca（OH）_2 was most favorable to form hydrated calcium silicates with high crystallinity（ e. g.,tobermorite）,thereby giving rise of an enhanced mechanical strength for hydrothermally solidified DC. Use of Na OH was beneficial in increasing the reaction activity of DC,but the NaOH content should not be more than10%. Under the hydrothermal reaction atmosphere,the tensile strength of hydrothermally solidified DC increased on increasing the temperature or time. Excessive temperature or time negatively affected the corresponding strength,with the most possible reasons being a phase transformation of the products or internal stress caused by overcrystallization.