纳米改性超高韧性水泥基复合材料保温防渗永久性模板研究

Permanent formwork of ultra high toughness cementitious composites added with nano-SiO_2

为解决大坝混凝土材料在大体积施工及运行中因温度梯度产生脆性开裂这一难题,采用纳米改性超高韧性水泥基复合材料保温防渗永久性模板,研究纳米Si O2对材料力学性能、抗渗性能和导热系数的影响,借助扫描电镜分析其微观结构变化,计算分析保温防渗永久性模板对大坝混凝土温度应力的改善效果。试验中纳米Si O2掺量分别为0%,1%,3%和5%,研究结果表明UHTCC材料28d抗压、抗弯强度及抗渗能力随着纳米Si O2掺量的增加逐渐增大;纳米Si O2掺量为5%时,抗压、抗弯强度可分别达到52.7MPa及15.77MPa,而抗渗系数仅为3.54×10-9cm/h,约为普通混凝土的1/1800,且材料微观结构逐渐密实。但材料导热系数与微观结构密实程度没有正相关性,纳米Si O2掺量为1%时UHTCC材料导热系数最低,仅为0.406 W/(m·K),约为普通混凝土的1/4。以越冬期间混凝土大坝为例,通过计算分析得到当永久性模板厚度大于75cm时,可有效控制混凝土材料内部温度应力,防止混凝土表层脆性开裂,起到良好的保温效果,改善无坝不裂的现状。

In massive concrete constructions,serious variation of environmental temperature can induce concrete cracks.This study proposes a new type of permanent formwork,made of ultra high toughness cementitious composites added with nano-Si O2,to preserve concrete structure of dams. The main purpose is to investigate the influence of nano-Si O2 on the mechanical strength,permeability,thermal conductivity and microstructure of concrete. In the study,the content of nano-Si O2 is 0%,1%,3% and 5% respectively. The results indicate that the mechanical strength,impermeability and microstructure are all improved remarkably along with the content of nano-Si O2. When the content is 5%, the compressive and flexural strength are 52. 7MPa and 15. 77 MPa respectively,and the permeability coefficient is only 3. 54× 10- 9cm / h which is about 1 /1800 of concrete. However,the thermal conductivity has not positive correlation with the compactness of microstructure. The lowest thermal conductivity is only 0. 406 W /( m·K) at the content of 1%,which is about 1 /4 of concrete. As an example of the concrete dam in winter,this permanent formwork can effectively prevent concrete cracks when the depth of formwork is larger than 75 cm.