磨细矿渣掺量对混凝土徐变性能的影响及其机理

为研究磨细矿渣对混凝土徐变性能的影响,在(20±1)℃,相对湿度为(60±5)%的条件下测试了33%载荷水平下磨细矿渣等量取代水泥量分别为0,30%,50%和80%4种情况下混凝土的徐变度.结果表明:磨细矿渣掺量(质量分数,下同)为30%和50%时,磨细矿渣对混凝士徐变性能的影响不明显,当磨细矿渣掺量增加为80%时,混凝土抵抗徐变的能力大大下降,其1 a的徐变度为不掺矿渣混凝土的1.74倍.通过扫描电镜二次电子成像观测,结合压汞法测试基体的孔隙率与孔径分布,对不同掺量下的磨细矿渣及水泥颗粒与基体的结合情况进行了分析研究.采用烧失量法测试水泥-矿渣体系中的非蒸发水量来表征水化产物数量,并基于纳米压痕技术测量了磨细矿渣与水泥颗粒的弹性模量,通过上述几种实验方法的联合观测分析,对磨细矿渣影响混凝土徐变性能的机理进行了详细研究.由于磨细矿渣颗粒的弹性模量略低于水泥颗粒,故不能通过"微集料效应"抑制混凝土的徐变.混凝土徐变性能受水泥及磨细矿渣颗粒与基体的界面结合状况的影响较大,当界面结合良好时,可忽略其对混凝土徐变的影响,混凝土的徐变度和体系的水化产物数量正相关;当界面结合不良时,其对抑制混凝土徐变的负面效应显著增强,徐变性能受到水化产物数量与界面结合情况的双重影响.

EFFECT OF GROUND GRANULATED BLAST-FURNACE SLAG PROPORTION ON CREEP CHARACTERISTICS OF CONCRETE

This paper presents the experimental results on the effect of ground granulated blast-furnace slag (GGBS) on the creep characteristics of concrete. The specific creep of concrete without and with the GGBS of 30%, 50% and 80% was examined in a stress strength ratio of 33% at (20±1) ℃ and humidity of 60%5±5%. The results show that the GGBS has a slight effect on the creep char-acteristics of concrete with the GGBS of 30 % or 50%. The GGBS proportion of 80% gives a negative effect on the creep characteris-tics of concrete. The specific creep after one year was 1.74 times as much as that of concrete without any GGBS. Scanning electron microscope was used to observe the interface bonding among the GGBS, cement particles and matrix. The porosities and pore size distributions were determined by mercttry intrusion porosimetry (MIP). The amount of hydration was determined by the unevaporated water. The elastic modulus of GGBS and cement were measured by nano-indentation. The creep mechanism of concrete with different GGBS proportions was analyzed. It is indicated that the GGBS particles can not reduce the creep of concrete through the mi-cro-aggregate effect due to the lower elastic modulus. The specific creep of concrete has a positive relation with the amount of hydra-tion products. The combined interface among cement, GGBS particles and matrix become worse, offering a negative effect on the specific creep of concrete at the GGBS of 80 %. The combined interface plays a role in the creep behavior of concrete and the amount of hydration products.