矿物掺和料对混凝土早期开裂的影响

针对高性能混凝土普遍存在的早期开裂问题,采用板式混凝土开裂架研究了掺硅灰、粉煤灰、矿渣粉对混凝土早期开裂的影响规律,同时测量了混凝土早期自收缩及在干燥条件下的总收缩。试验结果表明:掺硅灰对混凝土在干燥条件下的早期总收缩影响不大,但使混凝土早期开裂加重;掺粉煤灰使混凝土早期自收缩明显减小,而总收缩并不降低;掺矿渣粉使混凝土早期自收缩和总收缩都增大,而掺粉煤灰和矿渣粉均使混凝土早期抗裂性改善,且掺粉煤灰抗裂性优于矿渣粉。掺硅灰混凝土早期抗裂性差的主要原因是混凝土早期弹性模量增大,徐变和应力松弛能力降低;而掺矿渣粉或粉煤灰混凝土早期抗裂性改善的主要原因在于混凝土早期弹性模量减小、徐变和松弛能力提高。

Effect of Mineral Admixture on Early Age Cracking of Concrete

Early age cracking has been an ever-present problem during the application of high performance concrete.Influences of silica fume,fly-ash and ground granulated blast-furnace slag(GGBS) on early age cracking tendency of concrete were studied using the plate type concrete cracking frame,and autogenous shrinkage,total shrinkage of early age concrete under the drying condition were also measured in this experiment.The test results show that the addition of silica fume worsens the early age cracking of concrete,though it has little influence on the total shrinkage of early age concrete under drying condition.The addition of fly-ash reduces evidently the early age autogenous shrinkage of concrete and it doesn't decrease the total shrinkage of concrete.The addition of GGBS increases both autogenous shrinkage and total shrinkage of concrete at early ages.However,the addition of fly-ash or GGBS improves the early age cracking resistance of concrete,and fly-ash exceeds GGBS.As a result,the main reason of the lower cracking resistance of the silica fume concrete is that the addition of silica fume increases the elastic modulus and reduces the creep stress relaxation capability of concrete at early ages.The higher cracking resistance of the concrete added with fly-ash or GGBS is due to the lower elastic modulus and the better creep stress relaxation capability of concretes at early ages.