Study On Strength And Shrinkage Properties Of High Performance Concrete With Compound Mineral Admixtures

As a new substance used in building, high performance concrete attracts more and more attention in engineering field with the increased application. In recent years, high performance concrete is getting widely used gradually in bridge engineering. It brings a range of issues while improving the performance of bridge, such as concrete cracking for long span bridge. These issues can seriously influence safety and durability of bridges. Shrinkage of concrete is not only the main reason causing concrete cracking, but also the mian factors in respect of durability of long span bridge. As the mineral admixtures, fly ash(FA) and granulated blast furnace slag (GGBFS) affect shrinkage of concrete and cracking control. Therefore, it is necessary to study on strength and shrinkage of high performance concrete with compound mineral admixtures Usually, we more often aimed at one type of mineral admixtures, and there is less study on two or more compound mineral admixtures. The article has studied the influence of compound mineral admixtures on strength and shrinkage of high performance. The main contents and conclusions are summarized as follow:(1) By summarizing types and affecting factors of shrinkage of concrete, the action mechanism of drying and autogenous shrinkage and the action mechanism of mineral admixtures in concrete, the influence factors of shrinkage are the relative humidity of the ambient atmosphere and temperature, water-cement ratio, cement kinds, water quantity, kinds and amount of mineral admixture, size of structure and so on.(2) Strength and shrinkage test on high performance concrete which using a fixed water binder ratio and the amount of binder and using FA and GGBFS to replace cement with the same quality are carried out. By the contrast analysis, the influence of the ratio of FA to GGBFS(1:2,2:3,1:1) and the amount of FA and GGBFS(30%,40%,50%) on strength and shrinkage of concrete were obtained. The results show that, the strength of high performance concrete with compound mineral admixtures at early age is lower than ordinary concrete, but the strength is more in later. In the case of identical ratio of FA to GGBFS, the strength of concrete decreases with the increase of the amount of the compound mineral admixtures. In the case of identical amount of the compound mineral admixtures, the strength of concrete decreases at early age and increases later with the increase of ratio of FA to GGBFS. For the compound mineral admixtures, the strength of concrete decrease at early age with the increase of amount of FA or GGBFS. The total shrinkage and drying shrinkage of high performance concrete with compound mineral admixtures is lower than ordinary concrete, while autogenous shrinkage is more than ordinary concrete. In the case of identical ratio of FA to GGBFS, the total shrinkage strain and the drying shrinkage strain of the concrete decrease with the increase of the amount of the compound mineral admixtures, while the autogenous shrinkage strain increases. In the case of identical amount of the compound mineral admixtures, the total shrinkage strain and the autogenous shrinkage strain of concrete decreases with the increase of ratio of FA to GGBFS, while drying shrinkage strain increases. For the compound mineral admixtures, the total shrinkage strain of concrete decrease with the increase of amount of FA or GGBFS. Contrast to GGBFS, the influence of FA is greater than GGBFS. GGBFS is more marked for increasing of autogenous shrinkage than FA for decreasing autogenous shrinkage. the drying shrinkage strain of concrete decrease with the increase of amount of FA or GGBFS, Contrast to FA, the influence of GGBFS is greater than FA. GGBFS is more marked for decreasing drying shrinkage than GGBFS for increasing of autogenous shrinkage.(3) The feature and applications range of several common shrinkage prediction model at home and abroad were analyed. The results of prediction model and experiment data of concrete were compared. On the basis of the experimental data, new strength and shrinkage expressions considering ratio of FA to GGBFS and amount of the compound mineral admixtures has been established, and the result is satisfactory.