Research On Limestone Powder As Roller-Compacted Concrete Additive

To save cement and improving such performance of concrete as workability, strength and durability, some kinds of mineral materials are incorporated into concrete with aquantity of more than five percent of total cement account. These mineral materials are namend additives usually including fly ash, silica fume, ground-granulated blast-furnace slags, natural pozzolans, and zeolite powder etc. For mass concrete, in China, fly ash was the only additive which has been used in roller-compacted concrete except Dachaoshan Dam, and gets a favorable effect. In some area, there is abundant hydroelectric resource, but no fly ash and the transport cost is large. To solve this problem and constructing roller compacted concrete dam in this area, a new equivalent additive was researched in this paper.As an inert composition, the powder's impact on the performance of mortar or concrete is mainly depends on its fineness, grain-size distribution and morphology. In this paper, four kinds of grain-size distribution limestone powders were selected by sieving method, laser grain-size analsys and SEM (Scanning Electric Microscope). At the same time we comparedthe morphology of three kinds of additives------fly ash, limestone powder andground-granulated blast-furnace slag. Horsfield Modal, Fuller Curve and Andreason Equation were adopted to theoretically analyze the effect of the grain-size distribution on the filling effect of particles. Then this relationship was proved by Marsh Fluidity and Vibrating Table Method in experiment. Finally, we studied the influence of the limestone powder on the performance of mortar, and selected the best kinds of powder as the new additive by comparing the producing process, filling effect and the influence on mortar performance.Because of the inert property of the limestone powder, the idea of using limestone powder additive only and increasing the cement quantity was used in the concrete mix proportion. In experiments, four mix schemes of additives are choosed which were limestone fines, fly ash, mixture of the limestone powder and fly ash, mixture of the limestone powder and ground-granulated blast-furnace slag. The research is to reveal the influence of the limestone powder on water demand, workability, strength, dry shrinkage and durability of roller compacted concrete. The result shows that all the performances of the concrete with linestone powder are satisfactory and meet the design request, but there are some differences. As for concrete permeability, the pore-structure of the mortar with limestone powder was researched by Mercury Intrusion Method, the result shows that the number of the beneficial pores is less than other additives, especially the quantity of the pores with a diameter less than 20nm, but the number of the harmful pores is not more, that make the concrete with limestone powder have a satisfactory impermeability.The investigation demonstrated that the roller-compacted concrete mix with limestone powder substituting fly ash can be used in some parts of RCC dam.