Abstract: This paper studies the blast furnace slag glass phase structure by a series of analysis methods. In glass phase, both Si and Al ions are confirmed to occupy only tetrahedral sites, while the [SiO4]4- and [AlO4]5- are separated by Ca and Mg. Furthermore, the glass structure corresponds to micro-crystal model, which means it contains some nano-scaled micro-crystals in the glass phase. In addition, the slag glass may separate into two phases: a calcium rich phase and a silica rich phase. According to devitrification experiment, it has been inferred that the chemical composition and structure of silica rich phase are close to that of akermanite,which means most of Si is distribute around Mg.
Abstract: Preparation of α-calcium sulfate hemihydrate (α-HH) from flue gas desulfurization (FGD) gypsum is of great value in effectively utilizing the FGD gypsum. This paper focuses on the effect of seed crystal and some modifiers on the morphology of α-HH on a 500-1000 kg/batch setup based on a salt solution method established on the previous work. The pilot tests were carried out in a Ca-Mg-K chloride solution medium at 94 oC (±2 oC) under atmospheric pressure. The results show that a small amount of seeds is advantageous to prepare short-prism α-HH but results in needle-like and spherical crystals in the case of more than 1% addition. The well-shaped α-HH crystals can also be obtained by adding appropriate amounts of crystal modifiers like Fe3+ and the mixed salts of Al3+ and organics.
Abstract: Discrete element method is emerging as a useful numerical analysis tool for engineers interested in granular materials such as soil, concrete, or pharmaceutical powders. Simulated the concrete’s microscopic property and its impact on the macroscopic property by using particle discrete element method is one of the important research topics. Obviously, the first step in a discrete element simulation is the generation of the geometry of the system concerned, the quality of which will directly decide the quality of the simulation result. An integrated approach termed random adjusted calculation method is proposed in this paper after detailed analysis of the advantages and disadvantages of the existing aggregate delivery methods. The new method is a method which combined both the advantages of random method and non-geometry methods, such as hopper method and explosive repulsion method. Through out the analysis of the basic process of aggregate delivery and indicated by the result of the examples, random adjusted calculation method has the advantages of good overall density and easily controlled grading; and the computational time is smaller than the existing methods of non-geometry aggregate delivery; furthermore, the new method is easily carried out and provides a new idea for the delivery of concrete aggregate.
Abstract: Under different content of blast furnace slag and steel slag powder, cements were mixed to investigate the effect of dosage of these two mineral admixtures on strength, autoclave expansion and the relationship between strength and volume fraction of pore. The results indicated that the ratio of clinker content to ground granulated blast furnace slag(GGBS) content is the crucial factor for compressive strength of mortars incorporated GGBS and steel slag at 28d. With different dosage of steel slag, the compressive strength of 1:1 mixes of clinker and GGBS has the maximum strength. With the steel slag mixed in cement, the porosity of cement pastes was increased. With the blast furnace slag mixed in cement, the porosity and pore size of cement pastes was decreased. Compressive strength of mortars was closely related to the content of pore in the sizes greater than 50 nm at 28d. Incorporating GGBS can significantly decrease the autoclave expansion of cement deduced by blending steel slag.
Abstract: Traditional Rammed earth houses are still widespread in rural areas of western China. However, the seismic damage of earth houses is usually serious due to its poor seismic resistance and little research has been conducted on dynamic tests of rammed earth structure. A simple and low-cost method to reinforce the rammed earth wall is put forward in the paper. The shake table testing for both the wall panels with and without reinforcements has been carried out. The test results are analyzed from the aspects of damage phenomenon, dynamic behavior, and acceleration and displacement responses of both specimens. The results show the effectiveness of the reinforcement method on improving the seismic capacity of the rammed earth wall.
Abstract: Based on the multi-phase hydration dynamic model, taking into account the factors such as chemical composition of cement, curing temperature, water-cement ratio, the final hydration degree and fineness of cement, a theoretical hydration kinetics equation is established in this paper. It can be used to predict the hydration rate increases with the change of hydration degree. The results showed that: water-cement ratio will accelerate the phase boundary reaction, while not influence the early crystallization of nucleation and crystal growth; temperature can accelerate the hydration process, while it can not change the ultimate hydration degree.
Abstract: Based on the microstructure evolution of cement hydration, using the relationship between the hydration rate and hydration degree, chemical shrinkage prediction model of cementitious materials are proposed. This model can simulate chemical shrinkage curve of cement-based material well. In the early period, increasing water-cement ratio can increase chemical shrinkage. While in the middle period, its influence on chemical shrinkage is negligible. Increasing temperature accelerates the hydration process significantly, therefore, increases the chemical shrinkage.
Abstract: The influencing factors of sodium sulfate solution physical crystallization attack on cement mortars were investigated through analyzing the changes of macroscopical capability and microstructure of cement mortars in attack process. Results indicate that with partial soaking time increasing, more and more sulfate sodium crystals grow on cement mortars surface, and cement mortars surface is denuded gradually. Compressive and flexural strength increase first and then decrease in the deterioration process. In the attack process, porosity of cement mortars decreases first and then increases. Lots of sodium sulfate crystals accumulate in pores of cement mortars and crystallization pressure is on the rise, resulting in physical crystallization attack taking place.
Abstract: This paper is about the suppressing of the alkali-silica reactivity of limestone aggregate by using finely ground limestone aggregate. The accelerated mortar-bar expansion test (ASTM 1260) was used to evaluate the effectiveness of limestone powder in suppressing ASR expansion. Three mixes were used, respectively, 15%, 30% and 50% limestone power replacement of the cement. The results showed that deleterious expansions due to ASR could be suppressed by using reactive limestone powder. The effects depended on what the replacement amounts and the ages were. With appropriate replacement amounts, the deleterious expansions due to ASR could be reduced by using reactive limestone powder. Author believes that any type of mineral SiO2 with being grounded to certain fineness can suppress the ASR reactivity of aggregates, and the effectiveness of reactive aggregate powder is better than that of non-reactive aggregate powder. The replacement level that can control expansion varies with the type of mineral SiO2 and fineness of the aggregate powder.