摘要: Fly ash is a sustainable partial replacement of Portland cement that offers significant advantages in terms of fresh and hardened properties of concrete. This paper presents the findings of a study that aims at assessing the durability and strength properties of sustainable self-consolidating concrete (SCC) mixes in which Portland cement was partially replaced with 10%, 20%, 30%, and 40% fly ash. The study confirms that replacing Portland cement with fly ash at all of the percentages studied improves resistance of concrete to chloride penetration. The 40% fly ash mix exhibited the highest resistance to chloride penetration compared to the control mix. Despite the relative drop in compressive strength after 7 days of curing, the 28-day compressive strength of 40% SCC mix reached 55.75 MP, which is very close to the control mix. The study also confirms that adding 1%, 1.5%, and 2% basalt fibers, respectively, to the 40% fly ash mix improves the resistance to chloride penetration compared to the mix without basalt fibers.
摘要: One of the most useful innovations in concrete technology is Self Compacting Concrete that has the ability to flow efficiently and maintain material homogeneity. The rapid change in the behavior of concrete due to accelerating admixtures can significantly affect the workability properties of the mixture and reduce its ability to flow efficiently. To describe the influence of superplasticizers blended with accelerant on the rheological properties of SCC, several mixtures were tested for Slump Flow, L-Box, and Screen Stability tests. Artificial neural network was used to obtain a model describing the constitutive relationships between the material components and workability parameters of SCC and was optimized using Genetic Algorithm. Results showed that ANN was able to establish the relationship of rheology to the concrete material components and GA derived the optimum proportion for best rheological performance. Most of the design samples of SCC with blended superplasticizer and sodium lignosulfate accelerant were not able to perform well in the flowing ability due to inefficiency of the fresh SCC to flow. The increasing dosage of accelerant however rendered strong stability between the concrete particles allowing the SCC samples to resist segregation and maintain material homogeneity.
摘要: In order to evaluate more accurately the corrosion condition of reinforcing steel in chloride contaminated concrete, it is significant to investigate the error level in the linear polarization resistance measurement caused by IR drop. Concretes with eight levels of chloride ions (ranging from 0% to 2.0% by mass of cement) by adding different amounts of sodium chloride in the mixing water were prepared. Linear polarization measurements with and without IR compensation, were applied to determine the error level. Besides, half-cell potential method was employed to detect the corrosion condition of reinforcing steel. The results indicate that the error level is so low (less than 5.0%) that the IR drop can be negligible when the chloride content is relatively lower (0.6% or less by mass of cement). However, the error level is increased with the increase of chloride content. The IR drop is suggested to be compensated when the chloride content is relatively higher (more than 0.6% by mass of cement). At this time, the onset of active corrosion of reinforcing steel is also found.
摘要: Stockpiled high carbon-content fly ash and lime was used to prepare belite cement by hydrothermal reaction followed by low temperature calcination. Sodium hydroxide was added as an activator to accelerating the reaction. 0-1.5 wt% Na2O equivalent NaOH was added as a aqueous solution into the mixture of 20 wt%-35 wt% CaO and 65 wt%-80 wt% fly ash. The mixture was formed into granules and steam-curing the at 97°C for 12 h, followed by heating at 800°C for 1 h. The results show that adding 1.0 wt% Na2O to the mixture of fly ash and CaO can efficiently promote the hydrothermal reaction. Belite cement with practicable strength and characterized by rapid setting and high sulfate attack resistance was synthesized.
摘要: Various sources of uncertainty exist in concrete fatigue life prediction, such as variability in loading conditions, material parameters, experimental data and model uncertainty. In this article, the uncertainty model of concrete fatigue life prediction based on the S-N curve is built, and the evidence theory method is presented for uncertainty analysis in fatigue life prediction of concrete while considering the epistemic uncertainty of the parameter of the model. Based on the experimental of concrete four-point bending beams, the evidence theory method is applied to quantify the epistemic uncertainty stem from experimental data and model uncertainty. To improve the efficiency of computation, a method of differential evolution is adopted to speedup the works of uncertainty propagation. The efficiency and feasibility of the proposed approach are verified through a comparative analysis of probability theory.
摘要: It is well known that cement stabilization of granular materials is a cost-effective and environmentally friendly technique for the highway construction. However, the testing and design methods for these stabilized materials have not been sufficiently advanced scientifically, which hinders their full potential application. The proper characterization of the stabilized pavement materials is vital for the successful pavement design and construction. This paper presents the results from an experimental study on the effect of cement stabilization on pavement materials in terms of engineering properties essential for use in mechanistic design of road pavements. The test results from this study revealed that the index and shrinkage properties of the pavement materials are significantly influenced by cement content, and the tensile and compressive resistances of a cement stabilized pavement base layer increase significantly with the increasing cement content and increasing curing period. Based on the test results, it is concluded that the flexural modulus/UCS and the flexural strength/UCS ratios of the cement stabilized pavement materials depend on the material, age of curing, initial stage of the compacted material and laboratory testing practices.
摘要: In this study the effect of age, w/c ratio on mean distribution radius and dispersion of pores in Ordinary Portland Cement (OPC) sand mortar was determined through Mercury Intrusion Porosimetry (MIP) test. For this purpose the cement sand mortar specimens were prepared from two different types of OPC with varied w/c ratios such as 0.2, 0.3, 0.4, 0.5 and 0.6 and tested at different curing ages from 1 day to 90 days. Separate relationships relating the mix parameters such as w/c ratio and age with mean distribution radius (r0.5) and coefficient (d) representing dispersion of pores, are developed for OPC sand mortars.
摘要: Durable life of concrete structures under the chloride environment depends on the permeability of chloride ion, and the chloride ion diffusion coefficient is the main indicator that reflects the permeability of chloride ion. Based on the Fick’s second law, a multi-factor model of the chloride ion diffusion is established. In this model, the influences of temperature, humidity, age of the concrete, fly ash and carbonation are taken into consideration. And the model is verified by engineering test data from the concrete structure under the wet and dry areas of marine. The results show that the calculated and measured values of the chloride ion content agree well, the actual situation of the project could be basically reflected. The multi-factor model of the chloride ion diffusion is practical.
摘要: High Density concrete is commonly used for radiation shielding of nuclear-reactors and other structures like counter weights, coating of off-shore pipelines. High Density concrete or is designed by using heavy weight aggregates such as hematite, magnetite, barite etc. The material is called hematite is used in this special concrete. The mix used is for OPC 43grade of cement. High density concrete can be designed in same way as normal weight concretes, but the additional self-weight should be taken into account.