The objective of this study is to investigate the effect of the mineral admixtures on pipe flow of pumped concrete through analyzing the properties of lubrication layer playing a dominant role to facilitate concrete pumping. Concrete mixtures incorporating blast furnace slag (BFS), fly ash (FA) and silica fume (SF) were selected with three different replacement ratios for each case and pumped through 170 m circuit. The rheological properties were measured before pumping and the thickness of lubrication layer was also experimentally observed with a special sensor, ultrasonic veloc-ity profiler (UVP). An analytical equation considering the effect of the layer was adopted to calculate the thickness of the layer and to compare with full scale pumping results. The lubrication layer of BFS and FA indicated almost constant value regardless of replacement ratios but varied with SF mixtures. The concrete incorporating BFS or 5% SF represented satisfactory improvement of pumping efficiency.
For the purpose of performance evaluation of an existing reinforced concrete member, a computational simulation model to predict the spatial and temporal changes of physical properties of concrete in the member, named the “Computational Cement-Based Material Model (CCBM)”, was proposed. This proposed simulation model includes models of rate of hydration of cement minerals, phase composition, and resultant hygro-thermo-mechanical properties of cement paste (i.e., compressive strength, Young’s modulus, Poisson’s ratio, thermal expansion coefficient, autogenous shrinkage, drying shrinkage, heat capacity, heat transfer coefficient, water vapor sorption isotherms, and water transfer coefficient). Furthermore, the model for compressive strength of concrete considered the variation in cement paste strength due to its colloidal features as well as micro-defects produced around aggregate due to differences in volume between aggregates and mortar upon heating and drying. The concrete properties of spatial distribution and temporal changes were evaluated by coupling these models with heat and water transport. Validation of these models was achieved by using existing experimental data. Using this CCBM, a thick concrete wall made with moderate Portland cement with a water-to-cement ratio of 0.55 under one-sided heating was simulated and potential problems that can arise during an integrity evaluation were discussed. If the required compressive strength, which was assessed within 91 days of placement, remains unchanged, an additional hydration process can build an adequate strength margin to overcome the risk of strength reduction due to heat and drying. However, in the case that the required strength is increased due to a re-evaluated risk, such as the magnitude of an earthquake, performance evaluation is not trivial as the core sample taken from the side where the execution of sampling is possible could exhibit a greater strength than the average strength of the target concrete member. Therefore, numerical evaluation might aid in this kind of situation.
Following the publication of the Australian Standard AS 3972, “General purpose and blended (GP) cements” in 2010, a research programme was undertaken to determine the effect, if any, of increasing the maximum permissible mineral addition in Type GP cement. This paper involves the assessment of the variation in standard laboratory concrete properties due to increasing the limestone addition in cement. Workability, bleed water, compressive strength and drying shrinkage of concrete samples with different limestone contents in the range of 5% to 12% were examined. Based on the research results, it is recommended that the maximum allowable mineral addition in Type GP cement be increased from 7.5% to 12%.
A model to evaluate quantitatively the alkalinity of pore solution based on phase composition of cement hydrates with SCMs was proposed and was compared with suppressing effect of ASR expansion. The model is devised from the per-spective of alkali sorption by C-S-H gel, and the parameters for calculation can be evaluated thanks to phase composition analysis such as XRD/Rietveld analysis and selective dissolution. The experimental results have shown that ASR ex-pansion is strongly correlated to the alkalinity of the pore solution, which can be calculated with the proposed model. Based on the results, the ASR suppressing effects of SCMs are converted to the reduction in total alkali content as available alkali content. Finally, the required replacement level of SCM with the proposed model was compared to the CSA A23.2-27A standard based on numerous experiments and field experiences in Canada. The calculated result was well consistent with the minimum replacement level of SCMs specified in CSA A23.2-27A. A subsequent interpretation of this study supports that the dominant mechanism of SCMs for ASR suppression is a reduction of alkalinity of pore solution.
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