Curing plays a vital role in determining the mechanical properties of hardened concrete. The use of Super Absorbent polymer (SAP) has been found to be highly effective in reducing the water requirement for curing. Silica Fume (SF) is commonly used as a mineral admixture in High Performance Concrete (HPC) to improve mechanical and durability properties. But when silica fume was incorporated in SAPs, contradictory results with respect to strength after curing has been reported and this study aims to evaluate the effect of altering dosage of SAP and SF to maximize the strength and to reduce the water requirements in HPC. Concrete tested include traditional HPC and specimens of HPC with SAP, HPC with SF and HPC with combined dosage of SAP and SF. Compressive strength test, Split Tensile test and Sulphate attack test were conducted as per relevant Indian Standards. The dosage of SAP and SF were individually varied in the initial stage and from the experimental results, optimal dosage of SAP and SF was determined. The combined specimen with the optimal dosage of SAP and SF was tested in the final stage. The results showed that self-curing effect of SAP and the filler effect of SF maximize the compressive and tensile strength of hardened concrete. The optimal dosage was derived as 0.35% (by weight of cement) for SAP and 10% (by weight of cement) for SF and higher SAP or SF content in HPC was found to be detrimental with respect to strength.
The pool boiling characteristics of nanofluids is affected by the interaction between the nanoparticles and the heater surface which forms a sorption layer and this layer increases the surface wettability and thereby enhances the CHF. While deteriorated nucleate boiling has been attributed to the decreased activation of cavities due to the increased wettability, it fails to explain the enhanced performance observed by several researchers, which can be explained only by an increase in surface roughness and hence a direct increase in the number of cavities, thereby compensating for the increase in wettability. Attempts to characterize the roughness of heater surfaces have been restricted to magnified visualizations and intrusive probing. No non-intrusive tests have been reported on flat heaters, which are ideal to conduct surface analyses. The present work is aimed at conducting a non-intrusive experimental study to analyse the surface roughness modification due to the sorption layer on flat plate heaters. Experiments have been carried out using electro-stabilized aluminium oxide water based nanofluids of different concentrations with heaters having varying values of surface roughness. The burn-out heat flux was measured and the effect of sedimentation time was studied. The surface-particle interaction parameter (Ra/dp) was varied to capture the phenomena of plugging as well as splitting of nucleation sites. An experiment having a high value of the interaction parameter shows enhanced boiling performance and that with a value close to 1 shows deteriorated performance. Further it was seen that this behaviour is dependent on the particle concentration. Detailed surface characterization has been done using an optical measurements setup and atomic force microscopy. Boiling on nano-coated heaters has been investigated and presented as an effective solution to counter the disadvantageous transient boiling behavior of nanofluids.
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