Properties of high calcium fly ash geopolymer pastes with Portland cement as an additive

The effect of Portland cement （OPC） addition on the properties of high calcium fly ash geopolymer pastes was investigated in the paper. OPC partially replaced fly ash （FA） at the dosages of 0, 5%, 10%, and 15% by mass of binder. Sodium silicate （Na2SiO3） and sodium hydroxide （NaOH） solutions were used as the liquid portion in the mixture： NaOH 10 mol/L, Na2SiO3/NaOH with a mass ratio of 2.0, and alkaline liquid/binder （L/B） with a mass ratio of 0.6. The curing at 60℃ for 24 h was used to accelerate the geopolymerization. The setting time of all fresh pastes, porosity, and compressive strength of the pastes at the stages of 1, 7, 28, and 90 d were tested. The elastic modulus and strain capacity of the pastes at the stage of 7 d were determined. It is revealed that the use of OPC as an additive to replace part of FA results-in the decreases in the setting time, porosity, and strain capacity of the paste specimens, while the compressive strength and elastic modulus seem to increase.

Investigation of tungsten halogen lamp for possible usage as heat source for testing solar collector

Artificial sunlight is a heat source in solar collector testing,where the light intensity and ambient conditions are controlled to provide uniformity in each test.In this study,twenty-five tungsten halogen lamps of 300 W 220 V were investigated for possible usage as the heat source.The experiment was conducted by varying the height of the lamps to the light field(H_(d)).The EN-12975-2 Standard was used to control the quality of the heat source on the light field.The results showed that the average light intensity(I_(avg))decreased with an increase in Hd.When H_(d) was low,the%uniformity values(%u_(xy))met the criteria.The small light field area met the EN-12975-2 Standard better than the large area.A comparison of solar collector testing under a heat source from tungsten halogen lamps and natural sunlight was subsequently performed,and the experimental results were in accordance with the EN-12975-2 Standard.A single-channel flat plate solar collector was used as the test device and air was used as the working fluid.The experimental results revealed that the solar collector thermal efficiency(η_(avg))trends were similar for both the heat source from tungsten halogen lamps and natural sunlight testing.A low%u_(xy) resulted in a𝜂avg that was more similar to that of natural sunlight.