Effect Of Fly Ash Activity

Now the usage of fly ash is urgent problem. Low activation of fly-ash is the main reason that usage of fly ash is limited. Synthesizing research document of the fly ash early activation, chemical measure was taken to activate fly ash in fly-ash cement material. First, measuring the pH value in fly ash slurry and fly-ash cement slurry, how liquid alkalinity influences the activation of fly ash was ascertained preliminary; transiting strength test, the effect of several activators and combining activators was investigated. By using the strength index of the pozzolan effect and the pozzolan effect diagram, the laws of the pozzolan effect in the hardening process of the fly-ash cement was quantitively analyzed. Testing the non-evaporable water content and the quantity of Ca(OH)₂, the hydration of activating fly-ash cement was studied. Combining the macroscopic qualitative research, X-ray diffraction(XRD) technique,scanning electron microscopy(SEM) and energy dispersive spectroscopy(EDS) were adopted to investigate the mechanism of activating. Besides, the self-expansive property and the resistance capability to sulfate attack of activation fly-ash cement were studied.The following are main study results:1. pH=13.15 is the turning point of active mineral corrosion from fly ash. The active SiO₂,Al₂O₃ in fly ash glasses can be eroded quickly when the pH is greater than 13.15.2. When adding activator in fly-ash cement system, only Na₂SO₄ can make the pH value reach 13.15 in 7 days. The initial pH value of adding multi-component activator in fly-ash cement system is higher than adding each one alone. The composite activator of Na₂SO₄ and Ca(OH)₂ has the highest pH value.3. Comparing fly-ash cement paste compressive strength with single activator, Na₂SO₄ shows better performance in enhancing early compressive strength. And the composite activator of sulfate and strong alkalinity has superior effect.4. The increasing speed of the non-evaporable water content in fly-ash cement with activator is faster than without activator. And the quantity of Ca(0H)2 can reach maximum early.5. The self-expansive ratios of activating fly-ash cement increase when adding 2.5%CaCl₂ or when the dosage of Na₂SO₄ is higher than 2.5%. The self-expansive ratio descends after 28 days when adding composite activator.6. When Ca(OH)₂ and SO₄^2- added as activator superabound later, the cement sulphate-corrosion resistance will be reduced.