Study On The Rice Husk Ash From The Power Plants And Its Application In Concrete

With the gradual depletion of traditional energy and the increasingly degradation of the environment, human were paying much greater attention to energy saving, emission reduction and developing new energy. Supported by the national policies, more and more new kind of power plants which produced electricity by burning agricultural waste such as rice husks were created these years. However, there still were no appropriate ways to deal with or use the high-blackness rice husk ash from these power plants, causing the resource waste and environmental re-pollution.Because the temperatures in the power gasifiers were not symmetrical (600℃-850℃), the rice husks sustained high temperature in just a very short time during the being-ash process. Therefore, the SiO2in the rice husk ash probably had high reactivity. Referring to existing research data, the rice husk ash from the power plants (E-RHA) were tried to be as concrete mineral admixture in this paper. PIXE, XRD, pozzolanic activity test, cement mortar experiment and many other methods were utilized to synthetically test and evaluate the physical and chemical properties of the E-RHA. On the other hand, several groups of E-RHA which were milled for different times were added in different water-cement ratios of concretes in different contents, then the workability, mechanical properties and durability of these concretes were be tested to analyze the effect that the E-RHA brought to the concretes and verify the E-RHA’s potentiality to be the concrete mineral admixture. In addition, based on the characteristics of E-RHA, its applications in practical engineering were explored as well.After these tests, the results showed the E-RHA had87.89%of SiO2in total. Only23.92%of these SiO2had been turn into crystal, the last77.08%of SiO2were still amorphous because the high temperature phase in the power gasifiers was too short to let the amorphous SiO2turn into crystal, therefore, the E-RHA had87.89%of SiO2. The original E-RHA had part of coarse particles, the45um sieve remain ratio reached41.8%, whereas it also had a certain amount of nano-SiO2and the coarse particles had porous internal structure. These made the original E-RHA had large specific surface area that reached65m/g and92of pozzolanic activity index which was much larger than the fly ash and no less than the silica fume.The original E-RHA should be milled before it be added in concrete because its45μm sieve remain ratio was a little big, and the research results showed the best grinding time was30minutes. After30minutes milling, the45μm sieve remain ratio reduced to23.8%and the specific surface area reached60m2/g. The E-RHA would lower the slump of the concrete, and the effect was more conspicuous with bigger content of E-RHA. The adding of E-RHA would seriously affect the workability of the low water-cement ratio concrete. When the concrete had higher water-cement ratio, the effect of E-RHA took to the slump was weaker. The E-RHA was able to relieve the poor cohesiveness and water retention of the high water-cement ratio concrete and enhance the mechanical properties of concrete but the content of E-RHA was preferably not more than10%in the low water-cement ratio concrete. When the water-cement ratio was appropriate, the compressive strength of concrete increased with adding more E-RHA, and the best content was30%. Otherwise, the E-RHA minified the inner pore size of the concrete so the concrete had more compact structure and the volume stability, impermeability, frost resistance and anti-carbonation of concrete were also improved, and the water-cement ratio was bigger, the improving effect was greater.AS the reducing effect to the fluidity brought by the E-RHA was slight while the improving effect to the volume stability of the concrete was greater, the E-RHA was able to make self compacting concrete (SCC) which the intensity reached the C40grade and the self compacting properties met grade II. Otherwise, the E-RHA could play dual roles of mineral admixtures and coloring matters, the color of the concrete was deeper when the content of E-RHA was bigger, and the color stability and other capabilities of the concrete was also satisfactory, so the E-RHA could used to produce black structural and road concrete.