Road Reasonable Evaluation Of The Fly Ash Quality

Fly-ash used in roadbase courses should meet three requirements in the currently standard according to the specifications: ①The total content of silicon dioxide, aluminum oxide and ferric oxide should be more than 70%; ②Loss on ignition (LOI) should not be more than 20%; ③Specific surface area should be more than 2500 cm²/g. But even all requirements of some fly-ash meet the standards; its early stage strength may not be qualified. While some fly-ash materials do not meet the standard requirements, but its early stage strength satisfy the requirements of the technical standards. So there are some unreasonable aspects for the current standards of fly-ash used in roadbase, which means that present specifications can not evaluate fly-ash's pavement performance accurately. Based on the experiment research, this paper analysis systematically the impact factors on early stage strength formation for lime fly-ash mixtures from the physics index, chemistry index and pozzolanic activity respectively, evaluates the relativity between each index and strength at early stage one by one, and comes into a conclusion that some properties such as density, water requirement ratio, coal content etc. have great influence upon early stage strength of lime fly-ash mixtures.Compared with the single-factor evaluation system used in the current standards, the compound-factor evaluation system can consider the comprehensive effects of multiple factors about strength formation of lime fly-ash mixtures at the same time, and it can evaluate the pavement performance for fly-ash more reliably and more reasonably. According to experiment results this thesis puts forward the compound quota factor (CI₁, CI₂ and CI₃) by means of mathematical methods such as linearregression etc. for evaluating fly-ash quality, and suggests the limited value for each compound-factor to determine quality of fly-ash used in road for more reasonable basis.