The Manufacture of Concretes Based on Unburnt Ash Gravel

A new method of producing unburnt ash gravel of high strength has been developed. The gravel consists of fly ash obtained from the heat power industry, Portland cement screening from rock crushing and accelerator of hardening. The method involves proportioning and mixing the components, moistening the mixture, forming the granules of the required coarseness of grading, heating and moistening the grains and fractioning. As far as the strength of the gravel is concerned, it stems from two factors: the acceleration of clinker mineral hydration under the influence of Na2SO4 and the packing of the fly ash cement stone structure. As hornblendite is a chemically inert material, it is used as a filler agent. The unburnt ash gravel has the following properties: density 900 kg/m3; compressing strength 7.5 MPa; frost resistance, F50 and water absorption 10%. It is recommended to use the unburnt ash gravel developed as coarse aggregate to lighten the construction concretes. In fact, practical implementation of the method in question enables a 5–10% reduction in construction costs.