The Preparation And Performance Investigation Of Shale Gas Drilling Cuttings-coal Fly Ash Based Sintered Ceramsite And Ceramic Concrete

Plenty of oily drilling cuttings generates during the shale gas exploration in southwest China,which have been labeled as hazardous waste by environmental regulatory authorities and must be safe disposal.In this work,the fire tornado forming equipment and muffle furnace are used to harmless treat oily drilling cuttings at high temperature.The influences of fuel type and the initial oily drilling cuttings state on the effectiveness of incineration treatment are discussed,and the pozzolanic activity of drilling cuttings（solid components remaining after treatment of oily drilling cuttings）is evaluated.Furthermore,the sintered ceramsites with excellent strength are prepared from drillings cuttings（DCs）and coal fly ash（CFA）,and also the reaction behaviors and roles of barite in ceramsite precursors during the sintering process are investigated.Then the DCs-CFA based ceramsites act as coarse aggregates to prepare the ceramic concrete.The influences of ceramsites sizes（5-10,10-15,and 5-15 mm）on the compressive strength,splitting tensile strength,and flexural strength of ceramic concrete are determined,and the failure modes of ceramic concrete in mechanical property tests were analyzed.This study provides theoretical basis and guidance for the safe treatment and disposal of oily drilling cuttings.The preprocessing results indicate that the flame temperature of fire tornado triggered by alcohol and gasoline exhibits a pattern with high temperature in the middle（about 950℃）and low temperature at the top and bottom（800-850℃）,meeting the requirements of treating oily drilling cuttings.During the fire cyclone incineration process,the oily drilling cuttings are first heated to eliminate water and then approximately 66 wt.%of the organic component is removed by their spontaneous combustion.Thus,the treatment effect is not significantly influenced by the fuel type.Compared to dry oily drilling cuttings（3.62 wt.%）,wet oily drilling cuttings would bond during incineration,which causes more organic components（about 5 wt.%）to remain in the wet samples.Then the residual organic components are completely removed during the heat treatment in the muffle furnace.Moreover,the pozzolanic activity indexes of DCs obtained by fire tornado incineration treatment range from 0.65 to0.70,and then the pozzolanic activity index of DCs is increased to 0.82 after heat treatment in a muffle furnace.The high strength ceramsites are successfully prepared at high temperatures with DCs and CFA to further realize the safe disposal of DCs.The cylinder compressive strength of optimal ceramsites（S3）is 20.23 MPa and the breakage ratio meets the requirements of Chinese standard（Measurement of properties of proppants used in hydraulic fracturing and gravel-packing operations（SY/T5108-2014））for 2K grade ceramic proppants（CPs）.Barite mainly reacts with silica/alumina during the ceramsite sintering process.The main interactions not only fall the eutectic point of mixtures and form the barium-containing aluminosilicates,but also could release gases（SO₂ and O₂）to generate pores and further impair the CPs strength.The optimal sintering temperature range is 1170-1200°C with gentle weight loss,negligible gas generation,and suitable amount of the liquid phase（moderate viscosity）,which enforces the CPs densification and dense enamel layer formation.The composite reactions of barite in S3 follow the chemical reaction（one and a half order）mechanism in the range of 950-1200°C.The average activation energy and pre-exponential factor are 583.304 k J·mol^-1 and 5.81×10²⁰min^-1,respectively.The kinetic and reaction rate equations for the composite reactions were（1-α）^-1/2-1=(5.81×10²⁰×e^{-5.83×10^5/RT})×t and dα/dt=(2（1-α）^3/2)×(5.81×10²⁰×e^{-（5.83×10^5）/RT})),respectively.In order to further realize the application of DCs-CFA based ceramsites,the ceramic concrete is prepared using ceramsites（5-15 mm）as coarse aggregate.The 28 d compressive strength results show that the ceramic concrete prepared by ceramsites（particle sizes with 5-10 and 5-15 mm）as coarse aggregates greater than the concrete confected intensity of LC30（>38.23MPa）,meeting the requirements for structural concrete.In the particle size range of 5-15 mm,the reduction of the aggregate size does not produce remarkable influences on the density of concrete.Nevertheless,the reduction of the ceramsites size would improve the strength of ceramsites,and allow the more balanced distribution of ceramsites in the samples,and avoid the formation of a large interfacial transition zone in the concrete specimens,which ultimately increases the compressive,splitting tensile and flexural strength of concrete.Moreover,the cross-sectional morphology of ceramic concrete shows that the ceramsites in ceramic concrete are the main damaged positions under the force.