Subgrade Material Properties Of Red Mud Matrix Geopolymer Under Alkali Excitation By Fiber Reinforced

With the rapid development of industry,the demand for infrastructure is increasing and the requirement for it is also increasing day by day.As a by-product of industrial production,red mud is piled up in large quantities and continuously produced.Due to its low activity and high alkalinity,red mud restricts its utilization,which has caused land occupation and serious environmental problems.The treatment of red mud by geological polymerization is an effective,sustainable and environmentally friendly method to improve the properties of red mud.However,in the current relevant studies,the amount of red mud used as the matrix of geological polymerization reaction is relatively low,and the research on the large amount of red mud used is relatively limited,thus limiting the utilization related to the large consumption of red mud.In this study,GGBS and red mud with a large proportion(> 90%)were used for geological polymerization reaction,and a test scheme of two kinds of active GGBS under five additive amounts was designed to significantly improve the physical and mechanical properties of the red mud,such as compressive strength,compressibility and durability,and the structure of the red mud after the action of GGBS was analyzed through microscopic testing;on this basis,sodium silicate was added as an alkaline activator to react with red mud and GGBS,and the compressive properties,splitting tensile properties,brittleness,compression properties and durability of the composite geological polymerization products were studied;finally,three kinds of fibers,namely basalt fiber(BF),polypropylene fiber(PP)and polyester fiber(PET),were used to combine with alkali excited red mud based composite materials.After fiber treatment,mechanical properties of modified red mud were tested,and alkali excited red mud composite materials under the action of fiber were further studied and analyzed.The specific research content and conclusions of this paper are as follows:(1)In this study,a binary system of red mud(> 90%)and GGBS was established.The method of GGBS reacting with red mud through geological polymerization was used to effectively improve the mechanical properties of red mud,and it was obtained that the modified red mud under the action of GGBS > 5% had good mechanical properties.Two kinds of GGBS with different activity(S105 GGBS and S140 GGBS)were used for geological polymerization reaction with red mud under five additive amounts(0.5%-7%),and the unconfined compressive strength,compressibility and durability of the untreated red mud and red mud-GGBS samples were tested and compared.The results show that the compressive strength of red mud increases with the increase of GGBS content.Under the same addition amount,the performance improvement effect of S140 GGBS on red mud is better than that of S105 GGBS.SEM test of modified red mud shows that the structure of red mud treated with GGBS is more dense.XRD analysis of the red mud treated with GGBS also proves that geological polymerization has occurred.(2)The mechanical properties of red mud did not always increase with the addition of sodium silicate replacing part of GGBS,but the use of sodium silicate replacing part of GGBS improved the durability of red mud.By replacing part of GGBS with sodium silicate,the red mud matrix composite material under alkali excitation was tested for compressive strength,splitting tensile strength,disintegration and consolidation.The compressive strength does not always increase with the increase of sodium silicate and the decrease of GGBS.The compressive strength of red mud matrix composite under alkali excitation is the highest at 3%GGBS and 2% sodium silicate,up to 3.45 MPa,while UCS of 3% S105 GGBS and 2% sodium silicate can reach 3.35 MPa.At the same time,the splitting tensile strength of red mud composite is as high as 0.141 MPa.Combined with the failure mode analysis of red mud,the red mud composite becomes brittle gradually and the ductility decreases somewhat under alkali excitation.Compared with untreated red mud and GGBS treated red mud,the red mud with sodium silicate replacing part of GGBS has decreased porosity,and the red mud is more dense.At the same time,the durability of red mud has been significantly improved.After alkaline activator treatment,the red mud under the action of S105 GGBS and the red mud under the action of S140 GGBS both have good durability.No disintegration occurred during the 3-day test,and the red mud under the combined reaction of sodium silicate and GGBS could maintain good integrity in the early stage.(3)The red mud treated by geological polymerization with GGBS and sodium silicate showed brittleness,and with the increase of fiber content,the mechanical properties of the red mud gradually increased and the ductility improved relatively within a certain fiber content(1.5%).After polyester fiber(PET),polypropylene fiber(PP),basalt fiber(BF)respectively treated red mud and red mud matrix composite decreased brittleness.By conducting compressive strength tests,splitting tensile strength tests,consolidation tests and durability tests on red mud and red mud matrix composites with only fiber added,and analyzing their ductility,it can be seen that the addition of fiber has no obvious effect on the improvement of compressive strength of modified red mud,and there is no obvious trend of influence on the durability of red mud.After adding fiber,the porosity of red mud decreased,which has good resistance to pressure deformation.The splitting tensile strength of red mud can be improved obviously within a certain dosage(1.5%).The three kinds of fibers can improve the tensile strength of red mud.Compared with basalt fiber(BF),polypropylene fiber(PP)and polyester fiber(PET)can improve the red mud more obviously under the same dosage.The tensile strength of composite red mud can be increased by 1.71 times and 2.26 times at most by adding polyester fiber and polypropylene fiber respectively.According to the stress-strain curve,compared with the red mud without fiber,the brittleness decreases obviously and the ductility improves relatively.This indicates that the fiber can effectively improve the splitting tensile strength and ductility of red mud,and further enhance the mechanical properties of red mud matrix composites.