Experimental Study On Mechanical Performance Of Geopolymer Concrete Material And Columns With Demolished Concrete Lumps

Geopolymer,as a new environment friendly building material,has been reported to exhibit good mechanical properties.Recycled concrete with demolished concrete lumps(DCLs)is an efficient way to reuse waste concrete.It can further reduce the amount of cement using than common recycled concrete with DCLs to prepare geopolymer recycled concrete with DCLs by combining geopolymer with the recycled demolished concrete.So it is more energy-efficient and environmentally friendly.At present,there are few researches on geopolymer recycled concrete with DCLs.In order to furtherly study the basic mechanical properties and structural performance of geopolymer recycled concrete with DCLs,and to provide a theoretical basis for its engineering applications,the following works were carried out in this paper:1.Fifty-one 300 mm-cubic specimens fabricated by fresh geopolymer concrete(GC)or common concrete(CC)with DCLs were tested under uniaxial loading.The influences of the types and strength of fresh concrete(FC),strength of demolished concrete,replacement ratio and water content of DCLs,and waste mortar content in DCLs on the composite concrete strength,elastic modulus and non-dimensionalized stress-strain curves of the specimens were investigated.Based on the experiment results,predictions of composite concrete strength and elastic modulus of specimens were formulated.Test results show that:(1)the composite concrete strength decreased with an increase in the replacement ratio of DCLs;(2)when compressive strength of fresh geopolymer concrete is the same as fresh common concrete,the compressive strength of geopolymer recycled concrete with DCLs is slightly higher than specimens fabricated by common recycled concrete with DCLs at the same replacement ratio of DCLs,due to the strengthening effect of geopolymers on the DCLs;(3)the moisture content of the DCLs has no significant effect on the strength of the geopolymer recycled concrete with DCLs;(4)when the content of waste mortar in the DCLs is less than 10%,the waste mortar has little influence on the strength of specimens;(5)the predicted results from the proposed formula for composite compressive strength and elastic modulus of specimens agree well with the measured results;(6)the replacement ratio of DCLs has a greater effect on the non-dimensionalized stress-strain curves of specimens fabricated by geopolymer recycled concrete with DCLs than that of the common recycled concrete with DCLs.2.Twenty-four cylindrical specimens(300 mm-diameter,600 mm-height)prepared using geopolymer concrete and DCLs were tested under uniaxial loading.The influences of the types and strength of FC,strength of demolished concrete and replacement ratio of DCLs on the composite concrete‘s axial compressive strength,elastic modulus,Poisson’s ratio and peak strain of the specimens were studied.The experiment results of the cubic specimens and cylindrical specimens were compared,and then the size effect and shape effect of composite strength of geopolymer recycled concrete with DCLs were investigated.Test results show that:(1)the ratio of the axial compressive strength to the cubic compressive strength of GC with DCLs is between 0.75 and 0.85,which is higher than that of the common concrete with DCLs(the ratio of CC with DCLs ranged from 0.61 to 0.69);(2)the elastic modulus of the specimens increases with an increase in the replacement ratio of DCLs,and the higher the strength of the demolished concrete,the more significant effect of DCLs on the elastic modulus of specimens;(3)the Poisson’s ratio of the GC with DCLs is lower than that of ordinary concrete,and the replacement ratio of DCLs has no significant influence on Poisson‘s ratio;(4)the usage of DCLs can greatly reduce the hydration heat of geopolymer concrete;(5)The prediction formulas of axial compressive strength and elastic modulus of specimens made of GC with DCLs are in good agreement with experimental results.3.Twenty-two reinforced concrete short columns with DCLs were tested under axial loading.The influences of the types and strength of FC,strength of demolished concrete and replacement ratio of DCLs on the axial bearing capacity and deformation properties of specimens were investigated.The test results show that:(1)when the replacement ratio of DCLs is 25%,the bearing capacity of the columns decreases less than 10% compared with that of the columns fabricated by fresh geopolymer concrete,and the replacement ratio of DCLs has a greater effect on the axial compressive bearing capacity of the columns using GC than that of the specimens using CC;(2)the strength of demolished concrete has a significant influence on the axial bearing capacity and stiffness of the short columns fabricated by GC with DCLs,and the lower the strength of demolished concrete,the larger the effect;(3)the axial bearing capacity of the short columns fabricated by GC with DCLs can be directly calculated using the formulation for ordinary reinforced concrete short columns in GB50010-2010 code,and the calculated bearing capacity has a certain safety redundancy.