Study On Regulation Preparation And Mechanical Properties Of Calcium-based Geopolymer Modified By Nano-calcium Carbonate

Nano-calcium carbonate is a new functional material and it has many properties,such as size effect,large specific surface area,nucleation effect and interface effect.Therefore,the modification of Calcium-based geopolymer which has unique three-dimensional network structure with nano-calcium carbonate is of great help to the further improvement of its properties,in order to be better applied in the field of road and construction engineering.Different mixing methods,contents and dispersion times of nano-calcium carbonate were adopted for the preparation of Calcium-based geopolymer.Nano-calcium carbonate effect of the working performance,compression strength,splitting tensile strength,and flexural strength on the Calcium-based geopolymer's properties were analysed.Finally,the optimum mix ratio for material properties of nano-calcium carbonate modified Calcium-based geopolymer was obtained by investigating the excellent modification mechanism of nano-calcium carbonate.The main research results of this paper are as follows:(1)As an admixture,nano-calcium carbonate can effectively improve the fluidity of the Calcium-based geopolymer paste,and the improvement significant increases when the content is 4%.But the fluidity will decrease with the increase of nano-calcium carbonate,when nano-calcium carbonate as an additive.Nano-calcium carbonate can promote the polymerization of Calcium-based geopolymer and reduce the setting time of Calciumbased geopolymer.The final setting time decreased by 39 min when nano-calcium carbonate's replacement amount was 6% and reduced by 55 min,when nano-calcium carbonate's addition amount is 4%.(2)Nano-calcium carbonate can increase the compressive strength of Calcium-based geopolymer,and the best addition amount is 2%.The compressive strength of 28 d is 20% higher than that of the sample without adding nano-calcium carbonate,and the compressive strength of 28 d is 18% higher than that of the sample without nano-calcium carbonate when the content is 2%.The content of nano-calcium carbonate decreased obviously after ultrasonic dispersion for 30 min,in which the optimum content was changed from 2% to 1.5%,the compressive strength of 28 d was 60MPa;the optimum addition amount was changed from 2% to 1%,and the compressive strength of 28 d was 63 MPa.Combined with microscopic analysis,Nano-calcium carbonate has remarkable filling effect and can increase the compactness of the material.In addition,nano-calcium carbonate can accelerate the polymerization of Calcium-based geopolymer and promote the formation of amorphous gel products such as calcium silicate hydrate,thus effectively improving the mechanical properties of the material.(3)Nano-calcium carbonate can improve the tensile strength and bending strength of Calcium-based geopolymer,and the best addition amount is 1%,the tensile strength of 28 d is 5.2MPa,the flexural strength of 28 d is 6.78 MPa.The growth of split tensile strength and flexural strength of the modified Calcium-based geopolymer mainly focused on 0?7d,the relationship between two strength and curing age satisfied the logarithmic function.Microscopic analysis found that nano-calcium carbonate can enhance the degree of bonding between gels,improve the toughness of the sample,but the content should not be too high or the sample is prone to crack.The maximum tensile pressure ratio of the modified Calcium-based geopolymer appears when nano-calcium carbonate's addition amount is 1%,and the minimum pressure fold ratio appears when the addition amount is 0.5%.After comparing all conclusions,the best mix way is adding the nano-calcium carbonate to the Calcium-based geopolymer after dispersion 30 min,and the best amount is 1%.