Study On The Effect Of Stone Powder On The Properties Of Cement-Based Materials At Micro And Nano Scale

The production of cement not only consums large amounts of non-renewable resources,but also generates lots of carbon dioxide.Meanwhile,large quantities of stone powder is discarded during the production and processing of stone products,serious polluting the surrounding environment.While,the use of the waste stone powder as a cement replacement to preparethe cementitious material can reduce the pollution caused by cement manufacture and the stone powder disposal.At present,there are many studies on the application of stone powder in cementitious materials,but most of them focus on the influence of stone powder on the macroscopic properties of cementitious materials.There are few studies on the deeper mechanisms of the influence of stone powder in cementitious materials.In this study,the effects of different stone powders on the properties of cement-based materials were studied from micro/nano scale,and its mechanism was discussed.In this paper,six stone powder were used,namely limestone,marble,quartz,granite,dolomite and magnesite powder.Firstly,the basic properties of each stone powder and their effects on cement hydration were investigated by X-ray diffraction（XRD）,thermogravimetric analysis（TGA）,scanning electron microscopy（SEM）and laser particle size measurement.Then,simulated solutions of cement paste pore solutions were prepared and the adsorption of the stone powders with the relevant ions in the simulated solutions were investigated using the zeta potential measurement;Afterward,the effect of different stone powders on the fluidity of the paste was studied using rheometry;the effect of different stone powders on the nucleation and growth of hydrated calcium silicate was then studied;subsequently,the effect of stone powders on the pore structure of cement paste was investigated by means of mercury pressure;finally,the morphology of crack propagation and fracture surfaces in hardened cement paste mixed with different stone powders was observed via SEM.The results showed that:（1）the six stone powders have a relatively small effect on the hydration products,and no new hydration products are found.Limestone and marble powders have a relatively strong adsorption capacity for Ca²⁺due to a chmical interaction between their surface and Ca²⁺;quartz and granite powders have a relatively low adsorption capacity for Ca²⁺（electrostatic adsorption）;magnesite powder has an affinity to SO₄^2-rather than Ca²⁺;dolomite powders contain both properties of limestone and magnesite powders with an average level of Ca²⁺adsorption.（2）The fluidity of the cement paste has a great relationship with the potential of the added stone powder.Due to the strong adsorption of Ca²⁺by limestone powder and marble powder,their potential is relatively high and they have a certain repulsive force with the cement particles which also have a positive effect on the fluidity of paste;the surface potential of quartz powder,granite powder and dolomite powder is slightly lower and the repulsive force between them and the cement particles is relatively weak and the fluidity is reduced;the surface potential of magnesite powder is the lowest and it has a small repulsive force or even attractive force with the cement,resulting in the worst fluidity.（3）In the cement paste,the nucleation growth of hydrated calcium silicate is directly correlated with the adsorption capacity of stone powder particles for Ca²⁺.Limestone powder,marble powder and dolomite powder have a relatively strong adsorption capacity of Ca²⁺,and the nucleation and growth of C-S-H on their surfaces is significant;the s C-S-H grown at the surfaces of granite powder and quartz powder is relatively small;and magnesite powder,which has almost no adsorption capacity on Ca²⁺,has only a very small amount of C-S-H on its surface.（4）Due to the reduction of the total hydration products,the addition of stone powder deteriorates the pore structure of the cement paste to a certain extent in all cases.Relatively,limestone powder is more favourable to the pore structure of cement paste,followed by quartz powder;the paste mixed with dolomite powder has more large pores and less small pores;the pore structure of the paste mixed with magnesite powder is the worst.（5）Due to the specific adsorption of Ca²⁺on the surface of limestone powder,the surrounding hydrates are tightly connected to the limestone surface,and the cracks have a tendency to propagate into the cement matrix or directly through the limestone particles.The dolomite powder has a certain adsorption capacity for Ca²⁺and its surface is also favourable for the growth of C-S-H,and the cracks also have a tendency to develop along the cement matrix.Quartz and magnesite powders are not favourable to the growth of C-S-H,and the adhesion between surrounding hydrates and these two powders is also weak.Cracks in the paste mixed with these two powders have a tendency to develop along the edge of the particles,indicating that that the adhesion between the two powder particles and the surrounding hydrated is weak.