Study On Basic Properties And Wave Absorbing Properties Of Cement Matrix Composites

With the rapid development of modern information technology and the in-depth application of electronic and electronic equipment and wireless communication equipment,the public electromagnetic environment continues to deteriorate.The development of cement-based electromagnetic wave absorbing materials is conducive to improving the electromagnetic environment of building space and reducing the harm of electromagnetic radiation.In this paper,slag powder and coral powder were used to replace some cement,and electromagnetic wave absorbent with different contents were added to carry out basic performance research.The electromagnetic parameters of slag powder,coral powder,graphite,ferrite and cement paste were tested.The reflectivity test of cement-based composites was carried out,and the influence of material content on electromagnetic wave absorption was analyzed.The influence of thickness on the electromagnetic wave absorption performance of the material was studied by fixed mixture ratio.The influence of admixture on microstructure and hydration products of cement was analyzed by XRD and SEM.The main conclusions are as follows:(1)From the perspective of water consumption of standard consistency,the addition of slag powder,coral powder and ferrite will reduce the water consumption when the cementing system reaches the standard consistency,while the addition of graphite will increase the water consumption of standard consistency.The setting time was prolonged with the increase of the dosage of admixture,and the setting time difference was slightly increased.Among them,the initial and final setting time of samples mixed with ferrite were significantly prolonged compared with other samples.The test results of stability of each group are all qualified.(2)The effects of admixture and electromagnetic wave absorbent on the strength and resistivity of samples were studied.Slag powder,coral powder and ferrite all had adverse effects on the strength of colloidal sand.The graphite content within 5% increased the early strength of colloidal sand(3d,7d),but the sample strength decreased significantly when the content increased to 10%.Due to the different hydration activities of slag powder and coral powder,they have different effects on the resistivity.Adding graphite and ferrite is conducive to reducing the resistivity of the cement matrix.When the graphite content is 10%,it is close to the conductivity percolation threshold of the composite material,and when the ferrite content is 5%,the resistivity drops significantly and reaches the conductivity percolation threshold of the material.(3)The solid part of the dielectric constant of the slag powder is lower than the net cement slurry,and the dielectric constant of the cement matrix can be reduced after the addition of the slag powder.In the S～C band,the mixing of 30% slag powder has the best effect,which is more consistent with the thickness of 36 mm.The reflectivity of the sample was lower than that of the other three groups when the graphite content was 5%.The absorption performance was the best.Ferrite has a good ferromagnetism,which can reduce the reflectivity when mixed into the cement matrix.When the ferrite content is 15%,the sample width of-10 d B is 8GHz,and the lowest reflectivity is-17.6d B.When the ferrite content is 10%,the best matching thickness in the X～Ku band is 24 mm.The addition of graphite and ferrite does not significantly improve the absorbing effect.It is difficult to maintain a good absorbing effect on a single thickness in the whole frequency band.Combined with the analysis of mechanical properties,it is not recommended to mix graphite and ferrite into the cement matrix.The solid part of the dielectric constant of coral powder is slightly lower than that of pure cement,but there is almost no magnetic loss,and the absorption performance is poor.(4)By XRD analysis,each sample hydration at time of 3d main hydration products were CH crystal,a small amount of AFt,rhombic zeolite and calcium C-S-H gel,did not produce new crystal material.Therefore,the absorbing properties of admixtures and electromagnetic wave agents are only due to their own dissipation properties.It can be seen from SEM that the four materials have a certain influence on the microstructure of the colloidal sand,the slag content increases,the microstructure is looser,and the CH crystal is thinner.The graphite content was more than 5%,the pores and other defects in the colloidal sand increased,and the connection between hydration products was poor.Ferrite did not participate in hydration reaction in colloidal sand,and the unreacted ferrite had a certain filling effect on the microaggregate of the whole colloidal sand system.However,due to delayed coagulation,the AFt volume was smaller,and the hydration process of cement was slowed down.Coral powder is an inert material with poor hydration activity,which plays the role of microaggregate filling in the early stage and provides crystal nuclei for hydration products.