| The effects of shells, hydroxyapatite, and superfine slag on the microstructure, sulfateresistance, frost resistance and impermeability performance of Portland cement andsulphoaluminate cement were studied in this paper. The influences of the contents of shells,hydroxyapatite and superfine slag on the performance of the cement were investigated. Shellsand hydroxyapatite were grounded into3different degrees of fineness. The finenesses ofsuperfine slag were400mesh,1250mesh and2500mesh. The influence of the fineness ofshells, hydroxyapatite, and superfine slag on the performance of the cement was discussed. Inorder to study the effects of the3special admixtures on microstructure and durability ofPortland cement and sulphoaluminate cement, SEM-EDS, XRD, pore structure analysis andheat of hydration analysis were performed.The results showed that when hydroxyapatite was added into Portland cement andsulphoaluminate cement, the compressisve strengthes of the early stage were small, but thecompressive strengths reached a certain level at the later period. The compressive strength ofPortland cement increased firstly and decreased afterward with the shells, calcium carbonateand superfine slag content increasing. The mechanical property of Portland cement withsuperfine slag was the highest. Its compressive strength for3d,7d and28d were77.4MPa,83.0MPa and86.7MPa, respectively. As the contents of shells and CaCO3adding, thecompressive of sulphoaluminate cement reduced gradually. The compressive strength ofsulphoaluminate cement first increased and then decreased with the contents of superfine slagincreased, the strength reached highest when the content of superfine slag was15%. With thedecreased of the fineness of shells and hydroxyapatite, the compressive strength ofsulphoaluminate cement increased gradually. With the decrease of the fineness of superfineslag, the compressive strengths of Portland cement decreased, while the compressivestrengths of sulphoaluminate cement increased.When shells, hydroxyapatite and CaCO3were added into the Portland cement, the ratio ofharmless pore in the hardened cement paste increased, and it was greater than the ratio ofharmful pore. The total porosity declined when superfine slag was added into the cemnt. Itindicated that the adding of shells, hydroxyapatite, superfine slag and CaCO3could improve the density of hardened cement paste. The total porosity increased when shells and superfineslag were added into the sulphoaluminate cement, but this phonomina was not obvious. AsCaCO3was added into the sulphoaluminate cement, the total porosity of hardened cementpaste increased, but the ratio of harmful pore decreased, so it was still helpful to improve theperformance of sulphoaluminate cemen when CaCO3was added. The smaller the porosity ofhardened cement paste, the greater the compressive strength of cement.Among the three kinds of special admixtures, hydroxyapatite was most prominent toenhance the sulfate resistance of cement. The corrosion resistance coefficient of Portland with15%hydroxyapatite was the largest, and it was1.24. The corrosion resistance coefficient ofsulphoaluminate cement with5%hydroxyapatite was1.17, the sulfate resistance was betterthan sulphoaluminate cement with the other two special admixtures. And the corrosionresistance coefficients increased with the decreased of the finenesss of special materials.The smaller fineness of the special admixtures, the better frost resistance of Portlandcement was. The weight loss rate and strength loss rate of Portland cement with15%B3(finest) were smallest, they were0.35%and2.8%respectively. The frost resistance improvedwith the decreased of the fineness of special admixtures, the weight loss rate and strength lossrate were minimum when10%K3(finest) was added into sulphoaluminate cement, they were0.04%and1.5%separately.CaCO3and superfine slag were favorable for the improvement of Portland cementimpermeability. Sulphoaluminate cement with superfineslag showed good impermeability. |
PDF Full Text Request