Effect Of BaO On The Formation And Properties Of Phosphoaluminate Cement

The effects of BaO on the synthesis and properties of phosphoaluminate cement were investigated in this paper. It would increase the micro defects in crystal structure of the cement minerals by means of the substitutions of Ba2+ for Ca2+. This resulted in the improvement of the hydration activity and optimization of the clinker minerals. Moreover, it was expected to the get a new type of Ba-bearing phosphoaluminate cement with excellent mechanical properties. The main investigations were involved as following: The introduction of BaO into calcium phosphoaluminate solid solution(LHss) and CA would result in the distortion of mineral lattice. Thus appropriate addition of BaO could optimize their microstructure and activate their hydration activity of mineral. Iron oxide-rich phosphoaluminate cement clinker was prepared. Also the effect of Fe2O3 on the formation of cement clinker at low temperature was investigated. Based on the previous research, the Ba-bearing phosphoaluminate cement clinker was achieved by the introduction of BaO the iron-rich phosphoaluminate cement. The main conclusions were included:(1) The compressive strength of doped LHss was higher than the reference with the moderate content of BaO, the appropriate content of BaO in LHss was 20%(by mole, the substitution amount of BaO for Ca O). Its compressive strength of 3d, 7d, 28 d was 60.0MPa, 109.3MPa and 122.7MPa. Compared with the reference, the increase percent of its compressive strength of 3d, 28 d and 90 d was 38.5%, 26.0% and 18.2%, respectively.(2) The addition of BaO could effectively increase the hydration rate of LHss. It was found that the hydration degree of LHss with BaO cured for 7d was over 90% and Its hydration product C(A,P)H10 was much more stable. The morphology of the hydration products changed from plates to flakes, whose dimensions with small size were in the range from 2μm to 5μm. This would be benefit to make micro structure of hardened paste to be denser and lower porosity. From pore structure analysis it was conclude that the content of harmful holes was lower than that of reference sample.(3) The addition of BaO can increases the amount of liquid phase in the process of CA synthesis. The intermediate C12A7 gradually decreased with the increase of Ba2+ content. CA with 7% BaO has excellent compressive strength. The Ba2+ ions played an important role in stabilizing the lattice of hydration products CAH10 and prevent the transition from CAH10 to C3AH6. The maximum rate of decomposition temperature gradually increased with the content of BaO rise. The maximum addition of CA crystal of BaO was 15%(molar content, the substitution amount of BaO for Ca O). Excessive addition of BaO would lead to the formation of the appearance BA mineral.(4) The appropriate content of Fe2O3 in phosphoaluminate cement clinker was 11%(by mass), and its sintered temperature was 1350℃. Its compressive strength of 1d and 28 d could achieve 70.6MPa and 95.5MPa. The corresponding oxide constituents range were Al2O3 25.0~32.0%,Ca O 30.0~40.0%,P2O5 14.0~15.0%,Si O2 3.0~5.0%,Fe2O3 10.5~11.0%. Fe2O3 could acts as a constituent favouring the conversion of CA1-Y(PY) to LHss at lower temperature, which was a series of solid solution occupying primarily interstitial positions of clinker.(5) The optimal dosage of BaO in phosphoaluminate cement with 7% by weight was 11%(molar content, the substitution amount of BaO for Ca O) and the optimal sintering temperature was 1420 ℃. The corresponding oxide constituents range were Al2O3 25.0~32.0%,Ca O 30.0~37.0%,BaO 10.5~11.0%,P2O5 14.0~15.0%,Si O2 3.0~5.0%,Fe2O3 6.0~7.5%. Its compressive strength of 1d and 28 d was 106.5MPa and 143.2MPa. Compared with the iron oxide-rich phosphoaluminate cement clinker, the rate of strength growth at 1d, 3d, 7d and 28 d were 50.8%, 21.0%, 27.0% and 49.9%, respectively.