Effects of MgO and CaO on the Carbonization Resistance of Alkali-Activated Slag Concrete

Abstract

Abstract: Compared with ordinary Portland cement (OPC) concrete, alkali-activated slag concrete (AASC) has poor carbonization resistance. In this paper, part of slag was replaced by MgO and CaO to prepare AASC to improve its carbonization resistance. The compressive strength and carbonization depth of AASC seeded with MgO and CaO under accelerated carbonization environment at different carbonization ages were studied. The modification mechanism of MgO and CaO on the carbonization resistance of AASC was analyzed by X-ray diffraction (XRD), simultaneous thermal analysis (TG-DTG) and scanning electron microscopy-energy dispersive spectrometer (SEM-EDS). The results show that MgO and CaO promotes the formation of Mg-Al hydrotalcite and Ca-Al layered structure in AASC, respectively. These two hydration products absorb and consume CO₂ during the carbonization process, then alleviate the decomposition of C-S-H caused by carbonization. In addition, after accelerated carbonization, calcium magnesium carbonate and magnesium carbonate are formed in the AASC blended with MgO, and the amount of calcium carbonate in the AASC blended with CaO increase significantly. These carbonized products effectively fill the pores and hinder the further diffusion of CO₂ into the interior of AASC. Therefore, under the carbonization environment, the AASC blended with MgO and CaO has a higher compressive strength retention rate, a lower carbonization depth, and a better carbonization resistance than pure AASC.

Key words: alkali-activated slag concrete, magnesium oxide, calcium oxide, carbonization, microstructure

CLC Number:

TU528

ZHENG Hao, LIANG Yongning, ZHAN Jianwei, JI Tao. Effects of MgO and CaO on the Carbonization Resistance of Alkali-Activated Slag Concrete[J]. BULLETIN OF THE CHINESE CERAMIC SOCIETY, 2021, 40(8): 2564-2573.

References

[1] 蒲心诚.碱矿渣水泥与混凝土[M].北京:科学出版社,2010:4.
PU X C. Alkali slag cement and concrete[M].Beijing: Science Press, 2010: 4 (in Chinese).
[2] 孔德玉,张俊芝,倪彤元,等.碱激发胶凝材料及混凝土研究进展[J].硅酸盐学报,2009,37(1):151-159.
KONG D Y, ZHANG J Z, NI T Y, et al. Research progress on alkali-activated binders and concrete[J]. Journal of the Chinese Ceramic Society, 2009, 37(1): 151-159 (in Chinese).
[3] ROY D M. Alkali-activated cements Opportunities and challenges[J]. Cement and Concrete Research, 1999, 29(2): 249-254.
[4] BAKHAREV T, SANJAYAN J G, CHENG Y B. Resistance of alkali-activated slag concrete to carbonation[J]. Cement and Concrete Research, 2001, 31(9): 1277-1283.
[5] 杨长辉,吕春飞,陈科,等.碱矿渣水泥砂浆抗碳化性能研究[J].混凝土,2009(8):100-102.
YANG C H, LU C F, CHEN K, et al. Carbonation resistance of alkali-activated slag cement mortar[J]. Concrete, 2009(8): 100-102 (in Chinese).
[6] 何彤彤.碱激发矿渣的碳化性能研究[D].南京:东南大学,2018.
HE T T. Study on the carbonation performance of alkali-activated slag[D]. Nanjing: Southeast University, 2018 (in Chinese).
[7] 屠柳青.高性能补偿收缩混凝土碳化行为与机理研究[D].武汉:武汉理工大学,2011.
TU L Q. Researches on carbonation behavior and mechanism of shrinkage-compensated high performance concrete[D]. Wuhan: Wuhan University of Technology, 2011 (in Chinese).
[8] 何娟,何俊红,王宇斌.碱矿渣水泥基胶凝材料的碳化特征研究[J].硅酸盐通报,2015,34(4):927-930+936.
HE J, HE J H, WANG Y B. Carbonation characteristics of alkali-activated slag cementitious materials[J]. Bulletin of the Chinese Ceramic Society, 2015, 34(4): 927-930+936 (in Chinese).
[9] 何娟.碱矿渣水泥石碳化行为及机理研究[D].重庆:重庆大学,2011.
HE J. Research on the carbonation behavior and mechanism of hardened alkali-activated slag cement pastes[D]. Chongqing: Chongqing University, 2011 (in Chinese).
[10] HE J, GAO Q, WU Y, et al. Study on improvement of carbonation resistance of alkali-activated slag concrete[J]. Construction and Building Materials, 2018, 176: 60-67.
[11] PARK S M, JANG J, LEE H K. Unlocking the role of MgO in carbonation of alkali-activated slag cements[J]. Inorganic Chemistry Frontiers, 2018, 5: 1661-1670.
[12] BERNAL S A, NICOLAS R S, MYERS R J, et al. MgO content of slag controls phase evolution and structural changes induced by accelerated carbonation in alkali-activated binders[J]. Cement and Concrete Research, 2013, 57: 33-43.
[13] MORANDEAU A E, WHITE C E. Role of magnesium-stabilized amorphous calcium carbonate in mitigating the extent of carbonation in alkali-activated slag[J]. Chemistry of Materials, 2015, 27(19): 6625-6634.
[14] YUAN X H, CHEN W, LU Z A, et al. Shrinkage compensation of alkali-activated slag concrete and microstructural analysis[J]. Construction and Building Materials, 2014, 66: 422-428.
[15] LEE N K, KOH K T, KIM M O, et al. Physicochemical changes caused by reactive MgO in alkali-activated fly ash/slag blends under accelerated carbonation[J]. Ceramics International, 2017, 43(15): 12490-12496.
[16] ISMAIL I, BERNAL S A, PROVIS J L, et al. Drying-induced changes in the structure of alkali-activated pastes[J]. Journal of Materials Science, 2013, 48(9): 3566-3577.
[17] CHANG P H, CHANG Y P, CHEN S Y, et al. Ca-rich Ca-Al-oxide, high-temperature-stable sorbents prepared from hydrotalcite precursors: synthesis, characterization, and CO₂ capture capacity[J]. ChemSusChem, 2011, 4(12): 1844-1851.
[18] MO L W, PANESAR D K. Effects of accelerated carbonation on the microstructure of Portland cement pastes containing reactive MgO[J]. Cement and Concrete Research, 2012, 42(6): 769-777.
[19] SHI Z G, SHI C J, WAN S, et al. Effect of alkali dosage and silicate modulus on carbonation of alkali-activated slag mortars[J]. Cement and Concrete Research, 2018, 113: 55-64.
[20] JIN F, AL-TABBAA A. Thermogravimetric study on the hydration of reactive magnesia and silica mixture at room temperature[J]. Thermochimica Acta, 2013, 566: 162-168.
[21] TARTAGLIONE G, TABUANI D, CAMINO G. Thermal and morphological characterisation of organically modified sepiolite[J]. Microporous and Mesoporous Materials, 2008, 107(1/2): 161-168.
[22] JIN F, GU K, AL-TABBAA A. Strength and drying shrinkage of reactive MgO modified alkali-activated slag paste[J]. Construction and Building Materials, 2014, 51: 395-404.
[23] SHA W. Differential scanning calorimetry study of the hydration products in Portland cement pastes with metakaolin replacement[M]//Advances in Building Technology. Amsterdam: Elsevier, 2002: 881-888.
[24] DWECK J, FERREIRA DA SILVA P F, BÜCHLER P M, et al. Study by thermogravimetry of the evolution of ettringite phase during type II Portland cement hydration[J]. Journal of Thermal Analysis and Calorimetry, 2002, 69(1): 179-186.
[25] LI N, FARZADNIA N, SHI C J. Microstructural changes in alkali-activated slag mortars induced by accelerated carbonation[J]. Cement and Concrete Research, 2017, 100: 214-226.
[26] SAMTANI M, DOLLIMORE D, ALEXANDER K S. Comparison of dolomite decomposition kinetics with related carbonates and the effect of procedural variables on its kinetic parameters[J]. Thermochimica Acta, 2002, 392/393: 135-145.
[27] 牟善彬,孙振亚,苏小萍.高游离氧化钙水泥的显微结构与膨胀机理研究[J].武汉理工大学学报,2001,23(11):27-29.
MU S B, SUN Z Y, SU X P. A study on the microstructure and expanding mechanism of highly free-calcium oxide cements[J]. Journal of Wuhan University of Technology, 2001, 23(11): 27-29 (in Chinese).