Research on micro-mechanisms of dredged sludge solidified with alkali-activated fly ash
WANG Dongxing1，2，WANG Hongwei1，2，ZOU Weilie1，2，WANG Xiequn3，LI Lihua4
(1. Hubei Key Laboratory of Safety for Geotechnical and Structural Engineering，Wuhan University，Wuhan，Hubei 430072，China；2. School of Civil Engineering，Wuhan University，Wuhan，Hubei 430072，China；3. School of Civil Engineering and Architecture，Wuhan University of Technology，Wuhan，Hubei 430070，China；4. School of Civil Engineering，Architecture and Environment，Hubei University of Technology，Wuhan，Hubei 430068，China)
Abstract：To mitigate the thorny problems associated with traditional Portland cement production in terms of energy consumption，CO2 emissions and air pollution，a favorable alternative option-novel and low-carbon alkali-activated industrial by-products is proposed for sludge solidification. Based on unconfined compressive strength，X-ray diffraction，scanning electron microscopy，thermogravimetric and mercury intrusion porosimetry tests，a systematical study has been performed to analyze the mechanical strength，hydration product，section morphology，thermal stability and micropore structure of alkali-activated fly ash solidified sludge and to reveal finally their strength evolution and microstructural mechanisms. The test results demonstrate that the compressive strength of dredged sludge is significantly enhanced owning to the incorporation of alkali-activated fly ash. Compared to Na2CO3，NaOH and Na2SiO3?9H2O have gained much more attention because of their excellent performance to activate the potential activity of fly ash. Through the OH－ attack to the inner and outer glass sphere structure，fly ash is effectively activated by dissolution-polymerization to form aluminosilicate polymer gels N-A-S-H with different degrees of polymerization，binding fine particles together to increase the overall strength of solidified sludge. The increase in alkali activator content leads to an elevated production amount of N-A-S-H gels，an increase in thermogravimetric weight loss and a transformation of inter-aggregate pores to inter-particle pores. The above changes produce a denser micropore structure and better integrity，which promotes significantly the strength performance of solidified sludge. The obtained results deepen the understanding of macro- and micro- characteristics of alkali-activated fly ash solidified sludge，and establish the full microscopic reaction model of alkali-activated fly ash to clarify the intrinsic micro-mechanisms for strength improvement and to provide the theoretical basis for partial replacement of Portland cement by alkali-activated fly ash in sludge solidification.
LI Z J，DING Z，ZHANG Y S. Development of sustainable cementitious materials[C]// International Workshop on Sustainable Development and Concrete Technology. Ames USA：Iowa State University，2004：55–76.
[6]
杨长辉，蒲心诚，吴 芳. 碱矿渣水泥砂浆的碱集料反应膨胀研究[J]. 硅酸盐学报，1999，27(6)：651–657.(YANG Changhui，PU Xincheng，WU Fang. The studies on alkali aggregate reaction of alkali-activated slag cement mortars[J]. Journal of the Chinese Ceramic Society，1999，27(6)：651–657.(in Chinese))
[7]
SHI C J，ROY D，KRIVENKO P. Alkali-activated cements and concretes[M]. New York：Taylor and Francis，2006：6–26.
[9]
易耀林，李 晨，孙 川，等. 碱激发矿粉固化连云港软土试验研究[J]. 岩石力学与工程学报，2013，32(9)：1 820–1 826.(YI Yaolin，LI Chen，SUN Chuan，et al. Test on alkali-activated ground granulated blast-furnace slag(GGBS) for Lianyungang soft soil stabilization[J]. Chinese Journal of Rock Mechanics and Engineering，2013，32(9)： 1 820–1 826.(in Chinese))
[11]
孙秀丽，童 琦，刘文华，等. 碱激发粉煤灰和矿粉改性疏浚淤泥力学特性及显微结构研究[J]. 大连理工大学学报，2017，57(6)： 622–628.(SUN Xiuli，TONG Qi，LIU Wenhua，et al. Study of microstructure and mechanical properties of dredged silt solidified using fly ash and slag stimulated by alkali[J]. Journal of Dalian University of Technology，2017，57(6)：622–628.(in Chinese))
[14]
SHEAR D L，OLSEN H W，NELSON K R. Effects of desiccation on the hydraulic conductivity versus void ratio relationship for a natural clay[R]. Washington D C：National Academy Press，1993：1 365– 1 370.
cementitious materials with calcium silicate slag[J]. Bulletin of the Chinese Ceramic Society，2015，34(8)：2 334–2 339.(in Chinese))
[15]
FERNáNDEZ-JIMéNEZ A，PALOMO A，CRIADO M. Microstructure development of alkali-activated fly ash cement：a descriptive model[J]. Cement and Concrete Research，2005，35(6)： 1 204–1 209.
[4]
DING Y，DAI J G，SHI C J. Mechanical properties of alkali-activated concrete：a state-of-the-art review[J]. Construction and Building Materials，2016，127：68–79.
[13]
DUXSON P，LUKEY G C，DEVENTER J V. Thermal evolution of metakaolin geopolymers：part 1-Physical evolution[J]. Journal of Non-Crystalline Solids，2006，352(52/54)：5 541–5 555.
[1]
王宏伟，王东星，贺 扬. MgO改性淤泥固化土压缩特性试验[J]. 中南大学学报：自然科学版，2017，48(8)：2 133–2 141.(WANG Hongwei，WANG Dongxing，HE Yang. Experimental study on compressibility behavior of solidified dredged sludge with reactive MgO[J]. Journal of Central South University：Science and Technology，2017，48(8)：2 133–2 141.(in Chinese))
[8]
杨爱武，闫澍旺，杜东菊，等. 碱性环境对固化天津海积软土强度影响的试验研究[J]. 岩土力学，2010，31(9)：2 930–2 934.(YANG Aiwu，YAN Shuwang，DU Dongju，et al. Experimental study of alkaline environment effects on the strength of cement soil of Tianjin marine soft soil[J]. Rock and Soil Mechanics，2010，31(9)：2 930– 2 934.(in Chinese))
[10]
吴燕开，胡晓士，胡 锐，等. 烧碱激发钢渣粉在淤泥质土中的试验研究[J]. 岩土工程学报，2017，39(12)：2 187–2 194.(WU Yankai，HU Xiaoshi，HU Rui，et al. Experimental study on caustic soda- activated steel slag powder in muddy soil[J]. Chinese Journal of Geotechnical Engineering，2017，39(12)：2 187–2 194.(in Chinese))
[12]
崔源声. 中国粉煤灰利用现状及2050年展望[C]// 2014亚洲粉煤灰及脱硫石膏综合利用技术国际交流大会. 朔州：[s.n.]，2014：1–4.(CUI Yuansheng. Utilization status of fly ash in China and prospects for 2050[C]// Proceedings of the Annuel Meeting of Coal Ash Asia 2014. Shuozhou：[s.n.]，2014：1–4.(in Chinese))
2019, Vol. 38 
