郑克仁Keren Zheng

教授

教授 博士生导师 硕士生导师

入职时间:2005-11-22

所在单位:土木工程学院

学历:博士研究生毕业

办公地点:建工楼306/Jiangong Building 306

研究动态

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1. Controlling Alkali Silicate Reaction (ASR) by conditioning aqueous Al concentration in cement paste (2018-10-15)

 

Keren. Zheng    Jin Zhou

Cement Study Unity, School of Civil Engineering, Central South University, Changsha 410075, Hunan, China


Abstract  Studies indicated that aluminum-rich supplementary cementitious materials (SCMs) are more effective in inhibiting alkali-silica reaction (ASR) expansion than pure silica SCMs. The beneficial effects of aluminum-rich SCMs on ASR have been mainly attributed to (i) reducing silica dissolution rate by Al adsorption on the surface of reactive silica; (ii) formation of C-A-S-H, which enhances alkali fixation capacity over C–S–H. These findings indicate that conditioning the aqueous aluminum concentration in cementitious materials is a promising way to control ASR. Alumina of high reactivity (γ-Al2O3) was incorporated to increase aqueous Al concentration in pore solution, in order to control ASR. Based on phase assemblage predication by GEMs, 10% γ-Al2Owas incorporated to precipitate katoite, an Al-bearing solid phase with high equilibrium concentration of aqueous Al. Results show that the aqueous Al concentration in pore solution can reach the level of ~0.8 mM with the presence of katoite, and ASR induced expansion can be mitigated efficiently. The study shows the feasibility of controlling ASR by conditioning aqueous Al concentration in pore solution.


         

 

Relationship between aqueous Al concentration in pore solution and ASR expansion

 

ACKNOWLEDGEMENTS: The study was supported by National Natural Science Foundation of China (NSFC) [grant number 51578551].


2. Mechanical property, sorptivity and microstructure of steam-cured concrete incorporated with the combination of metakaolin-limestone(2018-11-5) (Submitted to Materials and Structures )

Lou Chen, Keren Zheng*, Taobing Xia Fuqiang He*


Abstract  To explore the feasibility of using metakaolin and limestone in steam-cured concrete, mechanical property, sorptivity and microstructure of steam-cured concrete incorporated with the combination of metakaolin-limestone powder were studied, with steam-cured concrete incorporated with ground granulated blast furnace slag and fly ash as a reference. Due to the high reactivity of metakaolin, the presence of metakaolin reduces the heterogeneous distribution of hydration products, thereby resulting in a refined microstructure and lowered sorptivity of steam-cured concrete. The synergistic effect of metakaolin with limestone powder leads to further improvements on strength, sorptivity associated with a more uniform microstructure at late ages. Moreover, concrete incorporated with metakaolin-limestone powder and steam-cured at 40oC can gain a comparable early strength (1 day) with concrete incorporated with the combination of ground granulated blast furnace slag - fly ash, and steam cured at 60oC; this indicates that the incorporation of metakaolin enables to reduce steam curing temperature without compromising early strength gain, which is of significance for mitigating steam curing induced detrimental effects and reducing energy consumption. 

Key Words: Metakaolin; limestone; steam curing; compressive strength; sorptivity; microstructure 

          



3. Reverse filling cementitious materials based on dense packing: the concept and application(2018-11-06) Submitted to Powder Technology

Keren Zheng* Yang Liu Jin Zhou  Wei Huang Dong Cui

Abstract  In order to improve the cement use efficiency, a reverse filling cementitious material based on dense packing is proposed, where finer Portland cement grains fill spaces between coarser grains of filler materials. The concept of proposed reverse filling cementitious material is applied to formulate a binary system of limestone powder-ultrafine Portland cement. For the examined binary reverse filling system, a maximum packing density can be achieved at a low content of ultrafine Portland cement (~25%), and the actual water to powder (cement + limestone filler) ratio can be reduced to 0.12 with the ultrafine Portland cement content between 25% and 30%. The compressive strength at 90 d reached 74.0 MPa and 94.0 MPa for the blends containing 25% and 30% of ultrafine Portland cement respectively. Quantitative XRD analysis shows that the hydration degree of cement reached a very high level of ~93% for the blend containing 25% cement. The cement use efficiency of the investigated binary reverse filling cementitious material is much higher than that of other dense packing cementitious materials with similar compressive strength.