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Qian C.,Nanjing Southeast University | Qian C.,Jiangsu Key Laboratory of Construction Material | Yang J.,Nanjing Southeast University | Yang J.,Yancheng Institute of Technology
Journal of Materials in Civil Engineering | Year: 2011

Magnesium potassium phosphate cement (MKPC) is usually produced by using dead burned MgO and potassium dihydrogen phosphate. A new MKPC was prepared by using combination of potassium dihydrogen phosphate (KH 2PO 4) and disodium hydrogen phosphate (Na 2HPO 4. 12H 2O) in certain ratios instead of potassium dihydrogen phosphate alone. To investigate the effect of disodium hydrogen phosphate on hydration and hardening of MKPC, pH value, hydration temperature, setting times, and strength development were measured. The results indicated that disodium hydrogen phosphate increased the pH value of MKPC paste, resulted in endothermic reactions, and cooled MKPC paste. Thus, it retarded early hydration, improved the fluidity, and increased setting times of MKPC paste. Although the early compressive strength of hardened MKPC made with a combination of the two phosphates was slightly lower than that of hardened MKPC prepared with single potassium dihydrogen phosphate, its strength development is sustaining and was higher than that of hardened MKPC with single potassium dihydrogen phosphate at 60 days because of better crystallization and more stable hydration products. © 2011 American Society of Civil Engineers.


Rong H.,Nanjing Southeast University | Rong H.,Jiangsu Key Laboratory of Construction Material | Qian C.-X.,Nanjing Southeast University | Qian C.-X.,Jiangsu Key Laboratory of Construction Material | And 2 more authors.
Construction and Building Materials | Year: 2012

A new generation of cement, microbe cement has been developed due to the ever increasing awareness of environmental protection. Microbe cement is a new strengthening technique based on microbiologically induced precipitation of calcium carbonate. This paper confirms the feasibility of microbe cement binding loose sand particles and presents results from a laboratory research on the influence of molding process (non-pressure molding, pressure molding, discontinuous non-pressure molding and pumping molding) on the mechanical properties of sandstone microbe cement bound. The results showed that the ways of molding procedure had a strong influence on the mechanical properties of bio-sandstone. The strength, which was up to 12.0 MPa, of sandstone microbe cement bound by adopting pumping molding process was higher than other three processes. Meanwhile, Scanning electron microscope (SEM) image analysis technique was adopted to measure the corresponding variation of porous characteristics caused by different molding processes. The results indicate that the microstructure of bio-sandstone adopted by pumping molding has lower porosity and higher content of precipitated calcium carbonate than other three molding processes. © 2011 Elsevier Ltd. All rights reserved.


Rong H.,Nanjing Southeast University | Rong H.,Jiangsu Key Laboratory of Construction Material | Qian C.,Nanjing Southeast University | Qian C.,Jiangsu Key Laboratory of Construction Material
Journal Wuhan University of Technology, Materials Science Edition | Year: 2013

The bio-sandstone, which was cemented by microbe cement, was firstly prepared, and then the microstructure evolution process was studied by X-ray computed tomography (X-CT) technique. The experimental results indicate that the microstructure of bio-sandstone becomes dense with the development of age. The evolution of inner structure at different positions is different due to the different contents of microbial induced precipitation calcite. Besides, the increase rate of microbial induced precipitation calcite gradually decreases because of the reduction of microbe absorption content with the decreasing pore size in bio-sandstone. © 2013 Wuhan University of Technology and Springer-Verlag Berlin Heidelberg.


Iian J.,Nanjing University of Technology | Iian J.,Nanjing Southeast University | Iian J.,Jiangsu Key Laboratory of Construction Material | Sun W.,Nanjing Southeast University | And 3 more authors.
Journal Wuhan University of Technology, Materials Science Edition | Year: 2013

In situ monitoring of the microstructure evolution of cement mortar in accelerated carbonation reaction for different carbonation ages was carried out by X-ray computed tomography (XCT). And the carbonation degrees of different time were measured by the volume fraction of uncarbonated and carbonated parts. Meanwhile,we presented a model for the carbonation of cement mortar by means of X-ray computed tomography (XCT). Based on the principles of chemical engineering processes,the reacted products become a solid inert ash layer. Finally,the model was validated with results of accelerated carbonation of cement mortar. The model is thus able to reasonably predict the carbonation phenomena for accelerated conditions. © Wuhan University of Technology and SpringerVerlag Berlin Heidelberg 2013.


Ba M.-F.,Nanjing Southeast University | Ba M.-F.,Jiangsu Key Laboratory of Construction Material | Qian C.-X.,Nanjing Southeast University | Qian C.-X.,Jiangsu Key Laboratory of Construction Material | And 2 more authors.
Construction and Building Materials | Year: 2011

A research program was carried out to investigate the effects of duration of initial steam curing at atmosphere pressure on compressive strength of concrete with low water/binder ratio. The results showed that the compressive strength of samples steam cured for 5, 10, 14 h increased, while it decreased distinctively for sample steam cured for 24 h. Mercury intrusion porosimetry (MIP) method and scanning electron microscope-backscattered electron (SEM-BSE) image analysis technique were adopted to measure the corresponding variation of porous characteristics caused by the increasing duration of steam curing. The changes in coarse porosity and total porosity calculated by SEM-BSE image analysis and MIP method respectively could indicate the relationship between porosity and mechanical properties of the concrete subjected to different duration of steam curing. Compared with total porosity obtained by MIP method, the coarse porosity by SEM-BSE image analysis was in better accord with the compressive strength because the coarse pores measured by SEM-BSE image analysis were larger than 0.5 μm and included not only the interconnected pores but also the closed ones. An empirical model was developed to evaluate the influence of duration of initial steam curing on the compressive strength of concrete. By comparison, the measured compressive strength was in great accordance with the compressive strength calculated by the proposed model. © 2010 Elsevier Ltd. All rights reserved.


Han J.,Nanjing Southeast University | Han J.,Jiangsu Key Laboratory of Construction Material | Pan G.,Nanjing Southeast University | Pan G.,Jiangsu Key Laboratory of Construction Material | And 6 more authors.
Science China Technological Sciences | Year: 2012

Nanoindentation technique was adopted to investigate the chemomechanical properties change of hardened cement paste before and after carbonation. It was found that the mean elastic modulus and mean hardness obviously increase after the carbonation reaction. Specifically, the probability of the elastic modulus showed a sharp reduction for the elastic modulus at the range of 7-34 and 83-160 GPa, in comparison of a large increase for the elastic modulus between 34-83 GPa. For the same reason, the probability of the hardness showed a large decrease when the hardness fell within 0.15-1.75 and 4.15-8.20 GPa and a dramatic increase for the hardness at the range of 1.75-4.15 GPa. In addition, low density C-S-H was affected by the carbonation degradation more seriously than high density C-S-H. The carbonation reaction led to distinct decrease of the number and size of unhydrated cement paste particles. © Science China Press and Springer-Verlag Berlin Heidelberg 2011.


Rong H.,Nanjing Southeast University | Rong H.,Jiangsu Key Laboratory of Construction Material | Qian C.-X.,Nanjing Southeast University | Qian C.-X.,Jiangsu Key Laboratory of Construction Material | And 2 more authors.
Construction and Building Materials | Year: 2012

Microbe cement as a biogrouting could consolidate loose particles to improve mechanical properties. Microbe cement has drawn much attention because of the ever increasing awareness of environmental protection. This paper confirms the feasibility of binding loose sand particles using microbe cement and details the cementation mechanism of microbe cement. In addition, the microstructure and properties of representative bio-sandstones have been analyzed by X-ray computed tomography (XRCT), Scanning electron microscopy (SEM) and Mercury Intrusion Porosimetry (MIP). The experimental results indicate that the compressive strength of bio-sandstone could be up to 6.1 MPa and the bottom region microstructure in bio-sandstone is denser and less fragile than the top region due to more calcite precipitated in the former one. © 2012 Elsevier Ltd. All rights reserved.


Han J.,Nanjing Southeast University | Han J.,Jiangsu Key Laboratory of Construction Material | Sun W.,Nanjing Southeast University | Sun W.,Jiangsu Key Laboratory of Construction Material | And 6 more authors.
Journal Wuhan University of Technology, Materials Science Edition | Year: 2012

The microstructure characteristics and meso-defect volume changes of hardened cement paste before and after carbonation were investigated by three-dimensional (3D) X-ray computed tomography (XCT), where three types water-to-cement ratio of 0.53, 0.35 and 0.23 were considered. The high-resolution 3D images of microstructure and filtered defects were reconstructed by an XCT VG Studio MAX 2.0 software. The meso-defect volume fractions and size distribution were analyzed based on 3D images through add-on modules of 3D defect analysis. The 3D meso-defects volume fractions before carbonation were 0.79%, 0.38% and 0.05% corresponding to w/c ratio=0.53, 0.35 and 0.23, respectively. The 3D meso-defects volume fractions after carbonation were 2.44%, 0.91% and 0.14% corresponding to w/c ratio=0.53, 0.35 and 0.23, respectively. The experimental results suggest that 3D meso-defects volume fractions after carbonation for above three w/c ratio increased significantly. At the same time, meso-cracks distribution of the carbonation shrinkage and gray values changes of the different w/c ratio and carbonation reactions were also investigated. © Wuhan University of Technology and Springer Verlag Berlin Heidelberg 2012.


Rong H.,Nanjing Southeast University | Rong H.,Jiangsu Key Laboratory of Construction Material | Qian C.,Nanjing Southeast University | Qian C.,Jiangsu Key Laboratory of Construction Material | And 2 more authors.
Science China Technological Sciences | Year: 2011

Microbe-based cement has been widely reported in recent literatures. It is a new method of consolidating loose fine particles, which relies on the bacterially induced formation of a compatible carbonate precipitation around individual particles and at particle-particle contacts. Materials and cementation procedure are two major factors that influence the cementation performance of microbe-based cement. Besides, there are some other factors related to the performance, such as pH, temperature, metabolism activity, the flushed times of bacterial solution, concentration of substrate and calcium ion, etc., which affect consolidation function. The assessment methods for cementation process are carried out by various techniques. The performance of consolidation loose grains based on microbe-based cement is tested with the help of experiment. In this paper a review is presented on the cementation mechanism of microbe-based cement, techniques utilized to monitor cementation process, the consolidated performance by microbe-based cement and bond factors. © 2011 Science China Press and Springer-Verlag Berlin Heidelberg.


Rong H.,Jiangsu Key Laboratory of Construction Material | Qian C.,Jiangsu Key Laboratory of Construction Material | Li L.,Jiangsu Key Laboratory of Construction Material
Kuei Suan Jen Hsueh Pao/Journal of the Chinese Ceramic Society | Year: 2012

The influence of magnesium additive concentrations (i.e., 0.5, 1.5, 2.5, 3.5 mol/L and 4.5 mol/L) on the mechanical properties of microbe cementitious material was investigated. In addition, the mineral composition produced by microbe and microstructure of microbe cementitious material was analyzed by X-ray diffraction and scanning electron microscopy. The results indicate that when the magnesium additive concentration is 2.5 mol/L, the microbe cementitious material has the denser microstructure with the lower porosity. The compressive strength could be superior. When the magnesium additive concentration was rather low, the precipitated minerals induced by microbe in the microbe cementitious material were mainly calcite and Mg-calcite, and the morphology of precipitated minerals appeared mainly cauliflower shape. However, the magnesium additive concentration is higher, the minerals were mainly monohydrocalcite and hydromagnesite, and the morphology was mainly ball cylindrical.

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