Jiangsu Key Laboratory of Construction Materials

Nanjing, China

Jiangsu Key Laboratory of Construction Materials

Nanjing, China
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Rong Z.D.,JiangSu Key Laboratory of Construction Materials | Rong Z.D.,Nanjing Southeast University | Sun W.,JiangSu Key Laboratory of Construction Materials | Xiao H.J.,JiangSu Key Laboratory of Construction Materials | Wang W.,JiangSu Key Laboratory of Construction Materials
Construction and Building Materials | Year: 2014

The hydration process of ultra-high performance cementitious composite (UHPCC) is distinctly different from common concrete owing to its low water-binder ratio (w/b). The effects of silica fume and fly ash on the hydration process and microstructure were investigated via different characterization methods in this work. The results indicated that the hydration process could be accelerated at the beginning by addition of silica fume, and fly ash, on the other hand, retarded hydration mainly in the dormant and acceleration periods. When they were incorporated together in cement, the result differed significantly from cement hydration at higher w/b (>0.35). As a result of Ca(OH)2 consumption by pozzolanic reaction, the porosity reduced (<4%) and the interface strengthened as the curing time increased. Nanoindentation results revealed that most hydration products of UHPCC were UHD C-S-H and unhydrated cement. The unhydrated cement particles were surrounded by UHD C-S-H, implying that the UHPCC had excellent mechanical performance and durability. © 2013 Elsevier Ltd. All rights reserved.


Wan K.,Jiangsu Key Laboratory of Construction Materials | Wan K.,Nanjing Southeast University | Xu Q.,Nanjing Southeast University
Science China Technological Sciences | Year: 2014

Porosity is one of the most important parameters for cement-based materials, which influences the mechanical property, transport property, and durability. The spatial and frequency distributions of local porosity of cement pastes are characterized using X-ray micro-tomography data and treating methods. The 3D spatial distributions for three cement paste specimens with different water cement (w/c) ratios show reasonable heterogeneity. The probability analysis also reveals this heterogeneity: the representative volume element (RVE) size based on porosity maps decreases with w/c ratio firstly, then increases with w/c ratio; and the heterogeneity on the characterized probe size or on the RVE size increases with w/c ratio. Average porosities obtained using the CT method are further compared with those by traditional methods. © 2014 Science China Press and Springer-Verlag Berlin Heidelberg.


Rong Z.,JiangSu Key Laboratory of Construction Materials | Rong Z.,Nanjing Southeast University | Sun W.,JiangSu Key Laboratory of Construction Materials | Sun W.,Nanjing Southeast University
Construction and Building Materials | Year: 2012

In order to investigate the dynamic tensile behavior of ultra-high performance cement based composites (UHPCCs) used in defense works, UHPCC with 200 MPa compressive strength is prepared by replacing a large quantity of cement by industrial waste residues such as silica fume, fly ash and slag; and substituting ground fine quartz sand (≤600 μm in diameter) with natural sand (2.5 mm in diameter). Dynamic tensile tests are conducted using Split Hopkinson pressure bar (SHPB) on UHPCC with different fiber volume fraction. By using this method, the dynamic tensile strength of UHPCC and its dependence on strain rates are measured and investigated. Results show that dynamic tensile strength of UHPCC is rate sensitive and also improved with an increase of fiber volume fraction. In addition, the finite element method (LS-DYNA) is employed to simulate the whole impact process of UHPCC. The numerical simulation results are in good agreement with experimental results and can be used for further research. © 2012 Elsevier Ltd. All rights reserved.


Zhang X.,Nanjing Southeast University | Zhang X.,Jiangsu Key Laboratory of Construction Materials | Sun W.,Nanjing Southeast University | Sun W.,Jiangsu Key Laboratory of Construction Materials
Cement and Concrete Composites | Year: 2010

Double-layer cementitious composites filled with Mn-Zn ferrite as microwave absorbers were designed based on the impedance matching theory and electromagnetic wave propagation laws. The results showed that the addition of silica fume can improve the impedance matching between the cementitious composites and free space. Comparing with the single-layer structure, the reflectivity of the double-layer cementitious plates can decrease by 6-8 dB and decrease by 15 dB maximum with 30 wt.% ferrite; in addition, the reflectivity of electromagnetic wave is lower than 10 dB in the frequency range of 11.4-18 GHz. These composites can be potentially used as electromagnetic interference (EMI) materials for buildings. © 2010 Elsevier Ltd. All rights reserved.


Wan K.,Jiangsu Key Laboratory of Construction Materials | Wan K.,Nanjing Southeast University | Xu Q.,Nanjing Southeast University | Li L.,Nanjing Southeast University | And 2 more authors.
Construction and Building Materials | Year: 2013

Calcium leaching of cement-based materials is one of durability concerns in concrete structures. Calcium leaching leads to high porosity and porosity gradient near the wet surfaces of cement-based materials. In this research, the 3D porosity distributions of partly leached cement pastes with different water-to-cement ratios are characterized for the first time, and the porosity evolution caused by calcium leaching are discussed. The results are verified using the average porosities of the partly leached specimen. From the quantitative porosity results, large porosities over 60% are observed on the leached parts, and very sharp porosity gradients are observed on the leaching fronts. The results of current research can be used for the verification of calcium leaching models and for understanding the leaching mechanism. © 2013 Elsevier Ltd. All rights reserved.


Wan K.,Jiangsu Key Laboratory of Construction Materials | Wan K.,Nanjing Southeast University | Li Y.,Nanjing Southeast University | Sun W.,Jiangsu Key Laboratory of Construction Materials | Sun W.,Nanjing Southeast University
Construction and Building Materials | Year: 2013

Calcium leaching of cement-based materials is of concern for scientific and application significance. Considering the altered solid-liquid equilibrium curve, an accelerated calcium leaching model of pure cement paste in 6 mol/L ammonium nitrate leaching solution was built up in this research. The model was numerically solved using finite difference method, and the influences of w/c ratio and initial cement composition on leaching were addressed. The accelerated model was further verified using elemental distributions and leaching fronts. Besides, through comparing the accelerated model in 6 mol/L ammonium nitrate solution and the un-accelerated model in deionized water, an accelerated factor of about 130 was found, which was slightly influenced by the initial material compositions. © 2012 Elsevier Ltd. All rights reserved.


Wan K.,Jiangsu Key Laboratory of Construction Materials | Wan K.,Nanjing Southeast University | Li Y.,Nanjing Southeast University | Sun W.,Jiangsu Key Laboratory of Construction Materials | Sun W.,Nanjing Southeast University
Construction and Building Materials | Year: 2012

Calcium leaching of cement-based materials is one of concerns in concrete structures used for radioactive waste disposal and underground/underwater environments. The solid calcium distribution is an important parameter for calcium leaching degrees and for model verifications. In this short communication, based on the additivity of X-ray linear attenuation coefficient, a method to deduce the solid calcium distributions is proposed, and the solid calcium distributions of different calcium leached cement paste specimens are given using the micro-tomography data. The solid calcium distributions using the proposed method are further verified using the energy dispersive spectrum (EDS) elemental analysis. © 2012 Elsevier Ltd. All rights reserved.


Wan K.,Jiangsu Key Laboratory of Construction Materials | Wan K.,Nanjing Southeast University | Xu Q.,Nanjing Southeast University | Wang Y.,Nanjing Southeast University | And 2 more authors.
Cement and Concrete Composites | Year: 2014

Carbonation of cement-based materials is one area of concern for the durability of concrete structures. The calcium carbonate caused by carbonation is an important indicator of carbonation degrees. The present paper, using 3D tomography data, proposes a nondestructive method to characterize the 3D spatial distributions of calcium carbonate. It allows monitoring of 3D carbonation evolutions. The evolution of the calcium carbonate distributions in a specimen of cement paste with different carbonation degrees is given using the current method. The results are compared with the average quantity of calcium carbonate determined by thermal analysis. From the sharp edge of the calcium carbonate distribution, we conclude that the accelerated carbonation in this experimental condition is a diffusion controlling process. © 2013 Elsevier Ltd. All rights reserved.


Rong Z.,JiangSu Key Laboratory of Construction Materials | Rong Z.,Nanjing Southeast University | Sun W.,JiangSu Key Laboratory of Construction Materials | Sun W.,Nanjing Southeast University | And 2 more authors.
International Journal of Impact Engineering | Year: 2010

In order to investigate the dynamic compression behavior of Ultra-high performance cement based composites (UHPCC) used in defense works, UHPCC with 200 MPa compressive strength is prepared by replacing a large quantity of cement by industrial waste residues such as silica fume, fly ash and slag; and substituting ground fine quartz sand (≤600 um in diameter) with natural sand (2.5 mm in diameter). Split Hopkinson pressure bar (SHPB) is performed on UHPCC with different fiber volume fraction to investigate the dynamic compression behavior. Results show that impact resistance of UHPCC is improved with an increase of fiber volume fraction. The dynamic compressive strength of UHPCC is also increased with an increase of strain rate. In addition, the finite element method (LS-DYNA) is employed to simulate the whole impact process of UHPCC. Numerical simulations demonstrate that the Johnson_Holmquist_Concrete material constitutive model can be used for the dynamic compression of concrete. The numerical values are in good agreement with experimental results. © 2009 Elsevier Ltd. All rights reserved.


Rong Z.,JiangSu Key Laboratory of Construction Materials | Sun W.,Nanjing Southeast University | Xiao H.,Nanjing Southeast University | Jiang G.,Nanjing Southeast University
Cement and Concrete Composites | Year: 2015

In this research the effects of nano-SiO2 particles on the mechanical performance, hydration process and microstructure evolution of ultra-high performance cementitious composites were investigated by different methods. The results showed that the compressive and flexural strength increased with the increase of the nano-SiO2 content up to 3% and due to agglomeration of nano-SiO2 particles, the mechanical properties decreased slightly when the nano-SiO2 content was more than 3%. The hydration process was accelerated by the addition of nano-SiO2. The porosity and the average pore diameter decreased with the increase of the nano-SiO2 content and aging. The microstructure was more homogenous and dense for nano-SiO2 specimens as compared to the control specimen. All of these improvements could be mainly attributed to the pozzolanic and filler effects of nano-SiO2. © 2014 Elsevier Ltd. All rights reserved.

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