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Shen D.,Hohai University | Wang X.,Hohai University | Cheng D.,Hohai University | Zhang J.,Hohai University | Jiang G.,Nanjing Construction Group CO.
Construction and Building Materials | Year: 2016

High-performance concrete (HPC) is used extensively in practice. However, this type of concrete has a low water-to-cement (w/c) ratio, which causes self-desiccation and leads to a rather high autogenous shrinkage (AS). AS then increases the risk of cracking if the concrete is restrained from shrinking freely at early age. Internal curing (IC) has been extensively used in reducing AS and consequently mitigating the high risk of early-age cracking of HPC. Super absorbent polymers (SAPs) can supply additional IC water for hydration of concrete, thereby counteracting the effects of self-desiccation. Although experimental studies were conducted to mitigate the AS of internally cured concrete with SAP, research on the relationship between the AS of concrete and the amount of IC water provided by SAP is still lacking. Thus, an experimental study on the effect of IC on the early age expansion, AS development, AS rate, and IC efficiency of concrete with SAP was conducted. Test results showed that (1) the early-age expansion occurred obviously prior to the first day for the internally cured concrete, and the maximum expansion increased with the increase of IC water; (2) the ultimate AS at 28 days and AS rate of internally cured concrete decreased with the increase of the amount of IC water; (3) the proposed model to estimate the AS of internally cured concrete with SAP considering the early-age expansion and amount of IC water indicated good correspondence with the experimental results; and (4) the IC efficiency of SAP decreased with the increase of IC water in concrete. © 2015 Elsevier Ltd. All rights reserved. Source


Shen D.,Hohai University | Jiang J.,Hohai University | Shen J.,Hohai University | Yao P.,Hohai University | Jiang G.,Nanjing Construction Group CO.
Construction and Building Materials | Year: 2016

High-performance concrete (HPC) is widely used in practice. The water-to-cement ratio of HPC is low, and self-desiccation occurs which will induce marked autogenous shrinkage. Autogenous shrinkage usually increases the risk of cracking if the concrete is restrained from shrinking freely at early age. The autogenous shrinkage and cracking resistance of early-age concrete is influenced by curing temperature. However, the effect of curing temperature on autogenous shrinkage of early-age concrete is not in consistency and how the curing temperature affects the cracking resistance of concrete remains lacking. Thus, investigation on the effect of curing temperature on cracking resistance of early age concrete must be further studied. In this study, experimental studies on early-age cracking of concrete under 100% restraint and different curing temperatures were carried out using Temperature Stress Test Machine (TSTM). The present study investigated autogenous shrinkage of early-age HPC cured at different curing temperatures. The experimental results indicate that (1) the ratios of cracking stress to tensile strength for HPC specimens were all lower than 1.0; (2) the autogenous shrinkage of HPC increased with the increase of curing temperature; (3) a prediction model for autogenous shrinkage of HPC was presented considering the effect of curing temperature; (4) cracking temperatures and stress reserves were selected as the main cracking evaluation indicators of TSTM, and the HPC specimen cured at isothermal 20 °C showed better cracking resistance than that at isothermal 45 °C and adiabatic condition. © 2015 Elsevier Ltd. Source


Shen D.,Hohai University | Shen D.,Tongji University | Deng S.,Hohai University | Zhang J.,Anhui and Huai River Water Resources Research Institute | And 2 more authors.
Journal of Reinforced Plastics and Composites | Year: 2015

Cracking is a common form of damage in reinforced concrete beams. Cracks affect the stiffness and load-carrying capacity of beams. Fiber-reinforced polymers, as an affordable and efficient composite material, are being used more extensively to repair and strengthen conventional reinforced concrete beams. Although numerous studies have been conducted to investigate the behavior of undamaged and corroded beams repaired with carbon fiber-reinforced polymers or glass fiber-reinforced polymers, research on the behavior of beams with initial flexural cracks using basalt fiber-reinforced polymers as a restoration material is still lacking. Two 60-year-old cracked beams without repair and with repair using basalt fiber-reinforced polymers were experimentally and analytically investigated. The effect of repair on the load-carrying capacity, cracking characteristics, frequency, and stiffness of the beams was analyzed. The theoretical load-carrying capacity, midspan moment-deflection relationship, and strain distribution along the basalt fiber-reinforced polymers sheet were calculated and compared with the experimental results. The theoretical and experimental results show that (1) the load-carrying capacity of the repaired beam increased at the rate of 27.2% compared with that of the beam without repair; (2) the load-carrying capacities calculated from the Chinese and American standards of specimen B1 were 3.5% and 19.4% higher than those of the test results, respectively; (3) the basalt fiber-reinforced polymers repair system had an evident confinement effect on concrete crack development; (4) the natural frequency and stiffness of the repaired beam increased at the rate of 8.0% and 16.6% compared with the beam without repair, respectively; (5) the calculated midspan moment-deflection relationship of the repaired beam with initial cracks based on Zhang€™s method showed good accuracy with the test results; and (6) the strain distribution on the fiber-reinforced polymers sheet could be predicted by calculating the transition point strain and the length of the total bond development zone. © The Author(s) 2015. Source


Shen D.,Hohai University | Shi X.,Hohai University | Zhang H.,Hohai University | Duan X.,Hohai University | Jiang G.,Nanjing Construction Group CO.
Construction and Building Materials | Year: 2016

High strength concrete (HSC) is used extensively in practice. However, HSC is prone to cracking at early age, which can be the first step in a construction's deterioration and its malfunction. Reinforcement is one possible way to prevent the negative effect of early-age cracks in HSC structures. The early-age bond behavior is necessary to determine the cracking width of structures. Although the bond behavior between steel bars and normal strength concrete has been studied, study on early-age bond behavior between steel bars and HSC is still lacking. This paper presents an experimental investigation on the bond behavior between steel bars and HSC of different ages using a pull-out test. Test results showed that: (1) the early-age bond strength between steel bars and HSC increased with the increase of age; (2) the bond strength between steel bars and HSC increased with the increase of concrete strength and a model for the early-age bond strength between steel bars and HSC was proposed; (3) the slip corresponding to bond strength decreased with the increase of concrete compressive strength and a model for the early-age slip corresponding to bond strength was proposed; (4) a prediction model for early-age bond stress-slip relationship between steel bars and HSC was proposed based on BPE model, which showed good agreement with test results. © 2016 Elsevier Ltd. All rights reserved. Source


Zhou X.,Jiangsu University | Zhou X.,Nanjing Construction Group CO. | Yang J.,Yancheng Institute of Technology | Wang J.,Nanjing Construction Group CO.
Jiangsu Daxue Xuebao (Ziran Kexue Ban)/Journal of Jiangsu University (Natural Science Edition) | Year: 2012

Bond behaviors of magnesium phosphate cement (MPC) matrix with glass fiber bundle (GFB) were investigated through measuring pullout force of GFB in MPC. The results show that the self-made inorganic adhesive can permeate into glass fibrils with markedly improved axial tensile strength of GFB. The pull-out force of GFB can be increased by mixing magnesium oxide powder. The micro structure of MPC paste is compacted by water glass to achieve pull-out force of GFB. The pull-out force can be effectively improved by the increasing of GFB length and MPC age. It can be confirmed that the optimized embedded length of GFB would exist and the maximum pull-out forces could be achieved in pullout destructive form. The pull-out force of GFB in MPC matrix with optimized embedded length is greater than that in epoxy resin matrix. Source

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