Journal of Materials in Civil Engineering

This paper investigates the transport properties altered by crack-induced damage of two structural concretes [ordinary portland cement concrete (OPC) and high-volume fly ash concrete (HVFC)]. The crack-induced damage is represented by axial residual strain, ultrasonic speed, open porosity, and crack geometry of specimens, and the transport properties were measured for gas permeability and water sorptivity on dried specimens. The hydraulic diffusivity is derived from water sorptivity and used to characterize the altered transport properties. Geometrical analysis of crack network confirms that the crack pattern is determinant for the altered extent of transport properties. Very limited change was observed for hydraulic diffusivity for cracks with low connectivity. The hydraulic diffusivity shows a strong and linear correlation with sorptivity while its correlation with gas permeability is nonlinear with scatter. The scatter comes from the connectivity of cracks in the gas flow direction. Accordingly, correct representation of crack pattern is crucial to quantify the altered transport properties by crack-induced damage.

In this study, two new approaches for pore structure assessment of cement paste are investigated and compared with mercury intrusion porosimetry (MIP)-based methods. One is based on a status-oriented computer model; the other is based on fractal analysis on the impedance measured by a noncontact impedance measurement system. In the computer model, cement paste microstructure is simulated as a function of cement properties, water-to-cement ratio (w/c), and degree of hydration. With the simulated microstructure, large capillary pores are characterized by image processing. A model developed based on nitrogen adsorption results and physical rules is applied to predict the small capillary pore structure, as a complementation to cover the whole range of capillary pores. In the impedance measurement based approach, fractal dimensions corresponding to specific pore size ranges are determined from the fractal networks and the impedance responses of the material. Then the pore size distribution curves are deduced. The former approach is capable of providing much more realistic representation of the pore structure as compared with the traditional MIP method, while the latter is also considered as a promising method for pore structure assessment, especially in large pore size range.

Moisture and cracks are scourges of structural concrete, and understanding the multiscale interactions between the two is key to determining long-term durability performance. This paper uses three-dimensional integrated micromaterial structural modeling to address moisture migration/balance and associated volume changes of concrete with creep in prestressed concrete bridge viaducts that are experiencing excessive deflections. It is found that moisture migration–related deflections driven by the capillary surface tension and disjoining pressures in cement micropores account for 25 to 45% of the macroscopic deflections. These apparent kinematics can be approximated by adding the moisture-related time-dependent deflections to the mechanistic-induced creep by external loads. This paper also addresses water–crack interaction in cracked RC bridge decks under moving loads in view of the coupled hygromechanics. It is found that the water presence on the upper deck parts, when subjected to high-speed traffic, can shorten the fatigue life of the deck by one-and-a-half order of life span. This reduction in life is discussed in terms of high-water pressure developing over large numbers of wheel passages, in addition to the reduced shear transfer along crack planes.

This paper reports an experimental study on recycled plastic concrete (RPC) that uses recycled acrylonitrile-butadiene-styrene/polycarbonate copolymer (ABS/PC) plastic particles to replace 5, 10, 15, and 20% (in volume) of fine aggregate sand. The plastic particles used in this research were recycled from waste plastic. The static and dynamic mechanical properties of specimens made of 5, 10, 15, and 20% plastic aggregate in volume were measured on a mechanical testing machine. The cube strength, axial compressive strength, and static stress-strain relationship of the RPC specimens with different plastic content were obtained. The ultimate compressive strength, ultimate strain, and dynamic stress-strain relationship of these specimens were measured with a split Hopkinson pressure bar device under four different strain rates. The stress-strain curves and energy absorption of the RPC specimens with different plastic content were obtained under the four different strain rate levels. The influences of plastic content and strain rates on the mechanical properties of RPC were analyzed. The results showed that the energy absorption capability of RPC was higher than that of normal concrete and increased with the plastic content. The impact resistance performance of RPC materials was superior to that of normal concrete.

This paper investigates the cyclic fatigue behavior of sandwich panels composed of glass fiber reinforced polymer (GFRP) skins connected by longitudinal $Z$-shape ribs and low-density polyurethane foam core. Eighteen $\mathrm{1,143}\times 635\times 78\text{-}\mathrm{mm}$ panels with ribs of two different flange widths, including three control static tests, were tested in fatigue under fully reversed loading ($R=-1$) and fully unloaded ($R=0$) conditions, to maximum loads ($P_{\text{max}}$) of 20–70% of their ultimate static strength ($P_{\text{ult}}$). Fatigue life curves were established and compared with those of panels without any ribs. It was shown that internal ribs increased static strength and stiffness by 80 and 66%, respectively, but were only beneficial within the low cycle fatigue range. Under $P_{\text{max}}$ of 50% $P_{\text{ult}}$, number of cycles to failure ($N_f$) at $R=-1$ was only 6% of $N_f$ at $R=0$ in the ribbed panels. Fatigue failure consistently initiated by flange debonding of the rib from skin. In panels loaded to higher than $P_{\text{ult}}$ of their nonribbed counterparts, final shear failure of foam core occurred simultaneously with rib debonding, whereas in panels loaded below this level, additional fatigue life was attained after rib debonding, until core shear failure, but at significantly lower stiffness. To achieve an $N_f$ of 2M cycles, $P_{\text{max}}$ should not exceed 35 and 21% of $P_{\text{ult}}$ at $R=0$ and $-1$, respectively. A three-dimensional (3D) failure surface (Haigh diagram) was established for the ribbed panels. It predicts fatigue life for a given mean and amplitude loads.

This paper focuses on early-age internal stress evolvement under restraining conditions and the fatigue behavior of ordinary concrete and crumb rubber concrete. The internal strain development in ordinary concrete and crumb rubber concrete slabs was monitored after the casting of concrete. Results show that the internal stress that developed in restrained rubber included concrete was lower than that in ordinary cement concrete. The stress relaxation effect due to the low elastic modulus of rubber included concrete may account for this result. A fatigue test of both concretes at room temperature and elevated temperature was conducted. At room temperature, crumb rubber concrete possessed much longer fatigue life than ordinary concrete. At 70°C, the fatigue life of both ordinary concrete or crumb rubber concrete is much lower than either concrete at normal temperature, no matter if the specimens are dry or water saturated. The moisture contained in the specimens during the fatigue test plays an important role in decreasing the fatigue life of both types of concrete. Furthermore, crumb rubber concrete always performs better than ordinary concrete under comparable conditions. With the help of acoustic emission (AE) analysis, it is revealed that the incorporation of rubble particles in the concrete alleviated the damage process of concrete.

Corrosion of steel reinforcement due to chloride penetration is a major deterioration mechanism of reinforced concrete (RC) structures exposed to marine environments. In the present paper, a probabilistic model is presented to predict the chloride penetration profile in concrete and the risk of steel corrosion considering the time dependence of both the diffusion coefficient and the surface chloride concentration of concrete. Abundant field data from two projects in China and Japan are respectively collected. The consistency between these field data and the model prediction verified the reliability of this probabilistic model, based on which further parametric analyses were carried out to investigate the effects of different design variables on the probability of steel corrosion.

In the context of long-term repository of high-level and long-lived nuclear waste, authors investigate different concrete properties related to fluid transport, in order to determine which is able to detect damage earliest. To this purpose, different protocols are tested, which impose progressive damage to two different Andra high-performance concretes (HPCs), based on pure portland (CEMI) or composed cement (CEMV)-type cements. The properties investigated are pore size distributions and porosity [by mercury intrusion porosimetry (MIP)], water retention curves, relative gas permeability, and gas migration properties (gas breakthrough pressure). Gas breakthrough pressure (GBP) is assessed rather than gas entry, by accurately measuring gas presence on the downstream side of a confined sample subjected to slowly increasing gas pressure on its upstream side. From MIP data, authors show that CEMI concrete has smaller porosity but greater pore sizes than CEMV. For CEMI concrete, all damage procedures significantly affect water retention curves and gas breakthrough pressures, yet they have no effect upon the relationship between relative gas permeability and water saturation. For CEMV concrete subjected to low damage levels, gas breakthrough measurements detect damage, whereas water retention and gas permeability do not.

Strengthening by fiber-reinforced polymers (FRPs) is one of the most common solutions to the ageing infrastructures. However, long-term durability of such systems under different environmental conditions needs to be understood properly before widely adopting these methods in the field. This paper presents research outcomes from an experimental program carried out to determine the influence of moisture on the durability of the bond between FRP and concrete along with its constituent materials. Performance was evaluated through single lap shear bond tests and various kinds of tests on the resin samples, including water absorption, mechanical characterization, and glass transition temperature ($T_g$) analysis. The specimens were exposed to continuous water immersion and wet-dry cycles for a maximum period of up to 24 and 18 months, respectively. The results show some deterioration on the material and the bond properties in both exposure conditions. The bond strength decreased up to 32 and 12% for high-strength and normal-strength concrete substrates, respectively, after continuous immersion, indicating the key role of the substrate in the durability of bonds. As a result of exposure, failure propagated towards the primer-concrete interface region. The failure mode changed from concrete cohesion to primer-concrete mixed failure for normal-strength concrete and from mixed failure to complete adhesion failure in case of high-strength concrete. These shifts in failure patterns are mainly due to destruction of the adhesion bond caused by water molecules at the interface. However, it is found that the loss of the adhesion bond is somehow compensated by the good mechanical interlocking obtained by proper surface roughness condition of the substrate. Finally, the effects of water were also investigated in interfacial bond stress-slip laws and fracture energies.

In this experimental study, the reinforcing effects of graphene oxide (GO) on portland cement paste are investigated. It is discovered that the introduction of 0.03% by weight GO sheets into the cement paste can increase the compressive strength and tensile strength of the cement composite by more than 40% due to the reduction of the pore structure of the cement paste. Moreover, the inclusion of the GO sheets enhances the degree of hydration of the cement paste. However, the workability of the GO-cement composite becomes somewhat reduced. The overall results indicate that GO could be a promising nanofillers for reinforcing the engineering properties of portland cement paste.