Long-term Mechanical Behavior Research Articles

Long term properties of Nano-engineered temperature self-controlled concrete served for mass concrete structure

Due to the advantages of low-cost and superior electrical conductivity, Nano-carbon black (NCB) can endow hydraulic concrete with long-term and stable self-heating capacities at affordable costs, thus allowing active and intelligent temperature control for high-altitude and high-latitude dams. This study, for the first time, investigated the long-term mechanical behaviors, freeze-thaw resistance and impermeability of temperature self-controlled concrete (TSC). Moreover, the modification mechanisms of TSC were revealed with the help of mercury intrusion porosimetry (MIP), thermogravimetric analysis (TGA) and scanning electron microscope (SEM). Finally, the long-term performance and cost assessment of TSC are comprehensively evaluated by the entropy weight method. The results indicate that the incorporation of 4.5wt% NCB improves the compressive and splitting tensile strengths of TSC at 180 days by 17.4% and 7.9%, respectively, and shows an excellent response against impermeability and a slightly lower response against frost resistance. Besides, NCB accelerates the hydration degree and repairs the interfacial transition zone of TSC. The presence of NCB densifies the microstructures of the matrix and reduces the content of harmful pores by nearly 50%. Finally, TSC with 4.5wt% NCB is the optimal mixture that shows excellent comprehensive performances.

A Review of the Mechanical Properties of and Long-Term Behavior Research on Box Girder Bridges with Corrugated Steel Webs

Based on an analysis of the extant literature, this paper summarizes the research progress on the mechanical properties and long-term behavior of corrugated steel web (CSW) box girder bridges. First, the research results of CSW box girder bridges in terms of the shear buckling performance (local shear buckling, overall shear buckling, and interaction buckling), bending performance, bending capacity, torsional capacity, and coefficient of internal force increase are summarized, along with the main factors affecting the mechanical performance of CSW box girder bridges. Second, based on research on the self-oscillation characteristics and dynamic response of CSW box girder bridges, the influence of structural parameters on the self-oscillation characteristics is analyzed. Finally, the long-term mechanical behavior of the CSW box girder bridges is analyzed in terms of fatigue, creep, and temperature effects. The existing research results demonstrate that there still exist deficiencies in the mechanical properties and long-term behavior of CSW box girder bridges, and this paper thus suggests a future research focus on CSW box girder bridges to provide a reference for further improving their basic theoretical system.

Mechanical Behavior of Sediment-Type High-Impurity Salt Cavern Gas Storage during Long-Term Operation

With the development of salt cavern gas storage technology, the construction of large-scale salt cavern gas storage using sediment voids is expected to solve the problems of low effective volume formation rate and poor construction economy of high-impurity salt mines. At present, there are few studies on the long-term operational mechanical behavior of salt cavern gas storage under the influence of sediment accumulation. The present paper studies the influence of sediment height, particle gradation, and operating pressure on the stability of salt caverns by constructing a coupling model of sediment particle discontinuous medium and surrounding rock continuous medium. The continuous–discontinuous coupling algorithm is suitable for analyzing the influence of sediment height and particle gradation on the creep shrinkage of salt caverns. The increase in sediment height slows down the creep shrinkage of the cavern bottom, which strengthens the restraining effect on the surrounding rock of the cavern. As a result, the position of the maximum displacement of the surrounding rock moves to the upper part of the cavern. The sediment particle gradation has little effect on the cavern volume shrinkage rate. The greater the coarse particle content, the smaller the cavern volume shrinkage rate. The greater the operating pressure, the more conducive to maintaining the stability of the cavern. This situation slows down the upward movement of the sediment accumulation and increases the gas storage space in the upper part of the cavern. The obtained results can provide a reference for evaluating the long-term operational stability of sediment-type high-impurity salt cavern gas storage.

Intervertebral disc creep behaviour through viscoelastic models: an in-vitro study

The intervertebral disc (IVD) is a complex biological structure that ensures the spine strength, stability, mobility, and flexibility. This is achieved due to its biphasic nature which is attained by its solid phase (annulus fibrosus) and fluid phases (nucleus pulposus). Hence, the IVD biomechanical response to long-term loads, which is critical as it affects hydration, and nutrients-water transport influencing disc height reduction, has been further explored and mathematically modelled in this paper. An in-vitro study was performed on seven human lumbar spine specimens (L4-5), to assess if the classical rheological models and Nutting's power law can model in a simple way the intermediate characteristics between solid and fluid of the IVD. Creep tests were conducted by applying a static compression load of 500 N for 15 min. A correlation analysis was done (Pearson, p < 0.05) between the model parameters and the maximum value of Disc Height Reduction, followed by a linear regression analysis. In summary, the long-term IVD mechanical behavior was modeled in a simple way, emphasizing that yet there is no mathematical certainty about this mechanical behavior. Hence, a future aim might be to develop intervertebral disc prostheses capable of replicating only the disc mechanical response, without necessarily considering the microscopic-level biological drivers. Therefore, a future goal is to fully understand and model the disc's mechanical response toward the design of new disc prostheses that would consider only the macroscopic aspect, without considering the biological aspects.

Study on shrinkage and creep effect of steel truss-stiffened continuous rigid frame bridge considering variable temperature and relative humidity

In this study, indoor-outdoor comparison tests of shrinkage and creep were carried out in northwest China. The experimental results were compared with commonly used models of shrinkage and creep, some of which have adapted different methods for temperature and humidity correction. A finite element model for a continuous rigid-frame bridge with steel truss bracing was established. The calculated values from different shrinkage and creep models were then compared with the measured deflection values. An analysis was conducted to determine the influence of variable temperature and humidity on the long-term mechanical behavior of the steel truss-stiffened continuous rigid-frame bridge.The results show that when the concrete reaches the age of one year, the creep coefficient for the outdoor environment is 18.5% smaller than that in the indoor environment, while the outdoor shrinkage strain is 16.0% smaller. The CEB 90 model agrees best with the indoor test results. The corrected shrinkage and creep model (CSCM) is the closest to the outdoor test results, and the fib2010 model ranked second. The predicted values from CSCM exhibit the best agreement with the measured deflection values after the bridge completion. The CEB 90 model's predicted values for deflection of the main girder, longitudinal displacement of the pier, the maximum stress in steel trusses, and prestressing loss are lower than those in the CSCM after 20 years of construction, indicating that the influence of temperature and relative humidity variations on shrinkage and creep effect of the bridge can not be negligible.

Influence of Cement Kiln Dust on Long-Term Mechanical Behavior and Microstructure of High-Performance Concrete.

Cement production in the world market is steadily increasing. In 2000, it was 1600 million tons, while as of 2013, the annual amount exceeded 4000 million tons. The burning of cement clinker is associated with the generation of waste. It is estimated that the amount of cement kiln dust (CKD), during combustion, reaches about 15-20%, which means 700 million tons per year. However, not all types of by-products are reusable due to high alkali, sulfate, and chloride contents, which can adversely affect the environment. One environmentally friendly solution may be to use CKD in the production of high-performance concrete (HPC), as a substitute for some of the cement. This paper presents a study of the short- and long-term physical and mechanical properties of HPC with 5%, 10%, 15%, and 20% CKD additives. The experiments determined density, water absorption, porosity, splitting tensile strength, compressive strength, modulus of elasticity, ultrasonic pulse velocity, and evaluated the microstructure of the concrete. The addition of CKD up to 10% caused an increase in the 28- and 730-day compressive strengths, while the values decreased slightly when CKD concentration increased to 20%. Splitting tensile strength decreased proportionally with 5-20% amounts of CKD regardless of HPC age. Porosity, absorbability, and ultrasonic pulse velocity decreased with increasing cement dust, while the bulk density increased for HPC with CKD. Microstructure analyses showed a decrease in the content of calcium silicate hydrate (C-S-H), acceleration of setting, and formation of wider microcracks with an increase in CKD. From the results, it was shown that a 15% percentage addition of CKD can effectively replace cement in the production of HPC and contribute to reducing the amount of by-product from the burning of cement clinker.

Laser-texturing and traditional surface modification to improve the adhesion of glass fiber-reinforced composite posts to resin cements

ObjectivesThe aim of this study was to perform an experimental evaluation of the synergistic effects of laser-texturing and different traditional surface modification approaches to improve the adhesion of glass fiber-reinforced composite (GFRC) posts to resin-matrix cements used in endodontically treated teeth rehabilitation. MethodsOne hundred and ten freshly extracted mandibular single-rooted premolars were endodontically treated and groups of specimens were divided according to the GFRC cementation after different surface treatment, as follow (n = 10): silane-based conditioning (SIL); 9.7 % HF acid-etching (HF); 35 % H2O2 etching (H2O2); grit-blasting (GB); HF plus H2O2 etching (HFH2O2); 6 W Nd:YAG laser-texturing (L6W); 4.5 W Nd:YAG laser-texturing (L4.5W); 3 W Nd:YAG laser-texturing (L3W); 3 W Nd:YAG plus 35 % H2O2 (L3WH2O2); 3 W Nd:YAG plus SIL (L3WSIL); and untreated (C). GFRC posts were cemented into the tooth root canals using a dual-cured resin cement. Then, specimens were cross-sectioned and mechanically assessed by push-out bond strength tests. Specimens were inspected by optical microscopy and scanning electron microscopy (SEM) at magnification from × 30 up to × 2000. The failure mode was recorded by microscopic analyses after the bond strenght tests. ResultsSurface analyses of the GFRC posts showed a rough and retentive morphological aspect with a removal of the outer epoxy matrix layer and exposure of glass fibers after laser-texturing, grit-blasting, or etching under 35 % H2O2. The highest bond strength values at 21.8 MPa was recorded for GFRC posts after laser-texturing on 3W plus silane-based conditioning followed by the group etched with 35 % H2O2 (20.5 MPa). The failure mode was microscopically characterized as cohesive and mixed pathways. The lowest bond strength values around 5 and 9 MPa and adhesive failure were recorded for the untreated GFRC group or specimens etched with HF. ConclusionsThe combination of acidic etching and silane conditioning with laser-texturing at moderate intensity promoted an adequate surface modification of GFRC posts and increased adhesion to a resin-matrix cement. Such combination of physicochemical approaches can enhance the long-term mechanical behavior of the restorative interface at endodontically treated teeth. Clinical relevanceCombining traditional and novel physicochemical approaches can provide promising adhesion pathways for glass fiber-reinforced composite posts to resin-matrix cements. A high mechanical interlocking of the resin-matrix cements and the stable retention of the teeth root intracanal posts can decrease the risks of clinical failures by fracture and detachment of the intraradicular interface.

NA

NA

A Review on Durability Analysis of FRP Bars based on Different Factors in Alkaline Environment

The primary issue with concrete structures is steel bar corrosion. Therefore, FRP (Fiber Reinforced Polymer) bars are often to substitute steel bars to tackle the issue of concrete swelling and cracking brought about by steel corrosion. FRP bars feature improved corrosion resistance, a stronger strength-to-quality ratio, and better fatigue resistance. However, the alkaline environment will affect the long-term strength and durability of FRP, according to certain research, which will cause the FRP bars mechanical characteristics to deteriorate. In this paper, the properties of FRP bars under alkaline conditions are reviewed, considering the harsh external environment and physical properties of FRP bars. Comprehensive investigation concludes that lowering the PH value of concrete and changing the kind of fiber material may considerably increase the endurance of FRP in alkaline environments. By demonstrating the microscopic breakdown process of FRP bars in an alkaline conditions using scanning electron microscopy. The Arrhenius acceleration theory was used to construct the present model for forecasting the long-term mechanical behavior of FRP bars, which shows how this material degrades under alkaline circumstances. This study may be utilized as a reference for FRP bars used in alkaline environments in terms of durability studies.

On the installation effects of open ended piles in chalk

Chalk is a highly porous rock formed by cemented calcite grains. It covers areas of the UK and is widespread under the North Sea where offshore wind turbines (OWT) are currently being installed and where future offshore expansion will be sited (Figure 1(a)) [1]. Large piles are often driven in chalk to support OWT. The installation process causes the intact rock below the pile tip to crush into a putty characterised by a mechanical behaviour very different from the intact chalk. The difficulty to predict the final state of the putty and the stress around the pile after installation is the underlying reason for inadequate current design guidance for piles in chalk. Considering that for OWT, foundations account for 20-25% of the total development cost , pile design improvements in chalk, would be extremely beneficial from an economical and environmental perspective.&#x0D; Current guidelines for the design of piles in chalk (CIRIA C574) originate from the analysis of a limited number of pile tests [2]. These guidelines suggest crude average ultimate unit shaft friction (tsf) design values of between 20 and 120 kPa for low-medium density and high/very-high density chalk, respectively. tsf estimates are thought to be conservative hence introducing significant increases in cost and carbon footprint (Figure 1(b)). Reducing the level of conservatism (e.g. enabling more confident use of higher tsf) would reflect in significant savings of steel and consequent reduction of the cost and embodied carbon. Such design considerations are possible but require a better understanding of the long-term mechanical behaviour of the damage processes intact chalk experiences during dynamic installation in hydro-mechanical (HM) coupled conditions.&#x0D; In this work the coupled HM effects developing during pile installation in chalk are investigated numerically using a robust and mesh-independent implementation of an elasto-plastic constitutive model at large strains. The model, implemented into an open-source Geotechnical Particle Finite Element (G-PFEM) code [3], is shown to be able to capture the damage of the rock until the formation of a chalk putty layer around the shaft of a model piles jacked in chalk. In particular the complex flow processes occurring in the soil around both open and closed ended piles of variable shape jacked into saturated chalk are investigated. A fully coupled hydro-mechanical formulation, based on regularized, mixed low-order linear strain triangles is used [5]. To capture the relevant features of the mechanical response of chalk, a finite deformation, non-associative structured modified cam clay is used [6]. The model formulation is based on a multiplicative decomposition of the deformation gradient and on the adoption of an elastic response based on the existence of a suitable free energy function. Bonding-related internal variables, quantifying the effects of structure on the yield locus, are used to provide a macroscopic description of mechanical destructuration effects. To deal with strain localization phenomena, the model is equipped with a non-local version of the hardening laws [7]. The G-PFEM model is shown to be capable of capturing the destructuration associated with plastic deformations below and around the pile shoulder; the space and time evolution of pore water pressure as the pile advances; the effect of soil permeability on predicted excess pore water pressures, and the effect of chalk putty formation on predicted values of the load displacement curve. Installation effects are highlighted by comparing the axial performance between wished in place piles and piles which considered the full installation process.

Multiscale analysis of long-term mechanical and durability behaviour of two alkali-activated slag-based types of concrete

Although alkali activated concretes (AACs) are promising for reducing the carbon emissions of concrete, in order to enable their wide application it is vital to understand their long-term behaviour. Herein, we report the development of mechanical properties of a ground granulated blast furnace slag (GGBFS)-based AAC and a binary fly ash (FA) /GGBFS-based AAC exposed to 55% relative humidity and 20 °C up to the age of 5 years. For comparison, two ordinary Portland cement (OPC) concretes were monitored for 3.5 years. For the GGBFS-based AAC, after an initial decrease within the first 6 months the elastic compressive modulus stabilized, while its tensile splitting strength continued to decrease for the tested period of 5 years. The binary AAC showed a continuous decrease in its tensile splitting strength for 5 years and a reduction in its compressive strength after 2 years. No decreases in mechanical properties were observed in OPC-based concretes. To reveal underlying mechanisms, additional analyses were performed. Permanent degradation was observed in both AACs; the binary AAC mainly suffered from carbonation, and the GGBFS-based AAC showed microcracking. These cracks were probably caused by drying shrinkage and drying-induced chemical changes. Based on the measured mechanical properties of AAC, crack widths and stiffness of reinforced AAC beams under bending were analytically evaluated and compared to experiments. Decreases in bending stiffness and increases in crack width were observed for reinforced AAC beams tested at later ages. A bimodular approach is proposed to predict the reduction of bending stiffness in the studied AACs over time. These findings are relevant to understand serviceability limit states of reinforced AACs.

Microseismic monitoring and experimental study on rockburst in water-rich area of tunnel

During the excavation of tunnels in the Hanjiang-to-Weihe River Diversion Project, many rockbursts occurred in water-rich (WR) areas. To study the mechanism of rockburst under such conditions, the features of microseismic events and rockbursts in WR tunnel sections excavated by both a tunnel boring machine (TBM) and “drilling and blasting” methods were statistically analysed and compared with those of adjacent water-poor (WP) areas. The results show that in both WR and WP areas, rockbursts are related to the classification of surrounding rock and are also affected by the excavation method. The rockbursts in most WP areas are more active than those in the nearby WR areas in sections excavated by TBM. However, the opposite is true under high in situ stress conditions. To explain the microseismic monitoring results, the mechanical behaviour of rock, including short- and long-term mechanical behaviour under different water and loading conditions, was also investigated, and the results show that under high stress conditions, water will accelerate the occurrence of rockburst. Therefore, the appropriate method to control rockburst is stress release, which can be achieved by advanced pilot tunnel excavation, hydraulic fracturing, and presplitting blasting, rather than high-pressure water spraying in the surrounding rock.

Hydromechanical modelling of salt caverns subjected to cyclic hydrogen injection and withdrawal

The present work is devoted to the study of underground hydrogen storage in salt caverns. Based on the hydromechanical characteristics of rock salts obtained from some laboratory experiments, we propose a novel model that includes short- and long-term mechanical behaviour. Specifically, the short-term part incorporates the elastoplastic and instantaneous damage mechanisms. Concerning the long-term behaviour, in addition to the primary and secondary creep phases, the tertiary phase takes into account a delayed damage mechanism.As application, we performed hydromechanical modelling of two vertical salt caverns with different depths based on existing hydrogen gas caverns, which are subjected to cyclic hydrogen injection and withdrawal (seasonal and daily scenarios). Gas transport is also modelled taking into account diffusion and advection mechanisms. Mechanical results indicate that the stability problem of a very deep cavern is more worrying in comparison with a shallow cavern, as expected. However, the gas extension is the same for both caverns because the gas flow is mainly by diffusion transport, while the permeability does not significantly increase. Since field data at very depths are limited, a sensibility analysis of material properties was carried out to provide insight into key mechanisms that may occur. Typically, a decrease in mechanical properties increases the extent of the damage around deep cavern but did not lead to significant increase in the extent of gas leakage. Under the assumptions made, these findings suggest that the use of salt caverns for green hydrogen storage, even with aggressive operating conditions to regulate variations between renewable energy production and peak power demands, should not significantly affect the stability of salt cavern nor promote an increase in hydrogen loss.

Long-term mechanical performance of high fluidity fiber reinforced concrete modified by metakaolin

To clarify the long-term strength and toughness of metakaolin (MK) and steel fiber (SF) modified concrete with higher fluidity and water/binder ratio, a series of tests including slump tests, compression tests, splitting tests, digital image processing and Scanning Electron Microscope (SEM) tests were performed on MK-SF concrete cured for 7–360 days. Results reveal that the slump of fresh concrete decreased with an increase in the MK and SF replacement rates. Moreover, the impact of MK on the slump of steel fiber reinforced concrete (SFRC) was more pronounced when combined with a lower water/binder ratio, resulting in increased viscosity. At the pre-peak stress region of the strain-stress curve, the compressive strength fc, tensile strength ft, Young’s modulus Ec, elastic modulus E0, and tensile strain at peak stress εt-max of high fluidity MK-SF concrete increased with increasing MK and SF admixing ratio, regardless of curing age. Notably, the coupling effects of MK and SF became more prominent after long-term curing. Without MK incorporation, the effects of SF and curing time on the above indices were relatively implicit. At the post-peak stress region of strain-stress curves, there existed a residual stage. The inclusion of MK significantly improved the long-term residual strength and strain of SFRC. Additionally, the toughness index Mc, which represents the total area of the compressive strain-stress curve containing both the pre-peak and post-peak regions, also exhibited substantial development with curing time, primarily attributed to the incorporation of MK and SF. The coupling of MK and SF led to a transformation of the concrete failure mode from brittle to ductile. Regression analysis reveals that a linear equation adequately described the long-term relationships of fc-ft, fc-Ec, fc-E0, fc-Mc, and fc-εt-max in MK-modified SFRC. Based on the testing data, a relative strength or toughness index λ and a new generalized hyperbola model were proposed to predict the long-term mechanical behavior mentioned above. Through crack morphology and microstructure analysis, the distinct roles of MK and SF in the composite material were examined.

On the experimental research of long-term hydrostatic performance and lifespan of polyethylene pipe

ABSTRACT Long-term hydrostatic (LTH) capacity test up to 10,000 h of polyethylene pipe (PE pipe) was successfully conducted according to Arrhenius theory. It was revealed that in some cases the pipe damage points initiate within the marker line on pipe body, indicating that the addictive of marker line could somehow weaken the mechanical property of pipe base materials. Test pressure test time data was fitted using dual-parameter model under the guidance of ISO9080: 2012, and its serving life was calculated as 28.9 years, ductile-brittle transition point was found at 8456 h. Conclusions drawn from this paper could contribute to understanding the long-term mechanical behaviour of PE pipe.

Experimental study on wayside monitoring method of train dynamic load based on strain of ballastless track slab

In the long-term service of ballastless track, which constantly bears the cyclic load from high-speed trains, it is important to obtain the long-term mechanical behavior of train dynamic load on the ballastless track. In this paper, a novel wayside monitoring method of train dynamic load is proposed, which takes CRTS III ballastless track as the research object and embeds Fiber Bragg grating (FBG) strain sensors into the track slab. The traditional wayside method installing strain gauges on the rail is used to compared with the sensors embedded in the track slab, which was tested in the field. Then, the time domain and frequency domain information of rail strain and slab strain are analyzed in detail, and the correlation analysis of signals is carried out. Finally, the calculation method of the running trains information and dynamic load is proposed. The results show that the vertical strain level of track slab is low under the action of high-speed train dynamic load. The time history curve shows that the adjacent wheel has obvious coupling effect on the slab strain signal, rather than rail strain. The frequency domain analysis of the signals indicates that the low-frequency components of the rail strain and slab strain have a strong correlation. However, the high-frequency components of train dynamic load are buffered out due to the effect of the fastener system. The mapping relationship between the track slab strain and the dynamic load can be found through calibration test, which provide a novel monitoring method of dynamic train load. The monitoring method can realize the real-time monitoring of train running information and record the long-term train dynamic load cycle law, and provide important parameters for the ballastless track boundary condition model.

Experimental and numerical investigations for compressive behavior of porous hydroxyapatite bone scaffold fabricated via freeze-gel casting method

Artificial bone scaffolds with a porosity of ≥64% were manufactured using hydroxyapatite (HA). The Freeze-gel Casting method using tert-butyl alcohol (TBA) as a solvent was adopted to maintain proper mechanical strength. The manufactured HA scaffold had excellent internal connectivity owing to the continuous connection of the long columnar pores and arrangement of the constant pore walls. For the HA scaffold, compression tests at different strain rates under uniaxially compressed loads were performed, and the compressive behavior according to the strain rate was analyzed. A maximum yield stress of 2–3 MPa was observed, and the overall compressive behavior was divided into elastic, plateau, and densification sections, which were different from the brittleness behavior of ordinary ceramics and similar to that of polymer materials. The compressive behavior of the HA scaffold was successfully simulated by applying the Frank–Brockman–Zairi constitutive model used to simulate elasto-viscoplastic material behavior. Seven material parameters belonging to the constitutive equation were proposed for the HA scaffold by adopting a deterministic approach for material parameter identification. Models can be developed from methods for simulating the mechanical behavior of a porous ceramic scaffold to predict the long-term mechanical behavior of the scaffold inserted in vivo, which may help in bone defects recovery.

Influence of polymeric molecular chain structure on the rheological-mechanical behavior of asphalt binders and porous asphalt mixes

This manuscript reports on two Styrene-Butadiene-Styrene (SBS) polymeric molecular chains so-called 1101AT and D0243, used to modify a 50/70 pen grade neat asphalt binder sample, generating the matrixes 60/85 E and Highly Modified Asphalt (HiMA), respectively. Some research gaps still exist and need to be investigated further, principally on why and how these distinct molecular chains influence the rheological-mechanical behavior of the asphalt binders and asphalt mixes, even pertaining to the same polymeric group. Dynamic Shear Rheometric (DSR) analyses describe the rheological spectra of the binder samples, considering the dynamic stiffness modulus in the complex plane |G*|. Porous asphalt mixes were evaluated considering the French formulation methodology and the following aspects: compaction ability, deleterious action of water, seepage speed and resistance to rutting. The results obtained indicate that HiMA matrix presented superior long-term rheological and mechanical behavior compared to 60/85 E, due to the more elaborate polymeric chain being associated to a bituminous matrix with rheological spectra providing less thermal and kinetic susceptibility, although its highest dynamic viscosity implies little reduction in the air void content and, consequently, lower seepage speeds to the porous asphalt mixes, but greater rutting resistance.

Influence of self-cementing properties on the mechanical behaviour of recycled concrete aggregates under monotonic loading

Recently, the use of recycled crushed concrete aggregates (RCA) as a substitution of natural aggregates in pavement base and subbase layers has become more popular. Occasionally, a growth of stiffness and strength in unbound base and subbase layers built with RCA can be observed, which can be considered as self-cementing properties of RCA. In this study, the potential self-cementing properties and the long-term mechanical behaviour of two different RCA (NRCA and ORCA), with significantly different self-cementing properties, were studied by pH value, thermogravimetric analysis (TGA) and monotonic triaxial tests under varying confining pressures (20/40/70 kPa) and varying curing times (1/28/360 days). Results show that the long-term storage can largely reduce the self-cementing properties of RCA (ORCA), while the RCA crushed recently (NRCA) exhibits much stronger self-cementing properties. Besides, the long-term mechanical behaviours are influenced by self-cementing properties and confining pressure as well as curing time, so that the strength and stiffness of RCA specimen, with stronger self-cementing properties (NRCA), increase more under low confining pressure and long curing time. The experimental results also indicate that the long-term mechanical behaviours of NRCA are consistent with cement treated materials, whose ductile stress–strain response gradually turns to stiff brittle behaviour as curing time increases.

Advanced modelling of concrete structures for improved sustainability

The safe and long-term serviceability of concrete structures is one of the methods how to improve the sustainability of the concrete industry. This study presents a pilot application of an~integrated system for online monitoring and service life prediction of concrete bridges. The system consists of strain gauges measuring the structural response coupled with a laser rangefinder for detection of the bridge-crossing traffic. The measured data were used for the development of a computational model of the bridge. Next, the deterioration models were applied to the model to assess the long-term mechanical behaviour. In this study, we considered chloride-induced reinforcement corrosion. The numerical data are given for 100-years-long service life prediction.