Long-term bond performance of GFRP bars in concrete under temperature ranging from 20 °C to 80 °C

Eighty pull-out specimens were used to study the effect of temperature ranging from 20 °C to 80 °C in dry environment on bond properties between Glass Fiber Reinforced Polymer (GFRP) bars and concrete. The pullout-test specimens were subjected during 4 and 8 months to high temperatures up to 80 °C and then compared to untreated specimens (20 °C). Experimental results showed no significant reduction on bond strength for temperatures up to 60 °C. However, a maximum of 14% reduction of the bond strength was observed for 80 °C temperature after 8 months of thermal loading. For treated specimens, the coefficient β in the CMR model, which predicts the bond–stress–displacement behavior, seems to be dependant with the temperature.     

Identification of the thermal properties of concrete for the temperature calculation of concrete slabs and columns subjected to a standard fire—Methodology and proposal for simplified formulations

The fire resistance of concrete members is controlled by the temperature distribution of the considered cross section. The thermal analysis can be performed with the advanced temperature dependent physical properties provided by EN 1992-1-2. But the recalculation of laboratory tests on columns from TU Braunschweig shows, that there are deviations between the calculated and measured temperatures. Therefore it can be assumed, that the mathematical formulation of these thermal properties could be improved. A sensitivity analysis is performed to identify the governing parameters of the temperature calculation and a nonlinear optimization method is used to enhance the formulation of the thermal properties. The proposed simplified properties are partly validated by the recalculation of measured temperatures of concrete columns. These first results show, that the scatter of the differences from the calculated to the measured temperatures can be reduced by the proposed simple model for the thermal analysis of concrete.     

Strength deterioration of reinforced concrete beam–column joints subjected to cyclic loading

This paper proposes a method to predict the ductile capacity of reinforced concrete beam–column joints failing in shear after the development of plastic hinges at both ends of the adjacent beams. After the plastic hinges occur at both ends of the beams, the longitudinal axial strain at the center of the beam section in the plastic hinge region is expected to increase abruptly because the neutral axis continues to move toward the extreme compressive fiber and the residual strains of the longitudinal bars continue to increase with each cycle of additional inelastic loading cycles. An increase in the axial strain of the beam section after flexural yielding contributes to a widening of the cracks in the beam–column joints, thus leading to a reduction in the shear strength of the beam–column joints. The proposed method includes the effect of longitudinal axial strain of a beam in the plastic hinge region of the beam on the joint longitudinal strain and the strength deterioration of the joint. In order to verify the shear strength and the corresponding deformability of the proposed method, test results of RC beam–column assembly were compared. Comparisons between the observed and calculated shear strengths and their corresponding deformability of the tested assemblies showed reasonable agreement.     

Evaluation of prestress losses in prestressed concrete specimens subjected to freeze–thaw cycles

Prestressed concrete structures are considered to be reliable and durable. However, their long-term performance when subjected to frost attack is still unclear. In this work, experiments were carried out to evaluate the prestress losses in post-tensioned prestressed concrete specimens subjected to freeze–thaw cycles (FTCs). Two cases were considered: in one case, a series of specimens were prepared and tested in a freeze–thaw chamber; in the second case, the same series of specimens were tested in an indoor environment (outside the chamber). The difference between the prestress losses of the specimens inside the freeze–thaw chamber and those outside the chamber equalled the prestress losses due to FTCs. When using mathematical models to predict the prestress losses due to the FTCs, it was found that they were relatively small when the concrete was slightly damaged. However, they increased rapidly when the FTCs were repeated. The eccentricity of the prestress wires led to larger prestress losses when subjected to FTCs. Moreover, the same cross section and eccentricity resulted in similar prestress losses due to the FTCs, and the relatively high-strength concrete could withstand more FTCs.     

Dynamic response of fiber–metal laminates (FMLs) subjected to low-velocity impact

Fiber–metal laminates (FMLs) are high-performance hybrid structures based on alternating stacked arrangements of fiber-reinforced plastic (FRP) plies and metal alloy layers. The response of FMLs subjected to low-velocity impact is studied in this paper. The aluminum (Al) sheets are placed instead of some of layers of FRP plies. The effect of the Al layers on contact force history, deflection, in-plane strains and stresses of the structure is studied. The first-order shear deformation theory as well as the Fourier series method is used to solve the governing equations of the composite plate analytically. The interaction between the impactor and the plate is modeled with the use of a two degrees-of-freedom system, consisting of springs-masses. The Choi's linearized Hertzian contact model is used in the impact analysis of the hybrid composite plate. The results indicated that some of the parameters like the layer sequence, mass and velocity of the impactor in a constant impact energy level, and the aspect ratio (a/b) of the plate are important factors affecting the dynamic response of the FMLs. Interaction among the mentioned geometrical parameters and material parameters like the aluminum 2024-T3 alloy layers is studied. The numerical results that are presented in this paper hitherto not reported in the published literature.     

Microstructure changes in mortars attacked by sulphates at 5 °C

In this study mortars have been produced using ordinary Portland cement (CEM I – 32.5) and limestone cement with 15% limestone addition (CEM II/A-LL – 32.5). The mortars were immersed in a solution of 5% Na₂SO₄ at 5 °C for 6 months and the caused deterioration was observed visually at a regular basis. The deterioration product of the surface of both mortars has been identified as thaumasite by the means of XRD, FT-IR, DTA and SEM/EDAX analysis. The damage caused due to formation of thaumasite in both mortars was approximately the same and not influenced by the addition of limestone. Furthermore, expansion and compressive strength of the mortars were studied as a function of time and it was proved they were not influenced by thaumasite formation at the age of 6 months.     

Response of GLARE© panels to blast loading

GLARE^© is a fibre-metal laminate that is widely used by the aircraft industry due to its excellent fatigue and impact properties. It has also been proposed as a blast resistant material. This article reports on a set of experiments on GLARE 3, one of the GLARE variants used in impact applications. Results from the preliminary blast tests indicate that the panels behaved similarly to monolithic metal plates and appeared to offer potential for blast resistance when the results are compared to those in the literature for monolithic metal plates.     

Experimental study on the physico-mechanical properties and temperature field evolution of granite subjected to different heating–cooling treatments

Bulletin of Engineering Geology and the Environment - Rock cracking caused by thermal shocking occurs widely in geothermal exploitation processes, such as wellbore drilling, reservoir stimulation,...     

Low-temperature (7 °C) anaerobic treatment of a trichloroethylene-contaminated wastewater: microbial community development

The feasibility of low-temperature (7 °C) anaerobic digestion for the treatment of a trichloroethylene (TCE) contaminated wastewater was investigated. Two expanded granular sludge bed (EGSB) bioreactors (R1 and R2) were employed for the mineralisation of a synthetic volatile fatty acid based wastewater at an initial organic loading rate (OLR) of 3 kg COD m⁻³ d⁻¹, and an operating temperature of 15 °C. Successive reductions in OLR to 0.75 kg COD m⁻³ d⁻¹, and operational temperature to 7 °C, resulted in stable bioreactor operation by day 417, with COD removal efficiency and biogas CH₄ content ≥74%, for both bioreactors. Subsequently, the influent to R1 was supplemented with increasing concentrations (10, 20, 30 mg l⁻¹) of TCE, while R2 acted as a control. At an influent TCE concentration of 30 mg l⁻¹, although phase average TCE removal rates of 79% were recorded, a sustained decrease in R1 performance was observed, with COD removal of 6%, and % biogas CH₄ of 3% recorded on days 595 and 607, respectively. Specific methanogenic activity (SMA) assays identified a general shift from acetate- to hydrogen-mediated methanogenesis in both R1 and R2 biomass, while toxicity assays confirmed an increased sensitivity of the acetoclastic community in R1 to TCE and dichloroethylene (DCE), which contributed to acetate accumulation. Quantitative Polymerase Chain Reaction (qPCR) analysis of the methanogenic community confirmed the dominance of hydrogenotrophic methanogens in both R1 and R2, representing 71-89% of the total methanogenic population, however acetoclastic Methanosaeta were the dominant organisms, based on 16S rRNA gene clone library analysis of reactor biomass. The greatest change in the bacterial community, as demonstrated by UPGMA analysis of DGGE banding profiles, was observed in R1 biomass between days 417 and 609, although 88% similarity was retained between these sampling points.     

Hydraulic and physicochemical properties of dense thin bentonite layers permeated with variably mixed alkaline solutions of KOH and CaCl2 at various temperatures (25–75 °C) for 3 years

Hydraulic conductivity tests were performed using mixed alkaline solutions of KOH and CaCl₂ (pH ～12) on thin Na-bentonite layers under various temperature conditions (25–75 °C) for 3 years. For dense thin Na-bentonite (dry density of 1.12 Mg/m³) in a mixed alkaline solution of 0.03 M KOH and 0.03 M CaCl₂, the hydraulic conductivities at 50 °C and 75 °C were approximately 10 times higher than that at 25 °C. The bentonite samples permeated with the mixed solution at 50 °C and 75 °C achieved almost complete cation exchange of Na ions by Ca and K ions. However, only slight cation exchange occurred in the bentonite specimens permeated at 25 °C, regardless of the type of permeant. The free swell index of the reacted bentonite permeated with a mixed solution of 0.03 M KOH and 0.03 M CaCl₂ significantly decreased at 50 °C and 75 °C compared with that at 25 °C. X-ray diffraction analysis revealed that the decreases in the relative intensities of the peaks of accessory minerals, such as opal-cristobalite/tridymite, quartz, and feldspar, were enhanced at 50 °C and 75 °C.     

Degradation of HDPE,LLDPE, and blended polyethylene geomembranes in extremely low and high pH mining solutions at 85 °C

The durability of five 1.5-mm thick geomembranes (GMBs) is investigated in pH 0.5 and 13.5 synthetic mining solutions using immersion tests. Two high density polyethylene (HDPE), two linear low density polyethylene (LLDPE), and one blended polyethylene (BPO) GMBs are investigated at 85 °C for incubation durations of 4.5–6.5 years. It is shown that the degradation of all five GMBs in the high pH solution is faster than in the low pH solution. In the pH 0.5 solution, one of the HDPEs and the BPO GMBs exhibited polymer degradation before or at the time of the depletion of their antioxidants. In pH 13.5, four out of the five GMBs exhibited degradation and followed the conceptual three-stage degradation model until nominal failure. However, there is no correlation between the long-term performance of these GMBs and their resin type or their initial properties since one of the examined LLDPEs outperformed all the higher density/crystallinity GMBs with higher initial properties while the other LLDPE did not perform well. Thus, when selecting a GMB for a desired application, the relative performance of different candidate GMBs can be only assessed using immersion tests using the solutions expected in the field.     

Analysis of the stabilising effect of ribs of reinforced sprayed concrete (RRS) in the Løren road tunnel

Bulletin of Engineering Geology and the Environment - The Løren tunnel is a road tunnel at Ring road 3 in Oslo, Norway. The tunnel has a length of 915 m in rock, has two tubes with...     

Ozonation of secondary treated wastewater reduces ecotoxicity to Gammarus fossarum (Crustacea; Amphipoda): are loads of (micro)pollutants responsible?

Ozone application is an effective tool to reduce loads of (micro)pollutants in wastewater, however, its ecotoxicological implications are largely unknown. Therefore, the feeding rates of a leaf-shredding invertebrate (Gammarus fossarum) exposed to secondary (=non-ozone) or ozone treated wastewater were investigated to assess potential ecotoxicological effects. Two repetitive experiments resulted in significantly higher feeding rates for gammarids exposed to ozone compared to non-ozone treated wastewater sampled from a treatment plant equipped with a full-scale ozonation. A further experiment confirmed these results also for wastewater from the same treatment plant, when ozonation was conducted at the lab-scale. However, the deviations in dissolved organic carbon profiles of ozone and non-ozone wastewater did not seem to be the driving factor for the effects observed. Two additional experiments displayed on the one hand a higher feeding rate of G. fossarum if exposed to ten-fold enriched eluates from solid phase extraction cartridges loaded with ozone compared to non-ozone treated wastewater. On the other hand, the mean feeding rate of gammarids exposed to non-ozone treated wastewater, which contained hardly any (micro)pollutants (i.e. pharmaceuticals), was at the same level as wastewater from the same source additionally treated with ozone. These results suggest that not an alteration in the organic matrix but a reduction in the load of micropollutants most likely triggered the effects in the bioassay applied. Hence, the feeding rate of G. fossarum appears to be a well-suited bioassay to indicate alterations in ecotoxicological properties of wastewater due to the application of advanced oxidation processes like ozonation.     

Characterization of dissolved organic matter in a coral reef ecosystem subjected to anthropogenic pressures (La Réunion Island, Indian Ocean) using multi-dimensional fluorescence spectroscopy

La Saline fringing reef is the most important coral reef complex of La Réunion Island (southwestern Indian Ocean; 21°07′S, 55°32′E). This ecosystem is subjected to anthropogenic pressures through river inputs and submarine groundwater discharge (SGD). The goal of this study was to characterize the pool of fluorescent dissolved organic matter (FDOM) in different water bodies of La Saline fringing reef ecosystem using excitation-emission matrix (EEM) spectrofluorometry. From EEMs, we identified the different fluorophores by the peak picking technique and determined two fluorescence indices issued from the literature: the humification index (HIX) and the biological index (BIX). The main known fluorophores were present within the sample set: humic-like A, humic-like C, marine humic-like M, tryptophan-like T1 and T2, and tyrosine-like B1 and B2. In some samples, unknown fluorophores (“U”) were also detected. The surface oceanic waters located beyond the reef front displayed a typical oligotrophic marine signature, with a dominance of autochthonous/biological material (presence of peaks: T1 > B1 > A > T2 > M > C; HIX: 0.9 ± 0.4; BIX: 2.3 ± 1.1). In the reef waters, the autochthonous/biological fingerprint also dominated even though the content in humic substances was higher (same relative distribution of peaks; HIX: 1.6 ± 0.6; BIX: 1.0 ± 0.1). Sedimentary and volcanic SGD showed very different patterns with a strong terrestrial source for the former (A > T1 > C > B1 and A > C > B1; HIX: 9.8 ± 2.0; BIX: 0.8 ± 0.0) and a weak terrestrial source for the latter (A > B1 > U3 > B2 > C and A > U4 > C; HIX: 2.4 ± 0.3; BIX: 0.9 ± 0.0). In the Hermitage River, both humic substances and protein-like material were abundant (T1 > A > U5 > B1 > C > B2; HIX: 2.3; BIX: 1.4). We provide evidences for the presence of anthropogenic DOM in some of these water bodies. Some oceanic samples (presence of peaks U1 and U2) were likely contaminated by oil-derived PAHs from ships navigating around the reef front, whereas the Hermitage River was highly impacted by sewage effluents, numerous in this coastal area of La Réunion Island. We conclude that multi-dimensional fluorescence spectroscopy (EEM) coupled to the determination of HIX and BIX is a good tool for assessing the origin and distribution of DOM in the coral reef ecosystems submitted to anthropogenic impacts.     

Engineering properties of tuffs in the Sandikli region (Afyon—Turkey) and their possible use as concrete aggregates

Sandikli is located in the western part of Central Anatolia in Turkey. Middle to Upper Miocene trachyandesitic, andesitic and phonolitic lavas, tuffs and tuffites are found in the study area. The tuffs are essentially vitritic and vitritic-crystal tuffs with varying proportions of pyroclasts, pyrogenetic and secondary minerals. In this study the engineering properties of Sandikli zeolithic tuffs and their possible use as concrete aggregate have been investigated. The 28 samples were examined to determine their physico-mechanical properties and their suitability as lightweight concrete. In particular, two materials were tested—with maximum size aggregates of 4 and 8 mm. The results indicate that tuffs from the Ballik, Soucak and Sütlüce region can be used as light-weight concrete aggregates. Other tuffs can satisfactorily be used as plaster, while all the materials form acceptable building stone.     

The contribution of Public–Private Partnerships (PPPs) to improving accessibility of low-income earners to housing in southern Nigeria

Public–Private Partnership is a relatively new approach to housing provision and was introduced in Nigeria to address the burgeoning housing challenges. To date, little is known about the contribution of this approach to improving the chances of low-income earners in gaining access to decent and affordable housing in urban areas in this country. Based on data obtained from a survey of selected government housing agencies in six cities in southern Nigeria, this study found that the Public–Private-Partnership approach, like most previous public housing delivery strategies, has not made any significant contribution to housing low-income earners; rather it is skewed towards providing housing for high- and middle-income earners. This paper identifies the state-market structure of the Public–Private Partnerships and the absence of a National Policy on Public–Private Partnership in housing in Nigeria as being responsible for this development. It therefore suggests that the development and adoption of a uniform National Policy on Public–Private Partnership in housing, government provision of land at no cost to private developers, lowering of the high building standards, and incorporation of assisted-self-help and incremental housing into the Public–Private-Partnership housing delivery system will ensure better results.