Abstract: The innovative 3D printing has been successfully applied to layeredly build-up construction-scale structures through the extrusion of various cementitious materials. Favourable buildability of fresh cement mixture and the hardened properties of the printed structures are essential requirement for the application of 3D concrete printing. This paper firstly proposed a 3D printable cement mixture containing 40% mining tailings. The influence of paste age on the buildability of forty-layer structure was evaluated, as well as the bending resistance of prism specimen sawed from the printed structure. The bonding between layers is a critical factor that influences the structural capacity. In particular, the weak bonding interface formed in the layered extrusion process was identified through high-resolution X-ray CT scanning. It is necessary and desirable for the cement paste to perform both well buildability and mechanical performances. Thereafter, a proper amount of viscosity modify agent (VMA) was used to improve the structural integrity by increasing the contact behaviour between the adjacent extruded layers. Meanwhile, the impact of curing method on the hardened properties of 3D printed structures was accessed. Results indicated that the prepared tailing mortar achieved sufficient buildability to be used in an extrusion-typed 3D printer at the paste age of 45 min. The mould-cast specimens process flexural strength of 7.87 MPa. In contrast, the flexural strength of printed specimens values 5.22 MPa and 12.93 MPa, respectively, after the addition of 1.5% VMA and 90 °C steam curing.

Abstract: Durability of reinforced concrete (RC) structures is affected by certain environmental conditions and operational actions which can reduce their lifetime significantly Among these actions, this paper proposes a stochastic model that accounts for the combined effects of chloride-induced corrosion, climate change and cyclic loading Separately, corrosion leads to cross-section reduction, climate change produces changes in temperature and humidity and fatigue induces nucleation and propagation of cracks in the rebars When considered together, pitting corrosion nucleates cracks while environmental factors affect the kinematics of chloride ingress and corrosion propagation The proposed approach is illustrated with the reliability analysis of a bridge girder subjected to cyclic loading under various environmental conditions The overall results indicate that climate change effect induces lifetime reductions ranging between 14 and 23% if fatigue load is neglected Under cyclic loading, total lifetime reduction increases up to 7%

Abstract: This paper proposes an advanced near-surface-mounted (NSM) technique with an Fe-based shape-memory alloy (Fe-SMA) strip which can solve issues of low workability and reduced ductility of reinforced concrete (RC) beams strengthened with an NSM technique using prestressed fiber-reinforced polymer (FRP) strips in the concrete tension section. The flexural behavior of the RC beam strengthened by the NSM technique with the Fe-SMA strip was investigated. A total of seven RC beams were tested by four-point bending tests under displacement control. The type of reinforcements, the quantity of Fe-SMA strips, and the pre-straining level of the Fe-SMA strips were considered as experimental variables. Cracking load, yielding load, and ultimate load increased, respectively, with larger quantities of Fe-SMA strip. In addition, activation of embedded Fe-SMA in the concrete by electrical resistance heating effectively induces a prestressing force on the concrete beam, resulting in a cambering effect. The introduced prestressing force to the RC beam by activation of the Fe-SMA increased the crack and yielding loads, and did not decrease the ductility of the RC beam compared to the RC beam with non-activated Fe-SMA. It can be concluded from the test results that the strengthening technique using the recovery stress of the Fe-SMA strip as the prestressing force solves the various problems of the existing prestressing strengthening systems, meaning that Fe-SMA can be used as a substitute for conventional prestressing strengthening systems.

Abstract: This paper presents the behaviour of potassium activators synthesized fly ash geopolymer containing carbon and basalt fibre at ambient and elevated temperature. Six series of fly ash based geopolymer were cast where carbon and basalt fibre were added as 0.5, 1 and 1.5% by weight of fly ash. One extra control series without any fibre was also cast. Each series of samples were tested at ambient temperature and also heated at 200, 400, 600 and 800 °C and thus a total of 35 series of samples were tested in this study. The result shows that the geopolymer containing 1 wt% basalt and 1 wt% carbon fibre exhibited better compressive strength, lower volumetric shrinkage and mass loss than other fibre contents. Among two fibres composites, the carbon fibre geopolymer exhibited better performance than its basalt fibre counterpart regardless of temperature. The microstructure of carbon fibre reinforced geopolymer composite is more compact containing fewer pores/voids than its basalt based counterpart at elevated temperatures. The results also support the fact that carbon fibre is better than basalt fibre at elevated temperature and showed better bonding with geopolymer at elevated temperature.

Abstract: This paper presents an experimental investigation on the stress–strain behavior and the damage mechanism of polypropylene fiber reinforced concrete (PFRC) under monotonic and cyclic compression. Fifty-four specimens for different fiber volume fractions and aspect ratios were tested. Acoustic emission (AE) technique was used to monitor the damage progression. The damage mechanism of concrete was analyzed based on the AE parametric analysis. The results show that the incorporation of polypropylene fiber (PF) has a positive effect on the monotonic and cyclic behaviors of concrete, especially for the post-cracking branch. The toughness and ultimate strain are enhanced and the performance degradation in terms of elastic stiffness and strength is alleviated by the addition of PF. However, PF has little influences on the plastic strain, and the damage process of concrete is mainly driven by the envelope strain. The effect of fiber volume fraction on the cyclic behavior of concrete shows more pronounced than that of aspect ratio. In addition, it is found from AE results that the damage, closely related to AE events, has a quick evolution just after the peak stress, with the AE hits having a concentrated release. The total amount of AE hits increases with increasing fiber volume fraction due to fiber pullout and sliding, while the concrete with fiber aspect ratio of 280 reaches the largest amount. Meanwhile, as substantiated by AE, the failure of PFRC shows an obvious shear mode, with shear cracks dominating the damage progression. Finally, a damage elasto-plastic model is developed to predict the monotonic and cyclic responses of PFRC and the prediction yields a fairly close estimation with experimental results.

Abstract: The concrete production processes including materials mixing, pumping, transportation, injection, pouring, moulding and compaction, are dependent on the rheological properties. Hence, in this research, the rheological properties of fresh cement paste with different content of graphene (0.03, 0.05 and 0.10% by weight of cement) were investigated. The parameters considered were test geometries (concentric cylinders and parallel plates), shear rate range (300–0.6, 200–0.6 and 100–0.6 s−1), resting time (0, 30 and 60 min) and superplasticizer dosage (0 and 0.1% by weight of cement). Four rheological prediction models such as Modified Bingham, Herschel–Bulkley, Bingham model and Casson model were chosen for the estimation of the yield stress, plastic viscosity and trend of the flow curves. The effectiveness of these rheological models in predicting the flow properties of cement paste was verified by considering the standard error method. Test results showed that the yield stress and the plastic viscosity increased with the increase in graphene content and resting time while the yield stress and the plastic viscosity decreased with the increase in the dosage of superplasticizer. At higher shear rate range, the yield stress increased while the plastic viscosities decreased. The Herschel–Bulkley model with the lowest average standard error and standard deviation value was found to best fit the experimental data, whereas, Casson model was found to be the most unfitted model. Graphene reduces the flow diameter and electrical resistivity up to 9.3 and 67.8% and enhances load carrying capacity and strain up to 16.7 and 70.1% of the composite specimen as compared with plain cement specimen. Moreover, it opened a new dimension for graphene-cement composite as smart sensing building construction material.

Abstract: High performance concrete especially self compacting concrete (SCC) has got wide popularity in construction industry because of its ability to flow through congested reinforcement without segregation and bleeding. Even though European Federation of National Associations Representing for Concrete (EFNARC) guidelines are available for the mix design of SCC, large number of trials are required for obtaining an SCC mix with the desired engineering properties. The material and time requirement is more to conduct such large number of trials. The main objective of the study presented in this paper is to demonstrate use of regularized least square algorithm (RLS) along with random kitchen sink algorithm (RKS) to effectively predict the fresh and hardened stage properties of SCC. The database for testing and training the algorithm was prepared by conducting tests on 40 SCC mixes. Parametric variation in the SCC mixes were the quantities of fine and coarse aggregates, superplasticizer dosage, its family and water content. Out of 40 test results, 32 results were used for training and 8 set results were used for testing the algorithm. Modelling of both fresh state properties viz., flowing ability (Slump Flow), passing ability (J Ring), segregation resistance (V funnel at 5 min) as well as hardened stage property (compressive strength) of the SCC mix was carried out using RLS and RKS algorithm. Accuracy of the model was checked by comparing the predicted and measured values. The model could accurately predict the properties of the SCC within the experimental domain.

Abstract: The effects of different contents and particle sizes of waste glass powder on alkali–silica reaction (ASR) expansion of cementitious composite bar were investigated in this study. Waste glass powder with particle size less than 300 μm exhibits an excellent mitigation effect on ASR expansion. With larger content and smaller particle size, the mitigation effect of waste glass powder on ASR expansion gradually increases. The mitigation effect of waste glass powder with particle size ranging from 38 to 53 μm and 20% by weight of cement seems relatively better than that of fly ash. When the waste glass powder content reaches 30%, the mitigation effect is still effective and almost the same as that of fly ash. However, the waste glass powder with particle size larger than 300 μm presents negative mitigation effect on ASR expansion when the replacement rate is larger than 30%. On the other hand, the waste glass powder and calcium hydroxide (CH) further react, and produce more calcium–silicate–hydrate gels, which apparently reduce the amount of CH. Moreover, the increasing content of waste glass powder results in a lower pH value in the pore solution of cementitious composite.

Abstract: Slag can increase late age strength of concrete, but impairs the concrete early-age strength due to low reactivity. Limestone powder can increase early-age strength, but impairs late-age strength due to dilution effect. The combination of slag and limestone powder can produce a composite concrete with adequate strength at both early ages and late ages. This study shows an integrated hydration-strength-optimization model for cement-slag-limestone ternary blends. First, a blended hydration model is put forward for simulating the hydration of composite binder containing slag and limestone powder. Reaction degrees of individual component of binders are calculated using this hydration model. Second, the gel-space ratio of ternary blended concrete is determined based on reaction degrees of composite binder and mixing proportions. Moreover concrete compressive strength is calculated using gel-space ratio. Third, based on parameters analysis, the isoresponse curves regarding strength of concrete are calculated. The optimum combinations of cement, slag, and limestone powder at different ages are calculated. The proposed numerical procedure is valuable for optimum strength design of cement-slag-limestone ternary concrete.

Abstract: Rehabilitation and repair of flexible pavements produce huge amounts of reclaimed asphalt pavement (RAP) material. Using RAP in the formulation of portland cement concrete (PCC) is a technique that is part of a sustainable development approach since it reduces on the consumption of new aggregates and reuses a material that is considered as waste. This paper describes the semi-adiabatic calorimetry test performed on a concrete mix incorporating RAP material as aggregate. Results showed that the cement hydration process is not affected by the presence of asphalt coated on the surface of RAP material. Classical tests (compressive strength, flexural and indirect-tensile strengths, elastic modulus, and free-shrinkage) were also performed on PCC mixes incorporating different percentages of RAP. It was found that as the percentage of RAP increases, the PCC mechanical properties decrease. This is mainly attributed to the presence of voids in the transition zone between the asphalt-coated aggregates and the hydrated cement paste as confirmed by scanning-electron microscope images. Unrestrained shrinkage testing showed statistically insignificant change in shrinkage strain with RAP content. The strength and shrinkage results lead to conclude that as much as 40% of RAP could be incorporated into the formulation of PCC and achieve properties that are acceptable for the construction of rigid pavements.

Abstract: Efflorescence which severely occurs in alkali-activated slag cement can cause reduction of strength and durability due to calcium leaching. In the work, efflorescence characteristics in pavement containing red mud which can be affected by strong alkaline were investigated through various tests such as compressive strength, porosity, absorption, efflorescence area, alkali leaching content, and properties of the efflorescence compound. The compressive strength of pavement was evaluated to be higher over 15.0 MPa in all cases regardless of replacement ratio of red-mud and binder type, which can provide a reasonable strength for walking and bike lanes. The pavement with red mud was applicable to parking lots only when the replacement ratio of red-mud is within 10%. The efflorescence area increased with a higher replacement ratio of red mud and its propagation appeared though the efflorescence was removed through evaporation of moisture. However, the area of efflorescence gradually decreased with the repetition of the test.

Abstract: When ultra-high performance concrete (UHPC) is fabricated as precast members such as in a UHPC segmental bridge, the joint design between the precast members can significantly affect the overall integrity and safety of the structure. Therefore, the structural behavior of the UHPC joint was experimentally investigated in this study with test variables including joint type, number and height of shear keys, type of filler, curing temperature, and lateral compressive stress. The UHPC considered in this study is the K-UHPC developed in Korea with a specified compressive strength as high as 180 MPa and high flowability. The joint shear strengths affected by the test variables were investigated in detail. The test results were also compared with two representative predictive equations for interface shear strength to determine an appropriate equation for the joint design of UHPC. These equations did not match well with the test data because they were originally proposed for normal strength concrete. However, the JSCE equation could be improved by modifying a coefficient to show good agreement with the test especially in the case of the dry joint with epoxy application.

Abstract: This paper aims to investigate the behavior of fiber reinforced polymer (FRP) strengthened reinforced concrete (RC) beams containing large rectangular web openings in the flexure zone. Studied parameters were type of loading, opening size and strengthening scheme. Seven RC beams categorized into two different groups were tested. In the first group, two unstrengthened beams (one solid without opening and one with large rectangular web opening in the pure flexure zone) were tested under four-point bending. In the second group, five beams were tested under center-point loading. They comprised of one reference solid beam and four beams with large rectangular web opening in the maximum-moment region. Out of the four beams with openings, two specimens were unstrengthened and the other two were strengthened with two different FRP schemes. A numerical study was also conducted and the results of analysis were validated with experiments. The calibrated analysis was then used for some useful parametric studies in which the effect of different parameters was investigated.

Abstract: Within the EC funded project smart elements for sustainable building envelopes, carbon textile reinforcement was incorporated into reactive powder concrete, namely textile reinforced reactive powder concrete (TRRPC), to additionally improve the post-cracking behaviour of the cementitious matrix. This high-performance composite material was included as outer and inner facade panels in prefabricated and non-load bearing sandwich elements along with low density foamed concrete (FC) and glass fibre reinforced polymer continuous connecting devices. Experiments and finite element analysis (FEA) were applied to characterize the structural performance of the developed sandwich elements. The mechanical behaviour of the individual materials, components and large-scale elements were quantified. Four-point bending tests were performed on large-scale TRRPC-FC sandwich element beams to quantify the flexural capacity, level of composite action, resulting deformation, crack propagation and failure mechanisms. Optical measurements based on digital image correlation were taken simultaneously to enable a detailed analysis of the underlying composite action. The structural behaviour of the developed elements was found to be highly dependent on the stiffness and strength of the connectors to ensure composite action between the two TRRPC panels. As for the FEA, the applied modelling approach was found to accurately describe the stiffness of the sandwich elements at lower load levels, while describing the stiffness in a conservative manner after the occurrence of connector failure mechanisms.

Abstract: This paper presents a study on the bond characteristics of glass fiber reinforced polymer (GFRP) bars in engineered cementitious composite (ECC) Ninety beam specimens having variable parameters namely bar diameter, GFRP bar types (standard low modulus ‘LM’ and high modulus ‘HM’), two concrete types (ECC and normal concrete ‘NC’) and embedded length (5, 7 and 10 times bar diameter) were tested as per RILEM specifications Bond stress–slip characteristics and failure modes of specimens as well as influence of variable parameters on bond strength are described The performance of various Codes and other existing equations in predicting bond strength of both low/high modulus GFRP bars embedded in ECC compared to NC is described based on experimental results The bond strength decreased with the increase of embedment length—maximum bond strength reduction of 36% was observed For both ECC and NC, bond strength reduced with the increase of bar size and ECC produced maximum 16 times higher bond strength compared to NC Code based and other existing equations were found conservative in predicting bond strength of GFRP bars embedded in ECC

Abstract: Sandwich panels comprising prefabricated ultra-high performance concrete (UHPC) composites can be used as eco-friendly and multi-functional structural elements. To improve the structural and thermal performance of composite sandwich panels, combinations of UHPC and expanded polystyrene (EPS) beads were investigated. High-performance expanded polystyrene concrete (HPEPC) was tested with various EPS bulk ratios to determine the suitability of the mechanical properties for use as a high-strength lightweight aggregate concrete. As a core material in composite sandwich panels, the mechanical properties of HPEPC were compared with those of EPS mortar. The compressive strength of HPEPC is approximately eight times greater than that of EPS mortar, and the thermal conductivity of approximately a quarter that of EPS mortar. The structural behavior of composite sandwich panels was empirically analyzed using different combinations of cores, face sheets, and adhesive materials. In the flatwise and edgewise compression tests, sandwich panels with HPEPC cores had high peak strengths, irrespective of the type of face sheets, as opposed to the specimens with EPS mortar cores. In the four-point bending tests, the sandwich panels with HPEPC cores, or reinforced UHPC face sheets combined with adhesive mortar, exhibited higher peak strengths than the other specimens, and failed in a stable manner, without delamination.

Abstract: Hydraulic facilities are subjected to significant siltation which, in a very short period of time, can render them unusable. In Algeria, the silting-up of a great number of dams, built for drinking water needs and for irrigation, implies the necessity and urgency to take action. Therefore, the maintenance work, which leads to dredging the deposited silt, constitutes an unbearable obligation for the preservation of the environment. Chorfa dam (western Algeria) may be mentioned as a concrete example. This study is part of a long research whose objective is to contribute to the valorization and the optimization of the formulations economically that are easy to implement and which enable to use the dredged materials in the formulation of ordinary concretes by partial substitution to cement (10, 20 and 30%) of dredged sediments, after calcination at 750 °C to make them active. Tests were carried out on concrete that was vibrated in the fresh state (setting time) and hardened state (compressive strengths and durability of concrete exposed to sulfuric acid attack) in order to determine their characteristics. The results obtained confirmed the possibility to develop concretes containing calcined silt, with proportions up to 30%, and which can meet the economic, ecological and technological objectives.

Abstract: This paper presents the strength and durability of cement mortars using 0–100% ferronickel slag (FNS) as replacement of natural sand and 30% fly ash or ground granulated blast furnace slag (GGBFS) as cement replacement. The maximum mortar compressive strength was achieved with 50% sand replacement by FNS. Durability was evaluated by the changes in compressive strength and mass of mortar specimens after 28 cycles of alternate wetting at 23 °C and drying at 110 °C. Strength loss increased by the increase of FNS content with marginal increases in the mass loss. Though a maximum strength loss of up to 26% was observed, the values were only 3–9% for 25–100% FNS contents in the mixtures containing 30% fly ash. The XRD data showed that the pozzolanic reaction of fly ash helped to reduce the strength loss caused by wet–dry cycles. Overall, the volume of permeable voids (VPV) and performance in wet–dry cycles for 50% FNS and 30% fly ash were better than those for 100% OPC and natural sand.

Abstract: The dissolution and release of active ions, such as Si4+, Al3+ and Ca2+, from fly ash directly affect the rate and extent of reaction product formation, which in turn affect the physical and mechanical properties of fly ash filling materials. In this study, low-calcium fly ash was soaked and activated in NaOH solutions with different concentrations (approximating the optimum dose range) for different lengths of time. The amounts of active ions leached and the changes in the mineral composition, chemical functional groups and surface morphology were tested and analyzed via ICP-OES, XRD, FTIR and SEM/EDS techniques. Based on these analyses, the reaction mechanism of alkali activation of low-calcium fly ash was further investigated. The results showed that the NaOH activation effect can significantly increase the amount of active ions leached from low-calcium fly ash. Notably, the amount of Si4+ and Al3+ leached clearly increased with increases in both NaOH concentration and soaking time. The plausible reaction mechanism is discussed in detail, which is that the alkali activator principally affected the surface of the vitreous particles of low-calcium fly ash and induced differing surface modifications in the dissolution stage, depolymerization stage, polycondensation and polymer gel stage and diffusion stage. It was observed that the progress of the reaction is controlled by dissolution in the early stages, whereas activation is governed by diffusion when the surfaces of the fly ash particles are covered by precipitates.

Abstract: The focus of this paper is to investigate the effect of column axial load levels on the performance of shear deficient reinforced concrete beam column joints (BCJs) under monotonic and cyclic loading The problem of interaction between shear stress in BCJ and axial load on column has been addressed in this work by initially postulating a mechanistic model and substantiated by an experimental test program This was achieved by conducting appropriate tests on seven BCJ sub-assemblies subjected to monotonic and reversed cyclic loading, with varying levels of the column axial load Experimental results were further validated using a finite element model in an ABAQUS environment The effect of variation of compressive strength of concrete was considered in a subsequent parametric study, in order to obtain sufficient data, and utilized to develop a new shear strength model for BCJs which includes influences of all the important parameters required to predict the shear strength of BCJs The results showed that column axial load affects the seismic performance of BCJs significantly Experimental results demonstrated that at initial stages of loading, increase in axial load enhances the shear capacity of the joint and reduces its ductility However, when the column axial load/axial strength ratio increases to about 06–07, shear strength starts to decrease rapidly, leading to pure axial failure of the joint The magnitude of axial load/axial capacity ratio also dictates the failure mode and development of crack patterns in BCJs Results of reverse cyclic tests on BCJs showed that high value of axial load/axial capacity ratio increases the initial stiffness of BCJ but rate of stiffness degradation is accelerated after peak strength attenuation

Abstract: The durability performance of stainless steel makes it an interesting alternative for the structural strengthening of reinforced concrete Like external steel plates or fibre reinforced polymers, stainless steel can be applied using externally bonded reinforcement (EBR) or the near surface mounted (NSM) bonding techniques In the present work, a set of single-lap shear tests were carried out using the EBR and NSM bonding techniques The evaluation of the performance of the bonding interfaces was done with the help of the digital image correlation (DIC) technique The tests showed that the measurements gathered with DIC should be used with caution, since there is noise in the distribution of the slips and only the slips greater than one-tenth of a millimetre were fairly well predicted For this reason, the slips had to be smoothed out to make it easier to determine the strains in the stainless steel and the bond stress transfer between materials, which helps to determine the bond–slip relationship of the interface Moreover, the DIC technique allowed to identify all the states developed within the interface through the load–slip responses which were also closely predicted with other monitoring devices Considering the NSM and the EBR samples with the same bonded lengths, it can be stated that the NSM system has the best performance due to their higher strength, being observed the rupture of the stainless steel in the samples with bond lengths of 200 and 300 mm Associated with this higher strength, the NSM specimens had an effective bond length of 168 mm which is 715% of that obtained for the EBR specimens (235 mm) A trapezoidal and a power functions are the proposed shapes to describe the interfacial bond–slip relationships of the NSM and EBR systems, respectively, where the maximum bond stress in the former system is 18 times the maximum bond stress of the latter one

Abstract: This paper presents the results of recent research on the interface shear behavior of normal weight and lightweight concrete composite T-beams. In the experimental program 12 beams and necessary control cylinders were tested to provide experimental cases with the variables of interface preparation, clamping stress and lightweight slab concrete strength. Compared with 7 equations developed previously, it has been found that those formulas, especially the ones from current AASHTO and ACI design codes, give a conservative theoretical prediction of horizontal shear capacity of composite T-beams. Based on the experimental results, a more accurate equation was developed to predict the interface shear transfer strength of composite concrete T-beam. By comparing the experimental results of previous beam tests and shear-friction push-off tests for different types of concrete with both rough and smooth interface published in literature, it has been found that the proposed formula is reliable in predicting the horizontal shear strength of concrete composite T-beams.

Abstract: Performance-based fire resistance design needs consideration of various influencing parameters of structures such as load levels and cross-sectional size. Therefore, the studies of fire damaged reinforced concrete (RC) structures are performed experimentally and analytically. Twelve RC beams with different load levels and cross sections are exposed to high temperatures following the ISO 834 standard time temperature. After the fire test, the fire-damaged beams are loaded using four-point loading to obtain its residual strength. In addition, ABAQUS 6.10-3 is used to preform structural analyses of the ductility of the fire-damaged beams. The results indicate that the temperature, stiffness and ductility of the fire-damaged beams are significantly influenced by the load level, cross-sectional size and time exposed to fire. Also, the ductility of the fire-damaged beam can be predicted using an analytical method, which is not easy to otherwise determine experimentally.

Abstract: This study aimed to investigate the bond properties of prestressing strands embedded in ultra-high-performance fiber-reinforced concrete (UHPFRC). Toward this end, two types of prestressing strands with diameters of 12.7 and 15.2 mm were considered, along with various concrete cover depths and initial prestressing force magnitudes. The average bond strength of the strands in UHPFRC was estimated by using pullout tests, and the transfer length was evaluated based on a 95% average maximum strain method. Test results indicated that the average bond strength of the pretensioned strand reduced as the diameter of the strand increased, and was between the bond strengths of round and deformed steel rebars. Higher bond strength was also obtained with a lower embedment length. Based on a comparison of p value, the bar diameter and embedment length most significantly influenced the bond strength of strands in UHPFRC, compared to a ratio of cover depth to diameter and initial prestressing force. Pretensioned strands in UHPFRC exhibited much higher bond strength and shorter transfer length compared with strands embedded in ordinary high-strength concrete. Lastly, ACI 318 and AASHTO LRFD codes significantly overestimated the transfer length of the strands embedded in UHPFRC.

Abstract: The possibility of recycling mixed colour waste glass as it is for manufacturing decorative architectural mortars, has been investigated. In mortars, the 0–33–66–100% of calcareous gravel volume has been replaced with recycled glass cullets, with no other inorganic addition. To mitigate the possible alkali–silica reaction, mixes with a hydrophobic admixture were also compared. The obtained results show that the replacement of calcareous gravel with glass cullets of similar grain size distribution permits to reduce the dosage of the superplasticizer admixture to obtain the same workability of fresh mortar; it does not affect significantly the mechanical performances, the water vapour permeability and the capillary water absorption but it reduces significantly the drying shrinkage deformation. The used recycled glass is classified as no reactive in terms of alkali–silica reaction neither in water nor in NaOH solution following the parameters of the current normative, even in the absence of the hydrophobic admixture. The hydrophobic admixture further delays the expansion trigger but not the speed of its propagation.

Abstract: The corrosion of steel reinforcement is commonly believed to be the primary cause of structural deterioration of reinforced concrete (RC) structures; as a result of this deterioration, a RC structure can incur a considerable reduction in structural serviceability and safety. Because of their inherent redundancy, statically indeterminate structures develop resistant mechanisms that can potentially assist in delaying the collapse of severely damaged RC structures. In order to experimentally demonstrate these resistant mechanisms, four groups of three two-span continuous RC beam members each were deteriorated using induced corrosion methods and tested to failure under monotonic loads. For control, one group of three RC beams was left uncorroded and similarly load tested. All the RC beam specimens subjected to corrosion demonstrated a significant reduction (a maximum reduction of 55% as compared to the uncorroded control group) of their ultimate capacity. The presence of corrosion induced a transition from flexural failure to anchorage failure in some specimens; despite the induced damage some redistributed structural capacity was observed. Modelling of deterioration effects by the inclusion of different aspects of corrosion was also conducted. Three-dimensional (3D) Finite-Element Method (FEM) models were developed to assess the variation in the mechanical properties of the corroded steel and the reduction in the bond interaction between concrete and steel due to the corrosion of the steel reinforcement. In general, the current 3D FEM models demonstrated a good agreement with the experimental data; however, 3D FEM models that exhibit greater sophistication are necessary to better describe the failure mode of some RC beam specimens when they are associated with local effects.

Abstract: The rapid-hardening method employing the injection of calcium sulfoaluminate (CSA) cement mortar into voids between preplaced ballast aggregates has recently emerged as a promising approach for the renovation of existing ballasted railway tracks to concrete tracks This method typically involves the use of a redispersible polymer powder to enhance the durability of the resulting recycled aggregate concrete However, the effects of the amount of polymer on the mechanical and durability properties of recycled ballast aggregate concrete were not clearly understood In addition, the effects of the cleanness condition of ballast aggregates were never examined This study aimed at investigating these two aspects through compression and flexure tests, shrinkage tests, freezing–thawing resistance tests, and optical microscopy The results revealed that an increase in the amount of polymer generally decreased the compressive strength at the curing age of 28 days However, the use of a higher polymer ratio enhanced the modulus of rupture, freezing–thawing resistance, and shrinkage resistance, likely because it improved the microstructure of the interfacial transition zones between recycled ballast aggregates and injected mortar In addition, a higher cleanness level of ballast aggregates generally improved the mechanical and durability qualities of concrete

Abstract: Nuclear power plants are constructed very close to the marine environments for cooling water and the structures are more susceptible to chloride induced corrosion. Cracking in RC structures in mass concrete is unavoidable when they are exposed to chloride contaminated chemical environments. This study is focused on the evaluation of crack and time effect on chloride diffusion rate. Two types of concrete strength grade were taken for nuclear power plant construction and the crack was induced with varying from 0.05 to 1.35 mm of width. The tests for chloride diffusion coefficients from steady-state condition were performed. The influence of crack width on the chloride transmission behavior was discussed and analyzed over an exposure period to one year. The diffusion coefficients due to growing crack width increase in crack width but they decrease with increasing curing period, which yields 57.8–61.6% reduction at the age of 180 days and 21.5–26.6% of reduction at 365 days. Through the parameters of age and crack width which are obtained from regression analysis, the evaluation technique which can consider the effect of crack and time on diffusion is proposed for nuclear power plant concrete.

Abstract: Recycled aggregates (RAs) production techniques are essential for the material circulation society because RAs from demolished concrete waste can sustainably be reused as a concrete material. However, RAs can bring about several performance decreases when they are used for recycled aggregate concrete (RAC) because of the low qualities (i.e., high water-absorption rate and low density) caused by the attached hydrated cement paste on the RA surface. Therefore, both the production of high-quality RAs and the surface modification of RAs are significantly important for the extension of RAC utilization. This paper focuses on the surface modification of RFA to reduce the water absorption rate and increase density. Hydrofluorosilicic acid (H2SiF6), which is one of the by-products in phosphoric acid manufacture, is used herein for the surface modification of the RFA. The physical properties and mechanical performance of mortar using RFA were evaluated after RFA modification. Consequently, the proposed method is effective in reducing water absorption rate and increasing density of RFA. The density of RFAs was slightly increased by 0.5–2.6% after modification. On the other hand, the water absorption rate decreased by 4–18% after modification. The compressive strengths of mortar at 28 days ages showed 18.1 MPa with modified RFA and 16.2 MPa with RFA.