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In recent years, the aging of existing reinforced concrete deck slabs of road bridges in Japan has been attributed to the deterioration of the concrete on the upper surface, and partial replacements have been carried out as a measure to extend service life. This study comparatively verifies the effectiveness of the partial cross-section replacement method, using a wheel load running test and focusing on the combination of the removal method of the existing concrete and the repair material. An appropriate method of partial replacement of existing reinforced concrete deck slabs is also proposed.

Large quantity of water is required during the conventional curing methods. This becomes challenging in the areas facing water scarcity and for concreting work in high rise structures. In this work, we present a solution for the need of concrete which does not require extra water for curing. In the proposed solution, calcium lignosulfonate in different percentage was introduced as a self-curing agent in fresh concrete. The hardened concrete with calcium lignosulfonate was cured at ambient condition whereas the hardened concrete without calcium lignosulfonate was submerged in water for curing. The properties of fresh and hardened concrete with and without calcium lignosulfonate are compared. The results show a continuous increase in slump with the increase in calcium lignosulfonate, however, 0.3% calcium lignosulfonate is identified as an optimum percentage for desired mechanical property. The durability under saline environment is studied in term of loss in strength. Further, the change in strength is correlated with the mineralogical changes studied using X-ray diffraction results.

The aim of this study is to produce durable self-compacting concrete (SCC) using different fractions of recycled steel slag aggregates (SSA) by replacing natural aggregate. For this purpose, a series of nine mixing proportions were designed with a constant water-to-cement ratio of 0.34 and a change of SSA ratio replacing natural coarse or fine aggregates by weight from 0 to 50% (increments of 12.5%). For freshly mixed SCC, the flowability, passing and filling abilities, segregation and viscosity were observed by slump flow, slump-flow time (T500), L-box and V-funnel empirical tests. Mechanical properties were tested for compressive and flexural strengths, while the durability characteristics were conducted for water absorption and permeability, sulfate attack and freeze–thaw action (F/T). Non-destructive measurement approaches (i.e. ultrasonic pulse velocity and resonance frequency) were involved in the F/T testing. The test results indicate that the incorporation of SSA in SCC is suitable and improves the mechanical strength and durability properties, and that enhancement is more pronounced at higher SSA increments, especially when replacing the coarse natural aggregate partially by coarse SSA.

Ground-granulated blast-furnace slag and dolomite are by-products from the steel manufacturing and rock crushing industries, respectively. The addition of dolomite to a slag-based geopolymer matrix can improve its engineering properties and reduce disposal problems. This paper discusses the effect of alkali solution concentration, curing temperature and different proportions of slag and dolomite on the strength of geopolymer mortars. For maximum strength, the optimum ratio of slag and dolomite was found to be 70:30. Microstructural studies such as scanning electron microscopy and X-ray diffraction showed the co-existence of both calcium silicate hydrate and aluminosilicate gel in the slag–dolomite geopolymer matrix. Improved durability properties such as high resistance to water absorption, sorptivity and chemical attack can lead to the application of slag–dolomite geopolymer matrices in all types of structural elements.

The valorization of local by-products in the manufacture of a new range of sand concrete and the improvement of their properties, will lead to seek an arrangement between performance and cost in order to achieve a resistant material. Waste recycling affects two very important affect namely the environmental impact and the economic impact. The main objective of our work is to contribute to optimize the formulation of sand concrete as part of the recovery of waste, which is harmful to the environment given its bulky and unattractive nature, it is waste plastic. Most PET bottles become waste after use, causing environmental problems. To solve this problem, a method for recycling PET bottles as fibers to strengthen concrete is proposed. Two types of plastic waste are added to sand concrete; the first concerns the recycling of post-consumer bottles in PET, in the form of polyester fiber supplied by the company RET-PLAST and the second type concerns the packaging belts made of polyethylene terephthalate (PET). The properties in the fresh state (workability and density) and in the hardened state (compressive strength, tensile strength and water absorption) of the various produced concretes are analyzed and compared against their respective controls. From the experimental results, it can be concluded that the reinforcement of the cement matrix with PET fibers with a rate of 1% improves the mechanical properties of sand concrete as well as a remarkable decrease in its water absorption capacity.

Specifications for durability that are based on performance tests on concrete during the early stages of construction are finding acceptance throughout the world. In South Africa the durability index (DI) approach has been accepted into local specifications. This raises a challenge in the design of a concrete mixture for a construction project that takes account of the variability in materials and test conditions to ensure that the concrete will achieve the specification requirements when subjected to DI testing on in-situ samples. This paper proposes a statistical approach to accounting for this variability in concrete mixture design with oxygen permeability index (OPI) testing, in a manner that acknowledges the variability of both laboratory-based and in-situ sample testing for compliance. The OPI test results obtained on nominally similar concretes on actual construction projects undertaken by the South African National Roads Agency Limited (SANRAL), which included the DI-based specifications, were used to illustrate the operation of the proposed approach. The results show that the target value of OPI to be achieved in the design of concrete mixtures is influenced by the level of quality control on construction sites but that this can be managed through an appropriate statistical approach.

The aim of this research was to study the effect of incorporating waste rubber aggregates on the physical, mechanical, thermal and durability performance of Self-Compacting Sand Concrete SCSC mixtures. For this purpose, the separately developed Rubberized Self-Compacting Sand Concrete RSCSC were prepared with three fractions of rubber grains where the natural aggregates were replaced with powder rubber, sand rubber and gravel rubber and four addition ratios (5, 10, 15 and 20%) as volume rates. The performed fresh properties using slump-flow, spreading, t500, sieve stability and air-entrained content tests proved better results for the RSCSC in comparison with reference concretes. Hardened state characterization of the concretes exhibited decreases in the mechanical properties of the RSCSC but the thermal conductivity and the dynamic elastic modulus were improved. Assessment of the concrete’s durability was accomplished through determination of apparent porosity, capillary absorption. Therefore, RSCSC to be can used in structural elements of dense reinforcement and complex formwork. Furthermore, this allows promising solution to reduce the impact of waste tyres on the environment and fight pollution.

Multi-storey car park buildings with steel–concrete composite floor structures are widespread in construction due to the distinct benefits of the implemented structural system. Although there are various possibilities for accomplishing composite action between a steel beam and a concrete slab, some solutions, such as friction-grip bolts commonly applied in the 1970s, did not show good durability. An example is the multi-storey car park building “Obilićev venac” in Belgrade. This case study presents two methods for life extension of the car park building structure. Both approaches focus on applying welded headed studs with the primary intention of providing a durable shear connection. While the first method has been applied during the structure’s reconstruction, the second method is proposed as a novel solution for implementation in steel–concrete composite floors. The application of the proposed connection is discussed and the results of the experimental and numerical research conducted are presented.

This paper aims to assess the mechanical and long-term durability performance of reactive powder concrete (RPC) containing granite powder (GrP) as cement replacement and waste glass powder (GP) as quartz sand replacement. The workability and mechanical behaviour of RPC containing various proportions of GrP and GP are assessed for different water/binder (w/b) ratios (0.3, 0.35, 0.4, and 0.45). The water resistance and tightness of RPC are measured by monitoring the electrical resistivity, water absorption, sorptivity, and chloride migration over a one-year period. Results reveal that substitution of GrP and GP at optimum levels of 15% and 30% respectively enhances the performance of RPC with the achievement of satisfiable workability at a 0.35 w/b ratio. A significant increase in the resistance towards chloride penetration and electrical resistivity was also observed with increasing ages. Thus, glass powder and granite powder can be considered as alternative construction materials providing economical and ecological efficiency.

Increased temperature and carbon dioxide concentration caused by climate change will aggravate the creep shrinkage and structural durability of concrete bridges. Overloading also has a great impact on the time-dependent reliability of existing bridges. This research paper analyses the time-dependent reliability of bridges based on climate change and overload. By improving the concrete carbonation model and referring to the B4 model of concrete creep, the effects of ambient temperature and humidity on concrete under different emission-reduction scenarios were considered. At the same time, given the serious problems of vehicle overload in China, combining different overload scenarios with climate change led to the establishment of a time-dependent reliability model for precast-concrete bridges. The results showed that as the overload rate increased, the time-dependent reliability degradation rate of a case study bridge accelerated. Under the scenario considering both high greenhouse gas emissions and the maximum overload rate, the service life of the case study bridge decreased to 50% of its design life.

A series of experimental tests on reinforced concrete specimens with normal uncoated and epoxy-coated reinforcing bars (ECRBs) was carried out. A comprehensive report of the specimens, from material level to overall performance, is presented in this paper. At the material level, evaluation of the epoxy coating thickness showed that the production quality was not good. Some mechanical properties of bars with a thinner coating were better than those of their uncoated counterparts, while an increase in coating thickness offset the better mechanical properties and decreased the bond strength. Regarding durability, a comparison of the corrosion behaviour of the reinforcing bars and chloride penetration of the concrete cover in unloaded, statically-loaded and fatigue-loaded test specimens showed that higher fatigue loads and longer fatigue loading cycles decreased the corrosion resistance of the bars and increased the chloride penetration. The ultimate loads of the specimens were reduced and comparatively lower values were obtained for beams with bars with thicker coatings. The results of this work highlight the interrelationships among materials performance, durability and ultimate performance to achieve sustainable design for concrete elements with ECRBs in chloride-containing environments.

International audience; Anaerobic digestion, a renewable energy source, is the degradation of organic waste into biogas, mainly composed of CH4 and CO2. The sector is expanding rapidly due to its multiple environmental and economic benefits. This process is implemented industrially in concrete structures that are in direct contact with the biowaste being digested and the gas produced. Both phases can damage concrete through (i) the presence of volatile fatty acids, dissolved CO2, ammonium, and microbial biofilm in the liquid phase, and (ii) high concentrations of CO2 and various concentrations of H2S in the gas phase. In order to develop more sustainable concrete biogas units, long-term, in-situ experiments were carried out in a semi-industrial scale digester to provide new insights into the performance levels and deterioration mechanisms of various low-CO2 binders, including alkali-activated metakaolin (geopolymer), alkali-activated slag (AAS), and supersulfated cements (SSC), in comparison to calcium aluminate cement (CAC) and Portland cement based matrices. In the running conditions explored, carbonation of the cementitious matrices was predominant over other deterioration phenomena in both the digester liquid and the gas phases. Alkali-activated metakaolin and calcium aluminate cement performed better with few degradations observed. Supersulfated cements and alkali-activated slag showed an intermediate behaviour with good performance in the acidic liquid phase but low performance in the CO2-rich gas phase.

Alkali-activated materials (AAM) and hybrid cements (HC) have become sustainable alternatives to Portland cement (PC) due to their low carbon footprint. The main differences between AAM and HC lie in their content of clinker (none in the AAM and usually lower than 30% for HCs) and the type of activator used (strong alkaline solutions for AAM and small amounts of solid alkalis for HC). Durability problems related with microstructural changes due to decalcification and leaching of the cementitious paste have been well researched for PC pastes, but it is still not well known for AAM and HC. The present work aims to study the leaching process for cement pastes of both types of sustainable pastes. Blast furnace slag (BFS) was selected as a precursor to manufacture hybrid slag (HS) pastes and alkali-activated slag (AAS) pastes. A commercial CEM IV was selected as reference material. A 6 M NH4NO3 solution was used to accelerate leaching kinetics. After 28 days of immersion, the mineralogical and microstructural changes were evaluated. Results show that AAS pastes exhibited the highest leaching resistance of all the pastes under study, due to the absence of portlandite and the high level of polymerization of silicate chains. In HS pastes, the presence of portlandite (due to PC in the material) and gypsum (due to the activator) explains their intermediate performance, in between CEM IV and AAS. The authors have been able to carry out the present research thanks to financial support from the Ministerio de Ciencia, Innovación y Universidades of Spain (RTI2018-096428-B-I00 and PID2020-116738RJ-I00 projects) and Madrid Government (Comunidad de Madrid) under the Multiannual Agreement UC3M in the line of "Fostering Young Doctors Research" (HORATSO-CS-UC3M) in the context of the V PRICIT (Regional Programme of Research and Technological Innovation).

Prefabricated pavement is increasingly applied worldwide due to the rapid construction on-site. This paper presents a state-of-the-art review of the precast systems and assembly connection of concrete slabs, as well as the precast pavement features. The previous research indicates that (1) Both Super-Slab and Michigan systems are recommended with the satisfied road performance close to the cast-in-place. (2) Flexible base material is suggested for the fabricated pavement for the satisfied leveling and stress distribution. (3) To prevent the voiding phenomenon of the fabricated pavement, the sand cushion course, dry mixed mortar or self-leveling mortar, and other flowable materials could be used for the secondary leveling of the base after the pavement splicing. (4) Two-direction dowel bars are recommended for slab connections of the fabricated pavement, which helps to improve the load transfer capacity of the joints and enhance the durability of the fabricated pavement structure. (5) The sealing treatment of precast slab joints needs strengthening to reduce the impact of surface runoff on the base course. (6) The further research focuses are designing with functional, composite, mechanized, intelligent, lightweight, and flexible pavement slabs. Besides, pavement mechanical properties induced by temperature overlapping traffic loads need to be revealed.

In the saline soil environment of western China, salts can corrode ordinary cement concrete seriously, and the durability of concrete structure deteriorates gradually until it fails. This impedes the application of ordinary Portland cement concrete in this area. Aiming at the problem of the short service life of concrete in the harsh environment of western China, this study examines the performance of nano-CaCO3 modified concrete in a sulfate environment. The durability of the concrete was evaluated by the apparent phenomena on the relative quality evaluation parameter, the relative dynamic elastic modulus evaluation parameter, and the comprehensive damage evaluation parameter. The microstructure of corroded products was investigated using scanning electron microscopy to reveal the deterioration mechanism. The results show that the addition of 1% nano-CaCO3 can enhance the resistance of concrete to sulfate corrosion, and the service life of concrete structures will increase significantly.

Fibre-reinforced engineered cementitious composites are increasing being used in construction due to their superior toughness and durability. For composite structural members additionally reinforced with steel bars, the bond–slip relationship between the composite and reinforcing bars is an important parameter for designers. To understand the bond behaviour between Chinese 500 MPa steel bars and composites, pull-out tests were conducted to study the influence of the bar diameter, cover thickness and embedded length on bond properties under tension. The results indicated that the process of the bond–slip failure for 500 MPa steel bars in composites can be divided into three stages: ascent, descent and remnant. The bond strength increased with a decrease in bar diameter, while shortening of the embedment length enhanced the bond strength. Specimens with a larger cover thickness achieved higher bond strength, but the enhancement in bond strength was negligible for specimens with a cover thickness greater than 55 mm. A formula for calculating the bond strength for Chinese 500 MPa reinforcing bars in composites was developed based on the experimental results and a consistent model for the bond stress–slip relationship was also obtained.

This paper presents a case study of the condition evaluation, structural assessment and durability analysis of the Al Maktoum bridges in the UAE to provide assurance that they will meet their 100-year service life. It is considered that this holistic analysis is the first of its kind in the UAE. The project included a detailed structural assessment utilising three-dimensional finite-element methods. The analysis indicated that the stresses in all the critical elements were well below the yield limit. The results of the structural assessment were used in combination with the durability assessment to inform the life cycle cost analysis and asset maintenance strategy. The durability analysis incorporated a probabilistic assessment method to verify the remaining service life of the structures. This method utilised a 90% confidence level using the fib Model Code for Service Life Design. The results of modelling were verified against the inspection and testing results, which included concrete strength tests, half-cell potential mapping and chloride ion sampling. Overall, this project case is the first of its kind in the UAE and provided a platform of asset management strategy implementation to establish the current condition of the structures, assess their structural integrity and verify their remaining service life.

Electric arc furnace slag (EAFS) is a material that emerges as a by-product in iron and steel plants and is in need of evaluation. To ensure its recovery by using it in concrete production, it was replaced 10%, 20% and 30% by weight with cement, and only this part of mixture was activated with alkalis. During the hydration of the cement, alkalinity of the environment increases. In order to facilitate the reaction of EAFS, the pH value of the medium was increased by adding alkaline materials from outside. Replaced EAFS was activated with three different alkali solution levels by changing sodium concentrations (4%, 6% and 8%) and silicate moduli (1 and 2). Alkali solution/binder ratio was kept the same as 0.4 for all slightly alkali-activated mixtures, and the binder dosage was 400 kg/m(3). The effects of the pH degree of the medium were determined by mechanical and permeability tests. Capillary water absorption, water absorption, pressurized water permeability, gas permeability and rapid chloride permeability (RCP) properties were determined, and results were analyzed statistically to know the effect of each variable. 4% sodium concentration and silica module 1 appear to be quite effective in reducing RCP. When the alkali level is too high, the strength decreased and the permeability increased. The visualization of gel formation in the scanning electron microscope image proved that EAFS can be alkali-activated.

The durability of ultra-high-performance concrete (UHPC) exposed to freezing–thawing (F–T) is closely associated with its micromechanical properties. In this study, the nanoindentation technique is employed to characterise the micromechanical properties of UHPC at different F–T cycles. It is observed that the indentation moduli of low-density calcium silicate hydrate, high-density calcium silicate hydrate, and calcium hydroxide in the studied UHPC decrease moderately with the decreasing ranges of 11.58, 14.56 and 3.3%, respectively, after undergoing 1500 F–T cycles. More micropores gradually form, converge and connect, and the volume fraction of micropores increases up to about 120%. The interfacial transition zone (ITZ) between steel fibre and cement paste is more prone to act as the weakest zone than that between fine sand and cement paste. The thickness of ITZ enlarges from 22 μm of the unconditioned stage to 60 μm at 1500 F–T cycles. Based on the micromechanical properties obtained from the nanoindentation test, the modulus of elasticity values of UHPC under different F–T cycles are predicted using the multiscale homogenisation model. It is proved that the combined micromechanical characterisation and multiscale homogenisation technique is capable of predicting the macromechanical properties of UHPC and their changes under F–T action.

Electrochemical repair is one of the most effective methods of removing chloride from offshore engineering structures to improve their durability. The diffusion of chloride and electrochemical repair are key stages in this process. In this paper, a new numerical chloride migration-diffusion model is established by using Nernst-Planck equation. The distributions of free chloride ions in concrete in the stage of free chloride diffusion and the stage of electrochemical repair are simulated, and the effects of external potential and cathode position on electrochemical repair efficiency are analyzed. The numerical results show that electrochemical repair can effectively remove chloride ions from concrete. After 12 weeks of the electrochemical repair, the electrochemical repair efficiency is more than 66%. With the increase of repair time, the increase amplitude of electrochemical repair efficiency decreases gradually. In the initial stage of electrochemical repair, the chloride concentration on reinforcing bar surface decreases rapidly. After 4 weeks of electrochemical repair, the chloride concentration tends to be stable. As external potential increases, the electrochemical repair efficiency is also improved, and the chloride concentration on reinforcing bar surface decreases rapidly. When the cathodes are set on both sides of the concrete, the electrochemical repair time should be extended, and external potential should be increased to achieve better repair effect.

This study evaluates the mechanical and durability characteristics of eco-friendly concrete incorporating electronic plastic waste (EPW) as partial replacement of fine aggregate. This strategy not only reduces the adverse impacts of EPW on the natural environment but also prevents the depletion of natural resources due to excessive quarrying. For this purpose, four M20 grade concrete mixes were prepared, substituting natural fine aggregates with plastic fine aggregates (PFA) using 0%, 10%, 15%, and 20% replacement levels. The mechanical performance of EPW concrete was evaluated based on the compressive and splitting tensile strength tests while the durability properties were assessed through fire resistance, ultrasonic pulse velocity (UPV), alternate wetting and drying, sorptivity coefficient, and abrasion resistance tests. The results revealed that the compressive strength was reduced by 2.6%, 9%, and 13.6%, and tensile strength was dropped by 4.95%, 8.20%, and 20.46% with the 10%, 15%, and 20% of PFA incorporation, respectively. Also, a substantial reduction in the compressive strength was observed during the fire resistance test at elevated temperatures. However, the EPW concrete offered satisfactory to superior outcomes in the workability, sorptivity coefficient, UPV, alternative wetting and drying, and resistance to abrasion tests, signifying the potential of EPW concrete for applications where durability is of prime concern.

Since unsaturated soil conditions are normally experienced above the groundwater table, most treated or stabilised soils for roadworks, earth dams’ embankments, landfill sites, hydraulic barriers etc. could be regarded as existing in this region. The soil–water characteristic (or retention) curve (SWCC) is a useful conceptual tool by which an evaluation of unsaturated soil's property functions and corresponding macro-scale behaviour (strength, volume change, hydraulic conductivity, fluid flow, diffusivity, etc.) can be carried out. Hence, an examination of some of the various factors that could affect the hydraulic or water retention property of the stabilised soil is very vital both for laboratory studies and field practice. However, a thorough assessment of the water retention behaviour of stabilised soils can be understandably limited sometimes. This could be partly due to some of the perculiar conditions associated with soil preparation methods, soil type, soil-stabiliser mix proportion used, curing conditions, method of compaction, durability assessment modalities and other logistical issues surrounding either laboratory instrumentation or in-situ application. This article presents a critical and comprehensive review of these factors on the stabilised soil’s water retention behaviour and also provides a systematic understanding of the mechanisms of stabilisation occurring at the micro- and macro-mechanical levels. Recommendations are also made to stimulate further discussions on the synthesis of SWCC of stabilised soils vis-a-vis factors influencing them with possible interpreted engineering behaviours such as shear strength and soil consolidation.

One of the major durability issues of Reinforced Concrete (RC) structures is the steel reinforcement corrosion. Its effect needs to be evaluated on the lateral load capacity of the structures for understanding their seismic performance. In the present paper, the precise FE modelling and simulation of corroded RC frames subjected to lateral loads and its validation with full scale shake table tests on corroded RC frames is demonstrated. The rebar corrosion is induced in RC frames by accelerated impressed current technique and shake table tests are performed by simulating real time earthquakes with increasing excitation till failure of the frames is achieved. The tests showed that there was higher degradation of the frequency of the corroded structure with respect to pristine structure with increase in earthquake excitation levels. Numerical simulation of the tests is carried out using 2D micro-modelling, incorporating the effect of bond strength reduction, reduction in rebar diameter and decrease in mechanical properties of corroded steel in the model. Nonlinear static pushover analysis is performed to evaluate load displacement characteristics of the corroded and uncorroded frames and the results are compared with dynamic pushover obtained from shake table tests. It was observed that compared to un-corroded frame there is 13% reduction in the failure load due to earthquake excitation for the 7.5% corroded frame and numerical results for 10% corroded frame showed 22% reduction in the lateral load carrying capacity.

This study proposes an innovative carbon fibre reinforced polymer composite-geopolymer concrete (CFRP-GPC) system to improve the durability and structural performance of existing deteriorated reinforced concrete (RC) bridges. A rigorous experimental program is designed to investigate the transport mechanism of corrosive agents such as acids and chloride in the constituents via mechanical and microstructural analysis and to develop diffusion models for CFRP-GPC systems considering synergistic effects of temperature and pH fluctuations. Experimental results show that tensile strength of CFRP and epoxy resin reduces by up to 25% and the failure of composite mainly occurs at the fibre-epoxy interface after exposure to acid. The compressive strength of geopolymer concrete decreases by 66% and 61.3% while the mass loss reduces by 5.3% and 3.7% for samples after exposure to the 10% and 32% hydrochloric acid solution, respectively. The diffusion coefficients of the constituent materials vary from 10-8 to 10-6 mm2/s whilst the diffusion rate within the CFRP is the lowest due to the presence of carbon fibres. Furthermore, a computational model is established to evaluate the performance of the proposed hybrid system in improving long term durability performance of a roadway geopolymer concrete bridge in Australia. The numerical results indicate that the proposed CFRP-confined GPC can substantially impede the acid diffusion into the bridge column, and reduce the level of diffusion and thereby improve the service-life. Parametric study shows that the diffusion rate in CFRP-GPC columns increases up to 58% and 394% for epoxy and CFRP when temperature elevates from 23 °C to 80 °C. In addition, elevation in the exposure temperature from 23 °C to 80 °C increases the mass loss to 22% and 25% under pH = 1 and 7. The findings of this research provide a framework for durability design of hybrid CFRP-GPC systems.

Recent industrial developments have focused more and more on the applications of lightweight foamed concrete (LFC) in the construction industry, having advantages over normal-strength concrete. LFC, however, has several drawbacks including brittleness, high porosity, excessive drying shrinkage, rapid cracking, and low deformation resistance. Practical engineering typically chooses steel fiber or polymer fiber to increase the tensile and fracture resistance of LFC. The polypropylene twisted bundle fiber (PTBF) was added to the LFC with varying weight fractions of 0.0%, 0.5%, 1.0%, 1.5%, 2.0% and 2.5%. Three low densities of LFC were prepared, specifically 500 kg/m3, 700 kg/m3 and 900 kg/m3. The mechanical and durability properties of PTBF-reinforced LFC were determined through compression, flexural, splitting tensile, flow table, porosity, and water absorption tests. The results show that the addition of PTBF in LFC significantly improves the strength properties (compressive, flexural, and splitting tensile strengths) and reduces the water absorption capacity and porosity. The optimal weight fraction of PTBF was between 1.5 and 2.0% for mechanical properties enhancement. The inclusion of PTBF increased the ductility of LFC, and the specimens remain intact from loading to failure. The PTBF reduces the original cracks of the LFC and inhibits the development of further cracks in the LFC.

Carbonation is a key mechanism for deterioration of reinforced concrete structures. In design for resistance to carbonation, the performance of mixes is often specified and measured in laboratory carbonation tests where initial carbonation is sometimes present in specimens. The coherent interpretation of results from carbonation tests is vital as they enable a more accurate prediction of the performance of concrete structures in situ. This paper assesses two different approaches to considering the initial carbonation depth when extracting the carbonation coefficient from results of carbonation testing. Experimental data is compared to models for either approach using least squares regression. Both linear and non-linear representations of the initial carbonation depth are shown to fit the data well. The non-linear approach gives a larger estimate of carbonation coefficient than the linear approach, and is more consistent with the mathematical derivation of the carbonation equation. The ramifications of this difference will be most significant when the initial carbonation depth is large relative to the depth of the carbonation front. The accurate modelling of carbonation progression underpins performance-based design of new concrete structures and the assessment of existing concrete infrastructure.

This article deals with the development of concretes intended to be used as construction materials in the Czech deep repository for radioactive waste. The basic requirements for this concrete are a reduced pH value, which must maintain a constant reduced pH with a value of around 11 in the long term, and mechanical properties comparable to conventional concrete. The raw materials for the production of the proposed low pH concrete come exclusively from the Czech Republic. Material characteristics were measured on fresh mixtures and concrete after 28, 56, and 90 days of curing. In addition to the basic raw materials (aggregate, cement, water), plasticizers, microsilica or slag, and defoaming agents were added to the mixture. The aggregate:binder ratio was approximately 5:1 and the w/c water coefficient was approximately 0.6. The mechanical properties of the final concrete were similar to the reference recipe of conventional concrete (the decrease was less than 10%) and the pH value was even below 11 after 90 days. The issue of a sprayed variant of the LPC mixture was solved within the project.

International audience; Studies conducted on alkali-activated materials in late years attested that they could be a replacement to ordinary Portland cement (OPC). Nevertheless, their performances in aggressive conditions require profound investigations to evaluate the ability to the fluid transfer. This article assesses the pore structure of alkali-activated mortars produced using one-part metakaolin combined with ground granulated blast furnace slag and other-part using only alkali-activated ground granulated blast furnace slag. The pore characteristics of alkali-activated mortars were compared to those of OPC as a reference. Tests consist in the measurement of the porosity accessible to water, water absorption and sorptivity. The results revealed that the alkali-activated based metakaolin combined with ground granulated blast furnace slag have greater porosity, water absorption, sorptivity and rate of water saturated porosity than alkali-activated based ground granulated blast furnace slag and Portland cement mortars.

Digital fabrication methods with concrete have been rapidly developing, with many problems related to component production and material control being solved in recent years. These processes produce inherently layered cementitious components that are anisotropic, and in many cases, produces a weak interface between layers, which are generally referred to as cold joints. While material strength at these interfaces has been well studied in recent years, durability has received less attention, even though cold joints can function as channels for aggressive agents, such as chlorides. This work presents a method using micro-X-ray fluorescence (μXRF) to image chloride ingress into layer interfaces of 3D printed fine-grained concrete specimens produced with varying layer deposition time intervals, and also compares it to neutron imaging of moisture uptake. The results show that cold joints formed after a 1 day time interval are highly susceptible to chloride ingress, and that curing conditions play a major role in how quickly interfacial transport can take place. The μXRF method is also shown to be useful for study of transport of chlorides in cold joints, due to its spatial resolution and direct analysis of an aggressive species of interest., Materials and Structures, 56 (3), ISSN:1359-5997, ISSN:0025-5432, ISSN:1871-6873

International audience; This paper studies the behavior of four different calcined clay-based geopolymers under sulfuric acid attack and gives insights into their degradation mechanisms. Pastes were cast using metakaolin and meta-illite and were activated by two different alkaline solutions. Mineralogical and microscopic characterizations were performed on pastes before and after attack. Results indicated that all pastes were affected by low leaching of alkali cations, and thus by a linkage disequilibrium of the geopolymer network. Meta-illite based geopolymers, which had not been addressed in the literature until now, hold promise for improving the durability of materials in aggressive environments.

Accurate estimation of wind-driven rain (WDR) load on building facades is of paramount importance for the assessment of moisture-induced damage risks. The response of the facade depends on the used meteorological data, which can show significant variation over time, especially considering climate change. In this study, a statistical approach based on a Latin Hypercube Sampling (LHS) is used to generate reduced samples, which accurately represent long-term meteorological conditions for WDR. Based on cumulative distribution functions, the generated samples with LHS are a subset of actual measured data, independent of the temporal information, and are clustered around values of highest frequency. Computational fluid dynamics (CFD) simulations of WDR are performed on a historical building located in Victoria, BC, Canada based on a previously validated methodology, determining the parts of facade receiving the highest WDR load. The sensitivity study shows that a sample size of 200 with LHS, corresponding to around 0.2% of the total measured data and 4.1% of the data during rainfall, is sufficient to replicate successfully the spatial distribution of WDR with a maximum discrepancy of 7%. The reduced samples can be easily modified to model various scenarios with respect to the climate change. The change in WDR load is presented for different scenarios in terms of rainfall intensity and wind speed as predicted by future climatic conditions. The results indicate that the future WDR load depends highly on the wind speed conditions, even when wind speed is kept constant and only rainfall intensity is varied., Building and Environment, 228, ISSN:0360-1323

The use of Ultra-High Performance Concrete (UHPC) has been growing rapidly in the past two decades because of its superior mechanical and durability properties compared to conventional concrete (CC). Flexural strength prediction models of CC components underestimate the flexural strength of non-prestressed UHPC components as they ignore the tensile strength of concrete and assume different stress–strain relationships and failure mode from those of UHPC. The objective of this paper is to evaluate the current flexural strength prediction models of non-prestressed UHPC components using test data collected from the literature and validate them using experimental data of a UHPC ribbed slab tested in flexure. Measured and predicted flexural strengths are compared at different curvatures. Evaluation results indicated that neglecting the tensile strength of UHPC significantly underestimates the flexural strength of non-prestressed UHPC components. Peak moment curvature of non-prestressed UHPC components is significantly smaller than ultimate moment curvature. In addition, the differences among idealized stress–strain relationships of UHPC in compression and tension do not have significant effect on the predicted flexural strength.

To assess the durability of the impermeability of composite geomembranes in hydraulic engineering projects, using nearly 20 years (2000–2018) of seepage monitoring data from the Wangfuzhou Hydraulic Engineering Project, this study conducts feedback analysis on the anti-seepage performance of the composite geomembranes of this project. Firstly, based on the seepage monitoring data, a qualitative analysis of the overall seepage behaviour of the embankment dams was carried out. Then, a typical section of the embankment dams was selected for quantitative analysis by establishing a statistical model of the water levels in piezometric pipes. Subsequently, orthogonal design, a neural network and a numerical calculation method were combined to invert the permeability coefficient of the composite geomembranes. Lastly, the working behaviour of the composite geomembranes was comprehensively analysed. The results show that the measured water level and separated time-dependent components of three piezometric pipes in the typical section GY5 decreased gradually during the study period. The permeability coefficient of the composite geomembranes inverted using the measured water level was 1.11 × 10–12 m/s. It is concluded that, after nearly 20 years of service, the composite geomembranes of the Wangfuzhou Hydraulic Engineering Project have experienced no apparent deterioration trend over time.

Preflex beam girders with remarkable advantages are widely used in bridge structures. With aging, preflex beam bridges undergo concrete cracking and degrade as the cracks propagate and deteriorate due to repeated service load application and exposure to humid and saline environment. The objective of this study was to evaluate concrete cracking, changes in prestress, and consequent changes in sectional properties as the preflex beam undergoes deterioration in its concrete casing under cyclic loading. The experimental study investigated the behavior of a preflex beam specimen under multiple cyclic loading ranges, reproducing different deterioration levels in the concrete casing of the specimen. Relating concrete deterioration to resulting changes in the girder’s structural behavior, the study outlined recommendations for monitoring approaches in actual bridges. The study concluded that with advancement in concrete deterioration, the preflex beam girder loses prestress that results in reduced strength of the girder and remarkable changes in its sectional properties. The study also concluded to minimize prestress loss and changes in sectional properties of the girder, closer spacing for shear ribs welded to the lower flange can be helpful., 論文

Concrete-filled fiber-reinforced polymer (FRP) tubes (CFFTs) are attractive as beams and arches in harsh environments due to their durability and ease of erection. A successful infrastructure application is the use of multiple, buried CFFT arches in short-span bridges. To effectively analyze and design CFFT arches under complex loadings, there is a need for numerical procedures that capture the structural behavior of CFFT arches including the effects of FRP confinement on the concrete core and second-order response. Here, a computationally efficient structural finite-element analysis technique for the second-order inelastic behavior of these CFFT arches is detailed. A curved, flexibility-based, layered-frame element is employed to handle geometric and material nonlinearities. A concrete constitutive model that explicitly considers the effect of dilation of the concrete core and confinement provided by the FRP tube is implemented. A bending test was performed on a CFFT arch, and experimental data compared with model predictions. Additional comparisons are made with CFFT arch and beam bending tests available in the literature. The model is shown to accurately predict the load-carrying capacity and ductility of CFFT members, and to capture arch collapse mechanisms arising from FRP rupture and concrete crushing.

Nano-zeolite was used in the present study as a substitute for a part of lime and then inclusion polypropylene fiber in stabilized soil matrix to develop the soil stabilization method with lime and to improve the efficiency of this technique. In so doing, specimens of soft soil with 5, 10 and 15% of modifier L (lime), LZ (lime-nano-zeolite) and LZF (lime-nano-zeolite-fiber) were prepared, and were subjected to 1–7 wet-dry cycles. Then, microstructure and macrostructure tests were performed on the specimens. The results of the analyses, indicated that the optimal replacement of lime with nano-zeolite would be 40%, and the optimal amount of polypropylene fibers inclusion would be 1% in the stabilized soil matrix. Major reduction in lime consumption would yield a 40% increase in compressive strength and a 21% improvement in durability. The results also showed that the specimen containing 15%LZF would have excellent durability against environmental conditions and very good performance in terms of unconfined compressive strength (UCS), tensile strength and weight loss. Before and after applying 7 wet-dry cycles, the UCS increased by 39% and 16%, respectively. The results of this study indicate that LZF modifier is a suitable option for lime-based stabilization in areas under wet-dry cycles.

Ultra high-performance concrete (UHPC) is becoming a promising solution in steel–concrete composite bridges to improve the structural performance and durability of bridge decks. In contrast with conventional concrete, the excellent properties of UHPC allow for thinner and lighter designs with more efficient connections. In this study, the feasibility of large-diameter (30 mm) stud connection in thin UHPC slab was investigated to fully utilize the mechanical advantages of UHPC. The proposed composite structures employed large-diameter short stud (aspect ratio of 2.0) and UHPC slab as thin as 75 mm. Push-out tests were performed on 15 specimens with varying stud length, diameter and slab thickness. The use of large-diameter studs significantly increased the shear strength and ensured desirable failure mode of stud fracturing. The reduction of slab thickness from 150 to 75 mm resulted in little change to the shear strength, but splitting cracks appeared on the outer slab surface. Marginal effect on the shear strength was observed for large-diameter studs as the stud aspect ratio decreased from 4 to 2 and the cover thickness was reduced to 15 mm. The test results showed two main failure modes, including stud fracture via local crushing and stud fracture with UHPC pry-out. Finite element model was established to further study the stud-UHPC composite mechanism. These findings demonstrated the suitability of using short large-diameter stud and thin UHPC slab to reduce the self-weight and improve shear performance of composite structures.

Ultra-High-Performance Concrete (UHPC) has the remarkable durability and outstanding mechanical properties such as exceptionally high compressive strength and superior tensile strength. Therefore, the cross section of UHPC structure is generally optimized to make members light and thin. This paper investigated the behavior of single bolt embedded in thin HSC (high strength concrete) and UHPC members under tension loading. Fourteen tension tests were conducted to study the influences of concrete type, embedment depth and diameter of bolt on anchorage performance. The anchorage performance of these anchors embedded in UHPC were significantly improved compared with the bolts in HSC concrete, in both load capacities and displacement capacities. The superior strength and fiber bridging reduced the Angle of fracture, which is approximately 20° to 24°. As a result, the concrete breakout failure area was improved, resulting in an increase in breakout strength and displacement capacity. The test results were discussed in detail to emphasize the influence of concrete splitting on the anchorage performance of bolts embedded in UHPC members. Compared with HSC members, due to the fiber bridging, failure of UHPC members did not happen when splitting. However, the concrete splitting resulted in the decrease of breakout strength. Finally, a splitting modification factor is proposed to predict anchorage strength based on the test results obtained in this paper and others.

This study investigated sewage sludge stabilized/solidified with soda residue (SR) and ground granulated blast furnace slag (GGBS) after being dewatered with quicklime. The soaking durability test was conducted on the solidified sludge in tap water or landfill leachate. The toxicity and mineralogical characteristics of the solidified sludge were evaluated. The results showed that the unconfined compressive strength (UCS) of the solidified sludge met the strength requirement for use as a temporary cover material (≥ 50 kPa) for a short time (< 7 d). The solidified sludge had considerable soaking durability because UCS increased with the soaking time. The increase in the GGBS dosage improved the soaking durability of the solidified sludge. The UCS values of sludge solidified with 50% SR and 30% GGBS (sample S5G3) and with 80% SR (sample S8G0) after soaking in leachate for 60 d were 712.9 and 82.6 kPa, respectively. The X-ray diffraction (XRD) analysis indicated that hydration products, such as ettringite, Friedel's salt, gismondine, brushite, and hydrocalumite, contributed to the strength, soaking durability, and leachability performance of the solidified sludge. The inhibition of some hydration reactions and precipitation of ettringite and calcite on the surface of the specimens soaked in leachate led to a lower strength than that soaked in tap water. Sample S5G3 has the potential to be used as a filling or construction material, and sample S8G0 is suitable to be used as a temporary cover material in landfill.

Reinforced concrete (RC) slabs of highway bridge decks are gradually deteriorated due to the traffic vehicle wheel-loading. Fatigue is one of a number of possible causes for the deterioration. Cantilever RC slabs of the bridge are also damaged by fatigue loading. To increase the fatigue durability of the bridge deck slab, the near-surface mounted (NSM) technique is used with carbon fiber reinforced polymer (CFRP) rods embedded in the RC slab as an effective strengthening method. This study presents the fatigue characteristics of cantilever RC slabs strengthened with CFRP rods with a high-modulus of elasticity. A cantilever RC slab specimen with embedded CFRP rods with high moduli was constructed on a moving-wheel load testing machine and tested for approximately 11 months. The slab had a minimum thickness of 160 mm (as stipulated by the Japanese design code), and the minimum number of steel reinforcements was embedded to ensure (negative) flexural failure of the RC slab where CFRP rods were not used. During the test, the CFRP strengthened slab specimen was subjected to a negative bending moment from repeated moving-wheel loads. Very limited experimental data are available for the evaluation of the structural behavior of cantilever bridge decks subjected to wheel loads. Therefore, the moving-wheel fatigue experiment of the cantilever RC slab with NSM CFRP rods would be useful information for strengthening. The moving-wheel loading test confirmed the increase in fatigue durability of the CFRP strengthened slab as the slab specimen endured approximately 3.56 million equivalent-cycles at an initial load of 60 kN, which was 32% higher than the designed service load. The experimental investigation revealed that the ultimate failure of the cantilever slab was punching shear failure attributed to the rupture of the CFRP rods.

There is a global drive to promote and optimize the design of high performance buildings at low cost and minimum environmental impact. Although reinforced masonry construction is known for its better fire protection, structural durability, and construction cost reduction, its use is hindered by a lack of understanding of its resistance to earthquake loads. This research aims to quantify the effect of influential parameters on the seismic performance of Reinforced Masonry Shear Walls (RMSW) with masonry boundary elements (MBEs). A new system/configuration for RMSW with C-shaped masonry units has been proposed. A new experimental test setup was designed and built to capture the response of the lower panel of RMSW in a 12-storey building subjected to quasi-static loading protocol. Test results showed that the proposed system could provide the lateral strength and ductility required to resist earthquake events and that the average measured compressive strain was almost four times the limit specified in CSA S304-14. The results also showed that single out-of-plane support at the loading beam level was inadequate, leading to out-of-plane failure. When additional out-of-supports were provided, the failure mode changed to web crushing and buckling of vertical web reinforcement.

Though fibres are being used in concrete structures for a couple of decades, the use of polymeric Synthetic Fibres (SyF) such as Polypropylene Fibre (PPF), Polyethylene Fibre (PEF) and Polyvinyl-alcohol Fibre (PVAF) found more rapid growth in recent years. The higher durability and physical properties of SyF increased its use in concrete despite there are some drawbacks in mechanical performances. However, the development of high modulus SyF and the use of hybrid Fibre Reinforced Concrete (FRC) systems helped to mitigate the mechanical performance drawbacks to produce superior Synthetic Fibre Reinforced Concrete (SyFRC) to use in structural elements. This paper presents the recent developments and applications of SyFRC in structural elements along with the material properties such as mechanical, fire and durability performances of SyFRC.

The present study investigated the performance of South African natural zeolite for potential use as a cement extender. To the best knowledge of the authors, the natural zeolite studied has not been employed before as pozzolan in the cement industry, and its proposed use would be new in concrete construction. In the investigation, mortar mixtures were prepared using ordinary Portland cement CEM I 52,5N blended with 0, 10, 20 and 30% natural zeolite. The effectiveness of natural zeolite was also compared with performance results of mixtures containing 30% fly ash. The tests conducted were workability, compressive strength, pozzolanic activity with lime, drying shrinkage, alkali-silica reaction, and sulphate resistance. Analytical studies were done using X-ray diffraction and scanning electron microscopy coupled with energy dispersive spectroscopy. It was found that, while incorporation of natural zeolite in cement reduces workability, its effects on mechanical properties and on durability characteristics were superior to those of fly ash, as the former effectively enhanced long-term strength and mitigated drying shrinkage, alkali-silica reaction and sulphate attack. Incorporation of 20% natural zeolite in cement gave an effective overall performance, meeting the ASTM C618 (2015) criteria for Class N pozzolan. Based on EN 197-1 (2000) / SANS 50197-1 (2013), the blend of natural zeolite and ordinary Portland cement met the criteria for its classification as CEM II/A-P 32.5N,R cement type.

Wasted tyres are commonly used in civil engineering applications for a variety of purposes, including as concrete ingredients. Wasted tires that are mechanically sheared into shreds ranging in size from 25 to 300 mm and intended for use in concrete are called " Waste Shreded Tyre Aggregate" to make a contribution to sustainable waste management. Currently, at this point, the basic philosophy of this study is to investigate the effects of Waste Tire Aggregate (WTA) on the mechanical and durability properties of Self Compacting Concrete (SCC) to provide a contribution to reusing waste tires in the construction industry. WTAs with 5, 10, and 15% volume ratios are substituted for fine aggregate in SCC production. In addition, 15% mixtures with a binder quantity of 550 kg/m3, including 20 and 30% fly ash (FA) were substituted and prepared to be compared with the control concrete. To measure the rheological properties of SCCs, slump flow, V-funnel and L-box tests were performed. Then, the produced concrete samples of different sizes were cured under laboratory conditions for 28 days and then subjected to hardened concrete tests on the 28th, 56th and 90th days. The hardened concrete tests were composed of axial compressive strength, flexural strength, splitting tensile, diagonal tensile, abrasion resistance, modulus of elasticity. Finally, a durability test was performed as chlorine penetration depth. The test results show that WTA positively affects the properties of fresh and hardened SCC. Only, the increase in the substitution rate of WTA in concrete mixtures decreased the hardened state strength of the SCC. However, the addition of WTA to up to 15% of the total fine aggregate volume indicates that it is possible to apply recycled WTA to SCC and successfully satisfy both fresh and hardened SCC specifications.

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