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The study explores the potential of recycling construction and demolition waste into recycled coarse aggregates (RCA) to decrease waste generation and carbon footprint, using a standard compacting effort to calculate compressive strength and particle packing density in a specific cylindrical volume. This study investigates the impact of RCA on concrete’s workability, compressive strength, flexural, split tensile, drying shrinkage, electrical resistivity, rapid chloride penetration, and microstructural characteristics using XRD, SEM, and EDAX. Test findings showed that increasing the replacement percentage beyond the optimum value (RCA 25) had detrimental effects on the strength and microstructure of the concrete. RCA 25 has a higher compressive, flexural, and split tensile strength in the order of 11.56%, 3.06%, and 5.17% respectively compared to reference concrete, as well as 5.23% increase in drying shrinkage, 8.79% higher electrical resistivity, and 4.68% higher resistance to chloride penetration than reference concrete.

Rice husk residues are generated within the rice industry. In this research, the environmental impact of the use of rice husk ash is evaluated as a replacement for cement in the production of concrete in the city of Ibagué (Colombia). The environmental criteria of cement and concrete production alternatives were evaluated through life cycle analysis methodology, using SimaPro 9.3.3 software and the Recipe 2016 Midpoint (H) evaluation method. The economic cost of each of these production alternatives was included. To carry out the study, surveys and interviews had to be undertaken with rice-producing plants, aggregates, cement and concrete plants in Tolima. It was corroborated that rice husk ash (RHA) generated during the rice husk (RH) gasification process for electricity and heat production was beneficial from an environmental and economic perspective when it was used in cement and concrete in the city of Ibague (Colombia).

The aim of this paper is to evaluate the influence of a crystallizing chemical admixture on precast micro concretes with two water contents (7% and 11%, by dried mass) and two different conditions of exposure. Thus, precast micro concretes with a composition of 1:3 (cement: fines) with and without crystalline chemical admixture were evaluated on compressive strength (at the age of 28 and 154 days) and water absorption by immersion (at the age of 154 days). Statistical analysis showed that the only significant factor was the effect of the water content on the compressive strength. Besides that, the most significant factors for the water absorption and voids index properties were the water content, followed by the exposure conditions, and the interaction between the water content and the presence of the chemical admixture. The crystalline admixture was insignificant in the conditions of this research.

Ladle furnace slag (LFS) shows excellent potential for valorization. Despite this, landfills are typically its final destination, mainly because of technological barriers in its valorization process. This work examines the potential use of LFS as a partial cement/fine aggregate replacement, focusing on the effects of LFS composition and particle size distribution on concrete physico-mechanical properties. Chemical/mineralogical characterization of raw/hydrated samples, fresh-/hardened-state concrete properties, and volumetric instability tests were evaluated. Our results show reduced mechanical performance with LFS replacement, reaching compressive strength values of 32-42 MPa after 28 days. LFS mineralogical characterization reveals the absence of free CaO and the presence of periclase with its hydration/carbonation products. Therefore, the weathering/maturity process mainly affects free CaO. Furthermore, the observed volumetric instability issues were within the Code on Structural Concrete (Spanish abbreviation: EHE) established limits (0.04%), suggesting that the remaining periclase could be responsible for this expansive behavior.

After 15 years of exploitation, numerous instances of damage to the concrete pavement motorway located in northern Germany were observed. Detailed macro and microscopic analysis and determination of mechanical properties were performed on the collected cores. It was found that cracks in the coarse and fine aggregate resulted from advanced alkali-silica reaction. No impact of de-icing agents on the destruction of the concrete pavement was found, while attention was paid to the potential intensification of concrete degradation resulting from the increase in traffic on motorways. The results obtained are a detailed supplement to the German research, as this region (Rostock) has not been analysed before.

Fatigue life has to be considered in the design of many concrete structures at various stress levels and stress ratios. Many flexural fatigue test results of plain normal-weight concrete are available in the literature and almost every set of test results provides different fatigue equations. It is necessary, though, to have a common fatigue equation to predict the design fatigue life of concrete structures under flexural load with reasonable accuracy. Therefore, a database of flexural fatigue test results was created for concrete with strengths ranging from 25 to 65 MPa; this database was used to derive new fatigue equations (Wöhler fatigue equation and S-N power relationship) for predicting the flexural fatigue life of normal-weight concrete. The concept of equivalent fatigue life was introduced to obtain a fatigue equation using the same stress ratio. A probabilistic analysis was also carried out to develop flexural fatigue equations that incorporate failure probabilities.

In a 5 years study on behalf of the German federal highway research institute (BASt), 71 pavement concretes from 53 highway sections across Germany were examined among other things regarding their residual potential for an alkali-silica reaction (ASR). An empirical approach could be derived for predicting the remaining service life of the concretes. By using earlier correlation data for the climate simulation concrete prism test (CS-CPT) compared to field performance, a translation of the testing period into service life was possible by using a fitted natural exponential function. In the result, the service life of all the pavement concretes could be estimated, ranging from 11 to 51 years, depending on the ASR potential of the concrete mixes with external alkali supply by NaCl de-icer solution. A first agreement between the prediction and the field performance could be found. Further monitoring is supposed to verify and improve the prediction.

The alkali-silica reaction (ASR) remains a major challenge regarding the durability of concrete structures. The reaction mechanism is not sufficiently understood owing to the difficulty in characterizing the structure of the alkali-silica reaction gel (ASR gel) in concrete. Synthetic ASR gels with different compositions, i.e. Na/Si and Ca/Si molar ratios, were synthesized and analysed by Raman spectroscopy and, for comparison, 29Si NMR spectroscopy. The results show that higher Na/Si ratios increase the number of non-bridging oxygens in the gel structure, thus leading to a decrease in the degree of cross-linking. With increasing calcium content of the sodium-calcium silica gel, the structure tends towards that of C-S-H phases. Raman spectroscopy is a promising method to characterise synthetic ASR gels and provide new information on the effect of alkalis on the gel structure.

The environmental problems associated with the construction sector have promoted the worldwide scientific community to pay attention to the use of recycled aggregates from construction and demolition waste. SciMAT and VOSviewer bibliometric tools have been applied in order to analyse, quantify and visualise the conceptual and social aspects of this scientific field, as well as its evolution between 1973 and 2019. The study of 843 scientific papers in this field has shown that the most important thematic area has been Recycling. In general, the common objective of the published papers was to study the efficient use of resources contained in construction and demolition waste due to their treatment to produce recycled aggregates, particularly for use in concrete. Likewise, some lacks have been observed in other areas of the analysed field, e.g. the use recycled aggregates in applications subject to less demanding regulations (mortars, precast concrete products, or green roofs).

A regulatory framework is required to ensure the correct design of Fibre-Reinforced Polymers (FRPs) increasingly being used as an externally-bonded strengthening system on concrete columns. Several design guidelines on the confinement of FRP concrete have been developed over the past few years worldwide, each proposing a different approach, resulting in different predictions. This study aims to evaluate and compare nine international design guidelines used to predict the compressive strength of confined concrete in FRP-strengthened concrete columns and weigh them against experimental results. The results of this investigation reveal that the predictions from the guidelines on the compressive strengthening of FRP-confined concrete are generally suitable for circular columns, with the ACI-440 and CNR-DT 200 guideline predictions being two of the most accurate. Nevertheless, the guidelines generally tend to overestimate the load-carrying capacity for the compressive strength of FRP-confined concrete in non-circular columns, for which further experimental work using large-scale specimens is required.

The current study aims at exploring the beneficial effect of silica fume (SF) and acrylic emulsion polymer (PR) on the enhanced properties of polypropylene fiber reinforced concrete (FRC) with the supplementary cementitious binder comprised of the Portland cement, slag, silica fume and fly ash. The compressive strength and impact-abrasion resistance were used for the estimation of engineering properties while the water absorption performance, surface electricity resistance, and rapid chloride penetration resistance were used for estimation of durability. Experimental results showed that a sole addition of SF increased the compressive strengths but decreased the abrasion-impact resistances of modified FRCs, which was just opposite to the influence of a sole addition of PR. A sole addition of either the SF or PR could moderately improve the durability of modified FRCs, respectively. However, due to the beneficial effect of the complementary interaction between SF and the optimal amount of PR, the mechanical properties and durability of modified FRCs seemed to become significantly improved.

Non-destructive measurement techniques are used to identify engineering construction components without causing any negative effects on their use as construction components in the future. Contrary to this, conventional techniques cause damage to the structure. The magnetic flux leakage (MFL) method is a non-destructive test technique commonly used to assess the physical status of construction materials. Within the framework of this study a magnetic flux leakage device was produced to detect the properties of reinforced concrete construction elements. The produced magnetic flux leakage device was used for measurements in 4 different test systems created in the laboratory environment and the results were interpreted. Thus, it was revealed that the detection of reinforcement in structures can be performed more rapidly and without damage with the MFL method.

One of the major challenges facing 3D printing for construction is the technological suitability, ‘printability’, of the materials used. These cement-based materials differ from those used in other sectors, which has a series of conditioning factors that are the object of the present analysis. This article first reviews the definition of the term ‘printability’ and its constituent stages. Those stages condition the requirements to be met by cement-based materials, whether designed for other uses or developed ad hoc, and therefore the tests applicable to determine their aptitude for use in additive manufacturing for construction. That is followed by a review of the standardised tests presently in place for mortars and concretes that can be used to verify a material’s compliance with such requirements. The paper concludes with a recommendation on the advisability of developing a standard test or suite of tests to ascertain printability.

Carbon fiber jacketing is an efficient technique for increasing the strength and strain capacity of concrete circular and square section columns subjected to axial load, although confinement efficiency decreases for rectangular cross-section members. The research project BIA 2016-80310-P includes an experimental program on intermediate-size plain concrete specimens strengthened with carbon fiber jackets, mostly with square and rectangular cross-sections. The results, alongside others with similar characteristics from two databases published, are compared to predictions of four international guides. The incidence of the key parameters in the experimental results is analyzed, such as the aspect ratio of the section, the effective strain in FRP jacket attained at failure or the rounded corner radius. As a result, two efficiency strain factors are proposed, one for circular and another for rectangular specimens. The predictions contained in certain guides, based on a simple linear design-model, are improved by using the proposed efficiency strain factor for rectangular sections.

The need for proactive maintenance of reinforced concrete structures with non-destructive testing (NDT) is less disputable today than ever. One of the most promising strategies in this regard is the in-situ measurement of the reinforcement corrosion rate. This study explored the reliability of modulated current confinement method (hereafter MCC) based on a review of in-situ measurements made with that technique in real-life structures over a 13-year period. The most prominent problems detected included defective confinement of the polarization current in low-resistivity environments and over-polarization of passive reinforcement. The findings, which showed enhancement of MCC reliability to depend on improving the electrochemical current regulation and control methodologies presently in place, are being applied to improve the design of the next generation of corrosion meters.

The determination of thermal conductivity of cement-based materials is relevant from the perspective of buildings’ energy efficiency. The absence of unified tests for its measurement in mortars and concrete results in a heterogeneity of the data available in the literature. This work’s purpose is to determine the relevant influence from a a statistical viewpoint that three factors; degree of saturation, measuring time and use of a conductive paste, have in the measurement of the conductivity using the hot-wire needle probe method in two concretes with different thermal behavior: standard-weight concrete and lightweight concrete. The results obtained allow for the establishment of recommendations for future researchers on the minimum information to be included in their reports of thermal conductivity of cement-based materials by the needle probe method, the need to treat outliers, the most favorable saturation conditions and measuring times, as well as the possible benefits of using conductive pastes.

Due to the increasing use of rapid construction methods and the challenges of maintaining construction schedules, a growing demand exists for procedures that can assure quality of work without sacrificing the pace of construction. The quality control of construction materials specifically, the mechanical properties of concrete are among the most important concerns in today’s construction industry. In the present study, the correlation between fiber-reinforced concrete’s compressive strength and dynamic modulus to its ultrasonic pulse velocity is investigated at early ages up to 7 days after mixing. An experimental program involving 189 FRC specimens were designed containing different types of structural fibers, fiber volume fractions, and water-to-cement ratios. Mathematical equations were developed to predict the early-age compressive strength and dynamic modulus of four different types of fiber-reinforced concrete based on ultrasonic pulse velocity. The predicted compressive strength and dynamic modulus from the proposed equations showed good agreement with the measured ones.

This paper deals with the possibility of the improvement of pervious concrete properties by incorporation of different types of fibres and studies the effect of short duration vibration of pervious concrete properties in comparison with compaction with wooden lath and hammer. Ten mixtures of pervious concrete were prepared, five of which were compacted with wooden lath and hammer and five by short duration vibration. Density, porosity, permeability and mechanical properties were tested for in hardened pervious concrete specimens. It was concluded that mixtures compacted by short duration vibration had better mechanical properties due to the formation of a viscous layer at the contact surface between the aggregate grain and the cement matrix during the compaction, as well as pore-related properties. The addition of fibres negatively affected porosity and permeability but generally improved mechanical properties of concrete. The positive effect of fibre addition was more emphasised in cases of vibrated mixtures.

Owing to complex aspects of cemented sand and gravel (CSG), such as included unscreened aggregates, CSG properties differ from those of ordinary concrete. Fractal theory is introduced to study the effects of aggregate characteristics on CSG properties, quantifying aggregate gradation and shape. Numerical simulation and analyses show that: (1) improved aggregate gradation decreases the gradation fractal dimension and increases the CSG peak stress and elastic modulus; (2) more irregularly shaped aggregates increase the shape fractal dimension and decrease the CSG peak stress and elastic modulus; (3) the relationship quantified between aggregate characteristics and CSG mechanical properties provides a theoretical basis for aggregate allocation in engineering design and construction. Mixing artificial aggregates can improve aggregate gradation but reduces CSG performance. Appropriately blending artificial and on-site aggregates achieves optimal CSG performance; in this study, this is attained using 20% artificial aggregates added under standard gradation.

The flexural strength of pavement concrete is generally deduced by testing beams or by applying empirical equations. In this investigation, concrete mixtures were manufactured, incorporating 0, 20, 50 and 100% Reclaimed Asphalt Pavement (RAP), by weight, as a replacement for natural aggregates. The compressive strength was measured using cubic specimens and the flexural strength was measured for three types of specimens; beam, semicircular (SCB) and modified beam. This study proposes logarithmic and power equations that allow the estimation of the flexural strength of a concrete mix that incorporates RAP as a function of its compressive strength. Linear or power models are proposed to predict beam flexural strength from SCB specimens and a logarithmic model for modified beam specimens. Statistical analyses show that the proposed prediction models can be considered sufficiently accurate and their use is justified.

Self-healing of concrete is the process in which the material regenerates itself repairing inner cracks. This process can be produced by autogenous or autonomous healing. Autogenous healing is a natural process, produced by carbonation and/or continuing hydration. Autonomous healing is based on the use of specific agents to produce self-healing, which can be added directly to the concrete matrix, embedded in capsules or introduced through vascular networks. Some examples are superabsorbent polymers, crystalline admixtures, microencapsulated sodium silicate, and bacteria. This review is structured into two parts. The first part is an overview of self-healing concrete that summarises the basic concepts and the main advances produced in the last years. The second part is a critical discussion on the feasibility of self-healing concrete, its possibilities, current weaknesses, and challenges that need to be addressed in the coming years.

The possibility of using free fatty acids for the synthesis of new organofunctional silanes is shown. In nature, fatty acids occur in the form of esters with glycerin (fats) and are widely used for production of soap, oil paints, medicines and cosmetics. Of particular interest in this study was the application of organosilicon derivatives of oleic acid for production of coating that would cover the surface of concrete and protect it from water permeation. As a result of proposed silanization, the concrete surface acquired hydrophobic character with the wetting angles up to 115°, and the concrete absorbability was reduced by up to 93%.

Recycled concrete has a microstructure more complex than natural concrete, as it includes new interfacial transition zones, the quality of which is conditioned by the state of humidity of the aggregates used, which in turn will affect the final properties of the concrete. Bearing in mind the greater absorption capacity of recycled aggregates, it is important to improve its properties by means of a treatment method that is capable of reducing the negative effects that this may produce in the new concrete. Therefore, the influence of the pre-soaking method of recycled aggregates on the formation of the microstructure of concretes manufactured with these aggregates is analysed, to determine which treatment is the most effective for the production of concretes for non-structural use. The results show that the microstructure of the evaluated concretes differs according to the treatment method used, the most optimal method being one that uses aggregates without pre-soaking.

This study proposes a method to convert non-structural calcium-rich construction and demoli­tion waste fines into adsorbents of heavy metal ions by mixing waste fines with diammonium hydrogen phos­phate solution to produce hydroxyapatite, which has high surface areas and excellent ion-exchange capacity with heavy metal ions. As a result, environmental polluting waste is converted into environmentally cleaning material. Waste putty powders was chosen as the representative waste to investigate the detailed formation process of hydroxyapatite and the key reaction parameters of the reaction. Results showed that hydroxyapatite can be pro­duced on waste putty particles. Higher ageing temperatures or longer ageing duration are beneficial to the yield and crystallinity of the produced hydroxyapatite. Adsorption testing confirmed that Ni2+ can replace Ca2+ in the hydroxyapatite lattice, leading to the formation of a new crystal, arupite (Ni3(PO4)2•8H2O), and contributing to a modest adsorption capacity for Ni2+ (15 mg/g) for the hydroxyapatite-containing waste putty.

Self-compacting concrete (SCC) contains fine mineral fillers such as limestone powder. The idea of this study was to partially replace limestone with waste sulfur since it is hydrophobic, insoluble in water and therefore chemically inert and to compare the properties of produced concrete samples. Fresh concrete proper­ties included: slump-flow, t500, V-funnel time, L-box ratio, segregation ratio, density, and entrained air content. Hardened concrete was tested for compressive, flexural and bond strengths, ultrasonic velocity, dynamic elas­ticity modulus, dynamic Poisson’s ratio, and microstructure. Flowability and segregation increased, while bulk density, compressive and flexural strength, dynamic elasticity modulus and ultrasonic velocity slight declined. Times t500 and V-funnel time, L-box ratio and entrained air changed insignificantly. Considering that all proper­ties should remain or improve in case of waste valorization and the criteria should set to satisfy requirements for SCC, this study proved that all mixtures can be used for structural applications.

Fibre-reinforced concrete (FRC) allows reduction in, or substitution of, steel-bars to reinforce concrete and led to the commonly named structural FRC, with steel fibres being the most widespread. Macro-polymer fibres are an alternative to steel fibres, being the main benefits: chemical stability and lower weight for analogous residual strengths of polyolefin-fibre-reinforced concrete (PFRC). Furthermore, polyolefin fibres offer additional advantages such as safe-handling, low pump-wear, light weight in transport and storage, and an absence of corrosion. Other studies have also revealed environmental benefits. After 30 years of research and practice, there remains a need to review the opportunities that such a type of fibre may provide for structural FRC. This study seeks to show the advances and future challenges of use of these polyolefin fibres and summarise the main properties obtained in both fresh and hardened states of PFRC, focussing on the residual strengths obtained from flexural tensile tests.

Carbonation is a deleterious concrete durability problem which may alter concrete microstructure and yield initiation of corrosion in reinforcing steel bars. Previous studies focused on the use of Artificial Neural Networks (ANN) for the prediction of concrete carbonation depth and to minimize the need for destructive and elaborated civil engineering laboratory tests. This study aims to provide improved accuracy of simulation and prediction of carbonation with an ANN architecture including eighteen input parameters employing alternative Scaled Conjugate Gradient (SCG) function. After ensuring a promising value of the coefficient of correlation as high as 0.98, the influence of proposed input parameters on the progress of carbonation depth was studied. The results of this parametric analysis were observed to successfully comply with the conventional civil engineering experience. Hence, the employed ANN model can be used as an efficient tool to study in detail and to provide insights into the carbonation problem in concrete.

The effect of recycled concrete aggregate (RCA) on concrete performance against external sulfate attack (ESA) is not yet fully known. In this paper, recycled aggregate concretes (RAC) with 0, 50, 75 and 100% of RCA contents were evaluated after 10 years of exposure immersed in 50g/l sodium sulfate solution. Sulfate ingress profiles were obtained by wet chemical analyses and FRX. Also, the mineralogy of the ingress profile was evaluated by thermogravimetric analyses. Finally, microcracking development in samples was evaluated by optical fluorescent microscopy image analysis. Although RAC showed a slight increase in sulfate ingress, due to its higher porosity (about 30% higher SO3 content near the surface for 50% or higher replacement ratio than control concrete), a dense new matrix still allows a good performance of RAC to external sulfate attack with even 100% RCA content.

The suitability of three new lightweight aggregates containing carbon fiber residues (CAs) as components in structural lightweight concrete has been studied. Prismatic concrete specimens were prepared using these CAs as a coarse fraction. Additional specimens of normal-weight aggregate, commercial lightweight aggregate and mortar were prepared for comparison. The CA-concrete samples (CACs) have yielded compressive strength values between 35 and 55 MPa as well as low density and thermal conductivity results. Furthermore, the CACs have displayed the highest ratios of mechanical strength over density and the thermal conductivity, which means that there is a better balance between their mechanical and physical properties than in the other samples studied. These results indicate that the new CAs could have great potential for use in structural lightweight concrete, also complying with the principles of the Circular Economy.

The use of porous concrete solutions with lightweight aggregates has become increasingly common in noise control due to their versatility in exterior and interior applications. In this work, samples of porous consolidated concrete with aggregates of expanded clay were produced, in order to study the influence of the grain size, thickness and water/aggregate/cement ratio on the sound absorption. Experimental techniques were used to obtain the surface impedance and sound absorption coefficient. In addition to experimental characterizations, an inverse method was used (based on a genetic algorithm) to obtain the macroscopic parameters capable of representing the materials studied through the theoretical model of Horoshenkov-Swift. Using the theoretical Horoshenkhov-Swift model it becomes possible to represent these materials in numerical models as equivalent fluids.

The study investigated the joint effect of freeze–thaw attack and ultraviolet (UV) radiation on concrete. Mass loss ratio, relative dynamic modulus of elasticity (RDME) and flexural strength of concrete were experimentally investigated. A two-way ANOVA was used to analyse the effect of UV radiation on the test results. Water–binder ratio significantly affected the mass loss ratio, RDME and flexural strength. Meanwhile, UV radiation only had a significant effect on mass loss ratio but had no evident effect on RDME and flexural strength. Concrete microstructure was demonstrated by microscopic analysis via scanning electron microscope to explore the insight into the damage evolution of concrete under the joint effect. Prediction models of the damage degree of concrete were proposed by incorporating the results in this investigation. Comparison results showed that the prediction values were consistent with the experimental values.

Constructing structural elements requires high performance materials. Important decisions about geometry and materials are made during the design and execution phases. This study analyzes and evaluates the relevant factors for reinforced concrete columns made in situ for residential buildings. This article identifies and highlights the most sensitive aspects in column design: geometry, type of cement, and concrete strength performance. Using C-40 concrete mixed with CEM-II proved to cut costs (up to 17.83%) and emissions (up to 13.59%). The ideal combination of rebar and concrete is between 1.47 and 1.73: this is the percentage of the ratio between the area of rebar and the area of the concrete section. The means used during the execution phase affect resource optimization. The location of a building has only a minor impact, wherein the wind zone exercises more influence than topographic altitude.

A total of 36 groups of sand-concrete interface loading and unloading direct shear tests were used to analyze the mechanical properties of the pile side-soil interface. The test results show that the interface residual shear stress for the same applied normal stress tends to be constant for the rough sand-concrete interface. The initial shear modulus and peak shear stress of the interface both decrease with the degree of unloading and increase with the interface roughness. The maximum amount of interface shear dilatancy increases with the degree of unloading, and the maximum amount of interface shear shrinkage decreases with unloading for the same interface roughness. A pile side resistance-displacement model is established using the shear displacement method. The proposed function considers both the radial unloading effect and modulus degradation of soil around the pile. The effect of radial unloading and interface roughness on the degradation of the equivalent shear modulus is analyzed using a single fitting parameter b. Good agreement of the proposed model is confirmed by applying the direct shear tests of the 36 groups.

The purpose of this study was to isolate microorganisms associated to surface-affected concrete structures and to measure the in vitro dissolution of concrete based on the release of elements such as calcium and silicon. Although many microorganisms were detected only a fungus was capable of significantly decreasing the culture medium pH and releasing both elements. The molecular characterization allowed to identify the microorganism as Aspergillus carbonaurius, a citric-acid producing fungus that dissolved concrete in the in vitro test. After seven days of incubation, the soluble calcium concentration in the uninoculated culture medium containing concrete was 172.3 mg/L, while in the inoculated medium it was 525.0 mg/L. The soluble silicon concentration in the uninoculated medium was 10.3 mg/L, while in the inoculated medium it was 50.1 mg/L. These findings showed that plants and microorganisms rendered a synergistic effect accelerating the biodeterioration of concrete.

The effect of the extension of the curing period and exposure time to a chloride source on the transport of these ions has been studied in concrete with 100% Portland cement (OPC) and with ternary cement composed of 64% OPC, 30% blast furnace slag (BFS) and 6% limestone filler (LF). The extension of the curing time (from 28 to 90 days) did not significantly affect the transport, even in concretes with supplementary cementitious materials (SCM’s). The exposure time to the chloride source (3, 6 and 12 months) is a parameter which had a major influence on the transport. At least 6 months of exposure were necessary to achieve stable chloride diffusion coefficients with more noticeable stabilization occurring when SCM’s were used. The presence of BFS significantly decreased the transport, due to its ability to combine chloride rather than the refinement of capillary pores as a consequence of its late hydration.

To investigate the behaviour of recycled aggregate concrete (RAC) under combined compression and shear stresses, 75 hollow cylinder specimens prepared with various replacement ratios of recycled coarse aggregate (RCA) were tested with a self-designed loading device. The results showed that the failure pattern was similar for RAC with different replacement ratios of RCA. The ultimate shear stress improved with an increasing axial compression ratio of less than 0.6 and declined after exceeding 0.6. A modified failure criterion for RAC with normal strength under combined compression and shear stresses was proposed. A new procedure to predict the shear strength for RAC beams without stirrups was developed based on the proposed failure criterion, showing a better correlation with the experimental results than the predictions calculated by GB50010, Eurocode 2, fib Model Code 2010 and ACI 318-11.

This research aimed to use of bagasse ash as a cement replacement in high-strength recycled aggregate concrete (HS-RAC). Crushed limestone was replaced with 100% recycled concrete aggregate (RCA) and the ground bagasse ash (GBA) was used to partially replace ordinary Portland cement (OPC) at 20, 35 and 50%wt of binder to cast HS-RAC. The results indicated that the replacing of crushed limestone with RCA had a negative impact on the properties of the concrete. Increasing the amount of GBA in HS-RAC resulted in a decrease in density and an increase in the volume of permeable pore space. The concrete mixtures prepared with 20%wt GBA replacement of OPC promoted greater the compressive strength than the conventional concrete (CT concrete) at 90 days or more. HS-RAC with GBA (up to 50%) was more durable in terms of chloride ion penetration resistance, although it had lower compressive strength than the CT concrete.

Self-compacting concrete has a characteristic microstructure inherent to its specific composition. The higher content of fine particles in self-compacting concrete relative to the equivalent vibrated concrete produces a different fracture behavior that affects the main fracture parameters. In this work, a comprehensive experimental investigation of the fracture behavior of self-compacting concrete has been carried out. Twelve different self-compacting concrete mixes with compressive strength ranging from 39 to 124 MPa (wider range than in other studies) have been subjected to three-point bending tests in order to determine the specific fracture energy. The influence of the mix design and its composition (coarse aggregate fraction, the water to binder ratio and the paste to solids ratio) on its fracture behavior has been analyzed. Moreover, further evidence of the objectivity of the size-independent fracture energy results, obtained by the two most commonly used methods, has been provided on the self-compacting concrete mixes.

The utilization of lightweight oil palm shell to produce high strength lightweight sustainable material has led many researchers towards its commercialization as structural concrete. However, the low tensile strength of Oil Palm Shell Concrete (OPSC) has hindered its development. This study aims to enhance the mechanical properties and flexural behaviours of OPSC by the addition of steel fibres of up to 3% by volume, to produce oil palm shell fibre-reinforced concrete (OPSFRC). The experimental results showed that the steel fibres significantly enhanced the mechanical properties of OPSFRC. The highest compressive strength, splitting tensile and flexural strengths of 55, 11.0 and 18.5 MPa, respectively, were achieved in the OPSFRC mix reinforced with 3% steel fibres. In addition, the flexural beam testing on OPSFRC beams with 3% steel fibres showed that the steel fibre reinforcement up to 3% produced notable increments in the moment capacity and crack resistance of OPSFRC beams, but accompanied by reduction in the ductility.

Installing utility pipelines generates a significant amount of trench arisings, which are usually transported to landfills instead of being reused as backfill material. This practice generates CO2 emissions and wastes raw materials. This paper presents a more sustainable solution, an eco-trench, which is based on re-using trench arisings as backfill and adding a top layer of expansive concrete to improve the eco-trench’s structural performance. The technical feasibility of the eco-trench was evaluated through a finite element model, which identified the degree of expansion in concrete required to avoid failure or subside the stresses caused by traffic. The potential expansion of concrete was measured under confined conditions in the laboratory by means of a novel test developed for this purpose. The results showed that adding calcium oxide generates the required internal stress. The results were then confirmed in a pilot experience.

Fracture of steel-fibre-reinforced-concrete occurs mostly in the form of a smeared crack band undergoing progressive microcracking. For FE modelling and design purposes, this crack band could be characterised by a stress-strain (σ-ε) relationship. For industrially-produced steel fibres, existing methodologies such as RILEM TC 162-TDF (2003) propose empirical equations to predict a trilinear σ-ε relationship directly from bending test results. This paper evaluates the accuracy of these methodologies and their applicability for roller-compacted-concrete and concrete incorporating steel fibres recycled from post-consumer tyres. It is shown that the energy absorption capacity is generally overestimated by these methodologies, sometimes up to 60%, for both conventional and roller-compacted concrete. Tensile behaviour of fibre-reinforced-concrete is estimated in this paper by inverse analysis of bending test results, examining a variety of concrete mixes and steel fibres. A multilinear relationship is proposed which largely eliminates the overestimation problem and can lead to safer designs.

If we are to monitor the chemical processes in cementitious materials, then pH assays in the pore solutions of cement pastes, mortars, and concretes are of key importance. However, there is no standard method that regulates the sample-preparation method for pH determination. The state-of-the-art of different methods for pH determination in cementitious materials is presented in this paper and the influence of sample preparation in each case. Moreover, an experimental campaign compares three different techniques for pH determination. Its results contribute to establishing a basic criterion to help researchers select the most suitable method, depending on the purpose of the research. A simple tool is described for selecting the easiest and the most economic pH determination method, depending on the objective; especially for researchers and those with limited experience in this field.

The paper focuses on the reuse of crushed asphalt (GA) as a partial replacement (up to 20%) of natural aggregates for concrete manufacture. Addition of GA aggregates produced a positive effect on workability loss. The GA mixes, however, showed a significant tendency to bleed and segregate at the highest replacement percentage applied. GA led to a decrease of compressive strength in concrete (with respect to that of the reference concrete) up to 50% due to the weakness of the cement paste / recycled aggregate interface. To compensate for this negative effect, a reduction of w/c for the GA concretes was necessary. A decrease of w/c allowed the GA concretes to show drying shrinkage values substantially similar to those of reference concrete with the same cement factor. The experimental results confirmed the possibility of partial substitution (max. 15%) of natural aggregates with crushed asphalt for making concrete.

This behaviour of low- and medium-strength concrete specimens confined with carbon fibre-reinforced polymer (CFRP) was analysed in three loading cycles. In some cases, stress levels were achieved that produced intemal microcracks, which allowed residual rigidity and the behaviour of completely microcraked concrete specimens to be studied. The specimens were subsequently tested to compression to the fracture point. Specimens reinforced in accordance with no manufacturing defects (100% CFRP reinforcement) and major manufacturing defects (50% CFRP reinforcement) were assessed for effectiveness and behaviour of the confined elements in less than ideal conditions. Results show that confinement was higher in low-resistance concretes, that the behaviour of reinforced specimens was unaffected by defective implementation conditions and that the reinforced specimens were less rigid than the non-reinforced specimens when tested up to 40% of ultimate fracture strength.

The scope of this investigation is to develop a material mainly composed (80% w/w) of ceramic wastes that can be applied in the manufacture of road traffic noise reducing devices. The characterization of the product has been carried out attending to its acoustic, physical and mechanical properties, by measuring the sound absorption coefficient at normal incidence, the open void ratio, density and compressive strength. Since the sound absorbing behavior of a porous material is related to the size of the pores and the thickness of the specimen tested, the influence of the particle grain size of the ceramic waste and the thickness of the samples tested on the properties of the final product has been analyzed. The results obtained have been compared to a porous concrete made of crushed granite aggregate as a reference commercial material traditionally used in similar applications. Compositions with coarse particles showed greater sound absorption properties than compositions made with finer particles, besides presenting better sound absorption behavior than the reference porous concrete. Therefore, a ceramic waste-based porous concrete can be potentially recycled in the highway noise barriers field.

The objective of this study was to demonstrate the possibility to obtain concretes in Cuba with values of effective porosity below of 10%, using limestone aggregates with high levels of absorption (higher than 1% in many cases), and values of Sorptivity below of 5 x 10-5 m/s1/2 as is established in the document prepared by the DURAR Latin Working Group, for structures exposed to very aggressive environments. The experimental results showed that the use of the trial method of capillary absorption of Göran Fagerlund, were obtained concretes with effective porosity below of the 10%, for water/cement ratios of 0.4 and 0.45, but the values of sorptivities were very high. Nevertheless the subsequent use of the trial method of the ASTM C1585, that use cylinders probes with bigger depth and different processing, permits to obtain the desired sorptivity values for water/cement ratios of 0.4 and 0.45 whenever would be fulfilled the Good Practices of the Construction.

In this article on the basis of analysis of the influence of different technological-environmental parameters, such as the type of cement, water/cement ratio, initial curing temperature, time of conservation work, content of cement, additions, additives and consistency in the evolution of the concrete compressive strength, obtained a calculation equations and some graphs to estimate the resistance evolution of the concrete HA-25/B/20/IIa and HA-30/B/20/IIa from 3 to 28 days for each initial temperature curing interval specified and for the sample of concrete. So are based on 67.782 data of different compressive strength of prepared concrete in the province of Valencia during the years 1996 to 2011, that has allowed to compare the equations obtained from regression with a significant database.

The purpose of this study is to evaluate the acoustic performance of lightweight concrete with ethylene vinyl acetate copolymer (EVA) residues to reduce impact noise on floors. Three types of concrete with three different mix proportions were evaluated. The method adopted includes the characterization of water absorption, voids and density of the samples. The experimental study of noise impact followed the procedures of ISO 140. The results indicate that the lightweight concrete with EVA recycled aggregate can reduce impact noise levels by up to 15 dB and the highest percentage of coarse aggregate EVA does not entail a higher acoustic performance.

In light of their excellent mechanical properties and other advantages over conventional systems for repairing and rehabilitating structures, fibre-reinforced polymers (FRPs) are commonly used to enhance the shear strength of RC members. Because of the relatively recent application of the technique in civil engineering, however, it is addressed in very few recommendations or guides. While the design guides in place contain a single, well defined and generally accepted procedure for calculating bending moments, they collectively propose a wide variety of numerical models for shear, none of which is universally acknowledged. The present article focuses on the calculation of ultimate shear strength and describes an experimental study in that context conducted on reinforced concrete beams retrofitted with unidirectional carbon fibre reinforced polymer (CFRP) fabric.

Recycled aggregate produced at construction and demolition waste plants is frequently used as an ingredient in structural concrete. Nevertheless, the physical, chemical and mechanical properties of this aggregate must be supervised in order to ensure the quality of the final product. Of these properties, one of the most important is particle size which depends to a great extend on the process used to manufacture the aggregate and it directly affects the consistency, workability, uniformity, and mechanical strength of concrete as well as its density, compactness, permeability and resistance to wear. This paper analyzes recycled aggregate samples with various size grading methods to determine their potential use in concrete. On the one hand, results have showed that some differences between different methods existed; on the other hand the manufacturing process should be modified so that the particle size of the recycled aggregate complied with the guidelines in the EHE-08 Code.