Circular Concrete Research Articles

Production of amorphous aluminosilicate and vaterite from acid leaching of hydrated cement paste

Acetic acid has been used to leach Portland cement paste, and the effect of acid concentration, liquid/solid ratio, temperature, and time on leaching of Ca, Al, Fe and Si is reported. The silica-rich solid residue (SR) remaining after leaching was washed, dried, and ground. This amorphous aluminosilicate has comparable pozzolanic reactivity to commercial supplementary cementitious materials (SCM) such as coal fly ash. The 28-day compressive strength of 0.5 w/b mortar containing 20% CEM 1 replaced with SR extracted from cement paste (63.6 MPa) was higher than the reference (51.2 MPa). The leachate from acid leaching contains high levels of Ca2+ ions, and these can sequester CO2 under controlled conditions to form vaterite, a spherical polymorph of CaCO3. Cement paste present in waste concrete can therefore be used to form a reactive silica-rich SCM in a process that sequesters carbon. The research has implications for the development of circular concrete.

Experimental Investigation of Nonlinear Cyclic Behavior of Circular Concrete Bridge Piers with Pitting Corrosion

Experimental Investigation of Nonlinear Cyclic Behavior of Circular Concrete Bridge Piers with Pitting Corrosion

Analysis Study of Lateral Bearing Capacity and Deformation of Square and Circular Concrete Piles as an Alternative Structure for Infrastructure Projects

Piles are one type of foundation that used to transmit the load acting on a structure to the ground below. The required embedment length value depends on the load acting on the superstructure, pile specifications, and soil type. This study was conducted to analyze the lateral bearing capacity and lateral deformation that occurred on square and circular piles with sizes of 30 cm, 35 cm, 40 cm, 45 cm and 50 cm with embedment lengths from 1 meter to 15 meters. The type of soil under review is cohesive soil. The calculation method used is the Broms’ Method and computer software. The results of the analysis show that the lateral bearing capacity of square piles is greater than that of circular piles. The change in L/d ratio does not affect the magnitude of the lateral bearing capacity of rectangular and circular long piles. The resulting lateral deflection value also does not exceed the allowable limit (2.54 cm).

Machine Learning–Aided Rapid Estimation of Multilevel Capacity of Flexure-Identified Circular Concrete Bridge Columns with Corroded Reinforcement

Machine Learning–Aided Rapid Estimation of Multilevel Capacity of Flexure-Identified Circular Concrete Bridge Columns with Corroded Reinforcement

Self-compacting concrete filled steel tube specimens with RHA and M-Sand replacement subjected to axial compression

ABSTRACT Because the cement content is inexorably growing, CO2 emissions from the cement industry are becoming unavoidable. The use of rice husk ash (RHA) makes the system environmentally benign. This paper investigates the effect of RHA and manufactured sand (M-Sand) on the axial capacity of circular Concrete Filled Steel Tube (CFST) specimens subjected to axial compression. Thirty-two CFST specimens infilled with self-compacting concrete (SCC) with a replacement of RHA and M-Sand to cement and fine aggregate in 0%, 15%, 20% and 25% proportions are subjected to axial compression. Results show that use of RHA beyond 20% decreased the compressive strength of concrete and eventually decreased the axial capacity of CFST and occurred higher local buckling irrespective of their L/D ratios. Failure modes, strength index, confinement along with steel and concrete contribution on axial capacities of CFST specimens are studied. The axial capacities of the specimens were compared with various design code results such as: American concrete institute, Australian Standards, Chinese code, Eurocode, and Japanese code. Among all the codes, Chinese code overestimated the test results and hence, the axial capacity equation is altered and compared the results with test data along with 278 circular CFST data available from literature and found the results to be accurate.

Biases in life cycle assessment of circular concrete

This investigation constitutes the fourth phase of a conceptual framework designed to produce circular concrete upon the main principals of circular economy reduce, reuse and recycle. Comparative life cycle assessment is carried out for conventional and circular concrete mixtures to identify biases in the results of common life cycle assessments. Ten midpoint and four endpoint indicators are assessed using the impact 2002+ method. In baseline scenarios, environmental performances of conventional and circular concrete mixtures are compared over identical service lifes, considering cradle-to-grave and cradle-to-cradle (closed-loop) system boundaries, respectively. Results reveal that by using optimal amounts of two industrial wastes i.e. Silica fume and ground granulated blast furnace slag, as binder materials, and recycled concrete aggregate, the environmental performance of concrete is significantly enhanced. Such condition is obtained by remarkable reduction of environmental indicators (up to 44%) at both midpoint and endpoint levels. Also, circular concrete embraces a considerable amount of Non-Renewable Energy saving (40%). Investigating the impact of different end-of-life scenarios indicates that limiting boundary conditions in the cradle-to-gate approach (lack of considering end-of-life stage) has offset the results. Furthermore, the comparison trends were completely reversed in some environmental indicators upon considering the impact of service life.

HEIDELBERG MATERIALS' CO2 roadmap On the way to carbon neutrality

AbstractAt its Capital Markets Day in May 2022 Heidelberg Materials published the commitment to reduce specific CO2 emissions by almost 50 % to 400 kg CO2 per ton of cementitious material by 2030, the most ambitious target in the sector. This article provides an overview of some key elements of the roadmap established to achieve this ambition and to pave the way to achieve carbon neutrality of concrete. Three central themes will be highlighted in this article: Carbon capture and storage projects are an indispensable cornerstone to ultimately produce CO2 free cement The reduction of clinker in cement and concrete and the development and utilization of new or alternative cementitious materials are highlighted as major levers to reduce CO2 The possibility to create fully circular concrete by advanced recycling technologies and to use recycled concrete paste for CO2 mineralization are illustratedCombined with several other initiatives ‐ energy efficiency, alternative fuels and raw materials, more efficient use of concrete, to name a few ‐ substantial progress can be made on the way to carbon neutrality of concrete.

Axial Stress-strain Behavior of Recycled Polypropylene Fiber Ropes-reinforced Polymer-confined Low Strength Circular Concrete

Axial Stress-strain Behavior of Recycled Polypropylene Fiber Ropes-reinforced Polymer-confined Low Strength Circular Concrete

Numerical Investigation of the Axially Compressive Behavior of Circular Concrete Encased Steel Composite (CESC) Columns

This research presents a numerical investigation of circular Concrete Encased Steel Composite (CESC) columns. To simulate the circular CESC columns under axial compression in the previous tests, a Finite Element Model (FEM) with some modifications of material models for the steel and concrete was established in ABAQUS software. The curves of load versus longitudinal displacement and the ultimate loads obtained from the FEM were compared with those measured in previous tests. The numerical results agreed well with the test results. Furthermore, the distribution of the stresses on the cross-section at different heights and the effect of initial imperfections were observed by the FEM results. A highly confined concrete zone enclosed by steel web and steel flanges was observed. Finally, the established FEM was used in the parametric study that investigated the influence of concrete strength, steel yield strength, and spacing of the spiral hoops.

Axial Compressive Behavior of Bubble-Size Plastic Straw Waste FRP-Confined Circular Concrete

Axial Compressive Behavior of Bubble-Size Plastic Straw Waste FRP-Confined Circular Concrete

Evaluation of Confining Pressure Models for Circular Concrete-Filled Steel Tube Short Columns under Concentric Loading

It is well known that the confinement effect provided by the steel tube significantly increases the strength and ductility of circular Concrete Filled Steel Tube (CFST) columns under concentric loading. The lateral pressure is an important factor to calculate the strength enhancement of CFST columns. To reliably predict the ultimate strength of circular CFST columns, many models have been developed for predicting the lateral pressure due to the confinement effect. This paper aims to evaluate some of these confining pressure models. The values of the compressive strength of confined concrete and lateral confining pressure of circular CFST short columns were calculated using these existing models and were compared with those obtained from previous test results. In addition, a comparison between the ultimate loads predicted by these models and by Eurocode 4 (EC4) was carried out. Based on the comparison results, some suitable models for circular CFST short columns with the use of normal-strength, high-strength, and ultra-high-strength concrete were indicated.

Axial compressive behavior of green sustainable Water Hyacinth & Bio-Resin (WHBR) FRP composites-confined circular concrete

This study examines the behavior of circular concretes externally confined by green sustainable WHBR FRP containing water hyacinth fiber ropes and bio-resin. This study principally purposes to discover the axial stress-strain relationship behavior of WHBR FRP-confined circular concrete. A total of 10 circular concretes with a dimension of 150×300 mm were cast, strengthened with one to four layers of WHBR FRP, and tested under compression. The stress and the deformability of WHBR FRP-confined circular concretes were observed to be increased along with the addition of WHBR FRP layers. The accurateness of existing ultimate stress and strain models of natural FRP-confined circular concrete was evaluated using the test results. Indicating the need for the newly developed models to precisely predict the ultimate stress and strain values of WHBR FRP-confined circular concrete, newly developed models were developed to be precise in estimating the ultimate stress and strain of WHBR FRP-confined circular concrete. Keywords concrete, confinement, disaster risk reduction, stress-strain, water hyacinth fiber.

BEARING CAPACITY OF HINGELESS CIRCULAR ARCHES MADE OF CONCRETE AND FIBER CONCRETE UNDER HYDROSTATIC PRESSURE

The authors presented a numerical and experimental study of the bearing capacity of circular concrete and fiber concrete arches The authors made a stand to determine the bearing capacity of arches models under hydrostatic pressure. The hingeless arches were made of C16/20 concrete; one arch was made of unreinforced concrete, and the second arch had 1% steel anchor fiber added to the mix. ANSYS software was used for computer modeling and numerical analysis by the finite element method. When testing the concrete arch, the breaking load was 710 kN, and when testing the fiber concrete arch, it was 810 kN, that is, the bearing capacity of the fiber concrete arch determined experimentally was 1.13 times higher. The results of experimental and numerical investigations agree well with each other and with the results of theoretical calculations. Comparison of normal stresses in the experiment determined at strain gauge points with their theoretical values gives a maximum discrepancy of 9.6 % for the concrete arch and 9.2 % for the fiber concrete one. It is recommended to increase the load-bearing capacity of the structure by means of a more uniform dispersed reinforcement of the arch.

Design of Performance-Based Concrete Using Sand Reclaimed from Construction and Demolition Waste-Comparative Study of Czechia and India.

The main goal and novelty of this study is to show the transferability of practices and experiences with the use of reclaimed sand worldwide in the case in two different regions, the Czech Republic and India, which is necessary for both regions due to the sand availability (Czech Republic) and illegal sand mining including criminal offences (India). Due to the deteriorating environmental impacts associated with sand mining, finding substitution possibilities for natural sand is becoming more important worldwide. It is realized that the reuse of construction demolition waste concrete is inevitable in the pursuit of circular concrete and cleaner production, envisioned by the United Nations (UN) as the attainment of ensuring sustainable consumption and production patterns (Sustainable Development Goal 12-SDG 12) with an inclusive approach of partnerships to achieve the goal (Sustainable Development Goal 17-SDG 17) for the validation of results. The basic material properties of reclaimed sand were examined, and its impact on the physical, mechanical, and durability properties of concrete with complete replacement of sand was evaluated. Generally, a slight decline in properties of concrete with fine recycled aggregate was found. No significant decrease was found from usage possibility in the point of view of its utilization in specific structures and conditions. The research shows the slight differences of results between the Czech and Indian investigations, which are not essential for the transferability of the results.

Developing circular concrete: Acid treatment of waste concrete fines

The development of circular concrete, to enable key components to be extracted and reused, is a key requirement to achieve sustainability in the built environment. Current industry practice for end-of-life concrete is best described as down-cycling because recycled concrete aggregate has limited use, with disposal of the associated crushed concrete fines. Acid treatment of waste concrete is being investigated to allow key concrete components to become circular and, in this work, the effect of acetic acid concentration, liquid/solid (L/S) ratio, reaction time and temperature on the leaching of waste concrete fines is reported. An acid concentration of 0.6 mol/L, an L/S ratio of 7 ml/g, and a reaction time of 6 h at ambient temperature allows clean sand to be extracted from concrete fines. This performs identically to new sand in mortar samples. We show for the first time that the dried and ground silica-rich residue produced by acid leaching has pozzolanic properties comparable to commercially available supplementary cementitious materials (SCM) such as blast furnace slag and coal fly ash. The potential for CO 2 sequestration using the Ca 2+ - rich leached solution to form CaCO 3 is calculated. The research shows that acid leaching of concrete fines can produce clean reusable sand, generates a viable SCM and sequester significant amounts of CO 2 by forming precipitated calcium carbonate.

Circular concrete: validating new technologies in the lab and on-site

The growing importance of a circular economy also holds possibilities for concrete. Some of the principles of circularity, like the re-use of "waste" as secondary raw material and the optimisation of the design with regards to lifespan, environmental impact and re-use, can be applied. Several technological innovations in this domain are in an advanced stage of development. However, the transition from research to full commercial applications is held back, mostly due to the absence of documented experience and the lack of a technical framework (prescriptions). In order to accelerate the adoption of new technologies, the Belgian Building Research Institute (BBRI) started the project "Circular.Concrete". In this paper, the results are presented of validation tests regarding 1) smart crushing technology, 2) the carbonation of recycled aggregates, 3) concrete using only recycled aggregates and 4) the use of alternative binders and supplementary cementitious materials.

Impact of diameter to thickness (D/t) on axial capacity of circular CFST columns: Experimental, parametric and numerical analysis

Twenty-four circular Concrete Filled Steel Tube (CFST) columns divided in to three series based on their cross-sectional dimensions were subjected to uni-axial compression and their behaviour is studied. This paper aims to develop the volume of experimental database as there is shortage in data that can assess the guidance from the codes and enhances their accuracy in determining the ultimate capacities and the behaviour of CFST specimens subjected to uni axial compression. This study consists of CFST specimens having outer diameter of 76 mm, 89 mm and 100 mm with same wall thickness of 3 mm having four Length to Diameter (L/D) ratios of 3, 4, 5 and 6. Impact of D/t on the parameters like confinement (ξ), strength index (SI), relative slenderness ratio (λ), percentage contribution of steel and concrete and ductility index (DI) were studied. Further, the axial compressive load values were compared with the predicted design values of codes, namely, Eurocode – 4 (EC4), American code (AISC 360-10), Australian code (AS5100), Chinese code (DBJ13-51) and American Concrete Institute (ACI-318). A design equation is proposed to calculate the ultimate axial load and the predicted results are near to the test results. To check the accuracy of the proposed equation, experimental results of 63 CFST circular columns from the literatures were compared with proposed equation and found the results to be conservative. At last, finite element analysis using ABAQUS was done to study the behaviour of column buckling, axial load and displacement curves. Results showed good agreement with experimental test results.

Seismic Behavior Experimental Study on the Joint of Circular Tubed Steel-Reinforced Concrete Columns

A new type joint of Circular Tubed Steel-Reinforced Concrete (CTSRC) columns was designed in this paper. The structural characteristics, manufacturing process, and mechanical properties of raw materials of the new joint were introduced. In order to simulate the earthquake action, two joint specimens were subjected to low-cycle cyclic loading at the end of the column. Based on the in-depth study of the failure characteristics, load-displacement hysteretic curve, skeleton curve, ductility index, load-strain hysteretic curve in the core area of the joint, energy dissipation performance, strength and stiffness degradation performance, and shear deformation in the core area of the joint during the whole loading process, the seismic behavior of this new type of joint was investigated. The results show that the new joint has reasonable failure characteristics, high bearing capacity, good ductility, excellent seismic energy dissipation performance, and strong resistance to strength and stiffness degradation, which meets the seismic design principle of “strong joint and weak component” and is suitable for the results with special requirements for seismic performance. In addition, preliminary design recommendations were put forward. The research results of this paper can provide a theoretical basis for the application of this kind of new structure.

ANALYSIS OF REINFORCED CONCRETE COLUMNS FITTED INSIDE STEEL CASINGS

Due to construction costs and operational issues have been in this study to discuss how to strengthen the concrete columns. The results of previous studies on the construction of some structures earthquake-prone weakness reinforced concrete columns. The inside steel casings surrounding the columns is a modern technique used in many countries today for columns of rectangular and circular concrete. The advantages of this method is convenient, economical and easy. Reference model in this study is a column concrete without casing steel and the others concrete columns were wrapped casings steel to study the amount of retrofitting, and which has been approved changing the thickness of the cover steel are the main variable in this research. Were analyzed columns under the effect of axial force using the finite element method by using the program ANSYS (version 11). The results showed that increase the susceptibility of the inside steel casings bearing concrete columns of force inflicted by the largest of the main form without the steel casing, as well as to increase the thickness of the cover leads to increased endurance.

Restoring Force Model Research on Joint of Circular Tubed Steel-Reinforced Concrete Column

In this paper, two joints of circular tubed steel-reinforced concrete (CTSRC) column were designed. The load-displacement hysteretic curve and skeleton curve of this new type of joint are obtained by the pseudostatic test under low cycle cyclic load on the top of the column. The results show that this new type of joint has good seismic energy dissipation performance. On the basis of the test, a three-fold skeleton curve model considering three characteristic points of yield, limit, and failure is proposed, and the expression of skeleton curve model is given. The load and unload stiffness degradation law of specimens under reciprocating load is studied, and the expression of stiffness degradation law is given. The hysteresis law of the new type joint specimens is described in detail. The validity of the model is verified by comparing the experimental curve with the model curve. The model can be used in the elastic-plastic seismic time-history analysis on the joint of circular tubed steel-reinforced concrete (CTSRC) column.