Self-compacting Concrete Mixtures Research Articles

Influence of calcined dam mud on the thermal conductivity of binary and ternary self-compacting concrete mixtures using the equivalent mortar method

Reducing energy consumption in concrete buildings requires cement-based structural materials that have low thermal conductivity. Moreover, low thermal conductivity is a crucial property of building materials used for thermal insulation to ensure the comfort of building occupants. The research evaluates the effect of using calcined mud (CM) and natural pozzolan (Pz) on the thermal conductivity of self-compacting concrete (SCC). To optimise SCC formulations, the equivalent concrete mortar method has been used. This communication mainly focuses on the equivalent self-compacting concrete mortars (ESCCMs). The current study consists of ten formulations: one control (based on Portland cement) and nine others containing binary and ternary systems of Portland cement, calcined mud, and natural pozzolan with 10%, 20%, and 30% replacement rates . The mixtures were prepared using tests of cement paste and equivalent mortar in a fresh state. Afterwards, they were assessed based on their compressive strength at 14, 28, 90, and 180 days and their thermal conductivity at 28 and 90 days in the hardened state. The self-compatibility, the thermal conductivity, and the mechanical performance results obtained by relevant tests on ESCCMs prove that the ternary systems (Portland cement, CM, and Pz) open up many techno-economic development avenues in SCC applications to be explored.

Design automation of sustainable self-compacting concrete containing fly ash via data driven performance prediction

Self-compacting concrete (SCC) is a highly flowable and segregation-resistant material, effectively facilitating proper filling and ensuring exceptional structural performance in confined spaces. Incorporating fly ash as a supplementary cementitious material in SCC mixtures yields numerous benefits, including enhanced cost-effectiveness in construction and the advancement of environmental sustainability. Nevertheless, the addition of fly ash in SCC poses significant challenges in modelling and predicting the properties of SCC due to lack of understanding of its influence on material rheology and bonding. It is therefore desirable to develop more appropriate machine learning approach to compliment the large scale and costly laboratory-based experiments. This paper presents four well trained supervised machine learning models for the prediction of fresh and hardened properties of SCC containing fly ash: support vector machine (SVM), decision tree, random forest, and artificial neural network (ANN). Training datasets gathered from publicly available existing relevant literature, were analysed and processed prior to shape the required machine learning models. Optimization strategies of hyperparameters were also implemented for each model. To evaluate the performance of these machine learning models and to compare their accuracy, regression error characteristic curves and Taylor diagrams were utilized. The findings reveal that all models demonstrate promising results, with the random forest model outperforming the others in predicting SCC properties with higher accuracy. This underscores the potential of random forest algorithms in accurately modelling and predicting the properties of fly ash-infused SCC. Finally, a data driven implementation framework has been developed, thereby offering robust and logical strategy for experimental designs and guidance for developing sustainable SCC.

Characteristics of non-steady-state chloride migration of self-compacting concrete containing recycled concrete aggregate made of fly ash and silica fume

Chloride migration poses a significant challenge to the long-term durability of concrete structures due to its potential to corrode reinforcement and deteriorate the structure. This study focuses on chloride migration in self-compacting concrete (SCC) made with pozzolans, namely silica fume (SF) and fly ash (FA), along with recycled concrete aggregate (RCA). Particularly, the effects of external electrical potential (power-on) duration and RCA content on the features of SCC were examined, alongside the influence of pozzolanic materials, focusing on the chloride migration coefficient and mechanical properties. Six groups of SCC mixtures were created with varying proportions of SF and FA, and different levels of RCA replaced the natural coarse aggregate. The findings reveal a multifaceted impact on SCC behaviour. The chloride migration coefficient exhibits a distinct pattern as the power-on duration increases from 12 to 36 h. Initially, the coefficient increases and then decreases, demonstrating a healing and sealing mechanism within the concrete matrix, which enhances resistance to chloride penetration. The chloride migration coefficient significantly decreased with adding SF and FA. With 15% SF and 30% FA, the coefficient decreased to 59.9% and 49.5%, respectively. Moreover, incorporating RCA in SCC mixtures significantly influences coefficient levels. RCA inclusion at 20% remarkably decreased the coefficient after 12 h by 16.17%. Subsequently, the levels decreased by 39.49% and 46.87% after 24 and 36 h, respectively, compared to the control mixture. This behaviour highlights the importance of RCA in enhancing the resistance of SCC to chloride ingress, a crucial factor for long-term durability. Additionally, mechanical properties such as splitting tensile strength, ultrasonic pulse velocity and surface hardness consistently improved with longer power-on durations and higher RCA and SF content. SCC with RCA and pozzolanic materials exhibits enhanced chloride resistance and superior mechanical performance, making it ideal for sustainable concrete production.

UTILIZATION OF BAUXITE RESIDUE IN SELF-COMPACTING CONCRETE AND EVALUATE RHEOLOGICAL BEHAVIOR AND MECHANICAL CHARACTERISTICS

This thesis aims to investigate the potential utilization of bauxite residue, by-product of aluminum production, in self-compacting concrete (SCC) and evaluate its impact on the rheological behavior and hardened state characteristics of the resulting concrete. Bauxite residue is a red mud waste generated during the extraction of alumina from bauxite ore. Finding sustainable solutions for its disposal or reuse is crucial for environmental and economic reasons. The research methodology involves laboratory experiments to determine the optimal proportion of bauxite residue in SCC mixtures. The rheological properties of fresh concrete, such as slump flow, flow time, and passing ability, will be assessed using standard tests. Additionally, the effects of bauxite residue on key mechanical properties of hardened concrete, including compressive strength, flexural strength, and durability, will be examined. It is reveled from the result that as the red mud percentage increases workability also increases but mechanical properties increases upto 30 percentage of red mud above 30% it get decreases. Key word – Red Mud, Workability, Self-Compacting Concrete, Mechanical Properties

The effect of using treated domestic wastewater with different pHs on workability, mechanical, and durability properties of self-compacting concrete.

In the present work, we used treated domestic wastewater with different pHs in self-compacting concrete (SCC) to find the effect of treated wastewater with different pHs on the workability, mechanical, and durability properties of SCC. Eight different SCC mixtures were designed, including two control samples using tap water with a water-to-cement ratio (W/C) of 0.5 with 400 kg/m3 of cement and W/C of 0.36 with 440 kg/m3 of cement. Six SCC samples with the same characteristics as control samples except using treated domestic treated wastewater with different pHs. The results indicate that the workability of the SCC sample using the treated domestic wastewater in acidic pH was higher than the alkalinity state. Using treated domestic wastewater instead of tap water in SCC samples decreased compressive, flexural strength, and fracture toughness by less than 10%. Also, carbonation, 30-min water adsorption, and capillary water adsorption of SCC samples increased when treated domestic wastewater was used. The compressive strength of SCC samples made with treated domestic wastewater in an acidic state is less than about 5% in an alkaline state. The energy dispersive spectroscopy and the scanning electron microscope images confirmed that using treated wastewater instead of tap water, in SCC samples, reduced compressive strength because the Ca/Si ratio increased when treated domestic wastewater was used. The SCC samples with treated domestic wastewater in the alkaline state have a lower Ca/Si ratio. The higher compressive strength belongs to concrete samples that used treated domestic wastewater in an alkaline environment with a lower Ca/Si ratio.

Analyzing the potency of Viscosity Modifying Agents on the Characteristics and Static Segregation of Fresh and Hardened Fluid Concrete

Self-compacting concrete (SCC) represents a recent advancement in the field of concrete technology due to its ease of handling and placement. In order to regulate the internal integrity of the concrete, a supplementary mixture component is employed. The term used to refer to this particular component is a viscosity-modifying agent (VMA). Different quantities of VMA were incorporated into the concrete mixture in order to evaluate its performance in both the fresh and hardened states. This study focused on the impact of VMA (Viscosity Modifying Agent) on various characteristics of concrete mixes. Specifically, the features under examination included flowing time, slump flow, flow time into a 500-mm diameter, and resistance to vertical segregation. In contrast, a measurement was conducted on the compressive strength of the cured concrete. The utilization of the column of segregation test allows for the identification and assessment of static segregation in SCC mixtures. This test offers a direct quantitative determination of the stability of segregation in fresh concrete. The purpose of this experiment is to determine the precise quantity of coarse aggregate with a diameter above 8 mm present within a specimen of 300 mm in height. This can be achieved by conducting sedimentation tests at a specific time interval of 30 minutes after the pouring of concrete. The research results indicate that the addition of VMA had a substantial impact on the rheological characteristics of the concrete mixture. It effectively stabilized the mixture, minimized static segregation, and improved the compressive strength when compared to the reference mixture without VMA. Furthermore, a comprehensive illustration of the segregation phenomenon is provided by the column of static segregation tests.

The Application of Neural Networks to Predict the Water Evaporation Percentage and the Plastic Shrinkage Size of Self-Compacting Concrete Structure

This article presents a solution using an artificial neural network and a neuro-fuzzy network to predict the rate of water evaporation and the size of the shrinkage of a self-compacting concrete mixture based on the concrete mixture parameters and the environment parameters. The concrete samples were mixed and measured at four different environmental conditions (i.e., humid, dry, hot with high humidity, and hot with low humidity), and two curing styles for the self-compacting concrete were measured. Data were collected for each sample at the time of mixing and pouring and every 60 minutes for the next ten hours to help create prediction models for the required parameters. A total of 528 samples were collected to create the training and testing data sets. The study proposed to use the classic Multi-Layer Perceptron and the modified Takaga-Sugeno-Kang neuro-fuzzy network to estimate the water evaporation rate and the shrinkage size of the concrete sample when using four inputs: the concrete water-to-binder ratio, environment temperature, relative humidity, and the time after pouring the concrete into the mold. Real-field experiments and numerical computations have shown that both of the models are good as parameter predictors, where low errors can be achieved. Both proposed networks achieved for testing results R2 bigger than 0.98, the mean of squared errors for water evaporation percentage was less than 1.43%, and the mean of squared errors for shrinkage sizes was less than 0.105 mm/m. The computation requirements of the two models in testing mode are also low, which can allow their easy use in practical applications. Doi: 10.28991/CEJ-2024-010-01-07 Full Text: PDF

Rheology, Mechanical Properties and Shrinkage of Self-Compacting Concrete Containing Cement Kiln and By-Pass Filter Dust

Self-compacting concrete (SCC) is a high-quality construction solution, combining high fluidity, passing and filling ability with improved mechanical properties and durability. In the present study, the effect of incorporating alternative waste materials, such as two by-products of the cement industry, namely cement kiln dust (CKD) and by-pass dust (BPD) into SCC, as a partial replacement for traditional filler material, was investigated. The produced compositions were compared with reference mixtures containing exclusively marble powder (MP), as a filler. A series of tests encompassing specific test methods for wet SCC, compressive, flexural and tensile-splitting strength tests, as well as drying-shrinkage determination, were undertaken to evaluate the quality of the produced SCC in terms of fresh and hardened properties. The use of alternative fine-filler materials resulted in a high-performance sustainable SCC, of low cement content. To be precise, incorporating CKD into the SCC enhanced its rheological behavior and marginally improved its mechanical properties, while the use of BPD led to SCC mixtures of adequate rheological characteristics, coupled with significantly improved mechanical and physical properties.

Mathematical Modeling of Technological Processes of Concreting Monolithic Structures From Fine-Grained Mixtures

Introduction. The introduction of innovative technologies and materials in the construction industry is constrained by a number of reasons associated with insufficient knowledge of technological processes and the increased cost of highly efficient innovative materials. Therefore, studies in the field of monolithic concrete technology, reflecting the features of concreting structures from self-compacting mixtures and aimed at reducing their cost due to the use of construction waste, are relevant. The purpose of this work is experimental and statistical modeling of rheological characteristics of finegrained self-compacting concrete mixtures and physical and mechanical properties of concretes depending on the influence of two recipe factors — consumption of superplastifying additive and particle size distribution of aggregate including construction wastes.Materials and Methods. For the preparation of fine-grained self-compacting concrete mixtures, portlandcement CEM 0 52,5N, natural quartz sand and crushed concrete sand of a mixture of three fractions of 0.63–5.0 mm and a chemical additive - a superplasticizer based on polycarboxylate esters Polyplast PK were used. Process characteristics of fine-grained self-compacting mixtures (workability, viscosity, fluidity) were determined by standard methods. The shear limits of the mixtures were set by means of an instrument comprising a cylinder with a nozzle and a glass base with circumferential marking. Modeling of rheological and physical-mechanical properties of fine-grained self-compacting concretes was carried out using a two-factor simplex-summed plan on a hexagon inscribed in a circle, which is one of the most convenient for solving technological problems of construction materials science.Results. Experimental-statistical models of rheological characteristics of fine-grained self-compacting mixtures and strength properties of concrete were obtained, adequately describing experimental data.Discussion and Conclusion. The use of mathematical planning methods of the experiment made it possible to comprehensively assess the influence of the two most significant recipe factors on the technological processes of concreting monolithic reinforced concrete structures from fine-grained self-compacting mixtures using aggregate from construction waste. It was established that optimal content of grains from crushed concrete in natural sand is 30–35 %, and dosage of superplasticizer Polyplast PK is 1.2–1.25 % of binder weight.

Effects of waste magnesia powder as partial cement replacement on self-compacting concrete

This experimental study investigated the performance of self-compacting concrete (SCC) mixes with magnesia (MgO) waste. In the series produced with a water/binder ratio of 0.40, cement was replaced by magnesia waste at 2%, 4% and 10% by weight in the SCC. Le Chatelier test, slump flow, compressive strength, flexural strength, depth of penetration of water under pressure, ultrasonic pulse velocity and water absorption by capillary testing was conducted to assess sample performance. X-ray diffraction, thermogravimetric analysis, mercury intrusion porosimetry, differential thermal analysis and scanning electron microscopy were used for the microstructural analysis and quantification of phases within each sample. The results indicated that concrete with magnesia waste contains magnesium silicate hydrate (M–S–H) and brucite ((Mg(OH)2) products. Brucite causes strength loss in concrete. Up to 90 days, specimens with magnesia showed increasing compressive and flexural strength. As the amount of magnesia waste increased, the porosity, depth of water penetration under pressure and water absorption by capillary increased. Incorporating more than 10% of magnesia waste in the SCC mixtures resulted in declining strength. The addition of magnesia waste enhanced the expansion of SCC. An optimum dosage (2%) of magnesia waste was the most advantageous to the strength of SCC.

Experimental Study on Direct Shear Strength of Fiber Reinforced Self Compacting Concrete under Acid and Sulfate Attack

This study primary is to investigate the shear strength of self-compacting concrete (SCC) reinforced by steel-fiber (SF) and polypropylene-fiber (PPF) in different environmental conditions: the air, sulfate (MgSO4 with a concentration of 5%) and acid (H2SO4 with a concentration of 5%). The study also examines the effect of fiber volume fraction on the workability, shear strength, compressive strength, and splitting tensile strength of fiber reinforced SCC. The article aims to determine the durability effects of both fibers and their resistance to aggressive environmental conditions. The contribution of this article is an experimental investigation on the shear strength of SCC reinforced by SF as well as PPF in 3 different environmental conditions after 30 days of exposure. The study also investigated the fresh and mechanical properties of 5 different mixtures of SCC with/out 0.1% and 0.2% fibers. The study also concluded that PPF decreased the workability of SCC badly, and special care must be taken when selecting its volume fraction. Also, it was found that generally shear strength of SCC mixes enhanced with increasing SF and PPF volume fraction. Moreover, it was found that both fibers have good durability effects, and resist aggressive environmental conditions, with the best results obtained from samples containing 0.2% SF. In the air condition, while the compressive strength, shear strength and tensile strength results were 52.6MPa, 6.43MPa and 3.91MPa, in the sulfate condition those were 46.37MPa, 6.55MPa and 3.59MPa, and in the acid condition those were 34.4MPa, 5.5MPa and 3.46MPa, respectively.

Evaluating the rapid chloride permeability of self-compacting concrete containing fly ash and silica fume exposed to different temperatures: An artificial intelligence framework

One of the major known challenges of improving durability of concrete structures is reducing the permeability of concrete to retard the transport of chloride ions. In this regard, the utilization of self-compacting concrete (SCC) incorporating supplementary cementitious materials such as fly ash and silica fume can aid to improve the resistance against chloride ion penetration. With the aim of evaluating the effectiveness of the SCCs, existing experimental methods, such as the rapid chloride permeability test (RCPT), demand time, financial resources, and skilled technicians. This study proposes three accurate and reliable predictive models through the combination of metaheuristic optimization techniques of particle swarm optimization (PSO), ant colony optimization (ACO) and biogeography-based optimization (BBO) with artificial neural network (ANN) in order to minimize the reliance on time-consuming and costly laboratory activities. To this end, 360 RCPT results on 60 SCC mixtures incorporating various percentages of fly ash and silica fume exposed to different temperatures during the RCPT were collected. The performance of the developed models was assessed by different statistical indicators. The results reveal that the proposed ANN-BBO model exhibits a higher accuracy than the single ANN, ANN-PSO and ANN-ACO models. It is also found that the input parameter of the sample temperature during testing is the most important variable in controlling the RCPT of SCC with a contribution of 25%. Comparing the performance of the best proposed model (ANN-BBO) with that of existing models in the literature reveals that the ANN-BBO model has a higher accuracy in predicting the chloride ion penetration resistance of SCCs.

Some Technological Parameters of Construction Joints Formation Using the Self-Compacting Concrete Mixtures

Introduction. The important condition ensuring the monolithicity of the erected massive monolithic reinforced concrete structures, divided in compliance with the standards into the heat-shrinkable blocks, is the quality of construction joints in terms of the new-to-old concrete bonding. The research on the bonding strength dependence on the technological parameters of the construction joints formation using the widely spread in recent years self-compacting concretes is a relevant task, because the number of publications on the respective topic is insufficient. The aim of the present paper is to develop a scientific concept regarding the influence of the certain technological parameters on the new-to-old concrete bonding strength during the construction joints formation.Materials and Methods. The research was carried out using the self-compacting and ordinary heavy vibratory-compacted concretes with the compressive strength ranged from 34.5 to 69.2 MPa. The object of the study was the dependence of the new-to-old concrete bonding strength on the method of standardised surface pre-treatment of the “old” concrete in a joint and the compressive strength of the grade of the “new” self-compacting concrete. The composite Mörsch specimens in which the “old” concrete was cured for up to 3 days were used as the main samples. The construction joint relative strength was considered to be the joint quality evaluation criterion equalling to the ratio of the shear strength of concrete in a composite Mörsch specimen to the minimum axial tension strength values of the “new” and “old” concrete. The quality indicators of the concrete were determined by applying the standard methodology. The specimens were cured under conditions simulating the production of works in the spring-summer season.Results. During the research, the construction joint quality criteria in terms of the “old” to “new” concrete bonding were analysed along with the changes they undergo depending on the studied recipe (concrete grade) and technological (length of the technological break, surface treatment method) factors. The dependences of the proposed construction joint quality criterion on the “new” concrete compressive strength (grade) were obtained and the inefficiency of the surface treatment with a metal brush was shown, especially if accompanied with the technological break extension. The required bonding strength values for B25 ... B35 grade concretes can be for sure provided by the surface pre-milling, whereas the extension of the technological break has negative affect on the bonding strength.Discussion and Conclusions. Due to the revealed low bonding strength of the “old” to “new” concretes, regardless the technological factors, it is expedient to look into the ways of ensuring the construction joint quality by implementing structural solutions such as keyed joints and (or) additional reinforcement.

Effect of recycled crushed glass and recycled coarse aggregate on the properties of self-compacting concrete

This research was developed to use recycled coarse aggregate (RCA) and recycled crushed glass (RCG) to produce self-compacting concrete (SCC) mixtures. Natural coarse aggregate (NCA) was replaced by RCA from 0% to 100%, and natural fine aggregate (NFA) was replaced by RCG from 0% to 20%. Slump flow with T500 time, L-box, and V-funnel tests were done to ascertain the workability properties of SCC mixtures. The mechanical properties studied were compressive, flexural, and splitting tensile strength at 28 and 56 days. Ultrasonic pulse velocities (UPV) were also measured for the SCC mixtures at 28 and 56 days. Ten shear-critical beams with different shear span-to-depth (a/d) ratios were also cast and tested under 4-point bending. Cracking load, failure load, load-midspan deflection curves, and deflection corresponding to ultimate load were observed. The recommendations of the American Concrete Institute (ACI 318–14 and ACI 318–19), Eurocode (EC2), and Japanese Society of Civil Engineers (JSCE) for shear design were also evaluated on a database of 222 beams cast with SCC and recycled aggregate concrete (RAC) along with the beams tested in the presented study. Results indicate that the workability and mechanical properties were reduced when the replacement level of RCA was increased. The use of RCG as a replacement for NFA enhanced the workability properties and mechanical properties at the age of 56 days. The replacement of NCA with RCA slightly reduced the shear capacity and stiffness of the RC beams. However, the shear capacity and stiffness of RC beams improved when NFA was replaced with RCG. The design provisions of ACI 318–19 yielded accurate estimates of shear capacity compared to JCSE, EC 2, and ACI 318–14.

Mechanical and shrinkage performance of steel fiber reinforced high strength self-compacting lightweight concrete

This study investigated the effects of mixture proportion on the mechanical and shrinkage behaviors of steel fiber reinforced high strength self-compacting lightweight concrete (SHSLC) mixtures incorporating bottom ash aggregates for internal curing. In this study, different types of fine aggregates, fine aggregate ratios, supplementary materials such as silica fume (SF) and colloidal nano-silica (CNS), and four types of steel fibers were considered to develop SHSLC. The self-compacting characteristics of concrete were evaluated by means of slump flow, J-ring flow, and V-funnel tests. The test results indicate that incorporation of SF and CNS had a positive effect on the mechanical properties, but 4% incorporation of CNS decreased workability and strength due to the agglomeration of mixture. The addition of steel fibers improved compressive strength, and flexural toughness of SHSLC, but reduced the flowability and passing ability with increased fiber contents. Due to the internal curing from coarse bottom ash, significant reduction of autogenous shrinkage up to 33% was observed, whereas 7% for drying shrinkage. The incorporation of fibers reduced the autogenous and drying shrinkage up to 31% and 22% compared with non-fiber reinforced concrete, respectively. Finally, the autogenous shrinkage behavior was simulated with several models in the literature, and a model for high strength self-compacting lightweight concrete with and without fibers considering equivalent age was proposed.

Microstructure and Water Retention Kinetics in Autogenous Cured Self-Compacting Concrete Blends Using Super Absorbent Polymer.

This research aimed to determine how a super absorbent polymer affects the microstructural characteristics and water retention kinetics of a new composite made by substituting granite pulver (GP) and fly ash (FA) for cement. Understanding the mechanics of water movement is crucial for comprehending the effectiveness of autogenous curing. Several experiments were conducted to analyze the water mitigation kinetics of super absorbent polymer (SAP) in the hydrating cement paste of autogenous cured self-compacting concrete (GP-ACSSC) mixtures. In the first hours following casting, water sorptivity, water retention, and hydration tests were carried out. The effects of various concentrations of SAP and GP, which was utilized as an alternative cement for the production of sustainable concrete that leads to reduction in carbon footprint, on the autogenous cured self-compacting concrete with reference to the abovementioned properties were explored. The investigation showed that releasing the curing water at a young age, even around the beginning of hydration, allowed homogenous and almost immediate distribution of water across the full cured paste volume, which improved the water retention kinetics. Compared to the control mixtures, the addition of SAP up to 0.6% and the substitution of cement with GP up to 15% had favorable impacts on all water kinetics parameters.

Synergistic effects of recycled plastic aggregate and nano-silica on the elevated temperature and durability performance of self-compacting concrete

A new approach to reusing plastic waste in construction is by incorporating recycled plastic aggregates (RPA) in concrete. However, this technique negatively affects concrete properties. Previous studies have treated RPAs to mitigate this issue, but none have investigated enhancing the properties of self-compacting concrete (SCC) made with RPAs through the addition of nano-silica (NS) particles. This study aims to explore the properties of SCC with RPAs modified by NS. Sixteen mixtures were tested in three stages: evaluating the impact of NS on SCC performance, examining various RPA percentages, and using the optimal NS percentage to improve negatively affected SCC mixtures. NS particles replaced cement at 1%, 2%, and 3% in the first stage, while RPAs replaced natural fine aggregate (NFA) at fractions of 5%, 10%, 15%, 20%, 30%, and 40% in the second stage. Compressive strength was assessed over different periods and at elevated temperatures. Durability performance, including water absorption, acid attack, electrical resistivity, chloride permeability, and bulk electrical conductivity, was extensively studied. The results revealed that the addition of the optimal NS percentage effectively restored the most degraded properties of SCCs, making it a safe and effective technique for utilizing RPAs in SCC mixtures without compromising concrete performance.

Bond conditions in wall-type steel-reinforced self-compacting concrete element

This work looks into the variations in the bond conditions between steel and self-compacting concrete (SCC). The bond conditions along the height and span of wall elements are compared with column and beam elements. The study involved pull-out bond tests and compressive strength tests on module samples derived from a wall element having 2240 × 160 × 1600 mm in length, width and height, respectively. SCC mixture casting was performed from a single point located at one of the short edges of the element. The pull-out tests were conducted on samples having deformed steel rebars with a diameter of 16 mm. We examined in detail the top-bar effect occurring across the entire wall element. The bond strengths at different heights within the element were compared to that at its bottom. On average, the reduction in the bond strength was 22%, and as much as 39% at the top of the wall. The bond strength increased by an average of 13% within the end part of the element as a result of the rebound effect. The phenomenon of bond strength reduction with an increasing depth of concrete under a reinforcing bar seems universal across different types and heights of elements.

Full Characterization of Self-Compacting Concrete Containing Recycled Aggregates and Limestone.

This work deals with the study of self-compacting concretes (SCCs) containing recycled aggregates (RAs) recovered from demolition waste and limestone filler as a partial replacement for natural aggregates (NAs) and cement, respectively. Four mix designs were developed and characterized in both the fresh and hardened states. In the fresh state, the properties studied included slump, sieve stability, and t500 viscosity. In the hardened state, the properties studied were compressive strength and porosity at 15 h and 28 days, thermogravimetric analysis, and durability tests involving freeze-thaw cycles and accelerated carbonation. The results indicate the RAs lead to a decrease in slump flow. However, the substitution rate of aggregate replacement does not affect the compressive strength. This can be attributed to the optimized mix design, resulting in all SCC mixtures achieving the same compressive strength class of 30-35 MPa. As for the durability tests, the incorporation of recycled aggregates modifies the behavior of the concrete during freeze-thaw cycles. Throughout the 300 freeze-thaw cycles, all concrete mixtures exhibited a mass loss accompanied by a slight strain increase, but the materials remained visually intact. Additionally, the carbonation depth is strongly influenced by the rate of aggregate replacement due to changes in the microstructure, particularly in porosity.

Long term durability assessment of self-compacting concrete made with crushed recycled glass and metakaolin

Sustainable production in construction industry can only be possible through a proper management and conservation of limited natural resources such as fine aggregates. This challenge can be tackled by efficient utilization of discarded waste material such as glass in production of sustainable concrete. This paper investigates the use of crushed recycled glass (CRG) and metakaolin (MK) in development of durable self-compacting concrete (SCC). Four groups of SCC mixtures were prepared using different proportions of CRG (0–50%), while keeping MK concentration equal to 0%, 4%, 8% and 12%. Durability performance of SCC was accessed using water absorption, sorptivity, chloride ion permeability, drying shrinkage, water penetrability under pressure and alkali-silica reaction (ASR) tests. As the CRG content increased, group 4 (having 12 % MK) was most efficient in improving drying shrinkage and pressurized water penetration results; whereas Group 1 (0% MK mixtures) exhibited a minimal change. Raising CRG content in the mix resulted in decrease of water absorption and chloride ion penetration for all groups with group 4 exhibiting maximum reduction. ASR testing revealed that incorporating glass at a higher concentration (40% and 50%) resulted in excessive expansion (more than prescribed limit of 0.1%), which can be suppressed by partially substituting cement with MK. FE-SEM and TGA analysis were carried out to understand the mechanism behind these changes, which revealed that the secondary hydration products formed by addition of MK in concrete can densify the pore structure and refine CRG particle-cement paste interfacial micro-crack width (was evident from FE-SEM micrographs), thus improving the durability of concrete. Indeed, simultaneous incorporation of CRG and MK proved to be advantageous for development of green SCC.