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A special issue of Sustainability (ISSN 2071-1050). This special issue belongs to the section "Sustainable Materials".

Deadline for manuscript submissions: closed (29 May 2023) | Viewed by 29109

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Special Issue Editor

Dr. Ahmed Salih Mohammed

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Guest Editor

1. College of Engineering, University of Sulaimani, Kurdistan Region, Sulaimani-Kirkuk Rd, Sulaymaniyah 46001, Iraq
2. College of Engineering, American University of Iraq, Sulaimani, Kurdistan region, Sulaimani-Kirkuk Rd, Sulaymaniyah 46001, Iraq
Interests: cement; concrete; soil mechanics; rock mechanics; sustainability; modeling
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Dear Colleagues,

Quality assurance (QA) procedures and cost-effective construction materials are commonly used during construction. They may also require several measurements using point-wise density measurement tools. The required tests are destructive in nature and a source of some performance issues, such as potholes that reduce the project's lifespan. In addition, any quality issues that are identified during this process cannot be easily rectified. Furthermore, the above QA methods are time-consuming to perform and are only helpful in determining the cost of the project. The Environmental Protection Agency defines sustainable construction as “the practice of creating structures and using environmentally responsible and resource-efficient processes throughout a building’s lifecycle, from siting to design, construction, operation, maintenance, renovation, and deconstruction.” The concept of sustainability, at its core, considers the resilience of the natural environment and the practices that impact it.

However, sustainability issues extend to community health, social equity, and wealth distribution—and the construction sector is in a position to make significant impacts on all of these areas. These objectives will only grow more intertwined as the world continues to urbanize.

The construction industry sits between a rock and a hard place. The Earth’s urbanizing, growing population is placing enormous demands on the construction sector; since 2007, more than half of the world’s population has lived in cities and this figure is projected to rise to 60% by 2030. To meet this surging human demand, global construction output is projected to grow by a staggering 2.5 trillion square feet by 2060. At the same time, concerns about climate change and dwindling natural resources place increasing pressure on construction firms to build green and reduce their environmental impact.

According to the World Green Building Council, the construction and operation of buildings account for 36% of global energy use and 39% of energy-related CO2 emissions.

This Special Issue of Sustainability is therefore dedicated to comprehensive reviews and original studies on the resource use (e.g., non-renewable energy consumption), environmental impacts (e.g., global potential warming), technical performance (e.g., durability and mechanical), and cost of cementitious materials and concrete containing less common, non-conventional materials. Additionally, techniques used or any attempts (listed below, though not exhaustively) to reuse the recycled materials as a cement replacement and reduce concrete resource use and environmental impacts are welcome.

Prof. Dr. Ahmed Salih Mohammed
Guest Editor

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Keywords

eco-friendly mortars and concrete
soil stabilization
mechanical and durability-related properties
supplementary cementitious materials
nanomaterials
unconventional reinforcement
recycled aggregates
alkali activation
natural or by-product fibers
industrial wastes
cement waste factories

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40 pages, 12470 KiB

Open AccessArticle

Soft Computing and Machine Learning-Based Models to Predict the Slump and Compressive Strength of Self-Compacted Concrete Modified with Fly Ash

by Dilshad Kakasor Ismael Jaf

Sustainability 2023, 15(15), 11554; https://doi.org/10.3390/su151511554 - 26 Jul 2023

Cited by 5 | Viewed by 1440

Abstract

Self-compacted concrete (SCC) is a special type of concrete; it is a liquid mixture appropriate for structural elements with excessive reinforcement without vibration. SCC is commonly produced by increasing the paste volume and cement content. As cement production is one of the huge factors in releasing CO₂ gas into the atmosphere, by-product materials such as fly ash are utilized as a cement replacement in concrete. In addition to the positive environmental impact, fly ash can maintain an excellent fresh and mechanical property. Incorporating fly ash into self-compacted concrete is widely applied in practice. However, its application is frequently limited by a lack of knowledge about the mixed material gained from laboratory tests. The most significant mechanical property for all concrete types is compressive strength (CS); also, the slump flow diameter (SL) in the fresh state is a crucial property for SCC. Hence, developing an accurate and reliable model for predicting the CS and SL is very important for saving time and energy, as well as lowering the cost. This research study proposed a projection of both the CS and SL of SCC modified with fly ash by three different model approaches: Nonlinear regression (NLR), Multi-Linear regression (MLR), and Artificial Neural Networks (ANN). In this regard, two different datasets were collected and analyzed for developing models: 308 data samples were used for predicting the CS, and 86 data samples for the SL. Each database included the same five independent parameters. The ranges for CS prediction were: cement (134.7–583 kg/m³), water-to-binder ratio (0.27–0.9), fly ash (0–525 kg/m³), sand (478–1180 kg/m³), coarse aggregate (578–1125 kg/m³), and superplasticizer (0–1.4%). The dependent parameter (CS) ranged from 9.7 to 81.3 MPa. On the other hand, the data ranges for the SL prediction included independent parameters such as cement (83–733 kg/m³), water-to-binder ratio (0.26–0.58), fly ash (0–468 kg/m³), sand (624–1038 kg/m³), coarse aggregate (590–966 kg/m³), and superplasticizer (0.087–21.84%). Also, the dependent parameter (SL) ranged from 615 to 800 m. Various statistical assessment tools, such as the coefficient of determination (R²), Root Mean Squared Error (RMSE), Mean Absolute Error (MAE), Objective value (OBJ), and Scatter Index (SI), were used to evaluate the performance of the developed models. The results showed that the ANN model best predicted the CS and SL of SCC mixtures modified with fly ash. Furthermore, the sensitivity analysis demonstrated that the cement content is the most effective factor in predicting the CS and SL of SCC mixtures. Full article

(This article belongs to the Special Issue Recent Developments in Environmentally Sustainable and Cost-Effective Construction Materials)

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19 pages, 6056 KiB

Open AccessArticle

Mechanical Properties of Polyamide Fiber-Reinforced Lime–Cement Concrete

by Mohammad Mostafa Jafari, Soheil Jahandari, Togay Ozbakkaloglu, Haleh Rasekh, Danial Jahed Armaghani and Aida Rahmani

Sustainability 2023, 15(15), 11484; https://doi.org/10.3390/su151511484 - 25 Jul 2023

Cited by 3 | Viewed by 1442

Abstract

Lime–cement concrete (LCC) is a type of lime-based concrete in which lime and cement are utilized as the main binding agents. This type of concrete has been extensively used to construct support layers for shallow footings and road backfills in some warm regions. So far, there has been no systematic research conducted to investigate the mechanical characteristics of polyamide fiber-reinforced LCC. To address this gap, LCC specimens were prepared with 0%, 0.5%, 1%, and 2% of polyamide fibers (a synthetic textile made of petroleum-based plastic polymers). Specimens were then cured for 3, 7, and 28 days at room and oven temperatures. Then, the effects of the fibers’ contents, curing conditions, and curing periods on the mechanical characteristics of LCC, such as secant modulus, deformability index, bulk modulus, shear modulus, stiffness ratio, strain energy, failure strain, strength ratio, and failure patterns, was investigated. The results of the unconfined compressive strength (UCS) tests showed that specimens with 1% fiber had the highest UCS values. The curing condition and curing period had significant effects on the strength of the LCC specimens, and oven-cured specimens developed higher UCS values. The aforementioned mechanical properties of the LCC specimens and the ability of the material to absorb energy significantly improved when the curing period under the oven-curing condition was increased, as well as through the application of fibers in the mix design. Based on the test results, a simple mathematical model was also established to forecast the mechanical properties of fiber-reinforced LCC. It is concluded that the use of polyamide fibers in the mix design of LCC can both improve mechanical properties and perhaps address the environmental issues associated with waste polyamide fibers. Full article

(This article belongs to the Special Issue Recent Developments in Environmentally Sustainable and Cost-Effective Construction Materials)

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18 pages, 4224 KiB

Open AccessArticle

Factorial Mixture Design for Properties Optimization and Modeling of Concrete Composites Incorporated with Acetates as Admixtures

by Ammar Ali Abed, Alireza Mojtahedi and Mohammad Ali Lotfollahi Yaghin

Sustainability 2023, 15(13), 10608; https://doi.org/10.3390/su151310608 - 5 Jul 2023

Cited by 3 | Viewed by 1445

Abstract

Nowadays, admixtures are used with the aim to provide strength and durability to concrete with less water use. New and low-cost admixtures gained a large amount of consideration to mitigate the problems associated with concrete’s durability and service life without upsetting its strength properties. The current work investigates the effect of three types of acetates on the workability, density, and compressive strength of concrete, which is used in structures of the Iraqi ports that suffer from corrosion damages and deterioration owing to the aggressive marine environments. Potassium acetate (KA), calcium acetate (CaA), and ethyl acetate (EA) are incorporated with different doses (1.38–5.6 wt.% of cement) in concrete mixtures using different water/cement ratios (0.48–0.54) based on an espoused central composite experimental design. The experimental results confirmed that the average workability increased with increasing the acetate dose, particularly with CaA. The density and compressive strength of 28 days of water-cured mixtures increased with increasing acetate dose following the order: Ca > K > Ethyl acetate and decreased with increasing w/c ratio. The high rise in compressive strength and workability linked to control mixtures was 30.8% and 77.3% as well as 15.7% and 64.3% for the mixtures incorporated with 5.6 wt.% CaA and KA, respectively. While it was 14.2% and 58.3% for the mixtures incorporated with 3.5 wt.% EA. RSM was employed to optimize and model the design and hardened properties of concrete mixtures. ANOVA results predicted the same trend, which was obtained from the experimental results. The mathematical models were valued with high-regression coefficients. The highest compressive strength of 42.68 MPa has been achieved for a concrete mixture of 0.48 w/c ratio by the incorporation of 5.1 wt.% CaA through a model with R² 96.97%. The relatively low-cost acetate admixtures, particularly CaA, seemed promising for the fabrication of concrete with outstanding properties. Full article

(This article belongs to the Special Issue Recent Developments in Environmentally Sustainable and Cost-Effective Construction Materials)

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20 pages, 4533 KiB

Open AccessArticle

Experimental Study and Modeling of the Fracture Behavior, Mechanical Properties, and Bonding Strength of Oil Well Cement

by Cumaraswamy Vipulanandan, Ahmed Salih Mohammed and Praveen Ramanathan

Sustainability 2023, 15(12), 9566; https://doi.org/10.3390/su15129566 - 14 Jun 2023

Cited by 5 | Viewed by 1570

Abstract

This study aimed to analyze the outcomes of stress intensity factor (K_I) and new bond strength tests of oil well cement (class H) with a water-to-cement ratio (w/c) of 0.38. Mechanical properties of the cement paste, such as the compressive and flexural strengths, were tested and qualified at 1, 7, and 28 days of curing. The relationship between the elastic modulus and axial strain using the differential of the Vipulanandan p-q model for the cement paste was obtained. The stress intensity factor of the cement paste was between 0.3 and 0.6 MPa.m, and the crack tip opening displacement (CTOD) was between 2.798 and 6.254 µm at three different ratios between the initial notch height (a) and the thickness of the beam (d) (a/d = 0.3, 0.4, and 0.5). The nonlinear Vipulanandan p-q model was used to model the compressive and flexural stress–strain behavior of the cement at three curing times. The bonding strength between the cement and steel tube representing the casing in the borehole was 0.75, 1.89, and 2.59 MPa at 1, 7, and 28 days respectively. Full article

(This article belongs to the Special Issue Recent Developments in Environmentally Sustainable and Cost-Effective Construction Materials)

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16 pages, 2521 KiB

Open AccessArticle

Synergistic Effect of Micro-Silica and Recycled Tyre Steel Fiber on the Properties of High-Performance Recycled Aggregate Concrete

by Muhammad Talha Amir, Sobia Riaz, Hawreen Ahmed, Syed Safdar Raza, Ahmed Ali A. Shohan and Saleh Alsulamy

Sustainability 2023, 15(11), 8642; https://doi.org/10.3390/su15118642 - 26 May 2023

Cited by 2 | Viewed by 1921

Abstract

The present research investigates the mechanical and physical properties of recycled aggregate concrete (RAC) modified with micro-silica (MS) and recycled tire steel fiber (RTSF). Natural coarse aggregates (NCA) were completely replaced by recycled coarse aggregates (RCA) to prepare RAC. High-strength RAC mixes were prepared by replacing 5% and 10% of Portland cement with MS. With each level of MS, RTSF was incorporated as 0%, 0.5%, 1 and 2% by volume fraction. In addition to mechanical properties, ultrasonic pulse velocity (UPV), electrical resistivity (ER), and water absorption (WA) of the mixes were also evaluated. The performance of modified RAC mixtures was also compared with plain natural aggregate concrete (PNAC). The experimental investigation revealed that RTSF substantially increased the tensile strength of RAC, whereas MS improved the durability of RTSF-reinforced RAC. RAC made with 1% RTSF and 10% MS showed 54% more splitting-tensile strength compared to the PNAC. The WA capacity of RAC incorporating 10% MS was 15–22% lower than that of the PNAC. Full article

(This article belongs to the Special Issue Recent Developments in Environmentally Sustainable and Cost-Effective Construction Materials)

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23 pages, 5746 KiB

Open AccessArticle

Effect of Silica Fume on Engineering Performance and Life Cycle Impact of Jute-Fibre-Reinforced Concrete

by Rawaz Kurda

Sustainability 2023, 15(11), 8465; https://doi.org/10.3390/su15118465 - 23 May 2023

Cited by 6 | Viewed by 1912

Abstract

The brittleness of plain concrete (PC) is a result of its lack of tensile strength and poor resistance to cracking, which in turn limits its potential uses. The addition of dispersed fibres into the binding material has been demonstrated to have a positive impact on the tensile properties of PC. Nevertheless, using new or engineered fibres in concrete significantly increases the overall cost and carbon footprint of concrete. Consequently, the main obstacle in creating environmentally friendly fibre-reinforced concrete is the traditional design process with energy-intensive materials. This study investigated how the engineering properties and life cycle impact of concrete were influenced by varying the volume fractions of jute fibre (JF). The impact of incorporating silica fume (SF) as a partial replacement of Portland cement was also studied. The studied parameters included mechanical behaviour, non-destructive durability indicators, and the life cycle impact of concrete using JF and SF. The efficiency of JF in mechanical performance improved with the increase in age and with the addition of SF. When using both SF and 0.3% JF, there was an improvement of around 28% in the compressive strength (CS). When 0.3% JF was added, in the presence and absence of SF, the splitting tensile strength (STS) improvement was around 20% and 40%, respectively. The addition of JF improved the residual flexural strength (FS) and flexural ductility of PC. The SF addition overcame the drawbacks of the poor resistance of JF-reinforced concrete (JFRC) against water absorption (WA) and rapid chloride ion penetration (RCIP). Full article

(This article belongs to the Special Issue Recent Developments in Environmentally Sustainable and Cost-Effective Construction Materials)

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20 pages, 2859 KiB

Open AccessArticle

Rheological Characterization of Ground Tire Rubber Modified Asphalt Binders with Parallel Plate and Concentric Cylinder Geometries

by Salih Kocak

Sustainability 2023, 15(4), 2880; https://doi.org/10.3390/su15042880 - 5 Feb 2023

Cited by 3 | Viewed by 1606

Abstract

Recently, scrap tire rubber-modified asphalt binders and pavements have been the preferred choice of state DOTs and parties involved due to the desirable engineering, as well as economic and environmental impacts. Rheological and mechanical properties of rubber modifications have been the main focus of researchers for the last couple of decades. This paper investigates the rutting potential, fatigue cracking resistance, and continuous performance grade (CPG) changes of waste tire rubber-modified, original, and aged asphalt binders. The CPG of asphalt binders is determined at high, intermediate, and low temperatures. A Delta T Critical comparison of the binder was carried out to establish a relationship between measured parameters. Linear amplitude sweep (LAS) tests at equi-stiffness temperatures were conducted to discover the fatigue life of all binders while the multiple stress creep recovery test is performed to assess the high-temperature rutting performance of asphalt binders as per the Superpave performance grading system at accepted regional (58 °C) as well as high PG temperatures. In addition, parallel-plate geometry and concentric cylinder geometry were used with the Multiple Stress Creep Recovery (MSCR) test to discover the impact of discrete particles available in crumb/ground tire rubber-modified asphalt binders as per standards. The results show that rubber modifications improved the base binder’s rutting resistance and continuous PGs without adversely affecting the fatigue cracking resistance. Based on the mathematical expressions developed, 2.71%, 7.82%, 12.94%, and 18.05% (by weight of binder), GTR modifications improved the high PG of the modified binders one, two, three, and four grade bumps, respectively. Similar linear correlations with R² 0.872 and 0.6 were established for continuous low and intermediate PGs, respectively. MSCR test results revealed that both 9% and 20% GTR modifications were achieved to enhance the H-grade traffic level of the original binder to E-grade. Full article

(This article belongs to the Special Issue Recent Developments in Environmentally Sustainable and Cost-Effective Construction Materials)

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24 pages, 5721 KiB

Open AccessArticle

Influence of Heat–Cool Cyclic Exposure on the Performance of Fiber-Reinforced High-Strength Concrete

by Ibrahim Hakeem, Md. Akter Hosen, Mana Alyami, Shaker Qaidi and Yasin Özkılıc

Sustainability 2023, 15(2), 1433; https://doi.org/10.3390/su15021433 - 12 Jan 2023

Cited by 6 | Viewed by 2127

Abstract

Sometimes civil engineering infrastructures have been constructed in hot and cold weathering regions such as desert areas. In such situations, the concrete is not only smashed by hot and cold processes but also spoiled by shrinkage cracking. Therefore, this study intends to examine the influence of heat–cool cycles on high-strength concrete comprising various fibers, such as natural date palm, polypropylene, and steel fibers, and their different volume percentages. The most popular technique for improving the structural behavior of concrete is fiber insertion. Fibers decrease cracking occurrences, enhance early strength under impact loads, and increase a structure’s ability to absorb additional energy. The main goal is to examine the effects of three different types of fibers on regular concrete exposed to heat–cool cycles. For each type of fiber, three dosages of 0.2%, 0.6%, and 1% were used to create high-strength concrete. After 28 days of regular water curing and six months of exposure to heat-and-cold cycles, all specimens were tested. The heat–cool cycles entailed heating for two days at 60 °C in the oven and cooling for another two days at room temperature. The results of the experiment showed that fiber reinforcement in concrete improves its strength and durability. The flexural strength was substantially improved by increasing the date palm, polypropylene, and steel fibers into the high-strength concrete with and without heat–cool cycles. Adding increments of date palm, polypropylene, and steel fibers into high-strength concrete revealed a significant improvement in energy absorption capacity in both cases, i.e., with or without the implementation of heat–cool cycles. Therefore, the natural date palm fibers might be utilized to produce sustainable fibrous high-strength concrete and be applicable in severe weathering conditions. Full article

(This article belongs to the Special Issue Recent Developments in Environmentally Sustainable and Cost-Effective Construction Materials)

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19 pages, 5421 KiB

Open AccessArticle

Influence of Vetiver Root Morphology on Soil–Water Characteristics of Plant-Covered Slope Soil in South Central China

by Xuan Wang, Zhenyu Li, Yongjun Chen and Yongsheng Yao

Sustainability 2023, 15(2), 1365; https://doi.org/10.3390/su15021365 - 11 Jan 2023

Cited by 4 | Viewed by 2373

Abstract

The soil–water characteristic curve is an important tool to evaluate the water-holding capacity of unsaturated soil. Plant roots can affect the matric suction of soil and the water-holding capacity and permeability of the soil. Therefore, the morphological characteristics of plant roots will lead to the difference in soil–water characteristics between soil slope and plant-covered slope. This study aims to investigate the effect of Vetiver root morphology on soil–water characteristic curves of plant-covered slope soil. The hydrological effect of the root distribution on the root–soil system was also discussed. The results showed that: (1) The root surface area index (RAI) and root volume ratio (R_v) of each soil section of the vetiver root system varied with depth in accordance with the Gaussian function distribution; (2) In the process of natural drying, the matric suction generated within the root system is significantly higher than that generated by evaporation of bare soil in the same soil layer. The ability of vegetation soil to enhance soil matrix suction increases with the increase of soil root surface area index; and (3) The α and n values of the SWCC model decreased with the increase of R_v (root volume ratio of soil), while the air entry value increased. Under the same water content, the matric suction corresponding to vegetation soil is significantly greater than bare soil. In addition, the soil–water characteristic curve can be effectively predicted by combining the R_v of vegetated soils. Full article

(This article belongs to the Special Issue Recent Developments in Environmentally Sustainable and Cost-Effective Construction Materials)

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12 pages, 3432 KiB

Open AccessArticle

Meso-Mechanical Simulation of the Mechanical Behavior of Different Types of Steel Fibers Reinforced Concretes

by Haifeng Wang, Yicheng Jiang and Ling Liu

Sustainability 2022, 14(23), 15803; https://doi.org/10.3390/su142315803 - 28 Nov 2022

Viewed by 1559

Abstract

Introducing steel fibers into traditional concrete can improve its mechanical properties and crack resistance, but few studies have considered how the steel fiber shape and the bond-slip effect between fibers and matrix affect the mechanical behavior of concrete. This paper establishes a three-dimensional representative volume element (3D RVE) of steel fiber-reinforced concrete (SFRC) with random distribution, different shapes, and different interfacial strengths of steel fibers using Python, Abaqus and Hypermesh. Uniaxial tensile behaviors and failure modes of the SFRC are systematically simulated and analyzed. The results show that when the interfacial strength of steel fiber/concrete is changed from 1 to 3 MPa, the tensile strength of the SFRC increases accordingly. When the interfacial strength is greater than 3 MPa, it has no effect on tensile strength. Additionally, if the interfacial strength is 1 MPa, the tensile strength of the SFRC with end-hook steel fibers is increased by 7% when compared to the SFRC with straight steel fibers, whereas if the interfacial strength reaches 2.64 MPa (strength of pure concrete), the fiber shape has little effect on the tensile strength of the SFRC. Moreover, the simulation results also show that interfacial damage dominates when the interfacial strength is less than 1 MPa, and the crack propagation rate in the end-hook steel fiber-modified SFRC is lower than that in a straight steel fiber-modified SFRC. Therefore, this research reveals that using end-hook steel fibers can improve the strength of the SFRC under low interfacial strength, but the ideal strength of the SFRC can be achieved only by using straight fibers when the interfacial strength between steel fibers and concrete is relatively high. Full article

(This article belongs to the Special Issue Recent Developments in Environmentally Sustainable and Cost-Effective Construction Materials)

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29 pages, 7047 KiB

Open AccessArticle

Performance of Self-Compacted Geopolymer Concrete Containing Fly Ash and Slag as Binders

by Aryan Far H. Sherwani, Khaleel H. Younis, Ralf W. Arndt and Kypros Pilakoutas

Sustainability 2022, 14(22), 15063; https://doi.org/10.3390/su142215063 - 14 Nov 2022

Cited by 19 | Viewed by 2648

Abstract

Geopolymers can replace cement and help reduce the environmental impact of concrete construction, but research is needed to ensure their mechanical properties, durability and practicability. The aim of this investigation is to examine the influence of ground granulated blast furnace slag (slag) content on the performance, at the fresh and hardened states, of fly ash (FA) based self-compacted geopolymer concrete (SCGC). For this purpose, four SCGC mixtures containing 450 kg/m³ of total binder were examined. The alkaline-to-binder ratio was 0.5 for all mixes. FA was substituted with slag at 0%, 30%, 50%, and 100% of the total binder content. The fresh properties in terms of flowability, passing ability, viscosity, and segregation resistance, as well as the mechanical properties in terms of compressive strength and splitting tensile strength, were quantified. The durability behavior of SCGC was also studied to determine sorptivity and long-term free drying shrinkage. The results confirm that slag adversely affects the workability of SCGC mixtures except for the resistance to sieve segregation. Performance of SCGC in hardened states is in general enhanced with slag inclusion but at increased shrinkage strain. Predictions of splitting tensile strength were made using the ACI 318, ACI 363, Eurocode CEB-FIB, and Lee and Lee models. The ACI 363 and Eurocode CEB-FIB models were found to be inaccurate, except for the 30% slag mix. Predicted values obtained from the Lee and Lee model were very close to the actual values of the FA-based SCGC mix. The results of this work could lead to more sustainable concretes using geopolymers instead of OPC. Full article

(This article belongs to the Special Issue Recent Developments in Environmentally Sustainable and Cost-Effective Construction Materials)

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16 pages, 5918 KiB

Open AccessArticle

Enhancing the Performance of Recycled Aggregate Concrete Using Micro-Carbon Fiber and Secondary Binding Material

by Syed Safdar Raza, Muhammad Fahad, Babar Ali, Muhammad Talha Amir, Yasser Alashker and Ahmed Babekar Elhag

Sustainability 2022, 14(21), 14613; https://doi.org/10.3390/su142114613 - 7 Nov 2022

Cited by 4 | Viewed by 1973

Abstract

In this study, the effect of micro-carbon fiber on the properties of concrete incorporating recycled coarse aggregate at three different levels, i.e., 0%, 50%, and 100% by volume replacement of natural coarse aggregate, was studied. Carbon fiber was incorporated at a dosage of 0.5% by volume fraction. The effect of silica fume or micro-silica on the efficacy of fiber reinforcement was also investigated. Studied parameters include important mechanical properties, such as compressive strength, splitting tensile strength, and flexural strength, and physical/quality parameters such as water absorption capacity and ultrasonic pulse velocity. The results showed that the mechanical and durability performance deteriorates with the increasing percentage of recycled coarse aggregate. Carbon fiber can significantly improve the tensile properties of recycled aggregate concrete. The combination of carbon fiber and silica fume proved to be highly useful in addressing both mechanical and durability concerns simultaneously. Concrete made with 50% recycled coarse aggregate, 8% silica fume, and 0.5% carbon fiber yielded 20% greater tensile and flexural strength compared to the control mix. Likewise, concrete containing 100% recycled coarse aggregate with silica fume and carbon fiber yielded higher tensile strength compared to the control mix. Silica fume ameliorated the bonding between fibers and matrix and improved the overall efficacy of fiber reinforcement. Full article

(This article belongs to the Special Issue Recent Developments in Environmentally Sustainable and Cost-Effective Construction Materials)

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18 pages, 4241 KiB

Open AccessArticle

Acid Resistance of Alkali-Activated Natural Pozzolan and Limestone Powder Mortar

by Khaled A. Alawi Al-Sodani, Adeshina A. Adewumi, Mohd Azreen Mohd Ariffin, Babatunde Abiodun Salami, Moruf O. Yusuf, Mohammed Ibrahim, Ali H. AlAteah, Mohammed M. H. Al-Tholaia, Sami M. Ibn Shamsah and Mohammad Ismail

Sustainability 2022, 14(21), 14451; https://doi.org/10.3390/su142114451 - 3 Nov 2022

Cited by 1 | Viewed by 2620

Abstract

The development of sustainable, environmentally friendly alkali-activated binder has emerged as an alternative to ordinary Portland cement. The engineering and durability properties of alkali-activated binder using various precursor combinations have been investigated; however, no study has focused on the impact of high-volume natural pozzolan (NP) on the acid resistance of alkali-activated NP and limestone powder. Therefore, the current study assesses the impact of high-volume natural pozzolan (volcanic ash) on the durability properties of alkali-activated natural pozzolan (NP) and limestone powder (LSP) mortar by immersion in 6% H₂SO₄ for 365 days. The samples were prepared with different binder ratios using alkaline activators (10 M NaOH_(aq) and Na₂SO₄) combined in a 1:1 ratio and cured at 75 °C. NP was combined with the LSP at three different combinations: NP:LSP = 40:60 (AAN₄₀L₆₀), 50:50 (AAN₅₀L₅₀), and 60:40 (AAN₆₀L₄₀), representing low-volume, balanced, and high-volume binder combinations. Water absorption, weight change, and compressive strength were examined. The microstructural changes were also investigated using FTIR, XRD, and SEM/EDS characterization tools. Visual examination showed insignificant deterioration in the sample with excess natural pozzolan (AAN₆₀L₄₀) after 1 year of acid exposure, and the maximum residual strengths were 20.8 MPa and 6.68 MPa in AAN₆₀L₄₀ and AAN₄₀L₆₀ with mass gain (1.37%) and loss (10.64%), respectively. The high sulfuric acid resistance of AAN₆₀L₄₀ mortar was attributed to the high Ca/Si = 10 within the C-A-S-H and N-A-S-H formed. The low residual strength recorded in AAN₄₀L₆₀ was a result of gypsum formation from an acid attack of calcium-dominated limestone powder. The controlling factor for the resistance of the binder to acid corrosion was the NP/LSP ratio, whose factor below 0.6 caused significant debilitating effects. Full article

(This article belongs to the Special Issue Recent Developments in Environmentally Sustainable and Cost-Effective Construction Materials)

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Mechanical and Durability Properties of Self-Compacted Concrete Incorporating Waste Crumb Rubber as Sand Replacement: A Review

by Yarivan J. Zrar and Khaleel H. Younis

Sustainability 2022, 14(18), 11301; https://doi.org/10.3390/su141811301 - 8 Sep 2022

Cited by 11 | Viewed by 2702

Abstract

The lack of disposal facilities for waste tires from various vehicles is a major environmental and economic problem. Crumb rubber (CR) generated from waste tires can be used to partially replace fine natural aggregates in self-compacted concrete (SCC), lowering sand usage and protecting raw material resources. The main objective of this study is to summarize the influence of CR as a partial replacement for sand on the behavior of SCC. For this aim, 42 papers were selected out of 89 that were relevant to the objective of this study. The mechanical properties, i.e., compressive strength, flexural strength, splitting tensile strength, modulus of elasticity, and bond strength, as well as the ultrasonic pulse velocity (UPV), were all reduced by the insertion of CR into SCC mixtures. With the addition of CR, fracture energy decreases, but the ductility of concrete in terms of characteristic length can be enhanced. Meanwhile, replacing sand with CR can also reduce the durability performance of SCC, such as sorptivity, free-drying shrinkage, rapid chloride permeability, and depth of chloride penetration, except for the electrical resistivity, depth of carbonation, and impact resistance, which exhibit a positive tendency. Based on the results of the reviewed articles, predicted reductions in the strength of the SCC incorporating CR were also recommended. Moreover, the results of the reviewed studies were employed to develop empirical models that demonstrate the relations between various mechanical properties. Full article

(This article belongs to the Special Issue Recent Developments in Environmentally Sustainable and Cost-Effective Construction Materials)

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