Recycled Lightweight Research Articles

Development of low carbon concrete and prospective of geopolymer concrete using lightweight coarse aggregate and cement replacement materials

The use of Ground Granulated Blast-furnace Slag (GGBS) as an alternative cement replacement material in combination with conventional coarse aggregate have been successful in the production of near green concrete. Undoubtedly, GGBS has exhibited good cementitious attributes, however, there are concerns with slow strength development and workability owing to its non-pozzolanic activities as well as some degree of porosity notwithstanding the sustainability potential. Therefore, this study presents a lytag based geopolymer lightweight concrete with high strength development, improved mechanical properties and reduced embodied carbon. To further improve and enhance the potential production of green concrete, complete replacement of conventional coarse aggregate with a recycled lightweight aggregate from industrial waste was carried out. The geopolymer precursors consisted of sodium hydroxide, sodium silicate, GGBS and silica fume to optimize the performance of the concrete at 60–80% cement replacement for a target design mix of 20, 30, 40, and 50 MPa. The performance of lytag based geopolymer concrete was compared with that of non-geopolymer lytag based concrete (control samples). The results show a 42% increase in compressive strength for the geopolymer lightweight concrete and a 22% increase in ultimate compressive strain which is an indication of improved moment of resistance in structural design. The results also show a 46–61% reduction in embodied carbon for the use of non-geopolymer lytag based concrete and 69–77% reduction for lytag based geopolymer concrete. The geopolymer concrete between 7 and 63 days of loading increases by 0.55% in creep strain compared with increases of 2.81% for non-geopolymer lytag based concrete and reduction to 27.96% for the normal weight concrete. Modulus of Elasticity reduces with age of loading for the geopolymer concrete during creep at 0.39% compared to reduction of 1.93% for non-geopolymer lytag based concrete and increase of 12% for the normal weight concrete.

Characteristics of Lightweight Concrete Fabricated with Different Types of Strengthened Lightweight Aggregates

The vast majority of different waste building units have negative environmental impacts around the world. Crushed building units can be recycled and utilized in the concrete industry to solve these problems and maintain natural resources. This study investigated the feasibility of employing crushed autoclaved aerated concrete (CAAC) and crushed clay brick (CCB) as a lightweight aggregate (LWA) to fabricate environmentally friendly recycled lightweight concrete (LWC). In addition, a lightweight expanded clay aggregate (LECA) was also used as an LWA, namely to study how the high porosity of an LWA can adversely affect the properties of LWC. Through the experimental program, all types of LWAs were pre-treated and strengthened with two cementitious grouts, and then the performance of the produced LWC was assessed by determining the slump of fresh concrete, the dry density, the unconfined compressive strength, and the splitting tensile strength at ages of 3, 7, 28, and 56 days. The laboratory results revealed that both CCB and CAAC can be reused as full substitutions for normal-weight coarse aggregate to manufacture LWC with appropriate properties. The obtained data show that the properties of an LECA, CCB, and CAAC were improved, and the porous structure can be strengthened by pre-treatment and coating with grouts. In the same way, the mechanical performance of produced LWC is also enhanced.

Highly secured authentication and fast handover scheme for mobility management in 5G vehicular networks

The Fifth Generation (5 G) networks exhibit high flexibility and diversity in their design and deployment strategies. Transitions between base stations (BSs), heterogeneous networks (HetNets) and other cellular networks provide significant vulnerabilities and expose users to substantial risks associated with cybersecurity attacks. This article evaluates current handover authentication methods in the context of 5 G networks while proposing a set of security criteria for handover authentication. This study presents a novel authentication technique called SHK (Secure Handover Key) that utilizes SDNs (Software Defined networks). The proposed scheme integrates recycled lightweight dynamic key cryptography and combines security features such as perfect forward secrecy and robustness to leakages. The significance of the proposed approach is assessed in terms of computations, communications, signals, and energy costs on 5 G mobility applications and Vehicular Communication Networks (VCNs). The scheme employed in this study demonstrates enhanced security measures and improved changeover performance compared to conventional schemes.

Sawdust-Based Concrete Composite-Filled Steel Tube Beams: An Experimental and Analytical Investigation

Incorporating waste byproducts into concrete is an innovative and promising way to minimize the environmental impact of waste material while maintaining and/or improving concrete’s mechanical characteristics and strength. The proper application of sawdust as a pozzolan in the building industry remains a significant challenge. Consequently, this study conducted an experimental evaluation of sawdust as a fill material. In particular, sawdust as a fine aggregate in concrete offers a realistic structural and economical possibility for the construction of lightweight structural systems. Failure under four-point loads was investigated for six concrete-filled steel tube (CFST) specimens. The results indicated that recycled lightweight concrete performed similarly to conventional concrete when used as a filler material in composite steel tube beams. The structural effects of sawdust substitution on ultimate load and initial stiffness were less substantial than the relative changes in the material properties, and the ultimate capacity of the tested samples decreased moderately as the substitution percentage of sawdust increased. Moreover, the maximum load capacity was observed to decrease by 6.43–30.71% for sawdust replacement levels between 5% and 45.1% across all tested samples. Additionally, when using lightweight concrete with 5% sawdust, the moment value of the CFST sample was reduced by 6.4%. Notably, the sawdust CFST samples exhibited a flexural behavior that was relatively comparable to that of the standard CFST samples.

Push-out test of waste sawdust-based steel-concrete – Steel composite sections: Experimental and environmental study

Considering their cost and strength benefits over traditional reinforced concrete, steel–concrete–steel (SCS) structural systems have become increasingly popular. The ultimate strength, ductility index, failure modes, cost, environment, and energy absorption capacities of SCS filled with sawdust concrete were explored in this study to better understand the impact of using SCS in modern structural projects. Wood chips were employed as an infill material to minimize the section's weight and expense. Push-out monotonic loading was used to inspect the mechanical characteristics of six SCS samples. One sample was built using the typical normal-weight concrete core to serve as a standard, while the other samples were made with changed core materials by partially replacing the fine aggregate with sawdust. The discovered failure modes are explained and analyzed, with the ultimate strength, ductility, and energy absorption index. The research suggests that recycled lightweight infill concrete has a slightly lesser effect on the performance of the SCS than conventional concrete (less than 10 %). It was observed that the percentage of sawdust had an impact on the specimens' compressive strengths, with the strength decreasing from 65 to 48 MPa as the sawdust levels climbed from 7.27 % to 29.63 %. The energy absorption of the SCS sawdust concrete was lower than the control sample. Conversely, the ductility index of the control specimen was higher than those of waste wood SCS samples. The results also revealed that using sawdust material has a positive impact on the economic and environmental systems.

Study on the Light Weight Geopolymer Concrete Made of Recycled Aggregates from Lightweight Blocks

Abstract: This study studied the properties of lightweight geopolymer concrete that contained recycled lightweight block aggregate. The recovered blocks are classified as coarse aggregates after being crushed.To reduce greenhouse gas emissions, geopolymers have the potential to be used to create new, environmentally beneficial materials. A new class of building materials called geopolymer concrete (GPC) has a replacement for regular Portland cement concrete (OPCC) and are capable of revolution in the construction sector. The impact of On the strength characteristics, alkaline activators have been investigated. Used fly ash was obtained for this study from a nearby thermal power plant. Samples were produced from low-calcium fly ash through activation with a combination of sodium silicate solution and sodium hydroxide. Fly ash was added to the concrete with a ratio of 0.5. Using a mix proportion and 5,10,15 Molar of sodium hydroxide solution, geopolymer specimens were cast. The samples underwent compression testing. test with ambient temperatures for curing. From the analysis ofLiterature suggests that the combination of the aforementioned ingredients is healing. FromAccording to a review of the literature, the amalgamation of the aforementioned elementshas a favorable effect on the strength properties of geopolymer concrete. Since fly ash is viewed as a waste product, geopolymer concrete made from low-calcium fly ash costs less than Portland cement concrete as a result. Lowcalcium fly ash-based geopolymer concrete has good compressive strength, very little drying shrinkage and minimum creep, great resistance to sulphate attack, and superior acid resistance.

Characterisation of Recycled Quarzitic and Plastic Aggregates for Sustainable Lightweight Screeds

The present contribution reports the results of the experimental investigation on a sustainable lightweight cementitious composite material, in which virgin sand is partially substituted by a very fine composite powder retrieved from the manufacturing process of kitchen and sanitary ware. In order to obtain lightweight structural concrete suitable for screeds, the mixture is completed by the addition of recycled polyethylene terephthalate aggregates and lightweight glass spherules. First, physical and morphological properties of the raw powder are thoroughly investigated. Then, the mechanical response of the composite is assessed by means of three-point bending tests and uni-axial compression tests. The conglomerates exhibit promising mechanical performance, thus being regarded as possible candidate for innovative and sustainable structural applications.

Development and characterization of lightweight aggregate recycled from construction and demolition waste mixed with other industrial by-products

The amount of construction and demolition waste and industrial by-products are increasingly high in Vietnam recently. The recycling of these wastes as new construction materials is an effective solution for sustainable development. This paper presents a method for the recycling of construction and demolition waste and other industrial by-products, such as fly ash and slag in Vietnam to produce lightweight aggregate . Experimental results show that masonry wastes including brick and mortar as well as fly ash are suitable materials for producing lightweight aggregates with a granule density of less than 1000 kg/m3 with the optimum sintering temperatures and the residence time in the range from 1220 °C to 1250 °C and, 6 to 9 min, respectively. These recycled lightweight aggregates can be used as valuable substitutes for natural aggregates to make lightweight concrete for new structures and therefore contribute to the construction industry's sustainability.

Mechanical Properties of Barchip Polypropylene Fibre-reinforced Lightweight Concrete Made With Recycled Crushed Lightweight Expanded Clay Aggregate

Concrete is one of the broadly used construction materials in the construction industry. This research intends to recommend the replacement of conventional coarse aggregates with recycled lightweight expanded clay aggregate (LECA) which offers several advantages such as lightweight, low cost, and easy availability. Lightweight concrete (LWC) offers numerous benefits; therefore, many researchers are using lightweight aggregate to produce lightweight structural composites concrete to compensate heavy loads by reducing the concrete self-weight due to lower density of lightweight concrete, improving in thermal properties and fire resistance, saving the cost of transportation and handling of precast units in the site. Different percentages (0, 0.15, 0.30, and 0.45%) of volume fraction of barchip polypropylene (BPP) fibre have been incorporated to improve the mechanical properties of lightweight aggregate concrete (LWA) concrete. In this study, the mixture of crushed lightweight expanded clay aggregate (CLECA) and barchip polypropylene (BPP) fibre have been used to achieve compressive strength between 28 and 37 MPa at 28-days with an oven-dry density ranged between 1900 and 2000 kg/m3. It is found that the inclusion of BPP fibres at an optimum volume fraction concrete enhances the compressive strength, splitting tensile strength and modulus of rupture. The compressive strength of the lightweight aggregate concrete containing 0.45% volume fraction of BPP fibre (CLLWAC-BPP0.45%) had achieved the highest compressive strength of 37 MPa at 28-days with a significant increment of about 31% compared to plain concrete. Hence, the findings of this research showed that the development of eco-friendly lightweight structural composites can be used as an alternative solution for conventional lightweight concrete, infrastructure and marine fields application.

Compressive Mechanical Properties of a Novel Recycled Aggregate Concrete with Recycled Lightweight Aggregate

A novel recycled aggregate concrete was prepared by replacing the natural aggregate with recycled lightweight aggregate. Subsequently, the mechanical properties and compressive stress‐strain constitutive relation of the recycled lightweight aggregate concrete (RLWAC) were explored. For this purpose, the recycled lightweight aggregate (RLWA) replacement ratio (0%, 25%, 50%, 75%, and 100%) was selected as a variable, and the compressive strength of 15 cube and 30 prism specimens was evaluated. The failure morphology of the specimen was subsequently characterized, along with the cubic compressive strength, axial compressive strength, peak strain, ultimate strain, and other performance indices. The influence of the replacement ratio for the specimen indices of the RLWAC was also analyzed. It was observed that the dry apparent density of RLWAC decreased gradually on increasing the replacement ratio. Compared with 0% replacement ratio, a decrease of 6.50%, 11.39%, 21.84%, and 27.54% was observed, respectively. On enhancing the RLWA replacement ratio, the compressive strength, peak strain, and ultimate strain of RLWAC were observed to be gradually reduced. As the replacement ratio was increased from 75% to 100%, the peak strain was noted to decrease the most by about 6.8%. As the replacement ratio was increased from 50% to 75%, the ultimate strain decreased the most by about 14.2%. Based on the experimental findings, the functional relationships of the strength indices and the conversion value of each strength index with the replacement ratio were also established. Finally, based on the model proposed by the existing model, the stress‐strain equation of RLWAC was developed, and the fitting results were observed to be in good agreement with the test results.

Recycling of the end-of-life lightweight aggregate concrete (LWAC) with a novel approach

This work proposed an environmental-friendly approach for high-grade recycling of the end-of-life LWAC. The mechanical performance of mortar with recycled powder (RP), mortar with recycled fine aggregate (RFA) and recycled lightweight aggregate concrete (RLWAC) were investigated. Microstructure of mortar and RLWAC was detected to identify the properties of interfacial transition zone (ITZ). RP can prolong the setting of reference cement and the 10% dosage is better than 2% in not only retarding effect but also strength development. An appropriate content of RFA is beneficial for compressive strength. Replacing standard sand with 10% RFA increases the compressive strength of mortar by approximately 10%. However, a high replacement content (40%) of RFA brings about a reduction of compressive strength. The amount of RFA below 20% will not increase the dry shrinkage of mortar. The compressive strength of RLWAC is reduced by 10% RLWA but it has a significant increase when the replacement content reaches 30%. In mortar with RFA, cracks initiate from the ITZ of new sand and new paste and few cracks generate from old paste and old sand. Four types of ITZ that have distinct features are observed between cement paste and LWA in RLWAC.

Seismic performance of structures composed of T-shaped and L-shaped recycled concrete columns and lightweight infill walls

ABSTRACT In this paper, a structure composed of a T- or L-shaped recycled concrete column frame (RCCF) and lightweight infill wall (LIW) with a herringbone brace has been proposed to investigate its seismic behavior. Two T-shaped and two L-shaped full-size experimental models of the structure have been built and tested under low-cyclic loading conditions. Consequently, bearing capacity, stiffness, ductility, hysteretic behavior, energy dissipation, and failure characteristics of each test specimen have been analyzed, identifying structure parts prone to damage and failure, understanding their yield mechanisms, and lastly providing constructive recommendations for the structural design. Studies show that the bearing capacity, ductility, and comprehensive seismic behavior of T- or L-shaped lattice-reinforced RCCF-LIW structures with a herringbone brace have been significantly improved. For the engineering practice, it is necessary to strengthen the performance of the herringbone brace-frame beam joint.

Investigation some properties of recycled lightweight concrete blocks as a fine aggregate in mortar under elevated temperature

The main objective of this study is to assess the effect of utilizing waste material (lightweight concrete blocks) as partial replacing of fine aggregate. To do so, seven mix designs were utilized to prepare 168 mortar specimens (84 cubes and 84 prism) with the replacement ratios of 10% and 20% waste material fine aggregate instead of traditional sand at different temperatures of 24 ᵒC, 200 ᵒC, 400 ᵒC, and 600 ᵒC. The combination of two type waste material together in one mixture (waste lightweight concrete blocks with waste clay bricks or waste lightweight concrete blocks with waste glass) was tested with and without fiber (1% polypropylene fiber by volume). The physico-mechanical properties of mortar specimens involving flow rate, fresh density, weight loss, compressive strength, flexural strength and water absorption were determined. The hardened tests were implemented at age of 28 days. The results demonstrated fresh density experienced a decrease when utilizing recycled materials especially waste lightweight concrete block at 20%. Compressive strength showed improving with replacing normal sand by waste materials and that enhancing was clear at high temperatures. The specimens that utilized waste lightweight concrete block with waste glass aggregate illustrated clearly reduction in water absorption comparing with control mix at different temperatures.

Structural Lightweight Concrete Containing Recycled Lightweight Concrete Aggregate

In this paper, Structural Lightweight Concrete (SLC) containing Recycled Lightweight Aggregate (RLA) is described. Damaged lightweight concrete was used as RLA by crushing it into fine particles, and used to replace fine limestone aggregate of up to 45% by weight. To enhance the strength development of SLC, silica fume and a superplasticizer were incorporated into the mixture. The compressive strength, density, water absorption, porosity, modulus of elasticity, and thermal conductivity of the concrete were tested. The results show that SLC with satisfactory 28-day compressive strengths of between 16.5 and 30.5 MPa, and densities of between 1600 and 1800 kg/m3, were obtained. The compressive strength, modulus of elasticity, and thermal conductivity decreased with an increase in RLA content, and the water absorption and porosity increased. Water absorption of 3.28–7.87%, porosity of 6.82–13.87%, modulus of elasticity of 16.5–25.2 GPa, and thermal conductivity of 0.49–0.75 W/mK were found to be within the working range of SLC.

Experimental study on the effect of volcanic residue on the performance of recycled lightweight aggregate concrete

Recycled lightweight aggregate concrete prepared with waste brick recycled light aggregate has high water absorption, large apparent density and poor frost resistance. The technical measures of regen-erating lightweight aggregate concrete with modified waste bricks from volcanic slag are put forward. The effects of volcanic slag on the properties of waste lightweight aggregate concrete were studied. The experi-mental results show that volcanic slag can significantly reduce the apparent density of recycled lightweight aggregate concrete and improve its frost resistance.

Study on conversion relationships of compressive strength indexes for recycled lightweight aggregate concrete

In order to study cube compressive strength and axial compressive strength of recycled lightweight aggregate concrete(RLAC), and conversion relationship between the two, with the replacement rate of recycled lightweight coarse aggregate as change parameters, 15 standard cube test specimens and 15 standard prism test specimens were produced to carry out the test. Then compressive strength of test specimens were measured, and the law of different replacement rate of recycled lightweight coarse aggregate influencing compressive strength of RLAC was analyzed, as the method of statistical regression adopted, the conversion relationships between of cube compressive strength and axial compressive strength of RLAC was obtained. It is shown that compressive strength of RLAC are lower than compressive strength of ordinary concrete; and that compressive strength of RLAC gradually decreases as replacement rate of recycled lightweight coarse aggregate increases; as well as, the conversion relationship between axial compressive strength and cube compressive strength of RLAC is different from ordinary concrete; based on the experimental data, conversion relationship formula between compressive strength indexes of RLAC was established. It is suggested that the replacement rate of recycled lightweight aggregate should be controlled within 25%.

Preliminary Study of Pressed Lightweight Geopolymer Block Using Fly Ash, Portland Cement and Recycled Lightweight Concrete

In this research, the properties of pressed lightweight fly ash geopolymer concrete block containing Portland cement and recycled lightweight concrete aggregate. The recycled lightweight concrete aggregate (RLCA) was crushed and classified as coarse aggregate (CA), medium aggregate (MA) and fine aggregate (FA). The RLCA with CA : MA : FA of 30 : 30 : 40 by weight was used to reduce the weight of concrete block. Lightweight geopolymer concrete block was produced from lignite fly ash, NaOH, Na2SiO3, RCLA and PC. The lightweight geopolymer concrete blocks with 28-day compressive strengths between 2.0 and 14.1 MPa and densities between 1130 and 1370 kg/m3 were obtained.

Pressed lightweight fly ash-OPC geopolymer concrete containing recycled lightweight concrete aggregate

In this paper, the density and strength of lightweight fly ash-OPC geopolymer concrete containing recycled lightweight concrete aggregate (RLCA) were studied. Waste lightweight concrete was crushed and used as lightweight aggregate. Geopolymer cement was produced from the blend of high calcium fly ash and ordinary Portland cement (OPC), sodium hydroxide and sodium silicate. The fly ash was replaced with OPC at the dosages of 0, 5, 10 and 15% by weight. The results showed that lightweight geopolymer concretes with densities between 1200 and 1500kg/m3 and 28-day compressive strengths between 4.5 and 17.5MPa could be fabricated. The incorporation of RLCA reduced both density and strength of lightweight concrete. The addition of OPC enhanced the strength development of geopolymer concrete but also increased the density. The optimum OPC content for strength development was 10%. The NaOH concentration of 10M, sodium silicate/NaOH ratio of 1.0, OPC content of 10% by weight of fly ash, liquid/solid binder ratio of 1.4, RLCA/solid binder ratio of 1.8 and curing temperature of 60°C were recommended for the lightweight fly ash-OPC geopolymer concrete.

Feasible Use of Biomass Bottom Ash as Addition in the Manufacture of Lightweight Recycled Concrete

Biomass is a renewable energy source that is increasingly being used worldwide. However, because of recent increases in production, waste products from biomass combustion are becoming a relevant environmental and economic problem. Other wastes from the construction and demolition sectors have been extensively studied. For this, several research studies have been performed to study the mechanical and some durability properties in concrete manufacturing with recycled concrete and mixed aggregates from different construction origins. In previous works, the lower density of recycled mixed aggregates (RMA) and biomass bottom ash (BBA) with respect to natural aggregates was studied. This feature can be exploited for the production of construction elements that require the use of low-density materials, such as lightweight concrete. For this, the aim of this work was to study the influence of the use of recycled mixed aggregates and biomass bottom ash, as replacements for the natural aggregates, on the mechanical behaviour, durability properties and environmental risk of recycled lightweight concrete. Several replacements for natural aggregates through recycled aggregates and biomass bottom ash were applied in the manufacture of lightweight concretes. To study the concrete behaviour, properties such as density, absorption, compressive strength, flexural strength, UPV, water penetration and drying shrinkage were measured. Due to the incorporation of RMA and BBA, a decrease of the density and mechanical properties of the recycled concrete manufactured was obtained with respect to the control mix. Therefore, the results showed the possibility of applying these types of recycled materials in lightweight concretes for their application in specific constructive elements. Through this study the possibility of reuse of waste and industrial by-products (RMA and BBA) that have so far been accumulated mainly in landfill is demonstrated. The positives results show the possibility of manufacture of lightweight concrete with these by-products, achieving a material with a lower density and mechanical requirements that comply with the current standards for concrete.

Using recycled aggregates in green roof substrates for plant diversity

Extensive green roofs are becoming a popular tool for restoring green infrastructure in urban areas, particularly biodiverse habitats such as post-industrial/brownfield sites. This study investigated the use of six recycled lightweight aggregates and combinations of them in green roof growing substrate, to determine their effectiveness for enhancing plant abundance and species diversity. In two separate experiments, we examined the roles of substrate type and depth on the establishment of a perennial wildflower mix over a 15-month period. We found that some of the alternative substrates are comparable to the widely used crushed red brick aggregate (predominantly found in commercial green roof growing substrate) for supporting plant establishment. For some materials such as clay pellets, there was increased plant coverage and a higher number of plant species than in any other substrate. Substrates that were produced from a blend of two or three aggregate types also supported higher plant abundance and diversity. Generally, increasing substrate depth improved plant establishment, however this effect was not consistent across substrates. We conclude that recycled materials may be viable constituents of growing substrate for green roofs and they may improve green roof resilience, through increased plant cover and diversity. The results could provide evidence to support the construction of mosaic habitat types on single roofs using various substrate blends.