Use Of Fine Recycled Aggregates Research Articles

THE IMPACT OF RECYCLED FINE AGGREGATE ON SELECTED PROPERTIES OF CONCRETE

The use of recycled fine aggregate in the production of concrete mixes is one of the elements of a circular economy. However, it is important to ensure that such a modification does not significantly affect the durability of the produced concrete elements. One possible criterion to check whether this condition is met is the practical application of the concept of equivalent concrete properties. The presented studies analyzed the properties of concrete with multi-component cement CEM V/A (S-V) and with recycled fine aggregate. The conducted analyses of the research results showed that with a 15% replacement level of natural sand with recycled sand, it is possible to maintain durability characteristics compared to concrete using only natural sand.

Sustainable use of recycled fine aggregates in steel fiber-reinforced concrete: Fresh, flexural, mechanical and durability characteristics

Recycling construction waste is a viable tactic for advancing environmentally friendly building methods. With regard to concrete applications, the purpose of this research is to determine whether it is feasible to use recycled fine concrete aggregates (RFA) in lieu of natural fine aggregates (NFA) and to lessen the environmental impact of natural resource depletion and landfill space. A sustainable steel fiber-reinforced concrete was created by replacing NFA with RFA at the replacement ratio of 0 %, 50 %, and 100 %. Steel fibers (SF) were also included to mixes at three different contents of 0, 25 and 50 kg/m3 in order to further improve the qualities of the concretes. Thus, the aim of this paper is to appraise how the addition of FRA affects the mechanical, freeze-thaw, fresh, and non-destructive qualities of concrete. Nine concrete mixtures were cast, and tests were made to evaluate the following properties: flowability, fresh concrete unit weight, tensile and compressive strengths, elastic modulus, surface hardness, crack mouth opening displacement (CMOD), freeze and thaw performance, sulfate resistance and abrasion. Moreover, microstructure properties of concrete were also analyzed. The outcomes revealed that the mechanical, flexural, and durability performances of the concrete mixtures were enhanced by substituting RFA for NFA. The mixture with 50%RFA and 50 kg/m3 SF gained maximum compressive strength of 44.82 MPa which was 20.7 % greater than the reference mixture (RFA0F0). The mixture containing 100 % RFA and 25 kg/m3 SF had the highest elastic modulus and showed an approximately 33 % augmentation in elastic modulus as per the reference mixture. The mixture with 100%RFA and 50 kg/m3 SF exhibited the largest tensile strength indicating 60 % tensile strength enhancement as per the reference mixture. Combined use of RFA and 50 kg/m3 SF in concrete mixtures had the best abrasion and freeze-thaw resistance. SF incorporated concrete mixtures with RFA exhibited worse sulfate resistance. This study contributed significantly to global resource efficiency and environmental preservation by shedding light on the sustainable use of RFA and SF in the making of concrete. The results made important contributions to global research and promote environmentally friendly building methods all throughout the world.

Experimental Study of Mechanical Properties and Theoretical Models for Recycled Fine and Coarse Aggregate Concrete with Steel Fibers.

With diminishing natural aggregate resources and increasing environmental protection efforts, the use of recycled fine aggregate is a more sustainable approach, although challenges persist in achieving comparable mechanical properties. Exploration into the incorporation of steel fibers with recycled aggregate has led to the development of steel-fiber-reinforced recycled aggregate concrete. This study investigates the shrinkage performance and compressive constitutive relationship of steel fiber recycled concrete with different steel fibers and recycled aggregate dosages. Initially, based on different replacement rates of recycled coarse aggregate and different volume contents of steel fiber, experimental results demonstrate that as the replacement rate of recycled coarse aggregate increases, shrinkage also increases, while the addition of steel fiber can mitigate this effect. An empirical shrinkage model for steel fiber recycled concrete under natural curing conditions is also proposed. Subsequently, based on the uniaxial compression test, findings indicate that with an increasing replacement rate of recycled fine aggregate, the peak stress and elastic modulus of concrete decrease, accompanied by an increase in peak strain, and the addition of steel fiber limits concrete crack development and enhances its brittleness while the peak stress and strain of recycled fine aggregate concrete are enhanced. However, the steel fiber volume percentage has a negligible effect on the elastic modulus. A constitutive relationship for concrete considering the effects of recycled fine aggregate and steel fiber is also proposed. This finding provides foundational support for the influence patterns of steel fiber dosage and recycled aggregate ratio on the mechanical properties of steel fiber recycled concrete.

Effect of surface activity of recycled fine aggregates from clay bricks on the hydration, microstructure and chloride transport of concrete

Use of recycled fine aggregates from clay bricks (RFCB) in the preparation of eco-friendly concrete was proposed to tackle the river sand (RS) shortage and satisfy the construction demand. This study explored the surface activity of RFCB influenced by additional water and particle size distribution (PSD) on the hydration, microstructure and chloride transport of concrete. Compared to the RS, more silica and alumina released from RFCB depending on its PSD under alkaline environment was noted, which verified its appreciable surface activity. Overall, the presence of RFCB could hinder early hydration process because of the higher additional water, while the surface activity and nucleation effect supplied from finer RFCB were beneficial for the improvement of the hydration kinetics. Furthermore, inclusion of RFCB increased the total pore volume and porosity but performed better in refining the pore size distribution, thus decreased the average pore diameter. The surface activity of RFCB decreased CH content while increased chemical bond water and additional hydrates, thereby leading to enhancement of the compactness of interface, cement matrix and surface rim. More importantly, RFCB helped to decrease the chloride migration coefficient and electric flux. Though the surface activity of RFCB was beneficial in the strength development, it could not offset a deteriorated influence of porous RFCB with a higher replacement.

Use of recycled fine aggregates and recycled powders in sustainable recycled concrete

The shortage of sand and gravel resources has become a global problem. Processing construction and demolition wastes (CDW) into recycled materials and using them to prepare new concrete is conducive to the sustainable development of the construction industry. In terms of recycled coarse aggregate (RCA), relatively mature technical accumulation and industrialization have been formed, but the utilization technology of recycled fine fractions (RF), accounting for more than 40%, is still scarce. In this study, the feasible use of RF, including recycled fine aggregates (RFA) and recycled powders (RP), in recycled concrete was studied from the perspective of fresh properties (empirical and rheological). The results showed that the reduction in the slump was more prominent in Series with RFA than RP. The highest reduction was observed around 31.71% (30% RP) in Series I at 30mins; and 60.98% (50% RFA) in Series II in mix with 50% RFA, which is due to higher friction and higher interlocking behavior due to their rough surface and higher amount of attached mortar. The mix with RP showed the most significant increase in the static viscosity of 271% at 30% RP and 149% with 100% RFA replacement at 30 min of the time interval. Static yield stress increases greater with RP, which may have caused slump expansion to decrease over time. The friction from RFA's rough surface texture and the mix's extra SP and water content enhance dynamic yield stress and decrease viscosity. The study found that the incorporation of RP and FA in the mixes resulted in a noteworthy reduction in carbon emissions compared to the control mix. Specifically, RPC2 and RPC3 exhibited a decrease of 24.35% and 25.00%, respectively. It is also seen that using recycled fines can lead to stable, low-carbon concrete for leading to a sustainable automated construction industry.

Potential pozzolanic reactivity of recycled aggregates and waste powders as cement mortar component

ABSTRACT In this study, the use of recycled fine aggregates and waste powders in mortar was discussed, in which the pozzolanic reaction and the effect on strength properties of the resulting mortar were experimentally investigated. Test results showed that the compressive strengths of mortars with fine recycled brick and tile particles were lower than those of the control mortar at age of 7 days in the range of 72–92%, but reached 82–98% at age of 90 days, respectively. Because of the cement reduction, the mortars with waste powder cannot reach the strength level of the control mortar, and the strength of the mortars decreased with the increase in the cement replacement ratio. The strength efficiency of cement in mortar with the waste powders mortars increases with the increase of waste powder replacement ratio at later ages (56 and 90 days). This may be interpreted by the waste powders, being composed of major acidic oxides, could trigger the pozzolanic reaction to provide additional strength gains for mortar.

The Effect of Cementitious Materials on the Engineering Properties and Pore Structure of Concrete with Recycled Fine Aggregate.

With the rapid development of urbanization, the construction industry consumes a lot of cement and produces a large amount of construction waste. To overcome this situation, the rational use of recycled aggregate produced from waste concrete is one of solutions. In some countries, the building industry has approved the use of recycled coarse aggregates in concrete, with some limits. However, practically all existing standards and regulations prohibit the use of recycled fine aggregate (RFA) in concrete. Therefore, study on improving the performance of RFA concrete is vital. In this study, the effects of fly ash and GGBS on concrete with RFA were investigated. Compressive strength, pore structure, drying shrinkage and accelerated carbonation were tested. The correlation between the pore structure and properties of concrete was analyzed. The results show that adding fly ash and GGBS to RFA concrete increased its compressive strength, modified pore structure, reduced drying shrinkage, and even achieved higher compressive strength and lower drying shrinkage than normal concrete. The compressive strength was mainly affected by the capillary pores, and the carbonation was mainly affected by the gel pores.

Influence of Recycled Fine Aggregate Content on Properties of Soft Soil Solidified by Industrial Waste Residue.

The influence of recycled fine aggregate content on the properties of soft soil solidified by industrial waste residue was systematically studied. First, the addition of recycled fine aggregate may provide skeleton support, which was conducive to improving the solidification properties. Comparing the addition of recycled fine aggregate content and a composite solidification agent separately, the compressive strength increased 48.01 times and 1.32 times, respectively. Second, the composition and quantity of the hydration products were analyzed by X-ray diffraction (XRD) and thermal gravity analysis (TG/DTG). In addition to silicon dioxide and aluminum oxide, a number of new minerals, including hydrated calcium silicate, calcium hydroxide and ettringite, were produced under different recycled fine aggregate contents. The diffraction peak of hydrated calcium hydroxide was weak, which indicated that the crystallinity and relative content was low. The main reason for this was that it was consumed as the activator of the secondary hydration reaction of blast furnace slag. With the increase in recycled fine aggregate content, the total weight loss (hydration products, crystal water, impurities) increased significantly, at rates of 6.9%, 7.0%, 7.2%, 8.8% and 9.7%. The addition of recycled fine aggregate does not change the composition and quantity of the hydration products, and the increased weight loss in this part might be caused by the cement paste attached to the surface of the recycled fine aggregate. Finally, their microstructure was analyzed by scanning electron microscopy (SEM). Larger and more pores appeared in the solidification system with the increase in recycled fine aggregate, and a large amount of ettringite was prepared. An excess in recycled fine aggregate caused more pores, and the negative impact of too many pores exceeded the lifting effect of the aggregate, resulting in the decline of its mechanical properties. Therefore, there was a suitable range for the use of recycled fine aggregate, which was not more than 40%. In conclusion, recycled fine aggregate not only acts as a skeleton to improve solidification strength, but could also realize the comprehensive utilization of waste, which provided a new scheme for solid waste utilization and soft soil solidification.

Re-use of concrete/brick debris emerged from big earthquake in recycled concrete with zero residues

Nepal’s big earthquake in 2015 caused the accumulation of about 18.85 million tons of debris. Nepal Government was failed to address the management of demolished concrete/brick debris. The samples of concrete/brick debris were collected from the demolished building site and were disintegrated into coarse aggregates, fine aggregates, and powder materials. The recycled coarse aggregate was properly washed to eliminate the contaminants. Recycled bricks were used in both oven-dry (OD) and saturated surface dry (SSD) conditions. The use of 100% recycled coarse aggregate increased the slump from 3 cm to 5 cm and 28-day compressive strength was increased by 4.5%. The slump value of 20% SSD brick aggregate was increased to 5 cm with the decrease of compressive strength by 15% respectively. However, the use of 20% OD aggregate did not affect the slump value. It increased the strength by 10.1%. The use of recycled fine aggregate decreased the slump but the powder increased it. 10% and 20% recycled powder decreased the strength by 24.2% and 27.3% respectively. It was 7.3% and 8.9% respectively for the case of recycled fine aggregates. It is recommended to use the proposed recycling system to manage all remaining concrete/brick debris to make the cities clean and smart.

Performance enhancement of the recycled aggregate concrete properties using blended sand

Massive consumption of River sand in construction activities around the world led to the depletion of natural resources. Demolition waste was gaining popularity as a substitute for sand, but recycled fine aggregate(RFA) exhibits poor performance in concrete in terms of strength and workability. Therefore, the current study is a small attempt to improve the properties of RAC (Recycled aggregate concrete) by applying blending of RFA with copper slag (CS) to form blended sand. The study investigates the use of recycled fine aggregate (RFA) and blended sand (RFA + CS) separately in M−40 grade of concrete at 20%, 40%, 60%, 80% and 100% replacement levels of natural sand. Then concrete mixes are checked for workability (slump value) and compressive strength at 7, 14 and 28 days of curing. Results show that RFA concrete presents poor properties. In contrast, improved results were obtained in the case of blended sand concrete, which performed even better than reference samples prepared with river sand at 20% replacement of natural sand. Therefore, the study concluded that the enhancement in properties of recycled aggregate concrete(RAC) was achieved by using proper blending material in the required proportion with RFA. Further, the finding reveals that blended sand can use to enhance the strength and workability of concrete and have the potential as a sustainable alternative to river sand that brings sustainability to the construction sector.

Evaluation of mortars with combined use of fine recycled aggregates and waste crumb rubber

The use of secondary materials from waste or debris is a strategy that has been considered a starting point for the successful transition to the circular economy model. Globally, waste from concrete debris like disused tires is highly concerning, not only due to the magnitude of the existing volumes, which are increasing exponentially, but also to the environmental problems that their elimination causes. In the search for new, more ecological construction materials that can reduce the environmental impact produced by industry and the management of its waste, several studies are being conducted that incorporate and replace two or more wastes to prepare cement-based material so as to maximize the environmental benefits. Thus, alternatives are being sought that can reduce the extraction of natural resources, such as river sand. This study analyzed the use of two wastes as a replacement for natural sand in mortars, separately and in combination:fine recycled concrete aggregates (FRCA) in replacement percentages of 0%, 15% and 30% in weight, and crumb rubber in replacement percentages of 0%, 10% and 15% in volume. Mortars were characterized in terms of their physical and mechanical properties and durability. The results obtained reveal that the use of crumb rubber (CR) reduced the mechanical performance of the series. However, used in combination with FRCA, which presented a good mechanical performance, managed to decrease the mechanical results, where together with the excellent thermal behavior of the samples with CR, mortar mixtures were obtained as an alternative for the recycling of waste tires and the disposal of concrete aggregate waste.

Valorizing the use of recycled fine aggregates in masonry cement production

The recycled fine aggregate (RFA) fraction generated during crushing of waste hardened concrete is hardly recyclable in new construction and building materials. This paper assesses the suitability of grinding RFA for use as filler materials during masonry cement (MC) production, which helps valorizing this fraction and conserving natural limestone (LS) resources. For given Blaine fineness of 3100 ± 200 cm2/g, test results showed that the RFA requires about 38% less grinding energy than LS, given the porous and weakly bonded natures of the adhered cement paste. The air content, water retention, setting time, and compressive strength for LS and RFA-based MC mortars were pretty close to each other; i.e., all complying to EN 413-1 and ASTM C91 requirements. This practically reveals that the LS and RFA materials can be exchanged with each other during MC production, with limited effects on the fresh and mechanical cement properties. Nevertheless, the various MC components (i.e., clinker, LS, and RFA) should be ground separately in the grinding mill, and then blended together according to the specified MC strength class. This allows adjusting the comminution energy to each component hardness and avoids the formation of excessive fines that could result from the inter-grinding process.

Enhancement of mechanical properties of fly ash geopolymer containing fine recycled concrete aggregate with micro carbon fiber

In this study, the micro carbon fiber (CF) was used to enhance the mechanical properties of fly ash geopolymer containing fine recycled concrete aggregate (RCA). Natural river sand was replaced with RCA at 0, 50, and 100% by volume. The CF was used as additive material by incorporating into the mixture at 0, 0.1, 0.2, and 0.3% by weight of fly ash. The results showed that the CF enhanced the mechanical properties of geopolymer containing RCA through the increased nucleation sites for geopolymerization reaction and the bridging effect of the fiber. For the mix with 100% RCA, the incorporation of 0.2% CF resulted geopolymer mortar with higher compressive and splitting tensile strengths. For the flexural strength and surface abrasion resistance, best results were obtained with the use of 50%RCA with significant improvement in both flexural strength and surface abrasion resistance. The incorporation of CF thus increases the use of recycled fine aggregate without resort to natural fine aggregate.

Preliminary Analysis of the Use of Construction Waste to Replace Conventional Aggregates in Concrete

This work aims to study the influence of using construction and demolition waste in the replacement of coarse and fine aggregate to produce recycled aggregate concrete (RAC). A moderate compressive strength concrete made with usual fine and coarse aggregate was used as a benchmark material. Compressive and split tensile tests were performed using 120 cylindrical concrete specimens with 150 mm diameter and 300 mm length. Four-point flexural tests in reinforced beams made with conventional concrete and RAC were performed. The results obtained showed that the use of recycled fine aggregates, in both percentages of substitution investigated—50% and 100%—did not generate any deleterious influence on the values of compressive strength and split tensile strength of the RACs produced. Tin fact, the mechanical strengths of RACs produced with recycled fine aggregate were equal or higher than those from the reference concrete. The same behavior was not observed, however, when the recycled coarse aggregate was used. For this case, decreases in concrete mechanical strengths were observed, especially in compressive strength, with values around 35% lower when compared to the reference concrete. Tensile mechanical tests results confirmed the excellent behavior of all RACs made with replacement of usual fine aggregates by recycled. Bending tests performed in reinforced RAC beams had as objective to evaluate the deformation profile of the beams. The obtained results showed that RAC beams with full replacement of usual fine aggregate by the recycled aggregates have presented little changes in the global behavior, an aspect that encourages its use.

Response and modeling of axially-loaded concrete-filled steel columns with recycled coarse and fine aggregate

Recycled aggregate concrete-filled steel tube (RACFST) could be a practical structural application of recycled aggregate concrete (RAC) with fine recycled aggregate (FRA). Despite its great potential, limited attention has been devoted to the compressive response of RACFST with FRA. This study investigates the effects of FRA on the structural response of RACFST with different coarse recycled aggregate (CRA) replacement ratios (rC), and how FRA influences the confinement effect of RACFST. Fifty-four RACFST specimens were tested to failure with different FRA and CRA replacement ratios (rF and rC), concrete strengths (fcm) and effective steel ratios (α). Experimental results show that FRA and CRA have a significant compounding effect (i.e., FRA effect is different at varying rC) on the strain at the maximum load (ε0) of RACFST. Unlike CRA which has an insignificant influence on the confinement effect, the use of FRA significantly reduces the confinement of RACFST. The test results were used to modify the existing mathematical expressions for normal concrete-filled steel tube (CFST) to predict the stress-strain relationships for RACFST. The predicted results matches well with the available test data.

On the Development of a Technical Specification for the Use of Fine Recycled Aggregates from Construction and Demolition Waste in Concrete Production.

The possibility of using recycled aggregates from construction and demolition waste (CDW) in concrete is rather widely agreed upon when it comes to the use of coarse recycled aggregates. However, this is not the case when fine recycled aggregates (FRA) are considered, as it is deemed that these seriously impair the behaviour of concrete. Hence, this work presents a technical specification proposal for the use of FRA from CDW in concrete, to attempt to fill this gap in legislation. The specification is based on a wide collection of experimental results, from which it is shown that for low incorporation ratios (up to 25%), the properties of concrete with FRA from CDW are comparable to those of a reference concrete. The intended international scope of the specification is ensured by the fact that FRA from CDW are typified by composition (percentage of concrete, masonry, glass, etc.) rather than by geographical origin or construction type. It is shown that, after typifying the FRA and assuming, as per design, the acceptable percentage losses (relative to a reference concrete) of mechanical, durability-related and long-term physical properties, if the maximum incorporation ratios proposed of each type of FRA are used, the variation of properties remains within the limits established.

Durability studies on recycled fine aggregate concrete

The use of recycled fine aggregates (RFA) from construction and demolition(C&D) waste in concrete gaining importance from past decades. The presence of excessive fines and old adhered mortar in RFA, make mediocre properties of RFA concrete. The influencing properties of RFA concrete on different durability aspects lacks research data. Several studies have quoted the unfavourable performance of RFA in concrete particularly in respect to shrinkage, permeability, chloride penetration. Whereas, most of the durability studies of recycled coarse aggregates (RCA) concrete are well established. Therefore, the aim of this paper is to study the judicious use of RFA in concrete and its performance in different durability environments. RFA is one of the major alternative materials that is produced in huge amount and can be utilized effectively with some additional care. Alkali silica reaction, porosity, water permeability, acid-alkaline immersion, drying shrinkage, rapid chlorine penetration, surface electrical resistivity and carbonation along with their microstructural changes were evaluated to understand the influence of RFA in concrete. The outcomes exhibited that increment in RFA content in concrete negatively distress its durability. Nevertheless, as the age of the concrete increases the resistance to water, chlorine and carbonation resistance increases. The optimum replacement of river sand by RFA in concrete was 30% (RFA30). The reduction in shrinkage and porosity were in order of 14%, and 25% respectively. The RFA30 was 21.25% higher resistance to chlorine penetration than control concrete. Micrograph illustrated highly distorted CSH and weak ITZ and voids, when 100% replacement of river sand with RFA after immersing them in concentrated HCl, H2SO4 at 90 days. However, dense microstructure with less voids were observed after immersing in NaOH.

Effect of recycled fine aggregate on properties of mortar: a factorial design approach

The influence of the use of recycled fine aggregates as replacement natural fine aggregate on properties of cement mortar has been investigated using the procedures of general factorial design. In this study, the incorporation percentage of recycled fine aggregate (RFA %) and water-cement (w/c) ratio are selected as factors and compressive strength and water absorption as responses. The levels of RFA (%) are fixed at 0%, 10%, 20%, and 30% and the levels of other factor w/c ratio was kept at 0.4, 0.45, and 0.5. Compressive strength (CS) and water absorption (WA) of mortar mixes prepared with varying levels of aforementioned factors are selected responses. Analysis of variance (ANOVA) has been performed over test results for analysing the significance of factors and their interaction on selected responses. The results of study depict that the selected factors are significantly affecting the responses; however, no substantial influence of interaction between the factors on responses are observed.

Durability of crushed fine recycled aggregate concrete assessed by permeability-related properties

One of the paths taken towards the greening of concrete has been through the use of recycled aggregates as replacement of their natural counterparts. After decades of studies, the partial use of coarse recycled aggregates is considered acceptable, yet the use of fine recycled aggregates (FRAs) is highly restricted in concrete production. This restriction is based on technical concerns; for example, the presence of FRAs in concrete allegedly hinders its performance beyond acceptance. More recently, several studies seem to point to different conclusions regarding the use of FRAs in concrete: if the materials’ specificities are considered during the mixing and composition design of concrete, FRAs may be considered a viable source for concrete production even if, from a durability point of view, they might still present some limitations. This paper presents some results for the durability of FRA concrete by assessing the materials’ permeability properties. Different compositions were cast and tested for durability-related properties, such as water absorption by immersion, capillary absorption, carbonation, chloride penetration and electrical resistivity. The results show that the use of FRAs in concrete production is viable, meaning that it is possible to use FRAs in concrete production without neglecting the existing criteria for structural purposes.

Influence of fluidity on mechanical and permeation performances of recycled aggregate mortar

Abstract The use of recycled fine aggregates in making mortar is an effective measure to increase the social and ecological values these days due to the pressing issues associated with the over-exploitation of natural sand as well as disposal of construction and demolition wastes. To counteract the synergetic effects of W/C ratio, recycled fine aggregates quality and its content, fluidity was considered as parameter to formulate the recycled aggregate mortar. The experimental results of this investigation elucidate the effectiveness of fluidity on mechanical and permeation performances of recycled aggregate mortar. A comparison with the outcomes of conventional mortar is also presented. The experimental outcomes reveal that, recycled aggregate mortar requires additional amount of water to attain the same fluidity of controlled mortar due to inferior characteristics of RFA, such as high initial water absorption and volume of voids with in mortar. The setting characteristics of recycled aggregate mortar were influenced by the fluidity, recycled fine aggregates quality and its content and their setting times were earlier than that of controlled mortar. However, recycled aggregate mortar corresponding to the fluidity of 110 ± 2.5 mm and 160 ± 2.5 mm attained lower strength characteristics, lower pulse velocity value, higher permeable void content, higher water absorption by immersion and higher sorptivity than those associated to the fluidity of 135 ± 2.5 mm. Therefore, recycled aggregate mortar associated to the moderate fluidity of 135 ± 2.5 mm is feasible and exhibits better mechanical and permeation performances.