Quantification of anthropogenic metabolism using spatially differentiated continuous MFA

Because of increasing waste production and public concerns about the environment, it is desirable to recycle materials from construction and building demolition. This study aimed to find a technique for producing recycled aggregate concrete obtained from construction and building demolition waste. Laboratory trials were conducted to investigate the possibility of using recycled aggregate from different sources in Iraq, as a partial replacement of both coarse and fine natural aggregates or one of them. Recycled aggregate consists of crushed concrete (CC) or acombination of crushed brick (CB) and crushed concrete (CC). The aggregate in concrete was replaced with 10%, 20%, 30% and 50% by weight of crushedconcrete (CC) or crushed brick (CB) and crushed concrete CC. Some of mechanical properties of recycled aggregate concrete as compared to those of conventional normal aggregate concrete are studied. Compressive strength and the splitting tensile strength were determined after curing for 7, 28, and 90 days while density was determined after28 days.From these results, it is reasonable to assume that the use of recycled concrete aggregate does not jeopardize the mechanical properties of concretefor replacement ratios up to 50%. The concrete prepared with the crushed concrete only as a partial replacement of natural aggregate achieved the highest strength values at 7, 28and 90 days. The results suggested that an aggregate that contains 50% recycled aggregate is optimum for producing recycled aggregate concrete The test results showed that the replacement of coarse or fine natural aggregate by recycled brick aggregate at the levels of 10,20,30 and 50% had little effect on the compressive strength of the specimens.

Conservation of natural resources, shortage of waste land and the high cost associated to treatment prior to disposal are driving growing interest in the recycling of construction and demolition waste materials (CDW). A challenging application for recycled CDW is the replacement of natural aggregates in the production of structural concrete. In the past few years several studies have examined the viability of this substitution. Although recycled aggregates are mostly heterogeneous, less dense and more porous than natural aggregates, satisfactory results have been attained by several authors regarding concrete workability, mechanical properties and durability. However, a systematic microstructural characterization of recycled aggregate concrete is still unaccomplished.In this context, the use of fine recycled concrete aggregates to replace natural fine aggregates in the production of structural concrete was tested, and attained microstructures are reported. The recycled aggregates were obtained from a standard concrete, produced and crushed under laboratorial conditions, thus allowing full control of concrete’s composition and setting. The used raw materials were natural aggregate (sand), recycled aggregates and Type 1 Portland cement. The substitution extent in the mixtures was 0, 10, 50 and 100 wt%; hydration was stopped at the ages of 9 h, 24 h, 96 h and 28 days. Microscopy study of the different mixtures enlightened the effect of the incorporation of recycled aggregates upon the formation and morphology of the different concrete hydration products. In this work, FEG-SEM (coupled with EDS microanalysis) was used on polished cross sections and fracture surfaces, to study the new mixtures. Focus was placed on the interfacial transition zone (ITZ) between cement matrix and aggregate.The natural aggregate-cement interfacial zone exhibits typical microstructural features of the ITZ of a normal strength concrete. After 28 days a large amount of well-crystallised C-S-H (and a small amount of poorly crystalline fibres) is present at the interface, together with CH deposits. Grains of unreacted clinker components (C2S, C3S, Ca2(Al,Fe), C3A) were also identified; ettringite crystals are barely present, even at the earlier hydration times. The ITZ is highly porous. Independently of the setting time, fracture takes place preferably along the surface between paste and aggregate, attesting the relatively loose nature of the interface. The structure of ITZ with recycled aggregates (Figure 1) is consistent with that observed in the reference natural concrete. Also, calculation based on EDS results rendered a lime to silica ratio (C/S) of 1.46 0.15, consistent with the typical 1.2-2.3 range. However, there are representative microstructural features that may contribute to variation of mechanical properties. Ettringite and plate-like CH hydrates are much more abundant, even at higher setting times. Overall porosity in the ITZ increases with the aggregate substitution extent; however maximum pore size decreases from approximately 30 µm for 0% substitution to 16 µm for 100 % substitution, as shown by image analysis results. In fresh natural concrete a water film forms around the aggregates, which is gradually replaced by the growing amount of hydration products. In recycled aggregates, active silica in residual cementitious materials reacts with the fresh cement hydration products. The secondary reaction products gradually fill the region, partially covering the recycled aggregates pore structure and creating additional interfacial bonding effects (Figure 2). In good agreement, it was observed that in substituted concretes fracture preferably takes place throughout the paste rather than throughout the contact surface.Concretes prepared with recycled aggregates exhibit typical microstructural features of the ITZ in normal strength concrete. Although porosity at the ITZ is affected by the extent of aggregate replacement, the interfacial bond is apparently stronger when recycled aggregates are used. This envisages an opportunity window for the development of increased strength Portland cement concretes.

The amount of concrete waste has increased significantly over the years due to reconstruction and the demolition of old buildings. Efforts have been made to utilise recycled aggregates to address some of the environmental problems associated with concrete waste and to promote the sustainability of concrete. A number of studies have been carried out to examine the mechanical properties, mixture design and structural performance of reinforced concrete (RC) beams comprising recycled aggregate. These studies report a reduction in strength, relatively large deflections and wider crack widths in reinforced recycled aggregate concrete beams compared with conventional concrete members. This study evaluates the flexural performance of RC beams with recycled aggregate and proposes strain limits for tension-controlled behaviour. Eight full-scale RC beams were cast using different types of recycled aggregate, including recycled fine and/or coarse aggregate, and using different grades of recycled aggregate that have different replacement ratios. This study also examines the flexural performance of reinforced recycled aggregate concrete beams in terms of crack patterns, flexural strength, ductility and failure modes. The flexural strength and material properties of the RC specimens with recycled aggregate are compared with the predicted values based on the ACI 318 code.

The reuse of recycled aggregates in the composition of concrete is a major challenge today in response to the high cost of construction and the environmental impact of waste This work evaluates the the physic-mechanical properties of concrete using recycled building demolition aggregates and bituminous concrete of pavements in the Republic of Congo. The idea was to check whether these recycled aggregates can have the same performance as when they were first used in concrete. From the results obtained, the recycled building aggregates have good mechanical strength according to the Los Angeles (32.5%) and Micro-Deval (29.3%) tests. Concrete made from building demolition aggregates (CRA1#) has a 28-day compressive strength of (28.8MPa), which is very close to that of the CNA# control concrete (31.11MPa). Concrete incorporating a mixture of asphalt concrete and building demolition aggregates (CRA3#) has a compressive strength of 20.32MPa. In terms of compressive strength, only CRA1# and CRA3# can be used as class C25 concrete for CRA1# and C20 for CRA3#.

In this article, attempt has been made to improve the performance of self compacting concrete using recycled coarse aggregate with adding of fly ash and glass fiber. Self compacting concrete has significant environmental advantages in compaction to the vibrated concrete. Absence of noise and vibrations during installing provides healthier working environment. In general, there is a scarcity of coarse aggregate throughout the world. Consumption of large amount of coarse aggregate affects the environment. For the purpose of reducing the consumption of coarse aggregate, a need for an alternative coarse aggregate arises. Recycled coarse aggregates are obtained from the demolition of buildings, culverts and also by-products from the industries. Hence, partial replacement of coarse aggregate by recycled aggregate is researched in this article, in view of consuming the ecological balance. SCC can also be used in situation where it is difficult or impossible to use mechanical compaction for fresh concrete, such as underwater concreting, cast in-situ pile foundations, machine bases and columns or wall with congested reinforcement. The self compacting concrete must meet the filling ability and passing ability with uniform composition throughout the process of transport and placing. Hence, Self compacting concrete demands large amount of powder (cementitious and pozzolanic materials) content and fines for its cohesiveness and ability to flow without bleeding and segregation. In this investigation, part of the cementitious material is replaced with pozzolanic material fly ash, and the properties of self compacting concrete in fresh and hardened states were studied. The increase of the percentage of the fly ash influences the bleeding and segregation in SCC. Hence, the addition of glass fibres can improve ductility, post crack resistance, energy absorption capacity and bleeding resistance. Taking these advantages into account a study was done. The various properties of the materials to be used in the experimental programme were determined. The specification of glass fibers and the advantages of using them along with concrete were studied. A detailed review of literature on glass fiber reinforced concrete was also done. The fresh and hardened properties of Self Compacting Concrete (SCC) using recycled coarse aggregate, fly ash with glass fibers were evaluated. The SCC mixtures are prepared with 40% of fly ash, 40% of recycled coarse aggregate and adding of 0.03% glass fiber. The strength test namely, Compressive Strength Test, Split Tensile Strength Test and Flexural Strength Test are carried out in this investigation. To test the characteristics of self compacting concrete, Slump cone test, J-ring test, L-box test were conducted to test the characteristic of self compacting concrete.

In Japan, it is forecasted that massive amounts of concrete waste material will be generated in the future as a result of demolition of many buildings, and expansion of the use of recycled aggregate is expected. In this study, it was verified the effect when relatively large amount of admixture is mixed, a combination of recycled fine aggregate of different quality and various admixtures, combination of each admixture in order to realize high strength and high durability by using recycled aggregate. The increase in the drying shrinkage ratio due to the deterioration of the recycled fine aggregate quality was larger than the fluctuation due to the admixture mixing ratio and the drying shrinkage ratio was distributed by forming a group for each quality of recycled fine aggregate. In the relationship between the pore volume and the compressive strength, when evaluated with pore volume of 2 μm or less in both cases, a good linear relationship could be confirmed. The relationship between the pore volume and the drying shrinkage rate was similar. Therefore, it was suggested that compressive strength and drying shrinkage ratio of mortar contained composite recycled fine aggregate and admixture could be predicted by evaluating with the pore volume of 2 μm or less.

This study's object is the concrete for general construction purposes that includes recycled aggregates formed from the processing and classification of residues from damaged or destroyed concrete buildings and structures, including those affected by military operations. The task addressed relates to the use of recycled concrete aggregates in conventional concrete, including the partial or complete replacement of natural aggregates. This area of research is aimed at devising a framework for the application of recycled concrete aggregates as a secondary raw material for the construction industry. This paper describes the characteristics of recycled concrete aggregates from recycled concrete structures. It was found that these aggregates have significant structural defects such as cracks and pores of various origins. They are also characterized by compositional heterogeneity and an increased content of weak grains, at around 18%. Meanwhile, the content of fine fractions is almost 34%. This naturally worsens the physical and mechanical properties of concrete made with such aggregates. However, a rational approach to using concrete mix components makes it possible to obtain concrete with appropriate performance characteristics, corresponding to class C20/25 (29.2 MPa) with 50% recycled concrete aggregate content. Using this type of aggregate could conserve natural minerals, tackle the issue of disposing of large-tonnage industrial waste, as well as significantly improve the potential for large-scale reconstruction in Ukraine. This may be achieved by accelerating the construction of damaged and destroyed housing stock and by obtaining a substantial raw material resource in the form of recycled aggregate as an alternative to local materials

Mortars produced with recycled aggregates from construction and demolition waste – analysis and construction site application

Recycled aggregate produced from demolished concrete and waste fresh concrete are classified into three types of quality using the density in oven-dry condition and water absorption ratio in Japan. Among the three types, compared to medium and high quality recycled aggregate (M and H), low quality recycled aggregate (L) can be produced with less energy and cost, and reduces the generation of fine powder by-product. However, concrete made from L have problems are it has lower strength and greater length change due to drying shrinkage. When considering the widespread use of L, these must be improved with less cost. For these modifications, we have been investigating the use of CO2 gas for accelerated carbonation technology. This technology focuses on the carbonation mechanism of concrete and blows CO2 gas on recycled aggregate to carbonate the cement paste that are attached mortar. It has been found that the physical properties of recycled fine aggregate are greatly improved using this technology. Therefore, to investigate the effect of recycled fine aggregate with accelerated carbonation on the hardened samples, we conducted tests on mortars made from that fine aggregate. It has shown that mortar has improved strength and durability due to the reduction of mortar voids attached on recycled fine aggregate. Especially, we reported that there was a large improvement in the out of specification of L (outside of L). There is a difference in amount of fine powder. L contains 3% fine powder, while outside of L contains 12%. We considered that the fine powder influenced the hardened samples. Therefore, in this study we focused on the granularity, such as fine powder of low quality recycled fine aggregate and conducted tests on mortar to compare the difference in the effect of accelerated carbonation modification technology.

The study reports results of tests, using only natural aggregates, of a control concrete and nine recycled aggregate concretes. The recycled aggregates were classified according to measured specific gravity and water absorption into three different types, namely: RS II for recycled fine aggregate having 2.36 specific gravity and 5.4% water absorption; RG III for recycled coarse aggregate having a 2.4 specific gravity and 6.2% water absorption; and RG I for recycled coarse aggregate having a 2.53 specific gravity and 1.9% water absorption. Both recycled coarse and fine aggregate replacement levels in separate mixtures were 30, 50, and 100%. For fresh concrete, slump loss and bleeding amount with time were recorded. For hardened concrete, there was also measurement of unrestrained shrinkage strain, moduli of rupture and elasticity, and compressive and tensile strengths. Fresh and hardened concrete properties tested, together with a literature-reported comprehensive database, were evaluated with respect to relative aggregate water absorption combined with recycled aggregate quality and volume. Hardened concrete properties, in addition, with different recycled aggregate replacement levels and quality were compared with ACI 318-05 design equation and empirical equality for natural aggregate concrete proposed by Oluokun, whenever possible. That the properties of recycled aggregate-containing fresh and hardened concrete were dependent on the aggregate relative water absorption was clearly shown in test results. In addition, the moduli of recycled aggregate concrete rupture and elasticity was lower than ACI 318-05-specified design equation, when relative aggregate water absorption is respectively above 2.5% and 3.0%.

Elastoplastic-damaged meso-scale modelling of concrete with recycled aggregates

Research in the field of recycled aggregate reuse in load-bearing structures is essential, as is the increase in awareness of the impact of construction on the environment. Using secondary raw materials also reduces landfilling and rock mining, and, from a practical point of view, this practice provides new materials for concrete. In this paper, the effect of using recycled aggregate concrete (RAC) on the basic properties of standard concrete is studied. Three types of concrete were studied: natural aggregate concrete (NAC) and two mixtures with 50 % and 75% replacement of natural coarse aggregates by recycled concrete aggregate. Results showed that using recycled aggregates reduces the mechanical properties of hardened concrete. The different properties of hardened concrete with a rate of recycled aggregate also impact the design process of the load-bearing structures of the buildings. The standard regulations in Slovakia allow using recycled concrete aggregate for up to 55% of all aggregates, but many designers do not trust this material. However, we cannot avoid using secondary raw materials in designing new structures in the future. The knowledge of recycled aggregate concrete presented in this paper provides directions for research and the concrete industry to focus on sustainable concrete products systematically.

Abundant waste is being generated in the demolition or renovation in the construction industry. Improper disposal of this waste creates environmental concern as they form huge landfills without proper use. This study examined the fresh, hardened, durability, and microstructural analysis of self-compacting concrete made with recycled aggregates (RA) and marble waste as a 10–30% granite substitute. Slump flow test, T50cm test, V-funnel test, and L-box test were conducted on the fresh concrete. Compressive strength, split tensile strength, flexural strength, microstructural properties, and carbonation of the hardened concrete were determined. The physical tests revealed that though the recycled aggregates and marble waste do not have properties as good as the natural coarse aggregates, recycled aggregates were observed to exhibit a better strength than marble waste. SCC with marble waste had better fresh state properties than those with recycled aggregates. SCC with recycled aggregates had better-hardened state properties than those with marble waste. It can be inferred from the microstructural analysis that the utilisation of partial granite replacement improved the interaction between the concrete constituents. However, the sample with recycled aggregate was still better than that with marble waste in this regard.

The effect of using recycled concrete aggregates (RCA) on the basic properties of normal concrete is studied. First, recycled aggregate properties have been determined and compared to those of normal aggregates. Except for absorption, there was not a significant difference between the two. Later, recycled aggregates were introduced in concrete mixes. In these mixes, natural coarse aggregate was partly or totally replaced by recycled aggregates. Results show that the use of recycled aggregates has an adverse effect on the workability and air content of fresh concrete. Depending on the water/cement ratio and on the percent of the normal aggregate replaced by RCA, the concrete strength is reduced by 5% to 25%, while the tensile strength is reduced by 4% to 14%. All results are compared with previous research. As new in this research, the paper introduces a simple formula for the prediction of the modulus of elasticity of RCA concrete. Furthermore, the paper shows the variation of the air content of RAC.

Lot of construction debris are generated during the construction and demolition of any concrete structure like buildings, roads, bridges etc. and sometimes, even from catastrophes like wars and earthquakes. Discarding these wastes is a very serious problem because it requires huge space for its disposal and very little demolished waste is recycled or reused. This debris after recycling can be used as aggregates in fresh concrete in order to protect natural resources and to reduce the space required for the landfill disposal thus minimising environmental pollution. In recent times, scarcity of river sand is also another major problem faced by the construction sector in India. In this paper, experimental investigations have been carried out to gauge the effect of partial replacement of natural coarse aggregates (NCA) and natural fine aggregates (NFA) by recycled coarse aggregates (RCA) and recycled fine aggregates (RFA) on compressive strength, tensile strength and flexural strength of recycled concrete. 10%, 20%, 30% of NCA and NFA were replaced with RCA and RFA respectively & the results obtained from compressive strength test, split tensile test and flexural test were compared with the conventional concrete. From the experimental study, it was observed that compressive strength & tensile strength of concrete with recycled aggregates increased up to 20% replacement of natural aggregates with recycled aggregates whereas the flexural strength of recycled concrete was found to decrease with increase in percentage of RCA & RFA. In this paper, feasibility of utilizing concrete debris after recycling in the construction industry from strength point of view has been studied.