•RCAs sourced from parent concretes with different service times and strengths.•Different increases in the shrinkage of RAC with varied parent concrete strengths.•A theoretical shrinkage model ...considering the influence of parent concrete strength.
The drying shrinkage of recycled aggregate concrete (RAC) varies considerably owing to the extensive sources of parent concrete from which recycled aggregates are obtained. This paper proposes a theoretical drying shrinkage model for RAC considering the properties of the parent concrete, including its service time and strength. To achieve this, shrinkage tests were conducted on 60 concrete specimens over 360 days. Five types of parent concrete with different service times (1 year, 20 years, and 42 years) and water-to-cement ratios (0.30, 0.45, and 0.60) were crushed to obtain recycled coarse aggregates (RCAs) that were used to prepare the RAC specimens. Three RCA replacement ratios (0%, 50%, and 100%) and three RAC water-to-cement ratios (0.30, 0.45, and 0.60) were assessed. The results indicated that the drying shrinkage of RAC was effectively reduced by an increase in the parent concrete strengths and vice versa. A theoretical RAC shrinkage model was developed considering the influence of the residual mortar content and parent concrete strength. A benchmarking analysis using 262 shrinkage samples demonstrated that the proposed model offers improved accuracy for estimating the long-term drying shrinkage of RAC over existing methods, particularly when the parent concrete and RAC have large strength variations.
Regioisomers of self‐assembling molecules resulted in the evolution of distinct 0D and 1D nanostructures, namely nanorings and nanorods (see picture). J‐ and H‐type excitonic coupling of naphthalene ...chromophores was found in the nanostructures. The bulk liquid‐crystalline states contain hydrogen‐bonded rosettes, which explains how the observed regioisomers generate distinct nanostructures with characteristic excitonic interactions.
The heterocyclic compound diethyl 6-anilino-5H-2,3-dithia-5,7-diazacyclopenta(cd)indene-1,4-dicarbox y late (D1) was found to form highly emissive aggregates in polar solvents, and the aggregate ...emission can be tuned by the simple addition of water to a dimethylsulfoxide solution. A theoretical study based on Density functional theory (DFT) calculations, shows that intermolecular interactions of D1 with solvent may be potential factors in the fluorescence change. In addition, the phenyl ring in D1 plays an important role because of its response to solvent. In the non-aggregated state, deprotonation of the N-H of D1 can proceed easily on the addition of base, and the deprotonated compound might interact with Ag super(+), resulting in a significant change in color and fluorescence quenching, which make it a potential chemosensor for the selective detection of trace amounts of Ag super(+). Copyright copyright 2013 John Wiley & Sons, Ltd.
This paper concerns the recovery of construction and demolition waste as coarse recycled aggregates for concrete. Coarse recycled aggregates may be used as a partial or total replacement of natural ...aggregates, contributing to the circular economy and minimizing landfill disposals as well as the consumption of natural mineral resources. However, construction and demolition waste is a heterogeneous material with undefined quality and the processing of this waste into recycled aggregates needs to ensure that the recycled aggregates have suitable properties for concrete. This paper summarizes several aspects related to coarse recycled aggregates, specifically addressing: (i) the typical composition of construction and demolition waste; (ii) the influence of different types of constituents on the properties of recycled aggregates and recycled aggregate concrete; (iii) requirements for recycled aggregates to be used in concrete; and (iv) production methods of recycled aggregates. It is argued that coarse recycled aggregates are a suitable construction material with adequate quality, even when common equipment is used in their production and preliminary separation as a key operation for ensuring the quality of the aggregates is recommended.
Compressive and flexural strength are the crucial properties of a material. The strength of recycled aggregate concrete (RAC) is comparatively lower than that of natural aggregate concrete. Several ...factors, including the recycled aggregate replacement ratio, parent concrete strength, water-cement ratio, water absorption, density of the recycled aggregate, etc., affect the RAC's strength. Several studies have been performed to study the impact of these factors individually. However, it is challenging to examine their combined impact on the strength of RAC through experimental investigations. Experimental studies involve casting, curing, and testing samples, for which substantial effort, price, and time are needed. For rapid and cost-effective research, it is critical to apply new methods to the stated purpose. In this research, the compressive and flexural strengths of RAC were predicted using ensemble machine learning methods, including gradient boosting and random forest. Twelve input factors were used in the dataset, and their influence on the strength of RAC was analyzed. The models were validated and compared using correlation coefficients (R
), variance between predicted and experimental results, statistical tests, and k-fold analysis. The random forest approach outperformed gradient boosting in anticipating the strength of RAC, with an R
of 0.91 and 0.86 for compressive and flexural strength, respectively. The models' decreased error values, such as mean absolute error (MAE) and root-mean-square error (RMSE), confirmed the higher precision of the random forest models. The MAE values for the random forest models were 4.19 MPa and 0.56 MPa, whereas the MAE values for the gradient boosting models were 4.78 MPa and 0.64 MPa, for compressive and flexural strengths, respectively. Machine learning technologies will benefit the construction sector by facilitating the evaluation of material properties in a quick and cost-effective manner.
Recycled fine concrete aggregates (RFA) are not enough used in the construction sector, mainly because of their high water absorption capacity. These fine particles are composed of crushed natural ...aggregate and adherent hardened cement paste. The main goal of this research is to compare the behaviors of mortars made either with RFA or with a model limestone fine natural aggregate (LFA). The LFA is prepared in order to obtain physical properties as close as possible to those of the RFA. A specific characterisation is carried out to compare the density, water absorption, morphology of grains, size distribution and packing density of both aggregates. Mortars are then manufactured with same composition and same volume of LFA and RFA. Different states of moisture of the RFA are studied. The fresh behaviour of the mortar made with saturated RFA is very close to that of the mortar made with LFA which confirms that the latter is a good reference compared to the RFA. Comparison of fresh behaviours of mortars made with RFA of different state of moisture to that of mortar made with saturated sand allows then to determine the water absorbed in the different moisture conditions. Afterwards, a mechanical study is realised, taking into consideration the exact quantity of absorbed water of the RFA in dry or saturated conditions. Knowing the exact effective water value allows us to study both the strength of mortar made with RFA, the strength of the matrix and the adherence between the fine aggregate and the paste.
Self‐compacting concrete (SCC) is a cementitious composite which serves complex formworks without mechanical vibrations with superior deformability and high resistance to segregation. Besides, the ...recycled aggregate concrete (RAC) is also developing rapidly and along with the ever‐increasing sustainable demand for infrastructure. The combination of the fibers, RAC, and SCC may create advantages for the construction industry. In this study, the polypropylene (PP) fiber at 0.1, 0.15, 0.2, and 0.25% volume fractions and steel fibers at 0.25, 0.5, 0.75, and 1% volume fractions are introduced into fiber‐reinforced recycled aggregate self‐compacting concrete (FR‐RASCC). Both fresh property and hardened mechanical performance, comprising compressive and tensile strengths and modulus of elasticity are analyzed. The fibers validate the optimal 0.1% volume fraction for PP fiber and 0.75% volume fraction for steel fiber. In addition, the results are proved to enhance the mechanical properties and reduce cracking despite the negative impact on the fresh property. Moreover, the experimental outcomes are compared with previous researches to establish the linear model, demonstrating the relationship between fiber fraction and the mechanical properties.
Soils contain a tangle of minerals, water, nutrients, gases, plant roots, decaying organic matter, and microorganisms which work together to cycle nutrients and support terrestrial plant growth. Most ...soil microorganisms live in periodically interconnected communities closely associated with soil aggregates, i.e., small (<2 mm), strongly bound clusters of minerals and organic carbon that persist through mechanical disruptions and wetting events. Their spatial structure is important for biogeochemical cycling, and we cannot reliably predict soil biological activities and variability by studying bulk soils alone. To fully understand the biogeochemical processes at work in soils, it is necessary to understand the micrometer-scale interactions that occur between soil particles and their microbial inhabitants. Here, we review the current state of knowledge regarding soil aggregate microbial communities and identify areas of opportunity to study soil ecosystems at a scale relevant to individual cells. We present a framework for understanding aggregate communities as "microbial villages" that are periodically connected through wetting events, allowing for the transfer of genetic material, metabolites, and viruses. We describe both top-down (whole community) and bottom-up (reductionist) strategies for studying these communities. Understanding this requires combining "model system" approaches (e.g., developing mock community artificial aggregates), field observations of natural communities, and broader study of community interactions to include understudied community members, like viruses. Initial studies suggest that aggregate-based approaches are a critical next step for developing a predictive understanding of how geochemical and community interactions govern microbial community structure and nutrient cycling in soil.
•The first study on the creep behavior and microstructure of recycled aggregate concrete (RAC) containing high-strength recycled aggregates is presented.•Long-term compressive strength, elastic ...modulus, splitting tensile strength, workability, drying shrinkage, and creep of RACs are studied.•Parent concrete strength of recycled aggregates significantly affects the time-dependent and long-term behavior of RACs.•High-strength RACs containing 110-MPa recycled aggregates exhibit long-term properties that are similar to or better than those of companion conventional concrete.•SEM and EDX analyses were performed to explain the mechanisms behind the mechanical test results.
It is now accepted that replacement of natural aggregates in concrete with recycled concrete aggregates obtained from construction and demolition waste is a promising technology to conserve natural resources and reduce the environmental impact of concrete. This paper presents a study on long-term properties of concretes manufactured with recycled aggregates of different parent concrete strengths. A total of six batches of recycled aggregate concretes (RACs) were manufactured. Tests were undertaken to establish the long-term compressive strength, elastic modulus, splitting tensile strength, workability, drying shrinkage, and creep of each batch. Scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX) characterizations were performed to explain the mechanisms behind the observed time-dependent and mechanical properties of RACs. Test parameters comprised the replacement ratio and parent concrete strength of the recycled aggregates used in the preparation of the new concrete mixes. The results indicate that the parent concrete strength of the recycled aggregates significantly affects the time-dependent and long-term mechanical properties of RACs. It is shown that concrete mixes containing lower strength recycled concrete aggregates develop lower mechanical properties and higher shrinkage strain and creep deformation compared to mixes prepared with higher strength recycled concrete aggregates. Normal-strength RAC mixes containing higher strength recycled concrete aggregates develop slightly lower splitting tensile strength at all curing ages but similar compressive strength and elastic modulus in longer term (i.e. over 90 days) compared to those of the control mix. It is also shown that high-strength RACs, prepared with full replacement of natural aggregates with recycled concrete aggregates having a higher parent concrete strength, exhibit time-dependent and long-term mechanical properties that are similar to or better than those of companion natural aggregate concretes.
The development of high‐efficiency and low‐cost organic emissive materials and devices is intrinsically limited by the energy‐gap law and spin statistics, especially in the near‐infrared (NIR) ...region. A novel design strategy is reported for realizing highly efficient thermally activated delayed fluorescence (TADF) materials via J‐aggregates with strong intermolecular charge transfer (CT). Two organic donor–acceptor molecules with strong and planar acceptor are designed and synthesized, which can readily form J‐aggregates with strong intermolecular CT in solid states and exhibit wide‐tuning emissions from yellow to NIR. Experimental and theoretical investigations expose that the formation of such J‐aggregates mixes Frenkel excitons and CT excitons, which not only contributes to a fast radiative decay rate and a slow nonradiative decay rate for achieving nearly unity photoluminescence efficiency in solid films, but significantly decreases the energy gap between the lowest singlet and triplet excited states (≈0.3 eV) to induce high‐efficiency TADF even in the NIR region. These organic light‐emitting diodes exhibit external quantum efficiencies of 15.8% for red emission and 14.1% for NIR emission, which represent the best result for NIR organic light‐emitting diodes (OLEDs) based on TADF materials. These findings open a new avenue for the development of high‐efficiency organic emissive materials and devices based on molecular aggregates.
A novel strategy is reported to realize highly efficient thermally activated delayed fluorescence (TADF) materials and devices via J‐aggregates with strong intermolecular charge transfer. The formation of such J‐aggregates not only contributes to fast radiative decay and slow nonradiative decay, but also significantly decreases the energy gap between the lowest singlet and triplet excited states to induce high‐efficiency TADF, even in the near‐infrared region.
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