Absorption Of Aggregates Research Articles

MANTA-Ray: Supercharging speeds for calculating the optical properties of fractal aggregates in the long-wavelength limit

Abstract Correctly modelling the absorptive properties of dust and haze particles is of great importance for determining the abundance of solid matter within protoplanetary disks and planetary atmospheres. Rigorous analyses such as the discrete dipole approximation (DDA) can be used to obtain accurate absorption cross-sections, but these require significant computing time and are often impractical to use in models. A simple analytical equation exists for spherical particles in the long-wavelength limit (where the wavelength is much larger than the size of the dust particle), but we demonstrate that this can significantly underestimate the absorption. This effect is found to depend strongly on refractive index, with values of m = 1 + 11i corresponding to an underestimate in absorption by a factor of 1,000. Here we present MANTA-Ray (Modified Absorption of Non-spherical Tiny Aggregates in the RAYleigh regime): a simple model that can calculate absorption efficiencies within 10-20% of the values predicted by DDA, but 1013 times faster. MANTA-Ray is very versatile and works for any wavelength and particle size in the long wavelength regime. It is also very flexible with regards to particle shape, and can correctly model structures ranging from long linear chains to tight compact clusters, composed of any material with refractive index 1+0.01i ≤m ≤ 11+11i. The packaged model is provided as publicly-available code for use by the astrophysical community.

Ensemble machine learning models for compressive strength and elastic modulus of recycled brick aggregate concrete

This study delivers an in-depth analysis of predicting the compressive strength and elastic modulus of recycled brick aggregate concrete (RBAC). It assembles an extensive database of 633 compression test results and develops five ensemble learning models—random forest (RF), gradient boosting regression trees (GBRT), extreme gradient boosting (XGB), light gradient boosting machine (LGBM) and stacking (St). These models are evaluated against existing empirical formulas with respect to their effectiveness. The findings reveal that machine learning (ML) models outperform existing formulas: for compressive strength prediction, traditional models achieve a maximum determination coefficient R² of 0.38, whereas ML models attain an R² range of 0.91–0.94. For elastic modulus, the highest R² values are 0.44 for traditional models and 0.97 for ML models. Notably, the LGBM and St models excel in predicting compressive strength and elastic modulus, respectively. The study also identifies critical parameters influencing RBAC’s compressive behavior and highlights their impact trends. Remarkably, while the mass-weighted water absorption of coarse aggregates and the replacement ratio of recycled brick aggregates (RBAs) have less impact on compressive strength compared to the effective water-to-cement ratio, they become more influential for elastic modulus. Additionally, the decrease in elastic modulus due to higher RBA replacement ratios or increased mass-weighted water absorption of coarse aggregates exceeds the corresponding reduction in compressive strength. This research not only deepens the understanding of RBAC’s mechanical properties but also provides valuable predictive tools for civil engineering applications.

Feasibility study of utilizing Autoclaved Aerated Concrete (AAC) waste for the production of cold bonded lightweight artificial aggregate using high volume fly ash (HVFA) binders

Autoclaved Aerated Concrete (AAC) is a popular construction material used for partitions and insulation in buildings. At the end of its service life, AAC (Autoclaved Aerated Concrete) will be demolished and subsequently disposed of in landfills, thereby creating depository problem. Therefore, the study of reutilization and recycling of AAC waste is imperative. Artificial aggregate production can be an alternative to the reutilization of AAC waste. This paper assesses the feasibility of using Autoclaved Aerated Concrete Powder (AACP) waste as a raw material for the production of artificial aggregate and investigate its physico-mechanical properties. The investigation incorporates the comparison of cement-based binder with high-volume fly ash (HVFA) binder with different replacement levels of cement. The study uses image analysis based on photographic, optical microscopic, and scanning electron microscopy (SEM) images, to describe the porosity of the aggregate. The results show that the AACP aggregates with both cement and HVFA binders meets the current industry requirement for density and cylinder crushing strength as lightweight artificial aggregate. The appropriate binder content lies between 30 % and 40 %. The best cement to fly ash ratio in HVFA binder is determined to be of 1:1 with 50 % replacement of cement with fly ash. Image analysis showed that the porosity largely affected the properties of the AACP aggregate such as density and water absorption. However, further investigation into the reducing high-water absorption of AACP aggregates is necessary to improve their overall quality.

Mechanical properties and repairing mechanism of recycled cement stabilized macadam for road base based on microbial induced carbonate precipitation technology

The utilization of recycled coarse aggregate derived from construction and demolition waste (CDW) in the construction of road cement stabilized macadam base could effectively alleviate the shortage of natural sand and aggregate resources. To explore the repairing effect of microbial induced carbonate precipitation (MICP) on recycled cement stabilized macadam (RCSM), the physical, mechanical, and microscopic properties of recycled concrete aggregate under different precipitation precursor concentrations were researched in this paper. The mechanical properties of RCSM with varying contents of recycled concrete aggregate were analyzed before and after repairing. Based on scanning electron microscopy (SEM) and mercury intrusion porosimeter (MIP) tests, the microstructure and pore structure parameters of recycled concrete aggregate were explored, and the repair mechanism of MICP on RCSM was revealed via the performance analysis of recycled concrete aggregate and RCSM. The results show that MICP could effectively reduce the water absorption of recycled concrete aggregates, while simultaneously enhancing its apparent density and crushing resistance. In a certain range, the higher the concentration of the precipitation precursor, the better the repairing effect on the performances of recycled concrete aggregates. However, while the concentration of urea or calcium source concentration exceeding 1.0 mol/L, the activity of urease would start to be inhibited. The unconfined compressive strength of RCSM after MICP repairing could be increased by 22.7 % with a maximum extent compared with that before repair, while the maximum increase of indirect tension strength and flexural tensile strength was 15 % and 8.2 %, respectively. The biological CaCO3 generated by MICP reaction could fill the micro-cracks and pores of the recycled concrete aggregate efficaciously. Besides, it could also optimize the pore parameters and pore size distribution parameters, and enhance the adhesive strength of interfacial transition zone (ITZ) between cement and recycled concrete aggregates, which could improve the mechanical properties of RCSM.

Carbonation of Recycled Concrete Aggregates for New Concrete and Concrete Fines to Make Cement-Free Hollow Blocks

Mineral carbonation provides a way to increase the recycling of concrete waste in added-value products, and contributes to the principles of the circular economy. At present, most concrete waste is still downcycled. The high water absorption of recycled concrete aggregates, among other factors, impedes their recycling in the concrete industry. The quality of coarse recycled concrete aggregates (RCA) can, however, be enhanced by carbonation. Even when starting with high-grade RCA obtained from a selective demolition process, the carbonation process can decrease the water absorption of the RCA to as low as 3.0%. Concrete with a 50% replacement rate of carbonated RCA can be produced without a significant compressive strength reduction. The research further shows that carbonation can be performed at atmospheric pressure and low CO2 concentrations (e.g., 10%). The recycled concrete fines (RCF, 0–4 mm) in combination with 25% stainless steel slag were used to make zero-cement hollow blocks (39 × 19 × 9 cm) by carbonation curing without using any hydraulic binder. The hollow blocks have a compressive strength of 15.4 MPa at the lab scale. Both technologies were demonstrated on a pilot scale. In both processes, CO2 is immobilized in the resulting construction product. The developed production processes use less primary raw materials and cause less greenhouse-gas emissions than the production of traditional concrete products.

Effects of Over-burnt Bricks on Gradation, Water Absorption and Specific Gravity of Aggregates, Workability and Compressive Strength of Concrete

Demand of bricks is increasing day by day by the requirement of new structures. Due to manufacturing of bricks, over-burnt bricks are also made. Generally over-burnt bricks are the waste materials which is generally used for dumping purpose and sometime it is thrown in useful land that create social and environmental problems. Therefore, this material should be properly treated, recycled and used in concrete as coarse aggregate. In this research work, six (06) batches were made with 1:2:4 mix and 0.5 water cement ratio. Each batch consists of five (05) samples. Six (06) batches were made with 0%, 20%, 40%, 60%, 80% and 100% replacement of natural coarse aggregates with over-burnt bricks aggregates. The outcome of study reveals that the gradation of both the aggregates shows same pattern and the trend of curve was almost similar, with minor difference in range values over a sieve. The water absorption of over-burnt bricks aggregates was more than the water absorption of natural coarse aggregates and the specific gravity of over-burnt bricks aggregates was less than the specific gravity of natural coarse aggregates. The result of slump test shows that there was continuous decrease in workability of concrete mix, as replacement of over-burnt bricks aggregates increased. 30 concrete cubes of (6” x 6” x 6”) size were prepared and cured for 28 days followed by compressive strength. The result shows that the concrete derived from over-burnt bricks aggregates attained lower compressive strength than the regular concrete. However, the values obtained from over-burnt bricks aggregates are still acceptable, especially for reasonable levels of the replacement ratio up-to 60%. This concrete can be used in new constructions, but it is proposed to be initially utilized in low load areas.

WATER ABSORPTION AND SPECIFIC GRAVITY OF RECYCLED CONCRETE AGGREGATE FROM DEMOLISHING WASTE OF NAWABSHAH CITY

Concrete has been proved to be a leading construction material all over the world. Because of the demand for new structures, new construction is increasing day by day. This rapid demand of structures has increased the requirement of concrete. New structures are being constructed and old structures are being demolished. This results in the generation of construction waste on a large scale. The throwing away of this huge mass of construction waste has happened to a major social and environmental issue all around the world, mostly in developing countries. Therefore, a proper utilization of demolished waste is important in order to deal with this waste and have an alternate material for utilization in concrete. Therefore, experimental research has been conducted to utilize this waste as recycled coarse aggregates to partially replace natural coarse aggregates. Old concrete was collected from 5 locations in Nawabshah. After collecting all the material we used 5 samples from each source, so we used 25 samples of recycled aggregates. 25 samples of recycled coarse aggregate are tested for water absorption and specific gravity to understand its properties and compare to the natural coarse aggregates. The water absorption of recycled coarse aggregate is greater than the water absorption of natural coarse aggregates. Among these five sites of Nawabshah city, New Naka area’s recycled coarse aggregates have greater water absorption which is 5.8%. The specific gravity of recycled coarse aggregate is lower than the specific gravity of natural coarse aggregates. Among these five sites of Nawabshah city, New Naka & Mehran Hotel area’s have lesser specific gravity which is 2.237. So, these aggregates can be used in new constructions, but it is proposed to be initially utilized in low load areas.

The Relationships Between Absorption, Alterability and Granulation of Coarse Aggregates from Different Lithologies from Southern Brazil

This paper studies the mathematical and statistical correlations between absorption, alterability, and granulation of aggregates from different lithological origins in southern Brazil. In order to achieve this goal, a petrographic analysis of the aggregates was carried out, in addition to a qualitative evaluation of granulation/alterability and absorption tests for the 1/2” (12.5 mm), 3/8” (9.5 mm), and #4 (4.75 mm) sieve. Statistical analysis relied on the Shapiro-Wilk and Breusch-Pagan tests, using R-Studio software. The results show that the variables “granulation” and “alteration” exhibit satisfactory correlations with the variable “absorption”, indicating that the larger the grain size the lower the absorption, while the higher the alteration the higher the absorption. The more the particle size decreases, the greater the variable “absorption” can explain “granulation”. Regarding the alteration and absorption degree, the analysis was not feasible, since the analyzed group that included high absorption and low alteration volcanic rocks could modify the trend, contradicting the consensus that the more altered the rock, the more it absorbs. Overall, the employed methodology proved to be satisfactory for the database analyzed, with the suggestion of increasing the number of samples in future studies.

Modification of multi-source industrial solid waste with porous materials to produce highly polymerizeosilica gel: Microstructure optimization and CO2 mineralization enhancement mechanism

The combination of solid waste into lightweight aggregates is a promising strategy for solid waste resource utilization and an effective method for carbon reduction. Herein, the lightweight aggregate with high CO2 adsorption and mineralization performance was prepared by multi-source solid waste combined with porous structural material. Based on the basic property parameters (density, water absorption and porosity) of lightweight aggregates, the effectiveness of multi-source solid waste (fly ash (FA), desulfurization gypsum (DG), coal gangue (CG), blast furnace slag (BFS) and steel slag (SS)) to improve the aggregate performance was determined. The water absorption rate reduced by 20 % and the mechanical strength increased by 49.1 % with the addition of five multi-source solid waste. Moreover, the amount of CO2 absorption could be steadily maintained above 20 % throughout the carbonization curing at room temperature. The decrease in bulk density and water absorption, as well as the increase in skeleton density and mechanical strength of aggregates, were the results of the synergistic effect of multi-source solid waste. This could be attributed to the correlation between the physical properties of the aggregate. The pathway of increasing carbon absorption was proposed based on product analysis and pore characterization. The inability of CO2 to diffuse into aggregate was referred to the accumulation of carbonate on the aggregate surface, resulting in a low carbon absorption rate. The porosity of aggregates was increased and the carbon absorption rate was improved by adding porous materials (diatomite and zeolite). The CO2 absorption of multi-source solid waste coupled with porous materials was increased to 26.3 % under 20 % CO2 (v/v) in nitrogen. Additionally, the synergistic effects of solid waste inhibited the content of heavy metals, and porous materials showed notable inhibiting effect on 8 heavy metals. Zn decreased by 28.7 % due to the addition of DE, and ZE had a better reduction effect by 42.9 %. This study provides a significant understanding of the porous materials modified cold-bonded aggregates by the utilization of multi-source industrial solid waste coupled with CO2 for building materials in engineering applications.

A simple method to address the high water absorption of recycled aggregates in cementitious mixes

The high water absorption of recycled concrete aggregates (RCA) can cause a significant reduction in the flow properties of cement-based materials in relation to mixes produced with natural aggregate. In order to compensate for this adverse effect, two extreme and simple approaches based on the water absorption of RCA in pure water are often used: using RCA in a saturated surface-dry (SSD) state or adding extra water based on the 24-hour water absorption of RCA in pure water (WA24h). However, these approaches can result in a significant drop in mix’s strength due to excessive water being used. Therefore, this study proposes a simple method to accurately evaluate the water absorption of RCA in cement paste (WAP) based on the variation in the mortar’s apparent density resulting from the RCA absorption of water from the cement paste. This study also investigates the effects of the aforementioned two approaches on the mortars’ performance. Recycled concrete sand (RCS) was adopted as the object of the study. The results show that, after an initial increase, the WAP of RCS stabilizes at 24 min. WAP also increases with the mortar’s W/C and WA24h, and decreases with the aggregate’s volume fraction. In addition, the maximum water absorption of RCS in cement paste (WAP_30min) is lower than WA24h, and the WAP at 6 min (WAP_6min) can reach 80% of the WAP_30min. A campaign of mortars was produced using the WAP_30min as previously assessed. It is found that the flowability of mortar prepared with RCS is poorer than that of mortar prepared with natural sand at the same effective W/C, but their strength is higher. Using RCS in a SSD state or adding extra water based on the WA24h of RCS can compensate for the flowability loss of the mortars to some extent, but at the expense of an excessive reduction in mechanical performance. Based on the results of this study, the authors suggest that the mix design of mortars prepared with RCA can be improved using WAP, namely adjusting the initial W/C to balance flowability and mechanical properties.

Simple way to model the mechanical properties of concretes with recycled concrete aggregates

Researchers have made efforts to model the mechanical properties of concretes with recycled aggregates joining large research databases. The replacement ratio criterion of natural aggregates by recycled ones has been widely used in the models, however, itself leads to a great dispersion of results and is inaccurate. In the manuscript, the weighted water absorption of both aggregates (coarse natural and recycled concrete one, Ww) and the effective water/cement ratio were used to easily predict accurately the porosity, compressive strength, and elastic modulus of the recycled concretes. For the modelling, a systematic review of the Brazilian studies from 1999 to 2020 was conducted compiling 169 concrete compositions and joined with 212 concrete mixes from international studies. A supplementary Excel file with the database and all existing correlations was provided. The 20%-replacement ratio limit of many standard codes for structural recycled concretes can be exceeded by using Ww < 5 % for structural concrete [40–60 MPa], or Ww < 8 % [25–40 MPa]. Aggregates with Ww > 8 % can be used for non-structural concretes, with little reduction in compressive strength in absolute terms (<5 MPa). The best %-replacement can be defined for each case, practical for concrete formulations in ready-mix companies.

Assembling of a Water-Soluble N^C^N-Coordinated Pt(II) Complex Aggregate Assisted by Carbon Dioxide in Basic Aqueous Solution.

We report an unprecedented result of self-aggregation of [Pt(L1 )Cl] (HL1 =1,3-di(5-carboxy-2-pyridyl)benzene) triggered by CO2 in basic aqueous solution. The color of basic aqueous solution containing [Pt(L1 )Cl] changes from yellow to blue-green during the aggregation resulted from a reaction with CO2 in air. Upon CO2 gas bubbling, strong and broad absorption bands of aggregate assigned to the metal-metal-to-ligand charge-transfer transition appeared at 701 and 1152 nm. Recrystallization of [Pt(L1 )Cl] from Na2 CO3 aqueous solution afforded polymorphic crystals of red and blue-green forms. A single X-ray crystallography revealed that the red form of crystal consists of a Pt-Pt stacked dimer bridged by CO3 2- ion and one of the carboxy groups of L1 is deprotonated. An elemental analysis provided evidence that the blue-green crystal is constructed by linear array consisting of the [Pt(L2 )(CO3 )]3- (HL2 =1,3-di(5-carboxylate-2-pyridyl)benzene) units. The formation process of blue-green aggregate in aqueous solution was monitored through a transient absorption spectrum, and the absorption of aggregates involved in the spectral change were examined by a global analysis. A singular value decomposition and kinetic analysis provide that there are four species resulted from the self-assembling reaction in the solution and the maximal degree of aggregation is at least 32-mer.

Systematic comparison of different recycled fine aggregates from construction and demolition wastes in OPC concrete and PPC concrete

River sand is widely used as fine aggregates in concrete. Several countries have prohibited the use of river sand in construction owing to the devastating effects of excessive river sand mining. Hence, the need for alternative fine aggregates is substantially enhanced in the construction sector. The disposal of construction and demolition wastes into landfills is a major concern due to the stringent environmental regulations. Using recycled fine aggregates from construction and demolition wastes as alternative fine aggregates is an environmentally viable solution for excessive river sand mining. Although numerous previous studies on recycled fine aggregates are available, a comprehensive review of the comparative assessment of different recycled aggregates derived from construction and demolition wastes is highly limited. Therefore, the potential reuse of various types of recycled fine aggregates from construction and demolition wastes such as concrete, brick, ceramic and marble wastes as fine aggregates in ordinary concrete and PPC concrete is presented in the review. The influence of recycled fine aggregates on fresh properties such as workability, air content and density is presented. Besides, compressive strength, tensile strength, flexural strength, water absorption, carbonation and shrinkage of recycled fine aggregates used in ordinary concrete and PPC concrete are methodically compared. High water absorption of the recycled fine aggregates lowers the workability of concrete. Reduction in the density of concrete is observed due to the increased porosity while replacing river sand with recycled fine aggregates. Increase in the carbonation depth, air content and shrinkage are witnessed for all types of recycled fine aggregates incorporated concretes.

Influence of the number and type of the electron-withdrawing groups of the benzene substituted perylene diimide at the imide position on the optoelectronic performance in the solution/solid

It is generally believed that the photoelectric properties of perylene diimide derivatives are more dependent on the substituent groups at the perylene core than on amine-position substituents. Here, we focus on the relations between the amine-position substituents' features, material state, and the perylene diimide's photoelectric properties. Three perylene diimide derivatives were designed. Their amine-position substituents are 2,3,5,6- fluorobenzene (FFPDI), 2,3,4,5,6-fluorobenzene (BFPDI) and 2,3,5,6-fluorine, 4-trifluoromethyl-benzene (TFPDI), respectively. BFPDI is more affected by solvation than the other two PDIs based on the normalized UV spectrum and enthalpy change caused by solvent. In dilute solution, these PDIs show similar spectra features in absorption and emission, TFPDI film shows the characteristic absorption of H-type aggregates, and other PDIs films show the characteristic absorption of J-type aggregates. The different stacking modes of PDIs result in the difference in the film's electronic structure and carrier mobility. It indicates that increasing the steric hindrance and reducing the number of F atoms have similar effects in solid or solution conditions; however, the appropriate increase in steric hindrance is more beneficial to improve the solvent resistance of the material and enhance the intermolecular dipole interaction in the solid state.

CO2 absorption of recycled concrete aggregates in natural conditions

Cement production is linked to a substantial CO2 emission contributing to about 5–8% of the man-made emissions. However, hardened cementitious materials can absorb CO2 in the process called carbonation, both during the service life of the structures and during their demolition and recycling phase. As experimental data of CO2 absorption during the recycling phase are scarce, the goal of the study is to experimentally determine the CO2 absorption of recycled concrete aggregates (RA) from the point of crushing until reuse in recycled aggregate concrete (RC). Samples from three plants producing both RA and RC were collected and stored both in the plants and in the laboratory for several months. The change in the amount of uncarbonated cement paste of the RA with time was determined by using a novel method: image analysis of samples embedded in epoxy, ground and sprayed with phenolphthalein. This allowed to calculate the CO2 absorption during the storage of RA. The amount of absorbed CO2 corresponds to about 5.4–12.6% of total CO2 emission originally stemming from the production of cement.

An Experimental Investigation On Strength Properties of Concrete with Partial Replacement of Cement and Coarse Aggregate by Silica Fume and Recycled Aggregate

Construction-Demolition waste is the major part of solid waste, which contributes almost 30% of solid waste every year and creates lot of environmental issues. Now a days building material crisis in construction industry also increasing every year. Use of Construction-Demolition waste in construction industry would be the sustainable solution for this problem. Use of C&amp;D waste in concrete have so many advantages in construction industry and also solve lot of environmental problems and also increase the economic contribution of construction industry in countries development. Use of C&amp;D waste in concrete would lead to eco-friendly concrete with sustainable development. The main moto of the present project is to use Construction demolition waste-Recycled aggregates in concrete without compromising the properties of concrete. The physical properties such as specific gravity, water absorption and sieve analysis of construction demolition waste-Recycled aggregates and natural aggregates are investigated and the natural aggregates are replaced by Construction demolition waste-Recycled aggregates in concrete in different proportions (i.e., 0%, 20%, 40% ,60%,80% and 100%). The properties of hardened concrete such as compressive strength, split-tensile strength, flexural strength and Non-destructive tests (Rebound Hammer, Ultrasonic Pulse velocity test) is investigated and compared with the conventional control concrete. The results are concluded that the strength properties of concrete won’t affected up to 40% replacement of Construction demolition waste Recycled aggregates.

Nano-engineering the interfacial transition zone between recycled concrete aggregates and fresh paste with graphene oxide

The high water absorption and porosity of recycled concrete aggregates (RCA) typically result in a weak interface transition zone (ITZ), thus severely limiting the mechanical property and durability of the prepared concrete. This study proposes a targeted approach to improve the microstructure of ITZ through conformally coating graphene oxide (GO) on RCA (i.e., GO@RCA). The experimental results reveal that the 28-day compressive/splitting tensile strength of concrete increases by 27%/40%, when GO@RCA replaces RCA. The GO coating significantly reduces the water absorption coefficient and the total charge passed by 15.1% and 63.4%, respectively. To further explore the practical application of such a strategy, instead of direct coating GO on RCA in the case of GO@RCA, RCA is pre-wetted with GO (termed WGO@RCA) before mixing with cement. Interestingly, the data show similar results as the case of concrete containing GO@RCA, strongly indicating the locality of GO at ITZ for WGO@RCA. The enhancement of concrete’s mechanical and durability properties resulted from the sub-nanometer thickness of GO coating and the hydrophilic functional groups to promote cement hydration at ITZ locally.

Optimization of sodium alginate aided bio-deposition treatment of recycled aggregates and its application in concrete

Bio-deposition treatment based on microbial induced carbonate precipitation is a promising method to enhance the properties of recycled aggregates, because the generated biological precipitates can repair the defects of recycled aggregates. However, the main problem of current bio-deposition treatment is the uneven distribution of the precipitates on aggregates, which greatly diminishes the enhancing efficiency. Therefore, sodium alginate (SA) was innovatively utilized to improve the uniformity of the precipitates on aggregates surface during the bio-deposition treatment in this study. The principle was that SA and the network structure of Ca-alginate were applied to uniformly “fix” the bacteria on the surface of recycled aggregates, which was supposed to promote the uniform in-situ precipitation on the surface of aggregates. The influences of the concentrations of bacteria and deposition solution (containing equimolar urea and Ca-nitrate), on the treatment efficiency were studied. The results indicated that the optimized SA-aided bio-deposition treatment group was under 0.2 wt% SA, 109 CFU/mL of bacterial solution, and 0.5 M of deposition solution, the water absorption of aggregates was reduced by 39.63% on average, the effective mass increase of calcium carbonate was increased by 3.14%, and the crush value decreased by about 13.8%. Using aggregates subjected to the optimized SA-aided bio-deposition treatment to produce concrete, it was found that, comparing with the untreated recycled aggregate concrete, the saturated water absorption of the treated recycled aggregate concrete decreased by about 15.3%. It can be concluded that the optimized SA-aided bio-deposition treatment can improve the strength of aggregates and durability of recycled concrete.

Role of inhomogeneities in resonance light absorption and luminescence of molecular aggregates

Within the linear response theory, we have calculated the resonance absorption of the light and resonance luminescence for the one-dimensional molecular aggregate. We have shown that the randomness of the distribution of signs of the interaction between dipoles of the aggregate dramatically changes the parameters of the absorption and luminescence. In the homogeneous case, the resonance response of the exciton band of the molecular aggregate produces narrow lines at edges of the band. On the other hand, inhomogeneities yield contributions to optical characteristics of all excitons of the band.

Using sodium alginate aided bio-treatment for improving the uniformity of precipitates on recycled aggregates.

The recycled concrete aggregates have high porosity and water absorption, which hinders their utilization in concrete production. Microbial-induced calcium carbonate precipitation was regarded as a very promising method for strengthening recycled aggregates. However, the uneven distribution of CaCO3 on surface of aggregates encountered in the current bio-deposition treatment weakened the efficiency, especially in the aspect of the decrease of water absorption. Therefore, this study innovatively applied a sodium alginate aided bio-deposition treatment to improve the uniform distribution of biogenic CaCO3. The principle was that sodium alginate was used to uniformly "fix" the bio-agents (urea or bacterial cells) on the surface of recycled aggregates, which was supposed to promote the uniform in-situ precipitation of CaCO3 on the surface of aggregates, and hence effectively blocking surface pores, and reducing the water absorption of the aggregates. Two concentrations of sodium alginate (0.2w% and 0.5w%) and four sodium alginate aided bio-deposition treatments were studied. It was found that CaCO3 (a mass increase of 4.05%) was formed on the aggregates after the suitable sodium alginate aided bio-deposition treatment. The participation of sodium alginate made CaCO3 uniformly deposited on full surface of the aggregates, resulting in a significant decrease (42.10%) of water absorption. The biogenic CaCO3 showed limited mass loss under ultrasonic attack, indicated a strong cohesion and bonding strength with aggregates. The results demonstrated that sodium alginate-aided bio-deposition treatment can enhance the efficiency, which was beneficial to improve the quality of recycled aggregates and their utilization of recycled aggregates in concrete production. KEY POINTS: • The SA-aided bio-treatment promoted the distribution uniformity of CaCO3 on aggregates. • The water absorption of aggregates decreased by 42.10%. • The formed CaCO3 showed excellent cohesion and adhesion.