scholarly journals Microstructural analysis of concretes manufactured with recycled coarse aggregates pre-soaked using different methods

2020 ◽  
Vol 70 (339) ◽  
pp. 228 ◽  
Author(s):  
Z. Sánchez-Roldán ◽  
I. Valverde-Palacios ◽  
I. Valverde-Espinosa ◽  
M. Martín-Morales
Keyword(s):  
Microstructural Analysis ◽  
Treatment Method ◽  
Absorption Capacity ◽  
Recycled Concrete ◽  
Recycled Aggregates ◽  
Negative Effects ◽  
Optimal Method ◽  
Transition Zones ◽  
Coarse Aggregates

Recycled concrete has a microstructure more complex than natural concrete, as it includes new interfacial transition zones, the quality of which is conditioned by the state of humidity of the aggregates used, which in turn will affect the final properties of the concrete. Bearing in mind the greater absorption capacity of recycled aggregates, it is important to improve its properties by means of a treatment method that is capable of reducing the negative effects that this may produce in the new concrete. Therefore, the influence of the pre-soaking method of recycled aggregates on the formation of the microstructure of concretes manufactured with these aggregates is analysed, to determine which treatment is the most effective for the production of concretes for non-structural use. The results show that the microstructure of the evaluated concretes differs according to the treatment method used, the most optimal method being one that uses aggregates without pre-soaking.

scholarly journals SEM Image Analysis in Permeable Recycled Concretes with Silica Fume. A Quantitative Comparison of Porosity and the ITZ

Materials ◽  
2019 ◽  
Vol 12 (13) ◽  
pp. 2201 ◽  
Author(s):  
Manuel J. Chinchillas-Chinchillas ◽  
Carlos A. Rosas-Casarez ◽  
Susana P. Arredondo-Rea ◽  
José M. Gómez-Soberón ◽  
Ramón Corral-Higuera
Keyword(s):  
Image Analysis ◽  
Silica Fume ◽  
Cement Paste ◽  
Chemical Elements ◽  
Energy Dispersive Spectrometer ◽  
Recycled Aggregates ◽  
Porous Network ◽  
Transition Zones ◽  
Sem Image ◽  
Coarse Aggregates

Recycled aggregates (RA) from construction and demolition can be used in permeable concretes (PC), improving the environment. PCs have a significant porous network, their cement paste and the interaction between the paste and the RA establishing their strength. Therefore, it is important to evaluate the porosity in the interfacial transition zones. The porosity of the cement paste, the aggregate and the interfacial transitional zones (ITZ) of a PC with recycled coarse aggregates (RCA) and silica fume (SF) is measured by means of image analysis–scanning electron microscope (IA)-(SEM) and by mapping the chemical elements with an SEM-EDS (energy dispersive spectrometer) detector microanalysis linked to the SEM and, as a contrast, the mercury intrusion porosimetry technique (MIP). In the IA process, a “mask” was created for the aggregate and another for the paste, which determined the porosity percentage (for the anhydrous material and the products of hydration). The results showed that using SF caused a reduction (32%) in the cement paste porosity in comparison with the PC with RA. The use of RA in the PC led to a significant increase (190%) in the porosity at different thicknesses of ITZ compared with the reference PC. Finally, the MIP study shows that the use of SF caused a decrease in the micropores, mesopores and macropores.

scholarly journals Reusing of Construction Debris in Plain Concrete Elements

2021 ◽  
Vol 9 (3) ◽  
pp. 81-87
Author(s):  
A. Abdelrahman Abuserriya ◽  
B. Bashir H. Osman ◽  
C. Salma Y. Mahmoud
Keyword(s):  
Compressive Strength ◽  
Sea Water ◽  
Plain Concrete ◽  
Absorption Capacity ◽  
Recycled Concrete ◽  
Recycled Aggregate ◽  
Recycled Aggregates ◽  
Aggregate Content ◽  
Concrete Production ◽  
Concrete Blocks

Construction is a serious environmental problem and a challenge for people who concerned with sustainability in the construction field. Previous studies showed positive results for the use of recycled aggregates in the concrete production. This study portrays the results for utilizing construction debris for casting different types of concrete blocks. The recycled concrete debris was used in different ratios (0%, 50%, and 100%) in replacement for natural coarse aggregates for different targeted compressive strength (B250, B300, B350 and B400). Two types of water (pure and sea water) were used for curing the blocks. In addition, hollow block and paving block were casted with different ratios of recycled aggregate (0%, 20%, 45% and 100%) and cured with two types of water. The results showed a decrease in compressive strength with the increase recycled aggregate content. It was also noticed that the absorption capacity increases with high recycled aggregate content.  

Structural behavior of recycled aggregates concrete filled steel tubular columns

2017 ◽  
Vol 8 (1) ◽  
pp. 17 ◽  
Author(s):  
Boshra Eltaly ◽  
Ahmed Bembawy ◽  
Nageh Meleka ◽  
Kameel Kandil
Keyword(s):  
Finite Element ◽  
Steel Tube ◽  
Recycled Concrete ◽  
Recycled Aggregates ◽  
Experimental Program ◽  
Element Analysis ◽  
Finite Element Program ◽  
Tubular Columns ◽  
Coarse Aggregates ◽  
Element Program

This paper presents an experimental and numerical investigation to determine the behavior of steel tubular columns filled with recycled aggregates concrete up to failure under constant axial compression loads. The experimental program included two steel tube columns, four recycled concrete columns and eight composite columns filled with different types of recycled coarse aggregates (granite and ceramic). Different percentages of recycled coarse aggregates: 0, 25 and 50 of the percentage of the coarse aggregates (dolomite) were used. The results of the numerical model that was employed by the finite element program, ANSYS, were compared with the experimental results. The results of the experimental study and the finite element analysis were compared with the design equations using different national building codes: AISC1999, AISC2005 and EC4. The results indicated that the recycled aggregates concrete infill columns have slightly lower but comparable ultimate capacities compared with the specimens filled with normal concrete.

An accelerated test to assess the quality of recycled concrete sands based on their absorption capacity

2015 ◽  
Vol 78 ◽  
pp. 464-469 ◽  
Author(s):  
Jorge Rueda ◽  
Enrique Dapena ◽  
Pilar Alaejos ◽  
Susana Menéndez de Llano
Keyword(s):  
Absorption Capacity ◽  
Recycled Concrete ◽  
Accelerated Test

New Concrete with Recycled Aggregates from Leftover Concrete

2015 ◽  
Vol 754-755 ◽  
pp. 389-394
Author(s):  
Ofelia Corbu ◽  
Attila Puskás ◽  
Andrei Victor Sandu ◽  
Adrian M. Ioani ◽  
Kamarudin Hussin ◽  
...  
Keyword(s):  
Concrete Strength ◽  
Ecological Impact ◽  
Experimental Tests ◽  
Recycled Concrete ◽  
Recycled Aggregates ◽  
Concrete Aggregate ◽  
River Sand ◽  
Coarse Aggregates ◽  
Concrete Type ◽  
Natural Aggregates

We live in an era where people should be more aware of pollution and its consequences. The present paper reveals a way protecting the environment while producing high quality concrete. What make this type of concrete environmentally friendly are the recycled aggregates in the concrete composition amongst with eliminating the ecological impact by saving large amounts of natural aggregates resources. Recycling concrete comes with many other advantages that lead to waste reduction, economy in waste transportation and storage taxes, which are becoming increasingly expensive. This research is based on mix design and experimental tests carried out on C20/25 strength class concrete with uncontaminated leftover concrete aggregates (LCAgg). It reveals favorable results in order to militate for recycled concrete aggregate uses in regular concrete strength classes respectively for common structural elements, mainly for slabs. River sand (0/4 mm) and coarse aggregates (4/8 mm and 8/16 mm): natural sources or recycled concrete type-alternatively used in several mixes-were utilized in concrete mixes.

scholarly journals Influence of the moisture content on the dynamic modulus of elasticity of concrete made with recycled aggregate

2019 ◽  
Vol 19 (2) ◽  
pp. 79-89
Author(s):  
Claudio de Souza Kazmierczak ◽  
Joana Kirchner Benetti Boaro ◽  
Monique Palavro Lunardi ◽  
Marlova Piva Kulakowski ◽  
Mauricio Mancio
Keyword(s):  
Moisture Content ◽  
Modulus Of Elasticity ◽  
Dynamic Modulus ◽  
Coarse Aggregate ◽  
Recycled Concrete ◽  
Recycled Aggregate ◽  
Recycled Aggregates ◽  
Coarse Aggregates ◽  
Codes Of Practice ◽  
Dynamic Modulus Of Elasticity

Abstract The elastic behavior of the concrete is estimated from its strength or determined by static or dynamic tests. However, because the codes of practice do not standardize the internal moisture content of the concrete and disregard the use of recycled aggregates when proposing equations for the estimation of the modulus of elasticity, discrepancies between the values measured and estimated are frequent. The influence of the moisture content of concrete containing basaltic coarse aggregates and coarse recycled concrete aggregate in the dynamic modulus of elasticity is discussed in this paper. A basalt coarse aggregate and two recycled coarse aggregates where used. For each type of coarse aggregate, concrete with compression strength between 25 MPa and 55 MPa were produced. The dynamic modulus of elasticity of the saturated samples were determined and range from 26 GPa to 46 GPa. There is a significant difference in the value of the dynamic modulus of elasticity for dry concrete versus saturated concrete, also influenced by the type of aggregate. Estimations of the modulus of elasticity from the compressive strength equations proposed by the codes of practice must be improved considering its characteristics.

Electropolishing of Coronary Stents

2008 ◽  
Vol 589 ◽  
pp. 367-372 ◽  
Author(s):  
Zsuzsa Edina Gellér ◽  
Katalin Albrecht ◽  
János Dobránszky
Keyword(s):  
Material Characterization ◽  
Microstructural Analysis ◽  
Coronary Stents ◽  
Composition Analysis ◽  
Optimal Method ◽  
Cutting Zone ◽  
Removal Weight ◽  
Stent Surface

Produce of coronary stents demands advanced precision. In the present study, electropolishing was performed on stainless steel slotted tube coronary stents made by laser cutting. The surface quality of stents has a significant influence on biocompatibility, therefore the optimal method for electropolishing were explored. Additionally, acid pickling as the pretreatment of electropolishing was also conducted. Pickling was necessary prior to electropolishing for decreasing roughness of the cutting zone and for removing the oxide films covering the stent surface. An optimal condition for electropolishing could also be established and it caused a smooth stent surface. Material removal (weight loss and strut width change) in the process of both pickling and electropolishing was investigated. Furthermore, material characterization of the stents was determined by means of composition analysis, metallographic characterization and microstructural analysis.

scholarly journals Effect of Mortar Reduction in Recycled Aggregates Used in Concrete

2017 ◽  
Vol 11 (1) ◽  
pp. 363-370 ◽  
Author(s):  
Viviana Letelier ◽  
Ester Tarela ◽  
Pedro Muñoz
Keyword(s):  
Environmental Concern ◽  
Recycled Concrete ◽  
Raw Material ◽  
Recycled Aggregates ◽  
Structural Concrete ◽  
Mechanical Abrasion ◽  
Coarse Aggregates ◽  
Global Environmental ◽  
Material Reuse ◽  
Global Environmental Concern

Background:Following a global environmental concern, concrete manufactured with recycled materials has been widely studied. The reuse of concrete as raw material can reduce the amount of debris and the amount of natural resources needed minimizing the environmental impact.Objective:One of the fundamental issues when using recycled aggregates is the mortar that remains adhered to their surfaces. The effect of this adhered mortar on aggregates, obtained from pavement demolition debris, used in recycled concrete is studied.Method:A mechanical abrasion process is used to reduce the amount of mortar in different degrees from the recycled aggregates that will be used to replace a 40 % of natural coarse aggregates in structural concrete. The mechanical behavior is studied through the compressive and flexural strength of the material and compared with the values obtained for a control concrete, with no recycled aggregates.Results:The abrasion process is proven to be effective eliminating the adhered mortar to the aggregates and the results show that a medium abrasion level, around 200rev, improves significantly the mechanical properties of the recycled concrete, increasing its compressive strength.Conclusion:The percentage of recycled aggregates used in structural concrete can be increased if these are treated with simple mechanical abrasion. The residuals of the eliminated mortar can be also reused as cement replacement, maximizing the material reuse.

scholarly journals Experimental Inspection on Shear Capacity in RCC Beams with Partial Replacement of Recycled Coarse Aggregates

2020 ◽  
Vol 9 (2) ◽  
pp. 321-326
Keyword(s):  
Compressive Strength ◽  
Load Ratio ◽  
Shear Capacity ◽  
Recycled Concrete ◽  
Recycled Aggregates ◽  
Partial Replacement ◽  
Age Group ◽  
Shear Span ◽  
Coarse Aggregates ◽  
The Relationship

Demolition waste increasing day by day. The old damaged building materials can be used in present buildings or other construction works. Especially the recycled aggregates are useful to the concrete structures. The experimental studies on the use of recycled coarse aggregate has been going on for many countries. This publication focuses on the relationship between the shear capacity and the flexural cracking load of reinforced recycled concrete beams with stirrups, this experimental Inspection with partial replacement of natural coarse aggregates (NAC) with recycled coarse aggregates (RAC) at different ages as 10, 20 and 30 years in various proportions as 20 per cent, 30 per cent, 40 per cent. For this, M30 grade of concrete is consider. Curing of specimens were done for 7 day and 28 days to conclude the maximum strengths. The obtained results of concrete with partial replacement of recycled aggregates of 10,20and 30 years age group conclude maximum compressive strength of 35.84 N/mm2 at 40% replacement of NCA with RCA of age group (10 years) and 34.12 N/mm2 at 30% replacement of NCA whit RCA of (20 years) age group and 36.14 N/mm2 20% replacement of NCA with RCA of age group (30 years). After the compressive strength, beam specimens were casted for 7day and 28 days. Based on test results of 8 beams, the relationship between the cracking load that causes a beam to crack in the middle of the shear span and the beam's shear capacity is confident. All beams are reinforced in the longitudinal direction only and only tested under two-point loading conditions. The average analytical cracking load ratio is 0.60.the mid-shear span at cracking load (Vcr-a/2) in comparison with the observed shear capacity (Vexp). The analytical cracking load ratio. The analytical cracking’s load was used in this exploration as it is more reliable than the observed cracking load. At mid-span, the shear capacity of most of the beams was shown to be 50%. The average shear capacity ratio to the related test crack load in the center of the shear span 0.43. The analysis showed that cracking loads are strongly related to the shear capacity of the members. This relationship can be used to develop recycled reinforced beam members ' shear design process.

scholarly journals The hygrothermal performance of concrete with coarse aggregates made of recycled concrete pavements

2020 ◽  
Vol 322 ◽  
pp. 01006
Author(s):  
Václav Kočí ◽  
Magdaléna Doleželová ◽  
Lukáš Fiala ◽  
Tomasz Tracz
Keyword(s):  
Computational Modelling ◽  
Recycled Concrete ◽  
Recycled Aggregates ◽  
Weather Data ◽  
Concrete Pavements ◽  
Coarse Aggregates ◽  
Crushed Concrete ◽  
Hygrothermal Performance ◽  
Coupled Heat And Moisture ◽  
Heat And Moisture

This paper deals with an investigation of the hygrothermal performance of concretes containing various amounts of recycled aggregates originating from crushed concrete pavements. The performance, which was obtained using computational modelling of coupled heat and moisture transport, is predicted on stand-alone samples as well as on built in samples in a real construction exposed to weather data of Ostrava, Czech Republic. The results revealed that the influence of recycled aggregates as substitution for natural stone does not negatively affect the hygrothermal performance of the concrete. The highest difference found was less than 1°C and 12% of RH in the case of stand-alone samples and only 2.2% of RH when built in. Therefore, the application of crushed concrete pavements as aggregates in concrete composition can be highly recommended as it brings other benefits such as economical and environmental.

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