scholarly journals Evaluation of the Ecotoxicological Potential of Fly Ash and Recycled Concrete Aggregates Use in Concrete

2020 ◽  
Vol 10 (1) ◽  
pp. 351 ◽  
Author(s):  
Patrícia Rodrigues ◽  
José D. Silvestre ◽  
Inês Flores-Colen ◽  
Cristina A. Viegas ◽  
Hawreen H. Ahmed ◽  
...  
Keyword(s):  
Fly Ash ◽  
Portland Cement ◽  
Daphnia Magna ◽  
Raw Materials ◽  
Construction Materials ◽  
Recycled Concrete ◽  
Experimental Program ◽  
Concrete Aggregates ◽  
Recycled Concrete Aggregates ◽  
Natural Aggregates

This study applies a methodology to evaluate the ecotoxicological potential of raw materials and cement-based construction materials. In this study, natural aggregates and Portland cement were replaced with non-conventional recycled concrete aggregates (RA) and fly ash (FA), respectively, in the production of two concrete products alternative to conventional concrete (used as reference). The experimental program involved assessing both the chemical properties (non-metallic and metallic parameters) and ecotoxicity data (battery of tests with the luminescent bacterium Vibrio fischeri, the freshwater crustacean Daphnia magna, and the yeast Saccharomyces cerevisiae) of eluates obtained from leaching tests of RA, FA, and the three concrete mixes. Even though the results indicated that RA and FA have the ability to release some chemicals into the water and induce its alkalinisation, the respective eluate samples presented no or low levels of potential ecotoxicity. However, eluates from concrete mixes produced with a replacement ratio of Portland cement with 60% of FA and 100% of natural aggregates and produced with 60% of FA and 100% of RA were classified as clearly ecotoxic mainly towards Daphnia magna mobility. Therefore, raw materials with weak evidences of ecotoxicity could lead to the production of concrete products with high ecotoxicological potential. Overall, the results obtained highlight the importance of integrating data from the chemical and ecotoxicological characterization of materials’ eluate samples aiming to assess the possible environmental risk of the construction materials, namely of incorporating non-conventional raw materials in concrete, and contributing to achieve construction sustainability.

scholarly journals Evaluation of Eco-Efficient Concretes Produced with Fly Ash and Uncarbonated Recycled Aggregates

Materials ◽  
2021 ◽  
Vol 14 (24) ◽  
pp. 7499
Author(s):  
Miren Etxeberria
Keyword(s):  
Fly Ash ◽  
Recycled Concrete ◽  
Recycled Aggregates ◽  
Hardened Concrete ◽  
Conventional Concrete ◽  
Concrete Aggregates ◽  
Recycled Concrete Aggregates ◽  
Carbonation Resistance ◽  
Chloride Resistance ◽  
Natural Aggregates

The fabrication of conventional concrete, as well as remains from demolition, has a high environmental impact. This paper assessed the eco-efficiency of concrete made with uncarbonated recycled concrete aggregates (RCA) and fly ash (FA). Two concrete series were produced with an effective water/cement ratio of 0.50 (Series 1) and 0.40 (Series 2). In both series, concretes were produced using 0% and 50% of RCA with 0%, 25% and 50% FA. After analysing the compressive strength, and carbonation and chloride resistance of those concretes, their eco-efficiency based on the binder intensity and CO2-eq intensity was assessed. We found that the use of 50% uncarbonated RCA improved the properties of concretes produced with FA with respect to using natural aggregates. The concrete made of 25% FA plus RCA was considered the most eco-efficient based on the tests of compressive, carbonation and chloride properties with the values of 4.1 kg CO2 m−3 MPa−1, 76.3 kg CO2 m−3 mm−1 year0.5 and 0.079 kg CO2 m−3 C−1, respectively. The uncarbonated RCA improved carbonation resistance, and FA improved chloride resistance. It can be concluded that the use of 50% un-carbonated RCA combined with FA considerably enhanced the properties of hardened concrete and their eco-efficiency with respect to concretes produced with natural aggregates.

scholarly journals Recycled Concrete Aggregates and Their Influences on Performances of Low and Normal Strength Concretes

Buildings ◽  
2020 ◽  
Vol 10 (9) ◽  
pp. 167
Author(s):  
Mohammed Seddik Meddah ◽  
Ali Al-Harthy ◽  
Mohamed A. Ismail
Keyword(s):  
Mechanical Properties ◽  
Compressive Strength ◽  
Portland Cement ◽  
Recycled Concrete ◽  
Construction And Demolition Waste ◽  
Recycled Materials ◽  
Concrete Aggregates ◽  
Recycled Concrete Aggregates ◽  
Natural Aggregates ◽  
Normal Strength

Recycled materials are now widely used in various industrial sectors to enhance sustainability and reduce environmental charges. Using recycled aggregates in concrete production significantly lowers demand for natural aggregates and the amount of solid waste sent to landfills. This paper summarizes the main results of a study undertaken to design low and normal strength concrete with various replacement ratios of coarse recycled concrete aggregates (RCA). To persuade the concrete industry to use recycled materials as one of the main components of concrete produced, the overall mechanical and durability performances of the RCA-concrete should be close or even similar to the concrete made with natural ingredients. The present research adopted an approach that consists of designing a series of low and normal strength with RCA having an equal target 28-day design strength to the corresponding natural aggregates concrete but while varying the water–cement ratios (w/c). Coarse recycled concrete aggregates, obtained by crushing waste concrete debris collected from different construction and demolition waste sources, were used in three different proportions of 30%, 50% and 100% (by weight) to produce new concrete with various w/c ratios and different compressive strength grades. Concrete mixes produced with general use Portland cement and various RCA contents were investigated in terms of their key mechanical and durability performances. The mechanical properties (crushing value) of the used RCA were visibly lower than the natural coarse aggregates (NCA). Thus, RCA-concrete showed lower performance than the NCA-concrete. It was found that by using up to 30% coarse RCA, the mechanical properties of concrete were not significantly affected. Beyond 30% of partial replacement of NCA by the coarse RCA, a continuing decrease in the mechanical performance with an increase in RCA amount was found. However, reducing the w/c ratio of concrete designed with the coarse RCA resulted in a compressive strength improvement, a better resistance to sulphate attack, carbonation, and chloride ion penetrations. Additionally, a proper design of Portland cement concrete produced with various proportions of RCA could also contribute to promoting sustainability in the construction industry and lowering its environmental impact.

scholarly journals Strength Property Study on Paver Block Made with Recycled Concrete Aggregates – An Experimental Review

2019 ◽  
pp. 480-485
Author(s):  
Gifty E ◽  
Harini Devi N ◽  
Meena P ◽  
Gunasekar S
Keyword(s):  
Natural Resources ◽  
Strength Property ◽  
Large Volume ◽  
Raw Materials ◽  
Recycled Concrete ◽  
Concrete Aggregates ◽  
Recycled Concrete Aggregates ◽  
Natural Aggregates ◽  
Save Energy

With increase in population and urbanization, demand of raw materials such as cement and aggregate has increased in the construction industries. Further it has been recognized that waste from construction &demolition sectors are of large volume and this volume is increasing every year. Utilization of demolished waste offers not only the solution of disposal problems but also helps to conserve natural resources for meeting increased demand of aggregates and save energy. This study deals with the fabrication of concrete paver blocks using construction and demolition (C&D) waste as a replacement of natural aggregates.

Review of Studies concerning Effects of Unbound Crushed Concrete Bases on PCC Pavement Drainage

1996 ◽  
Vol 1519 (1) ◽  
pp. 51-58 ◽  
Author(s):  
Mark B. Snyder ◽  
James E. Bruinsma
Keyword(s):  
Drainage System ◽  
Field Studies ◽  
Recycled Concrete ◽  
Concrete Aggregate ◽  
Drainage Systems ◽  
Concrete Aggregates ◽  
Recycled Concrete Aggregates ◽  
Crushed Concrete ◽  
Pavement Structures ◽  
Natural Aggregates

Recycled concrete aggregate (RCA) products are sometimes used as replacements for virgin aggregate products in concrete pavement structures. Recent concerns have centered on the deposit of RCA-associated fines and precipitate suspected of reducing the drainage capacity of RCA base layers and associated drainage systems. Environmental concerns have focused on the relatively high pH of the effluent produced by untreated RCA base layers. Several studies have examined these concerns and others; the results of some of these studies have not been published or publicized. The most relevant of these studies are summarized herein. These research efforts demonstrate that calcium-based compounds are present in most recycled concrete aggregates in quantities sufficient to be leached and precipitated in the presence of carbon dioxide. Precipitate potential appears to be related to the amount of freshly exposed cement paste surface. Thus, selective grading or blending with natural aggregates can reduce, but not eliminate, precipitate problems. It was also noted that insoluble, noncarbonate residue makes up a major portion of the materials found in and around pavement drainage systems. Washing the RCA products before using them in foundation layers appears to reduce the potential for accumulation of dust and other fines in the drainage system, but probably has little effect on precipitate potential. Field studies have shown that precipitate and insoluble materials can significantly reduce the permittivity of typical drainage fabrics but that attention to drainage design details can minimize the effects of these materials on pavement drainage.

scholarly journals Modulus and Strength of Concretes with Alternative Materials

Materials ◽  
2020 ◽  
Vol 13 (19) ◽  
pp. 4378
Author(s):  
Ana Elisabete Paganelli Guimarães de Avila Jacintho ◽  
Ivanny Soares Gomes Cavaliere ◽  
Lia Lorena Pimentel ◽  
Nádia Cazarim Silva Forti
Keyword(s):  
Recycled Concrete ◽  
Recycled Aggregates ◽  
Concrete Aggregates ◽  
Recycled Concrete Aggregates ◽  
Model Code ◽  
Alternative Materials ◽  
Model Code 2010 ◽  
The Difference ◽  
Natural Aggregates ◽  
Predicted Values

This paper presents a study with concretes produced with natural aggregates, recycled concrete aggregates (RCA) and waste porcelain aggregates (WPA). The study analyzed the influence of recycled aggregates in the mechanical properties of conventional concretes and evaluated the difference between measured and predicted values of elasticity modulus. The incorporation of WPA in concrete showed better mechanical results compared to the concretes produced with RCA. Measured elasticity moduli were lower than moduli predicted by NBR 6118:2014 and fib Model Code 2010, while measured results were greater than values predicted by Eurocode 2:2004 and ACI 318:2014, as expected, which indicated the safety of the latter two standards.

Experimental Study on Fundamental Characteristic of Recycled Concrete

2010 ◽  
Vol 146-147 ◽  
pp. 1925-1929
Author(s):  
Yuan Xu ◽  
Ru Heng Wang ◽  
Hua Chuan Yao
Keyword(s):  
Fly Ash ◽  
Maximum Size ◽  
Recycled Concrete ◽  
Concrete Aggregate ◽  
Fundamental Characteristic ◽  
Recycled Concrete Aggregate ◽  
Application Process ◽  
Concrete Aggregates ◽  
Recycled Concrete Aggregates ◽  
Natural Rock

First, the fundamental characteristic of recycled concrete aggregate wasstudied. Then, the recycled concrete spiciemen with different maximum size was tested. The results showed that: the apparent density and bulk density of recycled concrete aggregates was smaller than the natural rock, but the moisture content, crushed index, water absorption was higher. The workability of recycled concrete improved with increase of water and fly ash, but its strength decreased as the increase of water and fly ash. The research on performance and strength of recycled concrete aggregate will provide certain theoretical basis in the application process.

Quality Evaluation System for Description of Recycled Concrete Aggregates and Verification of its Functionality

2017 ◽  
Vol 902 ◽  
pp. 14-19 ◽  
Author(s):  
Iveta Nováková ◽  
Iveta Hájková
Keyword(s):  
Evaluation System ◽  
Quality Evaluation ◽  
Recycled Concrete ◽  
Demolition Waste ◽  
Concrete Aggregates ◽  
Recycled Concrete Aggregates ◽  
Concrete Mixtures ◽  
Natural Aggregates ◽  
Set Up ◽  
Quality Evaluation System

Article presents quality evaluation system for description of recycled concrete aggregates (RCA), verification of RCA properties and subsequent application in to concrete mixtures as a partial or total replacement of natural aggregates (NA). Modernization and rehabilitation of constructions is accompanied by creation of demolition waste from old buildings and structures. The necessity of recycling is unavoidable, because volume of construction and demolition waste (C&DW) is increasing and the landfills are reaching their maximum capacity. Nowadays, there are numerous research teams focused on analysis of characteristics and application of RCA into new concrete as a replacement of NA. Test samples of RCA have always different source, grain composition and other physical and mechanical properties, which are variously described in each different paper. Up to now, there is no any uniform quality evaluation system for description of recycled concrete aggregates, which can easily describe their source and assumed properties. Our aim is to set up rules for description of RCA and simplify the evaluation of properties of various RCA. Qualification system will be applied on three different samples of RCA and verified by the selected properties tests. Tested samples of RCA will be than used as a replacement of natural aggregates in concrete mixtures. The replacement amount was set up on 20%, 40% and 100% according to the reviewed literature, to have a comparable replacement amount and valuable results for discussion. The results of RCA testing and testing of concrete with partial and total replacement of NA showed that the evaluation system is working properly. It can be concluded, that accuracy of the quality evaluation system for description of recycled concrete aggregates is sufficient, but more tests on RCA should be done to prove all connections in between description of RCA and their properties.

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