Sustainable deployment of crushed concrete aggregates strengthened with cement and sand

Purpose: Paper assessed the feasibility of crushed concrete aggregates (CCA), a subsidiary of construction and demolition (C&D) waste, blended with cement and sand to form a composite for civil engineering field applications. Design/methodology/approach: The compaction and strength characteristics of CCA were observed by conducting Proctor compaction and California Bearing Ratio (CBR) tests. Different proportions of CCA, sand and cement were used. Moreover, the effect of curing period (0, 4, 7, 14 and 28 days) was also studied. In addition, regression analyses were performed to develop empirical expressions to predict the compaction and strength characteristics of the CCA composite. Findings: Increasing the CCA content up to 50% increases the maximum dry unit weight (MDUW) and decreases the optimum moisture content (OMC). However, on further increasing its content the MDUW decreases and OMC increases. Percent increase in the CBR value can go up to 412% if the CCA content is increased up to 50%. However, the percent reduction in CBR of about 20% can take place if 100% CCA content is used. Moreover, multiple regression shows that the experimental results are in good agreement with the predicted values. Research limitations/implications: The results obtained are purely dependent on the type of material. However, they are in favour of the used material as a probable option for road sub-base layer, and also for reducing burden on available natural resources. Therefore, it is recommended to conduct some initial tests to confirm the feasibility of the material. Practical implications: The proposed study will guide the design Engineers to choose CCA as one of the potential materials for road construction. Originality/value: It was observed that there is a need to maximize the utilization of C&D waste without making any compromise with its mechanical properties. So keeping that in view, the present study was conducted.

Use Of Alternative Aggregates In Pavement Concrete: Research And Practice In Belgium

Alternative aggregates, including recycled (concrete) aggregates as well as artificial aggregates (such as crushed stainless steel slag), are being increasingly used in road construction in the context of a more circular economy, e.g. in base and subbase layers. As these materials are applied higher up in the structure (surface and binder courses), stricter requirements are made to allow for higher loads and the stronger influence of the environment, and the application of these aggregates becomes less straightforward. The Belgian standard specifications, for instance, allow incorporation of recycled concrete aggregates in concrete pavements or linear elements in concrete, but only if certain stringent requirements are met and only up to certain percentages of substitution of the natural coarse aggregates. Furthermore, artificial aggregates originating from stainless steel slag are not even allowed for the time being in pavement quality concrete, although a Belgian standardization working group has recently been installed to investigate this matter in more detail. This paper presents an overview of laboratory research conducted in Belgium to characterize several types of alternative aggregates and concrete mixtures incorporating them, while focusing on practical execution as well as on the durability of pavement concrete. In addition, several concomitant pilot applications in Belgium are discussed in view of future perspectives for the application of alternative (recycled and/or artificial) aggregates in road construction.

Guidance for Increasing the Use of Recycled Concrete Pavement Materials

Recycling concrete pavements has been a common practice in the US for decades, and recently, public agencies have been more closely examining recycling opportunities. Reasons supporting recycling include the diminishing quantity of good natural materials, economics, improved project execution, minimizing traffic disruption, and supporting sustainability goals. Many states, however, have specifications or policies that restrict concrete pavement recycling. The contracting industry may overlook opportunities to use recycled concrete aggregates (RCAs) due to a lack of familiarity with technical requirements or uncertainty of performance. The National Concrete Pavement Technology Center (CP Tech Center) recently completed a comprehensive set of technical resources for the Federal Highway Administration to assist practitioners with sound approaches to project selection, scoping and construction requirements to support increased use of recycled concrete pavement materials. This paper describes the results of a 2016 survey of agency and industry RCA usage, presents an overview of the technical resources prepared as part of this initiative, and presents recommendations for supporting broader application of recycling concrete pavement materials.

RECYCLE GLASS WASTE AS A REPLACEMENT OF FINE AGGREGATE IN CONCRETE MIX STANDARD COMPARISON

Recycling is one way that is used to minimize the amount of waste that exists. Recycling is also a process to reduce the use of new raw materials, reduce energy use, reduce pollution, land degradation and greenhouse gas emissions. Materials that can be recycled consist of waste of glass, plastic, paper, metal, textiles and electronic goods. Glass has characteristics suitable as concrete aggregates, considering that glass is a material that does not absorb water. In addition, glass has high abrasion resistance. Meanwhile, the waste glass flux lowers the temperature to the temperature at which the formers will melt. Stabilizers in glass waste are made of calcium carbonate, which makes the glass waste solid and water-resistant. This glass waste is recycled by mixing it into the concrete mix. The recycling method is done by pounding the glass and putting it into the concrete mix stage. The purpose of mixing the glass waste is expected to increase the compressive strength of concrete. The use of glass waste as a mixed material affects the compressive strength of the concrete. The concrete with the most inferior to highest compressive strength is 4% variation concrete, 2% variation concrete, and traditional concrete. Optimal percentage addition of glass waste impacts on maximum concrete compressive strength is 2% mixture variation which obtained 11,88 Mpa & 11,32 Mpa.

Evaluation of Eco-Efficient Concretes Produced with Fly Ash and Uncarbonated Recycled 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.