Multidisciplinary approach is used to evaluate concrete with recycled concrete aggregates (RCA) from technical, environmental impacts and product circularity perspectives. Two RCA replacements investigated, RAC50: fine aggregates; RAC100: both coarse, fine aggregates. Reference, recycled concretes have same cement content, similar workability and compressive strength requirement, proven experimentally. RCA is sourced from pre-fab element discards of a Swedish plant, the logistical alternatives requiring environmental impact analysis. Alternatives are RCA crushing at plant and crushing at a different location including transportation. LCA shows transportation is second largest contributor after cement in all impact categories. RAC alternatives show lower total impact than reference concrete due to RCA replacement. A circularity index for concrete based on economic value of recirculated aggregates; supplements LCA for sustainability reporting. Circularity index results: RAC100 > RAC50 > RC. Combining circularity index with LCA helps optimize recycling process with regard to amount of recycled material and logistics respectively.

Objektsorienterad selektiv rivning för cirkulär ekonomi och minskad klimatpåverkan har varit  ett-årigt projekt som genomförts för att förbättra insamling av data och dokumentera rivning för delar av en byggnad där fastighetsägarna har för avsikt att återvinna/återbruk tegel, prefabricerade betongelement, platsgjuten betong samt fönsterglas. Projektet har varit ett samarbete mellan Högskolan i Borås, Riksbyggen, Bostäder i Borås och Borås Stad. Målet var att samla in data gällande rivningsteknik, logistik samt klimatpåverkan från objektsorienterade fastigheter som rivs och på samma ställe byggs nytt i stadsmiljö. Genom praktisk rivning av en tegelvägg, datainsamling för verifierad LCA och logistik har genomförts, cirkularitets- och klimatpotentialen för materialen uppskattats. Studenter från Byggingenjörsprogrammet vid Högskolan i Borås har deltagit i projektet och dokumenterat delar av resultaten genom sina examensarbeten. Denna rapport ger en översikt av metodologin, datainsamlings- och analysprocessen och grunden för ett säkrare beslutsunderlag för ägarna på objektsorienterade fastigheter. 

A report about the environmental impacts involved in the use of recycled concrete waste as aggregates in new concrete. The environmental impacts were assessed based on a simple LCA using a prefabricated concrete producing company in Sweden as a case study. The results of the LCA revealed that major environmental impacts arised from the crushing and extraction processes as these were diesel fuel intensive. Comparatively, the use of recycled concrete as aggregates in new concrete saw a reduction in the environmental impacts as the need for extraction had reduced with the introduction of recycled aggregates. 

Concrete waste as crushed concrete aggregates (CCA) in structural concrete gives a new purpose and prolongs the technical life of the reference concrete accomplishing closed loop recycling. This research investigates CCA as aggregate replacement in an industrial reference concrete recipe as fine aggregate fractions and overall aggregate replacement. Experimental study of CCA concrete is conducted by testing compressive strength and workability. Results show that CCA concrete has inferior compressive strength and workability than reference concrete due to the adhered mortar and flakiness index of CCA, properties which differentiate CCA from reference concrete aggregates. These properties influence the aggregate packing density and water absorption properties of CCA, crucial to concrete workability and compressive strength.  

To overcome the challenges with determining water absorption of fine CCA, the standard pycnometer method is modified in an innovative way to test a combined fine and coarse aggregate fraction. The water absorption is measured at 15 minutes to estimate the water absorbed by CCA during the concrete mixing. Workability corresponding to reference is achieved when CCA fractions are momentarily pre-soaked with water corresponding to 50% of the 15-minute water absorption value just before concrete mixing.  

To improve concrete properties, this research investigates two modifications: enhancing aggregate quality by adhered mortar removal and enhancing cement paste quality by adding secondary cementitious materials (SCM). Firstly, CCA is modified by a fraction-wise mechanical pre-processing in a horizontal rotating drum for 15 minutes to abrade adhered mortar which is then removed by washing. The abrasive nature of pre-processing results in the loss of aggregate material along with the adhered mortar accounted for by a mass-balance; resolved by adjustments in CCA particle grading. The loss of adhered mortar leads to reduction of CCA water absorption, influencing pre-soaking water content. Pre-processing also influences properties such as flakiness index, void-content, unit-weight and density, jointly seen as an increase in CCA packing density. After pre-processing, mixes with CCA as fine aggregates (CCA50) show mean compressive strength exceeding reference concrete. Mixes with overall CCA replacement (CCA100) show same compressive strength as reference concrete. The flow diameters of both mixes correspond to the same flow class F2 as reference concrete.   

Secondly, modifications of cement paste are investigated by replacing 30% of the reference cement, CEM II/A-LL with granulated blast furnace slag (GGBS). Mixes investigated are CCA with/without mechanical pre-processing at both 50% and 100% replacements. Among the GGBS mixes, CCA100 achieves reference concrete compressive strength while CCA50 reaches the reference concrete strength only when combined with mechanically pre-processing. Addressing early-age strength, an improved mixing method with pre-soaked GGBS is investigated on CCA100 mix. The resulting mean compressive strength at seven days fulfils 93% of the corresponding reference concrete strength. Addition of GGBS causes the concrete workability to resemble a mix with increased mixing water content. Therefore, CCA flow diameter values of reference concrete flow class are achieved at a lower water/binder ratio.  

The results are investigated with regard to statistical significance and sustainability. For concrete CCA100, GGBS addition results in statistically significant improvements of the compressive strength and a nearly 30% reduction of carbon dioxide-related emissions implying a green concrete. For CCA50 statistically significant improvements in compressive strength are realized for the combination of mechanical pre-processing and GGBS addition.  

Concrete waste as crushed concrete aggregates (CCA) in structural concrete prolongs the technical life of the reference concrete accomplishing closed loop recycling. CCA concrete reaches the reference concrete compressive strength and workability by the densification of CCA and cement paste. Our previous study demonstrates CCA densification by mechanical pre-processing, aggregate quality improvements discerned by increased packing density giving reference concrete strength and workability. This study addresses paste densification with blast furnace slag (GGBS) to replace 30 (wt.%) of Portland cement at reference concrete w/b ratio 0.5 and a lower w/b 0.42. Two CCA replacements are investigated: fine aggregates, CCA50; overall aggregate replacement, CCA100. Compressive strength results show that both CCA50, CCA100 mixes achieve reference values at w/b 0.42, only CCA100 achieves reference value at w/b 0.5 as a climate-optimized concrete. The CCA50 mix-w/b 0.5 reaches reference strength when paste densification by GGBS is combined with CCA densification from mechanical pre-processing of aggregates. The 7-day strength of CCA100 with GGBS increases by 11% by mixing with pre-soaked GGBS. Statistical analysis of CCA100 strength results shows significant improvements with GGBS compared to mechanical pre-processing. Significant improvements are possible in CCA50 mix for a combination of mechanical pre-processed aggregates and GGBS replacement.

Crushed Concrete Aggregates (CCA) as fine and coarse aggregates in new concrete helps achieve closed-loop recycling. Assessment of workability, mechanical properties and durability of concrete demands knowledge of the water absorbed by the CCA. The EN 1097-6standard method is difficult to execute due to the presence of entrapped air and CCAsedimentation while performing water absorption experiment for fine CCA. Additionally, the assessment of Saturated Surface Dry (SSD) state seems operator specific and nonreproducible;moreover, giving water absorption measurement only at 24 hours. However, findings from this paper show measurements at 15 minutes is influential for concrete workability. The modified pycnometer method analyses the water absorption of a combined fraction consisting of coarse and fine CCA as proportioned in a given concrete recipe. Furthermore, sedimentation and entrapped air are prevented by pre-soaking the CCA in a solution of distilled water and poly-carboxylate based superplasticizer before commencing the experiment. Ultimately, the combined fraction is drained to SSD condition by vacuum filtration, which is easy to handle by professional operators. In this way, the water absorption development is measured from starting point to 24 hours for the combined fraction to determine the appropriate water amount to saturate CCA during concrete mixing.

Concrete with crushed concrete aggregates (CCA) shows lesser compressive strength than reference concrete with natural aggregates. The goal of this study is to improve the strength of structural concrete with 53% and 100% CCA replacements without increasing the cement content. Thus, improvements in CCA quality are induced by combining mechanical and pre-soaking pre-processing techniques. Mechanical pre-processing by rotating drum is separately pursued on fine and coarse CCA for 10 and 15 min respectively. Results show, adhered mortar content and CCA water absorption reduces as pre-processing duration increases. Pre-processing influences CCA particle grading, flakiness index, shape index, void-content, unit-weight and density, jointly seen as packing density, which increases with pre-processing duration. Water amount to pre-soak CCA before concrete mixing is stable despite grading modifications, due to reduced water absorption resulting from mechanical pre-processing. Compressive strength and workability for pre-processed CCA50 and CCA100 concrete are comparable to reference concrete and show similar trends of improvement with packing density. Packing density markedly shows the quality improvements induced by pre-processing on CCA, maybe considered as one of the quality assessment indexes for CCA. Packing density should be investigated for other recipes to see the stability of the trend with workability and compressive strength.

The water absorption of crushed concrete aggregates (CCA) has a major influence on concrete workability. In order to determine the water absorption of CCA, a more porous material than natural aggregates, modifications to the standard pycnometer method are proposed as: (1) Water absorption is measured on a combined fraction CCA consisting of fine and coarse aggregates proportioned according to concrete recipe. (2) The CCA is pre-processed to mitigate sedimentation. (3) Saturated surface dry condition of aggregate is assessed by vacuum filtration and ocular technique. Water absorption development is measured at 0 min, 15 min, and 24 h. About 90% of the 24-h water absorption occurs in 15 min, value which is introduced in the concrete recipe; slump flow and compressive strength are determined. The modified pycnometer method shortens test duration, is operator insensitive and gives reliable water absorption result for CCA leading to concrete workability fitting industrial application.

Sweden’s concrete waste is recycled for use in low-utility purposes such as in the construction of sub-bases in roads but hardly as aggregates in new concrete. To analyse the potential for high-utility recycling, a literature study was conducted on the regulatory instruments, building standards, production and properties of recycled concrete aggregates and the recycled aggregate concrete for Sweden and European countries. Results urge statistics to quantify recycled concrete; regulations like source sorting of waste and selective demolition could potentially optimize recycled aggregate production. Also, the compressive strength of recycled concrete aggregate’s parent concrete influences the properties of the new concrete.

This paper investigates the fracture mechanical properties of concrete, using crushed concrete aggregates (CCA) and granulated blast furnace slag (GGBS) for partial cement replacement. CCAs made from prefabricated concrete replace 100% of the fine and coarse fractions in concrete recipes with w/c ratios of 0.42 and 0.48. Two pre-treatment methods, mechanical pre-processing (MPCCA) and accelerated carbonation (CO2CCA), are investigated for quality improvements in CCA. The resulting aggregates show an increased density, contributing to an increase in the concrete’s compressive strength. The novelty of this paper is the superposition of the effects of the composite parts of concrete, the aggregate and the cement mortar, and their contributions to concrete fracture. Investigations are directed toward the influence of fine aggregates on mortar samples and the influence of the combination of coarse and fine aggregates on concrete samples. The physical and mechanical properties of the aggregates are correlated with mortar and concrete fracture properties. The results show that CCA concrete achieves 70% of the fracture energy values of concrete containing natural aggregates, and this value increases to 80% for GGBS mixes. At lower w/c ratios, MPCCA and CO2CCA concretes show similar fracture energies. CO2CCA fine aggregates are the most effective at strengthening the mortar phase, showing ductile concrete behavior at a w/c ratio of 0.48. MPCCA aggregates contribute to higher compressive strengths for w/c ratios of 0.42 and 0.48. Thus, mechanical pre-processing can be improved to produce CCA, which contributes to more ductile concrete behavior.