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Recycling of concrete in new structural concrete
Högskolan i Borås, Akademin för textil, teknik och ekonomi.ORCID-id: 0000-0003-4804-382x
2021 (Engelska)Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
Hållbar utveckling
Verkets författare anser att innehållet i publikationen faller inom ämnet hållbar utveckling.
Abstract [en]

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.  

Ort, förlag, år, upplaga, sidor
Borås: Högskolan i Borås, 2021.
Serie
Skrifter från Högskolan i Borås, ISSN 0280-381X ; 117
Nyckelord [en]
concrete recycling, sustainability, closed-loop recycling, recycled aggregates, compressive strength, workability mechanical pre-processing, secondary cementitious materials, green concrete, climate-optimized concrete
Nationell ämneskategori
Materialteknik Samhällsbyggnadsteknik
Forskningsämne
Resursåtervinning
Identifikatorer
URN: urn:nbn:se:hb:diva-24594ISBN: 978-91-89271-19-7 (tryckt)ISBN: 978-91-89271-20-3 (digital)OAI: oai:DiVA.org:hb-24594DiVA, id: diva2:1515177
Disputation
2021-02-26, C203, Akademiplatsen 1, Borås, 10:00 (Engelska)
Opponent
Tillgänglig från: 2021-01-29 Skapad: 2021-01-08 Senast uppdaterad: 2021-04-06Bibliografiskt granskad
Delarbeten
1. RE:Concrete- Study on Recycling of Concrete in Sweden
Öppna denna publikation i ny flik eller fönster >>RE:Concrete- Study on Recycling of Concrete in Sweden
2017 (Engelska)Ingår i: Nordic Concrete Research, ISSN 0800-6377, nr 56, s. 83-99Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

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.

Ort, förlag, år, upplaga, sidor
Oslo: , 2017
Nyckelord
Recycled concrete aggregate, Structural concrete, Closed-loop recycling, Sustainability, Waste management
Nationell ämneskategori
Annan samhällsbyggnadsteknik
Forskningsämne
Resursåtervinning
Identifikatorer
urn:nbn:se:hb:diva-13709 (URN)000425406000008 ()
Projekt
RE:Concrete
Tillgänglig från: 2018-02-22 Skapad: 2018-02-22 Senast uppdaterad: 2021-01-29Bibliografiskt granskad
2. Modified pycnometer method to measure the water absorption of crushed concrete aggregates
Öppna denna publikation i ny flik eller fönster >>Modified pycnometer method to measure the water absorption of crushed concrete aggregates
2020 (Engelska)Ingår i: Journal of Sustainable Cement-Based Materials, ISSN 2165-0373, E-ISSN 2165-0381Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

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.

Nyckelord
Crushed concrete aggregates, recycled aggregates, water absorption, pycnometer, saturated surface dry condition, sustainability
Nationell ämneskategori
Samhällsbyggnadsteknik
Forskningsämne
Resursåtervinning
Identifikatorer
urn:nbn:se:hb:diva-23137 (URN)10.1080/21650373.2020.1715902 (DOI)000512023500001 ()2-s2.0-85078489111 (Scopus ID)
Projekt
RE:Concrete
Tillgänglig från: 2020-04-06 Skapad: 2020-04-06 Senast uppdaterad: 2024-02-01Bibliografiskt granskad
3. Improving Recycled Aggregate Quality by Mechanical Pre-Processing
Öppna denna publikation i ny flik eller fönster >>Improving Recycled Aggregate Quality by Mechanical Pre-Processing
2020 (Engelska)Ingår i: Materials, Vol. 13, nr 19Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

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.

Ort, förlag, år, upplaga, sidor
MDPI, 2020
Nyckelord
concrete recycling; sustainability; recycled aggregates; mechanical pre-processing; aggregate quality; packing density; aggregate shape; compressive strength; workability
Nationell ämneskategori
Samhällsbyggnadsteknik
Identifikatorer
urn:nbn:se:hb:diva-24811 (URN)10.3390/ma13194342 (DOI)000586581500001 ()2-s2.0-85093938328 (Scopus ID)
Tillgänglig från: 2021-01-25 Skapad: 2021-01-25 Senast uppdaterad: 2022-01-20Bibliografiskt granskad
4. Effects of slag inclusion and mechanical pre-processing on the properties ofrecycled concrete in terms of compressive strength and workability
Öppna denna publikation i ny flik eller fönster >>Effects of slag inclusion and mechanical pre-processing on the properties ofrecycled concrete in terms of compressive strength and workability
(Engelska)Manuskript (preprint) (Övrigt vetenskapligt)
Nationell ämneskategori
Samhällsbyggnadsteknik
Forskningsämne
Resursåtervinning
Identifikatorer
urn:nbn:se:hb:diva-24897 (URN)
Anmärkning

Submitted to Nordic Concrete Research.

Tillgänglig från: 2021-01-29 Skapad: 2021-01-29 Senast uppdaterad: 2021-02-08

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