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BENDING CHARACTERISTICS OF CLT FROM RECOVERED SPRUCE

Open access
Chúláin, Caitríona Uí, Llana, Daniel F., Hogan, Paul, McGetrick, Patrick, Harte, Annette M.·2023·World Conference on Timber Engineering (WCTE 2023)
DOI 10.52202/069179-0121
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Abstract

The circular use of construction materials is an essential step in the drive to reduce the environmental impact of the construction sector.Structural materials, such as timber, recovered from demolition of buildings is a valuable resource.Reuse or recycling these materials in new buildings products reduces waste and the overall carbon footprint of the build environment.This paper investigates the use of spruce recovered from demolition of a roof structure in the manufacture of CLT panels.Bending tests are performed on 3-layer panels made from this recovered material and also on panels made from new timber and hybrid panels with mixed new and recovered timber.Results show that the performance of CLT panels using recovered timber is equivalent to that of panels from new timber in terms of bending strength and stiffness.

AI snapshot

Written from the paper’s full text.

TL;DR

Three-layer CLT panels made from spruce recovered from a demolished roof structure showed bending strength and stiffness equivalent to panels made from new timber. The study concludes recovered softwood can be used in CLT, though testing was limited to a small number of panels from a single source.

Key findings

  • Mean global modulus of elasticity was 10300 N/mm² for recovered-timber panels, 10900 N/mm² for new-timber panels, and 10800 N/mm² for hybrid panels, with no significant difference between groups.
  • Mean bending strength was 49 N/mm² for recovered, 50 N/mm² for new, and 42 N/mm² for hybrid panels; coefficients of variation were low, 7.5%–8.7%.
  • All panels failed in bending, initiating at a knot or large slope of grain on the underside and propagating through the panel thickness.
  • Yield from the recovered timber was about 28% because the recovered cross-section (142 × 35 mm²) was much larger than the final board size (90 × 20 mm²); using boards closer to final dimensions, such as 130 × 30 mm², would increase yield to 70%.

Methods

  • Norway spruce boards were recovered from roof trusses of a 1970s office building in Dublin, Ireland; 78 boards were sampled, mostly 142 × 35 mm, with visible grade stamps indicating TR26. New reference timber was Irish-grown Douglas fir, selected from 101 boards because Irish spruce was normally graded C16 and not equivalent to TR26.
  • Non-destructive acoustic grading measured dynamic modulus of elasticity; recovered boards with adjusted values between 11000 and 13900 N/mm² and new boards between 10600 and 14600 N/mm² were selected. Boards were planed to 90 × 20 mm, and three-layer 60 mm CLT panels were manufactured in three designs: all recovered, all new, and hybrid with new outer layers and recovered core. Three panels of each design were made.
  • Panels were bonded with one-component polyurethane adhesive at 0.6 MPa for at least 2 hours, conditioned at 65% RH and 20°C, and tested in four-point bending over a 1560 mm span with load heads spaced at 6h, following EN 408 and EN 16351.

Limitations

  • The paper states that the number of specimens tested was small and that the recovered timber came from a single source; further testing of panels from a wide range of sources is recommended.
  • The paper notes that only three panels were tested per series and that timber strength variability from features such as knots means the lower hybrid-panel strength may not be significant.
  • Evident from the text: the study assessed bending properties only, while the authors state other properties, such as behavior perpendicular to grain and possible increased brittleness, still need investigation; the low yield of 28% also indicates a practical material-supply limitation.

Model-written summary. Check it against the paper before relying on it.

Integrity signals

Registry

Crossref · 10.52202/069179-0121

Cites

15 of 15 references verified0 citation errors · 0 not checkable

Statistics

Nothing to recompute.

Claims the paper makes

0 of 13 cited sources checked · 0 supported · 0 flagged

  • Findingown data

    The bending strength values for the hybrid panels were consistently lower than those of the recovered and new panels.

    “The strength values for the hybrid panels were consistently lower than those of the recovered and new panels (Figure 8).”
    Quote in the paperNot a substantial claim
    • Rests on an assumption: The new Douglas fir timber is a suitable reference material for comparing bending performance with recovered TR26 spruce.
  • Findingown data

    There is no significant difference between the mean modulus of elasticity of the recovered, new, and hybrid CLT panel groups.

    “There is no significant difference between the means of each group as can be observed visually in Figure 7.”
    Quote in the paperSubstantial claim
    • Rests on an assumption: The new Douglas fir timber is a suitable reference material for comparing bending performance with recovered TR26 spruce.
  • Findingown data

    CLT panels manufactured from recovered spruce have equivalent bending strength and stiffness to CLT panels manufactured from new timber.

    “Results show that the performance of CLT panels using recovered timber is equivalent to that of panels from new timber in terms of bending strength and stiffness.”
    • Also stated in: § 5. CONCLUSIONS · plain
      “Overall, this study has found no difference in the mechanical properties in bending of CLT manufactured from recovered and new softwood timber.”
    Quote in the paperSubstantial claim
    • Rests on an assumption: The new Douglas fir timber is a suitable reference material for comparing bending performance with recovered TR26 spruce.
  • Findingown data

    Similar linear load-displacement responses until close to failure are seen in each panel type.

    “Similar linear responses until close to failure are seen in each panel type.”
    Quote in the paperNot a substantial claim
  • Findingown data

    The new timber batch had Edyn,12,adj values between 10600 and 14600 N/mm2.

    “Based on acoustic measurements of 101 new boards, a batch of timber boards with Edyn,12,adj values between 10600 N/mm 2 and 14600 N/mm 2 was chosen for processing into CLT panels.”
    Quote in the paperNot a substantial claim
  • May combine two claims. 12
  • Classified as probably not a substantial claim. 13

  • May combine two claims.

    Findingown data

    The bending strength and stiffness of the CLT panels do not appear to be adversely affected by the timber being under load for 50 years.

    “While bending strength and stiffness do not appear to be adversely affected by being under load for 50 years, other properties need to be investigated.”
    Quote in the paperSubstantial claim
    • Rests on an assumption: The recovered timber was about 50 years old.

  • May combine two claims.

    Findingown data

    The mean bending strength was 49 N/mm2 for recovered, 50 N/mm2 for new, and 42 N/mm2 for hybrid CLT panels.

    “The mean bending strength was 49 N/mm 2 , 50 N/mm 2 and 42 N/mm 2 for the recovered, new and hybrid panels, respectively (Table 1), with low coefficients of variation in the range 7.5%-8.7%.”
    Quote in the paperSubstantial claim
    • Rests on an assumption: The new Douglas fir timber is a suitable reference material for comparing bending performance with recovered TR26 spruce.

  • May combine two claims.

    Findingown data

    All panels failed in bending, with failure initiating at a knot or large slope of grain on the underside and propagating through the panel thickness.

    “All panels failed in bending, which initiated at the location of a knot or large slope of grain on the underside of the panel and then propagated through the thickness of the panel as seen in Figure 6.”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Findingown data

    The mean global modulus of elasticity was 10300 N/mm2 for recovered, 10900 N/mm2 for new, and 10800 N/mm2 for hybrid CLT panels.

    “The mean modulus of elasticity was 10300 N/mm 2 , 10900 N/mm 2 and 10800 N/mm 2 for the recovered, new and hybrid panels, respectively.”
    Quote in the paperSubstantial claim
    • Rests on an assumption: The new Douglas fir timber is a suitable reference material for comparing bending performance with recovered TR26 spruce.

  • May combine two claims.

    Findingown data

    The recovered timber cross-section (142 x 35 mm2) was significantly larger than the required board dimensions (90 x 20 mm2), resulting in a yield of about 28% when length reductions are included.

    “the recovered timber cross-section (142 x 35 mm 2 ) was significantly larger than the board dimensions required for panel manufacture (90 x 20 mm 2 ) and this resulted in a yield of about 28% when length reductions are included.”
    Quote in the paperNot a substantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Findingown data

    The moisture content of the timber boards at the site was estimated to be between 18% and 23%.

    “Using a hand-held moisture meter, the moisture content of the timber boards at the site was estimated to be between 18% and 23%.”
    Quote in the paperNot a substantial claim

  • Probably not a substantial claim: may not pass S4 (based).

    Findingnone given

    The panels were manufactured with timber boards with similar dynamic modulus of elasticity values.

    “This is to be expected as the panels were manufactured with timber boards with similar dynamic modulus of elasticity values.”
    Quote in the paperNot a substantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Premisecitation

    Non-destructive testing based on acoustic measurements is widely used for evaluation of timber mechanical properties.

    “Non-destructive testing based on acoustic measurements is widely used for the evaluation of timber mechanical properties [22].”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [22]

      Couldn’t be matched to a paper in Crossref, so it can’t be checked.

  • Classified as probably not a substantial claim.

    Study design and conductcitation

    The testing was carried out in accordance with EN408 and EN 16351.

    “All panels were conditioned at 65% relative humidity and 20°C prior to testing in out-of-plane bending in accordance with EN408 [26] and EN 16351 [27].”
    Quote in the paperSubstantial claim0 of 2 sources checked
    • cites [26]

      Couldn’t be matched to a paper in Crossref, so it can’t be checked.

    • cites [27]

      Couldn’t be matched to a paper in Crossref, so it can’t be checked.

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Study design and conductcitation

    The adhesive selection and processing parameters were based on previous studies using new spruce timber.

    “The adhesive selection and processing parameters were based on previous studies carried out in the University of Galway using new spruce timber [24,25].”
    Quote in the paperNot a substantial claim0 of 2 sources checked
    • cites [24]

      Couldn’t be matched to a paper in Crossref, so it can’t be checked.

    • cites [25]

      Couldn’t be matched to a paper in Crossref, so it can’t be checked.

  • Classified as probably not a substantial claim.

    Premisecitation

    The mean shear modulus G is taken as 650 N/mm2 in accordance with EN 408 and EN 16351.

    “The mean shear modulus G is taken as 650 N/mm 2 in accordance with EN 408 [26] and EN 16351 [27].”
    Quote in the paperSubstantial claim0 of 2 sources checked
    • cites [26]

      Couldn’t be matched to a paper in Crossref, so it can’t be checked.

    • cites [27]

      Couldn’t be matched to a paper in Crossref, so it can’t be checked.

  • May combine two claims.

    Interpretationcitation

    The age of the recovered timber was about 50 years, so no deterioration in bending strength would be expected based on the conclusions of five different studies.

    “For the present study, the age of the recovered timber was about 50 years so no deterioration would be expected based on the conclusions of five different studies.”
    Quote in the paperSubstantial claim
    • Rests on an assumption: The recovered timber was about 50 years old.

  • May combine two claims.

    Interpretationreasoning

    The modulus of elasticity values of the CLT panels are consistent with the modulus of elasticity of the boards used in their manufacture, indicating that bonding of layers was successful for both recovered and new timber.

    “As the modulus of elasticity values of the CLT panels are consistent with the modulus of elasticity of the boards used in their manufacture, it indicates that the bonding of the layers was successful for both recovered and new timber.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Study design and conductreasoning

    The study's findings are limited by the small number of specimens tested and the use of recovered timber from a single source.

    “While these results are very positive, it should be borne in mind that the number of specimens tested was small and used recovered timber from a single source.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Interpretationreasoning

    The lack of significant difference in modulus of elasticity between panel types is expected because the panels were manufactured with timber boards with similar dynamic modulus of elasticity values.

    “This is to be expected as the panels were manufactured with timber boards with similar dynamic modulus of elasticity values.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Interpretationreasoning

    The observed differences in bending strength between panel types may not be statistically significant because only three panels were tested per series and timber strength has significant variability due to features such as knots.

    “However, as only three panels were tested in each series and significant variability is expected in timber strength due to the influence of features such as knots, these differences in strength values may not be significant.”
    Quote in the paperSubstantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

    Premisecitation

    TR26 grade timber has a mean modulus of elasticity in bending of 11000 MPa and a characteristic bending strength of 28.3 MPa.

    “TR26 grade timber has a mean modulus of elasticity in bending of 11000 MPa and a characterisitic bending strength of 28.3 MPa [21].”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [21]

      Couldn’t be matched to a paper in Crossref, so it can’t be checked.

  • Classified as probably not a substantial claim.

    Study design and conductreasoning

    The study selected boards with Edyn,12,adj values between 11000 and 13900 N/mm2 to reduce variability between specimens.

    “To reduce variability between specimens, from the full sample boards with Edyn,12,adj values between 11000 N/mm 2 and 13900 N/mm 2 were selected for the manufacture of CLT panels.”
    Quote in the paperSubstantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Premisecitation

    Rose et al. [17] reported a 60% lower bending strength for recovered softwood panels compared to new panels.

    “This finding is different to that reported by Rose et al. [17] who reported a 60% lower bending strength for recovered softwood panels compared to new panels.”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [17]

      Couldn’t be matched to a paper in Crossref, so it can’t be checked.

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Premisecitation

    Kránitz et al. [28] reported a decrease in bending strength for hardwoods.

    “Kránitz et al. [28] in their extensive literature review on the effects of aging on wood, reported a decrease in bending strength for hardwoods.”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [28]

      Couldn’t be matched to a paper in Crossref, so it can’t be checked.

  • Probably not a substantial claim: may not pass S3 (load-bearing), S4 (based).

    Interpretationreasoning

    The high moisture content is attributed to rain penetration of the roof through damaged slates and felt over an extended period prior to demolition.

    “This high moisture content is attributed to rain penetration of the roof through damaged slates and felt over an extended period of time prior to demolition.”
    Quote in the paperNot a substantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

    Premisecitation

    Kránitz et al. [28] reported an increase in brittleness, which may affect properties perpendicular to the grain.

    “Kránitz et al. [28] reported an increase in brittleness, which may affect the properties perpendicular to the grain.”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [28]

      Couldn’t be matched to a paper in Crossref, so it can’t be checked.

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Premisecitation

    Llana et al. [16] recorded a 50% reduction in bending strength for panels using recovered oak compared to those made from new oak.

    “For hardwoods, Llana et al. [16] recorded a 50% reduction in bending strength for panels using recovered oak compared to those made from new oak.”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [16]

      Couldn’t be matched to a paper in Crossref, so it can’t be checked.

23 of 23

  • The paper relies on this without support.

    The recovered timber was about 50 years old.

    “Spruce members were recovered from the demolition of a timber roof truss that had been under load for about 50 years and which was exposed high relative humidity during its later years.”
    “For the present study, the age of the recovered timber was about 50 years so no deterioration would be expected based on the conclusions of five different studies.”

  • The paper relies on this without support.

    The new Douglas fir timber is a suitable reference material for comparing bending performance with recovered TR26 spruce.

    “The most suitable available material was Irish grown Douglas fir (Pseudotsuga menziesii (Mirb.)Franco).”
    “As Irish-grown spruce is normally graded to C16, its properties are not equivalent to TR26 material and so it deemed unsuitable as reference new timber.”
2 of 2

Self-check

Percentages, sums and reported differences re-computed from the paper’s own numbers.

Each contradiction between two passages listed here was confirmed by an independent check.

  • Conflicting descriptions of recovered panels' bending strength

    Minor

    The first statement says the recovered panels had 60% of the new panels' bending strength, while the second says their strength was 60% lower, or 40% of the new panels' strength.

1 of 1

Cites

Flagged first, then by citations

Research works printed but not linked: 2

  1. Azambuja, R.R., De Vallance, D.B., McNeel, J., Hassler, C., Dahle, G., CLT panels from below-grade yellow-poplar sorted by non-destructive proof loading. In Proceeding of 63rd International Convention of Society of Wood Science and Technology (SWST). 106-107, 2020. Online.
  2. Stenstad, A., Lønbro Bertelsen, S., Modaresi, R., Comparison of strength tests for evaluating the secondary timber utilisation in Cross Laminated Timber (CLT). In Proceedings of 16th World Conference on Timber Engineering (WCTE 2021), 2201-2206, Santiago, Chile. Online, , 2021.

Cited by

Sorted by citations

Related

Authors
Chúláin, C. U., Llana, D. F., Hogan, P., McGetrick, P., & Harte, A. M.
Affiliations
  • Ollscoil na Gaillimhe – University of Galway (IE)
  • Universidad Politécnica de Madrid (ES)
  • Hegarty Demolition
ORCID
Venue
World Conference on Timber Engineering (WCTE 2023)
Publisher
World Conference on Timber Engineering (WCTE 2023)
Published
2023
Pages
888-894
DOI
10.52202/069179-0121
OpenAlex
W4380450898
Semantic Scholar
b8a433d0115e3d7a8f868f6d618b3f1d4f847127
Cited by
5
References
15
Citations by year
2026: 2 · 2025: 2 · 2023: 1
FWCI
3.25
Type
conference paper
Language
en
Open access
Locations
World Conference on Timber Engineering (WCTE) (publishedVersion)
Funders
  • European Commission (HORIZON2020, 773324)
  • University of Galway
Topics
  • Physical Sciences › Engineering › Building and Construction › Wood Treatment and Properties
  • Life Sciences › Agricultural and Biological Sciences › Plant Science › Bamboo properties and applications
  • Life Sciences › Agricultural and Biological Sciences › Forestry › Agricultural and Food Sciences
Keywords
cross-laminated timber, spruce, demolition waste, circular construction, flexural strength, bending stiffness, wood recycling, roofs

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Registry, retraction, Cites and statistics results are computed, not judged, with one exception: a printed reference that no index lists is read once by a model before it counts as a citation error. Claims are extracted by a model and kept only when their quote appears verbatim in the text; each cited source is then checked, with a model’s help, for whether it says what the claim relies on. Those verdicts can be wrong — read the claim’s quote and the cited source before relying on one.

Claims read by deepseek-v4.1-flash under definition version 3 (extract-v3) on 2026-10-23.

Classified by jev-1.13-20260917 (gold-guideline-v0.2) on 2026-10-23.

Statistics and arithmetic are recomputed, not judged.

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