CIC Construction Innovation Award 2019 Presentation...
Transcript of CIC Construction Innovation Award 2019 Presentation...
Category Local Innovators Subject Field Construction Productivity
Lead ApplicantProfessor Christopher KY Leung
Co-ApplicantKelvin KY To
Co-ApplicantDr Ivan ML Sham2 2
Rapid Repairing Mortar Material for Corroded Concrete Structures
CIC Construction Innovation Award 2019Presentation Ceremony & Technical Seminar
Presented by:
Professor Christopher LeungDept of Civil & Environmental Engineering
The Hong Kong University of Science & Technology
Background Information
• R2M2 is the result of a tri-partycollaboration
• …via a 21-month long research project funded by the Innovation & Technology Fund (ref no ITF/024/16NI)
• …with NAMI as the Applicant, Prof Christopher Leung (HKUST) being the Principal Investigator, and Chun Wo as the Industry Co-Applicant
R2M2
Applicant
Principal Investigator
Industry Co-Applicant
Need of R2M2
Technology• many buildings approaching
40 years of age have rebarcorrosion problems, leading to• reduction in steel rebar area• decrease in load-carrying
capacity• a problem very common for
slabs in old buildings with mild steel rebars
R2M2
Original rebar Corroded rebar
• approx 40,000 public housing units in Hong Kong with severely corroded rebars in slabs (up to 40% loss in steel area)
• number expected to triple in a few years
R2M2
Need of R2M2
Technology
• an effective repair technology, in terms of both time and cost, is highly desirable...
R2M2
Current Practice for Repair of Corroded Rebars
• current practice – where corrosion is severe, a new rebar is needed to lap with corroded one to recover tensile load-carrying capacity
expose corroded rebars for repair
NB – compensation rebar required
remove large volume of sound concrete along rebars to provide sufficient rebar lap length
fix compensation rebar
patch concrete voids with repair mortar material
substantial savingin...
R2M2
• new rebar is not needed as the fibres in R2M2 can carry tensile load• with R2M2 in direct contact with the rebar, a short bond length is
sufficient for stress transfer
Innovative Repair Approachusing R2M2
expose corroded rebars for repair
NB – compensation rebar not required
with R2M2, tensile loading is transferred directly from rebar to mortar, and hence rebar bond length is reduced significantly...R2M2
R2M2
R2M2 with tensile strength > 3.5MPa and ductile behavior has been designed for mild steel rebar with 40%area loss
R2M2hooked-endstainless steel fibres
• innovation – a novel fibre-reinforced mortar, R2M2, that can carry tensile force
Development ofNovel Mortar, R2M2
R2M2
• innovation – a repair mortar (ChunWo-Nami) meeting PCCS-RMClass 25 Mortar requirements and compatible with steel fibers
Development ofNovel Mortar, R2M2
PropertiesSpecification of
Class 25Repair Mortar
RonacreteUnicell 25 *
Mapei PlanitopHB 25 *
Nami MortarRM #
MeetingSpecification
(Y/N)
Compressive Strength(MPa) - 28 days, TM1 30 - 40 30 35.5 34.9 Y
Tensile Strength(MPa) - 7 days, TM3 ≥ 2 2.7 3.6 2.5 Y
Elastic Modulus(Gpa) - 28 day, TM4 9 - 15 10 12.8 12.7 Y
Bond Strength(MPa) - 7 days, TM5 ≥ 1.5 2.2 2.7 2.6 Y
Coutinho Ring(Cracks) - 28 days, TM6 No Cracks No Cracks No Cracks No Cracks Y
Air PermeabilityResistance(s) - 35 days, TM7
≥ 150 216 181 1399 Y
* From data sheets of relevant products
# Measured in Nami Laboratory
R2M2
Representative Test ResultsProving Applicability of R2M2 – Bond Tests
specimens (with 3 selected mortars) tested to determine a bond length for load transfer ; for 40% loss in rebar steel area, a bond length of 15 rebar diameter is found adequate
Repair Mortar, R2M2
20mm
100mm
12.5mm
20mm
10m
m
Corroded R10 rebar
RC Slab Soffit
Steel Fibre-ReinforcedMortar (R2M2)
12.5mm
20mm
20mm
100mm
Bond LengthCorroded Length
Full Force, FfullReduced Force, Freduced
Mortar Force, Fmortar
Repair Mortar, R2M2
Concrete
Interfacial Shear Stress
‘A’ ‘B’
L of SymCRC Slab
R2M2
Representative Test ResultsProving Applicability of R2M2 – Load Tests
10mmdia
mild steelbar
reduceddiameter
losing 40%of its area
* 150mm bond length for R2M2test specimen –discrete concrete strips reinforced by 10mm mild steel bar to simulate RC slab
strip soffit view
*bond length is150mm only(vs 400mm for new rebar)
R2M2
4-point bending testsload-displacement curves from bending test
load (kN)
displacement (mm)
full load recovery was achieved in test specimens (with rebar losing 40% steel area)
Representative Test ResultsProving Applicability of R2M2 – Load Tests
R2M2
Temperature vs time curve according to BS EN 1363-1
0
200
400
600
800
1000
1200
0 20 40 60 80
Tem
per
atu
re/
o C
Time / Minutes
BS EN 1363-1 Standard Temp.Curve
Actual Mean Furnace Temp.
• fire tests under dead load (BS EN 1363-1)
• 1 control sample + 3 with ‘corroded’ rebarsand repaired with different mortars
• Deflection WITHIN limit after 60mins of fire exposure
• no sign of cracking or spalling of repaired patches
Representative Test ResultsProving Applicability of R2M2 – Fire Tests
Control Sample Specimen using R2M2
Specimen using market product Specimen using market product
R2M2
Significant Time & Cost Savings
Items Conventional Method R2M2
length of concrete to be removed 1.0 0.44
plant and material costs 1.0 0.89labour cost 1.0 0.83repair time 1.0 0.60total equivalent cost 1.0 0.85
• time & cost savings – for a typical area with a corroded rebar length of say 100mm, the time and cost using R2M2 are shown non-dimensionally and compared to conventional method
R2M2
Other Measurable Improvements
• less construction waste– 60% less concrete hacking
• less dust– 60% less concrete hacking
• less noise– 40% shorter hacking time
• less time working-at-height– safer condition for workers
R2M2
Quality Assurance & Workmanship
• standardised mixing procedures for R2M2
• well-developed concrete patching method using R2M2
• comprehensive training programme for R2M2 qualified applicators
R2M2
Roadmap for R2M2 Development
Jan 2020 Sep 2020 Oct 2020 Commencing PSTS programme / Further test ing Sett ing up training workshops Training 1st batch of Qualified Applicators
Dec 2019 Finalising training manual and methodology
TrainingPublic Sector Trial Scheme
Production
Finalising suppliers / manufacturers Trial production / Sett ing up sales team Statutory approval by Bldgs Dept Commencing field trials at ArchSD / HD sites Dec 2019 Feb 2020 Aug 2020 Oct 2020
R2M2
Future Outlook forR2M2 Development
potentials for repair of civil structures with high yield rebars– repair mortar with tensile strength > 10MPa has recently been developed
current application on slabs can be extended to beamswith corrosion of both flexural & shearreinforcements – under investigationat HKUST
potentials application overseas as structural degradation due to rebar corrosion is a global problem…
R2M2
Thank You