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