Non-Destructive Testing &

Assessment of Concrete Structures Case Study: St. Mary Dam – Low-Level Conduit

Presented By: Clayton Weiss, P.L.(Eng.)

ESRD – Operations Infrastructure, Oldman Basin

• Constructed 1946-1951, 65 years old, high risk

• Low-level concrete riparian conduit, 646 meters long (426 m easy access via catwalk left side at 3m), 6m (20’) inside Dia., 0.6-0.75m thick walls, sub-grade under 50 meters fill.

St. Mary Dam - Background

Management & Optimization of Aging Infrastructure

• Challenge: approaching end of ‘theoretical’ design service life.

– How to determine ‘actual’ remaining life, justify need for high priority funding?

• Extreme high costs to repair or replace. Limited funding, many competing high priority projects:

– What is the Level of Risk??!! Dictates when is action is required

– PROVE IT

– Design & Construction will take many years due to size and unique challenges – start planning now.

Management & Optimization of Aging Infrastructure

• Current monitoring strategy:

– Standard Methods: Visual surface inspections, crack monitoring, leakage/seepage monitoring, Schmidt hammer testing.

– Very effective and essential to continue, but has limitations:

• Limited to surface only, no way to identify and map internal defects

• Limited precision, requires confirmation & quantitative data

• No early warning of internal degradation.

Management & Optimization of Aging Infrastructure

• How to increase level of scrutiny beyond the surface, and gather quantitative data, including:

– Directly measure internal quality and overall uniformity of the concrete

– Identify “red flag” defects. i.e. voids, delamination, honeycombing

– Confirm actual rebar arrangement (concerns regarding 1940’s construction standards).

– More inputs for identifying Level of Risk

Non-Destructive Testing Methods

- Options? - 1) Schmidt Hammer Test – lower precision for internal defects, needs confirmation

- 2) Hammer Sounding - lower precision for internal defects, subjective, needs confirmation

- 3) Ultra-Sonic Pulse Velocity (UPV) – Used to assess structural integrity of concrete members in bridges, and to map extents of defects. Limitation – requires 2-sided access, not possible in the case

- 4) Impact-Echo Scanning – LOW COST, FAST - collect ASTM approved measurements of thickness in concrete and identify and map location and extents of defects ex. Cracks, Delaminations, Voids, Honeycombing. Limited to 1 meter thickness, requires only 1-sided access – YES

- 5) Ground Penetrating Radar – LOW COST & FAST - Identify and map first layer of rebar - YES

- 6) Coring and Laboratory testing – by far the most detailed, complete & precise information, but HIGH COSTS and LONG TIMELINES in concrete of questionable quality, destructive testing can be risky until condition is first assessed with methods such as #4 and #5 above.

Evaluate New Methods for Monitoring &

Assessment of Concrete Structures

• Pilot Project: Evaluate the Effectiveness of Non-Destructive Testing Techniques as a useful Infra. Management Tool – augment existing methods.

– May, 2013 – Request for Proposals for Non-Destructive Testing, Impact Echo and GPR

– Awarded to AMEC Materials Group, Calgary.

– July, 2013 – Field Testing program begins

Field Testing Program – GPR Rebar

Locates - 5 Sample Locations

Field Testing Program – GPR - 5 Sample

Locations

Field Testing Program – GPR - 5 Sample

Locations – Results

• ‘Red Flag’ concerns/deficiencies

– Reinforcing bar highly variable pattern/orientation, vertical and horizontal

spacing far too wide, not close to conforming to current standards

– Not installed as per record drawings, record information incorrect!!

– Very deficient in spacing, orientation, consistency, and cover

Field Testing Program – Impact-Echo -

Sample Locations

Field Testing Program – Impact-Echo -

Sample Locations

Field Testing Program – Impact-Echo -

Sample Locations

Field Testing Program – Impact-Echo -

Results

Sound Concrete

Suspect/Low

Quality Concrete

Defective

Area

Field Testing Program – Impact-Echo -

Results

Defective

Concrete –

Multiple Defective

Areas

Field Testing Program – Impact-Echo -

Results

• Summary of Results – Strong correlation with visual and hammer

sounding results, >50% areas sampled were “red flag” concerns

– Sound/Good: 50%

– Suspect or Defective: 50%

– Delaminated Areas: 56%

• Interpretation? Next Steps?

– Consultant recommended collecting Core Samples for Lab Analysis to

calibrate readings, Impact-Echo Proof-of-Concept, increase confidence

– Also Collect additional Lab data:

• Compressive Strength & Hardened Density,

• Air entrainment, Permeable void analysis

• Alkali-aggregate reactivity

Confirmation of Non-Destructive Tests -

Core Sampling & Laboratory Analysis

• Jan., 2014 – 10 Cores Collected & Analyzed at AMEC’s Lab

» 3” diameter, Min. depth 200 mm

Concrete Coring for Lab Analysis

Concrete Coring for Lab Analysis

Concrete Condition – Core Laboratory

Findings and Conclusions

• Overall, highly variable concrete with many reasons for concern:

– Consistently High/Good Compressive Strength, Avg. >50 Mpa

– Absorption and Permeable Voids – Good Consolidation

– Air Content– Very Poor, not “air-entrained”,

– Evidence of stress due to prolonged moisture, sulphate attack, weakening

structure, Poor

– No evidence of Alkali-aggregate reactivity, Good

– Evidence of expansive distress, physical defects including cracking,

delamination and voids consistent with Impact Echo findings, Poor

– Rebar orientation, spacing and depth of cover – Very Poor

Evaluation of Methods - Conclusions

– Ground Penetrating Radar – Rebar Location Method

• Effective method for mapping rebar and cover, confirming as-

constructed records, id new deficiencies.

• No other equivalent substitute method

• Fast Real-Time Results, Cost Effective

Evaluation of Methods - Conclusions

• Testing Results: Strong correlation between

– A) Existing Visual & Hammer Surveys,

– B) Impact Echo and

– C) Actual lab test results

Evaluation of Methods - Conclusions

• Evaluation of Method - Impact Echo Testing Method:

• Reliable, Effective, Immediate Results in Real Time, No Waiting, Low

Cost, much cheaper than core & lab test

• Low Impact – No “Destruction” and can quickly access tight spots

• Confirmed results from current/past methods, i.e. areas of defect

• Expanded scrutiny into interior of concrete, confirmed thickness

• Provided quantitative data to add credibility and confidence to

conclusions i.e. Current Level of Risk, Remaining Service Life

• Limitations - Not a standalone solution for concrete evaluation, but is

complementary & adds value to a comprehensive program.

Conclusions

• When used in combination with existing surface monitoring, spot core

sampling and lab tests for calibration, Impact Echo and GPR are very

fast, cost effective testing methods for concrete structure assessment

and early detection of problems.

• Not a standalone solution, limitations must be understood

• Particularly valuable for buried sub-grade structures

• Adds credibility to current monitoring program and directly supports

maintenance & Capital Planning processes.

Next Steps

• Expand scope of testing & evaluation:

– Gather more data from more locations, including bottom and top of

conduit with access issues

– Uniformity?

– Areas of more severe defect, first point of failure? Risk?

– Continue to refine service life estimates, support Capital Planning

Process

– Track change over time

• Retain a Structural Engineer to analyze the data in detail, 3rd party

opinion on current level of risk and remaining life

Questions??

and Thank You: Mr. Shaun Radomski, M.Sc., P.Eng.

Materials Engineer

AMEC Environment & Infrastructure

Calgary, AB

Clayton Weiss, P.L.(Eng.)

ESRD – Operations Infrastructure, Oldman Basin

clayton.weiss@gov.ab.ca

403-381-5984