I wish to thank Principal C & S of QHSEL Consultancy Sdn. Bhd. for this sharing. Also I thank the team from C & S Consultant and HSSE Team for invaluable inputs.
Project: [....Access Road Project...] Location: [.......] NCR No.: NCR-AGG-ROAD-..... Date: ...... Issued To: [Contractor] Issued By: ............................ Prepared By: [........................]
1. Description of Non-Conformance
During routine quality assurance testing by the QA/QC Engineer of concrete intended for pavement slab construction, it was observed that the compressive strength did not meet the specified design strength of 30 MPa at 28 days, required for the (access) road surface to withstand heavy traffic loading.
Concrete cubes from Mix Design RC-30, tested at 28 days, achieved an average compressive strength of 26.2 MPa, indicating a non-conformance.
2. Reference Standards
BS EN 206: Concrete – Specification, performance, production, and conformity,
BS 882: Aggregates from natural sources for concrete,
JKR Specifications for Rigid Pavements (JKR Road Standard R5/R4)
Project Specification Section [........................]
Method Statement Ref........ Concrete Mix Design and Aggregate Quality Control (Rigid Pavement) - See below
2.1 Failure to Comply to the Method Statement
It was also noted that the Method Statement Ref........ Concrete Mix Design and Aggregate Quality Control (Rigid Pavement) was also not complied where it was mentioned clearly in the following points :
Aggregate Inspection and Testing: Verify coarse and fine aggregates meet specified grading, silt content, and crushing values, Conduct sieve analysis for fine and coarse aggregates according to BS 812, Test coarse aggregate crushing value (BS 812-110) and abrasion resistance for durability.
Concrete Mix Design: Prepare mix design (RC-30 for rigid pavement) based on target 28-day compressive strength, Determine cement content, water-cement ratio, aggregate proportions, and admixture dosage
Batching and Mixing: Use calibrated batching equipment, Ensure uniform mixing of cement, aggregates, water, and admixtures, Maintain proper slump and workability as per design,
Concrete Placement and Curing: Place concrete within recommended time to prevent segregation, Compact properly to eliminate voids, Cure concrete slabs for at least 7 days using wet curing or approved curing compounds,
Quality Control Testing: Take cube samples (150 × 150 × 150 mm) at every batch or per project specification, Conduct 7, 14, and 28-day compressive strength tests according to BS EN 12390, Record all results and compare with design strength to ensure compliance,
Non-Conformance Protocol: Any observed strength below specification triggers immediate investigation, Halt placement if aggregates or concrete do not meet standards, Implement corrective actions including retesting, sourcing compliant aggregates, or adjusting mix design.
3. Investigation and Findings
Sample cubes (150 mm × 150 mm × 150 mm) were prepared and tested at 7, 14, and 28 days. The 28-day results:
Average Strength = (26.0 + 26.5 + 26.2)/3 = 26.23 MPa
Mix design for road concrete: Cement: 400 kg/m³, Water/Cement ratio: 0.45, Coarse Aggregate: 20 mm nominal size, locally sourced, Fine Aggregate: River sand, Zone II
Aggregate testing: Coarse aggregate crushing value: 30% (at upper limit), Fine aggregate silt content: 5.5% (> max 3%), Expected strength reduction due to aggregate deviation (ACI approximate method):
Observed strength: 26.23 MPa - confirms aggregate quality is a primary factor in reduced concrete strength
4. Impact on Road Construction
Structural Risk: Pavement slabs may crack or fail prematurely under heavy vehicle loads (e.g., trucks, buses),
Serviceability: Potential increased deflection, roughness, and early maintenance requirements,
Project Schedule and Cost: Rework or additional testing may delay paving operations,
Non-Compliance: Does not meet JKR Rigid Pavement standard RC-30.
5. Immediate Actions
Halt placement of concrete for road slabs using the current aggregate batch,
Retest all delivered aggregates for compliance,
Source compliant aggregates or adjust mix design with additional cement or admixtures to achieve target strength,
Retest concrete cubes before resuming paving work.
6. Corrective Action Required
Contractor to submit a corrective action plan within 7 days,
Evaluate existing paved sections; remove or reinforce areas where concrete strength is below specification,
Document all changes and retesting results for Client verification.
7. Future Risk Assessment
8. Update of Risk Register
The project Risk Register is updated taking into account this NCR:
Concrete Cube Test Reports,
Aggregate Test Reports (crushing value, silt content, grading)
Mix Design Sheet for RC-30
Strength vs Traffic Load Diagram (see sample below)
No comments:
Post a Comment