Inspection and testing of sitework, concrete and masonry; capstone

Throughout this course, every material and method has come with checks: bearing surfaces confirmed, fill compacted and tested, reinforcement inspected, concrete tested, masonry reviewed. Inspection and testing are how the construction team, the owner and the authorities know that the work meets the design. They also protect the constructor, because accurate records show what was done and help resolve disputes. This final lesson brings those checks together: who inspects and tests, the inspection and test plan, the standard field tests for concrete, strength testing and acceptance criteria, what happens when results fail, testing of soils and masonry, documentation and nonconformance, and a capstone exercise that follows a small building from site preparation to masonry walls.

Who inspects and tests

Several parties share responsibility for quality:

• The contractor is responsible for building the work in accordance with the contract documents and for its own quality control, including checking its subcontractors.
• Independent testing agencies, usually retained by the owner, perform materials testing such as soil compaction, concrete and masonry tests, and report results to the owner, designer and contractor.
• The geotechnical engineer reviews bearing surfaces, fill and excavation conditions.
• The structural engineer and architect perform field reviews to confirm general conformance with the design.
• The authority having jurisdiction (the building department) performs code inspections at defined stages for permits.

In Canada, provincial building codes and professional engineering acts require field reviews by the registered professionals responsible for the design of many buildings, and municipalities perform permit inspections. Testing laboratories are commonly certified under CSA A283 for concrete testing, and many belong to the Canadian Council of Independent Laboratories (CCIL), which also certifies field technicians.

The inspection and test plan

An inspection and test plan (ITP) lists, for each part of the work, what will be inspected or tested, by whom, how often, against what criteria, which hold points require approval before work continues, and what records will be kept. For the work in this course, an ITP might include the following items.

Field tests on fresh concrete

When concrete arrives, the testing technician samples it according to standard procedures, usually from the middle of the load, and performs field tests:

• Slump test: concrete is placed in a cone 300 mm (12 in) high in three layers, each rodded 25 times; the cone is lifted and the drop of the concrete is measured. Slump measures consistency, not strength, and changes in slump from truck to truck often signal changes in water content. Self-consolidating concrete is tested by slump flow, the spread diameter.
• Air content: measured with a pressure meter for normal aggregates or a volumetric (roll-a-meter) method for lightweight aggregates; air-entrained concrete must fall within the specified range, often 5 % to 8 %.
• Temperature: measured with a thermometer to check against specified limits.
• Density (unit weight): used to check yield and air content.
• Making strength specimens: cylinders are filled in layers, rodded or vibrated, finished, covered and left on site under controlled conditions for the initial curing period, then transported to the laboratory for standard curing.

In Canada, the corresponding test methods are in CSA A23.2, including A23.2-1C (sampling), A23.2-3C (making and curing specimens), A23.2-4C (air content by the pressure method), A23.2-5C (slump), A23.2-6C (density and yield), A23.2-9C (compressive strength of cylinders) and A23.2-17C (temperature). Initial site curing must keep cylinders within a specified temperature range, commonly 15 °C to 25 °C.

If field tests fall outside the specification, the load may be adjusted where permitted (for example, by an allowed addition of admixture or limited water within the mix design), retested, or rejected. Rejection decisions should be made quickly, before the concrete is placed, and recorded on the ticket.

Compressive strength testing

Cylinders are tested by crushing them in a compression machine, usually at 7 days for early information and 28 days for acceptance, with extra cylinders held in reserve. Common sizes are 100 × 200 mm and 150 × 300 mm in Canada and 4 × 8 in and 6 × 12 in in the United States. The compressive strength is the maximum load divided by the cross-sectional area:

Acceptance criteria

Because concrete strength varies, acceptance criteria look at both the running average and individual tests.

Under CSA A23.1, a strength test is the average of the cylinders (typically two) from a sample tested at 28 days, and the concrete meets the specified strength when the average of any three consecutive strength tests equals or exceeds \(f'_c\) and no single test falls more than 3.5 MPa below \(f'_c\). Tests are typically required at least once for each 100 m³ of each class of concrete and at least once each day the class is placed, or as specified.

When strength tests fail

Low cylinder results do not necessarily mean the concrete in the structure is weak; cylinders may have been poorly made, handled or cured. The investigation usually proceeds in steps: review the testing records and field curing conditions; check the structural significance with the engineer, since a small shortfall may still be acceptable for the design; use non-destructive methods such as rebound hammers, ultrasonic pulse velocity or maturity data to identify suspect areas; and drill cores from the structure for testing.

Cores are taken and tested under CSA A23.2-14C, and CSA A23.1 sets acceptance criteria for core strengths, generally that the average of the cores is at least 85 % of \(f'_c\) with no single core below 75 %.

If cores confirm low strength, options include load testing, strengthening, restricting use, or removal and replacement. Contracts typically assign the cost of investigation and correction to the party responsible for the deficiency.

Testing soils and masonry

Soil testing during construction includes in-place density and moisture tests on fill and subgrade (Lesson 4), typically at a specified frequency such as one test per lift for every few hundred square metres of fill or every trench length, with retests after rework; proof-rolling observation; laboratory Proctor tests on each fill material; and geotechnical observation of bearing surfaces, piles and shafts (Lessons 5 and 6). Masonry testing may include mortar and grout specimens, prism tests, unit testing, and inspection of grout placement and reinforcement before cells are closed. In every case, results must be compared promptly with the specified criteria so that defective work is caught before it is buried.

Documentation and nonconformance

Quality records include inspection checklists, test reports, delivery tickets, pour logs, photographs, as-built surveys of footings and piles, maturity records and correspondence. A nonconformance report (NCR) documents work that does not meet requirements, its location and extent, the proposed disposition (use as is, repair, rework or reject), the engineer's approval, and verification that the corrective action was completed. Good documentation turns individual tests into evidence that the work as a whole conforms, and it is often essential in claims, warranty disputes and future renovations.

Capstone: from bare ground to masonry walls

Consider a single-storey commercial building, 30 m by 20 m (about 100 ft by 66 ft), with a slab-on-grade, spread footings and strip footings, a reinforced concrete block exterior wall with brick veneer, on a site with 300 mm (12 in) of topsoil over stiff clay, a groundwater table about 2.5 m (8 ft) down, and a winter start. Review the sequence and the main checks from each lesson:

• Site investigation (Lesson 1): read the geotechnical report for bearing pressures, frost depth, groundwater and recommendations for subgrade and fill.
• Site preparation (Lesson 2): survey control, utility locates, tree protection, erosion and sediment control, stripping and stockpiling topsoil, and proof-rolling the stripped surface.
• Earthwork (Lesson 3): calculate cut, fill and haul volumes with swell and shrink factors; plan protective systems for footing and service trench excavations; plan dewatering if excavations approach groundwater.
• Compaction (Lesson 4): place engineered fill in lifts at the specified moisture, with density tests on every lift, and prepare the granular base and vapour retarder for the slab.
• Shallow foundations (Lesson 5): size checks against the allowable bearing pressure, footings below frost depth, bearing surfaces reviewed and protected from frost, and drainage.
• Deep foundations (Lesson 6): not needed on this stiff clay, but know when soft soils or heavy loads would require piles or ground improvement.
• Concrete (Lesson 7): order mixes with the correct exposure class, strength, air content and maximum aggregate size, and check every ticket.
• Formwork (Lesson 8): engineered forms for the footings and walls, controlled placement rates, stripping by confirmed strength.
• Reinforcement (Lesson 9): bars per shop drawings, correct cover against earth, dowels set for block walls, inspection before concrete.
• Placing and curing (Lesson 10): a pour plan, cold weather protection with heated enclosures and blankets, maturity sensors, joints sawcut on time and curing for the specified period.
• Masonry (Lesson 11): units, mortar type, grout, reinforcement and ties; cold weather protection; bracing and restricted zones; flashings, weeps and movement joints.
• Inspection and testing (Lesson 12): an ITP with hold points, field tests, strength acceptance and documentation.

Working through such a case shows how the materials and methods connect: a mistake in an early stage, such as frozen subgrade or poorly compacted fill, can cause cracking in a slab and masonry walls built months later. The constructor's job is to understand the reasons behind each requirement, plan the work so those requirements can be met, and verify and document that they were.

Many testing agencies now issue results through online portals, and project teams can track strength trends across a whole project. Watching the trend is often more useful than reacting to single results: a gradual decline over several weeks may point to a change in materials or practices that can be corrected before tests begin to fail.