Concrete construction including placement procedures, reinforcement placement, and inspection requirements.
3
hours
0.3
CEUs
Building Construction
1.7.1
This course covers material relevant to the following ICC certification exams:
Concrete construction including placement procedures, reinforcement placement, and inspection requirements.
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On-Demand Online
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Certificate of Completion
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Contact our support teamUnderstand concrete mix design parameters and quality control procedures during placement
Concrete quality begins at the batch plant and must be verified continuously through delivery, placement, and curing. The inspector's role centers on confirming that the concrete delivered to the jobsite matches the approved mix design and that placement conditions will not compromise the hardened properties of the material. IBC Section 1905 requires that concrete conform to the provisions of ACI 318, which in turn establishes the framework for proportioning, mixing, and testing.
The water-to-cementitious-materials ratio (w/cm) is the single most important factor controlling concrete strength and durability. A lower w/cm ratio produces higher compressive strength and reduced permeability, but also reduces workability. ACI 318 Table 19.3.2.1 establishes maximum w/cm ratios based on exposure categories. For concrete exposed to freezing and thawing cycles (Exposure Class F1), the maximum w/cm ratio is 0.45. For concrete exposed to sulfates (Exposure Class S1), the limit drops further. Inspectors should verify the w/cm ratio on batch tickets against the approved mix design before allowing any placement.
Slump is the primary field measurement for workability and consistency. Standard structural concrete typically specifies a slump between 3 and 5 inches for conventional placement, though self-consolidating concrete may use slump flow measurements of 18 to 30 inches. Adding water to the mixer drum on site to increase slump is a common violation that directly increases the w/cm ratio, reducing both strength and durability. Inspectors should reject any load where unauthorized water has been added.
Air entrainment is required for concrete exposed to freezing and thawing per ACI 318 Section 19.3.3.1. The entrained air content typically ranges from 4% to 7% depending on aggregate size, with smaller maximum aggregate sizes requiring higher air content. Air entrainment creates microscopic bubbles that provide relief space for freezing water within the paste, preventing scaling and spalling. Field testing of air content should be performed using either the pressure method (ASTM C231) for normal-weight concrete or the volumetric method (ASTM C173) for lightweight concrete.
Compressive strength testing requires casting standard 6-inch by 12-inch or 4-inch by 8-inch cylinders per ASTM C31 at the frequency established by ACI 318 Section 26.12.1.1: at least one set of cylinders for each 150 cubic yards or each day of placement, whichever produces more specimens. A strength test result is the average of at least two cylinders tested at 28 days. Concrete is considered acceptable when no individual test falls more than 500 psi below the specified compressive strength and the running average of any three consecutive tests meets or exceeds the specified strength.
An inspector arrives at a commercial building foundation pour and reviews the batch tickets for the first three trucks. The approved mix design specifies 4,000 psi concrete with a maximum w/cm ratio of 0.45 and 6% air entrainment for Exposure Class F1. The first truck's batch ticket shows 325 pounds of water per cubic yard with 722 pounds of cementitious material, yielding a w/cm ratio of 0.45. The slump test reads 4.5 inches and air content is 5.8% -- both within specification. The second truck arrives 85 minutes after batching. Per ASTM C94, concrete must be discharged within 90 minutes or 300 drum revolutions, so placement must begin immediately. The inspector coordinates with the contractor to ensure continuous placement and proper vibration to avoid cold joints while still maintaining the testing frequency.
The most frequent violation is adding water to the truck to increase slump, which degrades the w/cm ratio and compromises strength. Inspectors should reject loads where unauthorized water was added and require re-batching. Another common error is insufficient cylinder curing -- test specimens must be stored in a controlled environment at 60-80 degrees Fahrenheit for the first 24 hours per ASTM C31, not left in the sun or exposed to freezing. Failing to test at the required frequency is a documentation gap that can invalidate the inspection record. Inspectors must also watch for delivery tickets showing excessive mixing time or drum revolutions, both of which can degrade concrete quality through slump loss and potential segregation.
Code Reference: IBC Section 1905, ACI 318 Chapter 19 and 26 - IBC Chapter 19 adopts ACI 318 by reference as the governing standard for structural concrete. Mix design must comply with the durability requirements of ACI 318 Chapter 19, which establishes exposure classes and corresponding maximum w/cm ratios, minimum strength, and air entrainment requirements.
Apply reinforcement placement, cover, spacing, and development length requirements per ACI 318
Reinforcement steel transforms concrete from a material that resists only compression into a structural system capable of carrying tension, flexure, and shear. Proper placement of reinforcing bars is essential to achieving the design intent, and inspectors must verify bar size, spacing, cover, and anchorage before any concrete is placed.
Reinforcing bar sizes follow ASTM A615 designations where the bar number corresponds to the nominal diameter in eighths of an inch. A No. 4 bar is 4/8 inch (0.500 inch) in diameter; a No. 8 bar is 1 inch. Grade 60 steel (fy = 60,000 psi) is the most common specification for structural applications. Inspectors should verify bar markings, which include the producing mill identification, bar size, steel type (S for carbon, W for low-alloy), and grade designation.
Concrete cover protects reinforcement from corrosion and fire exposure. ACI 318 Section 20.6.1 establishes minimum cover requirements based on exposure conditions and member type. For concrete cast against and permanently exposed to earth, the minimum cover is 3 inches. For concrete exposed to weather with No. 6 through No. 18 bars, the minimum is 2 inches; for No. 5 bars and smaller, 1.5 inches. For interior concrete not exposed to weather or ground contact, typical cover is 0.75 inches for slabs and 1.5 inches for beams and columns. Insufficient cover is one of the most common deficiencies found during pre-pour inspection and must be corrected before placement.
Bar spacing requirements serve two purposes: ensuring adequate concrete consolidation between bars and distributing reinforcement to control cracking. The minimum clear spacing between parallel bars in a layer is the greatest of one bar diameter, 1 inch, or 4/3 times the maximum aggregate size per ACI 318 Section 25.2.1. Maximum spacing for flexural reinforcement in slabs and walls is typically the lesser of 3 times the member thickness or 18 inches per ACI 318 Section 24.3.
Development length is the embedment length required to transfer the full tensile force in a bar to the surrounding concrete without pullout. ACI 318 Section 25.4 provides the equations for calculating development length based on bar size, concrete strength, bar coating, bar spacing, transverse reinforcement, and lightweight concrete factors. For a No. 5 Grade 60 uncoated bottom bar in normal-weight 4,000 psi concrete with adequate cover and spacing, the development length is approximately 19 inches. Epoxy-coated bars require a 1.5 factor increase in development length. Inspectors should verify that bars extend at least the required development length past the critical section for moment.
Lap splices transfer force from one bar to another through the surrounding concrete. The minimum lap splice length for tension is typically 1.0 times the development length for Class A splices (where the area of reinforcement provided is at least twice that required and no more than half the bars are spliced at one location) and 1.3 times the development length for Class B splices. ACI 318 Section 25.5 governs splice requirements. Mechanical splices and welded splices are alternatives that must develop at least 125% of the specified yield strength of the bar per ACI 318 Section 25.5.7.
During a foundation wall inspection, the inspector checks No. 5 vertical bars at 12 inches on center with No. 4 horizontal bars at 16 inches on center. The structural drawings specify 2 inches of clear cover to the earth face and 1.5 inches to the interior face. Using a cover meter (pachometer), the inspector measures cover at several locations and finds one area where the vertical bars are only 1.25 inches from the form face due to displaced bar supports. The inspector requires the contractor to reposition the bar chairs before the pour. The inspector also verifies that the vertical bars extend 24 inches into the footing (satisfying the required development length) and that horizontal bar lap splices are staggered and at least 25 inches long, meeting the Class B splice requirement.
Insufficient concrete cover is the most prevalent reinforcement deficiency, typically caused by missing, broken, or improperly spaced bar supports (chairs). Correction requires adding or repositioning support devices before placement. Incorrect bar size or spacing often results from field substitutions without engineering approval -- replacing two No. 5 bars with one No. 7 bar provides nearly equal area but may not satisfy crack control or development length requirements. Lap splices concentrated at a single location rather than staggered create a weak plane in the member. Inspectors should also verify that reinforcement is clean and free of excessive rust, oil, or other contaminants that would impair bond per ACI 318 Section 26.6.1.
Code Reference: ACI 318 Sections 20.6.1, 25.2, 25.4, 25.5 - Cover requirements are established in Section 20.6.1 based on exposure conditions. Development length calculations in Section 25.4 determine the minimum embedment needed for bar anchorage. Splice requirements in Section 25.5 classify lap splices and establish minimum lengths based on development length multipliers.
Understand formwork requirements, proper concrete placement and consolidation techniques, and curing procedures for different weather conditions
Formwork serves as the temporary mold for concrete and must be designed to support all applied loads without excessive deflection, leakage, or failure. ACI 318 Section 26.11.1 requires formwork to be designed for the weight of concrete, construction loads, and the lateral pressure of fresh concrete. For columns and walls, lateral pressure depends on the placement rate, concrete temperature, and concrete unit weight. At typical placement rates under 7 feet per hour and concrete temperatures above 50 degrees Fahrenheit, the maximum lateral pressure for walls can be calculated using established formulas from ACI 347. Inspectors should verify that form ties, bracing, and shores are installed per the approved shoring plan and that forms are clean, properly oiled, and free of gaps that would allow paste leakage.
Shores and reshores must remain in place until the concrete has achieved sufficient strength to support its own weight plus any construction loads. ACI 318 Section 26.11.3 requires that supporting construction remain in place until a structural analysis shows the concrete can carry the required loads. For multistory construction, this typically means maintaining shores on at least two floors below the level being placed. Premature removal of shores has caused numerous structural failures and progressive collapses during construction.
Concrete consolidation removes entrapped air voids and ensures full encasement of reinforcement. Internal vibration using mechanical vibrators is the standard method. The vibrator should be inserted vertically at intervals no greater than 1.5 times the radius of action (typically 18 to 24 inches apart), allowed to penetrate into the previous lift, and withdrawn slowly. Over-vibration causes segregation where heavy aggregate settles and paste rises to the surface. Under-vibration leaves honeycombs, bug holes, and voids around reinforcement. Inspectors should observe vibration practices throughout placement and require correction when operators vibrate too quickly or at excessive spacing.
Cold weather concrete placement requires protection when ambient temperatures fall below 40 degrees Fahrenheit. ACI 306 establishes procedures including heating mix water and aggregates, maintaining concrete temperature between 50 and 65 degrees Fahrenheit at placement, and providing insulated blankets or heated enclosures during initial curing. The minimum curing temperature must be maintained for a protection period that depends on the type of cement and the service category of the member -- typically 3 days for normal loading conditions. Concrete that freezes before achieving approximately 500 psi compressive strength can suffer permanent strength loss of up to 50%.
Hot weather placement presents different challenges when ambient temperatures exceed 90 degrees Fahrenheit or concrete temperature exceeds 95 degrees. High temperatures accelerate hydration, reduce working time, increase water demand, and promote plastic shrinkage cracking. ACI 305 recommends cooling mix water, using ice as part of the mixing water, shading aggregate stockpiles, and scheduling pours during cooler hours. Evaporation retarders, fog sprays, and windbreaks help prevent rapid surface moisture loss that causes plastic shrinkage cracks.
Curing maintains adequate moisture and temperature for cement hydration. ACI 318 Section 26.5.3 requires moist curing for at least 7 days for normal concrete. Acceptable methods include ponding, continuous sprinkling, wet burlap, plastic sheeting, or liquid membrane-forming curing compounds conforming to ASTM C309. Inadequate curing is perhaps the single most common cause of reduced surface strength, increased permeability, and premature deterioration of concrete.
An inspector is on site for a second-floor elevated slab pour in early December with temperatures forecasted to drop to 28 degrees Fahrenheit overnight. Before placement begins, the inspector confirms the shoring plan shows two floors of shores below, with the ground floor reshored. The contractor has provided heated concrete at 58 degrees Fahrenheit, which meets the ACI 306 placement temperature requirement. Insulated blankets are staged and ready for deployment immediately after finishing. The inspector reviews the cold weather protection plan, which calls for maintaining the slab at a minimum of 50 degrees Fahrenheit for 72 hours, with temperature monitoring using embedded sensors. The inspector documents the concrete temperature at delivery, the ambient conditions, and the protection measures being employed.
Premature shore removal is a life-safety hazard that has caused construction collapses; inspectors must verify strength verification before approving any shore removal. Adding water to the surface of a slab to aid finishing (known as "blessing" the concrete) weakens the surface layer and causes dusting, scaling, and delamination. Inadequate curing -- removing wet coverings or curing compounds after only one or two days -- reduces surface strength and abrasion resistance. In cold weather, failing to protect concrete from freezing during the first 24 hours causes irreversible damage. In hot weather, neglecting to apply evaporation retarders when the evaporation rate exceeds 0.2 pounds per square foot per hour leads to plastic shrinkage cracking.
Code Reference: ACI 318 Sections 26.5, 26.11; ACI 305, ACI 306 - Formwork and shoring requirements appear in ACI 318 Section 26.11. Curing provisions are in Section 26.5, requiring a minimum of 7 days moist curing. Hot weather (ACI 305) and cold weather (ACI 306) guides provide supplemental procedures for extreme temperature placement.
Understand special inspection requirements for concrete construction per IBC Section 1705.3
Special inspection of concrete construction is one of the most extensive inspection programs required by the IBC. Section 1705.3 establishes the specific items requiring special inspection, distinguishing between continuous inspection (inspector present at all times during the work) and periodic inspection (intermittent presence to verify compliance at defined intervals).
IBC Section 1705.3, Table 1705.3 identifies the following items requiring special inspection for concrete: reinforcement placement and welding, concrete batch plant operations, concrete placement, prestressed concrete tensioning, erection of precast concrete members, and concrete strength testing. The registered design professional (RDP) preparing the construction documents is responsible for designating the required special inspections on the drawings per IBC Section 1704.2.
Reinforcement placement requires periodic special inspection to verify bar size, grade, spacing, cover, support, lap splice lengths, and mechanical connections prior to concrete placement. This is one of the most critical inspection points because reinforcement deficiencies cannot be corrected after concrete is placed. The special inspector should review the structural drawings, verify bar markings, measure cover with appropriate tools, and check that all anchorage and splice requirements are met.
Concrete placement requires periodic special inspection to verify that the concrete is being placed in accordance with the construction documents. This includes confirming mix design compliance from batch tickets, performing field tests for slump, air content, unit weight, and temperature, and casting compressive strength test cylinders per the sampling frequency. The special inspector must observe consolidation practices and ensure that cold joints, segregation, and excessive free fall are avoided.
Prestressed concrete operations require continuous special inspection during stressing operations. The inspector verifies that the stressing sequence follows the approved procedure, records elongation measurements and gauge pressures, and confirms that the calculated force matches the elongation within the 5% tolerance specified in ACI 318. Grouting of post-tensioning ducts requires continuous inspection to verify that grout is pumped until it flows freely from the vent ports and that the grout meets the specified strength and fluidity requirements.
The special inspector must be qualified and approved by the building official per IBC Section 1704.2.1. Qualifications typically include ICC certification as a Reinforced Concrete Special Inspector or equivalent demonstration of competence. The special inspector reports to the building official and the RDP, not to the contractor, and must maintain independence from the construction operations being inspected. Discrepancies discovered during special inspection must be reported to the building official and the RDP for resolution.
A special inspector is assigned to a four-story concrete frame building. Before construction begins, the inspector reviews the statement of special inspections prepared by the RDP, which identifies all required special inspection items per IBC Section 1705.3. During foundation construction, the inspector performs periodic inspection of reinforcement placement in the footings, checking bar sizes, cover, dowel projection lengths, and splice details against the structural drawings. During each concrete placement, the inspector reviews batch tickets, performs slump and air tests, casts strength cylinders, and documents placement conditions. When a post-tensioned slab is stressed, the inspector provides continuous inspection, recording stressing force and elongation for each tendon and comparing results to the engineer's calculated values. All inspection reports are submitted to both the building official and the structural engineer of record.
Confusing periodic and continuous inspection requirements leads to either inadequate coverage or unnecessary cost. Special inspectors who work for the contractor rather than maintaining independence create a conflict of interest that violates IBC Section 1704.2.1. Failing to correlate batch tickets with the approved mix design is a documentation gap that undermines the purpose of the inspection. Special inspection reports that lack specific code references, measured values, or location descriptions are insufficient for the building official to make informed approval decisions. When discrepancies are found, the special inspector must immediately notify both the building official and the RDP rather than directing corrections independently.
Code Reference: IBC Section 1705.3, Table 1705.3; IBC Section 1704 - Section 1705.3 establishes specific special inspection requirements for concrete construction. Section 1704 provides the administrative framework for special inspections including inspector qualifications, reporting requirements, and the role of the registered design professional in designating required inspections.
This course provides building professionals with the technical knowledge required for competent inspection and oversight of concrete construction operations. From mix design verification through reinforcement placement, formwork, consolidation, curing, and special inspection documentation, each module addresses the practical skills needed to ensure that concrete work meets the structural and durability requirements of IBC Chapter 19 and ACI 318. The emphasis throughout is on understanding the engineering principles behind code requirements so that inspectors can recognize deficiencies, communicate clearly with contractors and engineers, and make sound professional judgments in the field.