ACI Strength Testing flashcards
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32 cards. Read the term and the definition here. The deck at the top of this page is optional.
- Standard cylinder length-to-diameter ratio
- Length must equal twice the diameter (2:1) for standard compressive strength testing. 4x8 in. and 6x12 in. cylinders meet this ratio.
- Tamping rod diameter
- 5/8 in. (16 mm) rod for 6 in. cylinders; 3/8 in. (10 mm) rod for 4 in. cylinders. Rod is rounded and smooth.
- Number of layers in 6x12 cylinder
- Three equal layers, each rodded 25 times with the tamping rod, per standard practice for 6 in. diameter molds.
- Number of layers in 4x8 cylinder
- Two equal layers, each rodded 25 times with the 3/8 in. rod, per standard practice for 4 in. diameter molds.
- Standard moist curing temperature
- 68 ± 2 °F (20 ± 2 °C) in a moist environment until the time of test. Applies to standard-cured strength specimens.
- Slump cone dimensions
- 12 in. tall, 4 in. top diameter, 8 in. base diameter. Filled in 3 layers, each rodded 25 times.
- Slump test layer count
- Three layers of equal volume, each rodded 25 times with the 5/8 in. rod. Strike off the top and measure vertical drop.
- Composite sampling procedure
- Sample from mid-discharge of the mixer, taking portions across the discharge. Test slump and air within 15 minutes.
- Concrete placement temperature range
- Typically 50-90 °F (10-32 °C) at placement for normal concrete per ACI 301. Record temperature at time of sampling.
- Air content measurement methods
- Pressure meter or volumetric method. Typical range for normal concrete is 4-8% depending on exposure requirements.
- Cylinder end preparation
- Ends are capped with sulfur or neoprene pads, or ground flat, before compression testing. Planeness affects measured strength.
- Capping thickness tolerance
- Cap thickness and planeness must meet tolerance; uneven caps cause eccentric loading and lower measured strength.
- Field-cured cylinder purpose
- Assesses structural adequacy under job-site curing conditions. Used to decide form removal and opening to traffic.
- Standard-cured cylinder purpose
- Assesses mix design compliance under controlled laboratory curing. Compared against specified f'c for acceptance.
- Cylinder mold diameter options
- 4 in. (100 mm) and 6 in. (150 mm) diameter molds are standard. Length must be twice the diameter.
- Consolidation by vibration
- Internal vibration may replace rodding for low-slump concrete; vibrator inserted at intervals, avoiding contact with mold walls.
- Design compressive strength f'c
- Specified compressive strength at 28 days, measured on standard moist-cured cylinders. Basis for structural design per ACI 318.
- Compressive stress formula
- Stress = load / cross-sectional area. 6 in. cylinder area = 28.27 in²; 4 in. cylinder area = 12.57 in².
- Standard compression loading rate
- 35 ± 7 psi/s (0.25 ± 0.05 MPa/s) for standard cylinders. Maintain rate within tolerance throughout the test.
- ACI 318 acceptance criterion (average)
- Average of any three consecutive strength tests must equal or exceed the specified f'c. Applies to standard-cured cylinders.
- ACI 318 acceptance criterion (single)
- No single strength test may fall below f'c minus 500 psi. Violation triggers investigation of the concrete.
- Splitting tensile strength formula
- fct = 2P/(π·L·d), where P is splitting load, L is length, d is diameter. Typically 6-8% of compressive strength.
- Modulus of rupture formula
- For third-point loading, fr = PL/(bd²). Typically about 7.5√f'c psi for normal-weight concrete.
- Elastic modulus estimate
- Ec ≈ 57,000√f'c psi for normal-weight concrete. Varies with aggregate type and concrete density.
- Proper compression failure mode
- A well-formed cone or shear cone indicates proper test. Columnar or cap-related failures suggest end preparation issues.
- 28-day strength basis
- Design strength f'c is typically specified at 28 days of standard moist curing. Earlier tests estimate strength gain.
- Flexural test loading configuration
- Third-point loading is standard for modulus of rupture. Load applied at two points at one-third span spacing.
- Strength test frequency
- Typically one set of cylinders per 150 yd³ or per day of placement, whichever is more frequent, per ACI 318.
- Cylinder diameter effect on strength
- Smaller 4 in. cylinders may show slightly higher strength than 6 in. cylinders due to reduced size effect and wall friction.
- Moist curing duration
- Standard specimens are moist-cured until testing at 28 days. Field-cured specimens follow job-site conditions.
- Rate of loading effect on strength
- Faster loading rates yield higher apparent strength; slower rates yield lower strength. Maintain the specified rate.
- Test result reporting
- Report average of at least two cylinders tested at the same age; a single cylinder result is not a valid strength test.