Concrete Technology: Aggregate Interlocks and Joints

Highway Design Seminar

• Pavement design analyzes flexible and rigid pavements.
• Design standards ensure motorist convenience, environmental safety, and aesthetic considerations.
• These standards are economical and consistent with highway service conditions.
• Design policies typically represent minimum values.

Effects of Poor Highway Design

• Poor design leads to issues like traffic congestion, potholes, and flooding, as illustrated in images.

Introduction to Pavement Design

• Two main types of pavement exist: asphalt and concrete.

Comparison of ACP and PCCP

• Asphalt Pavement: Loads are distributed across multiple layers. Easy and rapid construction, layered construction is possible, quiet and comfortable to travel on.
• Concrete Pavement: Loads spread across a larger area. Needs curing time, long lifespan, and durable for heavy trucks.

Rigid Pavement Design (Portland Cement Concrete Pavement)

• Usually consists of a roadbed and a pavement slab atop.
• Durable and maintains shape.

Types of Rigid Pavement

• Jointed Plain Concrete Pavement (JPCP)
• Jointed Reinforced Concrete Pavement (JRCP)
• Continuously Reinforced Concrete Pavement (CRCP)

Jointed Plain Concrete Pavement (JPCP)

• Uses contraction joints at equal distances to prevent transverse cracking.
• No reinforcing steel bars.
• Uses dowel bars for load transfer at transverse joints, and tie bars in longitudinal joints.

Typical Roadway Cross-section of Rigid Pavement

• A diagram showing the layers of a rigid pavement (PCC pavement, sub-base course, and surface course).
• Includes dimensions and percentages (slopes).

Design Controls

• Design life
• Pavement width
• Soil properties (CBR)
• Material properties (concrete and steel)
• Traffic loads

Design of Rigid Pavement

• Controls for slab length, joint load transfer, and slab thickness:
  • Slab length: Length of joint spacing.
  • Joint load transfer design: Dowels, keys, aggregate interlocks.
  • Slab thickness: Depth of PCCP.

Slab Length

• AASHTO Pavement Design Guide, page II-49.
• Joint spacing (transverse and longitudinal) depends on local material and environmental conditions.
• Expansion and construction joints depend on layout and construction capabilities.
• Contraction joint spacing depends on thermal coefficient, temperature change, subbase frictional resistance, and concrete tensile strength.
• A rough guide: joint spacing (feet) should not exceed twice the slab thickness (inches).
• L = 2D (empirical relationship), where D= thickness of slab (inches), L= Length (feet).
• DPWH Standards: L = 4.50m

Joint Designs (Load Transfer Devices for Discontinuities on Slab)

• Contraction/construction joints with dowel bars.
• Longitudinal (keyed) joints with tie bars.

Dowel Bars

• Usually applied to contraction and transverse construction joints.
• Diameter (Ø) = Thickness/8, spaced at 300mm on center.
• Length varies. AASHTO length is typically 18 inches (450 mm), DPWH standards length is 600 mm.

Butt Joint with Dowel Bars

• Typically used in transverse construction joints.

Dowel Bars with Steel Baskets

• Used for PCCP contraction joints for load transfer.

Keyed Joint with Tie Bars

• Usually installed in longitudinal and construction joints within the middle third of the slab.
• Spacing of tie bars varies.
• Tie bars are used for load transfer.

Aggregate Interlocks

• A mechanism that transfers load across cracks in concrete by interlocking irregular aggregate and cement paste surfaces.

Rigid Pavement Slab Thickness

• Values derived from Figure 3.7 of the AASHTO guide or by solving a given equation, will help determine the Design Slab thickness (D).
• The equation involves multiple variables including APSI, W18, log, S'c,D,Cd,Ec and J.

Thickness Design Parameters for PCCP

• Roadbed soil
• Resilient modulus of subgrade
• Composite modulus of subgrade reaction
• Design traffic load, W18
• Reliability (85%)
• Drainage coefficient
• Load transfer coefficient
• Modulus of Rupture
• Modulus of Elasticity

Reliability (R) and Standard Deviation (So)

• Accounts for variations in traffic prediction and pavement performance for a given traffic loading.
• R= 85%
• So= 0.35 range from 0.3 to 0.4 (Typical values for DPWH standards).

Serviceability

• Expressed in Present Serviceability Index (PSI) based on traveling public comfort.
• Measured from roughness or distress during the pavement's service life

Drainage Coefficient

• Derived from drainage quality and time pavement structure exposed to moisture levels approaching saturation.

Joint and Load Transfer Coefficient

• Represents pavement's ability to transfer load across discontinuities like joints or cracks.

PCC Modulus of Rupture (psi), S'c

• Flexural strength at 28 days using a third-point loading method.
• DPWH specification = 550 psi for 14 days.

PCC Modulus of Rupture (psi), S'c Distribution

• Standard normal deviate (Z) and percent of strength distribution (PS) values are tabulated.

Elastic Modulus (psi) Ec

• Materials behavior under normal pavement loading conditions.
• Calculated from the formula: Ec = 57,000(f'c)0.5

Design CBR

• Obtained from a set of samples, ensuring a 90% probability that the mean of the samples is within ±20% of the true mean.
• Includes the standard deviation formula.

Resilient Modulus of Subgrade, MR

• Obtained from recoverable strain under repeated loads.

Composite Modulus of Subgrade Reaction (k∞)

• Represents the slab support level based on subbase characteristics and seasonal variations.

Loss of Support

Computing for k corrected

• Addresses effective modulus of subgrade reaction.

Design Traffic Load

• Converts mixed traffic to a equivalent number of 18-kip single axle loads and sums over the design period.
• Calculations are based on DO 22 series of 2011.
• Design traffic is calculated for each vehicle type using traffic growth rate 4% and traffic life (n).
• Computes traffic equivalence factor
• Determines directional and lane distribution factors.
• Calculates Cumulative Single Axle Load (CESAL).

Flexible Pavement Design (Asphalt Concrete Pavement)

• Usually consists of prepared roadbed, subbase, base, and bituminous surface course.
• Loads distribute across multiple layers.

Typical Roadway Cross-section of Flexible Pavement

• Diagram of a flexible pavement's cross-section, showing layers like bit tack coat, prime coat, asphalt concrete, base course, and subbase course.
• Includes dimensions and slopes.

Flexible Pavement Design

• Two formulas for flexible pavement design: 1) for log W18 and 2) for structural number (SN) calculations. Multiple variables like ZR, So, SN, D, MR, APSI and others are used in the equations.

Structural Number, SN

• An abstract representation of structural design strength.
• Considerations for determining SN include soil support, design traffic, serviceability index, and environment.

Thickness Design Parameters for ACP

• Determines structural number SN using resilient modulus of subgrade (MR), design traffic load (W₁₈), standard normal deviate (Z_R), and design serviceability loss (APSI)
• Drainage Coefficient (m_i)

Structural Layer Coefficient, a_i

• Measures relative thickness of material as a structural component.

Drainage Coefficient, m_i

• Values determined based on percent of time the structure is exposed to moisture approaching saturation.

Flexible Pavement Design (recap)

• Solve for structural number using log W₁₈ and related formulas.

END

This quiz explores concepts related to aggregate interlocks and joint configurations in concrete pavements, focusing on their functions and types. Questions cover the roles of dowel bars, tie bars, and resilient modulus in concrete structures. Test your knowledge on how these components contribute to the overall durability and performance of concrete pavements.