Concrete Technology: Aggregate Interlocks and Joints

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Questions and Answers

What is the primary purpose of aggregate interlocks in concrete?

To reinforce the concrete against environmental factors

To increase the workability of the concrete mix

To enhance the aesthetic appeal of concrete structures

To transfer load across a crack in concrete (correct)

Aggregate interlocks are formed between which two components in concrete?

Irregular aggregates and steel reinforcement

Fine aggregate and coarse aggregate

Cement paste and water

Irregular aggregate and cement paste surfaces (correct)

Where do aggregate interlocks primarily function within a concrete structure?

Within the cured concrete matrix

In the form of expansion joints

At the outer surface of the concrete

Across cracks in weakened plane joints (correct)

Which characteristic of aggregates best supports the function of aggregate interlocks?

Irregular shapes and sizes Signup and view all the answers

What type of failure in concrete do aggregate interlocks help to mitigate?

Cracking along weakened planes Signup and view all the answers

What is the primary purpose of dowel bars in PCCP?

To serve as a load transfer device at contraction joints Signup and view all the answers

Where are keyed joints with tie bars typically installed?

On longitudinal joints and construction joints within the middle third of the slab Signup and view all the answers

Which construction feature is specifically associated with dowel bars?

Contraction joints Signup and view all the answers

What is the role of tie bars in joint configuration?

To facilitate proper alignment of slabs at longitudinal joints Signup and view all the answers

Dowel bars are primarily used in which type of pavement?

PCCP (Portland Cement Concrete Pavement) Signup and view all the answers

What is required to solve for S/X in a given context?

Checking if minimum CBR samples were met Signup and view all the answers

How is the resilient modulus of subgrade (MR) obtained?

From recoverable strain under repeated load Signup and view all the answers

What should be done if minimum CBR samples were not met during testing?

Provide additional samples and recompute Signup and view all the answers

What is the significance of recoverable strain in the context of resilient modulus?

It indicates how materials respond under repeated loading Signup and view all the answers

When computing for S/X, which of the following is unnecessary?

Using historical data without verification Signup and view all the answers

What is the primary purpose of calculating the Cumulative Equivalent Single Axle Load (CESAL)?

To determine the structural requirements for road design. Signup and view all the answers

In the CESAL formula, what does the term 'EF' represent?

Equivalent Factor Signup and view all the answers

Which part of the CESAL formula is multiplied by the Design Traffic?

Equivalent Factor (EF) Signup and view all the answers

What would be the result of adding CESAL for all vehicle types multiplied by distribution factors?

A single numerical value representing road impact. Signup and view all the answers

Why is it important to consider distribution factors in the CESAL calculation?

To reflect the varying impacts of different vehicle types on roadways. Signup and view all the answers

What does the term ∆L represent in the formula for joint opening?

Joint opening caused by temperature changes Signup and view all the answers

Which factor influences contraction joint spacing?

Subbase frictional resistance Signup and view all the answers

What is an empirical relationship that aids in determining joint spacing?

L = 2D Signup and view all the answers

What is the typical adjustment factor (C) for stabilized subbases?

0.65 Signup and view all the answers

What is the maximum allowable strain of joint sealant usually expressed as?

25% - 35% Signup and view all the answers

Which type of joint typically utilizes dowel bars?

Contraction joints Signup and view all the answers

What is the recommended maximum joint spacing based on slab thickness?

Should not exceed twice the slab thickness Signup and view all the answers

Which coefficient is involved in calculating joint opening due to temperature changes?

Thermal Coefficient (αc) Signup and view all the answers

What is the structural layer coefficient for a good condition asphalt concrete?

0.38 Signup and view all the answers

Which pavement component has the lowest structural layer coefficient?

Granular Sub-Base Signup and view all the answers

For cement concrete in a bad condition, what is the structural layer coefficient?

0.20 Signup and view all the answers

In the flexible pavement design equation, which variable does 'SN' represent?

Structural Number Signup and view all the answers

What is the structural layer coefficient for a crushed stone base course?

0.14 Signup and view all the answers

Which component's structural layer coefficient decreases with the condition of the surface?

Asphaltic Concrete Signup and view all the answers

What is the structural layer coefficient of a sandy gravel subbase?

0.11 Signup and view all the answers

What is the purpose of the flexible pavement design equation presented?

To determine the structural number Signup and view all the answers

Study Notes

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

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Description

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.