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Bonding in Multi-lift RCC Construction

Description:
Multi-lift RCC construction is common for intermodal facilities, ports, heavy industrial pavements and other applications where the design thickness exceeds approximately 10-inches. Placement and compaction of RCC is generally limited to 10-inches or less according to the literature and currently accepted practice. Most heavy duty RCC pavements are considerably thicker than 10-inches thereby necessitating placement of multiple lifts that must be adequately bonded to form a monolithic slab. From a design and performance standpoint, if full bonding between the lifts is not achieved, the behavior and load carrying capacity of the pavement is similar to an RCC slab placed on a very stiff cement treated base. The bonding of 2 or more RCC lifts is dependent on many factors related to placement, materials, compaction environment and others. The current recommendation for placement of the second lift is generally related to time, the standard being 60 minutes or less. While this has been shown to be adequate in many cases, there are notable exceptions leading to premature pavement failure. A better methodology is clearly needed to eliminate the possibility of delamination of the lifts. A comprehensive approach is required that incorporates many of the same tools as 2-lift PCC placement such as determining the rate of evaporation based on the RCC mix characteristics and relative humidity/temperature/wind velocity.
Objective:

The overall objective of the proposed research is to minimize or eliminate debonding between RCC lifts at the time of construction. A more complete characterization of the factors leading to debonding is required as a first step. Development of implementable procedures to address each of these factors, under a variety of placement conditions, will then be used to develop appropriate guidelines.

Benefits:
The benefit of this research will be the elimination of premature RCC pavement failure due to debonding or lack of bond development in multi-lift RCC construction. Several large-scale RCC projects have required complete reconstruction after only 1 to 3 years of service (design based on 20 year service) due to a lack of bond. The cost of reconstruction and the time out of service for even a single project far exceeds the potential research investment.
Related Research:

The RCC Guidelines developed by the Portland Cement Association (PCA) are still the basis for most decisions regarding RCC construction. Many of the factors previously discussed in this document are addressed to some extent but not to the degree that is required. For instance, the limitation on time between lifts is based on this document for most project specifications. However, the environmental conditions on site may result in significantly different requirements.

There has been considerable research into RCC design and to a lesser extent materials and construction. There are no studies that adequately address the research needs addressed in this document.

Tasks:

1. Conduct a comprehensive literature review to document factors that affect bond development between Portland cement bound layers.

2. Identify projects where the bond between RCC lifts was not adequately developed during construction or debonding occurred soon after placement.

3. Analyze the project data including but not limited to RCC materials, mix design, placement and compaction equipment, environmental conditions during and soon after placement, type, timing and extent of pavement distress and others.

4. Develop a matrix of key factors leading to the lack of bond development or debonding.

5. Develop a list of relevant test procedures and corresponding guidelines. For instance, use of a mini-weather station placed on the first lift to identify critical environmental factors (evaporation rate) that will be used to determine lift and construction sequencing.

6. Prepare draft guidelines using the key indicators and potential resolution steps.

7. Evaluate the guidelines on several multi-lift RCC projects around the country and under a variety of conditions to assess the reasonableness of the proposed solutions.

Develop final guidelines based on the results of the field trials. A revised guide specification will be included as an appendix.

Implementation:

Implementation will be relatively easy to achieve given that there are a limited number of multi-lift RCC projects constructed each year. The majority of these projects will be multi-modal, port and industrial facilities and are relatively easy to identify as early as the design and specification writing phases.

Distribution may be most advantageous through the PCA given that the original Guidelines are from this source.There are no known implementation barriers as major revisions to the basic RCC construction processes are unlikely.

Relevance:

The primary users of the proposed Guidelines will be design professionals, specification writers and contractors.

Sponsoring Committee:AKC50, Concrete Pavement Construction and Rehabilitation
Research Period:12 - 24 months
Research Priority:High
RNS Developer:Dr. Michael E. Ayers and Mr. Matthew W. Singel, P.E.
Date Posted:04/24/2020
Date Modified:05/06/2020
Index Terms:Concrete pavements, Roller compacted concrete pavements, Roller compacted concrete, Bonding, Delamination, Thickness, Paving,
Cosponsoring Committees: 
Subjects    
Highways
Construction
Materials
Pavements
Terminals and Facilities

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