Les White, Paving & Infrastructure Engineer-CEMEX, along with CEMEX, created 6 DOCUMENTS on “Suggestions On Specifying Concrete Pavements”. The International Society for Concrete Pavements (ISCP) featured the first document in May (www.concretepavements.org/2022/05/19/6-documents-bring-suggestions-on-specifying-concrete-pavements-1-may-22-concrete-supplier-bidding-topics-insights-experience/). ISCP will feature 2 in June, 2 in July, and 1 final in August.
The International Society for Concrete Pavements (ISCP) featured the first document of “6 Documents Bring Suggestions on Specifying Concrete Pavements:” in MAY ’22: www.concretepavements.org/2022/05/19/6-documents-bring-suggestions-on-specifying-concrete-pavements-1-may-22-concrete-supplier-bidding-topics-insights-experience/. For JUNE ’22, ISCP is featuring the next 2 volumes—Vol. II & Vol. III:
Document #2: “Vol. II: Partnering with Your Concrete Supplier”
Document #3: “Vol. III: Pavement Structure, Subgrade, & Base”
VOL II: Click to download 8-page PDF
#2: “Vol. II: Partnering with Your Concrete Supplier”:
This 8-page document of Suggestions on Specifying Concrete Pavements focuses on items related to concrete mixes that occasionally contribute to confusion or miscommunication between the design documents and contractors or material suppliers during the bidding process. Volume II looks at 9 topics related to placement of concrete after batching:
Delivery Methods–Transit Mixers—typically have drum capacities ranging from 8-11 cubic yards, with the maximum load size delivered to a project site often limited to 9 cubic yards, due to weight restrictions placed by governing Departments of Transportation. Time from batching to discharge is typically limited to 90 minutes which …
Dump Trucks & Roller Compacted Concrete (RCC): Concrete can also be delivered by Dump Truck. One of the more common concrete materials delivered by dump truck is Roller Compacted Concrete (RCC). This “zero slump” mix gives crews the ability to get on the pavement immediately behind the paver for real time quality control—RCC pavers are like those used for asphalt paving: high density pavers often preferred due to the higher level of compaction achievable prior to rolling. Once the RCC is placed, rollers are used …
Fixed Form or Slipform Placement Curing Concrete: In fixed-form placements, concrete is poured in areas where form boards have been placed in fixed locations around the perimeter of the slab, or pavement. Since concrete mixes are typically in a liquid state coming out of the mixer, these fixed forms contain the mix and provide shape until the concrete has cured enough …
Finishing Concrete: Finishing concrete involves working on visible surfaces, such as floor slabs, pavements, sidewalks, or other similar applications. Depending on the application, finishing can consist of several steps or just a few. Typically, interior floors require more steps than an exterior pavement, due to more stringent flatness and level requirements for the floors. For this discussion … about exterior pavements, like parking lots, where concrete is delivered in a mixer. Finishing of a parking lot can be narrowed to 3 steps; screeding, bull floating, and brooming …
Curing Concrete: According to The Craftsman Workbook for ACI (American Concrete Institute) Certification Concrete Flatwork Technician & Flatwork Finisher “Curing refers to the methods used to keep concrete moist and at the temperature needed to develop the required strength, wear resistance, and durability. The main concern is preventing moisture loss from the slab surface, especially at early ages.” There is typically enough, even extra, water in most common concrete mixes to complete hydration of the cement. However, after placement concrete starts to dry, quicker at the top of a slab than at the bottom, and water is lost, which slows hydration and can reduce strength gain. … some of the curing methods used to help keep moisture in the concrete and allow for full hydration. Curing …
Joints and Joint Layout: It has been said that you can divide concrete into 2 categories
Category 1 is concrete that has cracked
Category 2 is concrete that hasn’t cracked yet
There are several reasons why concrete cracks after placement including shrinkage from drying … jointing is a tool for controlling cracks. 3 types of joints used in concrete pavements … are introduced —
• Contraction (Control) Joints
• Construction Joints
• Isolation Joints
Dowels and Tie Bars: Dowels and Tie Bars across concrete joints serve two different purposes:
DOWELS are intended to aid in load transfer from one slab to another and allow for some movement in the slabs
TIE BARS are intended to hold slabs together and do not encourage movement. ACI 330.2R-17- “Guide for the Design and Construction of Concrete Site Paving from Industrial and Trucking Facilities” is a good resource for information on Dowels and Tie Bars, as well as other aspects related to concrete paving in commercial applications …
Sealing or Filling Joints: Sealing and filling joints are different treatments. …a sealed joint … treatment helps to prevent intrusion of water into the subgrade and also helps keep incompressible materials out of the pavement section. The Backer Rod helps create the seal keeping water out and reduce leaking of sealant material downward. Installation of sealed joints require two sawcuts and they with are relatively wide …
Reinforcing for Crack Control: While the use of joints is an effective means of controlling cracks in concrete pavements, the smaller panels can mean a relatively large number of joints. There are applications, such as interior floor slabs, where this increased number of joints may not be desired. Welded Wire Fabric or Fibers are two reinforcing methods used for the purpose of controlling cracks that form in concrete slabs…
Volume III: Click to download 8-page PDF
Document #3: “Suggestions on Specifying Concrete Pavements: Vol. III: Pavement Structure, Subgrade, & Base”:
In this series of documents, Volume I focused on items related to concrete mixes that occasionally contribute to confusion or miscommunication between the design documents and contractors or material suppliers during the bidding process.
Volume II looked at 9 topics related to delivery and placement of concrete after batching
Volume III looks at 8 topics related to pavement structure, subgrade, and base layers:
Structure of a Pavement Section: Pavements can typically be divided into 2 categories, flexible (asphalt) and rigid (concrete). Each type starts on a subgrade of existing soil with additional base layers added as needed before placement of the final wearing course. Flexible pavement sections often consist of one or more base layers of varying materials between the subgrade and asphalt wearing course. A flexible pavement will deflect under loading as pressure dips well into the supporting layers. Each independent, flexible layer contributes to the overall strength of the pavement, or its ability to withstand that loading…
A rigid pavement is not intended to deflect under load. Instead, the loading is distributed over a large area as shown in the picture at the left. As such, the strength of a rigid pavement section is not dependent on the relative strengths of any flexible layers, such as stone, underneath it. Instead, the base or subgrade materials must provide a uniform platform to support the concrete pavement …
LDCC as a Subgrade Replacement: One of the ways to address issues related to unsuitable subgrades, such as reduced load carrying capacity, increased maintenance costs, or premature failures is to replace poor subgrade materials with an engineered fill or other suitable material such as Low-Density Cellular Concrete (LDCC), also called Lightweight Cellular Concrete…
Soil Cement: According to the Guide to Cement-Stabilized Subgrade Soils published by the National Concrete Pavement Technology Center (CP Tech Center) at Iowa State University, “Soil-Cement refers to a compacted engineered mixture of soil, cement, and water designed and constructed for various pavement and geotechnical applications and characteristics”. Soil-cement, in common use, is a catch-all term that encompasses 4 different materials:
—Cement Modified Soils (CMS)
—Cement Stabilized Subgrade (CSS)
—Cement Treated Base (CTB)
—Full Depth Reclamation (FDR)…
Cement Treated Base (CTB): Cement Treated Base (CTB) is another material that falls under the overall umbrella of “Soil-Cement”. Again borrowing from the Guide to Cement-Stabilized Subgrade Soils published by the CP Tech Center, “Cement-treated base (CTB) is a fully bound, compacted, engineered mixture of aggregate, water, and sufficient cement to meet the project-specified minimum durability and strength requirements” …
Full Depth Reclamation (FDR): FDR is the last topic under the overall umbrella of Soil Cement that we will address. The volume of cement (4% – 6%) and seven-day Unconfined Compressive Strengths (300 – 600 psi) for FDR are consistent with the same properties in a Cement Treated Base (CTB). What makes Full Depth Reclamation different, and cost effective, is its use of existing deteriorated asphalt material as a component of the final pavement base, minimizing the amount of existing material removal and replacement when compared to the full reconstruction of a failed pavement …
Stone Base: While the use of a stone base under concrete pavement can, and frequently does, improve the Modulus of Subgrade Reaction (k-value), that improvement is rarely enough to result in a reduction of concrete thickness. The amount of stone required to affect a reduction in concrete thickness would not be cost effective …
Concrete Overlays Existing Asphalt: An intact asphalt pavement is another platform on which a concrete surface can be placed. Overlays of existing asphalt can be:
• Bonded (typically 2” – 6” thick): Bonded Concrete Overlays of asphalt, make use of the existing pavement as a structural component of the overall pavement section—also called
Thin Whitetopping (4” – 6” thick) or
Ultra-thin Whitetopping (2” – 4” thick)—the least commonly used. The existing pavement is generally in good structural condition with minor distresses such as shallow cracking, rutting, shoving, or localized alligator cracking. Prior to construction of a bonded overaly, the existing surface is cleaned and often milled to a depth that eliminates various shallow distresses to provide a suitable surface for bonding. For structural purposes, three inches of the exisitng asphalt section, minimum, is required to be left in place after milling.
• Unbonded (typically 5” – 11” thick)—the existing pavement is in poor structural condition with severe distresses that include, but are not limited to, widespread alligator cracking, potholes, and deep rutting. The existing pavement is not an integral part of the new concrete pavement section but functions as a base for the new concrete pavement. Unbonded overlays are designed as new pavements and are significantly thicker than the bonded overlays. Surface prepartion prior to installation is often limited to isolated full-depth repairs to restore some structural integrity for its function as a base course or milling in areas where distortions …
Composite Pavements: The various support layers discussed thus far become an integral part of the respective pavement section. A different type of pavement section, introduced with the topic of a concrete overlay on an existing asphalt pavement, is a Composite Pavement—one that uses both concrete and asphalt in its section …
To download the JUNE #2 PDF titled: “Suggestions on Specifying Concrete Pavements: Vol. II: Partnering with Your Concrete Supplier”, please click on the first image above, or go to:
www.concretepavements.org/wp-content/uploads/2022/06/2_Suggestions-on-Specifying-Concrete-Pavements-Volume-II-12-3-2020.pdf
To download the JUNE #3 PDF titled: “Suggestions on Specifying Concrete Pavements: Vol. III: Pavement Structure, Subgrade, & Base”, please click on image above, or go to: www.concretepavements.org/wp-content/uploads/2022/06/3_Suggestions-on-Specifying-Concrete-Pavements-Volume-III-4-21-2021-1.pdf
To download the May PDF titled “Suggestions On Specifying Concrete Pavements: Partnering with your Concrete Supplier”, please go to: www.concretepavements.org/wp-content/uploads/2022/05/1_Suggestions-on-Specifying-Concrete-Pavements-Partnering-with-Your-Concrete-Producer-7-6-2020-1-1.pdf
For QUESTIONS, please contact:
Les White, PE, Paving Solutions Engineer-CEMEX
E-mail: Leslie.white@cemex.com