Les White, Paving & Infrastructure Engineer-CEMEX, along with CEMEX, created six documents on “Suggestions On Specifying Concrete Pavements”. The International Society for Concrete Pavements (ISCP) will feature one to three over the next couple of months.
This 6-page document is intended to help clear up confusion or miscommunications that occasionally occur during the bidding process between the design documents and contractors or material suppliers. White looks at general topics and offers insights based on observations made when projects come to us for bidding:
Prescriptive or Performance Specifications—tell the contractor what the pavement must be capable of doing, such as reaching a certain compressive or flexural strength, once constructed without given much detail on the specific mix. These specifications are versatile and readily adapted to any location, and most projects, as they allow the contractor and producer to provide the appropriate mix, based on experience, for the desired result. Performance-based specifications can sometimes lack necessary mix information to help a pavement perform under unique conditions—like extreme temperature swings …
Types of Cement—Worldwide, the most commonly used cement type is Portland Cement, —from stone quarried on the Isle of Portland in Dorset, England. It is made from limestone and clay minerals which are heated in a kiln to form clinker. The clinker is ground into a fine powder and combined with a small amount of gypsum. It is this powder that reacts with water, in a process known as hydration, and acts as the binder for Portland Cement Concrete (PCC). Having five types, cements may meet requirements of more than one type, such as Type I/II or Type II/V. Type III, IV, and V cements may be rare or may be seeing diminishing use in some places …
Supplementary Cementitious Materials (SCM’s)—are frequently added to a concrete mix, in conjunction with the cement, to help enhance properties of hardened concrete including, but not limited to:
• Durability/Permeability
• Alkali-Silica Reactivity (ASR)
• Sulfate Resistance
Two of the most frequently discussed SCM’s are:
• Fly Ash—a byproduct of coal burning furnaces related to power generation
• Slag, although
• (others also exist) such as Silica Fume …
Water-Cement Ratio (w/cm ratio)—the relationship between the amount of water by weight, and the amount of cement, or cement plus supplementary cementitious materials, by weight, in a concrete mix. As shown in the figure below, there is a direct correlation between the w/cm ratio and the 28-day compressive strength …
Slump—often used to describe the workability, how easy it is to handle during placement, of a concrete mix. ASTM C143 describes the “Standard Test Method for Slump of Hydraulic-Cement Concrete”, or slump test. The test is placing a cone on a smooth flat surface and filling it with fresh concrete with:
• a bottom diameter of 8”
• a top diameter of 4”
• a height of 12”
The cone is carefully lifted off allowing the concrete to settle, or slump. The difference in height from the top of the cone to the top of the settled concrete is its slump …
Entrained Air—the process of creating tiny air bubbles in concrete. This is typically done during batching operations using air entraining admixtures. These bubbles are regular in shape, as shown in the picture to the left, and provide space to accommodate the expansion of moisture in the concrete when it freezes. This function increases durability in a concrete pavement exposed to freezing-and-thawing cycles …
Photo: Figure 1: Air-entrained Concrete
Portland Cement Association cement.org/Cement
& Concrete Applications/working-with-concrete/air-entrained-concrete
Admixtures—chemicals introduced to concrete before or during mixing to enhance certain properties of fresh or hardened concrete, or to help overcome challenging circumstances during construction. ASTM C-494 identifies seven admixture types used singularly and in combination. The most commonly used admixtures are:
• water reducers
• retarders
• accelerators
• entrained air …
Aggregates—typically make up a large percentage (60% – 75%) of a concrete mix and sizes are typically designated as coarse and fine. Aggregate sizes ranging from material retained on a No. 4 sieve (3/16 in.) up to a maximum of 1 1⁄2 inch are considered coarse and material passing a No. 4 sieve is considered fine aggregate …
Photo: Figure 2: Conventional Concrete
Click to download 6-page PDF titled
“Suggestions On Specifying Concrete Pavements”
To download the 6-page PDF titled “Suggestions On Specifying Concrete Pavements”, please click on image above, or go to: https://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