What’s Changed in ASTM C90 and TMS 602 Since 2000, and Why It Matters

Masonry has a long history of durable performance, but the standards that govern concrete masonry unit (CMU) construction have continued to change. As a result, ASTM C90 and the TMS 402/602 documents have been revised over time in ways that affect how masonry is specified and how compliance is documented. 

Project specifications for masonry are often reused across multiple projects, and older standard references can remain in place long after newer editions are published. When this occurs, it can introduce uncertainty during plan review and inspection, particularly when different parties are working from different versions of ASTM and TMS requirements. One common example is the use of legacy unit classifications such as “Type” and “Grade,” which no longer reflect how concrete masonry units are defined under current ASTM standards. 

The most significant revisions to ASTM C90 occurred in 2000 and again in 2011, with additional updates continuing through the current edition. ASTM standards include the revision year as part of the designation. For example, the current version of ASTM C90 is ASTM C90-24a, where the “a” indicates that multiple revisions were made in 2024. 

Several notable changes since 2000 are discussed below. 

Movement Control 

There are two common approaches to designing for anticipated shrinkage in masonry construction. CMHA TEC 009-25 describes both empirical and engineered crack control strategies. 

1. The empirical approach reflects long-standing construction practice using control joints and horizontal reinforcement. This method is based on observed field performance across a wide range of applications. 
2. Engineered crack control relies on a calculated Crack Control Coefficient (CCC) to evaluate anticipated shrinkage and cracking potential. This approach provides a performance-based alternative that accounts for unit properties and design conditions. 

Prior to 2000, masonry units were classified as Type I moisture controlled or Type II non-moisture controlled. This distinction was intended to predict drying shrinkage based on moisture content at the time of delivery. However, it did not account for changes in moisture after shipment or the influence of site exposure. 

As masonry standards have evolved, crack control guidance has increasingly moved toward approaches that recognize the combined effects of material properties, detailing and project-specific conditions. 

Crack control strategies should be clearly identified in the construction documents, including control joint spacing, horizontal reinforcement requirements and any engineered assumptions used to support the design.

Energy Code Compliance 

Energy codes were first adopted in the United States in the 1970s, and concrete masonry has long been recognized in these codes for its thermal mass properties. As codes evolved, greater attention was given to thermal bridging and its role in heat transfer through wall assemblies. 

For energy modeling purposes, the webs of a concrete masonry unit can act as thermal bridges. Historically, ASTM C90 addressed this by requiring a minimum equivalent web thickness, with many loadbearing units using three webs to connect the face shells. Subsequent research supported revisions that allowed greater flexibility in unit configuration while maintaining structural performance. 

In 2011, ASTM C90 replaced equivalent web thickness criteria with a normalized web area requirement of 6.5 square inches per square foot. This change permits a wider range of unit geometries, including single- and two-web configurations, provided strength and performance requirements are met.  

When properly documented, reduced thermal bridging through unit geometry and material density can improve modeled thermal performance. 

Energy codes, including the Florida Energy Code, offer multiple compliance paths such as R-Value, U-Factor and ASHRAE-based approaches. Only the R-Value path requires continuous insulation. When masonry walls are evaluated using U-Factor or ASHRAE methods, compliance is typically verified using Department of Energy software such as COMCHECK. 

When special-shaped units or assemblies with reduced thermal bridging are used to support energy compliance, modeling assumptions should be clearly documented. For COMCHECK evaluations, the appropriate wall classification is “Mass Wall” under the “Other (U-Factor Option).” 

Energy compliance submittals should identify the compliance path used and clearly document assumptions related to unit geometry, insulation placement and wall classification.

Strength of Masonry 

Another significant revision to ASTM C90 occurred in 2011, when the minimum net compressive strength of concrete masonry units was increased from 1,900 psi to 2,000 psi. 

A further shift affecting masonry design values followed in 2013 with revisions to TMS 602, which updated compressive strength provisions for masonry assemblies. 

Earlier strength values were based on test methods developed decades ago. Prior to 2013, a minimum unit strength of 1,900 psi corresponded to a specified compressive strength of masonry of 1,500 psi. More recent testing conducted by the National Concrete Masonry Association demonstrated that these values were conservative and could be revised to reflect updated research. 

As a result, a net compressive strength of 2,000 psi now corresponds to a specified compressive strength of masonry of 2,000 psi, representing a substantial increase compared to earlier code values. 

In practice, higher recognized masonry strength can support increased wall heights or greater compressive loads and may allow adjustments to reinforcement or grouting requirements in some designs, where permitted by applicable loads and detailing provisions. 

Ongoing updates to TMS 402 and 602 have improved masonry design efficiency. Using consistent baseline wall assumptions, newer provisions can allow wider reinforcement spacing than earlier editions, depending on project-specific requirements. 

Structural submittals should document the assumed specified compressive strength of masonry (f’m), reinforcement spacing, and grouting requirements and reference the current ASTM C90 and TMS 602 provisions used to establish design values.

Conclusion 

While updates to ASTM C90 and TMS 602 have been in place for years, they still influence how modern masonry assemblies are specified and reviewed. Knowing where those changes occurred can help streamline plan review and inspection. 

For more information about the Concrete Masonry Checkoff and its resources, visit beautyofblock.com. ICC members can also follow The Beauty of Block on LinkedIn.