A-Block Enhances Energy Performance

C90 modification shapes its future

Jody R Wall & Starling Johnson

 

Taking the best and making it better

As chairman of National Concrete Masonry Association and Executive Vice President of Johnson Concrete where he has worked for more than 40 years, Charles Newsome has been a huge advocate for the concrete masonry industry. He is always thinking proactively to encourage all in the industry to take the best wall system and make it better. Today, the structural masonry cavity wall is unparalleled in its performance. Tomorrow, it will surpass today’s expectations. He and other Industry leaders are determined to innovate new masonry products to address speed and cost of construction as well as energy optimization, addressing market demands.

Unparalleled Concrete masonry units (CMU) not only provide lasting value to a community with structure and resilience, they also contribute the added value of sustain – ability, durability and attractive aesthetics. Masonry stops fire cold. It does not burn. Masonry structures can be designed to be compartmentalized to prevent the spread of fire.

Today, this industry has wrapped itself around the environmental concerns of communities as well. It uses recycled product in its manufacture keeping it from landfills. It sequesters carbon. When a building is designed of a modular nature, waste is minimized. Masonry units may be reincorporated into the manufacture of new CMU, segmental retaining wall units, permeable pavers or simply recycled. It is manufactured locally using local ingredients, providing local jobs and minimizing transportation costs.

CMU plays a significant role in efficient building envelopes by providing not only the structure but often at least one wall of a cavity wall construction, optimizing energy performance. Newsome is never satisfied with resting on the industry’s laurels. Not even with its intrinsic attributes such as acoustic performance, noise abatement, sound isolation, and being inorganic, never a source for mold. Even the running bond pattern of laying one over two generates inherent structural redundancy.

Challenge

Newsome has challenged the entire industry to think about how we can improve the commodity CMU. And how we can improve the productivity of masonry construction. Have you ever thought about what you can do to make the best even better? Daunting. He is very forward thinking, always developing new products, new systems, new efficiencies. Always looking for an edge in the architect’s office. In the engineer’s office. Where he is very well respected. And maybe that is why. He queried the industry to see where it was going. What it needed. Newsome called a meeting of 20 some architects and engineers as a think tank. Every one attended. Consensus was weight saving effecting the speed and productivity of construction and optimization of energy performance.

Newsome’s dictum to his creative team was to create the biggest, lightest block we could and make it more energy efficient. It needed to be more architect friendly, more engineer friendly, more mason friendly. So now it is.

The first step was to study ASTM C90 Standard Specification for Hollow Load bearing Concrete Masonry Units. In order to minimize thermal bridging, the webs needed to be reduced. Research proved that the web area could be reduced a bit without losing any of the block’s compressive strength. It was determined that reduced thermal bridging could increase thermal performance by up to 264%. The ASTM C90 committee was on to something. Modifications could accommodate a new more energy efficient block.

After several brainstorming sessions, Newsome and his team decided to focus on how to craft their lightweight CMU using C90 modifications to achieve a product to be quicker and easier to install while enhancing CMU’s inherent attributes and, at the same time, perform more energy efficiently. This has been an eight-year development process. Molds are now available to block manufacturers throughout the States and Canada.

ASTM Modifications Expand Possibilities

CMU had not changed since 1931 with the original publication of ASTM C90 until 2011, with ASTM C90 2011b, which allows for, but does not require, a unit’s webs to be configured differently. As a result, CMU designs may be altered in order to • Utilize fewer raw materials in production • Reduce unit weight • Increase energy efficiency.

ASTM C90 changed from requiring a mini – mum web thickness to requiring a minimum web area of 6.5 square inch per square foot of face area. No longer were manufacturers required to have 1″ thick webs on 8″ block; instead an 8x8x16 block could have one web as thin as .75″ and still meet ASTM C90’s new minimum web area requirements.

Options in order to be successful, a new innovative product would have to improve a project’s bottom line by being lighter than standard CMU to improve mason productivity.

The concept of an open-ended “H” block presented challenges in both manufacturing and application. It cannot be partially grouted and may potentially incur more breakage during normal handling. An “A” block design (one end open) is a modified solution that enables partial grouting while reducing weight and maintaining dimensional stability. The one open end allows for faster work around reinforcing steel and addresses potential job site injuries as contractors can slide the masonry unit around rebar rather than lifting it up and over.

Maximizing R-Value

The key to maximizing thermal resistance (R-value) of CMU is minimizing its thermal bridges and increasing the thermal resistance of materials used in production. The code-recognized method for determining R-values of CMU is the series parallel (isothermal planes). Thermal bridging, material thermal resistance and internal insulation R-value are factors which affect the assembly R-value.

An option in making a new modified “A” block more energy efficient is utilizing expanded shale, clay and slate (ESCS) lightweight aggregate. ESCS lightweight aggregate has a density of about half that of typical normal weight aggregates and a thermal resistivity 2.5 to 3 times as high. Density of CMU made with ESCS lightweight aggregate is typically between 85 and 105 pcf. Based on published data, thermal resistivity (hr.ft2.ºF/btu.in) of 85 pcf lightweight masonry is 2.7 times higher than 130 pcf normal weight concrete masonry.

Lightweight block has other advantages as well. ESCS provides improved fire ratings with less material. Less equivalent thickness is required in lightweight block (3.8″) to achieve the same 2-hour fire rating as a normal weight unit (4.2″). High compressive strengths are also easily achievable with ESCS.

Modified “A” block is more energy efficient with only two webs smaller than those in typical units with three larger webs. Increase in energy efficiency is related to decrease in thermal bridging area. A thermal bridge allows heat to short circuit insulation. Typically, this occurs when a material of high thermal conductivity, such as steel framing or concrete, penetrates or interrupts a layer of low thermal conductivity material, such as insulation. In a single wythe CMU wall, webs and grouted cores can act as thermal bridges, particularly when cores of CMU are insulated. The web area for a modified “A” block is about half that of standard 8″ block, cutting thermal bridging in half.

Insulated Single Wythe Wall System

The combination of higher thermal resistivity materials and decreased thermal bridging make a high performance CMU in energy applications. For example, the R-value of a single wythe 8″ ungrouted wall made with this new block, cells filled with R4.6/” foam-injected insulation could have a value of R10.69, compared to a value of R3.28 for the same wall, having the same insulation, using typical normal weight masonry units. Substantial benefits arise even in walls partially grouted. R-value of a typical 8″ wall insulated using R-4.6/” foam-injected insulation grouted at 48″ vertically and 48″ horizon tally is R2.54, compared to R5.02 for the same wall assembly with this new block. Using higher R insulation will make the overall wall assembly R-value a little higher.

In the above example, R-value of the assembly using R5.91/” insulation would be R5.12 compared to R5.02 with R4.6/” foam injection.

Meeting Code

The first and most straight forward path to code compliance is by meeting prescriptive requirements laid out in 2009 IECC. Table 502.2(1) gives envelope requirements including continuous insulation, which cannot be met in a single wythe masonry wall. Table 502.1.2, however, provides maximum U-factor (reciprocal of R-value) allowed for the overall wall assembly. For a mass wall in climate zone 3, the maximum U-factor is 0.123 (reciprocal is R8.1 for the assembly).

In climate zone 4, the U-factor is 0.104 (reciprocal is R9.6 for the assembly). This insulated, modified “A” block could comply under this prescriptive requirement in these climate zones.

Using higher R-values associated with A-block in compliance software like the US Department of Energy’s COMcheck program can significantly impact results. Running the software using normal weight concrete masonry units and increasing roof insulation from R30 to R40, the building envelope fails by 9%.

For a simplified example of a 20,000 sf building with masonry walls (8,000 sf) containing steel reinforcement placed and grout ed at 48″ oc both vertically and horizontally, the roof contains R30 insulation. Running compliance software with normal weight CMU, the building envelope fails by 12%.

Running the software using a modified lightweight “A” block, the building envelope fails by 3%. Running the software using the A-Block and increasing the roof insulation from R30 to R40 will bring the building envelope into compliance.

Code compliance is dependent on exact design details and materials proposed for the building envelope. This example is intended only to demonstrate how the higher R-values of a modified “A” block contributes to the building envelope meeting code compliance.

In addition to code compliance, a modified “A” block yields savings on energy bills. A study published in ESCSI information sheet 3530 (March, 2000) Life Cycle Energy Cost Analysis Shows That SmartWall Systems Provides Significant Savings in All Climates, showed that the use of 90 pcf CMU can save $1.15 per block over the first 10 years and $2.86 over a 30 year time period. Energy use analysis compared 90 pcf lightweight masonry to 135 pcf CMU in an example building design in Omaha NE (climate zone 5). Another study published in ESCSI Information Sheet 3201 (August 2004) Energy Efficent Buildings with SmartWall Systems showed in an ENVSTD computer modeling program that a 12″, 93 pcf lightweight wall system insulated with generic perlite, which expands as heated from four to 20 times its original volume, uses less energy for heating and cooling than a metal frame/ brick veneer wall with R19 batt insulation. The use of lightweight aggregates in a the modified block, along with the improved energy performance of the web configuration, will yield even greater benefits compared to normal weight masonry units and other competing systems.

Productivity Estimates show that labor constitutes around 60% of the total masonry wall cost.

Unit weight impacts productivity, with normal weight CMU weighing in at about 36 lbs each. Not surprisingly, lighter weight units result in higher productivity rates. According to NCMA TEK Note 4-1A, Productivity and Modular Coordination in Concrete Masonry Construction, the use of lightweight CMU can increase productivity up to 54% over normal weight units when controlling for other factors.

While an “ A” shaped block has been around for some time, new “A” block designs are engineered with thinner webs, wedges at the open end and a center handhold to distribute weight equally across the block. Adding the handhold not only benefits masons, it moves the center of gravity higher in the block making it feel more balanced. Furthermore, these tweaks to the “ A ” block design improve R-values and thermal efficiency.

Competitive Edge

Design Professionals benefit from increased R-values making it easier to comply with ever tightening energy codes saving clients money on energy use for the life of the building. Mason contractors can realize tangible gains in productivity, potentially up to 165%, which translates to schedule sensitivity and in-the-wall cost savings.

Jody R Wall, PE, LEED AP BD+C, is director of research and development, quality control manager and geotechnical engineer for Carolina Stalite Company and Johnson Concrete Company in Salisbury NC. Wall has been the director of the research, development and quality control programs for Carolina Stalite and Johnson Concrete Company for the past 13+ years. He is a member of ACI, ASTM and ASCE. He is a graduate of the University of North Carolina at Charlotte and worked as a Geotechnical Engineer prior to joining Stalite/Johnson. jwall@theproblock.com | 704.640.8261

Starling Johnson, is corporate sales manager at Johnson Concrete Company in Salisbury NC. She has been part of the Johnson Concrete team since 2010 and oversees all aspects of sales. A graduate of Duke University with double majors in Economics and Sociology, Johnson worked for a global consulting firm prior to joining Johnson Concrete. She is a member of the North Carolina Masonry Contractors Association and Carolinas Concrete Masonry Association. sjohnson@theproblock.com 704.640.7300

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