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Environmental Impacts of Lightweight Aggregate

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This information has shown improvement over recent years due to awareness, process improvements, and improved efficiencies. While designers and green rating systems tend only to evaluate a product cradle-to-gate, numerous products on the market today need a look beyond the manufacturing facility to get the actual impact on the environment.

Life Cycle Inventory

ESCSI completed a production survey of 10 member plants in 2023. All producer members of the ESCSI participated in the study and presented data on expanded shale, clay, and slate (ESCS) lightweight aggregate production. The survey followed the previously used process, lifecycle inventory, and production survey reports to evaluate environmental impacts. The outcomes comply with the ESCS Product Category Rules (PCR) report and cover the cradle-to-gate portion of these documents (Table 1). An in-progress lifecycle assessment (LCA) and the following industry-average environmental product declaration (EPD) will report cradle-to-gate and beyond footprints for ESCS lightweight aggregates and applications.

Table 1: System Boundary Modules
Production A1 A2 A3
Cradle to Gate Raw Material Supply Transport Manufacturing

The 2023 production survey represents 2,880,000 tonnes (3,175,000 tons) or nearly 3,614,000 m3 (4,726,000 yd3) processed materials with an average bulk moist density of 800 kg/m3 (50 lb./ft3) at a 7% moisture content. This equates to an average dry bulk density of 750 kg/m3 (47 lb./ft3). These values are comparable to previously submitted data. However, energy and emissions indicate significant declines due to continuous plant improvements and enhanced process technology efficiencies.

Table 2: Production Use (A1-A3)
Embodied Energy 1.47 GJ/m3 (1.06 MMBtu/yd3)
Emissions (CO2) 111 kg/m3 (187 lb./yd3)
Waste Disposed 4.15 kg/m3 (6.99 lb./yd3)
Net Freshwater 400 liter/m3 (80.8 gal/yd3)

These values represent the average of the ESCSI member companies’ manufacturing facilities to produce one cubic meter of lightweight aggregate. These values represent only the production phase of the material. The complete PCR that outlines impacts for the construction, use, and end-of-life stages can be downloaded at no cost from the Underwriters Laboratory Website.

Comparative Study on Structural Lightweight Concrete

The use of ESCS structural lightweight concrete in multi-story building construction will help lower the environmental impact of the structure when compared to a similar structure constructed with normal weight concrete.

The reduction in concrete densities helps to reduce the use of other energy-intensive construction materials. These benefits were demonstrated in a study conducted by Walter P. Moore that compared the embodied energy in the structural system of a steel-framed building with lightweight concrete (LWC) floor slabs on composite steel deck to the same system using normal weight concrete (NWC). Four structural systems were compared; all had the same floor acceleration, fire rating, and live, wind, and seismic loads.

Read Full Report

This study only included the embodied energy of the building’s structural materials. It excluded any transportation energy impacts or the embodied energy in the building envelope (or other systems).

A material inventory was created after performing the structural design for each building scenario. For the concrete mixture proportions, Walter P. Moore used aggregated data from historical concrete mixture proportions used in its practice across the U.S. Energy intensities of the structural materials were taken from the Inventory of Carbon & Energy, version 2, by Hammond and Jones, which reports embodied energy of materials from a cradle-to-gate basis.

The results showed that one of the LWC scenarios had the lowest total embodied energy at 10,520 MMBTU. In contrast, the NWC scenario had a total embodied energy of 10,660 MMBTU for the structure. The study found that the energy required to produce LWA was offset by the following:

  • the reduced dead load of the scenario
  • the reduced concrete volume due to improved fire performance
  • thinner steel decks for a given beam spacing due to the reduced weight of the concrete floor

Lightweight aggregate is an environmentally friendly product with unique features that has been successfully used for well over two millennia. Rotary kiln-produced ESCS has been widely used for the past hundred years in a multitude of applications that contribute to the sustainability of the site and structure, long before the current green movement came to the forefront. It is important to consider all phases of a project’s life and evaluate the impacts on the environment and other materials required to construct and operate a building.

FAQs: Lightweight Concrete Masonry Units

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What is lightweight block?

ANSWER: Lightweight block is a concrete masonry unit made with low-density aggregates that reduces weight compared to standard concrete blocks.

This is typically achieved by using lightweight aggregates such as expanded clay or shale. ASTM C90 classifies a lightweight block as any block with an oven-dry density of 105 pounds per cubic foot or less.

How much does a lightweight block actually weigh?

ANSWER: ASTM C90 classifies lightweight blocks as having a density of 105 pounds per cubic foot. For a typical 8x8x16 unit, this translates to about 28 pounds per block.

Lightweight blocks can go much lighter, with some weighing as low as 18 pounds per unit.

How does that compare to traditional block?

ANSWER: A traditional block generally weighs about 35 pounds per cubic foot, making it significantly heavier.

Is lightweight block structural?

ANSWER: Yes, lightweight block is structural. For an average of three masonry units, the required strength is 2,000 PSI, with no unit below 1,800 PSI.

The actual strengths are typically much higher than these minimums. If needed, the design strength can be verified by testing the assemblies or prisms of the constructed unit.

What are the thermal properties of lightweight block?

ANSWER: Thermal resistance varies based on unit shape, size, density, and materials used. Factors like web and face shell dimensions are critical.

For example, a standard heavyweight 8” block has an R value of 1.99, which can increase to 4.02 when cores are filled with foam insulation. Reducing web configuration and using lightweight aggregate raises the R value to 2.3, and up to 9.39 when filled with foam insulation.

Is lightweight block easier to use than traditional block?

ANSWER: Yes, lighter weight means increased productivity for masons, as they can place more units per day.

This not only speeds up construction but also improves health and ease for the masons working on the project.

Can I get the appropriate fire rating with lightweight block?

ANSWER: Fire resistance depends on the equivalent thickness of the unit. For a typical 8” lightweight unit, the fire rating is approximately two hours.

Are there cost advantages with lightweight block?

ANSWER: Lightweight block offers cost savings post-construction due to enhanced fire rating and thermal properties.

These features can result in lower energy costs when compared to standard blocks or other applications.

Are there any other virtues of lightweight block?

ANSWER: Yes, lightweight blocks also improve logistics. Less weight per pallet means more blocks can be shipped on a truck, saving on transportation.

Using Lightweight Aggregates in Sustainable Construction

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Addressing the Environmental Impact of Construction

Sustainable construction practices continue to drive design and specifications throughout the building industry. Since concrete remains one of the most widely used building materials in the world, it’s crucial for concrete producers, engineers, and contractors to understand how concrete can be produced and used more sustainably.

To address the environmental impact of construction, it’s important to understand how a material interfaces with adjacent systems during production, use, and after construction. While some materials may have a higher environmental impact during production, they can offer substantial benefits during and after construction.

Expanded shale and clay lightweight aggregates, while energy-intensive to produce in rotary kilns, significantly offset their production footprint when used in structural lightweight concrete or to facilitate internal curing. These materials contribute to longer-lasting, more sustainable structures and reduce the environmental impact when evaluated from a cradle-to-grave perspective rather than just cradle-to-gate.

Longer-Lasting Concrete Structures

Lightweight aggregates can improve the resilience of concrete to chloride attack and water penetration by supporting internal curing and reducing chemical shrinkage. This increases the durability of concrete, reducing the need for repairs and replacements, and ultimately lowering the environmental impact of a structure’s lifecycle.

When prewetted Arcosa Lightweight aggregates are incorporated into concrete, they release water slowly as the concrete cures. This reduces cracking and microcracking, making the material more resistant to chloride penetration and corrosion, extending the lifespan of the structure.

Reducing Structural Material Needs

By replacing a portion of normal weight aggregates with lightweight aggregates, concrete producers can reduce the total weight of concrete from 145 pounds per cubic foot (pcf) to between 90 and 135 pcf. Structural lightweight concrete allows for thinner slabs and reduced dead loads, decreasing the need for steel columns, beams, and footings.

This leads to more cost-effective designs and lowers the environmental impact by reducing material quantities, shipping requirements, and embodied carbon. Additionally, structural lightweight concrete has lower thermal conductivity, providing insulation that enhances a building’s operational efficiency.

A More Environmentally Friendly Construction Process

While cradle-to-gate assessments often focus on the embodied carbon of building materials, it’s essential to consider the cradle-to-grave perspective. While ESCS lightweight aggregates may seem less eco-friendly based solely on their production impact, their long-term benefits in structural efficiency and energy savings make them a sustainable choice for the entire lifecycle of a structure.

By evaluating materials from cradle to grave, engineers and specifiers can develop a more comprehensive understanding of sustainability and support the building industry’s reduced emission goals. Lightweight aggregates are an integral part of making that possible.

Enhancing Performance with Internally Cured Concrete (EPIC2)

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FHWA describes internal curing as a “material-level technology that can be employed in any concrete mixture with an adjustment to mixture proportions. The most widely used approach includes pre-wetted lightweight aggregates, which have a high-absorption capacity and are naturally compatible with common concrete production practices. A portion of the normal-weight fine aggregate is replaced with a pre-wetted lightweight fine aggregate. The saturated, porous fine aggregates in the concrete mixture distribute the curing water throughout the concrete body. As the concrete loses water naturally due to continued hydration or environmental exposure, water is pulled out of the lightweight aggregate and creates internal curing. This allows cementitious microstructure pores to be refilled before they become empty, avoiding the negative pore pressures that cause concrete to shrink.”

Peer-to-Peer Exchange: Sharing Internal Curing Best Practices

To give State Departments of Transportation (DOT) an opportunity to learn about internal curing, a Peer-to-Peer Exchange was conducted on May 29-30, 2024, in Albany, N.Y. The group of 74 attendees included 29 different State DOTs, Federal Highway Administration officials, and representatives from the lightweight aggregate, ready-mixed concrete, and concrete contracting industries. The program provided a forum for State DOT representatives to share their experiences with internal curing and engage in open discussions about any concerns or questions they had.

The exchange featured a full day of presentations and best practices, followed by a half-day of demonstrations on testing, producing, and placing internally cured concrete. Attendees gained insights into how to apply internal curing in infrastructure projects and learned about the latest advancements in testing and production techniques.

Impact of the Program

The conference was a great success, with valuable information exchanged between participants. Representatives returned with new knowledge to share with colleagues, helping to develop programs in their respective states that will improve the concrete used in infrastructure. This knowledge will ultimately enhance the life span and sustainability of critical components within the transportation system, contributing to more durable and resilient infrastructure nationwide.

The Advantages of Lightweight Concrete Masonry Units (LWT CMU)

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Arcosa Lightweight’s expanded shale and clay aggregates add significant value to LWT CMU beyond reducing weight. The ceramic-like lightweight aggregate is made by expanding selected raw shale or clay minerals in a rotary kiln at temperatures over 2000°F. This expansion process creates an aggregate that is structurally strong, durable, inert, and lightweight, benefiting concrete masonry units at all stages of design, construction, and operation.

Masonry Blocks with Superior Fire Resistance

All CMU offer very good fire resistance ratings and perform as designed in real-life fire situations. LWT CMU perform even better because the expanded shale or clay LWAs in them contain trapped air bubbles, which act as an insulator. As a result, less concrete is required to achieve the fire resistance ratings when making LWT CMU versus normal weight CMU.

LWT CMU can easily and economically achieve two, three, and four-hour fire ratings based on the minimum equivalent thickness required by building codes. Because the LWAs in LWT CMU act as insulators, less concrete is required to withstand fire conditions. Additionally, more LWT CMU can be stacked on a single pallet, reducing the number of truckloads required for transportation, which in turn lowers fossil fuel consumption and benefits the environment.

SmartWall LWT CMU – Higher Compressive Strength and Lighter Units

According to ASTM C90, regular LWT CMU made with concrete weighing no more than 105 pounds per cubic foot (pcf) are required to have a minimum compressive strength of 2,000 pounds per square inch (psi). However, SmartWall units exceed both the minimum ASTM C90 density and strength requirements.

SmartWall blocks have a concrete density less than or equal to 93 pcf, a minimum compressive strength of 2500 psi, and are made using an optimized gradation of Arcosa Lightweight aggregates combined with regular aggregates. Higher strength allows structural engineers to design even more efficient load-bearing structures, and the lighter weight of these units improves mason productivity and can shorten construction schedules.

Meeting Energy Codes with LWT CMU in Cold Climates

Depending on the number of cross webs and web thicknesses, insulated LWT CMU can have R-values that are 2-3 times higher than identical NWT CMU. These higher R-values make meeting energy codes easier. It is recommended to use COMCheck software to determine energy code compliance for commercial buildings.

Whole building computer modeling studies have shown that LWT CMU, including traditional 3-web and newer 2-web units, perform well in all eight climate zones, especially in schools, supermarkets, and big-box retail stores.

LWT CMU Facilitates Mason Safety and Faster Construction

Using lightweight CMU benefits not only the design team but also masons and subcontractors. The 30-40 percent lighter weight of LWT CMU speeds up the construction of CMU walls and reduces back and musculoskeletal injuries. Reducing job site injuries significantly lowers Worker Compensation Claims, which in turn reduces insurance premiums for mason contractors and wall costs for building owners.

In most regions of the U.S., mason wages have reached a point where placing just two additional blocks per hour into the wall offsets the higher cost of LWT CMU. Since project owners are paying for a finished wall, if the finished cost is the same or less with LWT CMU, why not use it? LWT CMU provides a better product, enhances mason productivity, and preserves health and wellbeing, allowing contractors to complete more projects while delivering a superior product.

The Best of Both Worlds

LWT CMU made with Arcosa Lightweight aggregates benefits all stakeholders involved in the design, manufacturing, construction, and operational phases of a building’s life.