How It’s Made: Spherical Block

Words: Peter Roberts
Photos: Spherical Block, LLC

Masonry arched roofs date back at least 3,500 years. Concrete block are ubiquitous; they are found in every country around the world. Yet virtually no one uses concrete blocks to produce masonry arched roofs, until recently. Spherical Block, LLC has created methods and processes to provide concrete block masonry arches and domes as an engineered system, providing extremely high strength, affordability, energy efficiency, safety, and beautiful concrete block arched roofing systems. Governed by rigorous industry standards, the manufacturing of concrete masonry arched roof blocks in America is a testament to precision, innovation, and craftsmanship.

This article delves into the technical aspects of concrete block arched roofing, highlighting the processes, materials, and benefits of working with a Spherical Block, LLC producer.

Defining Concrete Block Masonry Roofs

Concrete Masonry Units, as defined by ASTM C90, are a well-known product which have been successfully produced and commercially developed for over 120 years. CMUs are renowned for their versatility, aesthetics, strength, and durability, making them a favored choice for architects and builders seeking a reliable, tried, and true method for building vertical walls. Now these benefits of concrete block masonry construction extend to the roof and to the entire building envelope. Typical concrete block is primarily specified for exterior vertical walls, trim, and ornamental elements. Typical applications include load-bearing structural walls, corners, columns, lintels, and interior applications including non-load-bearing walls and designs as specified by ASTM C129, including mantels, replicating and replacing deteriorated elements in historic structures, and landscaping features, including retaining walls.

There are two basic types of concrete block masonry roofing: Dome blocks and Arch blocks. Dome blocks are triangular blocks that assemble as geodesic patterns (both as hexagons and pentagons). Arch blocks assemble as vaulted arches. Together, these units create extensive design flexibility: allowing for round domes and square and rectangular roofs to be combined in a building’s design.

The Arch blocks can also be used to make flying buttresses, which can help resolve the thrusting forces created by a masonry arched roof. Arch blocks can also provide arched lintel sections, rounded windows, and more. There is much design flexibility created by this masonry system.

Key Characteristics:

Durability and Strength: Meets stringent compressive strength, high-density criteria; engineered to withstand weathering, freeze-thaw cycles, and environmental pollutants such as ultraviolet radiation and acid rain. Minimal shrinkage due to low water content. Can be reinforced for additional strength.
Aesthetic Versatility: Can be manufactured in custom colors and finishes to create an aesthetic palette including split-face, smooth finish, and polished faces. A masonry arched roof, whether domed or vaulted, creates a unique, attractive visual appearance to any building.
Sustainability and Cost-Effective: Concrete block masonry roofing systems maximize the well-known thermal mass benefits of concrete block construction. A complete masonry building envelope, including the roof, provides a means for storing thermal energy in the walls and roof of the building itself. This thermal mass creates a time lag between outdoor temperature changes and the interior temperature of a building. This thermal lag moves back the peak demand for heating and cooling buildings, reducing the peak load requirements on any given energy grid: whether it’s heating or cooling requirements created by changing outdoor temperatures. Buildings are kept at a more constant comfortable temperature, requiring less energy. Design mixes for the concrete used in these roofing blocks can include recycled materials and support green building certifications such as LEED. These manufactured units create no product waste during and post-installation.

Governed by industry standards such as ASTM C90 and ASTM C129, guidelines and technical bulletins published by the Concrete Masonry and Hardscape Association, and the guidelines set forth by the Masonry Society in TMS §§402/602, concrete block production in the United States represents a meticulous blend of artistry and technology.

Concrete Block Roofing Manufacturing

CMU manufacturing is very precise and automated; the quality of architectural concrete block depends upon the manufacturer’s experience and expertise and on the materials used in its production. Each component plays a crucial role in ensuring the final product’s performance and aesthetics. Quality assurance/quality control checks occur at each stage of the manufacturing process.

NOTE: Selecting a Spherical Block-certified manufacturer guarantees an industry-vetted and certified manufacturer and that all aesthetic and technical standards will be met and backed with a warranty.

From the outset, the manufacturer and customer work together to select the job’s concrete block roofing units' color (a standard color or a custom color match) and texture (smooth, split-faced, polished). If the units selected are not already in stock, custom units are produced.

The superior performance of concrete masonry roofing blocks depends on the quality and proportioning of its raw materials. Each ingredient contributes to the product’s strength, appearance, and durability. Precise batching of raw materials ensures consistency and compliance with ASTM C90. The four primary ingredients in a batch of cast stone “mix” are cement, aggregates, color pigment and admixtures, and water:

Cement: Portland cement (ASTM C150 Type I or Type II) provides the binding strength and rigidity required for architectural elements.
Fine and Coarse Aggregates: Aggregates, such as crushed limestone and river sand, are chosen for their strength, texture, and compatibility with pigments, and carefully graded to achieve desired texture and strength.
Pigments and Admixtures: Pigments meeting ASTM C90 ensure consistent custom coloration and long-term stability. Custom colors can replicate regional stone varieties or match project specifications. Admixtures like plasticizers, retarders, and accelerators are used to optimize workability and allow precise control over setting time.
Water: Clean, potable water is essential to prevent impurities that could weaken the mix or cause discoloration.

NOTE: Some manufacturers have added or replaced these ingredients to include alternative and sustainable materials such as the use of recycled materials (crushed glass, recycled concrete) and low-carbon cement options.

Required quality control and frequent quality checks throughout the manufacturing process include:

Standardization and Certification: Industry standards such as ASTM C90 and guidelines for block production.
Testing for Strength and Durability: Common tests, including compressive strength, water absorption, freeze-thaw resistance, and impact resistance.
Visual Inspection: Checking for defects like cracks, air pockets, and inconsistencies in color and texture.
Quality Assurance Protocols: Ongoing monitoring, batch sampling, and testing to ensure consistency in production runs.
Technological Innovations in Quality Control: Use of automated systems and digital tools to monitor mixing ratios, curing conditions, and product dimensions.

Curing of cast block typically involves a 28-day cure time before units achieve their specified compressive strength.

Roof Assembly

Concrete Block Masonry Roof Assembly begins with an engineered design of the entire building. The basic design principal is to keep the entire structure under compression (being squeezed together), which is how concrete is strongest. The roof itself is typically a catenary or rounded shape. Thrust line analysis is frequently used to keep the imaginary thrust line in the center third of the roof profile, between the inside surface (intrados) and the exterior surface (extrados).

The roof is tied to the vertical walls with reinforcement. The reinforcement (rebar) is located so that it aligns with grooves in the Spherical Block, which accepts the rebar. Thus, the rebar acts as support during assembly, making the assembly much easier and safer. This reinforcement also serves to make the arched roof safer once assembly is completed.

Typically, a support form is provided during assembly. This support helps ensure that the curved profile is accurate and precise. Support forms for the roof assembly do not need to be nearly as strong as traditional centering used for masonry arch assembly; this is because the rebar provides much support as the roof is assembled.

As a new technology, innovative assembly methods are still being tested. One promising approach is to use inflatable bladders as support forms during roof assembly. Once the roof is assembled, the inflated bladder is simply deflated and removed, for subsequent reuse. This method promises to provide a safe, rapid, and easy process of arch assembly.

The Benefits of Working with a Spherical Block Manufacturer

Choosing a Spherical Block manufacturer ensures adherence to industry best practices and superior product quality. Advantages include:

Compliance with Standards: Certified manufacturers meet or exceed ASTM C90 requirements.
Enhanced Durability: Products are rigorously tested for compressive strength (ASTM C90), absorption, and freeze-thaw resistance, and linear shrinkage.
Skilled Craftsmanship: Certified professionals employ advanced techniques to deliver precise, high-quality results.
Technical Support: Spherical Block producers provide design assistance and installation guidance.
Sustainability: Many certified manufacturers incorporate recycled materials and implement energy-efficient practices.

The Enduring Appeal of Concrete Masonry Roofs

Concrete Block Masonry Roofs arrive in the marketplace as an innovative material in American construction, valued for its durability, versatility, and aesthetic appeal. Partnering with a Spherical Block producer guarantees exceptional results, sustainable practices, and enduring value for architects, builders, and owners alike on every project.

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