Blocks – The ABCs of Green Building Materials

Blocks used for residential and commercial construction employ a wide variety of green building materials in their composition. The most popular and commonly used is the standard hollow concrete block, but there are many variations in shape, weight, and composition. Sand, cement, gravel, and water are the most commonly used elements in blocks, but there is a wide variety in the mix of materials used.

This latest article in our series, the ABCs of Green Building Materials, explores the various types of blocks used in the US and around the world. Look for future articles exploring many of these examples in more detail.

Block Construction Dates Back to the Pyramids

Over 50 years ago, Joseph Davidovits, Director of the Geopolymer Institute in St. Quentin, France, claimed that “the stones of the pyramids were actually made of a very early form of concrete created using a mixture of limestone, clay, lime, and water.”

Although this fascinating claim is still controversial, Michel Barsoum, a distinguished professor in the Department of Materials Science and Engineering at Pennsylvania’s Drexel University, confirmed this claim through electron microscopy.

Great Pyramid of Giza, Egypt. Credit: Wikipedia commons.

Ancient Roman mortar was formed from one part lime to three parts volcanic ash, according to First Century BC architect and engineer Vitruvius. This mortar was combined with rocks or chunks of brick, and “packed into place to form structures like walls or vaults.”

Precast concrete block came into modern use in the 1800’s, with the first commercially available blocks produced in 1868 by the Frear Stone Manufacturing Co. of Chicago. Builders appreciated the advantages of blocks over bricks, including larger unit size, superior load-bearing strength, weather insulation, and soundproofing qualities.

By the 1920’s, thousands of homes in the US Midwest were built from concrete block and advertised as fireproof and weatherproof. Today, entire commercial buildings, residential foundation walls and basements, and agricultural silos are still commonly built with concrete blocks.

Cement Contributes to Global Warming

Global warming is one of the major reasons why alternative blocks are appearing on the construction market. Cement manufacturing pumps around six billion tons of CO2 into the atmosphere every year. Sixty percent of emissions are due to transforming limestone, and the other 40 percent comes from using fossil fuels to heat the cement kilns to 2,732 degrees F (1500°C).

Recycled fly ash, considered a “green” alternative to cement, is used to replace 15-30 percent of the cement in concrete. Yes, it is a recycled by-product, but it comes from coal combustion, clearly on the top of pollution-producing, non-green practices. Finding a truly “green” alternative to cement is the new Holy Grail of building R&D efforts all over the world.

Exploring the Wide Variety of Building Blocks

Today, standard hollow concrete blocks are by far the most popularly employed, but there are many more types available. The most commonly used elements of sand, cement, gravel, and water, are often substituted in a wide variety of interesting ways.

Here is a sampling of block types used in the construction trades today, and their relative values as green building materials:

• Autoclaved Aerated Concrete (AAC) – also known as autoclaved cellular concrete (ACC), autoclaved lightweight concrete (ALC), autoclaved concrete, cellular concrete, porous concrete, Aircrete, Hebel Block, and Ytong. Precast, lightweight, foam AAC blocks are created with sand, calcined gypsum, lime, cement, water, and aluminum powder. This block offers low weight, strength, mold- and fire-resistance, as well as energy efficiency due to its high thermal insulation property. They are environmentally friendly because they are easy to cut precisely, reducing solid waste and related manufacturing CO2 emissions.

• Air-Purifying – also known as photocatalytic concrete block pavers, this product removes nitrogen oxide (NOx) emissions by means of a photocatalytic reaction of titanium dioxide. One example is concrete manufactured with TX Active Cement, a patented Portland cement that uses energy from UV rays to oxidize air pollutants, leaving only a residue that washes away in the rain.

• Bio-Composites – Block forms created from plant materials, such as Hemp, Mushroom, and rice straw. Bio-composites use a mix of plant material, lime, sand, and water. They are non-toxic, eco-friendly, and fully recyclable, offering earthquake-resistance, improved thermal mass, and insulation. Because plants absorb CO2, bio-composites essentially capture and lock in emissions, helping to alleviate global warming.

• Dense Aggregate Concrete – This block can be either solid or hollow and is made from sand, cement, and aggregate. They are high strength, for use in load bearing walls. “Enviroblock” is another type of dense aggregate block made from at least 73 percent seconds or recycled materials.

• Fly ash or “cinder block” – Fly ash, also known as “coal ash” or “pulverized fuel ash,” is electrostatically captured during coal combustion to produce electricity. Fly ash can replace up to 30 percent of Portland cement, and can increase concrete’s final strength and durability. However, coal combustion and cement production are equally egregious contributors to climate change, so fly ash is not a sustainable solution.

• Foam Concrete – also known as cellular lightweight concrete (CLC), this is air-cured, lightweight concrete block made from sand and cement or fly ash. No aggregate is used in the mix, as it is substituted with foam instead. Foam concrete block offers the same insulation results as normal concrete with only 20 percent of the weight and 10 percent of the raw materials.

• Gypsum Plaster – This lightweight block form is cast from gypsum plaster powder, water, and sometimes organic fibers. Though no longer manufactured in the US, they are very popular in Europe, Asia, Africa, and the Middle East. Used for non-load bearing walls, they offer fire- and soundproofing and are appreciated for low emissions of volatile organic compounds, extremely low radiation values, and a neutral pH value.

• Hollow – also known as a concrete block masonry unit (CMU). These are cast from Portland cement, sand, fine gravel, and water. The core is hollow, representing a reduction in over 25 percent of the block’s gross area, resulting in lighter weight and better insulation.

• Honeycomb clay block – Also known as “Ziegel”, this block is Popular in Europe. Made from fired clay, it has a “honeycomb” core, offering strength, insulation, and moisture protection.

• Insulated Concrete Forms (ICF) – These are interlocking modular units that stack like legos. Rebar is usually placed inside the forms and then they are filled with concrete. ICF blocks are typically manufactured from plastic or soy-based foams, wood chips, or wood fibers. Recycled styrofoam examples include BluBloc, Rastra, and ICE blocks. Recycled wood chips are used in Durisol and Faswall ICFs.

• Lightweight Aggregate Concrete – This block uses lightweight aggregate in the concrete mix. For example, concrete block made with “True Lite” aggregate are around 35 percent lighter than standard weight concrete blocks of equal thickness. “True Lite” is recycled aggregate used in iron production.

• Permeable Concrete – Also known as permeable interlocking concrete paving systems (PICP), this style of concrete block offers high porosity. They are made using large aggregates and with little to no fine aggregates. They reduce runoff by allowing water from rain or other sources to be directly absorbed.

• Solidia – Concrete block made with Solidia, a patented cement that is not cured with water. Made with Solidia cement, aggregate, sand, and water, Solidia concrete cures only by absorbing CO2 from the atmosphere. Solidia concrete blocks reduce up to 70 percent of the carbon footprint of conventional concrete block production and significantly reduces water use, as well.

–Don’t forget – watch for new posts every week in our new series, “The ABCs of Green Building Materials.” And if you’d like to give a shoutout for a project highlighting great green building materials, please add a comment below!