Hempcrete is a bio-composite material used as an alternative construction material. Unlike concrete, which lacks flexibility and plasticity, hempcrete is easier to work with since it’s versatile, but is it stronger than concrete?
Hempcrete is not stronger than concrete. It lacks the comprehensive strength associated with concrete as it’s lightweight and not dense. However, hempcrete is said to be a carbon sink, fire-resistant, pest-resistant, a strong insulator, stores, and releases moisture.
This guide will reveal whether hempcrete contains robust properties as a building material and whether it’s more durable than concrete. Read on.
How Strong Is Hempcrete?
Hempcrete features a combination of hemp hurds, lime, and water. It has been around since the 1990s and purported as a strong insulator, lightweight, biodegradable, flame, and pest resistant. It is also a moisture regulator and combines insulation and thermal mass.
According to hempcretewalls.com, hempcrete has a full potency of 0.5MPa to 3.5MPa or 72.5 psi to 507.6 psi. Thus, hempcrete has a density of 16.9 percent when compared to concrete. In effect, hempcrete provides a “permanent shuttering” to reinforced concrete elements.
Hempcrete includes little dense material and contains a lot of small voids and fewer contact points between all the individual particles. To put it into perspective, the bulk density of hempcrete is 9.5lb/ft3, whereas concrete has a bulk density of 137lb/ft3, which gives it considerable comprehensive strength that results from the mass.
Hempcrete is a low-density material, and unlike concrete, it can resist cracking under movement, making it suitable for earth-quake prone areas.
The Making and Composition of Hempcrete
When making hempcrete, the fiber materials reduce surface cracking and provide tensile strength. However, it does not increase the comprehensive strength like concrete. Further, when paired with steel and nylon, it rises in tensile strength.
Besides, some binder like hydrated lime is needed when processing hempcrete. Portland cement utilized as a binder to increase strength can interfere with a hempcrete wall’s thermal and moisture performance. Therefore, it is critical to use Portland cement strategically and deliberately.
Hempcrete made from lime, as opposed to Portland cement, takes a long time to reach its final strength. Limecrete and lime mortars feature a lower ultimate comprehensive intensity as compared to concrete.
However, lime gains strength from exposure to air as opposed to when it’s mixed with water. Therefore, hempcrete differs from concrete due to the presence of copious voids. It also traps air and slows the transfer of heat from the interior to the exterior of a structure.
Hempcrete walls used together with a load-bearing frame or another material that supports the vertical load in building construction are stronger. Besides, since it lacks the requisite strength of concrete, it cannot make a structure foundation.
However, a sixth-century hemp-reinforced bridge in France is known to have stone-like strength. Hempcrete lacks the brittleness of concrete and, therefore, does not need expansion joints. But it’s half as light and three times elastic than concrete, which makes it resistant to stress-induced cracking and breaking.
Additionally, hempcrete is lightweight, making it an excellent choice for most climates as it combines insulation and thermal mass. Besides, hempcrete structures make healthy buildings as they don’t grow toxic mold.Hempcrete can be used in new construction or retrofitted into an existing framing. It can also be pumped onto masonry walls or as pre-cast panels.
It is advisable that you mix hempcrete in a large (180 gallon) forced action pan mixer. It can also be mixed in a conventional drum cement mixer, although it’s more difficult to ensure that it’s done evenly. In a new project, the quantities needed for anything other than the smallest extension exclude this as an applicable method.
How Strong Is Concrete?
Concrete is a mixture of sand, stone pebbles, water, and Portland cement. It’s an inexpensive material widely used in construction all over the world. It has relatively high comprehensive strength compared to hempcrete; however, it’s much lower in tensile strength.The aggregate that makes concrete is bound in with a lime-based cement or hydraulic cement that includes calcium aluminate cement and water. It’s incredibly reliable with robust properties to resist compression, wind, rain, and fire. It’s also durable and gives long service life.
The aggregate in concrete efficiently carries the compression load, but it has weak plasticity as the cement holding the mixture in place can crack, allowing the structure to fail. However, concrete reinforced with steel fibers, glass fibers, steel reinforcing bars, or other materials that carry tensile loads increase the strength.
Strength of Concrete
Concrete’s function in construction measures the strength of concrete. Low strength concrete features 14MPa (2000psi) while concrete for routine use includes 20MPa (2900psi). High-strength concrete in large civil projects measure 40MPa (5800psi) in strength. Conversely, concrete with 130Mpa (18900psi) applies to commercial structures that are very rigid.
Just like hempcrete, concrete also increases energy efficiency thanks to its ability to retain heat. Besides, it’s an effective sound-proofer. It’s easy to mold concrete into any shape giving it an upper hand over hempcrete as it can be pumped into cracks and on damaged structures that need renovation.
Foundation slabs, bridges, sidewalks, dams, septic tanks, among other building constructions, are predominantly made of concrete. Due to its comprehensive strength, it acts as a bridge between the interior and exterior of a building.
The workability of concrete depends on the amount of water, shape, and size of the aggregate. Additionally, the cementitious content can define the workability of concrete. When more water and chemical admixtures combine in the amalgam, it increases concrete’s workability.
What You Need to Know When Using Concrete
When using concrete, it is important that:
- After pouring concrete on a surface, handle it well to achieve ultimate strength.
- Curing concrete is a necessary method that allows the concrete to reach optimal strength and durability. This process enables hydration to occur and allows calcium-silicate hydrate to form. Over four weeks, the concrete mix attains more than 90 percent of its strength.
- During the first three days, hydration and hardening of concrete are crucial. Fast drying and shrinkage can occur when water evaporates, leading to increased tensile stresses when it has not gained sufficient strength.
- Controlling temperature and humidity is essential in maintaining the process of curing. To ensure full hydration for ultimate strength, a water-retaining film over the concrete is necessary.
- Traditional curing involves ponding the surface of the concrete with water and wrapping with plastic to prevent dehydration.
- Additionally, high-strength applications involve heating the poured concrete with steam to keep it damp and raise the temperature to quicken the hydration process thoroughly.
- Conversely, since proper curing of concrete leads to increased strength, it also lowers permeability and reduces cracking where the surface dries out prematurely.
- Care must be taken into account to avoid freezing and overheating due to the exothermic setting of cement. More than 1984lbs of CO2 emitted in the atmosphere during the fabrication of every 2,000lbs of cement.
Depending on who you ask, whether a contractor or inspector, hempcrete doesn’t offer the same performance as concrete. However, when combined with some types of fiber, it increases in plasticity. Even if hempcrete doesn’t have the same performance as concrete, it is very durable and can naturally regulate a building’s humidity and temperature.
Additionally, whereas concrete gains strength over time, it offers durability to hold large amounts of water like dams for a long time with minimal degradation. On the other hand, hempcrete can biodegrade when in contact with water for extended periods. Also, it cannot guarantee the safety of a rigid building structure.
- Quora: Is hempcrete stronger than concrete.
- Hempcrete Walls: Building Journal – Changing the way we build and live by using the healthiest, most sustainable, and longest-lasting insulated wall material available today – for residential and commercial construction projects.
- Designing Buildings: Hempcrete
- Wikipedia: Concrete
- Natural Life Magazine: Hemp for Houses
- Materials Palette: HEMPCRETE
- Ukhemprete: Building with hempcrete (hemp-lime): Essential tips for the beginner (Part 2)