Tag Archives: Concrete

3D printer to print a house, is it the future of cementitious materials?

Construction industry, the only industry still does things manually.

Even in the 21st century, to build a house right now is still a slow, labour-intensive, dangerous process, and almost always over-budget. Unlike the motoring or technology industries which use automated production methods to complete routine construction tasks, housing construction is one of the only industry that still does things manually till now, as said by Professor Khoshnevis from USC.

It is time to change. With the achievement of the research in 3D printing filed, Professor Khoshnevis scaled up 3D printing to make this technology being able to construct buildings by using a process called Contour Crafting. He hope to use this method to improve the basic concept of house construction so that it was accessible to everyone, because with better shelter comes a more civilized society.

3D printer to build a house, is it the future of cementitous materials?

How does 3D printer work to print a house?

Here is how 3D printing works to “print” a house:

A CAD design is sent to a large-scale 3D printer that is mounted to a block of land. The printer lays out the concrete-like foundation of the home through a nozzle that can move anywhere on the property. Like any 3D print-out, the house is made layer-by-layer and reinforced with various materials — like electrical, plumbing and communication infrastructure — as the build progresses.

The process is super fast. In a TED presentation, Prof. Khoshnevis said that “we anticipate that an average house, like 2500 square foot house, can be built in about 20 hours from a custom design”.

As for the material used as the “printer ink”, concrete is the solution. The concrete used in the 3D house printer is a mixture of concrete and fibre polymers, meaning that it is more than three times stronger than traditional concrete used in today’s houses. The traditional concrete can withstand roughly 3000 pounds per square inch of pressure, while the new printed concrete can withstand around 10,000 pounds per square inch.

Is it the future of cementitious materials in construction industry?

Professor Khoshnevis says the method could be used to construct emergency or low-income housing. What is more, the concept is currently being supported by NASA so that the space agency can one day be used to build a colony on the Moon, and perhaps on the Mars, who knows.

As a cement researcher, I think the method is really revolutional in the construction industry, even just consider it from the theoretical concept. If the method is quite popular in the future, does it mean cementitious materials are the future of construction materials compared with steel? since the mixture “concrete” is the main material in the 3D printing machine used as “printing ink”.

How GGBS is used and its typical substitution rates

How is GGBS used?

GGBS (Ground Granulated Blastfurnace Slag) is used all over the world as a direct replacement for Portland cement. It is added to the concrete mixer along with ordinary cement, aggregates and water.

The normal ratios and proportions of aggregates and water to cementitious material in the mix remain unchanged. Mixing times are the same as for ordinary cement. Both wet mixing and dry mixing processes can be used for making concrete with GGBS.

What is the substitution rates of GGBS in concrete?

Usually, replacement rates for GGBS vary from 30% to up to 85%, depending on the application and technical requirements. Typically 50% is used in most instances. Higher replacement rates up to 85% are used in specialist applications such as in aggressive environments and to reduce heat of hydration.

According to the EU code “EN-197-1-2000 Cement. Composition, specifications and conformity criteria for common cements“, slag in Blastfurnace cement CEM III/C can be used at a substitution rate as high as 95%.

Below are some typical Substitution Rates

Ready-mix Concrete:
50% GGBS is used for most mixes.

Precast Concrete:
30% to 50% GGBS primarily depending on concrete curing conditions.

Special Concrete:
Mass concrete typically has at least 70% GGBS for temperature control. Concrete in aggressive environments usually contains from 50% to 70% GGBS for enhanced durability performance.

Concrete made with slag improves resistance to fire damage

Better performance of slag concrete exposing to high temperatures

Concrete made with GGBS cement is much better than concrete made with 100% OPC at maintaining its compressive strength when exposed to high temperatures.

OPC specimens heated to 400 °C or above have been shown to exhibit severe cracking to the point of disintegration after a few days. However, it was found that concrete made with blends of 35%, 50% and 65% GGBS performed much better. In the GGBS specimens there was no visible cracking after exposure to the higher temperatures. The concrete with 100% OPC degraded to powder over the following year, while the concrete made with GGBS maintained its strength over the same period.

Further studies showed that after exposure to 900 °C concrete with 0% GGBS maintained 6% of its original strength, concrete with 30% GGBS maintained 54% of its original strength and concrete with 70% GGBS maintained 70% of its original strength.

fire-slag-concrete
Date source: Ecocem.

How does slag improve the resistance to fire damage?

Why concrete made with GGBS has better resistance to fire damage? It is generally agreed that above 400 °C Ca(OH)2 which is the hydration products of OPC decomposes into CaO and H2O, then on cooling CaO and left H2O rehydrates into Ca(OH)2 which needs more space than CaO causing the concrete to crack and degrade. With the addition of GGBS into concrete, hydration product Ca(OH)2 is generally reduced compared with concrete made with 100% OPC, thus improving the performance of resisting fire damage.

House-Fire-concrete

Reference: Ecocem report–Technical Performance