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Lightweight Synthetic Concrete Additive

A vendor just added Lightweight Synthetic Concrete Additive to the Inventables marketplace. I'd never heard of that type of additive before so I decided to do some additional research to learn a bit about it. As a mechanical engineer focused on consumer product development I have very little experience with concrete and no experience with concrete additives so I decided to take a few minutes and quench my curiosity.

Here's a picture of the additive uploaded by the vendor:



A quick look at the Material Safety Data Sheet for the Lightweight Synthetic Concrete Additive indicates it is made of expanded or foamed polystyrene. The MSDS goes on to explain the product is solid, white foamed bead with a slightly fruity, aromatic odor. It's an interesting concept to mix a foam with concrete.

The vendor of the additive recently worked with Camp Logan Cement Works in Houston Texas to create light weight air conditioner pads. The combination of being light weight and crack resistant I'm guessing keeps transportation costs down but at the same time the product is strong enough to support an air conditioner. The manufacturer of the pads also claims they were able to move from a two-mix process down to a one-step process. I assume that saves them some time in production.

It sounds like pretty cool stuff. I wonder how much lighter the concrete pads are with this additive compared to a pad that is the same dimensions but made with traditional concrete.

Choosing the right thermoplastic Part 4 - Ultimate Performing Long Fiber

Welcome to part 4 in our series on plastic compounding. Our friends over at RTP Company have written a white paper to answer the question "“How do I choose the correct thermoplastic composite to meet the application?”". They have broken it down as follows:

1) Resin Morphology
2) Cost Comparison
3) Temperature Resistance
4) Property Enhancement Using Aspect Ratio
5) Ultimate Performing Long Fiber

Today's blog post is on Ultimate Performing Long Fiber.

The preceding physical property data indicates that the aspect ratio of the additive has a direct correlation to the strength, modulus, and heat distortion properties, and possibly the impact resistance of the composite. To maximize the performance of the composite, one should maximize the aspect ratio of the reinforcement fiber. To do this, you could minimize the fiber diameter and/or maximize the fiber length, which is the logic behind the long fiber composites. Long fiber composites are manufactured by a pultrusion process where a fiber roving is pulled through a die in which the base resin is forced to impregnate the individual fibers in the roving. The impregnated fiber rovings are pulled out of the die and into a pelletizer that cuts the strands into pellets. The fiber length in the pellets will be the same as the pellet length, which for most materials is 1/2 inch. If a 17 micron diameter fiber is used, this would result in a fiber aspect ratio of about 750 for a long fiber composite, which is about 10 times larger than that of chopped fiber compounds typically produced via the extrusion compounding process.

Prior to long fiber compounds, if one was looking to improve the impact resistance of a chopped fiber composite, the typical approach would be to add a rubber based impact modifier. This would improve the toughness of the material but would reduce the strength, modulus, and heat distortion of the composite. The effect of having an
extremely high aspect ratio fiber in long fiber composites has been the improvement of all the physical properties, which is depicted in this spider chart for 40% glass fiber nylon materials.

By having the ultimate in strength, modulus, impact, and heat distortion, long fiber composites have become the choice for demanding applications, such as replacing metal in load bearing applications. The high aspect ratio in the long fiber composites also allows these materials to have excellent creep resistance.


Well that concludes this series. Thanks to Kirk Fratzke and author Steve Maki of RTP for contributing this information.

Choosing the right thermoplastic Part 3 - Property Enhancement Using Aspect Ratio

Welcome to part 3 in our series on plastic compounding. Our friends over at RTP Company have written a white paper to answer the question "“How do I choose the correct thermoplastic composite to meet the application?”". They have broken it down to five sections.

1) Resin Morphology
2) Cost Comparison
3) Temperature Resistance
4) Property Enhancement Using Aspect Ratio
5) Ultimate Performing Long Fiber

Today's blog post is on Property Enhancement Using Aspect Ratio.

Choosing the resin is only half the story in building a composite. The next decision is "“What will I add to the resin to impart performance to the composite?"” To answer this question, one will need to understand another physical term: aspect ratio.

The aspect ratio can be defined as the length divided by the diameter of the additive. For a spherical bead, the length equals the diameter and thus the aspect ratio is 1. For a fiber, such as that shown in the diagram, it is also easy to calculate the aspect ratio because the length and diameter are usually well defined. For some additives with
an irregular shape, such as minerals, the aspect ratio is a little harder to calculate; but you can always measure a major length and a minor thickness on the particle, and thus, can calculate an aspect ratio.

It is this aspect ratio that will predict the type of physical property enhancement the additive will impart when it is compounded into the base resin.
Additives with aspect ratios of less than 10 have minimal ability to improve the tensile and flexural strength of the base thermoplastic resin to which
they are added. These additives are generally referred to as fillers and include species such as talc, calcium carbonate, and glass beads. Although these fillers do not improve strength, they do have the ability to moderately improve modulus (stiffness) and heat distortion temperature. They also can be added to reduce part warpage, improve dimensional stability, and reduce the overall cost
of the composite (especially with higher cost base resins). Because it will act as a contaminant and a stress crack initiator, fillers will always lower the impact resistance (toughness) of the plastic to which it is added.

Additives that have an aspect ratio above 50 have the ability to significantly improve the tensile and flexural strength of the base resin to which they
are added. These additives are generally referred to as reinforcements and include species such as glass fiber, carbon fiber, aramid fiber and basalt
fiber. Along with strength enhancements, reinforcements can significantly increase modulus(stiffness) and heat distortion of the composite.

Because they have a tendency to align themselves with the flow direction during molding,reinforcements contribute to anisotropic shrinkage (different in flow direction versus transverse direction), which could lead to part warpage.
Fillers such as glass beads or talc are sometimes added along with glass fiber to make the shrinkage more isotropic and reduce warp. Regarding impact resistance (toughness), reinforcements tend to make brittle resins tough and tough resins brittle.

Examples of this include a brittle polyphenylene sulfide resin becoming tougher when reinforced with glass fiber and a tough polycarbonate becoming more brittle when reinforced with glass fiber.

Additives with aspect ratios between 10 and 50 will have a moderate effect on improving the tensile and flexural strength properties of the base resin to which they are added. These additives are referred to as transition materials and include such species as wollastonite, mica, and milled glass fiber. These additives improve modulus and heat distortion slightly better than the fillers.

Transition materials are typically used in situations where dimensional stability is of prime importance and strength, modulus and heat distortion lower than that offered by glass fiber is acceptable.

About Inventables

Yesterday we launched a new page on our website called About Inventables. We designed the page to include a video that explains how Inventables marketplace works and also some frequently asked questions that customers keep asking us. Our intention is that this page will evolve as our business evolves. If you have additional questions about Inventables let us know by emailing help at inventables dot com. We read all your mail and when we see some repeat questions we'll be updating the page with the answers.

Developmentables - Inventables Technical Blog

Open source software has been critical in the development of the Inventables Marketplace. We have benefited from the work of others in the open source community by using tools that include Ruby, Rails, rSpec, Cucumber, and of course Linux and Apache.

We think it is important that our technical team has time to contribute back into the community by open sourcing software we write and sharing our knowledge about how we solved technical challenges that others may run into.

In the spirit of sharing, we launched Developmentables a blog by the development team at Inventables. On the blog we'll be sharing mostly topics relating to software engineering, web development, and user interface design.