Engineers in Australia have developed a new building material with about one quarter of concrete’s carbon footprint, while reducing waste going to landfill. The research is published in the journal Structures.

This innovative material, called cardboard-confined rammed earth, is composed entirely of cardboard, water and soil—making it reusable and recyclable.

In Australia alone, more than 2.2 million tons of cardboard and paper are sent to landfill each year. Meanwhile, cement and concrete production account for about 8% of annual global emissions.

Cardboard has previously been used in temporary structures and disaster shelters, such as Shigeru Ban’s iconic Cardboard Cathedral in Christchurch, New Zealand.

Inspired by such designs, the RMIT University team has, for the first time, combined the durability of rammed earth with the versatility of cardboard.

Lead author Dr. Jiaming Ma from RMIT said the development of cardboard-confined rammed earth marked a significant advancement toward a more sustainable construction industry.

“Modern rammed earth construction compacts soil with added cement for strength. Cement use is excessive given the natural thickness of rammed earth walls,” he said.

But cardboard-confined rammed earth, developed at RMIT University, eliminates the need for cement and boasts one quarter of the carbon footprint at under one third of the cost, compared to concrete.

“By simply using cardboard, soil and water, we can make walls robust enough to support low-rise buildings,” Ma said.

“This innovation could revolutionize building design and construction, using locally sourced materials that are easier to recycle.

“It also reflects the global revival of earth-based construction fueled by net zero goals and interest in local sustainable materials.”

Practical benefits

The cardboard-confined rammed earth can be made on the construction site by compacting the soil and water mixture inside the cardboard formwork, either manually or with machines.

Study corresponding author and leading expert in the field of structural optimization, Emeritus Professor Yi Min “Mike’ Xie, said this advancement can spearhead a leaner, greener approach to construction.

“Instead of hauling in tons of bricks, steel and concrete, builders would only need to bring lightweight cardboard, as nearly all material can be obtained on site,” Xie said.

“This would significantly cut transport costs, simplify logistics and reduce upfront material demands.”

Ma said cardboard-confined rammed earth could be an effective solution for construction in remote areas, such as regional Australia, where red soils—ideal for rammed earth construction—are plentiful.

“Rammed earth buildings are ideal in hot climates because their high thermal mass naturally regulates indoor temperatures and humidity, reducing the need for mechanical cooling and cutting carbon emissions,” he said.

The mechanical strength of the novel material varies based on the thickness of the cardboard tubes.

Ma said the team has developed the formula for this strength design.

“We’ve created a way to figure out how the thickness of the cardboard affects the strength of the rammed earth, allowing us to measure strength based on cardboard thickness,” Ma said.

In a separate study led by Ma and published in Composite Structures, carbon fiber was combined with rammed earth, proving it had a comparable strength to high-performance concrete.

Ma and the team are ready to partner with various industries to further develop this new material so it can be used widely.

After testing dozens of automatic litter boxes, I can say it’s been difficult to determine which is the best cat litter (or rather, if there is one). Most people will want to look for a low-tracking, clumping cat litter that’s compatible with their litter box. But there are other factors to consider, like allergens, material, the litter box itself, and how you’ll deal with the waste.

In recent years, there have been leaps and bounds in the pet tech sphere as a whole—including where our cats go potty and what litter they go potty in. In the past, the choices were an absorbent clay whose main compound was calcium bentonite, sawdust, or sand. Now, we have high-tech crystal litter, which aims to show health issues through changing color; eco-friendly tofu litter; and all types of clumping clay litter between. After a year of testing litter boxes and scooping tons of cat litter, let me sift through (get it?) the options so you can determine the best type of cat litter for you and your furry friend.

Should You Change Up Your Litter?

There are many reasons why you may want to change your litter. Your cat may be like mine, with sensitivities to strong odors or smells that can cause allergies or allergy-like symptoms like red eyes or itching. Or maybe your cat is long-haired, like mine, and you’re tired of litter sticking to their fur.

If you want to be more eco- (and budget-) friendly, a biodegradable tofu or wood pellet litter may be better, but for these, you’ll need to introduce the change slowly and oftentimes, you’ll have to change the box you’re using. (More on that below.)

As a helicopter pet parent who brushes their cats’ teeth and shaves their butts, I honestly just want to make sure I have a litter that keeps my cat (and me) comfortable, giving them a safe space to potty and an easier time to clean it for me.

I look for, and recommend folks do trial-and-error to find, a litter that has all of these elements:

• Clumping: Many brands claim to clump effectively, but you’ll need to monitor while scooping to see if they actually are, or if they’re leaving smaller bits that sneak through grates while cleaning.
• Scent-free or low scent: Cats can smell 14 times better than humans, and strong odors can irritate their respiratory system and lead to itching, watery eyes, and other symptoms, including not wanting to use the litter box at all because the scent is too overwhelming.
• Low–tracking: Same as clumping litters above, many litters claim to be low tracking, but I’ve found that the best way to lessen litter tracking around the house is to have a great clumping litter and add as much space between the box and the floor. This means that in addition to clumping litter, add accessories like stairs (if your cat is mobile enough), a ramp, or a litter-trapping mat to increase the distance between the box and your floor, to reduce litter tracking. Litters that aim to be low-tracking are generally better at dust control, which also help with general cleanliness and lower irritants.

I’ve tested several types of cat litter from Boxiecat, and although pricey, they have all managed odor well, had low dust/tracking, and scooped easily in clumps (and worked well with my automatic litter box).

Compare the Most Popular Types of Litter

As said before, there used to be super-limited litter options, now there’s tofu, wood, silica crystals, recycled paper, and even nut shells. While something like wood pellets is more-eco friendly and cheaper, you’ll have to factor in your litter box and whether your cat takes to the new litter. (Although slow introduction is key.)

• Clay cat litter: This is by far the most popular litter type, and most closely resembles what cats would be using in the wild. Clumping clay cat litter is what I recommend for most people, as it primarily uses a naturally absorbent bentonite clay. It expands when wet/soiled, making it “clump,” which is easier to scoop and generally more hygienic. However, it’s not as environmentally friendly because it’s not biodegradable and can contain carcinogenic silica dust.
• Tofu cat litter: This relatively new litter is great because it’s environmentally friendly. It’s made out of soybean fiber, making it naturally biodegradable, nontoxic, and way less dusty than traditional choices. If bought in pellet form (the most popular option), they clump well and can even be flushed in the toilet, although it can be pricey and can grow mold if in humid conditions.
• Crystal cat litter: This type of litter is made from silica mined from quartz sand and mixed with oxygen and water to make super absorbent pellets (akin to the absorbing powers of little silica gel packets found in many newly bought items). It’s lightweight and has great odor control. Crystal litter is pricey, not biodegradable or clumping (requires daily sifting), easily tracks, can be an uncomfortable texture for paws, and is difficult for some cats to get used to using. Popular brands like PrettyLitter actually use a special silica formula that aims to track health changes through changing colors based on urinary PH. Although I’m slightly cautious to use it because of reviews of the silica litter being ingested and harming cats and causing respiratory issues because of the particle dust.
• Paper or Wood pellets: Paper and wood pellets are cheap, have low dust and tracking, and are eco-friendly because they’re biodegradable. (Paper pellets are also great for injured or post-operation pets because the litter is low-dust and there’s less chance for litter to get stuck in wounds.) However, this doesn’t control odor well, is non-clumping, and needs to be changed frequently (you’ll probably need a sifting litter box). Wood pellets are also often made of pine and can have an overwhelming scent.
• Walnut shell cat litter: Made from crushed walnut shells, this is often used as a much lighter, more natural alternative to clay litter. It’s lightweight and has a similar texture to clay, and is biodegradable. Although it can track, spoil if in moist conditions, and requires frequent emptying/cleaning.
• We don’t recommend corn cat litter, as corn is prone to a toxic mold called aflatoxin. This can cause health issues for cats and in humans who have asthma or COPD and are immunocompromised or elderly.

Probabilistic Ising machines (PIMs) are advanced and specialized computing systems that could tackle computationally hard problems, such as optimization or integer factorization tasks, more efficiently than classical systems. To solve problems, PIMs rely on interacting probabilistic bits (p-bits), networks of interacting units of digital information with values that randomly fluctuate between 0 and 1, but that can be biased to converge to yield desired solutions.

A class of PIMs that are intensively investigated use magnetic devices to inject randomness into a digital transistor-based circuit. While these systems have been found to be promising for the rapid resolution of various domain-specific and advanced problems, their large-scale design and reliable fabrication have so far proved challenging. This is primarily because their upscaling requires the precise control of small magnetic moments and often also entails the use of large circuits that convert digital signals into analog voltages and other additional components.

Researchers at Northwestern University and other institutes recently developed a new application-specific integrated circuit (ASIC) that could be used to create better performing probabilistic computers. In a paper published in Nature Electronics, they presented a probabilistic computer based on the new circuit and showed that it could perform integer factorization tasks.

“We were interested in exploring how one could build a scalable probabilistic computer by custom-designing an ASIC using foundry CMOS technology,” Pedram Khalili Amiri, senior author of the paper, told Tech Xplore.

“Our intuition was that by taking advantage of the digital CMOS platform and the high transistor densities available in today’s semiconductor technology, one could eventually build very large-scale probabilistic computers that can tackle problems related to, for example, combinatorial optimization. As a first step, we decided to try out these ideas, and develop the computing architecture and design approach, using a less advanced (130 nm) foundry node.”

When reviewing previous literature in the field and experimenting with probabilistic computing architectures, Amiri and his colleagues realized that, despite its numerous advantages, CMOS technology does not appear to be well-suited for creating random bit sequences. Notably, the creation of these random sequences is central to the functioning of probabilistic computers.

To overcome this limitation of CMOS technology, the researchers adapted voltage-controlled magnetic tunnel junctions (V-MTJs), hardware components that they introduced in their earlier work and had previously applied to the creation of magnetic random-access memory (MRAM) devices. They changed some elements of these devices so that they would serve as high-throughput and compact sources of randomness (i.e., entropy).

“Our probabilistic computer consists of an array of bistable probabilistic elements (called probabilistic bits or p-bits),” explained Amiri. “The interactions between these p-bits can be programmed so that the p-bit network (called a probabilistic Ising machine or PIM) collectively searches through the solution space of a problem. Our p-bits are implemented using digital CMOS circuitry on our ASIC and use bit sequences read from an adjacent V-MTJ chip to provide the required randomness. The energy minimum of the PIM is designed to correspond to the solution of the computing problem of interest.”

The new probabilistic architecture developed by Amiri and his colleagues could theoretically be used to efficiently tackle many real-world problems, including various optimization tasks. As part of their study, however, the team specifically applied their architecture to integer factorization tasks, which are known to be very challenging to solve computationally.

“This was a good place to start, mainly because there is only one correct solution to be found in the entire energy landscape, and because it is easy to check whether we found the right factors or not,” said Amiri. “The same approach, however, can be applied to many other computing problems.”

Two central advantages of the architecture developed by this research team are that it is digital and synchronous. This is in contrast with most other PIMs introduced in earlier works.

“This means that the probabilistic computer works with a clock that determines a well-defined time interval upon which p-bits can update and does not require area-consuming circuits such as digital-to-analog converters,” said Amiri. “In addition, the use of V-MTJs, which are currently implemented in a separate chip from the ASIC but can eventually be integrated within it, saves area and can provide high-throughput random bit sequences to the p-bits.”

V-MTJs, the components that Amiri and his colleagues used to create their architecture, were found to be inherently more robust against device-to-device variations when used to generate random bits compared to other spintronic random bit generators used in the past. The team’s initial findings were highly promising, highlighting the promise of their approach for creating probabilistic computers.

Notably, although it relies on VMTJs, the new approach is also compatible with established CMOS manufacturing processes and digital design strategies. In the future, it could contribute to the large-scale fabrication of PIMs that could solve a wide range of real-world optimization problems faster and more efficiently.

“Our next step will be to adapt this design to implement problems other than factorization,” added Amiri. “For example, we have a chip in the works that is tailored to other optimization problems with real-world significance. In addition, we plan to integrate the V-MTJs directly on the CMOS in a more advanced foundry node, which would allow us to make the probabilistic computer even more compact.”

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