Defining UHPC - Ultra High Performance Concrete - From Chat GPT

I first started working with Ultra High Performance Concrete in 2015 after being approached by some guys from a French Cement Company at the World of Concrete. They were looking for a portable Mixer that could easily be transported to and from bridge sights. With these mixers they wanted to make a new and unique type of concrete, exceptionally strong, for bonding joints and resurfacing the road. This material was UHPC or Ultra High Performance Concrete. 

I had heard about UHPC a few times earlier in my career, and I had once, in Quebec been shown a test piece that was being considered for a culvert repair. The piece its self was small 30cm x 30cm and only 1cm thick, but so strong it could be dropped on a concrete shop floor without taking damage. It was impressive, but I didn't hear much about it for several years

We did a lot of testing at Mixer Systems to determine the correct type of mixer for the job and how it should be configured for safe and easy use and transport. Since those days we've done a lot of variations on those early portable mixers and plants. 

I also have a very good friend, Craig Heaney of Envel Facade, whose company builds wall claddings with UHPC and they are truly works of art. Envel is currently finishing up a special cladding project in Chicago, creating giant concrete excerpts from the speeches of former U.S. President Barack Obama for the exterior of the new Obama Presidential Library.

A recent image posted by Envel  

Below is a quick article I created for The Illinois Precast Association Newsletter:                        Written for you by ChatGPT answering: Tell me about Ultra High Performance Concrete

UHPC

By: ChatGPT 

Ultra High Performance Concrete (UHPC) is a class of advanced concrete that is distinguished by its exceptional strength, durability, and durability compared to conventional concrete. It is often used in applications where superior performance is required, such as in the construction of bridges, high-rise buildings, and other infrastructure projects.

Here are some key characteristics and benefits of UHPC:

1. Composition:

UHPC is made from a mixture of:

· Cement: Often uses a special type of cement such as Portland cement or blends with pozzolanic materials.

· Silica fume: Used as a supplementary cementitious material to improve strength and durability.

· Fine aggregates: Such as silica sand or other fine-grained materials.

· Superplasticizers: These help achieve a highly workable mix without increasing the water content.

· Steel or synthetic fibers: These are commonly incorporated to enhance the mechanical properties of the concrete, improve crack resistance, and reduce brittleness.

 2. Strength:

UHPC can achieve compressive strengths in the range of 150 MPa (megapascals) to over 200 MPa, significantly higher than conventional concrete, which typically has strengths around 25-40 MPa. This makes UHPC suitable for structural applications where high load-bearing capacity is needed.

3. Durability:

UHPC exhibits excellent resistance to environmental factors such as freeze-thaw cycles, chemical attacks (from chlorides or sulfates), abrasion, and corrosion. This is particularly beneficial in harsh environments like coastal areas or regions exposed to deicing salts.

4. Workability:

Despite its high strength, UHPC has excellent workability due to the use of superplasticizers, which enable the concrete to flow and be molded into complex shapes without sacrificing its integrity.

5. Longevity:

Due to its superior resistance to cracks and environmental deterioration, UHPC can extend the lifespan of infrastructure significantly. It is often used in applications where long-term durability is essential, such as bridges and offshore structures.

6. Applications:

· Bridges: UHPC is ideal for bridge decks, bridge components, and other structural parts due to its high strength and durability.

· Architectural Features: Its ability to be molded into thin, complex shapes makes it popular in architectural designs.

· High-rise Buildings: UHPC is used in the construction of high-rise buildings, where the high compressive strength is advantageous.

· Infrastructure: It’s used in infrastructure projects like tunnels, pavements, and barriers, particularly where enhanced durability is needed.

 7. Cost:

While UHPC is more expensive than regular concrete due to the special materials and processes involved, its long-term durability and lower maintenance costs can make it more cost-effective in the long run for certain high-performance applications.

8. Sustainability:

UHPC can contribute to sustainability goals due to its longevity and resistance to degradation, which can reduce the need for repairs and replacements. Additionally, some mixes of UHPC incorporate recycled materials or industrial byproducts, enhancing its environmental credentials.

9. Challenges:

· Mixing and Handling: The process for mixing UHPC is more demanding than for regular concrete, requiring precision in terms of ingredients and mixing procedures.

· Curing: Proper curing is essential to achieve its full strength, often requiring heat treatment or extended curing times.

· Specialized Equipment: Construction using UHPC might require specialized molds, mixing equipment, and placement techniques, which can make it less accessible for small-scale or less-experienced contractors.

In conclusion, Ultra High Performance Concrete represents a significant advancement in concrete technology, offering unmatched strength, durability, and versatility, especially in challenging environments. However, the complexity and cost of producing and working with UHPC should be carefully considered when planning its use.

 

Beautiful Hardscape From KVM Machines

This is a 3 Color Blend Slab with Face Mix. I snapped this photo while walking through the yard. The KVM machine that they were running was doing a single color face mix paver at an 11.57 second cycle time. That is the fastest I have personally seen a machine run facemix.

This is a Concrete Paver display from one of our KVM Customers in the United States. We again see a 3 color blend, but this time without a facemix. 

From the same U.S. Producer, We see a similar display but with aged pavers, I think they were run through a tumbler, but should really double check.

4" x 4" Pavers after being aged in a Tumbler.

Producing Pavers with Face-Mix

Face mix product fresh out of a KVM

Paver production in North America is changing drastically right now. Not only are there several new shapes and sizes and even colors, but there are also new ways being utilized to produce pavers that provide a much nicer looking installed paver at a lower cost to the producer of the product. I am, of course talking about utilizing a face-mix on a concrete pavers

Producing face-mix pavers is not all that new. In Europe it has been standard for decades. On the east coast of the U.S. It has been done for many years. However, in many North American markets this product is just emerging. This is a big change as there are many producers of pavers that make product on block machines. Block machines produce very attractive pavers, but it is not specifically what they are designed for. They quality of a block is determined by the dimensions, the quality of a paver is measured by its density. This difference becomes more significant when trying to produce more specialized pavers on a block machine. Face mix pavers fall deeply into this category.

To make a face mix paver you need a system that can lay down at least two layers of concrete in the pavervibration and compaction cycle. First you will place the base of the paver. Then you deliver and compact the face. The two layers must be properly prepare during the mixing and batching process to assure proper adhering between the face and the base.

So what is the difference between the face and the base? The base of the paver an be made of larger aggregate and less cement (as there is less surface area to cover). The base also needs little or no color, as it will never be seen once properly installed. The face of the paver is on the other hand made of fine materials, a greater amount of cement, nod more color. Colors are often even blended to create unique attractive surfaces, but that's another story.

Mixer Systems Plant for 3 color blend face-mix

There is significant material savings to be realized with face mix pavers, and the end product is more attractive and of higher quality. For producers that are currently producing concrete block and are looking for an avenue into this growing market it can be worth investigating a small board paver plant. Small board systems are ideal for meeting the paver needs of small to medium sized markets and can produce the face mix product the market is looking for.

KVM Machine with 2 Hoppers for Face-Mix

Face-mix paver are ideally made on a machine that is designed for the production of pavers, not block, as the process requires two separate feed drawers. The first must be able to precisely deliver the proper amount of base concrete into the form, while still leaving space for the finer face mix to be delivered by the second feed drawer.

There is often a two stage vibration to this process. The first vibration is delivered to get an initial compaction of the base concrete. The second vibration come following the delivery of the face-mix concrete blend. The second vibration is usually longer, stronger, and under pressure to insure that the pavers will meet the rigorous requirements of strength, and to assure that the face and base concrete are well bonded to each other.

The adherence between face and base mix is critical and can be very challenging. when the two layers separate, it is known as delamination. To be sure that this does not happen you need three important things. A good production machine, a good way to accurately batch and mix your concrete, and a good knowledge of what you are doing. Experience and practice make a huge difference.

Color Blending for Concrete Block and Pavers

The demand for concrete block and pavers with blended colors has been increasing rapidly over the last several years. People want precise, but random colors. The colors should be delivered evenly but without any sign uniformity. It sounds almost impossible to accomplish oxymoron.

 

Getting good color blending is not impossible and actually with the right equipment and a good plan of execution. There are several methods to getting an attractive blend of colors. Often to best the best finish a producer will need to make the correct moves not just with color blending equipment, but also with the mixing and batching process as well as on the block or paver machine. This doesn't necessarily mean that you need to buy the fanciest or latest thing-a-ma-jig, more that you need to know how to operate your equipment. the best tool can be worthless if it is not understood.

Color blending is done both with face mix products and with through mixed products. The idea is to mix multiple colors in the block/paver machine in a seemingly random and aesthetically pleasing way. Generally three color blends are the goal of most block and paver producers today. Colors such as browns, tans, and Grays, are often used in liberal quantities while a color such as black, or a vivid red may be used more sparingly, as they are more striking to the eye.

Mixing and Batching:

KVM Face Mix Batching System

Batching for color blending is essentially no different than it is for a standard paver plant or a block operation that is already incorporating color. You need two silos. One for white cement and the other for gray cement. You also need aggregate holding bins, this may be two or three for a through mix process or eight to twelve if you are making face mix and/or using specialty aggregates. For batching color into the mix, I recommend either a granular or powder color, as liquid is tough in such a moisture sensitive product.

The big thing is that you need to be able to feed you mixer fast, as every product will require three separate batches to be present. Planetary mixers are often used for color blending, as they are fast mixers. There are many other excellent options for mixing colors in zero slump, but the planetary is proven very well for through mix, and for many face mix applications. If perfect face mix is you goal, there are better mixers, but you will have to pay a much higher price.



Mixer Systems Color blending

A real advantage to planetary mixers when it comes to blending is the ability for the mixer to have multiple discharge doors. this way you can have a separate hopper and conveyor for the three colors. We have placed VFD (Variable Frequency Drives) on the color conveyors to control the quantity of various colors. These belts can feed onto a conveyor, into a skip hoist, or into a flying bucket. Each of these will produce very different color results
 

Block / Paver Machine:
There are many kinds of machines for the production of block and pavers. Each one works a little different. Many have systems for feeding and evenly across the mold and knowing how to control these operations on your machine is crucial. Uncontrolled spreading can lead to dulling of colors where you want them sharp. The best thing you can do is become an expert on the equipment your run with. Of course some machines are easier to work with than others. Check out KVM equipment.



Small Board Paver Plants

Small board paver plants are more than a passing trend in in the North American block on pavers market. They represent the future of a business that caters to customer tastes. Each person is unique and more and more people are expressing their individuality in the hardscapes they surround themselves with. Many people are no longer satisfied with going to the store at taking what is available. They what to go online or through a catalog to find the product that suits them best.

It is difficult to mass produce pavers at a rate of 2,500 - 3,500 square feet per hour and still have the ability to meet each customer's unique demands. It works if you are a large company in a heavily populated market with multiple plants and an excellent distribution network. In that case the big board production model makes sense, much of the time. But what if you are not in this situation? What if you you are trying to serve a medium to small market with one or two production facilities. Then maybe a small board machine is right for you.

In my travels, I have met many block and paver producers that would like to find a way to service a market with a small board plant that allow the easy versatility needed to produce custome jobs as they arise, and to produce a more reasonable amount of pavers, say 900 - 1,200 square feet, or even 1,200 - 1,600, per hour. As we see an up-turn in housing again, and with more commercial buildings, there is an increased need for more paver producers in more regions of North America. Small board production plants will in many cases be the answer.

The demand for small board machines has been on going, the supply has been the anchor. I know of several cases in which companies have ventured to supply small board paver plants, but never followed through to support and improve on these systems. I know this to be true, as I have come across several plants in my work and in my travels that have small board machines.

Having sold paver plants in the past, I have heard many reasons that people should not get small board machines for producing pavers. We would often get inquiries for a small board plant or even a half board plant, and always we sent over a quotation for a big board machine.  I was told it is for the best as small boards machines were nothing but trouble. I now know that the trouble was in trying to change gears from a machinery companies manufacturing perspective, not based on what would work for the concrete producer. Of all the plants I have visited with small board machines, the customers have been happy with the board size and the production versatility as they expected they would. What have been issues have been controls that are not designed for that style of production, that are over complicated. Handling was often a shrunken version of a version built for a pallet 4 times as large.

Over several years I have come to know the KVM company. They are a Danish machinery producer of concrete block and paver plants. While working for a Danish pipe machinery company I visited several of their installations in Europe. In the following years I have also had opportunities to see KVM equipment running here in North America. I am some one who is very familiar with paver machines, as they have been the family business since the early 1990's. I have spent years working with paver machine parts and selling the equipment. With what I know, I can clearly see that KVM makes a quality system.

What's more KVM is focussed on smaller board production plants, and that is a far cry from other companies that provide a one size fits all approach. You and your market are unique, evaluate systems and board sizes that are right for both.

Aging Block and Pavers

The production of block and pavers becomes more of an art every day. People want not only to see the shape and color that meet their expectations, but also wear that that they dream of. Wear? yes Wear. Many people want pavers to look as if they have been walked upon for a good hundred years or so. Ideally, this would make a neutral viewer think that you have snatched them off the streets of a beautiful European city.

Making a paver looked aged is a challenge, and certainly not everyone can agree on the best way to created such a finish. there are however several methods to making a pavers with the worn surface and rounded edges that people love so much.

First and most important, you must make a very high quality paver. No body wants paver that are broken in half on their drive way or patio. Broken pavers are junk. (Note: if you do have a lot of broken, junky pavers or block, we make a Hammermill crusher you may love). The product has to be able to stand up to the aging process. This means excellent compaction and density, and that means you need the right equipment and top notch people running it.

Tumbling:

One of the simplest ways to get an aged look on a paver is to tumble it. An offline aging method. The process is fairly straight forward. You take a pallet or two of pavers and dump them into a cylinder that has a 4' -6' diameter and is 20ish feet long and let them bang around for awhile. Then when they look right, you pour them out and have several people pick them up and stack them by hand (except for the broken ones which you can just toss into the Hammermill). Clearly this is labor intensive. the aging is random, which is nice, but sometimes it is too random, and it is better with some shape and sizes that others.


Inline Aging:
There are several inline aging systems available. Some drop bearings on the pavers surface others pound the product with chains or weights, Some even use the Hammer of Thor himself (which is an in-line tumbling system). Inline aging is great and if done right you end up with a minimum of waste and great looking product.

Splitting:

another way to get a nature and aged look on a product, especially a concrete block, it split it into two pieces. This leaves a rugged uneven surface where to block was separated. This has become very popular in commercial construction and on retaining walls. Splitting fits very well in line and can easily be incorporated into most plants without requiring additional labor.




Spraying and Blasting:
Another way to get a nice aged look on a paver or block is with either shot blasting, sand blasting or spraying the product. Blasting is often done post curing (on a dry, hard product), while the spraying is often done on green product (pre-cured)

Comparing Mixers for Precast Applications

There are a lot of concrete mixer out there in the market today for precasters to choose from. In my experience I have work closely with at least six distinct type of concrete, in passing with few other, from so many companies that it is beyond count. I have worked for three different companies that manufacture concrete mixers and worked for two other that sold concrete mixers as a part of Turn-Key projects (yes, that is five different employers...I know). Since I started in the concrete equipment industry 20 years ago I have learned quite abit about concrete mixer for a factory setting, and here is what (I think) I know:

 

Counter Current Mixers (Planetary Mixers):

This is the mixer that I mostly grew-up around Pedershaab (which was the first company I sold equipment for) often paired their plants with Skako and sometimes Haarup, both Danish companies making Planetary mixers. Masa and Wiggert both make planetary mixers, and are companies I sold equipment for. Mixer Systems here is the US, and my current employer, also produces a planetary mixer. I have more experience with these mixers than any other.

In a nutshell, the planetary has the design to be one of the fastest mixing mixers available. they are good and reliable mixers. in some applications they excel beyond the pan and horizontal shafts. Also, the ability to have multiple discharge door as on the pan, can be a huge advantage. However, which today's more complex mixes such as SCC and even a standard zero slump, the mixing speed advantage is reduced. As I grew up, I saw the planetary as a one-size-fits-all, be-all-end-all of mixers. Today I see the planetary as a very useful tool in a belt of very useful tools, it has it applications but there may be better options, depending on what needs to done.

Eirich R12 or Cyclone Mixer:

This is an exceptional mixer, especially for Face-Mix on pavers. When I was with Masa, who produces paver plants, they produced a version of this mixer, and I was amazed at its ability to use a single shaft with mixing tines, revolving at an exceptionally high speed to pulverize the materials. this was very important as face mix is often prone cement and color balls because of the fine materials used. This is what high-sheer really is. Price on a mixer of this sort is often the biggest issue, as they often run 2 -3 times the price of another style mixer in the same size. Additionally, this mixer design have only a single discharge door, though I believe with a bit more money equipment that can be overcome.
 

Horizontal Shaft Mixer (Paddle or Spiral Blade):

Slow and Steady Wins the Race! When I first started with Mixer Systems, I had a bias against this mixer. Now I think it is the best mixer ever made. OK… that may be a little much, but let me explain my enthusiasm on this.

At Mixer Systems we call this mixer the Praschaak. There are other producers with this same design concept including Besser and, I believe, Columbia. They are seen as old technology,  often eliciting jokes such as "This is how cavemen made concrete". Maybe it is true that the technology is old, Praschaak was making this mixer in the 1940's, I have seen many in my travels running daily that were produced in the 50's and 60's. So, yeah they are old. They are simple to. A single horizontal shaft with either paddles or blades mounted to it turning at a pedestrian revolution every 1.5 -2.5 seconds. The body I like a barrel on its side, and yet it's produces just about every kind of concrete on the market and does a good job of it time and again.

I have seen horizontal shat mixers used for producing concrete pavers on various block and paver machines, and making consistent concrete with consistent colors, 4-5 minute cycles. Indeed the US block industry developed using such mixers. However, the real magic of the horizontal shaft mixer is for the producers of SCC that pour with buckets, this mixer's door design allows for the least amount of drop from mixer to buckets and that saves on clean-up. Also, the difference in mixing times of the Horizontal shaft and mixers such as the planetary or twin shaft become far less noticeable, within seconds of each other, once a plasticizer and/or other admixes are properly mixed in. Good concrete takes time regardless of RPMs

Pan / Turbin:

The pan is an interesting mixer. It is unique among the other mixers listed here as it does not have an open body to mix in. Instead, the center of the mixers body is dedicated to the transmission while a trough is created between the inner and outer wall where the mixing takes place. I used to consider this mix a cheap alternative to the planetary, but that was an incorrect and unfair assumption on my part while there may be several applications in which the planetary is said to be superior, I have on numerous occasions seen pan mixers performing noticeably better. At Mixer Systems we produce Turbin/Pan mixers, as do companies such as Teka and Voeller.

I have seen pans running 90 second cycle time while feeding a concrete pump in a precast operation. I have spoken to Prestress producers running both Pan and Planetary Mixers side by side, who have told me that the Pan is far superior for zero slump concrete, and that the mixers run at nearly the same cycle. Indeed, Pan mixers have been a mainstay in the concrete pipe industry for years.

Because of the design of the mixer, pans will provide less volume by footprint than open body mixers. This also leads to additional wear where the concrete in focused. Pans often consume more wear parts than mixer such as the twin and horizontal shaft mixers. But they also offer additional versatility by allowing for multiple discharge doors

Ready Mix Truck:

I am not a ready mix expert. It is my understanding that mixing in a ready-mix truck requires up to 15% more cement than a batch mixer to get the same product strength. If I am wrong on this please correct me.

Ready mix is usually done in batches of 9-12 yards.

Twin-Shaft Mixer:

The twin shaft mixer is a truly fantastic mixer. It offers mixing times similar to the Planetary, durability similar to the horizontal shaft, and a very dynamic mixing action. It is usually is a pretty expensive mixer and if it is not…Beware! This mixer, unlike a horizontal shaft is designed to have the material being mixed over the height of the shaft. This means that the shaft seals are in constant contact with concrete. Not such a big deal for dry cast concrete, but a very big deal with wet-cast, and especially SCC. Those running concretes are as crafty as water when it comes to finding ways to escape, and standard shaft seals would last forever (and by forever I mean 6 months) for such a mix, an air-purge or similar seal is critical, and they are not free.

Another small and easily overcome drawback to the twin shaft is that there is a single discharge door and it is the length of the mixer usually. A chute is often needed to focus the flow of material.