Concrete is an invention that changed construction methods for thousands of years after its discovery, but how has the use of concrete changed today?
Deep set into the industry, you’d be hard pressed to find a technique more widely used in construction than the use of concrete. Concrete offers a versatile quality, while providing a solid foundation, which is a necessity for many ambitious construction projects. It’s cost-effective, plentiful and has proven to be a tried and tested method, time and again. Structures built using this substance often last for many years with a general service life of around 100 years.
Though the principle use of concrete remains the same, the aggregates industry has embarked on a technology revolution of its own. Health concerns surrounding the material, such as respiratory conditions are being tackled head-on, as are wider environmental concerns involving pollution.
Aggregate alchemy …
One such development has been established by a team at the Massachusetts Institute of Technology (MIT) in the US who created a way to make cement without heating, potentially eliminating the carbon produced in the process.
The most widely used variety is Portland cement, which is made by mixing limestone with sand and clay and then fusing them together at temperatures of around 1,450°C (2,642°F). During this process, carbon is emitted from the fuel used in the heating process and the limestone itself. It has been estimated that cement production accounts for 8% of global carbon emissions. Therefore, development of low-carbon production is a vital challenge that the industry has a responsibility to tackle.
The process that the team has developed involves the use of electrochemical processes rather than heat.
• Limestone is dissolved in acid
• Then placed in a tank with an electric current passing through it
• This splits water molecules into oxygen and hydrogen
• Creates an acid at the positive electrode
• Creates an alkali deposit of calcium hydroxide at the negative
• Deposit forms in flakes can then be used to produce Portland cement
The results were published in the Proceedings of the National Academy of Science, in a paper titled “Toward electrochemical synthesis of cement—An electrolyzer-based process for decarbonating CaCO3 while producing useful gas streams”, written Yet-Ming Chiang, Professor of Materials Science & Engineering-MIT, and four other MIT colleagues.
Chiang said, “About 1kg of carbon dioxide is released for 1kg of cement made. That adds up to 3-4 gigatonnes of cement and of carbon dioxide produced annually, and the number of buildings worldwide is expected to double by 2060—equivalent to building New York City every 30 days.”
So far, the team has demonstrated the process at laboratory scale, but the researchers said it could be scaled up to an industrial process. They warned, however, that it would be difficult to change such a basic process in such a large industry as construction.
Scaling up
In Kuala Lumpur, Malaysia, a concrete batching plant capable of producing 200m3/hr of material was recently deployed for use in the construction of the Malaysian “Jalan Tun Razak Traffic Dispersal Project”.
Lintec & Linnhoff ‘s Eurotec 4MZ6750Ti Plant model has provided the material for over 3km of road tunnels, utility service installation works, and tunnel fit-out works for the project, which aims to reduce traffic into the city by 30%.
The underground section for the proposed connection to the Stormwater Management and Road Tunnel (SMART) at “Jalan Sultan Ismail” is currently under construction. The loop tunnel, which will allow direct access to and from major highways and regulate the underground traffic, will take visitors to parking bays in the area rather than joining local traffic.
The company says that production of standard concrete types and special concrete, has now been optimized. In the company’s new design of TWO VEHICLES can be loaded simultaneously with different types of concrete.
This new concept was chosen because it enables the operation of two separate mixing plants within one mixing tower. Within its compact form factor, the Betomat holds up to 600m³ of stone in nine silo chambers. The mixing tower is fed with aggregates via two charging hoppers and a bucket elevator with an hourly output of 200m³/h. The plant itself has seven silos for a binder supply of around 840 tonnes.
Because the new mixing plant is equipped with two mixer systems—ring-pan mixer with agitator system and a double-shaft mixer—means that three concretes can be produced: normal standard, high-performance, and special. When in operation with both mixer systems, the plant achieves a possible output of around 160m³ of compacted fresh concrete per hour.
Electric evolution
Liebherr said its electrically-driven truck mixer range offers the reduced emissions now increasingly required in urban areas. They recently introduced two truck mixers to its ETM range—a fixed structure and a semitrailer with a fully electrical tractor. When tested under extreme conditions, the electrical drum drive proved effective, even with very thick concrete consistencies. A compact generator recharges the mixer’s battery during the journey, or can be charged at up to 22kW, using a standard plug.
How concrete is being dispatched is just one of the ways in which concrete applications are changing. The way in which concrete is installed varies between contractors and jobsites globally.
US-based manufacturer Reed has developed a high-performance pump that is said to be capable of delivering high enough pressure to form structural concrete columns and walls, without traditional formwork requirements. The pumps implement a Rexroth ‘Closed Loop’ hydraulic system, with twin axles, and twin-shifting cylinders making them capable of delivering a maximum pressure of 2000Psi. The company says that it is the first manufacturer to bring this technology to trailer line pumps.
A different strategy
Torrent Shotcrete is one such company that has invested in the new Reed products, as its pump of choice: Rather than the traditional method of forming concrete walls and structures using a form-and-pour strategy the shotcrete method requires substantially less formwork:
• Capable of achieving 2000Psi pumping power mark
• Pneumatic pump sprays the concrete into position over a single panel
• Minimum two reinforced bar layers
• Less formwork
• Saves setup time
• Reduced costs for labor
• Reduced costs for formwork
Ross King, Vice President, Business Development-Torrent Shotcrete, said, “Not too long ago, form-and-pour methodology completely dominated the forming marketplace, but that’s changing. Today, the marketplace is seeing structural shotcrete gain far greater acceptance as a more logical and efficient option for structural concrete applications.”
Elsewhere, Ammann has supplied ready-mix concrete supplier Betonbud with a new CBT 60 SL Elba concrete mixing plant in Lviv, Ukraine—a heavily urbanized region of Ukraine with a lot of construction activity. Ammann confirmed Lazar’s favourable impressions during the tender phase—fast and accurate processing! Ammann’s CBT Elba series has been designed for:
• Easy transportation
• Flexible modular technology—plant can be shipped in two open-top containers
• Easily assembled on site
The perfect finish with Wacker Neuson new battery-powered internal vibrator! This product is targeting the rental market: the new internal vibrator system is modular, allowing separate internal vibrators with different vibrator head sizes and protection hoses to be connected to the battery backpack. Therefore, rental firms can store the entire range of vibrator head and hose sizes to offer the right solution for a wide variety of applications:
• New, environmentally-friendly option
• Hardened vibrator head in the front third
• High-frequency operation to deliver stable revolutions per minute (rpm)
• Optimizes the quality that the vibrator can deliver in concrete consolidation
• Removes the trapped air more evenly
For more details and the jobs described in Austria, Ukraine, and elsewhere, please go to article titled “Concrete construction: Cemented in the industry”: https://www.khl.com/international-construction/concrete-construction-cemented-in-the-industry/141555.article
For Dr. Yet-Ming Chiang’s Paper titled “Toward electrochemical synthesis of cement—An electrolyzer-based process for decarbonating CaCO3 while producing useful gas streams”, please go to: https://www.pnas.org/content/early/2019/09/10/1821673116